## About this documentation# Welcome to the official API reference documentation for Node.js! Node.js is a JavaScript runtime built on the V8 JavaScript engine. ### Contributing# Report errors in this documentation in the issue tracker. See the contributing guide for directions on how to submit pull requests. ### Stability index# Throughout the documentation are indications of a section's stability. Some APIs are so proven and so relied upon that they are unlikely to ever change at all. Others are brand new and experimental, or known to be hazardous. The stability indexes are as follows: Stability: 0 - Deprecated. The feature may emit warnings. Backward compatibility is not guaranteed. Stability: 1 - Experimental. The feature is not subject to semantic versioning rules. Non-backward compatible changes or removal may occur in any future release. Use of the feature is not recommended in production environments. Experimental features are subdivided into stages: * 1.0 - Early development. Experimental features at this stage are unfinished and subject to substantial change. * 1.1 - Active development. Experimental features at this stage are nearing minimum viability. * 1.2 - Release candidate. Experimental features at this stage are hopefully ready to become stable. No further breaking changes are anticipated but may still occur in response to user feedback or the features' underlying specification development. We encourage user testing and feedback so that we can know that this feature is ready to be marked as stable. Experimental features leave the experimental status typically either by graduating to stable, or are removed without a deprecation cycle. Stability: 2 - Stable. Compatibility with the npm ecosystem is a high priority. Stability: 3 - Legacy. Although this feature is unlikely to be removed and is still covered by semantic versioning guarantees, it is no longer actively maintained, and other alternatives are available. Features are marked as legacy rather than being deprecated if their use does no harm, and they are widely relied upon within the npm ecosystem. Bugs found in legacy features are unlikely to be fixed. Use caution when making use of Experimental features, particularly when authoring libraries. Users may not be aware that experimental features are being used. Bugs or behavior changes may surprise users when Experimental API modifications occur. To avoid surprises, use of an Experimental feature may need a command-line flag. Experimental features may also emit a warning. ### Stability overview# ### JSON output# Added in: v0.6.12 Every `.html` document has a corresponding `.json` document. This is for IDEs and other utilities that consume the documentation. ### System calls and man pages# Node.js functions which wrap a system call will document that. The docs link to the corresponding man pages which describe how the system call works. Most Unix system calls have Windows analogues. Still, behavior differences may be unavoidable. ## Usage and example# ### Usage# `node [options] [V8 options] [script.js | -e "script" | - ] [arguments]` Please see the Command-line options document for more information. ### Example# An example of a web server written with Node.js which responds with `'Hello, World!'`: Commands in this document start with `$` or `>` to replicate how they would appear in a user's terminal. Do not include the `$` and `>` characters. They are there to show the start of each command. Lines that don't start with `$` or `>` character show the output of the previous command. First, make sure to have downloaded and installed Node.js. See Installing Node.js via package manager for further install information. Now, create an empty project folder called `projects`, then navigate into it. Linux and Mac: mkdir ~/projects cd ~/projects Windows CMD: mkdir %USERPROFILE%\projects cd %USERPROFILE%\projects Windows PowerShell: mkdir $env:USERPROFILE\projects cd $env:USERPROFILE\projects Next, create a new source file in the `projects` folder and call it `hello-world.js`. Open `hello-world.js` in any preferred text editor and paste in the following content: const http = require('node:http'); const hostname = '127.0.0.1'; const port = 3000; const server = http.createServer((req, res) => { res.statusCode = 200; res.setHeader('Content-Type', 'text/plain'); res.end('Hello, World!\n'); }); server.listen(port, hostname, () => { console.log(`Server running at http://${hostname}:${port}/`); }); Save the file. Then, in the terminal window, to run the `hello-world.js` file, enter: node hello-world.js Output like this should appear in the terminal: Server running at http://127.0.0.1:3000/ Now, open any preferred web browser and visit `http://127.0.0.1:3000`. If the browser displays the string `Hello, World!`, that indicates the server is working. ## Assert# Stability: 2 \- Stable Source Code: lib/assert.js The `node:assert` module provides a set of assertion functions for verifying invariants. ### Strict assertion mode# History VersionChanges v15.0.0 Exposed as `require('node:assert/strict')`. v13.9.0, v12.16.2 Changed "strict mode" to "strict assertion mode" and "legacy mode" to "legacy assertion mode" to avoid confusion with the more usual meaning of "strict mode". v9.9.0 Added error diffs to the strict assertion mode. v9.9.0 Added strict assertion mode to the assert module. v9.9.0 Added in: v9.9.0 In strict assertion mode, non-strict methods behave like their corresponding strict methods. For example, `assert.deepEqual()` will behave like `assert.deepStrictEqual()`. In strict assertion mode, error messages for objects display a diff. In legacy assertion mode, error messages for objects display the objects, often truncated. To use strict assertion mode: import { strict as assert } from 'node:assert'; import assert from 'node:assert/strict'; Example error diff: import { strict as assert } from 'node:assert'; assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]); // AssertionError: Expected inputs to be strictly deep-equal: // + actual - expected ... Lines skipped // // [ // [ // ... // 2, // + 3 // - '3' // ], // ... // 5 // ] To deactivate the colors, use the `NO_COLOR` or `NODE_DISABLE_COLORS` environment variables. This will also deactivate the colors in the REPL. For more on color support in terminal environments, read the tty `getColorDepth()` documentation. ### Legacy assertion mode# Legacy assertion mode uses the `==` operator in: * `assert.deepEqual()` * `assert.equal()` * `assert.notDeepEqual()` * `assert.notEqual()` To use legacy assertion mode: import assert from 'node:assert'; Legacy assertion mode may have surprising results, especially when using `assert.deepEqual()`: ### Class: `assert.AssertionError`# * Extends: Indicates the failure of an assertion. All errors thrown by the `node:assert` module will be instances of the `AssertionError` class. #### `new assert.AssertionError(options)`# Added in: v0.1.21 * `options` * `message` If provided, the error message is set to this value. * `actual` The `actual` property on the error instance. * `expected` The `expected` property on the error instance. * `operator` The `operator` property on the error instance. * `stackStartFn` If provided, the generated stack trace omits frames before this function. * `diff` If set to `'full'`, shows the full diff in assertion errors. Defaults to `'simple'`. Accepted values: `'simple'`, `'full'`. A subclass of that indicates the failure of an assertion. All instances contain the built-in `Error` properties (`message` and `name`) and: * `actual` Set to the `actual` argument for methods such as `assert.strictEqual()`. * `expected` Set to the `expected` value for methods such as `assert.strictEqual()`. * `generatedMessage` Indicates if the message was auto-generated (`true`) or not. * `code` Value is always `ERR_ASSERTION` to show that the error is an assertion error. * `operator` Set to the passed in operator value. import assert from 'node:assert'; // Generate an AssertionError to compare the error message later: const { message } = new assert.AssertionError({ actual: 1, expected: 2, operator: 'strictEqual', }); // Verify error output: try { assert.strictEqual(1, 2); } catch (err) { assert(err instanceof assert.AssertionError); assert.strictEqual(err.message, message); assert.strictEqual(err.name, 'AssertionError'); assert.strictEqual(err.actual, 1); assert.strictEqual(err.expected, 2); assert.strictEqual(err.code, 'ERR_ASSERTION'); assert.strictEqual(err.operator, 'strictEqual'); assert.strictEqual(err.generatedMessage, true); } ### Class: `assert.Assert`# Added in: v24.6.0 The `Assert` class allows creating independent assertion instances with custom options. #### `new assert.Assert([options])`# History VersionChanges v24.9.0 Added `skipPrototype` option. * `options` * `diff` If set to `'full'`, shows the full diff in assertion errors. Defaults to `'simple'`. Accepted values: `'simple'`, `'full'`. * `strict` If set to `true`, non-strict methods behave like their corresponding strict methods. Defaults to `true`. * `skipPrototype` If set to `true`, skips prototype and constructor comparison in deep equality checks. Defaults to `false`. Creates a new assertion instance. The `diff` option controls the verbosity of diffs in assertion error messages. const { Assert } = require('node:assert'); const assertInstance = new Assert({ diff: 'full' }); assertInstance.deepStrictEqual({ a: 1 }, { a: 2 }); // Shows a full diff in the error message. Important: When destructuring assertion methods from an `Assert` instance, the methods lose their connection to the instance's configuration options (such as `diff`, `strict`, and `skipPrototype` settings). The destructured methods will fall back to default behavior instead. const myAssert = new Assert({ diff: 'full' }); // This works as expected - uses 'full' diff myAssert.strictEqual({ a: 1 }, { b: { c: 1 } }); // This loses the 'full' diff setting - falls back to default 'simple' diff const { strictEqual } = myAssert; strictEqual({ a: 1 }, { b: { c: 1 } }); The `skipPrototype` option affects all deep equality methods: class Foo { constructor(a) { this.a = a; } } class Bar { constructor(a) { this.a = a; } } const foo = new Foo(1); const bar = new Bar(1); // Default behavior - fails due to different constructors const assert1 = new Assert(); assert1.deepStrictEqual(foo, bar); // AssertionError // Skip prototype comparison - passes if properties are equal const assert2 = new Assert({ skipPrototype: true }); assert2.deepStrictEqual(foo, bar); // OK When destructured, methods lose access to the instance's `this` context and revert to default assertion behavior (diff: 'simple', non-strict mode). To maintain custom options when using destructured methods, avoid destructuring and call methods directly on the instance. ### Class: `assert.CallTracker`# History VersionChanges v20.1.0 the `assert.CallTracker` class has been deprecated and will be removed in a future version. v14.2.0, v12.19.0 Added in: v14.2.0, v12.19.0 Stability: 0 \- Deprecated This feature is deprecated and will be removed in a future version. Please consider using alternatives such as the `mock` helper function. #### `new assert.CallTracker()`# Added in: v14.2.0, v12.19.0 Creates a new `CallTracker` object which can be used to track if functions were called a specific number of times. The `tracker.verify()` must be called for the verification to take place. The usual pattern would be to call it in a `process.on('exit')` handler. import assert from 'node:assert'; import process from 'node:process'; const tracker = new assert.CallTracker(); function func() {} // callsfunc() must be called exactly 1 time before tracker.verify(). const callsfunc = tracker.calls(func, 1); callsfunc(); // Calls tracker.verify() and verifies if all tracker.calls() functions have // been called exact times. process.on('exit', () => { tracker.verify(); }); #### `tracker.calls([fn][, exact])`# Added in: v14.2.0, v12.19.0 * `fn` Default: A no-op function. * `exact` Default: `1`. * Returns: A function that wraps `fn`. The wrapper function is expected to be called exactly `exact` times. If the function has not been called exactly `exact` times when `tracker.verify()` is called, then `tracker.verify()` will throw an error. import assert from 'node:assert'; // Creates call tracker. const tracker = new assert.CallTracker(); function func() {} // Returns a function that wraps func() that must be called exact times // before tracker.verify(). const callsfunc = tracker.calls(func); #### `tracker.getCalls(fn)`# Added in: v18.8.0, v16.18.0 * `fn` * Returns: An array with all the calls to a tracked function. * Object * `thisArg` * `arguments` the arguments passed to the tracked function import assert from 'node:assert'; const tracker = new assert.CallTracker(); function func() {} const callsfunc = tracker.calls(func); callsfunc(1, 2, 3); assert.deepStrictEqual(tracker.getCalls(callsfunc), [{ thisArg: undefined, arguments: [1, 2, 3] }]); #### `tracker.report()`# Added in: v14.2.0, v12.19.0 * Returns: An array of objects containing information about the wrapper functions returned by `tracker.calls()`. * Object * `message` * `actual` The actual number of times the function was called. * `expected` The number of times the function was expected to be called. * `operator` The name of the function that is wrapped. * `stack` A stack trace of the function. The arrays contains information about the expected and actual number of calls of the functions that have not been called the expected number of times. import assert from 'node:assert'; // Creates call tracker. const tracker = new assert.CallTracker(); function func() {} // Returns a function that wraps func() that must be called exact times // before tracker.verify(). const callsfunc = tracker.calls(func, 2); // Returns an array containing information on callsfunc() console.log(tracker.report()); // [ // { // message: 'Expected the func function to be executed 2 time(s) but was // executed 0 time(s).', // actual: 0, // expected: 2, // operator: 'func', // stack: stack trace // } // ] #### `tracker.reset([fn])`# Added in: v18.8.0, v16.18.0 * `fn` a tracked function to reset. Reset calls of the call tracker. If a tracked function is passed as an argument, the calls will be reset for it. If no arguments are passed, all tracked functions will be reset. import assert from 'node:assert'; const tracker = new assert.CallTracker(); function func() {} const callsfunc = tracker.calls(func); callsfunc(); // Tracker was called once assert.strictEqual(tracker.getCalls(callsfunc).length, 1); tracker.reset(callsfunc); assert.strictEqual(tracker.getCalls(callsfunc).length, 0); #### `tracker.verify()`# Added in: v14.2.0, v12.19.0 Iterates through the list of functions passed to `tracker.calls()` and will throw an error for functions that have not been called the expected number of times. import assert from 'node:assert'; // Creates call tracker. const tracker = new assert.CallTracker(); function func() {} // Returns a function that wraps func() that must be called exact times // before tracker.verify(). const callsfunc = tracker.calls(func, 2); callsfunc(); // Will throw an error since callsfunc() was only called once. tracker.verify(); ### `assert(value[, message])`# Added in: v0.5.9 * `value` The input that is checked for being truthy. * `message` | An alias of `assert.ok()`. ### `assert.deepEqual(actual, expected[, message])`# History VersionChanges v24.0.0 Recursion now stops when either side encounters a circular reference. v22.2.0, v20.15.0 Error cause and errors properties are now compared as well. v18.0.0 Regular expressions lastIndex property is now compared as well. v16.0.0, v14.18.0 In Legacy assertion mode, changed status from Deprecated to Legacy. v14.0.0 NaN is now treated as being identical if both sides are NaN. v12.0.0 The type tags are now properly compared and there are a couple minor comparison adjustments to make the check less surprising. v9.0.0 The `Error` names and messages are now properly compared. v8.0.0 The `Set` and `Map` content is also compared. v6.4.0, v4.7.1 Typed array slices are handled correctly now. v6.1.0, v4.5.0 Objects with circular references can be used as inputs now. v5.10.1, v4.4.3 Handle non-`Uint8Array` typed arrays correctly. v0.1.21 Added in: v0.1.21 * `actual` * `expected` * `message` | Strict assertion mode An alias of `assert.deepStrictEqual()`. Legacy assertion mode Stability: 3 \- Legacy: Use `assert.deepStrictEqual()` instead. Tests for deep equality between the `actual` and `expected` parameters. Consider using `assert.deepStrictEqual()` instead. `assert.deepEqual()` can have surprising results. Deep equality means that the enumerable "own" properties of child objects are also recursively evaluated by the following rules. #### Comparison details# * Primitive values are compared with the `==` operator, with the exception of . It is treated as being identical in case both sides are . * Type tags of objects should be the same. * Only enumerable "own" properties are considered. * names, messages, causes, and errors are always compared, even if these are not enumerable properties. * Object wrappers are compared both as objects and unwrapped values. * `Object` properties are compared unordered. * keys and items are compared unordered. * Recursion stops when both sides differ or either side encounters a circular reference. * Implementation does not test the `[[Prototype]]` of objects. * properties are not compared. * and comparison does not rely on their values but only on their instances. * lastIndex, flags, and source are always compared, even if these are not enumerable properties. The following example does not throw an `AssertionError` because the primitives are compared using the `==` operator. import assert from 'node:assert'; // WARNING: This does not throw an AssertionError! assert.deepEqual('+00000000', false); "Deep" equality means that the enumerable "own" properties of child objects are evaluated also: import assert from 'node:assert'; const obj1 = { a: { b: 1, }, }; const obj2 = { a: { b: 2, }, }; const obj3 = { a: { b: 1, }, }; const obj4 = { __proto__: obj1 }; assert.deepEqual(obj1, obj1); // OK // Values of b are different: assert.deepEqual(obj1, obj2); // AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } } assert.deepEqual(obj1, obj3); // OK // Prototypes are ignored: assert.deepEqual(obj1, obj4); // AssertionError: { a: { b: 1 } } deepEqual {} If the values are not equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.deepStrictEqual(actual, expected[, message])`# History VersionChanges v24.0.0 Recursion now stops when either side encounters a circular reference. v22.2.0, v20.15.0 Error cause and errors properties are now compared as well. v18.0.0 Regular expressions lastIndex property is now compared as well. v9.0.0 Enumerable symbol properties are now compared. v9.0.0 The `NaN` is now compared using the SameValueZero comparison. v8.5.0 The `Error` names and messages are now properly compared. v8.0.0 The `Set` and `Map` content is also compared. v6.1.0 Objects with circular references can be used as inputs now. v6.4.0, v4.7.1 Typed array slices are handled correctly now. v5.10.1, v4.4.3 Handle non-`Uint8Array` typed arrays correctly. v1.2.0 Added in: v1.2.0 * `actual` * `expected` * `message` | Tests for deep equality between the `actual` and `expected` parameters. "Deep" equality means that the enumerable "own" properties of child objects are recursively evaluated also by the following rules. #### Comparison details# * Primitive values are compared using `Object.is()`. * Type tags of objects should be the same. * `[[Prototype]]` of objects are compared using the `===` operator. * Only enumerable "own" properties are considered. * names, messages, causes, and errors are always compared, even if these are not enumerable properties. `errors` is also compared. * Enumerable own properties are compared as well. * Object wrappers are compared both as objects and unwrapped values. * `Object` properties are compared unordered. * keys and items are compared unordered. * Recursion stops when both sides differ or either side encounters a circular reference. * and instances are not compared structurally. They are only equal if they reference the same object. Any comparison between different `WeakMap` or `WeakSet` instances will result in inequality, even if they contain the same entries. * lastIndex, flags, and source are always compared, even if these are not enumerable properties. import assert from 'node:assert/strict'; // This fails because 1 !== '1'. assert.deepStrictEqual({ a: 1 }, { a: '1' }); // AssertionError: Expected inputs to be strictly deep-equal: // + actual - expected // // { // + a: 1 // - a: '1' // } // The following objects don't have own properties const date = new Date(); const object = {}; const fakeDate = {}; Object.setPrototypeOf(fakeDate, Date.prototype); // Different [[Prototype]]: assert.deepStrictEqual(object, fakeDate); // AssertionError: Expected inputs to be strictly deep-equal: // + actual - expected // // + {} // - Date {} // Different type tags: assert.deepStrictEqual(date, fakeDate); // AssertionError: Expected inputs to be strictly deep-equal: // + actual - expected // // + 2018-04-26T00:49:08.604Z // - Date {} assert.deepStrictEqual(NaN, NaN); // OK because Object.is(NaN, NaN) is true. // Different unwrapped numbers: assert.deepStrictEqual(new Number(1), new Number(2)); // AssertionError: Expected inputs to be strictly deep-equal: // + actual - expected // // + [Number: 1] // - [Number: 2] assert.deepStrictEqual(new String('foo'), Object('foo')); // OK because the object and the string are identical when unwrapped. assert.deepStrictEqual(-0, -0); // OK // Different zeros: assert.deepStrictEqual(0, -0); // AssertionError: Expected inputs to be strictly deep-equal: // + actual - expected // // + 0 // - -0 const symbol1 = Symbol(); const symbol2 = Symbol(); assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 }); // OK, because it is the same symbol on both objects. assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 }); // AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal: // // { // Symbol(): 1 // } const weakMap1 = new WeakMap(); const weakMap2 = new WeakMap(); const obj = {}; weakMap1.set(obj, 'value'); weakMap2.set(obj, 'value'); // Comparing different instances fails, even with same contents assert.deepStrictEqual(weakMap1, weakMap2); // AssertionError: Values have same structure but are not reference-equal: // // WeakMap { // // } // Comparing the same instance to itself succeeds assert.deepStrictEqual(weakMap1, weakMap1); // OK const weakSet1 = new WeakSet(); const weakSet2 = new WeakSet(); weakSet1.add(obj); weakSet2.add(obj); // Comparing different instances fails, even with same contents assert.deepStrictEqual(weakSet1, weakSet2); // AssertionError: Values have same structure but are not reference-equal: // + actual - expected // // WeakSet { // // } // Comparing the same instance to itself succeeds assert.deepStrictEqual(weakSet1, weakSet1); // OK If the values are not equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.doesNotMatch(string, regexp[, message])`# History VersionChanges v16.0.0 This API is no longer experimental. v13.6.0, v12.16.0 Added in: v13.6.0, v12.16.0 * `string` * `regexp` * `message` | Expects the `string` input not to match the regular expression. import assert from 'node:assert/strict'; assert.doesNotMatch('I will fail', /fail/); // AssertionError [ERR_ASSERTION]: The input was expected to not match the ... assert.doesNotMatch(123, /pass/); // AssertionError [ERR_ASSERTION]: The "string" argument must be of type string. assert.doesNotMatch('I will pass', /different/); // OK If the values do match, or if the `string` argument is of another type than `string`, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.doesNotReject(asyncFn[, error][, message])`# Added in: v10.0.0 * `asyncFn` | * `error` | * `message` * Returns: Awaits the `asyncFn` promise or, if `asyncFn` is a function, immediately calls the function and awaits the returned promise to complete. It will then check that the promise is not rejected. If `asyncFn` is a function and it throws an error synchronously, `assert.doesNotReject()` will return a rejected `Promise` with that error. If the function does not return a promise, `assert.doesNotReject()` will return a rejected `Promise` with an `ERR_INVALID_RETURN_VALUE` error. In both cases the error handler is skipped. Using `assert.doesNotReject()` is actually not useful because there is little benefit in catching a rejection and then rejecting it again. Instead, consider adding a comment next to the specific code path that should not reject and keep error messages as expressive as possible. If specified, `error` can be a `Class`, or a validation function. See `assert.throws()` for more details. Besides the async nature to await the completion behaves identically to `assert.doesNotThrow()`. import assert from 'node:assert/strict'; await assert.doesNotReject( async () => { throw new TypeError('Wrong value'); }, SyntaxError, ); import assert from 'node:assert/strict'; assert.doesNotReject(Promise.reject(new TypeError('Wrong value'))) .then(() => { // ... }); ### `assert.doesNotThrow(fn[, error][, message])`# History VersionChanges v5.11.0, v4.4.5 The `message` parameter is respected now. v4.2.0 The `error` parameter can now be an arrow function. v0.1.21 Added in: v0.1.21 * `fn` * `error` | * `message` Asserts that the function `fn` does not throw an error. Using `assert.doesNotThrow()` is actually not useful because there is no benefit in catching an error and then rethrowing it. Instead, consider adding a comment next to the specific code path that should not throw and keep error messages as expressive as possible. When `assert.doesNotThrow()` is called, it will immediately call the `fn` function. If an error is thrown and it is the same type as that specified by the `error` parameter, then an `AssertionError` is thrown. If the error is of a different type, or if the `error` parameter is undefined, the error is propagated back to the caller. If specified, `error` can be a `Class`, , or a validation function. See `assert.throws()` for more details. The following, for instance, will throw the because there is no matching error type in the assertion: import assert from 'node:assert/strict'; assert.doesNotThrow( () => { throw new TypeError('Wrong value'); }, SyntaxError, ); However, the following will result in an `AssertionError` with the message 'Got unwanted exception...': import assert from 'node:assert/strict'; assert.doesNotThrow( () => { throw new TypeError('Wrong value'); }, TypeError, ); If an `AssertionError` is thrown and a value is provided for the `message` parameter, the value of `message` will be appended to the `AssertionError` message: import assert from 'node:assert/strict'; assert.doesNotThrow( () => { throw new TypeError('Wrong value'); }, /Wrong value/, 'Whoops', ); // Throws: AssertionError: Got unwanted exception: Whoops ### `assert.equal(actual, expected[, message])`# History VersionChanges v16.0.0, v14.18.0 In Legacy assertion mode, changed status from Deprecated to Legacy. v14.0.0 NaN is now treated as being identical if both sides are NaN. v0.1.21 Added in: v0.1.21 * `actual` * `expected` * `message` | Strict assertion mode An alias of `assert.strictEqual()`. Legacy assertion mode Stability: 3 \- Legacy: Use `assert.strictEqual()` instead. Tests shallow, coercive equality between the `actual` and `expected` parameters using the `==` operator. `NaN` is specially handled and treated as being identical if both sides are `NaN`. import assert from 'node:assert'; assert.equal(1, 1); // OK, 1 == 1 assert.equal(1, '1'); // OK, 1 == '1' assert.equal(NaN, NaN); // OK assert.equal(1, 2); // AssertionError: 1 == 2 assert.equal({ a: { b: 1 } }, { a: { b: 1 } }); // AssertionError: { a: { b: 1 } } == { a: { b: 1 } } If the values are not equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.fail([message])`# Added in: v0.1.21 * `message` | Default: `'Failed'` Throws an `AssertionError` with the provided error message or a default error message. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. import assert from 'node:assert/strict'; assert.fail(); // AssertionError [ERR_ASSERTION]: Failed assert.fail('boom'); // AssertionError [ERR_ASSERTION]: boom assert.fail(new TypeError('need array')); // TypeError: need array Using `assert.fail()` with more than two arguments is possible but deprecated. See below for further details. ### `assert.fail(actual, expected[, message[, operator[, stackStartFn]]])`# History VersionChanges v10.0.0 Calling `assert.fail()` with more than one argument is deprecated and emits a warning. v0.1.21 Added in: v0.1.21 Stability: 0 \- Deprecated: Use `assert.fail([message])` or other assert functions instead. * `actual` * `expected` * `message` | * `operator` Default: `'!='` * `stackStartFn` Default: `assert.fail` If `message` is falsy, the error message is set as the values of `actual` and `expected` separated by the provided `operator`. If just the two `actual` and `expected` arguments are provided, `operator` will default to `'!='`. If `message` is provided as third argument it will be used as the error message and the other arguments will be stored as properties on the thrown object. If `stackStartFn` is provided, all stack frames above that function will be removed from stacktrace (see `Error.captureStackTrace`). If no arguments are given, the default message `Failed` will be used. import assert from 'node:assert/strict'; assert.fail('a', 'b'); // AssertionError [ERR_ASSERTION]: 'a' != 'b' assert.fail(1, 2, undefined, '>'); // AssertionError [ERR_ASSERTION]: 1 > 2 assert.fail(1, 2, 'fail'); // AssertionError [ERR_ASSERTION]: fail assert.fail(1, 2, 'whoops', '>'); // AssertionError [ERR_ASSERTION]: whoops assert.fail(1, 2, new TypeError('need array')); // TypeError: need array In the last three cases `actual`, `expected`, and `operator` have no influence on the error message. Example use of `stackStartFn` for truncating the exception's stacktrace: import assert from 'node:assert/strict'; function suppressFrame() { assert.fail('a', 'b', undefined, '!==', suppressFrame); } suppressFrame(); // AssertionError [ERR_ASSERTION]: 'a' !== 'b' // at repl:1:1 // at ContextifyScript.Script.runInThisContext (vm.js:44:33) // ... ### `assert.ifError(value)`# History VersionChanges v10.0.0 Instead of throwing the original error it is now wrapped into an [`AssertionError`][] that contains the full stack trace. v10.0.0 Value may now only be `undefined` or `null`. Before all falsy values were handled the same as `null` and did not throw. v0.1.97 Added in: v0.1.97 * `value` Throws `value` if `value` is not `undefined` or `null`. This is useful when testing the `error` argument in callbacks. The stack trace contains all frames from the error passed to `ifError()` including the potential new frames for `ifError()` itself. import assert from 'node:assert/strict'; assert.ifError(null); // OK assert.ifError(0); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0 assert.ifError('error'); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error' assert.ifError(new Error()); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error // Create some random error frames. let err; (function errorFrame() { err = new Error('test error'); })(); (function ifErrorFrame() { assert.ifError(err); })(); // AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error // at ifErrorFrame // at errorFrame ### `assert.match(string, regexp[, message])`# History VersionChanges v16.0.0 This API is no longer experimental. v13.6.0, v12.16.0 Added in: v13.6.0, v12.16.0 * `string` * `regexp` * `message` | Expects the `string` input to match the regular expression. import assert from 'node:assert/strict'; assert.match('I will fail', /pass/); // AssertionError [ERR_ASSERTION]: The input did not match the regular ... assert.match(123, /pass/); // AssertionError [ERR_ASSERTION]: The "string" argument must be of type string. assert.match('I will pass', /pass/); // OK If the values do not match, or if the `string` argument is of another type than `string`, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.notDeepEqual(actual, expected[, message])`# History VersionChanges v16.0.0, v14.18.0 In Legacy assertion mode, changed status from Deprecated to Legacy. v14.0.0 NaN is now treated as being identical if both sides are NaN. v9.0.0 The `Error` names and messages are now properly compared. v8.0.0 The `Set` and `Map` content is also compared. v6.4.0, v4.7.1 Typed array slices are handled correctly now. v6.1.0, v4.5.0 Objects with circular references can be used as inputs now. v5.10.1, v4.4.3 Handle non-`Uint8Array` typed arrays correctly. v0.1.21 Added in: v0.1.21 * `actual` * `expected` * `message` | Strict assertion mode An alias of `assert.notDeepStrictEqual()`. Legacy assertion mode Stability: 3 \- Legacy: Use `assert.notDeepStrictEqual()` instead. Tests for any deep inequality. Opposite of `assert.deepEqual()`. import assert from 'node:assert'; const obj1 = { a: { b: 1, }, }; const obj2 = { a: { b: 2, }, }; const obj3 = { a: { b: 1, }, }; const obj4 = { __proto__: obj1 }; assert.notDeepEqual(obj1, obj1); // AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } } assert.notDeepEqual(obj1, obj2); // OK assert.notDeepEqual(obj1, obj3); // AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } } assert.notDeepEqual(obj1, obj4); // OK If the values are deeply equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.notDeepStrictEqual(actual, expected[, message])`# History VersionChanges v9.0.0 The `-0` and `+0` are not considered equal anymore. v9.0.0 The `NaN` is now compared using the SameValueZero comparison. v9.0.0 The `Error` names and messages are now properly compared. v8.0.0 The `Set` and `Map` content is also compared. v6.1.0 Objects with circular references can be used as inputs now. v6.4.0, v4.7.1 Typed array slices are handled correctly now. v5.10.1, v4.4.3 Handle non-`Uint8Array` typed arrays correctly. v1.2.0 Added in: v1.2.0 * `actual` * `expected` * `message` | Tests for deep strict inequality. Opposite of `assert.deepStrictEqual()`. import assert from 'node:assert/strict'; assert.notDeepStrictEqual({ a: 1 }, { a: '1' }); // OK If the values are deeply and strictly equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.notEqual(actual, expected[, message])`# History VersionChanges v16.0.0, v14.18.0 In Legacy assertion mode, changed status from Deprecated to Legacy. v14.0.0 NaN is now treated as being identical if both sides are NaN. v0.1.21 Added in: v0.1.21 * `actual` * `expected` * `message` | Strict assertion mode An alias of `assert.notStrictEqual()`. Legacy assertion mode Stability: 3 \- Legacy: Use `assert.notStrictEqual()` instead. Tests shallow, coercive inequality with the `!=` operator. `NaN` is specially handled and treated as being identical if both sides are `NaN`. import assert from 'node:assert'; assert.notEqual(1, 2); // OK assert.notEqual(1, 1); // AssertionError: 1 != 1 assert.notEqual(1, '1'); // AssertionError: 1 != '1' If the values are equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.notStrictEqual(actual, expected[, message])`# History VersionChanges v10.0.0 Used comparison changed from Strict Equality to `Object.is()`. v0.1.21 Added in: v0.1.21 * `actual` * `expected` * `message` | Tests strict inequality between the `actual` and `expected` parameters as determined by `Object.is()`. import assert from 'node:assert/strict'; assert.notStrictEqual(1, 2); // OK assert.notStrictEqual(1, 1); // AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to: // // 1 assert.notStrictEqual(1, '1'); // OK If the values are strictly equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.ok(value[, message])`# History VersionChanges v10.0.0 The `assert.ok()` (no arguments) will now use a predefined error message. v0.1.21 Added in: v0.1.21 * `value` * `message` | Tests if `value` is truthy. It is equivalent to `assert.equal(!!value, true, message)`. If `value` is not truthy, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is `undefined`, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. If no arguments are passed in at all `message` will be set to the string: `'No value argument passed to `assert.ok()`'`. Be aware that in the `repl` the error message will be different to the one thrown in a file! See below for further details. import assert from 'node:assert/strict'; assert.ok(true); // OK assert.ok(1); // OK assert.ok(); // AssertionError: No value argument passed to `assert.ok()` assert.ok(false, 'it\'s false'); // AssertionError: it's false // In the repl: assert.ok(typeof 123 === 'string'); // AssertionError: false == true // In a file (e.g. test.js): assert.ok(typeof 123 === 'string'); // AssertionError: The expression evaluated to a falsy value: // // assert.ok(typeof 123 === 'string') assert.ok(false); // AssertionError: The expression evaluated to a falsy value: // // assert.ok(false) assert.ok(0); // AssertionError: The expression evaluated to a falsy value: // // assert.ok(0) import assert from 'node:assert/strict'; // Using `assert()` works the same: assert(0); // AssertionError: The expression evaluated to a falsy value: // // assert(0) ### `assert.rejects(asyncFn[, error][, message])`# Added in: v10.0.0 * `asyncFn` | * `error` | | | * `message` * Returns: Awaits the `asyncFn` promise or, if `asyncFn` is a function, immediately calls the function and awaits the returned promise to complete. It will then check that the promise is rejected. If `asyncFn` is a function and it throws an error synchronously, `assert.rejects()` will return a rejected `Promise` with that error. If the function does not return a promise, `assert.rejects()` will return a rejected `Promise` with an `ERR_INVALID_RETURN_VALUE` error. In both cases the error handler is skipped. Besides the async nature to await the completion behaves identically to `assert.throws()`. If specified, `error` can be a `Class`, , a validation function, an object where each property will be tested for, or an instance of error where each property will be tested for including the non-enumerable `message` and `name` properties. If specified, `message` will be the message provided by the `AssertionError` if the `asyncFn` fails to reject. import assert from 'node:assert/strict'; await assert.rejects( async () => { throw new TypeError('Wrong value'); }, { name: 'TypeError', message: 'Wrong value', }, ); import assert from 'node:assert/strict'; await assert.rejects( async () => { throw new TypeError('Wrong value'); }, (err) => { assert.strictEqual(err.name, 'TypeError'); assert.strictEqual(err.message, 'Wrong value'); return true; }, ); import assert from 'node:assert/strict'; assert.rejects( Promise.reject(new Error('Wrong value')), Error, ).then(() => { // ... }); `error` cannot be a string. If a string is provided as the second argument, then `error` is assumed to be omitted and the string will be used for `message` instead. This can lead to easy-to-miss mistakes. Please read the example in `assert.throws()` carefully if using a string as the second argument gets considered. ### `assert.strictEqual(actual, expected[, message])`# History VersionChanges v10.0.0 Used comparison changed from Strict Equality to `Object.is()`. v0.1.21 Added in: v0.1.21 * `actual` * `expected` * `message` | Tests strict equality between the `actual` and `expected` parameters as determined by `Object.is()`. import assert from 'node:assert/strict'; assert.strictEqual(1, 2); // AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal: // // 1 !== 2 assert.strictEqual(1, 1); // OK assert.strictEqual('Hello foobar', 'Hello World!'); // AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal: // + actual - expected // // + 'Hello foobar' // - 'Hello World!' // ^ const apples = 1; const oranges = 2; assert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`); // AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2 assert.strictEqual(1, '1', new TypeError('Inputs are not identical')); // TypeError: Inputs are not identical If the values are not strictly equal, an `AssertionError` is thrown with a `message` property set equal to the value of the `message` parameter. If the `message` parameter is undefined, a default error message is assigned. If the `message` parameter is an instance of then it will be thrown instead of the `AssertionError`. ### `assert.throws(fn[, error][, message])`# History VersionChanges v10.2.0 The `error` parameter can be an object containing regular expressions now. v9.9.0 The `error` parameter can now be an object as well. v4.2.0 The `error` parameter can now be an arrow function. v0.1.21 Added in: v0.1.21 * `fn` * `error` | | | * `message` Expects the function `fn` to throw an error. If specified, `error` can be a `Class`, , a validation function, a validation object where each property will be tested for strict deep equality, or an instance of error where each property will be tested for strict deep equality including the non-enumerable `message` and `name` properties. When using an object, it is also possible to use a regular expression, when validating against a string property. See below for examples. If specified, `message` will be appended to the message provided by the `AssertionError` if the `fn` call fails to throw or in case the error validation fails. Custom validation object/error instance: import assert from 'node:assert/strict'; const err = new TypeError('Wrong value'); err.code = 404; err.foo = 'bar'; err.info = { nested: true, baz: 'text', }; err.reg = /abc/i; assert.throws( () => { throw err; }, { name: 'TypeError', message: 'Wrong value', info: { nested: true, baz: 'text', }, // Only properties on the validation object will be tested for. // Using nested objects requires all properties to be present. Otherwise // the validation is going to fail. }, ); // Using regular expressions to validate error properties: assert.throws( () => { throw err; }, { // The `name` and `message` properties are strings and using regular // expressions on those will match against the string. If they fail, an // error is thrown. name: /^TypeError$/, message: /Wrong/, foo: 'bar', info: { nested: true, // It is not possible to use regular expressions for nested properties! baz: 'text', }, // The `reg` property contains a regular expression and only if the // validation object contains an identical regular expression, it is going // to pass. reg: /abc/i, }, ); // Fails due to the different `message` and `name` properties: assert.throws( () => { const otherErr = new Error('Not found'); // Copy all enumerable properties from `err` to `otherErr`. for (const [key, value] of Object.entries(err)) { otherErr[key] = value; } throw otherErr; }, // The error's `message` and `name` properties will also be checked when using // an error as validation object. err, ); Validate instanceof using constructor: import assert from 'node:assert/strict'; assert.throws( () => { throw new Error('Wrong value'); }, Error, ); Validate error message using : Using a regular expression runs `.toString` on the error object, and will therefore also include the error name. import assert from 'node:assert/strict'; assert.throws( () => { throw new Error('Wrong value'); }, /^Error: Wrong value$/, ); Custom error validation: The function must return `true` to indicate all internal validations passed. It will otherwise fail with an `AssertionError`. import assert from 'node:assert/strict'; assert.throws( () => { throw new Error('Wrong value'); }, (err) => { assert(err instanceof Error); assert(/value/.test(err)); // Avoid returning anything from validation functions besides `true`. // Otherwise, it's not clear what part of the validation failed. Instead, // throw an error about the specific validation that failed (as done in this // example) and add as much helpful debugging information to that error as // possible. return true; }, 'unexpected error', ); `error` cannot be a string. If a string is provided as the second argument, then `error` is assumed to be omitted and the string will be used for `message` instead. This can lead to easy-to-miss mistakes. Using the same message as the thrown error message is going to result in an `ERR_AMBIGUOUS_ARGUMENT` error. Please read the example below carefully if using a string as the second argument gets considered: import assert from 'node:assert/strict'; function throwingFirst() { throw new Error('First'); } function throwingSecond() { throw new Error('Second'); } function notThrowing() {} // The second argument is a string and the input function threw an Error. // The first case will not throw as it does not match for the error message // thrown by the input function! assert.throws(throwingFirst, 'Second'); // In the next example the message has no benefit over the message from the // error and since it is not clear if the user intended to actually match // against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error. assert.throws(throwingSecond, 'Second'); // TypeError [ERR_AMBIGUOUS_ARGUMENT] // The string is only used (as message) in case the function does not throw: assert.throws(notThrowing, 'Second'); // AssertionError [ERR_ASSERTION]: Missing expected exception: Second // If it was intended to match for the error message do this instead: // It does not throw because the error messages match. assert.throws(throwingSecond, /Second$/); // If the error message does not match, an AssertionError is thrown. assert.throws(throwingFirst, /Second$/); // AssertionError [ERR_ASSERTION] Due to the confusing error-prone notation, avoid a string as the second argument. ### `assert.partialDeepStrictEqual(actual, expected[, message])`# History VersionChanges v24.0.0 partialDeepStrictEqual is now Stable. Previously, it had been Experimental. v23.4.0, v22.13.0 Added in: v23.4.0, v22.13.0 * `actual` * `expected` * `message` | Tests for partial deep equality between the `actual` and `expected` parameters. "Deep" equality means that the enumerable "own" properties of child objects are recursively evaluated also by the following rules. "Partial" equality means that only properties that exist on the `expected` parameter are going to be compared. This method always passes the same test cases as `assert.deepStrictEqual()`, behaving as a super set of it. #### Comparison details# * Primitive values are compared using `Object.is()`. * Type tags of objects should be the same. * `[[Prototype]]` of objects are not compared. * Only enumerable "own" properties are considered. * names, messages, causes, and errors are always compared, even if these are not enumerable properties. `errors` is also compared. * Enumerable own properties are compared as well. * Object wrappers are compared both as objects and unwrapped values. * `Object` properties are compared unordered. * keys and items are compared unordered. * Recursion stops when both sides differ or both sides encounter a circular reference. * and instances are not compared structurally. They are only equal if they reference the same object. Any comparison between different `WeakMap` or `WeakSet` instances will result in inequality, even if they contain the same entries. * lastIndex, flags, and source are always compared, even if these are not enumerable properties. * Holes in sparse arrays are ignored. import assert from 'node:assert'; assert.partialDeepStrictEqual( { a: { b: { c: 1 } } }, { a: { b: { c: 1 } } }, ); // OK assert.partialDeepStrictEqual( { a: 1, b: 2, c: 3 }, { b: 2 }, ); // OK assert.partialDeepStrictEqual( [1, 2, 3, 4, 5, 6, 7, 8, 9], [4, 5, 8], ); // OK assert.partialDeepStrictEqual( new Set([{ a: 1 }, { b: 1 }]), new Set([{ a: 1 }]), ); // OK assert.partialDeepStrictEqual( new Map([['key1', 'value1'], ['key2', 'value2']]), new Map([['key2', 'value2']]), ); // OK assert.partialDeepStrictEqual(123n, 123n); // OK assert.partialDeepStrictEqual( [1, 2, 3, 4, 5, 6, 7, 8, 9], [5, 4, 8], ); // AssertionError assert.partialDeepStrictEqual( { a: 1 }, { a: 1, b: 2 }, ); // AssertionError assert.partialDeepStrictEqual( { a: { b: 2 } }, { a: { b: '2' } }, ); // AssertionError ## Asynchronous context tracking# Stability: 2 \- Stable Source Code: lib/async_hooks.js ### Introduction# These classes are used to associate state and propagate it throughout callbacks and promise chains. They allow storing data throughout the lifetime of a web request or any other asynchronous duration. It is similar to thread-local storage in other languages. The `AsyncLocalStorage` and `AsyncResource` classes are part of the `node:async_hooks` module: import { AsyncLocalStorage, AsyncResource } from 'node:async_hooks'; ### Class: `AsyncLocalStorage`# History VersionChanges v16.4.0 AsyncLocalStorage is now Stable. Previously, it had been Experimental. v13.10.0, v12.17.0 Added in: v13.10.0, v12.17.0 This class creates stores that stay coherent through asynchronous operations. While you can create your own implementation on top of the `node:async_hooks` module, `AsyncLocalStorage` should be preferred as it is a performant and memory safe implementation that involves significant optimizations that are non-obvious to implement. The following example uses `AsyncLocalStorage` to build a simple logger that assigns IDs to incoming HTTP requests and includes them in messages logged within each request. import http from 'node:http'; import { AsyncLocalStorage } from 'node:async_hooks'; const asyncLocalStorage = new AsyncLocalStorage(); function logWithId(msg) { const id = asyncLocalStorage.getStore(); console.log(`${id !== undefined ? id : '-'}:`, msg); } let idSeq = 0; http.createServer((req, res) => { asyncLocalStorage.run(idSeq++, () => { logWithId('start'); // Imagine any chain of async operations here setImmediate(() => { logWithId('finish'); res.end(); }); }); }).listen(8080); http.get('http://localhost:8080'); http.get('http://localhost:8080'); // Prints: // 0: start // 0: finish // 1: start // 1: finish Each instance of `AsyncLocalStorage` maintains an independent storage context. Multiple instances can safely exist simultaneously without risk of interfering with each other's data. #### `new AsyncLocalStorage([options])`# History VersionChanges v24.0.0 Add `defaultValue` and `name` options. v19.7.0, v18.16.0 Removed experimental onPropagate option. v19.2.0, v18.13.0 Add option onPropagate. v13.10.0, v12.17.0 Added in: v13.10.0, v12.17.0 * `options` * `defaultValue` The default value to be used when no store is provided. * `name` A name for the `AsyncLocalStorage` value. Creates a new instance of `AsyncLocalStorage`. Store is only provided within a `run()` call or after an `enterWith()` call. #### Static method: `AsyncLocalStorage.bind(fn)`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v19.8.0, v18.16.0 Added in: v19.8.0, v18.16.0 * `fn` The function to bind to the current execution context. * Returns: A new function that calls `fn` within the captured execution context. Binds the given function to the current execution context. #### Static method: `AsyncLocalStorage.snapshot()`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v19.8.0, v18.16.0 Added in: v19.8.0, v18.16.0 * Returns: A new function with the signature `(fn: (...args) : R, ...args) : R`. Captures the current execution context and returns a function that accepts a function as an argument. Whenever the returned function is called, it calls the function passed to it within the captured context. const asyncLocalStorage = new AsyncLocalStorage(); const runInAsyncScope = asyncLocalStorage.run(123, () => AsyncLocalStorage.snapshot()); const result = asyncLocalStorage.run(321, () => runInAsyncScope(() => asyncLocalStorage.getStore())); console.log(result); // returns 123 AsyncLocalStorage.snapshot() can replace the use of AsyncResource for simple async context tracking purposes, for example: class Foo { #runInAsyncScope = AsyncLocalStorage.snapshot(); get() { return this.#runInAsyncScope(() => asyncLocalStorage.getStore()); } } const foo = asyncLocalStorage.run(123, () => new Foo()); console.log(asyncLocalStorage.run(321, () => foo.get())); // returns 123 #### `asyncLocalStorage.disable()`# Added in: v13.10.0, v12.17.0 Stability: 1 \- Experimental Disables the instance of `AsyncLocalStorage`. All subsequent calls to `asyncLocalStorage.getStore()` will return `undefined` until `asyncLocalStorage.run()` or `asyncLocalStorage.enterWith()` is called again. When calling `asyncLocalStorage.disable()`, all current contexts linked to the instance will be exited. Calling `asyncLocalStorage.disable()` is required before the `asyncLocalStorage` can be garbage collected. This does not apply to stores provided by the `asyncLocalStorage`, as those objects are garbage collected along with the corresponding async resources. Use this method when the `asyncLocalStorage` is not in use anymore in the current process. #### `asyncLocalStorage.getStore()`# Added in: v13.10.0, v12.17.0 * Returns: Returns the current store. If called outside of an asynchronous context initialized by calling `asyncLocalStorage.run()` or `asyncLocalStorage.enterWith()`, it returns `undefined`. #### `asyncLocalStorage.enterWith(store)`# Added in: v13.11.0, v12.17.0 Stability: 1 \- Experimental * `store` Transitions into the context for the remainder of the current synchronous execution and then persists the store through any following asynchronous calls. Example: const store = { id: 1 }; // Replaces previous store with the given store object asyncLocalStorage.enterWith(store); asyncLocalStorage.getStore(); // Returns the store object someAsyncOperation(() => { asyncLocalStorage.getStore(); // Returns the same object }); This transition will continue for the entire synchronous execution. This means that if, for example, the context is entered within an event handler subsequent event handlers will also run within that context unless specifically bound to another context with an `AsyncResource`. That is why `run()` should be preferred over `enterWith()` unless there are strong reasons to use the latter method. const store = { id: 1 }; emitter.on('my-event', () => { asyncLocalStorage.enterWith(store); }); emitter.on('my-event', () => { asyncLocalStorage.getStore(); // Returns the same object }); asyncLocalStorage.getStore(); // Returns undefined emitter.emit('my-event'); asyncLocalStorage.getStore(); // Returns the same object #### `asyncLocalStorage.name`# Added in: v24.0.0 * Type: The name of the `AsyncLocalStorage` instance if provided. #### `asyncLocalStorage.run(store, callback[, ...args])`# Added in: v13.10.0, v12.17.0 * `store` * `callback` * `...args` Runs a function synchronously within a context and returns its return value. The store is not accessible outside of the callback function. The store is accessible to any asynchronous operations created within the callback. The optional `args` are passed to the callback function. If the callback function throws an error, the error is thrown by `run()` too. The stacktrace is not impacted by this call and the context is exited. Example: const store = { id: 2 }; try { asyncLocalStorage.run(store, () => { asyncLocalStorage.getStore(); // Returns the store object setTimeout(() => { asyncLocalStorage.getStore(); // Returns the store object }, 200); throw new Error(); }); } catch (e) { asyncLocalStorage.getStore(); // Returns undefined // The error will be caught here } #### `asyncLocalStorage.exit(callback[, ...args])`# Added in: v13.10.0, v12.17.0 Stability: 1 \- Experimental * `callback` * `...args` Runs a function synchronously outside of a context and returns its return value. The store is not accessible within the callback function or the asynchronous operations created within the callback. Any `getStore()` call done within the callback function will always return `undefined`. The optional `args` are passed to the callback function. If the callback function throws an error, the error is thrown by `exit()` too. The stacktrace is not impacted by this call and the context is re-entered. Example: // Within a call to run try { asyncLocalStorage.getStore(); // Returns the store object or value asyncLocalStorage.exit(() => { asyncLocalStorage.getStore(); // Returns undefined throw new Error(); }); } catch (e) { asyncLocalStorage.getStore(); // Returns the same object or value // The error will be caught here } #### Usage with `async/await`# If, within an async function, only one `await` call is to run within a context, the following pattern should be used: async function fn() { await asyncLocalStorage.run(new Map(), () => { asyncLocalStorage.getStore().set('key', value); return foo(); // The return value of foo will be awaited }); } In this example, the store is only available in the callback function and the functions called by `foo`. Outside of `run`, calling `getStore` will return `undefined`. #### Troubleshooting: Context loss# In most cases, `AsyncLocalStorage` works without issues. In rare situations, the current store is lost in one of the asynchronous operations. If your code is callback-based, it is enough to promisify it with `util.promisify()` so it starts working with native promises. If you need to use a callback-based API or your code assumes a custom thenable implementation, use the `AsyncResource` class to associate the asynchronous operation with the correct execution context. Find the function call responsible for the context loss by logging the content of `asyncLocalStorage.getStore()` after the calls you suspect are responsible for the loss. When the code logs `undefined`, the last callback called is probably responsible for the context loss. ### Class: `AsyncResource`# History VersionChanges v16.4.0 AsyncResource is now Stable. Previously, it had been Experimental. The class `AsyncResource` is designed to be extended by the embedder's async resources. Using this, users can easily trigger the lifetime events of their own resources. The `init` hook will trigger when an `AsyncResource` is instantiated. The following is an overview of the `AsyncResource` API. import { AsyncResource, executionAsyncId } from 'node:async_hooks'; // AsyncResource() is meant to be extended. Instantiating a // new AsyncResource() also triggers init. If triggerAsyncId is omitted then // async_hook.executionAsyncId() is used. const asyncResource = new AsyncResource( type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false }, ); // Run a function in the execution context of the resource. This will // * establish the context of the resource // * trigger the AsyncHooks before callbacks // * call the provided function `fn` with the supplied arguments // * trigger the AsyncHooks after callbacks // * restore the original execution context asyncResource.runInAsyncScope(fn, thisArg, ...args); // Call AsyncHooks destroy callbacks. asyncResource.emitDestroy(); // Return the unique ID assigned to the AsyncResource instance. asyncResource.asyncId(); // Return the trigger ID for the AsyncResource instance. asyncResource.triggerAsyncId(); #### `new AsyncResource(type[, options])`# * `type` The type of async event. * `options` * `triggerAsyncId` The ID of the execution context that created this async event. Default: `executionAsyncId()`. * `requireManualDestroy` If set to `true`, disables `emitDestroy` when the object is garbage collected. This usually does not need to be set (even if `emitDestroy` is called manually), unless the resource's `asyncId` is retrieved and the sensitive API's `emitDestroy` is called with it. When set to `false`, the `emitDestroy` call on garbage collection will only take place if there is at least one active `destroy` hook. Default: `false`. Example usage: class DBQuery extends AsyncResource { constructor(db) { super('DBQuery'); this.db = db; } getInfo(query, callback) { this.db.get(query, (err, data) => { this.runInAsyncScope(callback, null, err, data); }); } close() { this.db = null; this.emitDestroy(); } } #### Static method: `AsyncResource.bind(fn[, type[, thisArg]])`# History VersionChanges v20.0.0 The `asyncResource` property added to the bound function has been deprecated and will be removed in a future version. v17.8.0, v16.15.0 Changed the default when `thisArg` is undefined to use `this` from the caller. v16.0.0 Added optional thisArg. v14.8.0, v12.19.0 Added in: v14.8.0, v12.19.0 * `fn` The function to bind to the current execution context. * `type` An optional name to associate with the underlying `AsyncResource`. * `thisArg` Binds the given function to the current execution context. #### `asyncResource.bind(fn[, thisArg])`# History VersionChanges v20.0.0 The `asyncResource` property added to the bound function has been deprecated and will be removed in a future version. v17.8.0, v16.15.0 Changed the default when `thisArg` is undefined to use `this` from the caller. v16.0.0 Added optional thisArg. v14.8.0, v12.19.0 Added in: v14.8.0, v12.19.0 * `fn` The function to bind to the current `AsyncResource`. * `thisArg` Binds the given function to execute to this `AsyncResource`'s scope. #### `asyncResource.runInAsyncScope(fn[, thisArg, ...args])`# Added in: v9.6.0 * `fn` The function to call in the execution context of this async resource. * `thisArg` The receiver to be used for the function call. * `...args` Optional arguments to pass to the function. Call the provided function with the provided arguments in the execution context of the async resource. This will establish the context, trigger the AsyncHooks before callbacks, call the function, trigger the AsyncHooks after callbacks, and then restore the original execution context. #### `asyncResource.emitDestroy()`# * Returns: A reference to `asyncResource`. Call all `destroy` hooks. This should only ever be called once. An error will be thrown if it is called more than once. This must be manually called. If the resource is left to be collected by the GC then the `destroy` hooks will never be called. #### `asyncResource.asyncId()`# * Returns: The unique `asyncId` assigned to the resource. #### `asyncResource.triggerAsyncId()`# * Returns: The same `triggerAsyncId` that is passed to the `AsyncResource` constructor. #### Using `AsyncResource` for a `Worker` thread pool# The following example shows how to use the `AsyncResource` class to properly provide async tracking for a `Worker` pool. Other resource pools, such as database connection pools, can follow a similar model. Assuming that the task is adding two numbers, using a file named `task_processor.js` with the following content: import { parentPort } from 'node:worker_threads'; parentPort.on('message', (task) => { parentPort.postMessage(task.a + task.b); }); a Worker pool around it could use the following structure: import { AsyncResource } from 'node:async_hooks'; import { EventEmitter } from 'node:events'; import { Worker } from 'node:worker_threads'; const kTaskInfo = Symbol('kTaskInfo'); const kWorkerFreedEvent = Symbol('kWorkerFreedEvent'); class WorkerPoolTaskInfo extends AsyncResource { constructor(callback) { super('WorkerPoolTaskInfo'); this.callback = callback; } done(err, result) { this.runInAsyncScope(this.callback, null, err, result); this.emitDestroy(); // `TaskInfo`s are used only once. } } export default class WorkerPool extends EventEmitter { constructor(numThreads) { super(); this.numThreads = numThreads; this.workers = []; this.freeWorkers = []; this.tasks = []; for (let i = 0; i < numThreads; i++) this.addNewWorker(); // Any time the kWorkerFreedEvent is emitted, dispatch // the next task pending in the queue, if any. this.on(kWorkerFreedEvent, () => { if (this.tasks.length > 0) { const { task, callback } = this.tasks.shift(); this.runTask(task, callback); } }); } addNewWorker() { const worker = new Worker(new URL('task_processor.js', import.meta.url)); worker.on('message', (result) => { // In case of success: Call the callback that was passed to `runTask`, // remove the `TaskInfo` associated with the Worker, and mark it as free // again. worker[kTaskInfo].done(null, result); worker[kTaskInfo] = null; this.freeWorkers.push(worker); this.emit(kWorkerFreedEvent); }); worker.on('error', (err) => { // In case of an uncaught exception: Call the callback that was passed to // `runTask` with the error. if (worker[kTaskInfo]) worker[kTaskInfo].done(err, null); else this.emit('error', err); // Remove the worker from the list and start a new Worker to replace the // current one. this.workers.splice(this.workers.indexOf(worker), 1); this.addNewWorker(); }); this.workers.push(worker); this.freeWorkers.push(worker); this.emit(kWorkerFreedEvent); } runTask(task, callback) { if (this.freeWorkers.length === 0) { // No free threads, wait until a worker thread becomes free. this.tasks.push({ task, callback }); return; } const worker = this.freeWorkers.pop(); worker[kTaskInfo] = new WorkerPoolTaskInfo(callback); worker.postMessage(task); } close() { for (const worker of this.workers) worker.terminate(); } } Without the explicit tracking added by the `WorkerPoolTaskInfo` objects, it would appear that the callbacks are associated with the individual `Worker` objects. However, the creation of the `Worker`s is not associated with the creation of the tasks and does not provide information about when tasks were scheduled. This pool could be used as follows: import WorkerPool from './worker_pool.js'; import os from 'node:os'; const pool = new WorkerPool(os.availableParallelism()); let finished = 0; for (let i = 0; i < 10; i++) { pool.runTask({ a: 42, b: 100 }, (err, result) => { console.log(i, err, result); if (++finished === 10) pool.close(); }); } #### Integrating `AsyncResource` with `EventEmitter`# Event listeners triggered by an `EventEmitter` may be run in a different execution context than the one that was active when `eventEmitter.on()` was called. The following example shows how to use the `AsyncResource` class to properly associate an event listener with the correct execution context. The same approach can be applied to a `Stream` or a similar event-driven class. import { createServer } from 'node:http'; import { AsyncResource, executionAsyncId } from 'node:async_hooks'; const server = createServer((req, res) => { req.on('close', AsyncResource.bind(() => { // Execution context is bound to the current outer scope. })); req.on('close', () => { // Execution context is bound to the scope that caused 'close' to emit. }); res.end(); }).listen(3000); ## Async hooks# Stability: 1 \- Experimental. Please migrate away from this API, if you can. We do not recommend using the `createHook`, `AsyncHook`, and `executionAsyncResource` APIs as they have usability issues, safety risks, and performance implications. Async context tracking use cases are better served by the stable `AsyncLocalStorage` API. If you have a use case for `createHook`, `AsyncHook`, or `executionAsyncResource` beyond the context tracking need solved by `AsyncLocalStorage` or diagnostics data currently provided by Diagnostics Channel, please open an issue at https://github.com/nodejs/node/issues describing your use case so we can create a more purpose-focused API. Source Code: lib/async_hooks.js We strongly discourage the use of the `async_hooks` API. Other APIs that can cover most of its use cases include: * `AsyncLocalStorage` tracks async context * `process.getActiveResourcesInfo()` tracks active resources The `node:async_hooks` module provides an API to track asynchronous resources. It can be accessed using: import async_hooks from 'node:async_hooks'; ### Terminology# An asynchronous resource represents an object with an associated callback. This callback may be called multiple times, such as the `'connection'` event in `net.createServer()`, or just a single time like in `fs.open()`. A resource can also be closed before the callback is called. `AsyncHook` does not explicitly distinguish between these different cases but will represent them as the abstract concept that is a resource. If `Worker`s are used, each thread has an independent `async_hooks` interface, and each thread will use a new set of async IDs. ### Overview# Following is a simple overview of the public API. import async_hooks from 'node:async_hooks'; // Return the ID of the current execution context. const eid = async_hooks.executionAsyncId(); // Return the ID of the handle responsible for triggering the callback of the // current execution scope to call. const tid = async_hooks.triggerAsyncId(); // Create a new AsyncHook instance. All of these callbacks are optional. const asyncHook = async_hooks.createHook({ init, before, after, destroy, promiseResolve }); // Allow callbacks of this AsyncHook instance to call. This is not an implicit // action after running the constructor, and must be explicitly run to begin // executing callbacks. asyncHook.enable(); // Disable listening for new asynchronous events. asyncHook.disable(); // // The following are the callbacks that can be passed to createHook(). // // init() is called during object construction. The resource may not have // completed construction when this callback runs. Therefore, all fields of the // resource referenced by "asyncId" may not have been populated. function init(asyncId, type, triggerAsyncId, resource) { } // before() is called just before the resource's callback is called. It can be // called 0-N times for handles (such as TCPWrap), and will be called exactly 1 // time for requests (such as FSReqCallback). function before(asyncId) { } // after() is called just after the resource's callback has finished. function after(asyncId) { } // destroy() is called when the resource is destroyed. function destroy(asyncId) { } // promiseResolve() is called only for promise resources, when the // resolve() function passed to the Promise constructor is invoked // (either directly or through other means of resolving a promise). function promiseResolve(asyncId) { } ### `async_hooks.createHook(callbacks)`# Added in: v8.1.0 * `callbacks` The Hook Callbacks to register * `init` The `init` callback. * `before` The `before` callback. * `after` The `after` callback. * `destroy` The `destroy` callback. * `promiseResolve` The `promiseResolve` callback. * Returns: Instance used for disabling and enabling hooks Registers functions to be called for different lifetime events of each async operation. The callbacks `init()`/`before()`/`after()`/`destroy()` are called for the respective asynchronous event during a resource's lifetime. All callbacks are optional. For example, if only resource cleanup needs to be tracked, then only the `destroy` callback needs to be passed. The specifics of all functions that can be passed to `callbacks` is in the Hook Callbacks section. import { createHook } from 'node:async_hooks'; const asyncHook = createHook({ init(asyncId, type, triggerAsyncId, resource) { }, destroy(asyncId) { }, }); The callbacks will be inherited via the prototype chain: class MyAsyncCallbacks { init(asyncId, type, triggerAsyncId, resource) { } destroy(asyncId) {} } class MyAddedCallbacks extends MyAsyncCallbacks { before(asyncId) { } after(asyncId) { } } const asyncHook = async_hooks.createHook(new MyAddedCallbacks()); Because promises are asynchronous resources whose lifecycle is tracked via the async hooks mechanism, the `init()`, `before()`, `after()`, and `destroy()` callbacks must not be async functions that return promises. #### Error handling# If any `AsyncHook` callbacks throw, the application will print the stack trace and exit. The exit path does follow that of an uncaught exception, but all `'uncaughtException'` listeners are removed, thus forcing the process to exit. The `'exit'` callbacks will still be called unless the application is run with `--abort-on-uncaught-exception`, in which case a stack trace will be printed and the application exits, leaving a core file. The reason for this error handling behavior is that these callbacks are running at potentially volatile points in an object's lifetime, for example during class construction and destruction. Because of this, it is deemed necessary to bring down the process quickly in order to prevent an unintentional abort in the future. This is subject to change in the future if a comprehensive analysis is performed to ensure an exception can follow the normal control flow without unintentional side effects. #### Printing in `AsyncHook` callbacks# Because printing to the console is an asynchronous operation, `console.log()` will cause `AsyncHook` callbacks to be called. Using `console.log()` or similar asynchronous operations inside an `AsyncHook` callback function will cause an infinite recursion. An easy solution to this when debugging is to use a synchronous logging operation such as `fs.writeFileSync(file, msg, flag)`. This will print to the file and will not invoke `AsyncHook` recursively because it is synchronous. import { writeFileSync } from 'node:fs'; import { format } from 'node:util'; function debug(...args) { // Use a function like this one when debugging inside an AsyncHook callback writeFileSync('log.out', `${format(...args)}\n`, { flag: 'a' }); } If an asynchronous operation is needed for logging, it is possible to keep track of what caused the asynchronous operation using the information provided by `AsyncHook` itself. The logging should then be skipped when it was the logging itself that caused the `AsyncHook` callback to be called. By doing this, the otherwise infinite recursion is broken. ### Class: `AsyncHook`# The class `AsyncHook` exposes an interface for tracking lifetime events of asynchronous operations. #### `asyncHook.enable()`# * Returns: A reference to `asyncHook`. Enable the callbacks for a given `AsyncHook` instance. If no callbacks are provided, enabling is a no-op. The `AsyncHook` instance is disabled by default. If the `AsyncHook` instance should be enabled immediately after creation, the following pattern can be used. import { createHook } from 'node:async_hooks'; const hook = createHook(callbacks).enable(); #### `asyncHook.disable()`# * Returns: A reference to `asyncHook`. Disable the callbacks for a given `AsyncHook` instance from the global pool of `AsyncHook` callbacks to be executed. Once a hook has been disabled it will not be called again until enabled. For API consistency `disable()` also returns the `AsyncHook` instance. #### Hook callbacks# Key events in the lifetime of asynchronous events have been categorized into four areas: instantiation, before/after the callback is called, and when the instance is destroyed. ##### `init(asyncId, type, triggerAsyncId, resource)`# * `asyncId` A unique ID for the async resource. * `type` The type of the async resource. * `triggerAsyncId` The unique ID of the async resource in whose execution context this async resource was created. * `resource` Reference to the resource representing the async operation, needs to be released during destroy. Called when a class is constructed that has the possibility to emit an asynchronous event. This does not mean the instance must call `before`/`after` before `destroy` is called, only that the possibility exists. This behavior can be observed by doing something like opening a resource then closing it before the resource can be used. The following snippet demonstrates this. import { createServer } from 'node:net'; createServer().listen(function() { this.close(); }); // OR clearTimeout(setTimeout(() => {}, 10)); Every new resource is assigned an ID that is unique within the scope of the current Node.js instance. ###### `type`# The `type` is a string identifying the type of resource that caused `init` to be called. Generally, it will correspond to the name of the resource's constructor. The `type` of resources created by Node.js itself can change in any Node.js release. Valid values include `TLSWRAP`, `TCPWRAP`, `TCPSERVERWRAP`, `GETADDRINFOREQWRAP`, `FSREQCALLBACK`, `Microtask`, and `Timeout`. Inspect the source code of the Node.js version used to get the full list. Furthermore users of `AsyncResource` create async resources independent of Node.js itself. There is also the `PROMISE` resource type, which is used to track `Promise` instances and asynchronous work scheduled by them. Users are able to define their own `type` when using the public embedder API. It is possible to have type name collisions. Embedders are encouraged to use unique prefixes, such as the npm package name, to prevent collisions when listening to the hooks. ###### `triggerAsyncId`# `triggerAsyncId` is the `asyncId` of the resource that caused (or "triggered") the new resource to initialize and that caused `init` to call. This is different from `async_hooks.executionAsyncId()` that only shows when a resource was created, while `triggerAsyncId` shows why a resource was created. The following is a simple demonstration of `triggerAsyncId`: import { createHook, executionAsyncId } from 'node:async_hooks'; import { stdout } from 'node:process'; import net from 'node:net'; import fs from 'node:fs'; createHook({ init(asyncId, type, triggerAsyncId) { const eid = executionAsyncId(); fs.writeSync( stdout.fd, `${type}(${asyncId}): trigger: ${triggerAsyncId} execution: ${eid}\n`); }, }).enable(); net.createServer((conn) => {}).listen(8080); Output when hitting the server with `nc localhost 8080`: TCPSERVERWRAP(5): trigger: 1 execution: 1 TCPWRAP(7): trigger: 5 execution: 0 The `TCPSERVERWRAP` is the server which receives the connections. The `TCPWRAP` is the new connection from the client. When a new connection is made, the `TCPWrap` instance is immediately constructed. This happens outside of any JavaScript stack. (An `executionAsyncId()` of `0` means that it is being executed from C++ with no JavaScript stack above it.) With only that information, it would be impossible to link resources together in terms of what caused them to be created, so `triggerAsyncId` is given the task of propagating what resource is responsible for the new resource's existence. ###### `resource`# `resource` is an object that represents the actual async resource that has been initialized. The API to access the object may be specified by the creator of the resource. Resources created by Node.js itself are internal and may change at any time. Therefore no API is specified for these. In some cases the resource object is reused for performance reasons, it is thus not safe to use it as a key in a `WeakMap` or add properties to it. ###### Asynchronous context example# The context tracking use case is covered by the stable API `AsyncLocalStorage`. This example only illustrates async hooks operation but `AsyncLocalStorage` fits better to this use case. The following is an example with additional information about the calls to `init` between the `before` and `after` calls, specifically what the callback to `listen()` will look like. The output formatting is slightly more elaborate to make calling context easier to see. import async_hooks from 'node:async_hooks'; import fs from 'node:fs'; import net from 'node:net'; import { stdout } from 'node:process'; const { fd } = stdout; let indent = 0; async_hooks.createHook({ init(asyncId, type, triggerAsyncId) { const eid = async_hooks.executionAsyncId(); const indentStr = ' '.repeat(indent); fs.writeSync( fd, `${indentStr}${type}(${asyncId}):` + ` trigger: ${triggerAsyncId} execution: ${eid}\n`); }, before(asyncId) { const indentStr = ' '.repeat(indent); fs.writeSync(fd, `${indentStr}before: ${asyncId}\n`); indent += 2; }, after(asyncId) { indent -= 2; const indentStr = ' '.repeat(indent); fs.writeSync(fd, `${indentStr}after: ${asyncId}\n`); }, destroy(asyncId) { const indentStr = ' '.repeat(indent); fs.writeSync(fd, `${indentStr}destroy: ${asyncId}\n`); }, }).enable(); net.createServer(() => {}).listen(8080, () => { // Let's wait 10ms before logging the server started. setTimeout(() => { console.log('>>>', async_hooks.executionAsyncId()); }, 10); }); Output from only starting the server: TCPSERVERWRAP(5): trigger: 1 execution: 1 TickObject(6): trigger: 5 execution: 1 before: 6 Timeout(7): trigger: 6 execution: 6 after: 6 destroy: 6 before: 7 >>> 7 TickObject(8): trigger: 7 execution: 7 after: 7 before: 8 after: 8 As illustrated in the example, `executionAsyncId()` and `execution` each specify the value of the current execution context; which is delineated by calls to `before` and `after`. Only using `execution` to graph resource allocation results in the following: root(1) ^ | TickObject(6) ^ | Timeout(7) The `TCPSERVERWRAP` is not part of this graph, even though it was the reason for `console.log()` being called. This is because binding to a port without a host name is a synchronous operation, but to maintain a completely asynchronous API the user's callback is placed in a `process.nextTick()`. Which is why `TickObject` is present in the output and is a 'parent' for `.listen()` callback. The graph only shows when a resource was created, not why, so to track the why use `triggerAsyncId`. Which can be represented with the following graph: bootstrap(1) | ˅ TCPSERVERWRAP(5) | ˅ TickObject(6) | ˅ Timeout(7) ##### `before(asyncId)`# * `asyncId` When an asynchronous operation is initiated (such as a TCP server receiving a new connection) or completes (such as writing data to disk) a callback is called to notify the user. The `before` callback is called just before said callback is executed. `asyncId` is the unique identifier assigned to the resource about to execute the callback. The `before` callback will be called 0 to N times. The `before` callback will typically be called 0 times if the asynchronous operation was cancelled or, for example, if no connections are received by a TCP server. Persistent asynchronous resources like a TCP server will typically call the `before` callback multiple times, while other operations like `fs.open()` will call it only once. ##### `after(asyncId)`# * `asyncId` Called immediately after the callback specified in `before` is completed. If an uncaught exception occurs during execution of the callback, then `after` will run after the `'uncaughtException'` event is emitted or a `domain`'s handler runs. ##### `destroy(asyncId)`# * `asyncId` Called after the resource corresponding to `asyncId` is destroyed. It is also called asynchronously from the embedder API `emitDestroy()`. Some resources depend on garbage collection for cleanup, so if a reference is made to the `resource` object passed to `init` it is possible that `destroy` will never be called, causing a memory leak in the application. If the resource does not depend on garbage collection, then this will not be an issue. Using the destroy hook results in additional overhead because it enables tracking of `Promise` instances via the garbage collector. ##### `promiseResolve(asyncId)`# Added in: v8.6.0 * `asyncId` Called when the `resolve` function passed to the `Promise` constructor is invoked (either directly or through other means of resolving a promise). `resolve()` does not do any observable synchronous work. The `Promise` is not necessarily fulfilled or rejected at this point if the `Promise` was resolved by assuming the state of another `Promise`. new Promise((resolve) => resolve(true)).then((a) => {}); calls the following callbacks: init for PROMISE with id 5, trigger id: 1 promise resolve 5 # corresponds to resolve(true) init for PROMISE with id 6, trigger id: 5 # the Promise returned by then() before 6 # the then() callback is entered promise resolve 6 # the then() callback resolves the promise by returning after 6 #### `async_hooks.executionAsyncResource()`# Added in: v13.9.0, v12.17.0 * Returns: The resource representing the current execution. Useful to store data within the resource. Resource objects returned by `executionAsyncResource()` are most often internal Node.js handle objects with undocumented APIs. Using any functions or properties on the object is likely to crash your application and should be avoided. Using `executionAsyncResource()` in the top-level execution context will return an empty object as there is no handle or request object to use, but having an object representing the top-level can be helpful. import { open } from 'node:fs'; import { executionAsyncId, executionAsyncResource } from 'node:async_hooks'; console.log(executionAsyncId(), executionAsyncResource()); // 1 {} open(new URL(import.meta.url), 'r', (err, fd) => { console.log(executionAsyncId(), executionAsyncResource()); // 7 FSReqWrap }); This can be used to implement continuation local storage without the use of a tracking `Map` to store the metadata: import { createServer } from 'node:http'; import { executionAsyncId, executionAsyncResource, createHook, } from 'node:async_hooks'; const sym = Symbol('state'); // Private symbol to avoid pollution createHook({ init(asyncId, type, triggerAsyncId, resource) { const cr = executionAsyncResource(); if (cr) { resource[sym] = cr[sym]; } }, }).enable(); const server = createServer((req, res) => { executionAsyncResource()[sym] = { state: req.url }; setTimeout(function() { res.end(JSON.stringify(executionAsyncResource()[sym])); }, 100); }).listen(3000); #### `async_hooks.executionAsyncId()`# History VersionChanges v8.2.0 Renamed from `currentId`. v8.1.0 Added in: v8.1.0 * Returns: The `asyncId` of the current execution context. Useful to track when something calls. import { executionAsyncId } from 'node:async_hooks'; import fs from 'node:fs'; console.log(executionAsyncId()); // 1 - bootstrap const path = '.'; fs.open(path, 'r', (err, fd) => { console.log(executionAsyncId()); // 6 - open() }); The ID returned from `executionAsyncId()` is related to execution timing, not causality (which is covered by `triggerAsyncId()`): const server = net.createServer((conn) => { // Returns the ID of the server, not of the new connection, because the // callback runs in the execution scope of the server's MakeCallback(). async_hooks.executionAsyncId(); }).listen(port, () => { // Returns the ID of a TickObject (process.nextTick()) because all // callbacks passed to .listen() are wrapped in a nextTick(). async_hooks.executionAsyncId(); }); Promise contexts may not get precise `executionAsyncIds` by default. See the section on promise execution tracking. #### `async_hooks.triggerAsyncId()`# * Returns: The ID of the resource responsible for calling the callback that is currently being executed. const server = net.createServer((conn) => { // The resource that caused (or triggered) this callback to be called // was that of the new connection. Thus the return value of triggerAsyncId() // is the asyncId of "conn". async_hooks.triggerAsyncId(); }).listen(port, () => { // Even though all callbacks passed to .listen() are wrapped in a nextTick() // the callback itself exists because the call to the server's .listen() // was made. So the return value would be the ID of the server. async_hooks.triggerAsyncId(); }); Promise contexts may not get valid `triggerAsyncId`s by default. See the section on promise execution tracking. #### `async_hooks.asyncWrapProviders`# Added in: v17.2.0, v16.14.0 * Returns: A map of provider types to the corresponding numeric id. This map contains all the event types that might be emitted by the `async_hooks.init()` event. This feature suppresses the deprecated usage of `process.binding('async_wrap').Providers`. See: DEP0111 ### Promise execution tracking# By default, promise executions are not assigned `asyncId`s due to the relatively expensive nature of the promise introspection API provided by V8. This means that programs using promises or `async`/`await` will not get correct execution and trigger ids for promise callback contexts by default. import { executionAsyncId, triggerAsyncId } from 'node:async_hooks'; Promise.resolve(1729).then(() => { console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`); }); // produces: // eid 1 tid 0 Observe that the `then()` callback claims to have executed in the context of the outer scope even though there was an asynchronous hop involved. Also, the `triggerAsyncId` value is `0`, which means that we are missing context about the resource that caused (triggered) the `then()` callback to be executed. Installing async hooks via `async_hooks.createHook` enables promise execution tracking: import { createHook, executionAsyncId, triggerAsyncId } from 'node:async_hooks'; createHook({ init() {} }).enable(); // forces PromiseHooks to be enabled. Promise.resolve(1729).then(() => { console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`); }); // produces: // eid 7 tid 6 In this example, adding any actual hook function enabled the tracking of promises. There are two promises in the example above; the promise created by `Promise.resolve()` and the promise returned by the call to `then()`. In the example above, the first promise got the `asyncId` `6` and the latter got `asyncId` `7`. During the execution of the `then()` callback, we are executing in the context of promise with `asyncId` `7`. This promise was triggered by async resource `6`. Another subtlety with promises is that `before` and `after` callbacks are run only on chained promises. That means promises not created by `then()`/`catch()` will not have the `before` and `after` callbacks fired on them. For more details see the details of the V8 PromiseHooks API. ### JavaScript embedder API# Library developers that handle their own asynchronous resources performing tasks like I/O, connection pooling, or managing callback queues may use the `AsyncResource` JavaScript API so that all the appropriate callbacks are called. #### Class: `AsyncResource`# The documentation for this class has moved `AsyncResource`. ### Class: `AsyncLocalStorage`# The documentation for this class has moved `AsyncLocalStorage`. ## Buffer# Stability: 2 \- Stable Source Code: lib/buffer.js `Buffer` objects are used to represent a fixed-length sequence of bytes. Many Node.js APIs support `Buffer`s. The `Buffer` class is a subclass of JavaScript's class and extends it with methods that cover additional use cases. Node.js APIs accept plain s wherever `Buffer`s are supported as well. While the `Buffer` class is available within the global scope, it is still recommended to explicitly reference it via an import or require statement. import { Buffer } from 'node:buffer'; // Creates a zero-filled Buffer of length 10. const buf1 = Buffer.alloc(10); // Creates a Buffer of length 10, // filled with bytes which all have the value `1`. const buf2 = Buffer.alloc(10, 1); // Creates an uninitialized buffer of length 10. // This is faster than calling Buffer.alloc() but the returned // Buffer instance might contain old data that needs to be // overwritten using fill(), write(), or other functions that fill the Buffer's // contents. const buf3 = Buffer.allocUnsafe(10); // Creates a Buffer containing the bytes [1, 2, 3]. const buf4 = Buffer.from([1, 2, 3]); // Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries // are all truncated using `(value & 255)` to fit into the range 0–255. const buf5 = Buffer.from([257, 257.5, -255, '1']); // Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést': // [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation) // [116, 195, 169, 115, 116] (in decimal notation) const buf6 = Buffer.from('tést'); // Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74]. const buf7 = Buffer.from('tést', 'latin1'); ### Buffers and character encodings# History VersionChanges v15.7.0, v14.18.0 Introduced `base64url` encoding. v6.4.0 Introduced `latin1` as an alias for `binary`. v5.0.0 Removed the deprecated `raw` and `raws` encodings. When converting between `Buffer`s and strings, a character encoding may be specified. If no character encoding is specified, UTF-8 will be used as the default. import { Buffer } from 'node:buffer'; const buf = Buffer.from('hello world', 'utf8'); console.log(buf.toString('hex')); // Prints: 68656c6c6f20776f726c64 console.log(buf.toString('base64')); // Prints: aGVsbG8gd29ybGQ= console.log(Buffer.from('fhqwhgads', 'utf8')); // Prints: console.log(Buffer.from('fhqwhgads', 'utf16le')); // Prints: Node.js buffers accept all case variations of encoding strings that they receive. For example, UTF-8 can be specified as `'utf8'`, `'UTF8'`, or `'uTf8'`. The character encodings currently supported by Node.js are the following: * `'utf8'` (alias: `'utf-8'`): Multi-byte encoded Unicode characters. Many web pages and other document formats use UTF-8. This is the default character encoding. When decoding a `Buffer` into a string that does not exclusively contain valid UTF-8 data, the Unicode replacement character `U+FFFD` � will be used to represent those errors. * `'utf16le'` (alias: `'utf-16le'`): Multi-byte encoded Unicode characters. Unlike `'utf8'`, each character in the string will be encoded using either 2 or 4 bytes. Node.js only supports the little-endian variant of UTF-16. * `'latin1'`: Latin-1 stands for ISO-8859-1. This character encoding only supports the Unicode characters from `U+0000` to `U+00FF`. Each character is encoded using a single byte. Characters that do not fit into that range are truncated and will be mapped to characters in that range. Converting a `Buffer` into a string using one of the above is referred to as decoding, and converting a string into a `Buffer` is referred to as encoding. Node.js also supports the following binary-to-text encodings. For binary-to-text encodings, the naming convention is reversed: Converting a `Buffer` into a string is typically referred to as encoding, and converting a string into a `Buffer` as decoding. * `'base64'`: Base64 encoding. When creating a `Buffer` from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC 4648, Section 5. Whitespace characters such as spaces, tabs, and new lines contained within the base64-encoded string are ignored. * `'base64url'`: base64url encoding as specified in RFC 4648, Section 5. When creating a `Buffer` from a string, this encoding will also correctly accept regular base64-encoded strings. When encoding a `Buffer` to a string, this encoding will omit padding. * `'hex'`: Encode each byte as two hexadecimal characters. Data truncation may occur when decoding strings that do not exclusively consist of an even number of hexadecimal characters. See below for an example. The following legacy character encodings are also supported: * `'ascii'`: For 7-bit ASCII data only. When encoding a string into a `Buffer`, this is equivalent to using `'latin1'`. When decoding a `Buffer` into a string, using this encoding will additionally unset the highest bit of each byte before decoding as `'latin1'`. Generally, there should be no reason to use this encoding, as `'utf8'` (or, if the data is known to always be ASCII-only, `'latin1'`) will be a better choice when encoding or decoding ASCII-only text. It is only provided for legacy compatibility. * `'binary'`: Alias for `'latin1'`. The name of this encoding can be very misleading, as all of the encodings listed here convert between strings and binary data. For converting between strings and `Buffer`s, typically `'utf8'` is the right choice. * `'ucs2'`, `'ucs-2'`: Aliases of `'utf16le'`. UCS-2 used to refer to a variant of UTF-16 that did not support characters that had code points larger than U+FFFF. In Node.js, these code points are always supported. import { Buffer } from 'node:buffer'; Buffer.from('1ag123', 'hex'); // Prints , data truncated when first non-hexadecimal value // ('g') encountered. Buffer.from('1a7', 'hex'); // Prints , data truncated when data ends in single digit ('7'). Buffer.from('1634', 'hex'); // Prints , all data represented. Modern Web browsers follow the WHATWG Encoding Standard which aliases both `'latin1'` and `'ISO-8859-1'` to `'win-1252'`. This means that while doing something like `http.get()`, if the returned charset is one of those listed in the WHATWG specification it is possible that the server actually returned `'win-1252'`-encoded data, and using `'latin1'` encoding may incorrectly decode the characters. ### Buffers and TypedArrays# History VersionChanges v3.0.0 The `Buffer` class now inherits from `Uint8Array`. `Buffer` instances are also JavaScript and instances. All methods are available on `Buffer`s. There are, however, subtle incompatibilities between the `Buffer` API and the API. In particular: * While `TypedArray.prototype.slice()` creates a copy of part of the `TypedArray`, `Buffer.prototype.slice()` creates a view over the existing `Buffer` without copying. This behavior can be surprising, and only exists for legacy compatibility. `TypedArray.prototype.subarray()` can be used to achieve the behavior of `Buffer.prototype.slice()` on both `Buffer`s and other `TypedArray`s and should be preferred. * `buf.toString()` is incompatible with its `TypedArray` equivalent. * A number of methods, e.g. `buf.indexOf()`, support additional arguments. There are two ways to create new instances from a `Buffer`: * Passing a `Buffer` to a constructor will copy the `Buffer`'s contents, interpreted as an array of integers, and not as a byte sequence of the target type. import { Buffer } from 'node:buffer'; const buf = Buffer.from([1, 2, 3, 4]); const uint32array = new Uint32Array(buf); console.log(uint32array); // Prints: Uint32Array(4) [ 1, 2, 3, 4 ] * Passing the `Buffer`'s underlying will create a that shares its memory with the `Buffer`. import { Buffer } from 'node:buffer'; const buf = Buffer.from('hello', 'utf16le'); const uint16array = new Uint16Array( buf.buffer, buf.byteOffset, buf.length / Uint16Array.BYTES_PER_ELEMENT); console.log(uint16array); // Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ] It is possible to create a new `Buffer` that shares the same allocated memory as a instance by using the `TypedArray` object's `.buffer` property in the same way. `Buffer.from()` behaves like `new Uint8Array()` in this context. import { Buffer } from 'node:buffer'; const arr = new Uint16Array(2); arr[0] = 5000; arr[1] = 4000; // Copies the contents of `arr`. const buf1 = Buffer.from(arr); // Shares memory with `arr`. const buf2 = Buffer.from(arr.buffer); console.log(buf1); // Prints: console.log(buf2); // Prints: arr[1] = 6000; console.log(buf1); // Prints: console.log(buf2); // Prints: When creating a `Buffer` using a 's `.buffer`, it is possible to use only a portion of the underlying by passing in `byteOffset` and `length` parameters. import { Buffer } from 'node:buffer'; const arr = new Uint16Array(20); const buf = Buffer.from(arr.buffer, 0, 16); console.log(buf.length); // Prints: 16 The `Buffer.from()` and `TypedArray.from()` have different signatures and implementations. Specifically, the variants accept a second argument that is a mapping function that is invoked on every element of the typed array: * `TypedArray.from(source[, mapFn[, thisArg]])` The `Buffer.from()` method, however, does not support the use of a mapping function: * `Buffer.from(array)` * `Buffer.from(buffer)` * `Buffer.from(arrayBuffer[, byteOffset[, length]])` * `Buffer.from(string[, encoding])` ### Buffers and iteration# `Buffer` instances can be iterated over using `for..of` syntax: import { Buffer } from 'node:buffer'; const buf = Buffer.from([1, 2, 3]); for (const b of buf) { console.log(b); } // Prints: // 1 // 2 // 3 Additionally, the `buf.values()`, `buf.keys()`, and `buf.entries()` methods can be used to create iterators. ### Class: `Blob`# History VersionChanges v18.0.0, v16.17.0 No longer experimental. v15.7.0, v14.18.0 Added in: v15.7.0, v14.18.0 A encapsulates immutable, raw data that can be safely shared across multiple worker threads. #### `new buffer.Blob([sources[, options]])`# History VersionChanges v16.7.0 Added the standard `endings` option to replace line-endings, and removed the non-standard `encoding` option. v15.7.0, v14.18.0 Added in: v15.7.0, v14.18.0 * `sources` | | | | An array of string, , , , or objects, or any mix of such objects, that will be stored within the `Blob`. * `options` * `endings` One of either `'transparent'` or `'native'`. When set to `'native'`, line endings in string source parts will be converted to the platform native line-ending as specified by `require('node:os').EOL`. * `type` The Blob content-type. The intent is for `type` to convey the MIME media type of the data, however no validation of the type format is performed. Creates a new `Blob` object containing a concatenation of the given sources. , , , and sources are copied into the 'Blob' and can therefore be safely modified after the 'Blob' is created. String sources are encoded as UTF-8 byte sequences and copied into the Blob. Unmatched surrogate pairs within each string part will be replaced by Unicode U+FFFD replacement characters. #### `blob.arrayBuffer()`# Added in: v15.7.0, v14.18.0 * Returns: Returns a promise that fulfills with an containing a copy of the `Blob` data. ##### `blob.bytes()`# Added in: v22.3.0, v20.16.0 The `blob.bytes()` method returns the byte of the `Blob` object as a `Promise`. const blob = new Blob(['hello']); blob.bytes().then((bytes) => { console.log(bytes); // Outputs: Uint8Array(5) [ 104, 101, 108, 108, 111 ] }); #### `blob.size`# Added in: v15.7.0, v14.18.0 The total size of the `Blob` in bytes. #### `blob.slice([start[, end[, type]]])`# Added in: v15.7.0, v14.18.0 * `start` The starting index. * `end` The ending index. * `type` The content-type for the new `Blob` Creates and returns a new `Blob` containing a subset of this `Blob` objects data. The original `Blob` is not altered. #### `blob.stream()`# Added in: v16.7.0 * Returns: Returns a new `ReadableStream` that allows the content of the `Blob` to be read. #### `blob.text()`# Added in: v15.7.0, v14.18.0 * Returns: Returns a promise that fulfills with the contents of the `Blob` decoded as a UTF-8 string. #### `blob.type`# Added in: v15.7.0, v14.18.0 * Type: The content-type of the `Blob`. #### `Blob` objects and `MessageChannel`# Once a object is created, it can be sent via `MessagePort` to multiple destinations without transferring or immediately copying the data. The data contained by the `Blob` is copied only when the `arrayBuffer()` or `text()` methods are called. import { Blob } from 'node:buffer'; import { setTimeout as delay } from 'node:timers/promises'; const blob = new Blob(['hello there']); const mc1 = new MessageChannel(); const mc2 = new MessageChannel(); mc1.port1.onmessage = async ({ data }) => { console.log(await data.arrayBuffer()); mc1.port1.close(); }; mc2.port1.onmessage = async ({ data }) => { await delay(1000); console.log(await data.arrayBuffer()); mc2.port1.close(); }; mc1.port2.postMessage(blob); mc2.port2.postMessage(blob); // The Blob is still usable after posting. blob.text().then(console.log); ### Class: `Buffer`# The `Buffer` class is a global type for dealing with binary data directly. It can be constructed in a variety of ways. #### Static method: `Buffer.alloc(size[, fill[, encoding]])`# History VersionChanges v20.0.0 Throw ERR_INVALID_ARG_TYPE or ERR_OUT_OF_RANGE instead of ERR_INVALID_ARG_VALUE for invalid input arguments. v15.0.0 Throw ERR_INVALID_ARG_VALUE instead of ERR_INVALID_OPT_VALUE for invalid input arguments. v10.0.0 Attempting to fill a non-zero length buffer with a zero length buffer triggers a thrown exception. v10.0.0 Specifying an invalid string for `fill` triggers a thrown exception. v8.9.3 Specifying an invalid string for `fill` now results in a zero-filled buffer. v5.10.0 Added in: v5.10.0 * `size` The desired length of the new `Buffer`. * `fill` | | | A value to pre-fill the new `Buffer` with. Default: `0`. * `encoding` If `fill` is a string, this is its encoding. Default: `'utf8'`. * Returns: Allocates a new `Buffer` of `size` bytes. If `fill` is `undefined`, the `Buffer` will be zero-filled. import { Buffer } from 'node:buffer'; const buf = Buffer.alloc(5); console.log(buf); // Prints: If `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, `ERR_OUT_OF_RANGE` is thrown. If `fill` is specified, the allocated `Buffer` will be initialized by calling `buf.fill(fill)`. import { Buffer } from 'node:buffer'; const buf = Buffer.alloc(5, 'a'); console.log(buf); // Prints: If both `fill` and `encoding` are specified, the allocated `Buffer` will be initialized by calling `buf.fill(fill, encoding)`. import { Buffer } from 'node:buffer'; const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64'); console.log(buf); // Prints: Calling `Buffer.alloc()` can be measurably slower than the alternative `Buffer.allocUnsafe()` but ensures that the newly created `Buffer` instance contents will never contain sensitive data from previous allocations, including data that might not have been allocated for `Buffer`s. A `TypeError` will be thrown if `size` is not a number. #### Static method: `Buffer.allocUnsafe(size)`# History VersionChanges v20.0.0 Throw ERR_INVALID_ARG_TYPE or ERR_OUT_OF_RANGE instead of ERR_INVALID_ARG_VALUE for invalid input arguments. v15.0.0 Throw ERR_INVALID_ARG_VALUE instead of ERR_INVALID_OPT_VALUE for invalid input arguments. v7.0.0 Passing a negative `size` will now throw an error. v5.10.0 Added in: v5.10.0 * `size` The desired length of the new `Buffer`. * Returns: Allocates a new `Buffer` of `size` bytes. If `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, `ERR_OUT_OF_RANGE` is thrown. The underlying memory for `Buffer` instances created in this way is not initialized. The contents of the newly created `Buffer` are unknown and may contain sensitive data. Use `Buffer.alloc()` instead to initialize `Buffer` instances with zeroes. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(10); console.log(buf); // Prints (contents may vary): buf.fill(0); console.log(buf); // Prints: A `TypeError` will be thrown if `size` is not a number. The `Buffer` module pre-allocates an internal `Buffer` instance of size `Buffer.poolSize` that is used as a pool for the fast allocation of new `Buffer` instances created using `Buffer.allocUnsafe()`, `Buffer.from(array)`, `Buffer.from(string)`, and `Buffer.concat()` only when `size` is less than `Buffer.poolSize >>> 1` (floor of `Buffer.poolSize` divided by two). Use of this pre-allocated internal memory pool is a key difference between calling `Buffer.alloc(size, fill)` vs. `Buffer.allocUnsafe(size).fill(fill)`. Specifically, `Buffer.alloc(size, fill)` will never use the internal `Buffer` pool, while `Buffer.allocUnsafe(size).fill(fill)` will use the internal `Buffer` pool if `size` is less than or equal to half `Buffer.poolSize`. The difference is subtle but can be important when an application requires the additional performance that `Buffer.allocUnsafe()` provides. #### Static method: `Buffer.allocUnsafeSlow(size)`# History VersionChanges v20.0.0 Throw ERR_INVALID_ARG_TYPE or ERR_OUT_OF_RANGE instead of ERR_INVALID_ARG_VALUE for invalid input arguments. v15.0.0 Throw ERR_INVALID_ARG_VALUE instead of ERR_INVALID_OPT_VALUE for invalid input arguments. v5.12.0 Added in: v5.12.0 * `size` The desired length of the new `Buffer`. * Returns: Allocates a new `Buffer` of `size` bytes. If `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, `ERR_OUT_OF_RANGE` is thrown. A zero-length `Buffer` is created if `size` is 0. The underlying memory for `Buffer` instances created in this way is not initialized. The contents of the newly created `Buffer` are unknown and may contain sensitive data. Use `buf.fill(0)` to initialize such `Buffer` instances with zeroes. When using `Buffer.allocUnsafe()` to allocate new `Buffer` instances, allocations less than `Buffer.poolSize >>> 1` (4KiB when default poolSize is used) are sliced from a single pre-allocated `Buffer`. This allows applications to avoid the garbage collection overhead of creating many individually allocated `Buffer` instances. This approach improves both performance and memory usage by eliminating the need to track and clean up as many individual `ArrayBuffer` objects. However, in the case where a developer may need to retain a small chunk of memory from a pool for an indeterminate amount of time, it may be appropriate to create an un-pooled `Buffer` instance using `Buffer.allocUnsafeSlow()` and then copying out the relevant bits. import { Buffer } from 'node:buffer'; // Need to keep around a few small chunks of memory. const store = []; socket.on('readable', () => { let data; while (null !== (data = readable.read())) { // Allocate for retained data. const sb = Buffer.allocUnsafeSlow(10); // Copy the data into the new allocation. data.copy(sb, 0, 0, 10); store.push(sb); } }); A `TypeError` will be thrown if `size` is not a number. #### Static method: `Buffer.byteLength(string[, encoding])`# History VersionChanges v7.0.0 Passing invalid input will now throw an error. v5.10.0 The `string` parameter can now be any `TypedArray`, `DataView` or `ArrayBuffer`. v0.1.90 Added in: v0.1.90 * `string` | | | | | A value to calculate the length of. * `encoding` If `string` is a string, this is its encoding. Default: `'utf8'`. * Returns: The number of bytes contained within `string`. Returns the byte length of a string when encoded using `encoding`. This is not the same as `String.prototype.length`, which does not account for the encoding that is used to convert the string into bytes. For `'base64'`, `'base64url'`, and `'hex'`, this function assumes valid input. For strings that contain non-base64/hex-encoded data (e.g. whitespace), the return value might be greater than the length of a `Buffer` created from the string. import { Buffer } from 'node:buffer'; const str = '\u00bd + \u00bc = \u00be'; console.log(`${str}: ${str.length} characters, ` + `${Buffer.byteLength(str, 'utf8')} bytes`); // Prints: ½ + ¼ = ¾: 9 characters, 12 bytes When `string` is a | | | | , the byte length as reported by `.byteLength` is returned. #### Static method: `Buffer.compare(buf1, buf2)`# History VersionChanges v8.0.0 The arguments can now be `Uint8Array`s. v0.11.13 Added in: v0.11.13 * `buf1` | * `buf2` | * Returns: Either `-1`, `0`, or `1`, depending on the result of the comparison. See `buf.compare()` for details. Compares `buf1` to `buf2`, typically for the purpose of sorting arrays of `Buffer` instances. This is equivalent to calling `buf1.compare(buf2)`. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from('1234'); const buf2 = Buffer.from('0123'); const arr = [buf1, buf2]; console.log(arr.sort(Buffer.compare)); // Prints: [ , ] // (This result is equal to: [buf2, buf1].) #### Static method: `Buffer.concat(list[, totalLength])`# History VersionChanges v8.0.0 The elements of `list` can now be `Uint8Array`s. v0.7.11 Added in: v0.7.11 * `list` | List of `Buffer` or instances to concatenate. * `totalLength` Total length of the `Buffer` instances in `list` when concatenated. * Returns: Returns a new `Buffer` which is the result of concatenating all the `Buffer` instances in the `list` together. If the list has no items, or if the `totalLength` is 0, then a new zero-length `Buffer` is returned. If `totalLength` is not provided, it is calculated from the `Buffer` instances in `list` by adding their lengths. If `totalLength` is provided, it is coerced to an unsigned integer. If the combined length of the `Buffer`s in `list` exceeds `totalLength`, the result is truncated to `totalLength`. If the combined length of the `Buffer`s in `list` is less than `totalLength`, the remaining space is filled with zeros. import { Buffer } from 'node:buffer'; // Create a single `Buffer` from a list of three `Buffer` instances. const buf1 = Buffer.alloc(10); const buf2 = Buffer.alloc(14); const buf3 = Buffer.alloc(18); const totalLength = buf1.length + buf2.length + buf3.length; console.log(totalLength); // Prints: 42 const bufA = Buffer.concat([buf1, buf2, buf3], totalLength); console.log(bufA); // Prints: console.log(bufA.length); // Prints: 42 `Buffer.concat()` may also use the internal `Buffer` pool like `Buffer.allocUnsafe()` does. #### Static method: `Buffer.copyBytesFrom(view[, offset[, length]])`# Added in: v19.8.0, v18.16.0 * `view` The to copy. * `offset` The starting offset within `view`. Default: `0`. * `length` The number of elements from `view` to copy. Default: `view.length - offset`. * Returns: Copies the underlying memory of `view` into a new `Buffer`. const u16 = new Uint16Array([0, 0xffff]); const buf = Buffer.copyBytesFrom(u16, 1, 1); u16[1] = 0; console.log(buf.length); // 2 console.log(buf[0]); // 255 console.log(buf[1]); // 255 #### Static method: `Buffer.from(array)`# Added in: v5.10.0 * `array` * Returns: Allocates a new `Buffer` using an `array` of bytes in the range `0` – `255`. Array entries outside that range will be truncated to fit into it. import { Buffer } from 'node:buffer'; // Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'. const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]); If `array` is an `Array`-like object (that is, one with a `length` property of type `number`), it is treated as if it is an array, unless it is a `Buffer` or a `Uint8Array`. This means all other `TypedArray` variants get treated as an `Array`. To create a `Buffer` from the bytes backing a `TypedArray`, use `Buffer.copyBytesFrom()`. A `TypeError` will be thrown if `array` is not an `Array` or another type appropriate for `Buffer.from()` variants. `Buffer.from(array)` and `Buffer.from(string)` may also use the internal `Buffer` pool like `Buffer.allocUnsafe()` does. #### Static method: `Buffer.from(arrayBuffer[, byteOffset[, length]])`# Added in: v5.10.0 * `arrayBuffer` | An , , for example the `.buffer` property of a . * `byteOffset` Index of first byte to expose. Default: `0`. * `length` Number of bytes to expose. Default: `arrayBuffer.byteLength - byteOffset`. * Returns: This creates a view of the without copying the underlying memory. For example, when passed a reference to the `.buffer` property of a instance, the newly created `Buffer` will share the same allocated memory as the 's underlying `ArrayBuffer`. import { Buffer } from 'node:buffer'; const arr = new Uint16Array(2); arr[0] = 5000; arr[1] = 4000; // Shares memory with `arr`. const buf = Buffer.from(arr.buffer); console.log(buf); // Prints: // Changing the original Uint16Array changes the Buffer also. arr[1] = 6000; console.log(buf); // Prints: The optional `byteOffset` and `length` arguments specify a memory range within the `arrayBuffer` that will be shared by the `Buffer`. import { Buffer } from 'node:buffer'; const ab = new ArrayBuffer(10); const buf = Buffer.from(ab, 0, 2); console.log(buf.length); // Prints: 2 A `TypeError` will be thrown if `arrayBuffer` is not an or a or another type appropriate for `Buffer.from()` variants. It is important to remember that a backing `ArrayBuffer` can cover a range of memory that extends beyond the bounds of a `TypedArray` view. A new `Buffer` created using the `buffer` property of a `TypedArray` may extend beyond the range of the `TypedArray`: import { Buffer } from 'node:buffer'; const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements console.log(arrA.buffer === arrB.buffer); // true const buf = Buffer.from(arrB.buffer); console.log(buf); // Prints: #### Static method: `Buffer.from(buffer)`# Added in: v5.10.0 * `buffer` | An existing `Buffer` or from which to copy data. * Returns: Copies the passed `buffer` data onto a new `Buffer` instance. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from('buffer'); const buf2 = Buffer.from(buf1); buf1[0] = 0x61; console.log(buf1.toString()); // Prints: auffer console.log(buf2.toString()); // Prints: buffer A `TypeError` will be thrown if `buffer` is not a `Buffer` or another type appropriate for `Buffer.from()` variants. #### Static method: `Buffer.from(object[, offsetOrEncoding[, length]])`# Added in: v8.2.0 * `object` An object supporting `Symbol.toPrimitive` or `valueOf()`. * `offsetOrEncoding` | A byte-offset or encoding. * `length` A length. * Returns: For objects whose `valueOf()` function returns a value not strictly equal to `object`, returns `Buffer.from(object.valueOf(), offsetOrEncoding, length)`. import { Buffer } from 'node:buffer'; const buf = Buffer.from(new String('this is a test')); // Prints: For objects that support `Symbol.toPrimitive`, returns `Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding)`. import { Buffer } from 'node:buffer'; class Foo { [Symbol.toPrimitive]() { return 'this is a test'; } } const buf = Buffer.from(new Foo(), 'utf8'); // Prints: A `TypeError` will be thrown if `object` does not have the mentioned methods or is not of another type appropriate for `Buffer.from()` variants. #### Static method: `Buffer.from(string[, encoding])`# Added in: v5.10.0 * `string` A string to encode. * `encoding` The encoding of `string`. Default: `'utf8'`. * Returns: Creates a new `Buffer` containing `string`. The `encoding` parameter identifies the character encoding to be used when converting `string` into bytes. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from('this is a tést'); const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex'); console.log(buf1.toString()); // Prints: this is a tést console.log(buf2.toString()); // Prints: this is a tést console.log(buf1.toString('latin1')); // Prints: this is a tést A `TypeError` will be thrown if `string` is not a string or another type appropriate for `Buffer.from()` variants. `Buffer.from(string)` may also use the internal `Buffer` pool like `Buffer.allocUnsafe()` does. #### Static method: `Buffer.isBuffer(obj)`# Added in: v0.1.101 * `obj` * Returns: Returns `true` if `obj` is a `Buffer`, `false` otherwise. import { Buffer } from 'node:buffer'; Buffer.isBuffer(Buffer.alloc(10)); // true Buffer.isBuffer(Buffer.from('foo')); // true Buffer.isBuffer('a string'); // false Buffer.isBuffer([]); // false Buffer.isBuffer(new Uint8Array(1024)); // false #### Static method: `Buffer.isEncoding(encoding)`# Added in: v0.9.1 * `encoding` A character encoding name to check. * Returns: Returns `true` if `encoding` is the name of a supported character encoding, or `false` otherwise. import { Buffer } from 'node:buffer'; console.log(Buffer.isEncoding('utf8')); // Prints: true console.log(Buffer.isEncoding('hex')); // Prints: true console.log(Buffer.isEncoding('utf/8')); // Prints: false console.log(Buffer.isEncoding('')); // Prints: false #### Class property: `Buffer.poolSize`# Added in: v0.11.3 * Type: Default: `8192` This is the size (in bytes) of pre-allocated internal `Buffer` instances used for pooling. This value may be modified. #### `buf[index]`# * `index` The index operator `[index]` can be used to get and set the octet at position `index` in `buf`. The values refer to individual bytes, so the legal value range is between `0x00` and `0xFF` (hex) or `0` and `255` (decimal). This operator is inherited from `Uint8Array`, so its behavior on out-of-bounds access is the same as `Uint8Array`. In other words, `buf[index]` returns `undefined` when `index` is negative or greater or equal to `buf.length`, and `buf[index] = value` does not modify the buffer if `index` is negative or `>= buf.length`. import { Buffer } from 'node:buffer'; // Copy an ASCII string into a `Buffer` one byte at a time. // (This only works for ASCII-only strings. In general, one should use // `Buffer.from()` to perform this conversion.) const str = 'Node.js'; const buf = Buffer.allocUnsafe(str.length); for (let i = 0; i < str.length; i++) { buf[i] = str.charCodeAt(i); } console.log(buf.toString('utf8')); // Prints: Node.js #### `buf.buffer`# * Type: The underlying `ArrayBuffer` object based on which this `Buffer` object is created. This `ArrayBuffer` is not guaranteed to correspond exactly to the original `Buffer`. See the notes on `buf.byteOffset` for details. import { Buffer } from 'node:buffer'; const arrayBuffer = new ArrayBuffer(16); const buffer = Buffer.from(arrayBuffer); console.log(buffer.buffer === arrayBuffer); // Prints: true #### `buf.byteOffset`# * Type: The `byteOffset` of the `Buffer`'s underlying `ArrayBuffer` object. When setting `byteOffset` in `Buffer.from(ArrayBuffer, byteOffset, length)`, or sometimes when allocating a `Buffer` smaller than `Buffer.poolSize`, the buffer does not start from a zero offset on the underlying `ArrayBuffer`. This can cause problems when accessing the underlying `ArrayBuffer` directly using `buf.buffer`, as other parts of the `ArrayBuffer` may be unrelated to the `Buffer` object itself. A common issue when creating a `TypedArray` object that shares its memory with a `Buffer` is that in this case one needs to specify the `byteOffset` correctly: import { Buffer } from 'node:buffer'; // Create a buffer smaller than `Buffer.poolSize`. const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]); // When casting the Node.js Buffer to an Int8Array, use the byteOffset // to refer only to the part of `nodeBuffer.buffer` that contains the memory // for `nodeBuffer`. new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length); #### `buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])`# History VersionChanges v8.0.0 The `target` parameter can now be a `Uint8Array`. v5.11.0 Additional parameters for specifying offsets are supported now. v0.11.13 Added in: v0.11.13 * `target` | A `Buffer` or with which to compare `buf`. * `targetStart` The offset within `target` at which to begin comparison. Default: `0`. * `targetEnd` The offset within `target` at which to end comparison (not inclusive). Default: `target.length`. * `sourceStart` The offset within `buf` at which to begin comparison. Default: `0`. * `sourceEnd` The offset within `buf` at which to end comparison (not inclusive). Default: `buf.length`. * Returns: Compares `buf` with `target` and returns a number indicating whether `buf` comes before, after, or is the same as `target` in sort order. Comparison is based on the actual sequence of bytes in each `Buffer`. * `0` is returned if `target` is the same as `buf` * `1` is returned if `target` should come before `buf` when sorted. * `-1` is returned if `target` should come after `buf` when sorted. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from('ABC'); const buf2 = Buffer.from('BCD'); const buf3 = Buffer.from('ABCD'); console.log(buf1.compare(buf1)); // Prints: 0 console.log(buf1.compare(buf2)); // Prints: -1 console.log(buf1.compare(buf3)); // Prints: -1 console.log(buf2.compare(buf1)); // Prints: 1 console.log(buf2.compare(buf3)); // Prints: 1 console.log([buf1, buf2, buf3].sort(Buffer.compare)); // Prints: [ , , ] // (This result is equal to: [buf1, buf3, buf2].) The optional `targetStart`, `targetEnd`, `sourceStart`, and `sourceEnd` arguments can be used to limit the comparison to specific ranges within `target` and `buf` respectively. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]); const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]); console.log(buf1.compare(buf2, 5, 9, 0, 4)); // Prints: 0 console.log(buf1.compare(buf2, 0, 6, 4)); // Prints: -1 console.log(buf1.compare(buf2, 5, 6, 5)); // Prints: 1 `ERR_OUT_OF_RANGE` is thrown if `targetStart < 0`, `sourceStart < 0`, `targetEnd > target.byteLength`, or `sourceEnd > source.byteLength`. #### `buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])`# Added in: v0.1.90 * `target` | A `Buffer` or to copy into. * `targetStart` The offset within `target` at which to begin writing. Default: `0`. * `sourceStart` The offset within `buf` from which to begin copying. Default: `0`. * `sourceEnd` The offset within `buf` at which to stop copying (not inclusive). Default: `buf.length`. * Returns: The number of bytes copied. Copies data from a region of `buf` to a region in `target`, even if the `target` memory region overlaps with `buf`. `TypedArray.prototype.set()` performs the same operation, and is available for all TypedArrays, including Node.js `Buffer`s, although it takes different function arguments. import { Buffer } from 'node:buffer'; // Create two `Buffer` instances. const buf1 = Buffer.allocUnsafe(26); const buf2 = Buffer.allocUnsafe(26).fill('!'); for (let i = 0; i < 26; i++) { // 97 is the decimal ASCII value for 'a'. buf1[i] = i + 97; } // Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`. buf1.copy(buf2, 8, 16, 20); // This is equivalent to: // buf2.set(buf1.subarray(16, 20), 8); console.log(buf2.toString('ascii', 0, 25)); // Prints: !!!!!!!!qrst!!!!!!!!!!!!! import { Buffer } from 'node:buffer'; // Create a `Buffer` and copy data from one region to an overlapping region // within the same `Buffer`. const buf = Buffer.allocUnsafe(26); for (let i = 0; i < 26; i++) { // 97 is the decimal ASCII value for 'a'. buf[i] = i + 97; } buf.copy(buf, 0, 4, 10); console.log(buf.toString()); // Prints: efghijghijklmnopqrstuvwxyz #### `buf.entries()`# Added in: v1.1.0 * Returns: Creates and returns an iterator of `[index, byte]` pairs from the contents of `buf`. import { Buffer } from 'node:buffer'; // Log the entire contents of a `Buffer`. const buf = Buffer.from('buffer'); for (const pair of buf.entries()) { console.log(pair); } // Prints: // [0, 98] // [1, 117] // [2, 102] // [3, 102] // [4, 101] // [5, 114] #### `buf.equals(otherBuffer)`# History VersionChanges v8.0.0 The arguments can now be `Uint8Array`s. v0.11.13 Added in: v0.11.13 * `otherBuffer` | A `Buffer` or with which to compare `buf`. * Returns: Returns `true` if both `buf` and `otherBuffer` have exactly the same bytes, `false` otherwise. Equivalent to `buf.compare(otherBuffer) === 0`. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from('ABC'); const buf2 = Buffer.from('414243', 'hex'); const buf3 = Buffer.from('ABCD'); console.log(buf1.equals(buf2)); // Prints: true console.log(buf1.equals(buf3)); // Prints: false #### `buf.fill(value[, offset[, end]][, encoding])`# History VersionChanges v11.0.0 Throws `ERR_OUT_OF_RANGE` instead of `ERR_INDEX_OUT_OF_RANGE`. v10.0.0 Negative `end` values throw an `ERR_INDEX_OUT_OF_RANGE` error. v10.0.0 Attempting to fill a non-zero length buffer with a zero length buffer triggers a thrown exception. v10.0.0 Specifying an invalid string for `value` triggers a thrown exception. v5.7.0 The `encoding` parameter is supported now. v0.5.0 Added in: v0.5.0 * `value` | | | The value with which to fill `buf`. Empty value (string, Uint8Array, Buffer) is coerced to `0`. * `offset` Number of bytes to skip before starting to fill `buf`. Default: `0`. * `end` Where to stop filling `buf` (not inclusive). Default: `buf.length`. * `encoding` The encoding for `value` if `value` is a string. Default: `'utf8'`. * Returns: A reference to `buf`. Fills `buf` with the specified `value`. If the `offset` and `end` are not given, the entire `buf` will be filled: import { Buffer } from 'node:buffer'; // Fill a `Buffer` with the ASCII character 'h'. const b = Buffer.allocUnsafe(50).fill('h'); console.log(b.toString()); // Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh // Fill a buffer with empty string const c = Buffer.allocUnsafe(5).fill(''); console.log(c.fill('')); // Prints: `value` is coerced to a `uint32` value if it is not a string, `Buffer`, or integer. If the resulting integer is greater than `255` (decimal), `buf` will be filled with `value & 255`. If the final write of a `fill()` operation falls on a multi-byte character, then only the bytes of that character that fit into `buf` are written: import { Buffer } from 'node:buffer'; // Fill a `Buffer` with character that takes up two bytes in UTF-8. console.log(Buffer.allocUnsafe(5).fill('\u0222')); // Prints: If `value` contains invalid characters, it is truncated; if no valid fill data remains, an exception is thrown: import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(5); console.log(buf.fill('a')); // Prints: console.log(buf.fill('aazz', 'hex')); // Prints: console.log(buf.fill('zz', 'hex')); // Throws an exception. #### `buf.includes(value[, byteOffset][, encoding])`# Added in: v5.3.0 * `value` | | | What to search for. * `byteOffset` Where to begin searching in `buf`. If negative, then offset is calculated from the end of `buf`. Default: `0`. * `encoding` If `value` is a string, this is its encoding. Default: `'utf8'`. * Returns: `true` if `value` was found in `buf`, `false` otherwise. Equivalent to `buf.indexOf() !== -1`. import { Buffer } from 'node:buffer'; const buf = Buffer.from('this is a buffer'); console.log(buf.includes('this')); // Prints: true console.log(buf.includes('is')); // Prints: true console.log(buf.includes(Buffer.from('a buffer'))); // Prints: true console.log(buf.includes(97)); // Prints: true (97 is the decimal ASCII value for 'a') console.log(buf.includes(Buffer.from('a buffer example'))); // Prints: false console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8))); // Prints: true console.log(buf.includes('this', 4)); // Prints: false #### `buf.indexOf(value[, byteOffset][, encoding])`# History VersionChanges v8.0.0 The `value` can now be a `Uint8Array`. v5.7.0, v4.4.0 When `encoding` is being passed, the `byteOffset` parameter is no longer required. v1.5.0 Added in: v1.5.0 * `value` | | | What to search for. * `byteOffset` Where to begin searching in `buf`. If negative, then offset is calculated from the end of `buf`. Default: `0`. * `encoding` If `value` is a string, this is the encoding used to determine the binary representation of the string that will be searched for in `buf`. Default: `'utf8'`. * Returns: The index of the first occurrence of `value` in `buf`, or `-1` if `buf` does not contain `value`. If `value` is: * a string, `value` is interpreted according to the character encoding in `encoding`. * a `Buffer` or , `value` will be used in its entirety. To compare a partial `Buffer`, use `buf.subarray`. * a number, `value` will be interpreted as an unsigned 8-bit integer value between `0` and `255`. import { Buffer } from 'node:buffer'; const buf = Buffer.from('this is a buffer'); console.log(buf.indexOf('this')); // Prints: 0 console.log(buf.indexOf('is')); // Prints: 2 console.log(buf.indexOf(Buffer.from('a buffer'))); // Prints: 8 console.log(buf.indexOf(97)); // Prints: 8 (97 is the decimal ASCII value for 'a') console.log(buf.indexOf(Buffer.from('a buffer example'))); // Prints: -1 console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8))); // Prints: 8 const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le'); console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le')); // Prints: 4 console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le')); // Prints: 6 If `value` is not a string, number, or `Buffer`, this method will throw a `TypeError`. If `value` is a number, it will be coerced to a valid byte value, an integer between 0 and 255. If `byteOffset` is not a number, it will be coerced to a number. If the result of coercion is `NaN` or `0`, then the entire buffer will be searched. This behavior matches `String.prototype.indexOf()`. import { Buffer } from 'node:buffer'; const b = Buffer.from('abcdef'); // Passing a value that's a number, but not a valid byte. // Prints: 2, equivalent to searching for 99 or 'c'. console.log(b.indexOf(99.9)); console.log(b.indexOf(256 + 99)); // Passing a byteOffset that coerces to NaN or 0. // Prints: 1, searching the whole buffer. console.log(b.indexOf('b', undefined)); console.log(b.indexOf('b', {})); console.log(b.indexOf('b', null)); console.log(b.indexOf('b', [])); If `value` is an empty string or empty `Buffer` and `byteOffset` is less than `buf.length`, `byteOffset` will be returned. If `value` is empty and `byteOffset` is at least `buf.length`, `buf.length` will be returned. #### `buf.keys()`# Added in: v1.1.0 * Returns: Creates and returns an iterator of `buf` keys (indexes). import { Buffer } from 'node:buffer'; const buf = Buffer.from('buffer'); for (const key of buf.keys()) { console.log(key); } // Prints: // 0 // 1 // 2 // 3 // 4 // 5 #### `buf.lastIndexOf(value[, byteOffset][, encoding])`# History VersionChanges v8.0.0 The `value` can now be a `Uint8Array`. v6.0.0 Added in: v6.0.0 * `value` | | | What to search for. * `byteOffset` Where to begin searching in `buf`. If negative, then offset is calculated from the end of `buf`. Default: `buf.length - 1`. * `encoding` If `value` is a string, this is the encoding used to determine the binary representation of the string that will be searched for in `buf`. Default: `'utf8'`. * Returns: The index of the last occurrence of `value` in `buf`, or `-1` if `buf` does not contain `value`. Identical to `buf.indexOf()`, except the last occurrence of `value` is found rather than the first occurrence. import { Buffer } from 'node:buffer'; const buf = Buffer.from('this buffer is a buffer'); console.log(buf.lastIndexOf('this')); // Prints: 0 console.log(buf.lastIndexOf('buffer')); // Prints: 17 console.log(buf.lastIndexOf(Buffer.from('buffer'))); // Prints: 17 console.log(buf.lastIndexOf(97)); // Prints: 15 (97 is the decimal ASCII value for 'a') console.log(buf.lastIndexOf(Buffer.from('yolo'))); // Prints: -1 console.log(buf.lastIndexOf('buffer', 5)); // Prints: 5 console.log(buf.lastIndexOf('buffer', 4)); // Prints: -1 const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le'); console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le')); // Prints: 6 console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le')); // Prints: 4 If `value` is not a string, number, or `Buffer`, this method will throw a `TypeError`. If `value` is a number, it will be coerced to a valid byte value, an integer between 0 and 255. If `byteOffset` is not a number, it will be coerced to a number. Any arguments that coerce to `NaN`, like `{}` or `undefined`, will search the whole buffer. This behavior matches `String.prototype.lastIndexOf()`. import { Buffer } from 'node:buffer'; const b = Buffer.from('abcdef'); // Passing a value that's a number, but not a valid byte. // Prints: 2, equivalent to searching for 99 or 'c'. console.log(b.lastIndexOf(99.9)); console.log(b.lastIndexOf(256 + 99)); // Passing a byteOffset that coerces to NaN. // Prints: 1, searching the whole buffer. console.log(b.lastIndexOf('b', undefined)); console.log(b.lastIndexOf('b', {})); // Passing a byteOffset that coerces to 0. // Prints: -1, equivalent to passing 0. console.log(b.lastIndexOf('b', null)); console.log(b.lastIndexOf('b', [])); If `value` is an empty string or empty `Buffer`, `byteOffset` will be returned. #### `buf.length`# Added in: v0.1.90 * Type: Returns the number of bytes in `buf`. import { Buffer } from 'node:buffer'; // Create a `Buffer` and write a shorter string to it using UTF-8. const buf = Buffer.alloc(1234); console.log(buf.length); // Prints: 1234 buf.write('some string', 0, 'utf8'); console.log(buf.length); // Prints: 1234 #### `buf.parent`# Deprecated since: v8.0.0 Stability: 0 \- Deprecated: Use `buf.buffer` instead. The `buf.parent` property is a deprecated alias for `buf.buffer`. #### `buf.readBigInt64BE([offset])`# Added in: v12.0.0, v10.20.0 * `offset` Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: Reads a signed, big-endian 64-bit integer from `buf` at the specified `offset`. Integers read from a `Buffer` are interpreted as two's complement signed values. #### `buf.readBigInt64LE([offset])`# Added in: v12.0.0, v10.20.0 * `offset` Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: Reads a signed, little-endian 64-bit integer from `buf` at the specified `offset`. Integers read from a `Buffer` are interpreted as two's complement signed values. #### `buf.readBigUInt64BE([offset])`# History VersionChanges v14.10.0, v12.19.0 This function is also available as `buf.readBigUint64BE()`. v12.0.0, v10.20.0 Added in: v12.0.0, v10.20.0 * `offset` Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: Reads an unsigned, big-endian 64-bit integer from `buf` at the specified `offset`. This function is also available under the `readBigUint64BE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]); console.log(buf.readBigUInt64BE(0)); // Prints: 4294967295n #### `buf.readBigUInt64LE([offset])`# History VersionChanges v14.10.0, v12.19.0 This function is also available as `buf.readBigUint64LE()`. v12.0.0, v10.20.0 Added in: v12.0.0, v10.20.0 * `offset` Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: Reads an unsigned, little-endian 64-bit integer from `buf` at the specified `offset`. This function is also available under the `readBigUint64LE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]); console.log(buf.readBigUInt64LE(0)); // Prints: 18446744069414584320n #### `buf.readDoubleBE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: Reads a 64-bit, big-endian double from `buf` at the specified `offset`. import { Buffer } from 'node:buffer'; const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]); console.log(buf.readDoubleBE(0)); // Prints: 8.20788039913184e-304 #### `buf.readDoubleLE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: Reads a 64-bit, little-endian double from `buf` at the specified `offset`. import { Buffer } from 'node:buffer'; const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]); console.log(buf.readDoubleLE(0)); // Prints: 5.447603722011605e-270 console.log(buf.readDoubleLE(1)); // Throws ERR_OUT_OF_RANGE. #### `buf.readFloatBE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: Reads a 32-bit, big-endian float from `buf` at the specified `offset`. import { Buffer } from 'node:buffer'; const buf = Buffer.from([1, 2, 3, 4]); console.log(buf.readFloatBE(0)); // Prints: 2.387939260590663e-38 #### `buf.readFloatLE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: Reads a 32-bit, little-endian float from `buf` at the specified `offset`. import { Buffer } from 'node:buffer'; const buf = Buffer.from([1, 2, 3, 4]); console.log(buf.readFloatLE(0)); // Prints: 1.539989614439558e-36 console.log(buf.readFloatLE(1)); // Throws ERR_OUT_OF_RANGE. #### `buf.readInt8([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.0 Added in: v0.5.0 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 1`. Default: `0`. * Returns: Reads a signed 8-bit integer from `buf` at the specified `offset`. Integers read from a `Buffer` are interpreted as two's complement signed values. import { Buffer } from 'node:buffer'; const buf = Buffer.from([-1, 5]); console.log(buf.readInt8(0)); // Prints: -1 console.log(buf.readInt8(1)); // Prints: 5 console.log(buf.readInt8(2)); // Throws ERR_OUT_OF_RANGE. #### `buf.readInt16BE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: Reads a signed, big-endian 16-bit integer from `buf` at the specified `offset`. Integers read from a `Buffer` are interpreted as two's complement signed values. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0, 5]); console.log(buf.readInt16BE(0)); // Prints: 5 #### `buf.readInt16LE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: Reads a signed, little-endian 16-bit integer from `buf` at the specified `offset`. Integers read from a `Buffer` are interpreted as two's complement signed values. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0, 5]); console.log(buf.readInt16LE(0)); // Prints: 1280 console.log(buf.readInt16LE(1)); // Throws ERR_OUT_OF_RANGE. #### `buf.readInt32BE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: Reads a signed, big-endian 32-bit integer from `buf` at the specified `offset`. Integers read from a `Buffer` are interpreted as two's complement signed values. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0, 0, 0, 5]); console.log(buf.readInt32BE(0)); // Prints: 5 #### `buf.readInt32LE([offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: Reads a signed, little-endian 32-bit integer from `buf` at the specified `offset`. Integers read from a `Buffer` are interpreted as two's complement signed values. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0, 0, 0, 5]); console.log(buf.readInt32LE(0)); // Prints: 83886080 console.log(buf.readInt32LE(1)); // Throws ERR_OUT_OF_RANGE. #### `buf.readIntBE(offset, byteLength)`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to read. Must satisfy `0 < byteLength <= 6`. * Returns: Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as a big-endian, two's complement signed value supporting up to 48 bits of accuracy. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]); console.log(buf.readIntBE(0, 6).toString(16)); // Prints: 1234567890ab console.log(buf.readIntBE(1, 6).toString(16)); // Throws ERR_OUT_OF_RANGE. console.log(buf.readIntBE(1, 0).toString(16)); // Throws ERR_OUT_OF_RANGE. #### `buf.readIntLE(offset, byteLength)`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to read. Must satisfy `0 < byteLength <= 6`. * Returns: Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as a little-endian, two's complement signed value supporting up to 48 bits of accuracy. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]); console.log(buf.readIntLE(0, 6).toString(16)); // Prints: -546f87a9cbee #### `buf.readUInt8([offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.readUint8()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.0 Added in: v0.5.0 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 1`. Default: `0`. * Returns: Reads an unsigned 8-bit integer from `buf` at the specified `offset`. This function is also available under the `readUint8` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([1, -2]); console.log(buf.readUInt8(0)); // Prints: 1 console.log(buf.readUInt8(1)); // Prints: 254 console.log(buf.readUInt8(2)); // Throws ERR_OUT_OF_RANGE. #### `buf.readUInt16BE([offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.readUint16BE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: Reads an unsigned, big-endian 16-bit integer from `buf` at the specified `offset`. This function is also available under the `readUint16BE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56]); console.log(buf.readUInt16BE(0).toString(16)); // Prints: 1234 console.log(buf.readUInt16BE(1).toString(16)); // Prints: 3456 #### `buf.readUInt16LE([offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.readUint16LE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: Reads an unsigned, little-endian 16-bit integer from `buf` at the specified `offset`. This function is also available under the `readUint16LE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56]); console.log(buf.readUInt16LE(0).toString(16)); // Prints: 3412 console.log(buf.readUInt16LE(1).toString(16)); // Prints: 5634 console.log(buf.readUInt16LE(2).toString(16)); // Throws ERR_OUT_OF_RANGE. #### `buf.readUInt32BE([offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.readUint32BE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: Reads an unsigned, big-endian 32-bit integer from `buf` at the specified `offset`. This function is also available under the `readUint32BE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]); console.log(buf.readUInt32BE(0).toString(16)); // Prints: 12345678 #### `buf.readUInt32LE([offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.readUint32LE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: Reads an unsigned, little-endian 32-bit integer from `buf` at the specified `offset`. This function is also available under the `readUint32LE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]); console.log(buf.readUInt32LE(0).toString(16)); // Prints: 78563412 console.log(buf.readUInt32LE(1).toString(16)); // Throws ERR_OUT_OF_RANGE. #### `buf.readUIntBE(offset, byteLength)`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.readUintBE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to read. Must satisfy `0 < byteLength <= 6`. * Returns: Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as an unsigned big-endian integer supporting up to 48 bits of accuracy. This function is also available under the `readUintBE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]); console.log(buf.readUIntBE(0, 6).toString(16)); // Prints: 1234567890ab console.log(buf.readUIntBE(1, 6).toString(16)); // Throws ERR_OUT_OF_RANGE. #### `buf.readUIntLE(offset, byteLength)`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.readUintLE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `offset` Number of bytes to skip before starting to read. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to read. Must satisfy `0 < byteLength <= 6`. * Returns: Reads `byteLength` number of bytes from `buf` at the specified `offset` and interprets the result as an unsigned, little-endian integer supporting up to 48 bits of accuracy. This function is also available under the `readUintLE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]); console.log(buf.readUIntLE(0, 6).toString(16)); // Prints: ab9078563412 #### `buf.subarray([start[, end]])`# Added in: v3.0.0 * `start` Where the new `Buffer` will start. Default: `0`. * `end` Where the new `Buffer` will end (not inclusive). Default: `buf.length`. * Returns: Returns a new `Buffer` that references the same memory as the original, but offset and cropped by the `start` and `end` indexes. Specifying `end` greater than `buf.length` will return the same result as that of `end` equal to `buf.length`. This method is inherited from `TypedArray.prototype.subarray()`. Modifying the new `Buffer` slice will modify the memory in the original `Buffer` because the allocated memory of the two objects overlap. import { Buffer } from 'node:buffer'; // Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte // from the original `Buffer`. const buf1 = Buffer.allocUnsafe(26); for (let i = 0; i < 26; i++) { // 97 is the decimal ASCII value for 'a'. buf1[i] = i + 97; } const buf2 = buf1.subarray(0, 3); console.log(buf2.toString('ascii', 0, buf2.length)); // Prints: abc buf1[0] = 33; console.log(buf2.toString('ascii', 0, buf2.length)); // Prints: !bc Specifying negative indexes causes the slice to be generated relative to the end of `buf` rather than the beginning. import { Buffer } from 'node:buffer'; const buf = Buffer.from('buffer'); console.log(buf.subarray(-6, -1).toString()); // Prints: buffe // (Equivalent to buf.subarray(0, 5).) console.log(buf.subarray(-6, -2).toString()); // Prints: buff // (Equivalent to buf.subarray(0, 4).) console.log(buf.subarray(-5, -2).toString()); // Prints: uff // (Equivalent to buf.subarray(1, 4).) #### `buf.slice([start[, end]])`# History VersionChanges v17.5.0, v16.15.0 The buf.slice() method has been deprecated. v7.0.0 All offsets are now coerced to integers before doing any calculations with them. v7.1.0, v6.9.2 Coercing the offsets to integers now handles values outside the 32-bit integer range properly. v0.3.0 Added in: v0.3.0 * `start` Where the new `Buffer` will start. Default: `0`. * `end` Where the new `Buffer` will end (not inclusive). Default: `buf.length`. * Returns: Stability: 0 \- Deprecated: Use `buf.subarray` instead. Returns a new `Buffer` that references the same memory as the original, but offset and cropped by the `start` and `end` indexes. This method is not compatible with the `Uint8Array.prototype.slice()`, which is a superclass of `Buffer`. To copy the slice, use `Uint8Array.prototype.slice()`. import { Buffer } from 'node:buffer'; const buf = Buffer.from('buffer'); const copiedBuf = Uint8Array.prototype.slice.call(buf); copiedBuf[0]++; console.log(copiedBuf.toString()); // Prints: cuffer console.log(buf.toString()); // Prints: buffer // With buf.slice(), the original buffer is modified. const notReallyCopiedBuf = buf.slice(); notReallyCopiedBuf[0]++; console.log(notReallyCopiedBuf.toString()); // Prints: cuffer console.log(buf.toString()); // Also prints: cuffer (!) #### `buf.swap16()`# Added in: v5.10.0 * Returns: A reference to `buf`. Interprets `buf` as an array of unsigned 16-bit integers and swaps the byte order in-place. Throws `ERR_INVALID_BUFFER_SIZE` if `buf.length` is not a multiple of 2. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]); console.log(buf1); // Prints: buf1.swap16(); console.log(buf1); // Prints: const buf2 = Buffer.from([0x1, 0x2, 0x3]); buf2.swap16(); // Throws ERR_INVALID_BUFFER_SIZE. One convenient use of `buf.swap16()` is to perform a fast in-place conversion between UTF-16 little-endian and UTF-16 big-endian: import { Buffer } from 'node:buffer'; const buf = Buffer.from('This is little-endian UTF-16', 'utf16le'); buf.swap16(); // Convert to big-endian UTF-16 text. #### `buf.swap32()`# Added in: v5.10.0 * Returns: A reference to `buf`. Interprets `buf` as an array of unsigned 32-bit integers and swaps the byte order in-place. Throws `ERR_INVALID_BUFFER_SIZE` if `buf.length` is not a multiple of 4. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]); console.log(buf1); // Prints: buf1.swap32(); console.log(buf1); // Prints: const buf2 = Buffer.from([0x1, 0x2, 0x3]); buf2.swap32(); // Throws ERR_INVALID_BUFFER_SIZE. #### `buf.swap64()`# Added in: v6.3.0 * Returns: A reference to `buf`. Interprets `buf` as an array of 64-bit numbers and swaps byte order in-place. Throws `ERR_INVALID_BUFFER_SIZE` if `buf.length` is not a multiple of 8. import { Buffer } from 'node:buffer'; const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]); console.log(buf1); // Prints: buf1.swap64(); console.log(buf1); // Prints: const buf2 = Buffer.from([0x1, 0x2, 0x3]); buf2.swap64(); // Throws ERR_INVALID_BUFFER_SIZE. #### `buf.toJSON()`# Added in: v0.9.2 * Returns: Returns a JSON representation of `buf`. `JSON.stringify()` implicitly calls this function when stringifying a `Buffer` instance. `Buffer.from()` accepts objects in the format returned from this method. In particular, `Buffer.from(buf.toJSON())` works like `Buffer.from(buf)`. import { Buffer } from 'node:buffer'; const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]); const json = JSON.stringify(buf); console.log(json); // Prints: {"type":"Buffer","data":[1,2,3,4,5]} const copy = JSON.parse(json, (key, value) => { return value && value.type === 'Buffer' ? Buffer.from(value) : value; }); console.log(copy); // Prints: #### `buf.toString([encoding[, start[, end]]])`# Added in: v0.1.90 * `encoding` The character encoding to use. Default: `'utf8'`. * `start` The byte offset to start decoding at. Default: `0`. * `end` The byte offset to stop decoding at (not inclusive). Default: `buf.length`. * Returns: Decodes `buf` to a string according to the specified character encoding in `encoding`. `start` and `end` may be passed to decode only a subset of `buf`. If `encoding` is `'utf8'` and a byte sequence in the input is not valid UTF-8, then each invalid byte is replaced with the replacement character `U+FFFD`. The maximum length of a string instance (in UTF-16 code units) is available as `buffer.constants.MAX_STRING_LENGTH`. import { Buffer } from 'node:buffer'; const buf1 = Buffer.allocUnsafe(26); for (let i = 0; i < 26; i++) { // 97 is the decimal ASCII value for 'a'. buf1[i] = i + 97; } console.log(buf1.toString('utf8')); // Prints: abcdefghijklmnopqrstuvwxyz console.log(buf1.toString('utf8', 0, 5)); // Prints: abcde const buf2 = Buffer.from('tést'); console.log(buf2.toString('hex')); // Prints: 74c3a97374 console.log(buf2.toString('utf8', 0, 3)); // Prints: té console.log(buf2.toString(undefined, 0, 3)); // Prints: té #### `buf.values()`# Added in: v1.1.0 * Returns: Creates and returns an iterator for `buf` values (bytes). This function is called automatically when a `Buffer` is used in a `for..of` statement. import { Buffer } from 'node:buffer'; const buf = Buffer.from('buffer'); for (const value of buf.values()) { console.log(value); } // Prints: // 98 // 117 // 102 // 102 // 101 // 114 for (const value of buf) { console.log(value); } // Prints: // 98 // 117 // 102 // 102 // 101 // 114 #### `buf.write(string[, offset[, length]][, encoding])`# Added in: v0.1.90 * `string` String to write to `buf`. * `offset` Number of bytes to skip before starting to write `string`. Default: `0`. * `length` Maximum number of bytes to write (written bytes will not exceed `buf.length - offset`). Default: `buf.length - offset`. * `encoding` The character encoding of `string`. Default: `'utf8'`. * Returns: Number of bytes written. Writes `string` to `buf` at `offset` according to the character encoding in `encoding`. The `length` parameter is the number of bytes to write. If `buf` did not contain enough space to fit the entire string, only part of `string` will be written. However, partially encoded characters will not be written. import { Buffer } from 'node:buffer'; const buf = Buffer.alloc(256); const len = buf.write('\u00bd + \u00bc = \u00be', 0); console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`); // Prints: 12 bytes: ½ + ¼ = ¾ const buffer = Buffer.alloc(10); const length = buffer.write('abcd', 8); console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`); // Prints: 2 bytes : ab #### `buf.writeBigInt64BE(value[, offset])`# Added in: v12.0.0, v10.20.0 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. `value` is interpreted and written as a two's complement signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(8); buf.writeBigInt64BE(0x0102030405060708n, 0); console.log(buf); // Prints: #### `buf.writeBigInt64LE(value[, offset])`# Added in: v12.0.0, v10.20.0 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian. `value` is interpreted and written as a two's complement signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(8); buf.writeBigInt64LE(0x0102030405060708n, 0); console.log(buf); // Prints: #### `buf.writeBigUInt64BE(value[, offset])`# History VersionChanges v14.10.0, v12.19.0 This function is also available as `buf.writeBigUint64BE()`. v12.0.0, v10.20.0 Added in: v12.0.0, v10.20.0 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. This function is also available under the `writeBigUint64BE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(8); buf.writeBigUInt64BE(0xdecafafecacefaden, 0); console.log(buf); // Prints: #### `buf.writeBigUInt64LE(value[, offset])`# History VersionChanges v14.10.0, v12.19.0 This function is also available as `buf.writeBigUint64LE()`. v12.0.0, v10.20.0 Added in: v12.0.0, v10.20.0 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy: `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(8); buf.writeBigUInt64LE(0xdecafafecacefaden, 0); console.log(buf); // Prints: This function is also available under the `writeBigUint64LE` alias. #### `buf.writeDoubleBE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a JavaScript number. Behavior is undefined when `value` is anything other than a JavaScript number. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(8); buf.writeDoubleBE(123.456, 0); console.log(buf); // Prints: #### `buf.writeDoubleLE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 8`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a JavaScript number. Behavior is undefined when `value` is anything other than a JavaScript number. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(8); buf.writeDoubleLE(123.456, 0); console.log(buf); // Prints: #### `buf.writeFloatBE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. Behavior is undefined when `value` is anything other than a JavaScript number. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeFloatBE(0xcafebabe, 0); console.log(buf); // Prints: #### `buf.writeFloatLE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian. Behavior is undefined when `value` is anything other than a JavaScript number. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeFloatLE(0xcafebabe, 0); console.log(buf); // Prints: #### `buf.writeInt8(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.0 Added in: v0.5.0 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 1`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset`. `value` must be a valid signed 8-bit integer. Behavior is undefined when `value` is anything other than a signed 8-bit integer. `value` is interpreted and written as a two's complement signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(2); buf.writeInt8(2, 0); buf.writeInt8(-2, 1); console.log(buf); // Prints: #### `buf.writeInt16BE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid signed 16-bit integer. Behavior is undefined when `value` is anything other than a signed 16-bit integer. The `value` is interpreted and written as a two's complement signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(2); buf.writeInt16BE(0x0102, 0); console.log(buf); // Prints: #### `buf.writeInt16LE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid signed 16-bit integer. Behavior is undefined when `value` is anything other than a signed 16-bit integer. The `value` is interpreted and written as a two's complement signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(2); buf.writeInt16LE(0x0304, 0); console.log(buf); // Prints: #### `buf.writeInt32BE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid signed 32-bit integer. Behavior is undefined when `value` is anything other than a signed 32-bit integer. The `value` is interpreted and written as a two's complement signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeInt32BE(0x01020304, 0); console.log(buf); // Prints: #### `buf.writeInt32LE(value[, offset])`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid signed 32-bit integer. Behavior is undefined when `value` is anything other than a signed 32-bit integer. The `value` is interpreted and written as a two's complement signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeInt32LE(0x05060708, 0); console.log(buf); // Prints: #### `buf.writeIntBE(value, offset, byteLength)`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to write. Must satisfy `0 < byteLength <= 6`. * Returns: `offset` plus the number of bytes written. Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than a signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(6); buf.writeIntBE(0x1234567890ab, 0, 6); console.log(buf); // Prints: #### `buf.writeIntLE(value, offset, byteLength)`# History VersionChanges v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.11.15 Added in: v0.11.15 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to write. Must satisfy `0 < byteLength <= 6`. * Returns: `offset` plus the number of bytes written. Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than a signed integer. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(6); buf.writeIntLE(0x1234567890ab, 0, 6); console.log(buf); // Prints: #### `buf.writeUInt8(value[, offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.writeUint8()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.0 Added in: v0.5.0 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 1`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset`. `value` must be a valid unsigned 8-bit integer. Behavior is undefined when `value` is anything other than an unsigned 8-bit integer. This function is also available under the `writeUint8` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeUInt8(0x3, 0); buf.writeUInt8(0x4, 1); buf.writeUInt8(0x23, 2); buf.writeUInt8(0x42, 3); console.log(buf); // Prints: #### `buf.writeUInt16BE(value[, offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.writeUint16BE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid unsigned 16-bit integer. Behavior is undefined when `value` is anything other than an unsigned 16-bit integer. This function is also available under the `writeUint16BE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeUInt16BE(0xdead, 0); buf.writeUInt16BE(0xbeef, 2); console.log(buf); // Prints: #### `buf.writeUInt16LE(value[, offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.writeUint16LE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 2`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid unsigned 16-bit integer. Behavior is undefined when `value` is anything other than an unsigned 16-bit integer. This function is also available under the `writeUint16LE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeUInt16LE(0xdead, 0); buf.writeUInt16LE(0xbeef, 2); console.log(buf); // Prints: #### `buf.writeUInt32BE(value[, offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.writeUint32BE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as big-endian. The `value` must be a valid unsigned 32-bit integer. Behavior is undefined when `value` is anything other than an unsigned 32-bit integer. This function is also available under the `writeUint32BE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeUInt32BE(0xfeedface, 0); console.log(buf); // Prints: #### `buf.writeUInt32LE(value[, offset])`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.writeUint32LE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - 4`. Default: `0`. * Returns: `offset` plus the number of bytes written. Writes `value` to `buf` at the specified `offset` as little-endian. The `value` must be a valid unsigned 32-bit integer. Behavior is undefined when `value` is anything other than an unsigned 32-bit integer. This function is also available under the `writeUint32LE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(4); buf.writeUInt32LE(0xfeedface, 0); console.log(buf); // Prints: #### `buf.writeUIntBE(value, offset, byteLength)`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.writeUintBE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to write. Must satisfy `0 < byteLength <= 6`. * Returns: `offset` plus the number of bytes written. Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than an unsigned integer. This function is also available under the `writeUintBE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(6); buf.writeUIntBE(0x1234567890ab, 0, 6); console.log(buf); // Prints: #### `buf.writeUIntLE(value, offset, byteLength)`# History VersionChanges v14.9.0, v12.19.0 This function is also available as `buf.writeUintLE()`. v10.0.0 Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore. v0.5.5 Added in: v0.5.5 * `value` Number to be written to `buf`. * `offset` Number of bytes to skip before starting to write. Must satisfy `0 <= offset <= buf.length - byteLength`. * `byteLength` Number of bytes to write. Must satisfy `0 < byteLength <= 6`. * Returns: `offset` plus the number of bytes written. Writes `byteLength` bytes of `value` to `buf` at the specified `offset` as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined when `value` is anything other than an unsigned integer. This function is also available under the `writeUintLE` alias. import { Buffer } from 'node:buffer'; const buf = Buffer.allocUnsafe(6); buf.writeUIntLE(0x1234567890ab, 0, 6); console.log(buf); // Prints: #### `new Buffer(array)`# History VersionChanges v10.0.0 Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. v7.2.1 Calling this constructor no longer emits a deprecation warning. v7.0.0 Calling this constructor emits a deprecation warning now. v6.0.0 Deprecated since: v6.0.0 Stability: 0 \- Deprecated: Use `Buffer.from(array)` instead. * `array` An array of bytes to copy from. See `Buffer.from(array)`. #### `new Buffer(arrayBuffer[, byteOffset[, length]])`# History VersionChanges v10.0.0 Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. v7.2.1 Calling this constructor no longer emits a deprecation warning. v7.0.0 Calling this constructor emits a deprecation warning now. v6.0.0 The `byteOffset` and `length` parameters are supported now. v6.0.0 Deprecated since: v6.0.0 v3.0.0 Added in: v3.0.0 Stability: 0 \- Deprecated: Use `Buffer.from(arrayBuffer[, byteOffset[, length]])` instead. * `arrayBuffer` | An , or the `.buffer` property of a . * `byteOffset` Index of first byte to expose. Default: `0`. * `length` Number of bytes to expose. Default: `arrayBuffer.byteLength - byteOffset`. See `Buffer.from(arrayBuffer[, byteOffset[, length]])`. #### `new Buffer(buffer)`# History VersionChanges v10.0.0 Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. v7.2.1 Calling this constructor no longer emits a deprecation warning. v7.0.0 Calling this constructor emits a deprecation warning now. v6.0.0 Deprecated since: v6.0.0 Stability: 0 \- Deprecated: Use `Buffer.from(buffer)` instead. * `buffer` | An existing `Buffer` or from which to copy data. See `Buffer.from(buffer)`. #### `new Buffer(size)`# History VersionChanges v10.0.0 Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. v8.0.0 The `new Buffer(size)` will return zero-filled memory by default. v7.2.1 Calling this constructor no longer emits a deprecation warning. v7.0.0 Calling this constructor emits a deprecation warning now. v6.0.0 Deprecated since: v6.0.0 Stability: 0 \- Deprecated: Use `Buffer.alloc()` instead (also see `Buffer.allocUnsafe()`). * `size` The desired length of the new `Buffer`. See `Buffer.alloc()` and `Buffer.allocUnsafe()`. This variant of the constructor is equivalent to `Buffer.alloc()`. #### `new Buffer(string[, encoding])`# History VersionChanges v10.0.0 Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory. v7.2.1 Calling this constructor no longer emits a deprecation warning. v7.0.0 Calling this constructor emits a deprecation warning now. v6.0.0 Deprecated since: v6.0.0 Stability: 0 \- Deprecated: Use `Buffer.from(string[, encoding])` instead. * `string` String to encode. * `encoding` The encoding of `string`. Default: `'utf8'`. See `Buffer.from(string[, encoding])`. ### Class: `File`# History VersionChanges v23.0.0 Makes File instances cloneable. v20.0.0 No longer experimental. v19.2.0, v18.13.0 Added in: v19.2.0, v18.13.0 * Extends: A provides information about files. #### `new buffer.File(sources, fileName[, options])`# Added in: v19.2.0, v18.13.0 * `sources` | | | | | An array of string, , , , , or objects, or any mix of such objects, that will be stored within the `File`. * `fileName` The name of the file. * `options` * `endings` One of either `'transparent'` or `'native'`. When set to `'native'`, line endings in string source parts will be converted to the platform native line-ending as specified by `require('node:os').EOL`. * `type` The File content-type. * `lastModified` The last modified date of the file. Default: `Date.now()`. #### `file.name`# Added in: v19.2.0, v18.13.0 * Type: The name of the `File`. #### `file.lastModified`# Added in: v19.2.0, v18.13.0 * Type: The last modified date of the `File`. ### `node:buffer` module APIs# While, the `Buffer` object is available as a global, there are additional `Buffer`-related APIs that are available only via the `node:buffer` module accessed using `require('node:buffer')`. #### `buffer.atob(data)`# Added in: v15.13.0, v14.17.0 Stability: 3 \- Legacy. Use `Buffer.from(data, 'base64')` instead. * `data` The Base64-encoded input string. Decodes a string of Base64-encoded data into bytes, and encodes those bytes into a string using Latin-1 (ISO-8859-1). The `data` may be any JavaScript-value that can be coerced into a string. This function is only provided for compatibility with legacy web platform APIs and should never be used in new code, because they use strings to represent binary data and predate the introduction of typed arrays in JavaScript. For code running using Node.js APIs, converting between base64-encoded strings and binary data should be performed using `Buffer.from(str, 'base64')` and `buf.toString('base64')`. #### `buffer.btoa(data)`# Added in: v15.13.0, v14.17.0 Stability: 3 \- Legacy. Use `buf.toString('base64')` instead. * `data` An ASCII (Latin1) string. Decodes a string into bytes using Latin-1 (ISO-8859), and encodes those bytes into a string using Base64. The `data` may be any JavaScript-value that can be coerced into a string. This function is only provided for compatibility with legacy web platform APIs and should never be used in new code, because they use strings to represent binary data and predate the introduction of typed arrays in JavaScript. For code running using Node.js APIs, converting between base64-encoded strings and binary data should be performed using `Buffer.from(str, 'base64')` and `buf.toString('base64')`. #### `buffer.isAscii(input)`# Added in: v19.6.0, v18.15.0 * `input` | | The input to validate. * Returns: This function returns `true` if `input` contains only valid ASCII-encoded data, including the case in which `input` is empty. Throws if the `input` is a detached array buffer. #### `buffer.isUtf8(input)`# Added in: v19.4.0, v18.14.0 * `input` | | The input to validate. * Returns: This function returns `true` if `input` contains only valid UTF-8-encoded data, including the case in which `input` is empty. Throws if the `input` is a detached array buffer. #### `buffer.INSPECT_MAX_BYTES`# Added in: v0.5.4 * Type: Default: `50` Returns the maximum number of bytes that will be returned when `buf.inspect()` is called. This can be overridden by user modules. See `util.inspect()` for more details on `buf.inspect()` behavior. #### `buffer.kMaxLength`# Added in: v3.0.0 * Type: The largest size allowed for a single `Buffer` instance. An alias for `buffer.constants.MAX_LENGTH`. #### `buffer.kStringMaxLength`# Added in: v3.0.0 * Type: The largest length allowed for a single `string` instance. An alias for `buffer.constants.MAX_STRING_LENGTH`. #### `buffer.resolveObjectURL(id)`# History VersionChanges v24.0.0 Marking the API stable. v16.7.0 Added in: v16.7.0 * `id` A `'blob:nodedata:...` URL string returned by a prior call to `URL.createObjectURL()`. * Returns: Resolves a `'blob:nodedata:...'` an associated object registered using a prior call to `URL.createObjectURL()`. #### `buffer.transcode(source, fromEnc, toEnc)`# History VersionChanges v8.0.0 The `source` parameter can now be a `Uint8Array`. v7.1.0 Added in: v7.1.0 * `source` | A `Buffer` or `Uint8Array` instance. * `fromEnc` The current encoding. * `toEnc` To target encoding. * Returns: Re-encodes the given `Buffer` or `Uint8Array` instance from one character encoding to another. Returns a new `Buffer` instance. Throws if the `fromEnc` or `toEnc` specify invalid character encodings or if conversion from `fromEnc` to `toEnc` is not permitted. Encodings supported by `buffer.transcode()` are: `'ascii'`, `'utf8'`, `'utf16le'`, `'ucs2'`, `'latin1'`, and `'binary'`. The transcoding process will use substitution characters if a given byte sequence cannot be adequately represented in the target encoding. For instance: import { Buffer, transcode } from 'node:buffer'; const newBuf = transcode(Buffer.from('€'), 'utf8', 'ascii'); console.log(newBuf.toString('ascii')); // Prints: '?' Because the Euro (`€`) sign is not representable in US-ASCII, it is replaced with `?` in the transcoded `Buffer`. #### Class: `SlowBuffer`# Deprecated since: v6.0.0 Stability: 0 \- Deprecated: Use `Buffer.allocUnsafeSlow()` instead. See `Buffer.allocUnsafeSlow()`. This was never a class in the sense that the constructor always returned a `Buffer` instance, rather than a `SlowBuffer` instance. ##### `new SlowBuffer(size)`# Deprecated since: v6.0.0 * `size` The desired length of the new `SlowBuffer`. See `Buffer.allocUnsafeSlow()`. #### Buffer constants# Added in: v8.2.0 ##### `buffer.constants.MAX_LENGTH`# History VersionChanges v22.0.0 Value is changed to 253 \- 1 on 64-bit architectures. v15.0.0 Value is changed to 232 on 64-bit architectures. v14.0.0 Value is changed from 231 \- 1 to 232 \- 1 on 64-bit architectures. v8.2.0 Added in: v8.2.0 * Type: The largest size allowed for a single `Buffer` instance. On 32-bit architectures, this value currently is 230 \- 1 (about 1 GiB). On 64-bit architectures, this value currently is 253 \- 1 (about 8 PiB). It reflects `v8::TypedArray::kMaxLength` under the hood. This value is also available as `buffer.kMaxLength`. ##### `buffer.constants.MAX_STRING_LENGTH`# Added in: v8.2.0 * Type: The largest length allowed for a single `string` instance. Represents the largest `length` that a `string` primitive can have, counted in UTF-16 code units. This value may depend on the JS engine that is being used. ### `Buffer.from()`, `Buffer.alloc()`, and `Buffer.allocUnsafe()`# In versions of Node.js prior to 6.0.0, `Buffer` instances were created using the `Buffer` constructor function, which allocates the returned `Buffer` differently based on what arguments are provided: * Passing a number as the first argument to `Buffer()` (e.g. `new Buffer(10)`) allocates a new `Buffer` object of the specified size. Prior to Node.js 8.0.0, the memory allocated for such `Buffer` instances is not initialized and can contain sensitive data. Such `Buffer` instances must be subsequently initialized by using either `buf.fill(0)` or by writing to the entire `Buffer` before reading data from the `Buffer`. While this behavior is intentional to improve performance, development experience has demonstrated that a more explicit distinction is required between creating a fast-but-uninitialized `Buffer` versus creating a slower-but-safer `Buffer`. Since Node.js 8.0.0, `Buffer(num)` and `new Buffer(num)` return a `Buffer` with initialized memory. * Passing a string, array, or `Buffer` as the first argument copies the passed object's data into the `Buffer`. * Passing an or a returns a `Buffer` that shares allocated memory with the given array buffer. Because the behavior of `new Buffer()` is different depending on the type of the first argument, security and reliability issues can be inadvertently introduced into applications when argument validation or `Buffer` initialization is not performed. For example, if an attacker can cause an application to receive a number where a string is expected, the application may call `new Buffer(100)` instead of `new Buffer("100")`, leading it to allocate a 100 byte buffer instead of allocating a 3 byte buffer with content `"100"`. This is commonly possible using JSON API calls. Since JSON distinguishes between numeric and string types, it allows injection of numbers where a naively written application that does not validate its input sufficiently might expect to always receive a string. Before Node.js 8.0.0, the 100 byte buffer might contain arbitrary pre-existing in-memory data, so may be used to expose in-memory secrets to a remote attacker. Since Node.js 8.0.0, exposure of memory cannot occur because the data is zero-filled. However, other attacks are still possible, such as causing very large buffers to be allocated by the server, leading to performance degradation or crashing on memory exhaustion. To make the creation of `Buffer` instances more reliable and less error-prone, the various forms of the `new Buffer()` constructor have been deprecated and replaced by separate `Buffer.from()`, `Buffer.alloc()`, and `Buffer.allocUnsafe()` methods. Developers should migrate all existing uses of the `new Buffer()` constructors to one of these new APIs. * `Buffer.from(array)` returns a new `Buffer` that contains a copy of the provided octets. * `Buffer.from(arrayBuffer[, byteOffset[, length]])` returns a new `Buffer` that shares the same allocated memory as the given . * `Buffer.from(buffer)` returns a new `Buffer` that contains a copy of the contents of the given `Buffer`. * `Buffer.from(string[, encoding])` returns a new `Buffer` that contains a copy of the provided string. * `Buffer.alloc(size[, fill[, encoding]])` returns a new initialized `Buffer` of the specified size. This method is slower than `Buffer.allocUnsafe(size)` but guarantees that newly created `Buffer` instances never contain old data that is potentially sensitive. A `TypeError` will be thrown if `size` is not a number. * `Buffer.allocUnsafe(size)` and `Buffer.allocUnsafeSlow(size)` each return a new uninitialized `Buffer` of the specified `size`. Because the `Buffer` is uninitialized, the allocated segment of memory might contain old data that is potentially sensitive. `Buffer` instances returned by `Buffer.allocUnsafe()`, `Buffer.from(string)`, `Buffer.concat()` and `Buffer.from(array)` may be allocated off a shared internal memory pool if `size` is less than or equal to half `Buffer.poolSize`. Instances returned by `Buffer.allocUnsafeSlow()` never use the shared internal memory pool. #### The `--zero-fill-buffers` command-line option# Added in: v5.10.0 Node.js can be started using the `--zero-fill-buffers` command-line option to cause all newly-allocated `Buffer` instances to be zero-filled upon creation by default. Without the option, buffers created with `Buffer.allocUnsafe()`, `Buffer.allocUnsafeSlow()`, and `new SlowBuffer(size)` are not zero-filled. Use of this flag can have a measurable negative impact on performance. Use the `--zero-fill-buffers` option only when necessary to enforce that newly allocated `Buffer` instances cannot contain old data that is potentially sensitive. $ node --zero-fill-buffers > Buffer.allocUnsafe(5); #### What makes `Buffer.allocUnsafe()` and `Buffer.allocUnsafeSlow()` "unsafe"?# When calling `Buffer.allocUnsafe()` and `Buffer.allocUnsafeSlow()`, the segment of allocated memory is uninitialized (it is not zeroed-out). While this design makes the allocation of memory quite fast, the allocated segment of memory might contain old data that is potentially sensitive. Using a `Buffer` created by `Buffer.allocUnsafe()` without completely overwriting the memory can allow this old data to be leaked when the `Buffer` memory is read. While there are clear performance advantages to using `Buffer.allocUnsafe()`, extra care must be taken in order to avoid introducing security vulnerabilities into an application. ## C++ addons# Addons are dynamically-linked shared objects written in C++. The `require()` function can load addons as ordinary Node.js modules. Addons provide an interface between JavaScript and C/C++ libraries. There are three options for implementing addons: * Node-API * `nan` (Native Abstractions for Node.js) * direct use of internal V8, libuv, and Node.js libraries Unless there is a need for direct access to functionality which is not exposed by Node-API, use Node-API. Refer to C/C++ addons with Node-API for more information on Node-API. When not using Node-API, implementing addons becomes more complex, requiring knowledge of multiple components and APIs: * V8: the C++ library Node.js uses to provide the JavaScript implementation. It provides the mechanisms for creating objects, calling functions, etc. The V8's API is documented mostly in the `v8.h` header file (`deps/v8/include/v8.h` in the Node.js source tree), and is also available online. * libuv: The C library that implements the Node.js event loop, its worker threads and all of the asynchronous behaviors of the platform. It also serves as a cross-platform abstraction library, giving easy, POSIX-like access across all major operating systems to many common system tasks, such as interacting with the file system, sockets, timers, and system events. libuv also provides a threading abstraction similar to POSIX threads for more sophisticated asynchronous addons that need to move beyond the standard event loop. Addon authors should avoid blocking the event loop with I/O or other time-intensive tasks by offloading work via libuv to non-blocking system operations, worker threads, or a custom use of libuv threads. * Internal Node.js libraries: Node.js itself exports C++ APIs that addons can use, the most important of which is the `node::ObjectWrap` class. * Other statically linked libraries (including OpenSSL): These other libraries are located in the `deps/` directory in the Node.js source tree. Only the libuv, OpenSSL, V8, and zlib symbols are purposefully re-exported by Node.js and may be used to various extents by addons. See Linking to libraries included with Node.js for additional information. All of the following examples are available for download and may be used as the starting-point for an addon. ### Hello world# This "Hello world" example is a simple addon, written in C++, that is the equivalent of the following JavaScript code: module.exports.hello = () => 'world'; First, create the file `hello.cc`: // hello.cc #include namespace demo { using v8::FunctionCallbackInfo; using v8::Isolate; using v8::Local; using v8::NewStringType; using v8::Object; using v8::String; using v8::Value; void Method(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); args.GetReturnValue().Set(String::NewFromUtf8( isolate, "world", NewStringType::kNormal).ToLocalChecked()); } void Initialize(Local exports) { NODE_SET_METHOD(exports, "hello", Method); } NODE_MODULE(NODE_GYP_MODULE_NAME, Initialize) } // namespace demo All Node.js addons must export an initialization function following the pattern: void Initialize(Local exports); NODE_MODULE(NODE_GYP_MODULE_NAME, Initialize) There is no semi-colon after `NODE_MODULE` as it's not a function (see `node.h`). The `module_name` must match the filename of the final binary (excluding the `.node` suffix). In the `hello.cc` example, then, the initialization function is `Initialize` and the addon module name is `addon`. When building addons with `node-gyp`, using the macro `NODE_GYP_MODULE_NAME` as the first parameter of `NODE_MODULE()` will ensure that the name of the final binary will be passed to `NODE_MODULE()`. Addons defined with `NODE_MODULE()` can not be loaded in multiple contexts or multiple threads at the same time. #### Context-aware addons# There are environments in which Node.js addons may need to be loaded multiple times in multiple contexts. For example, the Electron runtime runs multiple instances of Node.js in a single process. Each instance will have its own `require()` cache, and thus each instance will need a native addon to behave correctly when loaded via `require()`. This means that the addon must support multiple initializations. A context-aware addon can be constructed by using the macro `NODE_MODULE_INITIALIZER`, which expands to the name of a function which Node.js will expect to find when it loads an addon. An addon can thus be initialized as in the following example: using namespace v8; extern "C" NODE_MODULE_EXPORT void NODE_MODULE_INITIALIZER(Local exports, Local module, Local context) { /* Perform addon initialization steps here. */ } Another option is to use the macro `NODE_MODULE_INIT()`, which will also construct a context-aware addon. Unlike `NODE_MODULE()`, which is used to construct an addon around a given addon initializer function, `NODE_MODULE_INIT()` serves as the declaration of such an initializer to be followed by a function body. The following three variables may be used inside the function body following an invocation of `NODE_MODULE_INIT()`: * `Local exports`, * `Local module`, and * `Local context` Building a context-aware addon requires careful management of global static data to ensure stability and correctness. Since the addon may be loaded multiple times, potentially even from different threads, any global static data stored in the addon must be properly protected, and must not contain any persistent references to JavaScript objects. The reason for this is that JavaScript objects are only valid in one context, and will likely cause a crash when accessed from the wrong context or from a different thread than the one on which they were created. The context-aware addon can be structured to avoid global static data by performing the following steps: * Define a class which will hold per-addon-instance data and which has a static member of the form static void DeleteInstance(void* data) { // Cast `data` to an instance of the class and delete it. } * Heap-allocate an instance of this class in the addon initializer. This can be accomplished using the `new` keyword. * Call `node::AddEnvironmentCleanupHook()`, passing it the above-created instance and a pointer to `DeleteInstance()`. This will ensure the instance is deleted when the environment is torn down. * Store the instance of the class in a `v8::External`, and * Pass the `v8::External` to all methods exposed to JavaScript by passing it to `v8::FunctionTemplate::New()` or `v8::Function::New()` which creates the native-backed JavaScript functions. The third parameter of `v8::FunctionTemplate::New()` or `v8::Function::New()` accepts the `v8::External` and makes it available in the native callback using the `v8::FunctionCallbackInfo::Data()` method. This will ensure that the per-addon-instance data reaches each binding that can be called from JavaScript. The per-addon-instance data must also be passed into any asynchronous callbacks the addon may create. The following example illustrates the implementation of a context-aware addon: #include using namespace v8; class AddonData { public: explicit AddonData(Isolate* isolate): call_count(0) { // Ensure this per-addon-instance data is deleted at environment cleanup. node::AddEnvironmentCleanupHook(isolate, DeleteInstance, this); } // Per-addon data. int call_count; static void DeleteInstance(void* data) { delete static_cast(data); } }; static void Method(const v8::FunctionCallbackInfo& info) { // Retrieve the per-addon-instance data. AddonData* data = reinterpret_cast(info.Data().As()->Value()); data->call_count++; info.GetReturnValue().Set((double)data->call_count); } // Initialize this addon to be context-aware. NODE_MODULE_INIT(/* exports, module, context */) { Isolate* isolate = context->GetIsolate(); // Create a new instance of `AddonData` for this instance of the addon and // tie its life cycle to that of the Node.js environment. AddonData* data = new AddonData(isolate); // Wrap the data in a `v8::External` so we can pass it to the method we // expose. Local external = External::New(isolate, data); // Expose the method `Method` to JavaScript, and make sure it receives the // per-addon-instance data we created above by passing `external` as the // third parameter to the `FunctionTemplate` constructor. exports->Set(context, String::NewFromUtf8(isolate, "method").ToLocalChecked(), FunctionTemplate::New(isolate, Method, external) ->GetFunction(context).ToLocalChecked()).FromJust(); } ##### Worker support# History VersionChanges v14.8.0, v12.19.0 Cleanup hooks may now be asynchronous. In order to be loaded from multiple Node.js environments, such as a main thread and a Worker thread, an add-on needs to either: * Be an Node-API addon, or * Be declared as context-aware using `NODE_MODULE_INIT()` as described above In order to support `Worker` threads, addons need to clean up any resources they may have allocated when such a thread exits. This can be achieved through the usage of the `AddEnvironmentCleanupHook()` function: void AddEnvironmentCleanupHook(v8::Isolate* isolate, void (*fun)(void* arg), void* arg); This function adds a hook that will run before a given Node.js instance shuts down. If necessary, such hooks can be removed before they are run using `RemoveEnvironmentCleanupHook()`, which has the same signature. Callbacks are run in last-in first-out order. If necessary, there is an additional pair of `AddEnvironmentCleanupHook()` and `RemoveEnvironmentCleanupHook()` overloads, where the cleanup hook takes a callback function. This can be used for shutting down asynchronous resources, such as any libuv handles registered by the addon. The following `addon.cc` uses `AddEnvironmentCleanupHook`: // addon.cc #include #include #include using node::AddEnvironmentCleanupHook; using v8::HandleScope; using v8::Isolate; using v8::Local; using v8::Object; // Note: In a real-world application, do not rely on static/global data. static char cookie[] = "yum yum"; static int cleanup_cb1_called = 0; static int cleanup_cb2_called = 0; static void cleanup_cb1(void* arg) { Isolate* isolate = static_cast(arg); HandleScope scope(isolate); Local obj = Object::New(isolate); assert(!obj.IsEmpty()); // assert VM is still alive assert(obj->IsObject()); cleanup_cb1_called++; } static void cleanup_cb2(void* arg) { assert(arg == static_cast(cookie)); cleanup_cb2_called++; } static void sanity_check(void*) { assert(cleanup_cb1_called == 1); assert(cleanup_cb2_called == 1); } // Initialize this addon to be context-aware. NODE_MODULE_INIT(/* exports, module, context */) { Isolate* isolate = context->GetIsolate(); AddEnvironmentCleanupHook(isolate, sanity_check, nullptr); AddEnvironmentCleanupHook(isolate, cleanup_cb2, cookie); AddEnvironmentCleanupHook(isolate, cleanup_cb1, isolate); } Test in JavaScript by running: // test.js require('./build/Release/addon'); #### Building# Once the source code has been written, it must be compiled into the binary `addon.node` file. To do so, create a file called `binding.gyp` in the top-level of the project describing the build configuration of the module using a JSON-like format. This file is used by node-gyp, a tool written specifically to compile Node.js addons. { "targets": [ { "target_name": "addon", "sources": [ "hello.cc" ] } ] } A version of the `node-gyp` utility is bundled and distributed with Node.js as part of `npm`. This version is not made directly available for developers to use and is intended only to support the ability to use the `npm install` command to compile and install addons. Developers who wish to use `node-gyp` directly can install it using the command `npm install -g node-gyp`. See the `node-gyp` installation instructions for more information, including platform-specific requirements. Once the `binding.gyp` file has been created, use `node-gyp configure` to generate the appropriate project build files for the current platform. This will generate either a `Makefile` (on Unix platforms) or a `vcxproj` file (on Windows) in the `build/` directory. Next, invoke the `node-gyp build` command to generate the compiled `addon.node` file. This will be put into the `build/Release/` directory. When using `npm install` to install a Node.js addon, npm uses its own bundled version of `node-gyp` to perform this same set of actions, generating a compiled version of the addon for the user's platform on demand. Once built, the binary addon can be used from within Node.js by pointing `require()` to the built `addon.node` module: // hello.js const addon = require('./build/Release/addon'); console.log(addon.hello()); // Prints: 'world' Because the exact path to the compiled addon binary can vary depending on how it is compiled (i.e. sometimes it may be in `./build/Debug/`), addons can use the bindings package to load the compiled module. While the `bindings` package implementation is more sophisticated in how it locates addon modules, it is essentially using a `try…catch` pattern similar to: try { return require('./build/Release/addon.node'); } catch (err) { return require('./build/Debug/addon.node'); } #### Linking to libraries included with Node.js# Node.js uses statically linked libraries such as V8, libuv, and OpenSSL. All addons are required to link to V8 and may link to any of the other dependencies as well. Typically, this is as simple as including the appropriate `#include <...>` statements (e.g. `#include `) and `node-gyp` will locate the appropriate headers automatically. However, there are a few caveats to be aware of: * When `node-gyp` runs, it will detect the specific release version of Node.js and download either the full source tarball or just the headers. If the full source is downloaded, addons will have complete access to the full set of Node.js dependencies. However, if only the Node.js headers are downloaded, then only the symbols exported by Node.js will be available. * `node-gyp` can be run using the `--nodedir` flag pointing at a local Node.js source image. Using this option, the addon will have access to the full set of dependencies. #### Loading addons using `require()`# The filename extension of the compiled addon binary is `.node` (as opposed to `.dll` or `.so`). The `require()` function is written to look for files with the `.node` file extension and initialize those as dynamically-linked libraries. When calling `require()`, the `.node` extension can usually be omitted and Node.js will still find and initialize the addon. One caveat, however, is that Node.js will first attempt to locate and load modules or JavaScript files that happen to share the same base name. For instance, if there is a file `addon.js` in the same directory as the binary `addon.node`, then `require('addon')` will give precedence to the `addon.js` file and load it instead. ### Native abstractions for Node.js# Each of the examples illustrated in this document directly use the Node.js and V8 APIs for implementing addons. The V8 API can, and has, changed dramatically from one V8 release to the next (and one major Node.js release to the next). With each change, addons may need to be updated and recompiled in order to continue functioning. The Node.js release schedule is designed to minimize the frequency and impact of such changes but there is little that Node.js can do to ensure stability of the V8 APIs. The Native Abstractions for Node.js (or `nan`) provide a set of tools that addon developers are recommended to use to keep compatibility between past and future releases of V8 and Node.js. See the `nan` examples for an illustration of how it can be used. ### Node-API# Stability: 2 \- Stable Node-API is an API for building native addons. It is independent from the underlying JavaScript runtime (e.g. V8) and is maintained as part of Node.js itself. This API will be Application Binary Interface (ABI) stable across versions of Node.js. It is intended to insulate addons from changes in the underlying JavaScript engine and allow modules compiled for one version to run on later versions of Node.js without recompilation. Addons are built/packaged with the same approach/tools outlined in this document (node-gyp, etc.). The only difference is the set of APIs that are used by the native code. Instead of using the V8 or Native Abstractions for Node.js APIs, the functions available in the Node-API are used. Creating and maintaining an addon that benefits from the ABI stability provided by Node-API carries with it certain implementation considerations. To use Node-API in the above "Hello world" example, replace the content of `hello.cc` with the following. All other instructions remain the same. // hello.cc using Node-API #include namespace demo { napi_value Method(napi_env env, napi_callback_info args) { napi_value greeting; napi_status status; status = napi_create_string_utf8(env, "world", NAPI_AUTO_LENGTH, &greeting); if (status != napi_ok) return nullptr; return greeting; } napi_value init(napi_env env, napi_value exports) { napi_status status; napi_value fn; status = napi_create_function(env, nullptr, 0, Method, nullptr, &fn); if (status != napi_ok) return nullptr; status = napi_set_named_property(env, exports, "hello", fn); if (status != napi_ok) return nullptr; return exports; } NAPI_MODULE(NODE_GYP_MODULE_NAME, init) } // namespace demo The functions available and how to use them are documented in C/C++ addons with Node-API. ### Addon examples# Following are some example addons intended to help developers get started. The examples use the V8 APIs. Refer to the online V8 reference for help with the various V8 calls, and V8's Embedder's Guide for an explanation of several concepts used such as handles, scopes, function templates, etc. Each of these examples using the following `binding.gyp` file: { "targets": [ { "target_name": "addon", "sources": [ "addon.cc" ] } ] } In cases where there is more than one `.cc` file, simply add the additional filename to the `sources` array: "sources": ["addon.cc", "myexample.cc"] Once the `binding.gyp` file is ready, the example addons can be configured and built using `node-gyp`: node-gyp configure build #### Function arguments# Addons will typically expose objects and functions that can be accessed from JavaScript running within Node.js. When functions are invoked from JavaScript, the input arguments and return value must be mapped to and from the C/C++ code. The following example illustrates how to read function arguments passed from JavaScript and how to return a result: // addon.cc #include namespace demo { using v8::Exception; using v8::FunctionCallbackInfo; using v8::Isolate; using v8::Local; using v8::Number; using v8::Object; using v8::String; using v8::Value; // This is the implementation of the "add" method // Input arguments are passed using the // const FunctionCallbackInfo& args struct void Add(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); // Check the number of arguments passed. if (args.Length() < 2) { // Throw an Error that is passed back to JavaScript isolate->ThrowException(Exception::TypeError( String::NewFromUtf8(isolate, "Wrong number of arguments").ToLocalChecked())); return; } // Check the argument types if (!args[0]->IsNumber() || !args[1]->IsNumber()) { isolate->ThrowException(Exception::TypeError( String::NewFromUtf8(isolate, "Wrong arguments").ToLocalChecked())); return; } // Perform the operation double value = args[0].As()->Value() + args[1].As()->Value(); Local num = Number::New(isolate, value); // Set the return value (using the passed in // FunctionCallbackInfo&) args.GetReturnValue().Set(num); } void Init(Local exports) { NODE_SET_METHOD(exports, "add", Add); } NODE_MODULE(NODE_GYP_MODULE_NAME, Init) } // namespace demo Once compiled, the example addon can be required and used from within Node.js: // test.js const addon = require('./build/Release/addon'); console.log('This should be eight:', addon.add(3, 5)); #### Callbacks# It is common practice within addons to pass JavaScript functions to a C++ function and execute them from there. The following example illustrates how to invoke such callbacks: // addon.cc #include namespace demo { using v8::Context; using v8::Function; using v8::FunctionCallbackInfo; using v8::Isolate; using v8::Local; using v8::Null; using v8::Object; using v8::String; using v8::Value; void RunCallback(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); Local context = isolate->GetCurrentContext(); Local cb = Local::Cast(args[0]); const unsigned argc = 1; Local argv[argc] = { String::NewFromUtf8(isolate, "hello world").ToLocalChecked() }; cb->Call(context, Null(isolate), argc, argv).ToLocalChecked(); } void Init(Local exports, Local module) { NODE_SET_METHOD(module, "exports", RunCallback); } NODE_MODULE(NODE_GYP_MODULE_NAME, Init) } // namespace demo This example uses a two-argument form of `Init()` that receives the full `module` object as the second argument. This allows the addon to completely overwrite `exports` with a single function instead of adding the function as a property of `exports`. To test it, run the following JavaScript: // test.js const addon = require('./build/Release/addon'); addon((msg) => { console.log(msg); // Prints: 'hello world' }); In this example, the callback function is invoked synchronously. #### Object factory# Addons can create and return new objects from within a C++ function as illustrated in the following example. An object is created and returned with a property `msg` that echoes the string passed to `createObject()`: // addon.cc #include namespace demo { using v8::Context; using v8::FunctionCallbackInfo; using v8::Isolate; using v8::Local; using v8::Object; using v8::String; using v8::Value; void CreateObject(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); Local context = isolate->GetCurrentContext(); Local obj = Object::New(isolate); obj->Set(context, String::NewFromUtf8(isolate, "msg").ToLocalChecked(), args[0]->ToString(context).ToLocalChecked()) .FromJust(); args.GetReturnValue().Set(obj); } void Init(Local exports, Local module) { NODE_SET_METHOD(module, "exports", CreateObject); } NODE_MODULE(NODE_GYP_MODULE_NAME, Init) } // namespace demo To test it in JavaScript: // test.js const addon = require('./build/Release/addon'); const obj1 = addon('hello'); const obj2 = addon('world'); console.log(obj1.msg, obj2.msg); // Prints: 'hello world' #### Function factory# Another common scenario is creating JavaScript functions that wrap C++ functions and returning those back to JavaScript: // addon.cc #include namespace demo { using v8::Context; using v8::Function; using v8::FunctionCallbackInfo; using v8::FunctionTemplate; using v8::Isolate; using v8::Local; using v8::Object; using v8::String; using v8::Value; void MyFunction(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); args.GetReturnValue().Set(String::NewFromUtf8( isolate, "hello world").ToLocalChecked()); } void CreateFunction(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); Local context = isolate->GetCurrentContext(); Local tpl = FunctionTemplate::New(isolate, MyFunction); Local fn = tpl->GetFunction(context).ToLocalChecked(); // omit this to make it anonymous fn->SetName(String::NewFromUtf8( isolate, "theFunction").ToLocalChecked()); args.GetReturnValue().Set(fn); } void Init(Local exports, Local module) { NODE_SET_METHOD(module, "exports", CreateFunction); } NODE_MODULE(NODE_GYP_MODULE_NAME, Init) } // namespace demo To test: // test.js const addon = require('./build/Release/addon'); const fn = addon(); console.log(fn()); // Prints: 'hello world' #### Wrapping C++ objects# It is also possible to wrap C++ objects/classes in a way that allows new instances to be created using the JavaScript `new` operator: // addon.cc #include #include "myobject.h" namespace demo { using v8::Local; using v8::Object; void InitAll(Local exports) { MyObject::Init(exports); } NODE_MODULE(NODE_GYP_MODULE_NAME, InitAll) } // namespace demo Then, in `myobject.h`, the wrapper class inherits from `node::ObjectWrap`: // myobject.h #ifndef MYOBJECT_H #define MYOBJECT_H #include #include namespace demo { class MyObject : public node::ObjectWrap { public: static void Init(v8::Local exports); private: explicit MyObject(double value = 0); ~MyObject(); static void New(const v8::FunctionCallbackInfo& args); static void PlusOne(const v8::FunctionCallbackInfo& args); double value_; }; } // namespace demo #endif In `myobject.cc`, implement the various methods that are to be exposed. In the following code, the method `plusOne()` is exposed by adding it to the constructor's prototype: // myobject.cc #include "myobject.h" namespace demo { using v8::Context; using v8::Function; using v8::FunctionCallbackInfo; using v8::FunctionTemplate; using v8::Isolate; using v8::Local; using v8::Number; using v8::Object; using v8::ObjectTemplate; using v8::String; using v8::Value; MyObject::MyObject(double value) : value_(value) { } MyObject::~MyObject() { } void MyObject::Init(Local exports) { Isolate* isolate = exports->GetIsolate(); Local context = isolate->GetCurrentContext(); Local addon_data_tpl = ObjectTemplate::New(isolate); addon_data_tpl->SetInternalFieldCount(1); // 1 field for the MyObject::New() Local addon_data = addon_data_tpl->NewInstance(context).ToLocalChecked(); // Prepare constructor template Local tpl = FunctionTemplate::New(isolate, New, addon_data); tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject").ToLocalChecked()); tpl->InstanceTemplate()->SetInternalFieldCount(1); // Prototype NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne); Local constructor = tpl->GetFunction(context).ToLocalChecked(); addon_data->SetInternalField(0, constructor); exports->Set(context, String::NewFromUtf8( isolate, "MyObject").ToLocalChecked(), constructor).FromJust(); } void MyObject::New(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); Local context = isolate->GetCurrentContext(); if (args.IsConstructCall()) { // Invoked as constructor: `new MyObject(...)` double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue(context).FromMaybe(0); MyObject* obj = new MyObject(value); obj->Wrap(args.This()); args.GetReturnValue().Set(args.This()); } else { // Invoked as plain function `MyObject(...)`, turn into construct call. const int argc = 1; Local argv[argc] = { args[0] }; Local cons = args.Data().As()->GetInternalField(0) .As().As(); Local result = cons->NewInstance(context, argc, argv).ToLocalChecked(); args.GetReturnValue().Set(result); } } void MyObject::PlusOne(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); MyObject* obj = ObjectWrap::Unwrap(args.This()); obj->value_ += 1; args.GetReturnValue().Set(Number::New(isolate, obj->value_)); } } // namespace demo To build this example, the `myobject.cc` file must be added to the `binding.gyp`: { "targets": [ { "target_name": "addon", "sources": [ "addon.cc", "myobject.cc" ] } ] } Test it with: // test.js const addon = require('./build/Release/addon'); const obj = new addon.MyObject(10); console.log(obj.plusOne()); // Prints: 11 console.log(obj.plusOne()); // Prints: 12 console.log(obj.plusOne()); // Prints: 13 The destructor for a wrapper object will run when the object is garbage-collected. For destructor testing, there are command-line flags that can be used to make it possible to force garbage collection. These flags are provided by the underlying V8 JavaScript engine. They are subject to change or removal at any time. They are not documented by Node.js or V8, and they should never be used outside of testing. During shutdown of the process or worker threads destructors are not called by the JS engine. Therefore it's the responsibility of the user to track these objects and ensure proper destruction to avoid resource leaks. #### Factory of wrapped objects# Alternatively, it is possible to use a factory pattern to avoid explicitly creating object instances using the JavaScript `new` operator: const obj = addon.createObject(); // instead of: // const obj = new addon.Object(); First, the `createObject()` method is implemented in `addon.cc`: // addon.cc #include #include "myobject.h" namespace demo { using v8::FunctionCallbackInfo; using v8::Isolate; using v8::Local; using v8::Object; using v8::String; using v8::Value; void CreateObject(const FunctionCallbackInfo& args) { MyObject::NewInstance(args); } void InitAll(Local exports, Local module) { MyObject::Init(exports->GetIsolate()); NODE_SET_METHOD(module, "exports", CreateObject); } NODE_MODULE(NODE_GYP_MODULE_NAME, InitAll) } // namespace demo In `myobject.h`, the static method `NewInstance()` is added to handle instantiating the object. This method takes the place of using `new` in JavaScript: // myobject.h #ifndef MYOBJECT_H #define MYOBJECT_H #include #include namespace demo { class MyObject : public node::ObjectWrap { public: static void Init(v8::Isolate* isolate); static void NewInstance(const v8::FunctionCallbackInfo& args); private: explicit MyObject(double value = 0); ~MyObject(); static void New(const v8::FunctionCallbackInfo& args); static void PlusOne(const v8::FunctionCallbackInfo& args); static v8::Global constructor; double value_; }; } // namespace demo #endif The implementation in `myobject.cc` is similar to the previous example: // myobject.cc #include #include "myobject.h" namespace demo { using node::AddEnvironmentCleanupHook; using v8::Context; using v8::Function; using v8::FunctionCallbackInfo; using v8::FunctionTemplate; using v8::Global; using v8::Isolate; using v8::Local; using v8::Number; using v8::Object; using v8::String; using v8::Value; // Warning! This is not thread-safe, this addon cannot be used for worker // threads. Global MyObject::constructor; MyObject::MyObject(double value) : value_(value) { } MyObject::~MyObject() { } void MyObject::Init(Isolate* isolate) { // Prepare constructor template Local tpl = FunctionTemplate::New(isolate, New); tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject").ToLocalChecked()); tpl->InstanceTemplate()->SetInternalFieldCount(1); // Prototype NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne); Local context = isolate->GetCurrentContext(); constructor.Reset(isolate, tpl->GetFunction(context).ToLocalChecked()); AddEnvironmentCleanupHook(isolate, [](void*) { constructor.Reset(); }, nullptr); } void MyObject::New(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); Local context = isolate->GetCurrentContext(); if (args.IsConstructCall()) { // Invoked as constructor: `new MyObject(...)` double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue(context).FromMaybe(0); MyObject* obj = new MyObject(value); obj->Wrap(args.This()); args.GetReturnValue().Set(args.This()); } else { // Invoked as plain function `MyObject(...)`, turn into construct call. const int argc = 1; Local argv[argc] = { args[0] }; Local cons = Local::New(isolate, constructor); Local instance = cons->NewInstance(context, argc, argv).ToLocalChecked(); args.GetReturnValue().Set(instance); } } void MyObject::NewInstance(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); const unsigned argc = 1; Local argv[argc] = { args[0] }; Local cons = Local::New(isolate, constructor); Local context = isolate->GetCurrentContext(); Local instance = cons->NewInstance(context, argc, argv).ToLocalChecked(); args.GetReturnValue().Set(instance); } void MyObject::PlusOne(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); MyObject* obj = ObjectWrap::Unwrap(args.This()); obj->value_ += 1; args.GetReturnValue().Set(Number::New(isolate, obj->value_)); } } // namespace demo Once again, to build this example, the `myobject.cc` file must be added to the `binding.gyp`: { "targets": [ { "target_name": "addon", "sources": [ "addon.cc", "myobject.cc" ] } ] } Test it with: // test.js const createObject = require('./build/Release/addon'); const obj = createObject(10); console.log(obj.plusOne()); // Prints: 11 console.log(obj.plusOne()); // Prints: 12 console.log(obj.plusOne()); // Prints: 13 const obj2 = createObject(20); console.log(obj2.plusOne()); // Prints: 21 console.log(obj2.plusOne()); // Prints: 22 console.log(obj2.plusOne()); // Prints: 23 #### Passing wrapped objects around# In addition to wrapping and returning C++ objects, it is possible to pass wrapped objects around by unwrapping them with the Node.js helper function `node::ObjectWrap::Unwrap`. The following examples shows a function `add()` that can take two `MyObject` objects as input arguments: // addon.cc #include #include #include "myobject.h" namespace demo { using v8::Context; using v8::FunctionCallbackInfo; using v8::Isolate; using v8::Local; using v8::Number; using v8::Object; using v8::String; using v8::Value; void CreateObject(const FunctionCallbackInfo& args) { MyObject::NewInstance(args); } void Add(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); Local context = isolate->GetCurrentContext(); MyObject* obj1 = node::ObjectWrap::Unwrap( args[0]->ToObject(context).ToLocalChecked()); MyObject* obj2 = node::ObjectWrap::Unwrap( args[1]->ToObject(context).ToLocalChecked()); double sum = obj1->value() + obj2->value(); args.GetReturnValue().Set(Number::New(isolate, sum)); } void InitAll(Local exports) { MyObject::Init(exports->GetIsolate()); NODE_SET_METHOD(exports, "createObject", CreateObject); NODE_SET_METHOD(exports, "add", Add); } NODE_MODULE(NODE_GYP_MODULE_NAME, InitAll) } // namespace demo In `myobject.h`, a new public method is added to allow access to private values after unwrapping the object. // myobject.h #ifndef MYOBJECT_H #define MYOBJECT_H #include #include namespace demo { class MyObject : public node::ObjectWrap { public: static void Init(v8::Isolate* isolate); static void NewInstance(const v8::FunctionCallbackInfo& args); inline double value() const { return value_; } private: explicit MyObject(double value = 0); ~MyObject(); static void New(const v8::FunctionCallbackInfo& args); static v8::Global constructor; double value_; }; } // namespace demo #endif The implementation of `myobject.cc` remains similar to the previous version: // myobject.cc #include #include "myobject.h" namespace demo { using node::AddEnvironmentCleanupHook; using v8::Context; using v8::Function; using v8::FunctionCallbackInfo; using v8::FunctionTemplate; using v8::Global; using v8::Isolate; using v8::Local; using v8::Object; using v8::String; using v8::Value; // Warning! This is not thread-safe, this addon cannot be used for worker // threads. Global MyObject::constructor; MyObject::MyObject(double value) : value_(value) { } MyObject::~MyObject() { } void MyObject::Init(Isolate* isolate) { // Prepare constructor template Local tpl = FunctionTemplate::New(isolate, New); tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject").ToLocalChecked()); tpl->InstanceTemplate()->SetInternalFieldCount(1); Local context = isolate->GetCurrentContext(); constructor.Reset(isolate, tpl->GetFunction(context).ToLocalChecked()); AddEnvironmentCleanupHook(isolate, [](void*) { constructor.Reset(); }, nullptr); } void MyObject::New(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); Local context = isolate->GetCurrentContext(); if (args.IsConstructCall()) { // Invoked as constructor: `new MyObject(...)` double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue(context).FromMaybe(0); MyObject* obj = new MyObject(value); obj->Wrap(args.This()); args.GetReturnValue().Set(args.This()); } else { // Invoked as plain function `MyObject(...)`, turn into construct call. const int argc = 1; Local argv[argc] = { args[0] }; Local cons = Local::New(isolate, constructor); Local instance = cons->NewInstance(context, argc, argv).ToLocalChecked(); args.GetReturnValue().Set(instance); } } void MyObject::NewInstance(const FunctionCallbackInfo& args) { Isolate* isolate = args.GetIsolate(); const unsigned argc = 1; Local argv[argc] = { args[0] }; Local cons = Local::New(isolate, constructor); Local context = isolate->GetCurrentContext(); Local instance = cons->NewInstance(context, argc, argv).ToLocalChecked(); args.GetReturnValue().Set(instance); } } // namespace demo Test it with: // test.js const addon = require('./build/Release/addon'); const obj1 = addon.createObject(10); const obj2 = addon.createObject(20); const result = addon.add(obj1, obj2); console.log(result); // Prints: 30 ## Node-API# Stability: 2 \- Stable Node-API (formerly N-API) is an API for building native Addons. It is independent from the underlying JavaScript runtime (for example, V8) and is maintained as part of Node.js itself. This API will be Application Binary Interface (ABI) stable across versions of Node.js. It is intended to insulate addons from changes in the underlying JavaScript engine and allow modules compiled for one major version to run on later major versions of Node.js without recompilation. The ABI Stability guide provides a more in-depth explanation. Addons are built/packaged with the same approach/tools outlined in the section titled C++ Addons. The only difference is the set of APIs that are used by the native code. Instead of using the V8 or Native Abstractions for Node.js APIs, the functions available in Node-API are used. APIs exposed by Node-API are generally used to create and manipulate JavaScript values. Concepts and operations generally map to ideas specified in the ECMA-262 Language Specification. The APIs have the following properties: * All Node-API calls return a status code of type `napi_status`. This status indicates whether the API call succeeded or failed. * The API's return value is passed via an out parameter. * All JavaScript values are abstracted behind an opaque type named `napi_value`. * In case of an error status code, additional information can be obtained using `napi_get_last_error_info`. More information can be found in the error handling section Error handling. ### Writing addons in various programming languages# Node-API is a C API that ensures ABI stability across Node.js versions and different compiler levels. With this stability guarantee, it is possible to write addons in other programming languages on top of Node-API. Refer to language and engine bindings for more programming languages and engines support details. `node-addon-api` is the official C++ binding that provides a more efficient way to write C++ code that calls Node-API. This wrapper is a header-only library that offers an inlinable C++ API. Binaries built with `node-addon-api` will depend on the symbols of the Node-API C-based functions exported by Node.js. The following code snippet is an example of `node-addon-api`: Object obj = Object::New(env); obj["foo"] = String::New(env, "bar"); The above `node-addon-api` C++ code is equivalent to the following C-based Node-API code: napi_status status; napi_value object, string; status = napi_create_object(env, &object); if (status != napi_ok) { napi_throw_error(env, ...); return; } status = napi_create_string_utf8(env, "bar", NAPI_AUTO_LENGTH, &string); if (status != napi_ok) { napi_throw_error(env, ...); return; } status = napi_set_named_property(env, object, "foo", string); if (status != napi_ok) { napi_throw_error(env, ...); return; } The end result is that the addon only uses the exported C APIs. Even though the addon is written in C++, it still gets the benefits of the ABI stability provided by the C Node-API. When using `node-addon-api` instead of the C APIs, start with the API docs for `node-addon-api`. The Node-API Resource offers an excellent orientation and tips for developers just getting started with Node-API and `node-addon-api`. Additional media resources can be found on the Node-API Media page. ### Implications of ABI stability# Although Node-API provides an ABI stability guarantee, other parts of Node.js do not, and any external libraries used from the addon may not. In particular, none of the following APIs provide an ABI stability guarantee across major versions: * the Node.js C++ APIs available via any of #include #include #include #include * the libuv APIs which are also included with Node.js and available via #include * the V8 API available via #include Thus, for an addon to remain ABI-compatible across Node.js major versions, it must use Node-API exclusively by restricting itself to using #include and by checking, for all external libraries that it uses, that the external library makes ABI stability guarantees similar to Node-API. #### Enum values in ABI stability# All enum data types defined in Node-API should be considered as a fixed size `int32_t` value. Bit flag enum types should be explicitly documented, and they work with bit operators like bit-OR (`|`) as a bit value. Unless otherwise documented, an enum type should be considered to be extensible. A new enum value will be added at the end of the enum definition. An enum value will not be removed or renamed. For an enum type returned from a Node-API function, or provided as an out parameter of a Node-API function, the value is an integer value and an addon should handle unknown values. New values are allowed to be introduced without a version guard. For example, when checking `napi_status` in switch statements, an addon should include a default branch, as new status codes may be introduced in newer Node.js versions. For an enum type used in an in-parameter, the result of passing an unknown integer value to Node-API functions is undefined unless otherwise documented. A new value is added with a version guard to indicate the Node-API version in which it was introduced. For example, `napi_get_all_property_names` can be extended with new enum value of `napi_key_filter`. For an enum type used in both in-parameters and out-parameters, new values are allowed to be introduced without a version guard. ### Building# Unlike modules written in JavaScript, developing and deploying Node.js native addons using Node-API requires an additional set of tools. Besides the basic tools required to develop for Node.js, the native addon developer requires a toolchain that can compile C and C++ code into a binary. In addition, depending upon how the native addon is deployed, the user of the native addon will also need to have a C/C++ toolchain installed. For Linux developers, the necessary C/C++ toolchain packages are readily available. GCC is widely used in the Node.js community to build and test across a variety of platforms. For many developers, the LLVM compiler infrastructure is also a good choice. For Mac developers, Xcode offers all the required compiler tools. However, it is not necessary to install the entire Xcode IDE. The following command installs the necessary toolchain: xcode-select --install For Windows developers, Visual Studio offers all the required compiler tools. However, it is not necessary to install the entire Visual Studio IDE. The following command installs the necessary toolchain: npm install --global windows-build-tools The sections below describe the additional tools available for developing and deploying Node.js native addons. #### Build tools# Both the tools listed here require that users of the native addon have a C/C++ toolchain installed in order to successfully install the native addon. ##### node-gyp# node-gyp is a build system based on the gyp-next fork of Google's GYP tool and comes bundled with npm. GYP, and therefore node-gyp, requires that Python be installed. Historically, node-gyp has been the tool of choice for building native addons. It has widespread adoption and documentation. However, some developers have run into limitations in node-gyp. ##### CMake.js# CMake.js is an alternative build system based on CMake. CMake.js is a good choice for projects that already use CMake or for developers affected by limitations in node-gyp. `build_with_cmake` is an example of a CMake-based native addon project. #### Uploading precompiled binaries# The three tools listed here permit native addon developers and maintainers to create and upload binaries to public or private servers. These tools are typically integrated with CI/CD build systems like Travis CI and AppVeyor to build and upload binaries for a variety of platforms and architectures. These binaries are then available for download by users who do not need to have a C/C++ toolchain installed. ##### node-pre-gyp# node-pre-gyp is a tool based on node-gyp that adds the ability to upload binaries to a server of the developer's choice. node-pre-gyp has particularly good support for uploading binaries to Amazon S3. ##### prebuild# prebuild is a tool that supports builds using either node-gyp or CMake.js. Unlike node-pre-gyp which supports a variety of servers, prebuild uploads binaries only to GitHub releases. prebuild is a good choice for GitHub projects using CMake.js. ##### prebuildify# prebuildify is a tool based on node-gyp. The advantage of prebuildify is that the built binaries are bundled with the native addon when it's uploaded to npm. The binaries are downloaded from npm and are immediately available to the module user when the native addon is installed. ### Usage# In order to use the Node-API functions, include the file `node_api.h` which is located in the src directory in the node development tree: #include This will opt into the default `NAPI_VERSION` for the given release of Node.js. In order to ensure compatibility with specific versions of Node-API, the version can be specified explicitly when including the header: #define NAPI_VERSION 3 #include This restricts the Node-API surface to just the functionality that was available in the specified (and earlier) versions. Some of the Node-API surface is experimental and requires explicit opt-in: #define NAPI_EXPERIMENTAL #include In this case the entire API surface, including any experimental APIs, will be available to the module code. Occasionally, experimental features are introduced that affect already-released and stable APIs. These features can be disabled by an opt-out: #define NAPI_EXPERIMENTAL #define NODE_API_EXPERIMENTAL__OPT_OUT #include where `` is the name of an experimental feature that affects both experimental and stable APIs. ### Node-API version matrix# Up until version 9, Node-API versions were additive and versioned independently from Node.js. This meant that any version was an extension to the previous version in that it had all of the APIs from the previous version with some additions. Each Node.js version only supported a single Node-API version. For example v18.15.0 supports only Node-API version 8. ABI stability was achieved because 8 was a strict superset of all previous versions. As of version 9, while Node-API versions continue to be versioned independently, an add-on that ran with Node-API version 9 may need code updates to run with Node-API version 10. ABI stability is maintained, however, because Node.js versions that support Node-API versions higher than 8 will support all versions between 8 and the highest version they support and will default to providing the version 8 APIs unless an add-on opts into a higher Node-API version. This approach provides the flexibility of better optimizing existing Node-API functions while maintaining ABI stability. Existing add-ons can continue to run without recompilation using an earlier version of Node-API. If an add-on needs functionality from a newer Node-API version, changes to existing code and recompilation will be needed to use those new functions anyway. In versions of Node.js that support Node-API version 9 and later, defining `NAPI_VERSION=X` and using the existing add-on initialization macros will bake in the requested Node-API version that will be used at runtime into the add-on. If `NAPI_VERSION` is not set it will default to 8. This table may not be up to date in older streams, the most up to date information is in the latest API documentation in: Node-API version matrix Node-API version Supported In 10 v22.14.0+, 23.6.0+ and all later versions 9 v18.17.0+, 20.3.0+, 21.0.0 and all later versions 8 v12.22.0+, v14.17.0+, v15.12.0+, 16.0.0 and all later versions 7 v10.23.0+, v12.19.0+, v14.12.0+, 15.0.0 and all later versions 6 v10.20.0+, v12.17.0+, 14.0.0 and all later versions 5 v10.17.0+, v12.11.0+, 13.0.0 and all later versions 4 v10.16.0+, v11.8.0+, 12.0.0 and all later versions 3 v6.14.2*, 8.11.2+, v9.11.0+*, 10.0.0 and all later versions 2 v8.10.0+*, v9.3.0+*, 10.0.0 and all later versions 1 v8.6.0+**, v9.0.0+*, 10.0.0 and all later versions * Node-API was experimental. ** Node.js 8.0.0 included Node-API as experimental. It was released as Node-API version 1 but continued to evolve until Node.js 8.6.0. The API is different in versions prior to Node.js 8.6.0. We recommend Node-API version 3 or later. Each API documented for Node-API will have a header named `added in:`, and APIs which are stable will have the additional header `Node-API version:`. APIs are directly usable when using a Node.js version which supports the Node-API version shown in `Node-API version:` or higher. When using a Node.js version that does not support the `Node-API version:` listed or if there is no `Node-API version:` listed, then the API will only be available if `#define NAPI_EXPERIMENTAL` precedes the inclusion of `node_api.h` or `js_native_api.h`. If an API appears not to be available on a version of Node.js which is later than the one shown in `added in:` then this is most likely the reason for the apparent absence. The Node-APIs associated strictly with accessing ECMAScript features from native code can be found separately in `js_native_api.h` and `js_native_api_types.h`. The APIs defined in these headers are included in `node_api.h` and `node_api_types.h`. The headers are structured in this way in order to allow implementations of Node-API outside of Node.js. For those implementations the Node.js specific APIs may not be applicable. The Node.js-specific parts of an addon can be separated from the code that exposes the actual functionality to the JavaScript environment so that the latter may be used with multiple implementations of Node-API. In the example below, `addon.c` and `addon.h` refer only to `js_native_api.h`. This ensures that `addon.c` can be reused to compile against either the Node.js implementation of Node-API or any implementation of Node-API outside of Node.js. `addon_node.c` is a separate file that contains the Node.js specific entry point to the addon and which instantiates the addon by calling into `addon.c` when the addon is loaded into a Node.js environment. // addon.h #ifndef _ADDON_H_ #define _ADDON_H_ #include napi_value create_addon(napi_env env); #endif // _ADDON_H_ // addon.c #include "addon.h" #define NODE_API_CALL(env, call) \ do { \ napi_status status = (call); \ if (status != napi_ok) { \ const napi_extended_error_info* error_info = NULL; \ napi_get_last_error_info((env), &error_info); \ const char* err_message = error_info->error_message; \ bool is_pending; \ napi_is_exception_pending((env), &is_pending); \ /* If an exception is already pending, don't rethrow it */ \ if (!is_pending) { \ const char* message = (err_message == NULL) \ ? "empty error message" \ : err_message; \ napi_throw_error((env), NULL, message); \ } \ return NULL; \ } \ } while(0) static napi_value DoSomethingUseful(napi_env env, napi_callback_info info) { // Do something useful. return NULL; } napi_value create_addon(napi_env env) { napi_value result; NODE_API_CALL(env, napi_create_object(env, &result)); napi_value exported_function; NODE_API_CALL(env, napi_create_function(env, "doSomethingUseful", NAPI_AUTO_LENGTH, DoSomethingUseful, NULL, &exported_function)); NODE_API_CALL(env, napi_set_named_property(env, result, "doSomethingUseful", exported_function)); return result; } // addon_node.c #include #include "addon.h" NAPI_MODULE_INIT(/* napi_env env, napi_value exports */) { // This function body is expected to return a `napi_value`. // The variables `napi_env env` and `napi_value exports` may be used within // the body, as they are provided by the definition of `NAPI_MODULE_INIT()`. return create_addon(env); } ### Environment life cycle APIs# Section Agents of the ECMAScript Language Specification defines the concept of an "Agent" as a self-contained environment in which JavaScript code runs. Multiple such Agents may be started and terminated either concurrently or in sequence by the process. A Node.js environment corresponds to an ECMAScript Agent. In the main process, an environment is created at startup, and additional environments can be created on separate threads to serve as worker threads. When Node.js is embedded in another application, the main thread of the application may also construct and destroy a Node.js environment multiple times during the life cycle of the application process such that each Node.js environment created by the application may, in turn, during its life cycle create and destroy additional environments as worker threads. From the perspective of a native addon this means that the bindings it provides may be called multiple times, from multiple contexts, and even concurrently from multiple threads. Native addons may need to allocate global state which they use during their life cycle of an Node.js environment such that the state can be unique to each instance of the addon. To this end, Node-API provides a way to associate data such that its life cycle is tied to the life cycle of a Node.js environment. #### `napi_set_instance_data`# Added in: v12.8.0, v10.20.0 N-API version: 6 napi_status napi_set_instance_data(node_api_basic_env env, void* data, napi_finalize finalize_cb, void* finalize_hint); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] data`: The data item to make available to bindings of this instance. * `[in] finalize_cb`: The function to call when the environment is being torn down. The function receives `data` so that it might free it. `napi_finalize` provides more details. * `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection. Returns `napi_ok` if the API succeeded. This API associates `data` with the currently running Node.js environment. `data` can later be retrieved using `napi_get_instance_data()`. Any existing data associated with the currently running Node.js environment which was set by means of a previous call to `napi_set_instance_data()` will be overwritten. If a `finalize_cb` was provided by the previous call, it will not be called. #### `napi_get_instance_data`# Added in: v12.8.0, v10.20.0 N-API version: 6 napi_status napi_get_instance_data(node_api_basic_env env, void** data); * `[in] env`: The environment that the Node-API call is invoked under. * `[out] data`: The data item that was previously associated with the currently running Node.js environment by a call to `napi_set_instance_data()`. Returns `napi_ok` if the API succeeded. This API retrieves data that was previously associated with the currently running Node.js environment via `napi_set_instance_data()`. If no data is set, the call will succeed and `data` will be set to `NULL`. ### Basic Node-API data types# Node-API exposes the following fundamental data types as abstractions that are consumed by the various APIs. These APIs should be treated as opaque, introspectable only with other Node-API calls. #### `napi_status`# Added in: v8.0.0 N-API version: 1 Integral status code indicating the success or failure of a Node-API call. Currently, the following status codes are supported. typedef enum { napi_ok, napi_invalid_arg, napi_object_expected, napi_string_expected, napi_name_expected, napi_function_expected, napi_number_expected, napi_boolean_expected, napi_array_expected, napi_generic_failure, napi_pending_exception, napi_cancelled, napi_escape_called_twice, napi_handle_scope_mismatch, napi_callback_scope_mismatch, napi_queue_full, napi_closing, napi_bigint_expected, napi_date_expected, napi_arraybuffer_expected, napi_detachable_arraybuffer_expected, napi_would_deadlock, /* unused */ napi_no_external_buffers_allowed, napi_cannot_run_js } napi_status; If additional information is required upon an API returning a failed status, it can be obtained by calling `napi_get_last_error_info`. #### `napi_extended_error_info`# Added in: v8.0.0 N-API version: 1 typedef struct { const char* error_message; void* engine_reserved; uint32_t engine_error_code; napi_status error_code; } napi_extended_error_info; * `error_message`: UTF8-encoded string containing a VM-neutral description of the error. * `engine_reserved`: Reserved for VM-specific error details. This is currently not implemented for any VM. * `engine_error_code`: VM-specific error code. This is currently not implemented for any VM. * `error_code`: The Node-API status code that originated with the last error. See the Error handling section for additional information. #### `napi_env`# `napi_env` is used to represent a context that the underlying Node-API implementation can use to persist VM-specific state. This structure is passed to native functions when they're invoked, and it must be passed back when making Node-API calls. Specifically, the same `napi_env` that was passed in when the initial native function was called must be passed to any subsequent nested Node-API calls. Caching the `napi_env` for the purpose of general reuse, and passing the `napi_env` between instances of the same addon running on different `Worker` threads is not allowed. The `napi_env` becomes invalid when an instance of a native addon is unloaded. Notification of this event is delivered through the callbacks given to `napi_add_env_cleanup_hook` and `napi_set_instance_data`. #### `node_api_basic_env`# Stability: 1 \- Experimental This variant of `napi_env` is passed to synchronous finalizers (`node_api_basic_finalize`). There is a subset of Node-APIs which accept a parameter of type `node_api_basic_env` as their first argument. These APIs do not access the state of the JavaScript engine and are thus safe to call from synchronous finalizers. Passing a parameter of type `napi_env` to these APIs is allowed, however, passing a parameter of type `node_api_basic_env` to APIs that access the JavaScript engine state is not allowed. Attempting to do so without a cast will produce a compiler warning or an error when add-ons are compiled with flags which cause them to emit warnings and/or errors when incorrect pointer types are passed into a function. Calling such APIs from a synchronous finalizer will ultimately result in the termination of the application. #### `napi_value`# This is an opaque pointer that is used to represent a JavaScript value. #### `napi_threadsafe_function`# Added in: v10.6.0 N-API version: 4 This is an opaque pointer that represents a JavaScript function which can be called asynchronously from multiple threads via `napi_call_threadsafe_function()`. #### `napi_threadsafe_function_release_mode`# Added in: v10.6.0 N-API version: 4 A value to be given to `napi_release_threadsafe_function()` to indicate whether the thread-safe function is to be closed immediately (`napi_tsfn_abort`) or merely released (`napi_tsfn_release`) and thus available for subsequent use via `napi_acquire_threadsafe_function()` and `napi_call_threadsafe_function()`. typedef enum { napi_tsfn_release, napi_tsfn_abort } napi_threadsafe_function_release_mode; #### `napi_threadsafe_function_call_mode`# Added in: v10.6.0 N-API version: 4 A value to be given to `napi_call_threadsafe_function()` to indicate whether the call should block whenever the queue associated with the thread-safe function is full. typedef enum { napi_tsfn_nonblocking, napi_tsfn_blocking } napi_threadsafe_function_call_mode; #### Node-API memory management types# ##### `napi_handle_scope`# This is an abstraction used to control and modify the lifetime of objects created within a particular scope. In general, Node-API values are created within the context of a handle scope. When a native method is called from JavaScript, a default handle scope will exist. If the user does not explicitly create a new handle scope, Node-API values will be created in the default handle scope. For any invocations of code outside the execution of a native method (for instance, during a libuv callback invocation), the module is required to create a scope before invoking any functions that can result in the creation of JavaScript values. Handle scopes are created using `napi_open_handle_scope` and are destroyed using `napi_close_handle_scope`. Closing the scope can indicate to the GC that all `napi_value`s created during the lifetime of the handle scope are no longer referenced from the current stack frame. For more details, review the Object lifetime management. ##### `napi_escapable_handle_scope`# Added in: v8.0.0 N-API version: 1 Escapable handle scopes are a special type of handle scope to return values created within a particular handle scope to a parent scope. ##### `napi_ref`# Added in: v8.0.0 N-API version: 1 This is the abstraction to use to reference a `napi_value`. This allows for users to manage the lifetimes of JavaScript values, including defining their minimum lifetimes explicitly. For more details, review the Object lifetime management. ##### `napi_type_tag`# Added in: v14.8.0, v12.19.0 N-API version: 8 A 128-bit value stored as two unsigned 64-bit integers. It serves as a UUID with which JavaScript objects or externals can be "tagged" in order to ensure that they are of a certain type. This is a stronger check than `napi_instanceof`, because the latter can report a false positive if the object's prototype has been manipulated. Type-tagging is most useful in conjunction with `napi_wrap` because it ensures that the pointer retrieved from a wrapped object can be safely cast to the native type corresponding to the type tag that had been previously applied to the JavaScript object. typedef struct { uint64_t lower; uint64_t upper; } napi_type_tag; ##### `napi_async_cleanup_hook_handle`# Added in: v14.10.0, v12.19.0 An opaque value returned by `napi_add_async_cleanup_hook`. It must be passed to `napi_remove_async_cleanup_hook` when the chain of asynchronous cleanup events completes. #### Node-API callback types# ##### `napi_callback_info`# Added in: v8.0.0 N-API version: 1 Opaque datatype that is passed to a callback function. It can be used for getting additional information about the context in which the callback was invoked. ##### `napi_callback`# Added in: v8.0.0 N-API version: 1 Function pointer type for user-provided native functions which are to be exposed to JavaScript via Node-API. Callback functions should satisfy the following signature: typedef napi_value (*napi_callback)(napi_env, napi_callback_info); Unless for reasons discussed in Object Lifetime Management, creating a handle and/or callback scope inside a `napi_callback` is not necessary. ##### `node_api_basic_finalize`# Added in: v21.6.0, v20.12.0, v18.20.0 Stability: 1 \- Experimental Function pointer type for add-on provided functions that allow the user to be notified when externally-owned data is ready to be cleaned up because the object it was associated with has been garbage-collected. The user must provide a function satisfying the following signature which would get called upon the object's collection. Currently, `node_api_basic_finalize` can be used for finding out when objects that have external data are collected. typedef void (*node_api_basic_finalize)(node_api_basic_env env, void* finalize_data, void* finalize_hint); Unless for reasons discussed in Object Lifetime Management, creating a handle and/or callback scope inside the function body is not necessary. Since these functions may be called while the JavaScript engine is in a state where it cannot execute JavaScript code, only Node-APIs which accept a `node_api_basic_env` as their first parameter may be called. `node_api_post_finalizer` can be used to schedule Node-API calls that require access to the JavaScript engine's state to run after the current garbage collection cycle has completed. In the case of `node_api_create_external_string_latin1` and `node_api_create_external_string_utf16` the `env` parameter may be null, because external strings can be collected during the latter part of environment shutdown. Change History: * experimental (`NAPI_EXPERIMENTAL`): Only Node-API calls that accept a `node_api_basic_env` as their first parameter may be called, otherwise the application will be terminated with an appropriate error message. This feature can be turned off by defining `NODE_API_EXPERIMENTAL_BASIC_ENV_OPT_OUT`. ##### `napi_finalize`# Added in: v8.0.0 N-API version: 1 Function pointer type for add-on provided function that allow the user to schedule a group of calls to Node-APIs in response to a garbage collection event, after the garbage collection cycle has completed. These function pointers can be used with `node_api_post_finalizer`. typedef void (*napi_finalize)(napi_env env, void* finalize_data, void* finalize_hint); Change History: * experimental (`NAPI_EXPERIMENTAL` is defined): A function of this type may no longer be used as a finalizer, except with `node_api_post_finalizer`. `node_api_basic_finalize` must be used instead. This feature can be turned off by defining `NODE_API_EXPERIMENTAL_BASIC_ENV_OPT_OUT`. ##### `napi_async_execute_callback`# Added in: v8.0.0 N-API version: 1 Function pointer used with functions that support asynchronous operations. Callback functions must satisfy the following signature: typedef void (*napi_async_execute_callback)(napi_env env, void* data); Implementations of this function must avoid making Node-API calls that execute JavaScript or interact with JavaScript objects. Node-API calls should be in the `napi_async_complete_callback` instead. Do not use the `napi_env` parameter as it will likely result in execution of JavaScript. ##### `napi_async_complete_callback`# Added in: v8.0.0 N-API version: 1 Function pointer used with functions that support asynchronous operations. Callback functions must satisfy the following signature: typedef void (*napi_async_complete_callback)(napi_env env, napi_status status, void* data); Unless for reasons discussed in Object Lifetime Management, creating a handle and/or callback scope inside the function body is not necessary. ##### `napi_threadsafe_function_call_js`# Added in: v10.6.0 N-API version: 4 Function pointer used with asynchronous thread-safe function calls. The callback will be called on the main thread. Its purpose is to use a data item arriving via the queue from one of the secondary threads to construct the parameters necessary for a call into JavaScript, usually via `napi_call_function`, and then make the call into JavaScript. The data arriving from the secondary thread via the queue is given in the `data` parameter and the JavaScript function to call is given in the `js_callback` parameter. Node-API sets up the environment prior to calling this callback, so it is sufficient to call the JavaScript function via `napi_call_function` rather than via `napi_make_callback`. Callback functions must satisfy the following signature: typedef void (*napi_threadsafe_function_call_js)(napi_env env, napi_value js_callback, void* context, void* data); * `[in] env`: The environment to use for API calls, or `NULL` if the thread-safe function is being torn down and `data` may need to be freed. * `[in] js_callback`: The JavaScript function to call, or `NULL` if the thread-safe function is being torn down and `data` may need to be freed. It may also be `NULL` if the thread-safe function was created without `js_callback`. * `[in] context`: The optional data with which the thread-safe function was created. * `[in] data`: Data created by the secondary thread. It is the responsibility of the callback to convert this native data to JavaScript values (with Node-API functions) that can be passed as parameters when `js_callback` is invoked. This pointer is managed entirely by the threads and this callback. Thus this callback should free the data. Unless for reasons discussed in Object Lifetime Management, creating a handle and/or callback scope inside the function body is not necessary. ##### `napi_cleanup_hook`# Added in: v19.2.0, v18.13.0 N-API version: 3 Function pointer used with `napi_add_env_cleanup_hook`. It will be called when the environment is being torn down. Callback functions must satisfy the following signature: typedef void (*napi_cleanup_hook)(void* data); * `[in] data`: The data that was passed to `napi_add_env_cleanup_hook`. ##### `napi_async_cleanup_hook`# Added in: v14.10.0, v12.19.0 Function pointer used with `napi_add_async_cleanup_hook`. It will be called when the environment is being torn down. Callback functions must satisfy the following signature: typedef void (*napi_async_cleanup_hook)(napi_async_cleanup_hook_handle handle, void* data); * `[in] handle`: The handle that must be passed to `napi_remove_async_cleanup_hook` after completion of the asynchronous cleanup. * `[in] data`: The data that was passed to `napi_add_async_cleanup_hook`. The body of the function should initiate the asynchronous cleanup actions at the end of which `handle` must be passed in a call to `napi_remove_async_cleanup_hook`. ### Error handling# Node-API uses both return values and JavaScript exceptions for error handling. The following sections explain the approach for each case. #### Return values# All of the Node-API functions share the same error handling pattern. The return type of all API functions is `napi_status`. The return value will be `napi_ok` if the request was successful and no uncaught JavaScript exception was thrown. If an error occurred AND an exception was thrown, the `napi_status` value for the error will be returned. If an exception was thrown, and no error occurred, `napi_pending_exception` will be returned. In cases where a return value other than `napi_ok` or `napi_pending_exception` is returned, `napi_is_exception_pending` must be called to check if an exception is pending. See the section on exceptions for more details. The full set of possible `napi_status` values is defined in `napi_api_types.h`. The `napi_status` return value provides a VM-independent representation of the error which occurred. In some cases it is useful to be able to get more detailed information, including a string representing the error as well as VM (engine)-specific information. In order to retrieve this information `napi_get_last_error_info` is provided which returns a `napi_extended_error_info` structure. The format of the `napi_extended_error_info` structure is as follows: Added in: v8.0.0 N-API version: 1 typedef struct napi_extended_error_info { const char* error_message; void* engine_reserved; uint32_t engine_error_code; napi_status error_code; }; * `error_message`: Textual representation of the error that occurred. * `engine_reserved`: Opaque handle reserved for engine use only. * `engine_error_code`: VM specific error code. * `error_code`: Node-API status code for the last error. `napi_get_last_error_info` returns the information for the last Node-API call that was made. Do not rely on the content or format of any of the extended information as it is not subject to SemVer and may change at any time. It is intended only for logging purposes. ##### `napi_get_last_error_info`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_last_error_info(node_api_basic_env env, const napi_extended_error_info** result); * `[in] env`: The environment that the API is invoked under. * `[out] result`: The `napi_extended_error_info` structure with more information about the error. Returns `napi_ok` if the API succeeded. This API retrieves a `napi_extended_error_info` structure with information about the last error that occurred. The content of the `napi_extended_error_info` returned is only valid up until a Node-API function is called on the same `env`. This includes a call to `napi_is_exception_pending` so it may often be necessary to make a copy of the information so that it can be used later. The pointer returned in `error_message` points to a statically-defined string so it is safe to use that pointer if you have copied it out of the `error_message` field (which will be overwritten) before another Node-API function was called. Do not rely on the content or format of any of the extended information as it is not subject to SemVer and may change at any time. It is intended only for logging purposes. This API can be called even if there is a pending JavaScript exception. #### Exceptions# Any Node-API function call may result in a pending JavaScript exception. This is the case for any of the API functions, even those that may not cause the execution of JavaScript. If the `napi_status` returned by a function is `napi_ok` then no exception is pending and no additional action is required. If the `napi_status` returned is anything other than `napi_ok` or `napi_pending_exception`, in order to try to recover and continue instead of simply returning immediately, `napi_is_exception_pending` must be called in order to determine if an exception is pending or not. In many cases when a Node-API function is called and an exception is already pending, the function will return immediately with a `napi_status` of `napi_pending_exception`. However, this is not the case for all functions. Node-API allows a subset of the functions to be called to allow for some minimal cleanup before returning to JavaScript. In that case, `napi_status` will reflect the status for the function. It will not reflect previous pending exceptions. To avoid confusion, check the error status after every function call. When an exception is pending one of two approaches can be employed. The first approach is to do any appropriate cleanup and then return so that execution will return to JavaScript. As part of the transition back to JavaScript, the exception will be thrown at the point in the JavaScript code where the native method was invoked. The behavior of most Node-API calls is unspecified while an exception is pending, and many will simply return `napi_pending_exception`, so do as little as possible and then return to JavaScript where the exception can be handled. The second approach is to try to handle the exception. There will be cases where the native code can catch the exception, take the appropriate action, and then continue. This is only recommended in specific cases where it is known that the exception can be safely handled. In these cases `napi_get_and_clear_last_exception` can be used to get and clear the exception. On success, result will contain the handle to the last JavaScript `Object` thrown. If it is determined, after retrieving the exception, the exception cannot be handled after all it can be re-thrown it with `napi_throw` where error is the JavaScript value to be thrown. The following utility functions are also available in case native code needs to throw an exception or determine if a `napi_value` is an instance of a JavaScript `Error` object: `napi_throw_error`, `napi_throw_type_error`, `napi_throw_range_error`, `node_api_throw_syntax_error` and `napi_is_error`. The following utility functions are also available in case native code needs to create an `Error` object: `napi_create_error`, `napi_create_type_error`, `napi_create_range_error` and `node_api_create_syntax_error`, where result is the `napi_value` that refers to the newly created JavaScript `Error` object. The Node.js project is adding error codes to all of the errors generated internally. The goal is for applications to use these error codes for all error checking. The associated error messages will remain, but will only be meant to be used for logging and display with the expectation that the message can change without SemVer applying. In order to support this model with Node-API, both in internal functionality and for module specific functionality (as its good practice), the `throw_` and `create_` functions take an optional code parameter which is the string for the code to be added to the error object. If the optional parameter is `NULL` then no code will be associated with the error. If a code is provided, the name associated with the error is also updated to be: originalName [code] where `originalName` is the original name associated with the error and `code` is the code that was provided. For example, if the code is `'ERR_ERROR_1'` and a `TypeError` is being created the name will be: TypeError [ERR_ERROR_1] ##### `napi_throw`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_throw(napi_env env, napi_value error); * `[in] env`: The environment that the API is invoked under. * `[in] error`: The JavaScript value to be thrown. Returns `napi_ok` if the API succeeded. This API throws the JavaScript value provided. ##### `napi_throw_error`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_throw_error(napi_env env, const char* code, const char* msg); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional error code to be set on the error. * `[in] msg`: C string representing the text to be associated with the error. Returns `napi_ok` if the API succeeded. This API throws a JavaScript `Error` with the text provided. ##### `napi_throw_type_error`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_throw_type_error(napi_env env, const char* code, const char* msg); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional error code to be set on the error. * `[in] msg`: C string representing the text to be associated with the error. Returns `napi_ok` if the API succeeded. This API throws a JavaScript `TypeError` with the text provided. ##### `napi_throw_range_error`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_throw_range_error(napi_env env, const char* code, const char* msg); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional error code to be set on the error. * `[in] msg`: C string representing the text to be associated with the error. Returns `napi_ok` if the API succeeded. This API throws a JavaScript `RangeError` with the text provided. ##### `node_api_throw_syntax_error`# Added in: v17.2.0, v16.14.0 N-API version: 9 NAPI_EXTERN napi_status node_api_throw_syntax_error(napi_env env, const char* code, const char* msg); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional error code to be set on the error. * `[in] msg`: C string representing the text to be associated with the error. Returns `napi_ok` if the API succeeded. This API throws a JavaScript `SyntaxError` with the text provided. ##### `napi_is_error`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_is_error(napi_env env, napi_value value, bool* result); * `[in] env`: The environment that the API is invoked under. * `[in] value`: The `napi_value` to be checked. * `[out] result`: Boolean value that is set to true if `napi_value` represents an error, false otherwise. Returns `napi_ok` if the API succeeded. This API queries a `napi_value` to check if it represents an error object. ##### `napi_create_error`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_create_error(napi_env env, napi_value code, napi_value msg, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error. * `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`. * `[out] result`: `napi_value` representing the error created. Returns `napi_ok` if the API succeeded. This API returns a JavaScript `Error` with the text provided. ##### `napi_create_type_error`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_create_type_error(napi_env env, napi_value code, napi_value msg, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error. * `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`. * `[out] result`: `napi_value` representing the error created. Returns `napi_ok` if the API succeeded. This API returns a JavaScript `TypeError` with the text provided. ##### `napi_create_range_error`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_create_range_error(napi_env env, napi_value code, napi_value msg, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error. * `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`. * `[out] result`: `napi_value` representing the error created. Returns `napi_ok` if the API succeeded. This API returns a JavaScript `RangeError` with the text provided. ##### `node_api_create_syntax_error`# Added in: v17.2.0, v16.14.0 N-API version: 9 NAPI_EXTERN napi_status node_api_create_syntax_error(napi_env env, napi_value code, napi_value msg, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] code`: Optional `napi_value` with the string for the error code to be associated with the error. * `[in] msg`: `napi_value` that references a JavaScript `string` to be used as the message for the `Error`. * `[out] result`: `napi_value` representing the error created. Returns `napi_ok` if the API succeeded. This API returns a JavaScript `SyntaxError` with the text provided. ##### `napi_get_and_clear_last_exception`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_and_clear_last_exception(napi_env env, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[out] result`: The exception if one is pending, `NULL` otherwise. Returns `napi_ok` if the API succeeded. This API can be called even if there is a pending JavaScript exception. ##### `napi_is_exception_pending`# Added in: v8.0.0 N-API version: 1 napi_status napi_is_exception_pending(napi_env env, bool* result); * `[in] env`: The environment that the API is invoked under. * `[out] result`: Boolean value that is set to true if an exception is pending. Returns `napi_ok` if the API succeeded. This API can be called even if there is a pending JavaScript exception. ##### `napi_fatal_exception`# Added in: v9.10.0 N-API version: 3 napi_status napi_fatal_exception(napi_env env, napi_value err); * `[in] env`: The environment that the API is invoked under. * `[in] err`: The error that is passed to `'uncaughtException'`. Trigger an `'uncaughtException'` in JavaScript. Useful if an async callback throws an exception with no way to recover. #### Fatal errors# In the event of an unrecoverable error in a native addon, a fatal error can be thrown to immediately terminate the process. ##### `napi_fatal_error`# Added in: v8.2.0 N-API version: 1 NAPI_NO_RETURN void napi_fatal_error(const char* location, size_t location_len, const char* message, size_t message_len); * `[in] location`: Optional location at which the error occurred. * `[in] location_len`: The length of the location in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[in] message`: The message associated with the error. * `[in] message_len`: The length of the message in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. The function call does not return, the process will be terminated. This API can be called even if there is a pending JavaScript exception. ### Object lifetime management# As Node-API calls are made, handles to objects in the heap for the underlying VM may be returned as `napi_values`. These handles must hold the objects 'live' until they are no longer required by the native code, otherwise the objects could be collected before the native code was finished using them. As object handles are returned they are associated with a 'scope'. The lifespan for the default scope is tied to the lifespan of the native method call. The result is that, by default, handles remain valid and the objects associated with these handles will be held live for the lifespan of the native method call. In many cases, however, it is necessary that the handles remain valid for either a shorter or longer lifespan than that of the native method. The sections which follow describe the Node-API functions that can be used to change the handle lifespan from the default. #### Making handle lifespan shorter than that of the native method# It is often necessary to make the lifespan of handles shorter than the lifespan of a native method. For example, consider a native method that has a loop which iterates through the elements in a large array: for (int i = 0; i < 1000000; i++) { napi_value result; napi_status status = napi_get_element(env, object, i, &result); if (status != napi_ok) { break; } // do something with element } This would result in a large number of handles being created, consuming substantial resources. In addition, even though the native code could only use the most recent handle, all of the associated objects would also be kept alive since they all share the same scope. To handle this case, Node-API provides the ability to establish a new 'scope' to which newly created handles will be associated. Once those handles are no longer required, the scope can be 'closed' and any handles associated with the scope are invalidated. The methods available to open/close scopes are `napi_open_handle_scope` and `napi_close_handle_scope`. Node-API only supports a single nested hierarchy of scopes. There is only one active scope at any time, and all new handles will be associated with that scope while it is active. Scopes must be closed in the reverse order from which they are opened. In addition, all scopes created within a native method must be closed before returning from that method. Taking the earlier example, adding calls to `napi_open_handle_scope` and `napi_close_handle_scope` would ensure that at most a single handle is valid throughout the execution of the loop: for (int i = 0; i < 1000000; i++) { napi_handle_scope scope; napi_status status = napi_open_handle_scope(env, &scope); if (status != napi_ok) { break; } napi_value result; status = napi_get_element(env, object, i, &result); if (status != napi_ok) { break; } // do something with element status = napi_close_handle_scope(env, scope); if (status != napi_ok) { break; } } When nesting scopes, there are cases where a handle from an inner scope needs to live beyond the lifespan of that scope. Node-API supports an 'escapable scope' in order to support this case. An escapable scope allows one handle to be 'promoted' so that it 'escapes' the current scope and the lifespan of the handle changes from the current scope to that of the outer scope. The methods available to open/close escapable scopes are `napi_open_escapable_handle_scope` and `napi_close_escapable_handle_scope`. The request to promote a handle is made through `napi_escape_handle` which can only be called once. ##### `napi_open_handle_scope`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_open_handle_scope(napi_env env, napi_handle_scope* result); * `[in] env`: The environment that the API is invoked under. * `[out] result`: `napi_value` representing the new scope. Returns `napi_ok` if the API succeeded. This API opens a new scope. ##### `napi_close_handle_scope`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_close_handle_scope(napi_env env, napi_handle_scope scope); * `[in] env`: The environment that the API is invoked under. * `[in] scope`: `napi_value` representing the scope to be closed. Returns `napi_ok` if the API succeeded. This API closes the scope passed in. Scopes must be closed in the reverse order from which they were created. This API can be called even if there is a pending JavaScript exception. ##### `napi_open_escapable_handle_scope`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_open_escapable_handle_scope(napi_env env, napi_handle_scope* result); * `[in] env`: The environment that the API is invoked under. * `[out] result`: `napi_value` representing the new scope. Returns `napi_ok` if the API succeeded. This API opens a new scope from which one object can be promoted to the outer scope. ##### `napi_close_escapable_handle_scope`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_close_escapable_handle_scope(napi_env env, napi_handle_scope scope); * `[in] env`: The environment that the API is invoked under. * `[in] scope`: `napi_value` representing the scope to be closed. Returns `napi_ok` if the API succeeded. This API closes the scope passed in. Scopes must be closed in the reverse order from which they were created. This API can be called even if there is a pending JavaScript exception. ##### `napi_escape_handle`# Added in: v8.0.0 N-API version: 1 napi_status napi_escape_handle(napi_env env, napi_escapable_handle_scope scope, napi_value escapee, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] scope`: `napi_value` representing the current scope. * `[in] escapee`: `napi_value` representing the JavaScript `Object` to be escaped. * `[out] result`: `napi_value` representing the handle to the escaped `Object` in the outer scope. Returns `napi_ok` if the API succeeded. This API promotes the handle to the JavaScript object so that it is valid for the lifetime of the outer scope. It can only be called once per scope. If it is called more than once an error will be returned. This API can be called even if there is a pending JavaScript exception. #### References to values with a lifespan longer than that of the native method# In some cases, an addon will need to be able to create and reference values with a lifespan longer than that of a single native method invocation. For example, to create a constructor and later use that constructor in a request to create instances, it must be possible to reference the constructor object across many different instance creation requests. This would not be possible with a normal handle returned as a `napi_value` as described in the earlier section. The lifespan of a normal handle is managed by scopes and all scopes must be closed before the end of a native method. Node-API provides methods for creating persistent references to values. Currently Node-API only allows references to be created for a limited set of value types, including object, external, function, and symbol. Each reference has an associated count with a value of 0 or higher, which determines whether the reference will keep the corresponding value alive. References with a count of 0 do not prevent values from being collected. Values of object (object, function, external) and symbol types are becoming 'weak' references and can still be accessed while they are not collected. Any count greater than 0 will prevent the values from being collected. Symbol values have different flavors. The true weak reference behavior is only supported by local symbols created with the `napi_create_symbol` function or the JavaScript `Symbol()` constructor calls. Globally registered symbols created with the `node_api_symbol_for` function or JavaScript `Symbol.for()` function calls remain always strong references because the garbage collector does not collect them. The same is true for well-known symbols such as `Symbol.iterator`. They are also never collected by the garbage collector. References can be created with an initial reference count. The count can then be modified through `napi_reference_ref` and `napi_reference_unref`. If an object is collected while the count for a reference is 0, all subsequent calls to get the object associated with the reference `napi_get_reference_value` will return `NULL` for the returned `napi_value`. An attempt to call `napi_reference_ref` for a reference whose object has been collected results in an error. References must be deleted once they are no longer required by the addon. When a reference is deleted, it will no longer prevent the corresponding object from being collected. Failure to delete a persistent reference results in a 'memory leak' with both the native memory for the persistent reference and the corresponding object on the heap being retained forever. There can be multiple persistent references created which refer to the same object, each of which will either keep the object live or not based on its individual count. Multiple persistent references to the same object can result in unexpectedly keeping alive native memory. The native structures for a persistent reference must be kept alive until finalizers for the referenced object are executed. If a new persistent reference is created for the same object, the finalizers for that object will not be run and the native memory pointed by the earlier persistent reference will not be freed. This can be avoided by calling `napi_delete_reference` in addition to `napi_reference_unref` when possible. Change History: * Version 10 (`NAPI_VERSION` is defined as `10` or higher): References can be created for all value types. The new supported value types do not support weak reference semantic and the values of these types are released when the reference count becomes 0 and cannot be accessed from the reference anymore. ##### `napi_create_reference`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_create_reference(napi_env env, napi_value value, uint32_t initial_refcount, napi_ref* result); * `[in] env`: The environment that the API is invoked under. * `[in] value`: The `napi_value` for which a reference is being created. * `[in] initial_refcount`: Initial reference count for the new reference. * `[out] result`: `napi_ref` pointing to the new reference. Returns `napi_ok` if the API succeeded. This API creates a new reference with the specified reference count to the value passed in. ##### `napi_delete_reference`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_delete_reference(napi_env env, napi_ref ref); * `[in] env`: The environment that the API is invoked under. * `[in] ref`: `napi_ref` to be deleted. Returns `napi_ok` if the API succeeded. This API deletes the reference passed in. This API can be called even if there is a pending JavaScript exception. ##### `napi_reference_ref`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_reference_ref(napi_env env, napi_ref ref, uint32_t* result); * `[in] env`: The environment that the API is invoked under. * `[in] ref`: `napi_ref` for which the reference count will be incremented. * `[out] result`: The new reference count. Returns `napi_ok` if the API succeeded. This API increments the reference count for the reference passed in and returns the resulting reference count. ##### `napi_reference_unref`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_reference_unref(napi_env env, napi_ref ref, uint32_t* result); * `[in] env`: The environment that the API is invoked under. * `[in] ref`: `napi_ref` for which the reference count will be decremented. * `[out] result`: The new reference count. Returns `napi_ok` if the API succeeded. This API decrements the reference count for the reference passed in and returns the resulting reference count. ##### `napi_get_reference_value`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_get_reference_value(napi_env env, napi_ref ref, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] ref`: The `napi_ref` for which the corresponding value is being requested. * `[out] result`: The `napi_value` referenced by the `napi_ref`. Returns `napi_ok` if the API succeeded. If still valid, this API returns the `napi_value` representing the JavaScript value associated with the `napi_ref`. Otherwise, result will be `NULL`. #### Cleanup on exit of the current Node.js environment# While a Node.js process typically releases all its resources when exiting, embedders of Node.js, or future Worker support, may require addons to register clean-up hooks that will be run once the current Node.js environment exits. Node-API provides functions for registering and un-registering such callbacks. When those callbacks are run, all resources that are being held by the addon should be freed up. ##### `napi_add_env_cleanup_hook`# Added in: v10.2.0 N-API version: 3 NODE_EXTERN napi_status napi_add_env_cleanup_hook(node_api_basic_env env, napi_cleanup_hook fun, void* arg); Registers `fun` as a function to be run with the `arg` parameter once the current Node.js environment exits. A function can safely be specified multiple times with different `arg` values. In that case, it will be called multiple times as well. Providing the same `fun` and `arg` values multiple times is not allowed and will lead the process to abort. The hooks will be called in reverse order, i.e. the most recently added one will be called first. Removing this hook can be done by using `napi_remove_env_cleanup_hook`. Typically, that happens when the resource for which this hook was added is being torn down anyway. For asynchronous cleanup, `napi_add_async_cleanup_hook` is available. ##### `napi_remove_env_cleanup_hook`# Added in: v10.2.0 N-API version: 3 NAPI_EXTERN napi_status napi_remove_env_cleanup_hook(node_api_basic_env env, void (*fun)(void* arg), void* arg); Unregisters `fun` as a function to be run with the `arg` parameter once the current Node.js environment exits. Both the argument and the function value need to be exact matches. The function must have originally been registered with `napi_add_env_cleanup_hook`, otherwise the process will abort. ##### `napi_add_async_cleanup_hook`# History VersionChanges v14.10.0, v12.19.0 Changed signature of the `hook` callback. v14.8.0, v12.19.0 Added in: v14.8.0, v12.19.0 N-API version: 8 NAPI_EXTERN napi_status napi_add_async_cleanup_hook( node_api_basic_env env, napi_async_cleanup_hook hook, void* arg, napi_async_cleanup_hook_handle* remove_handle); * `[in] env`: The environment that the API is invoked under. * `[in] hook`: The function pointer to call at environment teardown. * `[in] arg`: The pointer to pass to `hook` when it gets called. * `[out] remove_handle`: Optional handle that refers to the asynchronous cleanup hook. Registers `hook`, which is a function of type `napi_async_cleanup_hook`, as a function to be run with the `remove_handle` and `arg` parameters once the current Node.js environment exits. Unlike `napi_add_env_cleanup_hook`, the hook is allowed to be asynchronous. Otherwise, behavior generally matches that of `napi_add_env_cleanup_hook`. If `remove_handle` is not `NULL`, an opaque value will be stored in it that must later be passed to `napi_remove_async_cleanup_hook`, regardless of whether the hook has already been invoked. Typically, that happens when the resource for which this hook was added is being torn down anyway. ##### `napi_remove_async_cleanup_hook`# History VersionChanges v14.10.0, v12.19.0 Removed `env` parameter. v14.8.0, v12.19.0 Added in: v14.8.0, v12.19.0 NAPI_EXTERN napi_status napi_remove_async_cleanup_hook( napi_async_cleanup_hook_handle remove_handle); * `[in] remove_handle`: The handle to an asynchronous cleanup hook that was created with `napi_add_async_cleanup_hook`. Unregisters the cleanup hook corresponding to `remove_handle`. This will prevent the hook from being executed, unless it has already started executing. This must be called on any `napi_async_cleanup_hook_handle` value obtained from `napi_add_async_cleanup_hook`. #### Finalization on the exit of the Node.js environment# The Node.js environment may be torn down at an arbitrary time as soon as possible with JavaScript execution disallowed, like on the request of `worker.terminate()`. When the environment is being torn down, the registered `napi_finalize` callbacks of JavaScript objects, thread-safe functions and environment instance data are invoked immediately and independently. The invocation of `napi_finalize` callbacks is scheduled after the manually registered cleanup hooks. In order to ensure a proper order of addon finalization during environment shutdown to avoid use-after-free in the `napi_finalize` callback, addons should register a cleanup hook with `napi_add_env_cleanup_hook` and `napi_add_async_cleanup_hook` to manually release the allocated resource in a proper order. ### Module registration# Node-API modules are registered in a manner similar to other modules except that instead of using the `NODE_MODULE` macro the following is used: NAPI_MODULE(NODE_GYP_MODULE_NAME, Init) The next difference is the signature for the `Init` method. For a Node-API module it is as follows: napi_value Init(napi_env env, napi_value exports); The return value from `Init` is treated as the `exports` object for the module. The `Init` method is passed an empty object via the `exports` parameter as a convenience. If `Init` returns `NULL`, the parameter passed as `exports` is exported by the module. Node-API modules cannot modify the `module` object but can specify anything as the `exports` property of the module. To add the method `hello` as a function so that it can be called as a method provided by the addon: napi_value Init(napi_env env, napi_value exports) { napi_status status; napi_property_descriptor desc = { "hello", NULL, Method, NULL, NULL, NULL, napi_writable | napi_enumerable | napi_configurable, NULL }; status = napi_define_properties(env, exports, 1, &desc); if (status != napi_ok) return NULL; return exports; } To set a function to be returned by the `require()` for the addon: napi_value Init(napi_env env, napi_value exports) { napi_value method; napi_status status; status = napi_create_function(env, "exports", NAPI_AUTO_LENGTH, Method, NULL, &method); if (status != napi_ok) return NULL; return method; } To define a class so that new instances can be created (often used with Object wrap): // NOTE: partial example, not all referenced code is included napi_value Init(napi_env env, napi_value exports) { napi_status status; napi_property_descriptor properties[] = { { "value", NULL, NULL, GetValue, SetValue, NULL, napi_writable | napi_configurable, NULL }, DECLARE_NAPI_METHOD("plusOne", PlusOne), DECLARE_NAPI_METHOD("multiply", Multiply), }; napi_value cons; status = napi_define_class(env, "MyObject", New, NULL, 3, properties, &cons); if (status != napi_ok) return NULL; status = napi_create_reference(env, cons, 1, &constructor); if (status != napi_ok) return NULL; status = napi_set_named_property(env, exports, "MyObject", cons); if (status != napi_ok) return NULL; return exports; } You can also use the `NAPI_MODULE_INIT` macro, which acts as a shorthand for `NAPI_MODULE` and defining an `Init` function: NAPI_MODULE_INIT(/* napi_env env, napi_value exports */) { napi_value answer; napi_status result; status = napi_create_int64(env, 42, &answer); if (status != napi_ok) return NULL; status = napi_set_named_property(env, exports, "answer", answer); if (status != napi_ok) return NULL; return exports; } The parameters `env` and `exports` are provided to the body of the `NAPI_MODULE_INIT` macro. All Node-API addons are context-aware, meaning they may be loaded multiple times. There are a few design considerations when declaring such a module. The documentation on context-aware addons provides more details. The variables `env` and `exports` will be available inside the function body following the macro invocation. For more details on setting properties on objects, see the section on Working with JavaScript properties. For more details on building addon modules in general, refer to the existing API. ### Working with JavaScript values# Node-API exposes a set of APIs to create all types of JavaScript values. Some of these types are documented under Section language types of the ECMAScript Language Specification. Fundamentally, these APIs are used to do one of the following: 1. Create a new JavaScript object 2. Convert from a primitive C type to a Node-API value 3. Convert from Node-API value to a primitive C type 4. Get global instances including `undefined` and `null` Node-API values are represented by the type `napi_value`. Any Node-API call that requires a JavaScript value takes in a `napi_value`. In some cases, the API does check the type of the `napi_value` up-front. However, for better performance, it's better for the caller to make sure that the `napi_value` in question is of the JavaScript type expected by the API. #### Enum types# ##### `napi_key_collection_mode`# Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6 typedef enum { napi_key_include_prototypes, napi_key_own_only } napi_key_collection_mode; Describes the `Keys/Properties` filter enums: `napi_key_collection_mode` limits the range of collected properties. `napi_key_own_only` limits the collected properties to the given object only. `napi_key_include_prototypes` will include all keys of the objects's prototype chain as well. ##### `napi_key_filter`# Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6 typedef enum { napi_key_all_properties = 0, napi_key_writable = 1, napi_key_enumerable = 1 << 1, napi_key_configurable = 1 << 2, napi_key_skip_strings = 1 << 3, napi_key_skip_symbols = 1 << 4 } napi_key_filter; Property filter bit flag. This works with bit operators to build a composite filter. ##### `napi_key_conversion`# Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6 typedef enum { napi_key_keep_numbers, napi_key_numbers_to_strings } napi_key_conversion; `napi_key_numbers_to_strings` will convert integer indexes to strings. `napi_key_keep_numbers` will return numbers for integer indexes. ##### `napi_valuetype`# typedef enum { // ES6 types (corresponds to typeof) napi_undefined, napi_null, napi_boolean, napi_number, napi_string, napi_symbol, napi_object, napi_function, napi_external, napi_bigint, } napi_valuetype; Describes the type of a `napi_value`. This generally corresponds to the types described in Section language types of the ECMAScript Language Specification. In addition to types in that section, `napi_valuetype` can also represent `Function`s and `Object`s with external data. A JavaScript value of type `napi_external` appears in JavaScript as a plain object such that no properties can be set on it, and no prototype. ##### `napi_typedarray_type`# typedef enum { napi_int8_array, napi_uint8_array, napi_uint8_clamped_array, napi_int16_array, napi_uint16_array, napi_int32_array, napi_uint32_array, napi_float32_array, napi_float64_array, napi_bigint64_array, napi_biguint64_array, } napi_typedarray_type; This represents the underlying binary scalar datatype of the `TypedArray`. Elements of this enum correspond to Section TypedArray objects of the ECMAScript Language Specification. #### Object creation functions# ##### `napi_create_array`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_array(napi_env env, napi_value* result) * `[in] env`: The environment that the Node-API call is invoked under. * `[out] result`: A `napi_value` representing a JavaScript `Array`. Returns `napi_ok` if the API succeeded. This API returns a Node-API value corresponding to a JavaScript `Array` type. JavaScript arrays are described in Section Array objects of the ECMAScript Language Specification. ##### `napi_create_array_with_length`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_array_with_length(napi_env env, size_t length, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] length`: The initial length of the `Array`. * `[out] result`: A `napi_value` representing a JavaScript `Array`. Returns `napi_ok` if the API succeeded. This API returns a Node-API value corresponding to a JavaScript `Array` type. The `Array`'s length property is set to the passed-in length parameter. However, the underlying buffer is not guaranteed to be pre-allocated by the VM when the array is created. That behavior is left to the underlying VM implementation. If the buffer must be a contiguous block of memory that can be directly read and/or written via C, consider using `napi_create_external_arraybuffer`. JavaScript arrays are described in Section Array objects of the ECMAScript Language Specification. ##### `napi_create_arraybuffer`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_arraybuffer(napi_env env, size_t byte_length, void** data, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] length`: The length in bytes of the array buffer to create. * `[out] data`: Pointer to the underlying byte buffer of the `ArrayBuffer`. `data` can optionally be ignored by passing `NULL`. * `[out] result`: A `napi_value` representing a JavaScript `ArrayBuffer`. Returns `napi_ok` if the API succeeded. This API returns a Node-API value corresponding to a JavaScript `ArrayBuffer`. `ArrayBuffer`s are used to represent fixed-length binary data buffers. They are normally used as a backing-buffer for `TypedArray` objects. The `ArrayBuffer` allocated will have an underlying byte buffer whose size is determined by the `length` parameter that's passed in. The underlying buffer is optionally returned back to the caller in case the caller wants to directly manipulate the buffer. This buffer can only be written to directly from native code. To write to this buffer from JavaScript, a typed array or `DataView` object would need to be created. JavaScript `ArrayBuffer` objects are described in Section ArrayBuffer objects of the ECMAScript Language Specification. ##### `napi_create_buffer`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_buffer(napi_env env, size_t size, void** data, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] size`: Size in bytes of the underlying buffer. * `[out] data`: Raw pointer to the underlying buffer. `data` can optionally be ignored by passing `NULL`. * `[out] result`: A `napi_value` representing a `node::Buffer`. Returns `napi_ok` if the API succeeded. This API allocates a `node::Buffer` object. While this is still a fully-supported data structure, in most cases using a `TypedArray` will suffice. ##### `napi_create_buffer_copy`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_buffer_copy(napi_env env, size_t length, const void* data, void** result_data, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] size`: Size in bytes of the input buffer (should be the same as the size of the new buffer). * `[in] data`: Raw pointer to the underlying buffer to copy from. * `[out] result_data`: Pointer to the new `Buffer`'s underlying data buffer. `result_data` can optionally be ignored by passing `NULL`. * `[out] result`: A `napi_value` representing a `node::Buffer`. Returns `napi_ok` if the API succeeded. This API allocates a `node::Buffer` object and initializes it with data copied from the passed-in buffer. While this is still a fully-supported data structure, in most cases using a `TypedArray` will suffice. ##### `napi_create_date`# Added in: v11.11.0, v10.17.0 N-API version: 5 napi_status napi_create_date(napi_env env, double time, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] time`: ECMAScript time value in milliseconds since 01 January, 1970 UTC. * `[out] result`: A `napi_value` representing a JavaScript `Date`. Returns `napi_ok` if the API succeeded. This API does not observe leap seconds; they are ignored, as ECMAScript aligns with POSIX time specification. This API allocates a JavaScript `Date` object. JavaScript `Date` objects are described in Section Date objects of the ECMAScript Language Specification. ##### `napi_create_external`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_external(napi_env env, void* data, napi_finalize finalize_cb, void* finalize_hint, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] data`: Raw pointer to the external data. * `[in] finalize_cb`: Optional callback to call when the external value is being collected. `napi_finalize` provides more details. * `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection. * `[out] result`: A `napi_value` representing an external value. Returns `napi_ok` if the API succeeded. This API allocates a JavaScript value with external data attached to it. This is used to pass external data through JavaScript code, so it can be retrieved later by native code using `napi_get_value_external`. The API adds a `napi_finalize` callback which will be called when the JavaScript object just created has been garbage collected. The created value is not an object, and therefore does not support additional properties. It is considered a distinct value type: calling `napi_typeof()` with an external value yields `napi_external`. ##### `napi_create_external_arraybuffer`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_external_arraybuffer(napi_env env, void* external_data, size_t byte_length, napi_finalize finalize_cb, void* finalize_hint, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] external_data`: Pointer to the underlying byte buffer of the `ArrayBuffer`. * `[in] byte_length`: The length in bytes of the underlying buffer. * `[in] finalize_cb`: Optional callback to call when the `ArrayBuffer` is being collected. `napi_finalize` provides more details. * `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection. * `[out] result`: A `napi_value` representing a JavaScript `ArrayBuffer`. Returns `napi_ok` if the API succeeded. Some runtimes other than Node.js have dropped support for external buffers. On runtimes other than Node.js this method may return `napi_no_external_buffers_allowed` to indicate that external buffers are not supported. One such runtime is Electron as described in this issue electron/issues/35801. In order to maintain broadest compatibility with all runtimes you may define `NODE_API_NO_EXTERNAL_BUFFERS_ALLOWED` in your addon before includes for the node-api headers. Doing so will hide the 2 functions that create external buffers. This will ensure a compilation error occurs if you accidentally use one of these methods. This API returns a Node-API value corresponding to a JavaScript `ArrayBuffer`. The underlying byte buffer of the `ArrayBuffer` is externally allocated and managed. The caller must ensure that the byte buffer remains valid until the finalize callback is called. The API adds a `napi_finalize` callback which will be called when the JavaScript object just created has been garbage collected. JavaScript `ArrayBuffer`s are described in Section ArrayBuffer objects of the ECMAScript Language Specification. ##### `napi_create_external_buffer`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_external_buffer(napi_env env, size_t length, void* data, napi_finalize finalize_cb, void* finalize_hint, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] length`: Size in bytes of the input buffer (should be the same as the size of the new buffer). * `[in] data`: Raw pointer to the underlying buffer to expose to JavaScript. * `[in] finalize_cb`: Optional callback to call when the `ArrayBuffer` is being collected. `napi_finalize` provides more details. * `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection. * `[out] result`: A `napi_value` representing a `node::Buffer`. Returns `napi_ok` if the API succeeded. Some runtimes other than Node.js have dropped support for external buffers. On runtimes other than Node.js this method may return `napi_no_external_buffers_allowed` to indicate that external buffers are not supported. One such runtime is Electron as described in this issue electron/issues/35801. In order to maintain broadest compatibility with all runtimes you may define `NODE_API_NO_EXTERNAL_BUFFERS_ALLOWED` in your addon before includes for the node-api headers. Doing so will hide the 2 functions that create external buffers. This will ensure a compilation error occurs if you accidentally use one of these methods. This API allocates a `node::Buffer` object and initializes it with data backed by the passed in buffer. While this is still a fully-supported data structure, in most cases using a `TypedArray` will suffice. The API adds a `napi_finalize` callback which will be called when the JavaScript object just created has been garbage collected. For Node.js >=4 `Buffers` are `Uint8Array`s. ##### `napi_create_object`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_object(napi_env env, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[out] result`: A `napi_value` representing a JavaScript `Object`. Returns `napi_ok` if the API succeeded. This API allocates a default JavaScript `Object`. It is the equivalent of doing `new Object()` in JavaScript. The JavaScript `Object` type is described in Section object type of the ECMAScript Language Specification. ##### `napi_create_symbol`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_symbol(napi_env env, napi_value description, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] description`: Optional `napi_value` which refers to a JavaScript `string` to be set as the description for the symbol. * `[out] result`: A `napi_value` representing a JavaScript `symbol`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `symbol` value from a UTF8-encoded C string. The JavaScript `symbol` type is described in Section symbol type of the ECMAScript Language Specification. ##### `node_api_symbol_for`# Added in: v17.5.0, v16.15.0 N-API version: 9 napi_status node_api_symbol_for(napi_env env, const char* utf8description, size_t length, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] utf8description`: UTF-8 C string representing the text to be used as the description for the symbol. * `[in] length`: The length of the description string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[out] result`: A `napi_value` representing a JavaScript `symbol`. Returns `napi_ok` if the API succeeded. This API searches in the global registry for an existing symbol with the given description. If the symbol already exists it will be returned, otherwise a new symbol will be created in the registry. The JavaScript `symbol` type is described in Section symbol type of the ECMAScript Language Specification. ##### `napi_create_typedarray`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_typedarray(napi_env env, napi_typedarray_type type, size_t length, napi_value arraybuffer, size_t byte_offset, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] type`: Scalar datatype of the elements within the `TypedArray`. * `[in] length`: Number of elements in the `TypedArray`. * `[in] arraybuffer`: `ArrayBuffer` underlying the typed array. * `[in] byte_offset`: The byte offset within the `ArrayBuffer` from which to start projecting the `TypedArray`. * `[out] result`: A `napi_value` representing a JavaScript `TypedArray`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `TypedArray` object over an existing `ArrayBuffer`. `TypedArray` objects provide an array-like view over an underlying data buffer where each element has the same underlying binary scalar datatype. It's required that `(length * size_of_element) + byte_offset` should be <= the size in bytes of the array passed in. If not, a `RangeError` exception is raised. JavaScript `TypedArray` objects are described in Section TypedArray objects of the ECMAScript Language Specification. ##### `node_api_create_buffer_from_arraybuffer`# Added in: v23.0.0, v22.12.0 N-API version: 10 napi_status NAPI_CDECL node_api_create_buffer_from_arraybuffer(napi_env env, napi_value arraybuffer, size_t byte_offset, size_t byte_length, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] arraybuffer`: The `ArrayBuffer` from which the buffer will be created. * `[in] byte_offset`: The byte offset within the `ArrayBuffer` from which to start creating the buffer. * `[in] byte_length`: The length in bytes of the buffer to be created from the `ArrayBuffer`. * `[out] result`: A `napi_value` representing the created JavaScript `Buffer` object. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `Buffer` object from an existing `ArrayBuffer`. The `Buffer` object is a Node.js-specific class that provides a way to work with binary data directly in JavaScript. The byte range `[byte_offset, byte_offset + byte_length)` must be within the bounds of the `ArrayBuffer`. If `byte_offset + byte_length` exceeds the size of the `ArrayBuffer`, a `RangeError` exception is raised. ##### `napi_create_dataview`# Added in: v8.3.0 N-API version: 1 napi_status napi_create_dataview(napi_env env, size_t byte_length, napi_value arraybuffer, size_t byte_offset, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] length`: Number of elements in the `DataView`. * `[in] arraybuffer`: `ArrayBuffer` underlying the `DataView`. * `[in] byte_offset`: The byte offset within the `ArrayBuffer` from which to start projecting the `DataView`. * `[out] result`: A `napi_value` representing a JavaScript `DataView`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `DataView` object over an existing `ArrayBuffer`. `DataView` objects provide an array-like view over an underlying data buffer, but one which allows items of different size and type in the `ArrayBuffer`. It is required that `byte_length + byte_offset` is less than or equal to the size in bytes of the array passed in. If not, a `RangeError` exception is raised. JavaScript `DataView` objects are described in Section DataView objects of the ECMAScript Language Specification. #### Functions to convert from C types to Node-API# ##### `napi_create_int32`# Added in: v8.4.0 N-API version: 1 napi_status napi_create_int32(napi_env env, int32_t value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: Integer value to be represented in JavaScript. * `[out] result`: A `napi_value` representing a JavaScript `number`. Returns `napi_ok` if the API succeeded. This API is used to convert from the C `int32_t` type to the JavaScript `number` type. The JavaScript `number` type is described in Section number type of the ECMAScript Language Specification. ##### `napi_create_uint32`# Added in: v8.4.0 N-API version: 1 napi_status napi_create_uint32(napi_env env, uint32_t value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: Unsigned integer value to be represented in JavaScript. * `[out] result`: A `napi_value` representing a JavaScript `number`. Returns `napi_ok` if the API succeeded. This API is used to convert from the C `uint32_t` type to the JavaScript `number` type. The JavaScript `number` type is described in Section number type of the ECMAScript Language Specification. ##### `napi_create_int64`# Added in: v8.4.0 N-API version: 1 napi_status napi_create_int64(napi_env env, int64_t value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: Integer value to be represented in JavaScript. * `[out] result`: A `napi_value` representing a JavaScript `number`. Returns `napi_ok` if the API succeeded. This API is used to convert from the C `int64_t` type to the JavaScript `number` type. The JavaScript `number` type is described in Section number type of the ECMAScript Language Specification. Note the complete range of `int64_t` cannot be represented with full precision in JavaScript. Integer values outside the range of `Number.MIN_SAFE_INTEGER` `-(2**53 - 1)` \- `Number.MAX_SAFE_INTEGER` `(2**53 - 1)` will lose precision. ##### `napi_create_double`# Added in: v8.4.0 N-API version: 1 napi_status napi_create_double(napi_env env, double value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: Double-precision value to be represented in JavaScript. * `[out] result`: A `napi_value` representing a JavaScript `number`. Returns `napi_ok` if the API succeeded. This API is used to convert from the C `double` type to the JavaScript `number` type. The JavaScript `number` type is described in Section number type of the ECMAScript Language Specification. ##### `napi_create_bigint_int64`# Added in: v10.7.0 N-API version: 6 napi_status napi_create_bigint_int64(napi_env env, int64_t value, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] value`: Integer value to be represented in JavaScript. * `[out] result`: A `napi_value` representing a JavaScript `BigInt`. Returns `napi_ok` if the API succeeded. This API converts the C `int64_t` type to the JavaScript `BigInt` type. ##### `napi_create_bigint_uint64`# Added in: v10.7.0 N-API version: 6 napi_status napi_create_bigint_uint64(napi_env env, uint64_t value, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] value`: Unsigned integer value to be represented in JavaScript. * `[out] result`: A `napi_value` representing a JavaScript `BigInt`. Returns `napi_ok` if the API succeeded. This API converts the C `uint64_t` type to the JavaScript `BigInt` type. ##### `napi_create_bigint_words`# Added in: v10.7.0 N-API version: 6 napi_status napi_create_bigint_words(napi_env env, int sign_bit, size_t word_count, const uint64_t* words, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] sign_bit`: Determines if the resulting `BigInt` will be positive or negative. * `[in] word_count`: The length of the `words` array. * `[in] words`: An array of `uint64_t` little-endian 64-bit words. * `[out] result`: A `napi_value` representing a JavaScript `BigInt`. Returns `napi_ok` if the API succeeded. This API converts an array of unsigned 64-bit words into a single `BigInt` value. The resulting `BigInt` is calculated as: (–1)`sign_bit` (`words[0]` × (264)0 \+ `words[1]` × (264)1 \+ …) ##### `napi_create_string_latin1`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_string_latin1(napi_env env, const char* str, size_t length, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing an ISO-8859-1-encoded string. * `[in] length`: The length of the string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[out] result`: A `napi_value` representing a JavaScript `string`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `string` value from an ISO-8859-1-encoded C string. The native string is copied. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. ##### `node_api_create_external_string_latin1`# Added in: v20.4.0, v18.18.0 N-API version: 10 napi_status node_api_create_external_string_latin1(napi_env env, char* str, size_t length, napi_finalize finalize_callback, void* finalize_hint, napi_value* result, bool* copied); * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing an ISO-8859-1-encoded string. * `[in] length`: The length of the string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[in] finalize_callback`: The function to call when the string is being collected. The function will be called with the following parameters: * `[in] env`: The environment in which the add-on is running. This value may be null if the string is being collected as part of the termination of the worker or the main Node.js instance. * `[in] data`: This is the value `str` as a `void*` pointer. * `[in] finalize_hint`: This is the value `finalize_hint` that was given to the API. `napi_finalize` provides more details. This parameter is optional. Passing a null value means that the add-on doesn't need to be notified when the corresponding JavaScript string is collected. * `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection. * `[out] result`: A `napi_value` representing a JavaScript `string`. * `[out] copied`: Whether the string was copied. If it was, the finalizer will already have been invoked to destroy `str`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `string` value from an ISO-8859-1-encoded C string. The native string may not be copied and must thus exist for the entire life cycle of the JavaScript value. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. ##### `napi_create_string_utf16`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_string_utf16(napi_env env, const char16_t* str, size_t length, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing a UTF16-LE-encoded string. * `[in] length`: The length of the string in two-byte code units, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[out] result`: A `napi_value` representing a JavaScript `string`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `string` value from a UTF16-LE-encoded C string. The native string is copied. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. ##### `node_api_create_external_string_utf16`# Added in: v20.4.0, v18.18.0 N-API version: 10 napi_status node_api_create_external_string_utf16(napi_env env, char16_t* str, size_t length, napi_finalize finalize_callback, void* finalize_hint, napi_value* result, bool* copied); * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing a UTF16-LE-encoded string. * `[in] length`: The length of the string in two-byte code units, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[in] finalize_callback`: The function to call when the string is being collected. The function will be called with the following parameters: * `[in] env`: The environment in which the add-on is running. This value may be null if the string is being collected as part of the termination of the worker or the main Node.js instance. * `[in] data`: This is the value `str` as a `void*` pointer. * `[in] finalize_hint`: This is the value `finalize_hint` that was given to the API. `napi_finalize` provides more details. This parameter is optional. Passing a null value means that the add-on doesn't need to be notified when the corresponding JavaScript string is collected. * `[in] finalize_hint`: Optional hint to pass to the finalize callback during collection. * `[out] result`: A `napi_value` representing a JavaScript `string`. * `[out] copied`: Whether the string was copied. If it was, the finalizer will already have been invoked to destroy `str`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `string` value from a UTF16-LE-encoded C string. The native string may not be copied and must thus exist for the entire life cycle of the JavaScript value. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. ##### `napi_create_string_utf8`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_string_utf8(napi_env env, const char* str, size_t length, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing a UTF8-encoded string. * `[in] length`: The length of the string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[out] result`: A `napi_value` representing a JavaScript `string`. Returns `napi_ok` if the API succeeded. This API creates a JavaScript `string` value from a UTF8-encoded C string. The native string is copied. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. #### Functions to create optimized property keys# Many JavaScript engines including V8 use internalized strings as keys to set and get property values. They typically use a hash table to create and lookup such strings. While it adds some cost per key creation, it improves the performance after that by enabling comparison of string pointers instead of the whole strings. If a new JavaScript string is intended to be used as a property key, then for some JavaScript engines it will be more efficient to use the functions in this section. Otherwise, use the `napi_create_string_utf8` or `node_api_create_external_string_utf8` series functions as there may be additional overhead in creating/storing strings with the property key creation methods. ##### `node_api_create_property_key_latin1`# Added in: v22.9.0, v20.18.0 N-API version: 10 napi_status NAPI_CDECL node_api_create_property_key_latin1(napi_env env, const char* str, size_t length, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing an ISO-8859-1-encoded string. * `[in] length`: The length of the string in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[out] result`: A `napi_value` representing an optimized JavaScript `string` to be used as a property key for objects. Returns `napi_ok` if the API succeeded. This API creates an optimized JavaScript `string` value from an ISO-8859-1-encoded C string to be used as a property key for objects. The native string is copied. In contrast with `napi_create_string_latin1`, subsequent calls to this function with the same `str` pointer may benefit from a speedup in the creation of the requested `napi_value`, depending on the engine. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. ##### `node_api_create_property_key_utf16`# Added in: v21.7.0, v20.12.0 N-API version: 10 napi_status NAPI_CDECL node_api_create_property_key_utf16(napi_env env, const char16_t* str, size_t length, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing a UTF16-LE-encoded string. * `[in] length`: The length of the string in two-byte code units, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[out] result`: A `napi_value` representing an optimized JavaScript `string` to be used as a property key for objects. Returns `napi_ok` if the API succeeded. This API creates an optimized JavaScript `string` value from a UTF16-LE-encoded C string to be used as a property key for objects. The native string is copied. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. ##### `node_api_create_property_key_utf8`# Added in: v22.9.0, v20.18.0 N-API version: 10 napi_status NAPI_CDECL node_api_create_property_key_utf8(napi_env env, const char* str, size_t length, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] str`: Character buffer representing a UTF8-encoded string. * `[in] length`: The length of the string in two-byte code units, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[out] result`: A `napi_value` representing an optimized JavaScript `string` to be used as a property key for objects. Returns `napi_ok` if the API succeeded. This API creates an optimized JavaScript `string` value from a UTF8-encoded C string to be used as a property key for objects. The native string is copied. The JavaScript `string` type is described in Section string type of the ECMAScript Language Specification. #### Functions to convert from Node-API to C types# ##### `napi_get_array_length`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_array_length(napi_env env, napi_value value, uint32_t* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing the JavaScript `Array` whose length is being queried. * `[out] result`: `uint32` representing length of the array. Returns `napi_ok` if the API succeeded. This API returns the length of an array. `Array` length is described in Section Array instance length of the ECMAScript Language Specification. ##### `napi_get_arraybuffer_info`# History VersionChanges v24.9.0 Added support for `SharedArrayBuffer`. v8.0.0 Added in: v8.0.0 N-API version: 1 napi_status napi_get_arraybuffer_info(napi_env env, napi_value arraybuffer, void** data, size_t* byte_length) * `[in] env`: The environment that the API is invoked under. * `[in] arraybuffer`: `napi_value` representing the `ArrayBuffer` or `SharedArrayBuffer` being queried. * `[out] data`: The underlying data buffer of the `ArrayBuffer` or `SharedArrayBuffer` is `0`, this may be `NULL` or any other pointer value. * `[out] byte_length`: Length in bytes of the underlying data buffer. Returns `napi_ok` if the API succeeded. This API is used to retrieve the underlying data buffer of an `ArrayBuffer` or `SharedArrayBuffer` and its length. WARNING: Use caution while using this API. The lifetime of the underlying data buffer is managed by the `ArrayBuffer` or `SharedArrayBuffer` even after it's returned. A possible safe way to use this API is in conjunction with `napi_create_reference`, which can be used to guarantee control over the lifetime of the `ArrayBuffer` or `SharedArrayBuffer`. It's also safe to use the returned data buffer within the same callback as long as there are no calls to other APIs that might trigger a GC. ##### `napi_get_buffer_info`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_buffer_info(napi_env env, napi_value value, void** data, size_t* length) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing the `node::Buffer` or `Uint8Array` being queried. * `[out] data`: The underlying data buffer of the `node::Buffer` or `Uint8Array`. If length is `0`, this may be `NULL` or any other pointer value. * `[out] length`: Length in bytes of the underlying data buffer. Returns `napi_ok` if the API succeeded. This method returns the identical `data` and `byte_length` as `napi_get_typedarray_info`. And `napi_get_typedarray_info` accepts a `node::Buffer` (a Uint8Array) as the value too. This API is used to retrieve the underlying data buffer of a `node::Buffer` and its length. Warning: Use caution while using this API since the underlying data buffer's lifetime is not guaranteed if it's managed by the VM. ##### `napi_get_prototype`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_prototype(napi_env env, napi_value object, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] object`: `napi_value` representing JavaScript `Object` whose prototype to return. This returns the equivalent of `Object.getPrototypeOf` (which is not the same as the function's `prototype` property). * `[out] result`: `napi_value` representing prototype of the given object. Returns `napi_ok` if the API succeeded. ##### `napi_get_typedarray_info`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_typedarray_info(napi_env env, napi_value typedarray, napi_typedarray_type* type, size_t* length, void** data, napi_value* arraybuffer, size_t* byte_offset) * `[in] env`: The environment that the API is invoked under. * `[in] typedarray`: `napi_value` representing the `TypedArray` whose properties to query. * `[out] type`: Scalar datatype of the elements within the `TypedArray`. * `[out] length`: The number of elements in the `TypedArray`. * `[out] data`: The data buffer underlying the `TypedArray` adjusted by the `byte_offset` value so that it points to the first element in the `TypedArray`. If the length of the array is `0`, this may be `NULL` or any other pointer value. * `[out] arraybuffer`: The `ArrayBuffer` underlying the `TypedArray`. * `[out] byte_offset`: The byte offset within the underlying native array at which the first element of the arrays is located. The value for the data parameter has already been adjusted so that data points to the first element in the array. Therefore, the first byte of the native array would be at `data - byte_offset`. Returns `napi_ok` if the API succeeded. This API returns various properties of a typed array. Any of the out parameters may be `NULL` if that property is unneeded. Warning: Use caution while using this API since the underlying data buffer is managed by the VM. ##### `napi_get_dataview_info`# Added in: v8.3.0 N-API version: 1 napi_status napi_get_dataview_info(napi_env env, napi_value dataview, size_t* byte_length, void** data, napi_value* arraybuffer, size_t* byte_offset) * `[in] env`: The environment that the API is invoked under. * `[in] dataview`: `napi_value` representing the `DataView` whose properties to query. * `[out] byte_length`: Number of bytes in the `DataView`. * `[out] data`: The data buffer underlying the `DataView`. If byte_length is `0`, this may be `NULL` or any other pointer value. * `[out] arraybuffer`: `ArrayBuffer` underlying the `DataView`. * `[out] byte_offset`: The byte offset within the data buffer from which to start projecting the `DataView`. Returns `napi_ok` if the API succeeded. Any of the out parameters may be `NULL` if that property is unneeded. This API returns various properties of a `DataView`. ##### `napi_get_date_value`# Added in: v11.11.0, v10.17.0 N-API version: 5 napi_status napi_get_date_value(napi_env env, napi_value value, double* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing a JavaScript `Date`. * `[out] result`: Time value as a `double` represented as milliseconds since midnight at the beginning of 01 January, 1970 UTC. This API does not observe leap seconds; they are ignored, as ECMAScript aligns with POSIX time specification. Returns `napi_ok` if the API succeeded. If a non-date `napi_value` is passed in it returns `napi_date_expected`. This API returns the C double primitive of time value for the given JavaScript `Date`. ##### `napi_get_value_bool`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_bool(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript `Boolean`. * `[out] result`: C boolean primitive equivalent of the given JavaScript `Boolean`. Returns `napi_ok` if the API succeeded. If a non-boolean `napi_value` is passed in it returns `napi_boolean_expected`. This API returns the C boolean primitive equivalent of the given JavaScript `Boolean`. ##### `napi_get_value_double`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_double(napi_env env, napi_value value, double* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript `number`. * `[out] result`: C double primitive equivalent of the given JavaScript `number`. Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in it returns `napi_number_expected`. This API returns the C double primitive equivalent of the given JavaScript `number`. ##### `napi_get_value_bigint_int64`# Added in: v10.7.0 N-API version: 6 napi_status napi_get_value_bigint_int64(napi_env env, napi_value value, int64_t* result, bool* lossless); * `[in] env`: The environment that the API is invoked under * `[in] value`: `napi_value` representing JavaScript `BigInt`. * `[out] result`: C `int64_t` primitive equivalent of the given JavaScript `BigInt`. * `[out] lossless`: Indicates whether the `BigInt` value was converted losslessly. Returns `napi_ok` if the API succeeded. If a non-`BigInt` is passed in it returns `napi_bigint_expected`. This API returns the C `int64_t` primitive equivalent of the given JavaScript `BigInt`. If needed it will truncate the value, setting `lossless` to `false`. ##### `napi_get_value_bigint_uint64`# Added in: v10.7.0 N-API version: 6 napi_status napi_get_value_bigint_uint64(napi_env env, napi_value value, uint64_t* result, bool* lossless); * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript `BigInt`. * `[out] result`: C `uint64_t` primitive equivalent of the given JavaScript `BigInt`. * `[out] lossless`: Indicates whether the `BigInt` value was converted losslessly. Returns `napi_ok` if the API succeeded. If a non-`BigInt` is passed in it returns `napi_bigint_expected`. This API returns the C `uint64_t` primitive equivalent of the given JavaScript `BigInt`. If needed it will truncate the value, setting `lossless` to `false`. ##### `napi_get_value_bigint_words`# Added in: v10.7.0 N-API version: 6 napi_status napi_get_value_bigint_words(napi_env env, napi_value value, int* sign_bit, size_t* word_count, uint64_t* words); * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript `BigInt`. * `[out] sign_bit`: Integer representing if the JavaScript `BigInt` is positive or negative. * `[in/out] word_count`: Must be initialized to the length of the `words` array. Upon return, it will be set to the actual number of words that would be needed to store this `BigInt`. * `[out] words`: Pointer to a pre-allocated 64-bit word array. Returns `napi_ok` if the API succeeded. This API converts a single `BigInt` value into a sign bit, 64-bit little-endian array, and the number of elements in the array. `sign_bit` and `words` may be both set to `NULL`, in order to get only `word_count`. ##### `napi_get_value_external`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_external(napi_env env, napi_value value, void** result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript external value. * `[out] result`: Pointer to the data wrapped by the JavaScript external value. Returns `napi_ok` if the API succeeded. If a non-external `napi_value` is passed in it returns `napi_invalid_arg`. This API retrieves the external data pointer that was previously passed to `napi_create_external()`. ##### `napi_get_value_int32`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_int32(napi_env env, napi_value value, int32_t* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript `number`. * `[out] result`: C `int32` primitive equivalent of the given JavaScript `number`. Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in `napi_number_expected`. This API returns the C `int32` primitive equivalent of the given JavaScript `number`. If the number exceeds the range of the 32 bit integer, then the result is truncated to the equivalent of the bottom 32 bits. This can result in a large positive number becoming a negative number if the value is > 231 \- 1. Non-finite number values (`NaN`, `+Infinity`, or `-Infinity`) set the result to zero. ##### `napi_get_value_int64`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_int64(napi_env env, napi_value value, int64_t* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript `number`. * `[out] result`: C `int64` primitive equivalent of the given JavaScript `number`. Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in it returns `napi_number_expected`. This API returns the C `int64` primitive equivalent of the given JavaScript `number`. `number` values outside the range of `Number.MIN_SAFE_INTEGER` `-(2**53 - 1)` \- `Number.MAX_SAFE_INTEGER` `(2**53 - 1)` will lose precision. Non-finite number values (`NaN`, `+Infinity`, or `-Infinity`) set the result to zero. ##### `napi_get_value_string_latin1`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_string_latin1(napi_env env, napi_value value, char* buf, size_t bufsize, size_t* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript string. * `[in] buf`: Buffer to write the ISO-8859-1-encoded string into. If `NULL` is passed in, the length of the string in bytes and excluding the null terminator is returned in `result`. * `[in] bufsize`: Size of the destination buffer. When this value is insufficient, the returned string is truncated and null-terminated. If this value is zero, then the string is not returned and no changes are done to the buffer. * `[out] result`: Number of bytes copied into the buffer, excluding the null terminator. Returns `napi_ok` if the API succeeded. If a non-`string` `napi_value` is passed in it returns `napi_string_expected`. This API returns the ISO-8859-1-encoded string corresponding the value passed in. ##### `napi_get_value_string_utf8`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_string_utf8(napi_env env, napi_value value, char* buf, size_t bufsize, size_t* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript string. * `[in] buf`: Buffer to write the UTF8-encoded string into. If `NULL` is passed in, the length of the string in bytes and excluding the null terminator is returned in `result`. * `[in] bufsize`: Size of the destination buffer. When this value is insufficient, the returned string is truncated and null-terminated. If this value is zero, then the string is not returned and no changes are done to the buffer. * `[out] result`: Number of bytes copied into the buffer, excluding the null terminator. Returns `napi_ok` if the API succeeded. If a non-`string` `napi_value` is passed in it returns `napi_string_expected`. This API returns the UTF8-encoded string corresponding the value passed in. ##### `napi_get_value_string_utf16`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_string_utf16(napi_env env, napi_value value, char16_t* buf, size_t bufsize, size_t* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript string. * `[in] buf`: Buffer to write the UTF16-LE-encoded string into. If `NULL` is passed in, the length of the string in 2-byte code units and excluding the null terminator is returned. * `[in] bufsize`: Size of the destination buffer. When this value is insufficient, the returned string is truncated and null-terminated. If this value is zero, then the string is not returned and no changes are done to the buffer. * `[out] result`: Number of 2-byte code units copied into the buffer, excluding the null terminator. Returns `napi_ok` if the API succeeded. If a non-`string` `napi_value` is passed in it returns `napi_string_expected`. This API returns the UTF16-encoded string corresponding the value passed in. ##### `napi_get_value_uint32`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_value_uint32(napi_env env, napi_value value, uint32_t* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: `napi_value` representing JavaScript `number`. * `[out] result`: C primitive equivalent of the given `napi_value` as a `uint32_t`. Returns `napi_ok` if the API succeeded. If a non-number `napi_value` is passed in it returns `napi_number_expected`. This API returns the C primitive equivalent of the given `napi_value` as a `uint32_t`. #### Functions to get global instances# ##### `napi_get_boolean`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_boolean(napi_env env, bool value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The value of the boolean to retrieve. * `[out] result`: `napi_value` representing JavaScript `Boolean` singleton to retrieve. Returns `napi_ok` if the API succeeded. This API is used to return the JavaScript singleton object that is used to represent the given boolean value. ##### `napi_get_global`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_global(napi_env env, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[out] result`: `napi_value` representing JavaScript `global` object. Returns `napi_ok` if the API succeeded. This API returns the `global` object. ##### `napi_get_null`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_null(napi_env env, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[out] result`: `napi_value` representing JavaScript `null` object. Returns `napi_ok` if the API succeeded. This API returns the `null` object. ##### `napi_get_undefined`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_undefined(napi_env env, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[out] result`: `napi_value` representing JavaScript Undefined value. Returns `napi_ok` if the API succeeded. This API returns the Undefined object. ### Working with JavaScript values and abstract operations# Node-API exposes a set of APIs to perform some abstract operations on JavaScript values. These APIs support doing one of the following: 1. Coerce JavaScript values to specific JavaScript types (such as `number` or `string`). 2. Check the type of a JavaScript value. 3. Check for equality between two JavaScript values. #### `napi_coerce_to_bool`# Added in: v8.0.0 N-API version: 1 napi_status napi_coerce_to_bool(napi_env env, napi_value value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to coerce. * `[out] result`: `napi_value` representing the coerced JavaScript `Boolean`. Returns `napi_ok` if the API succeeded. This API implements the abstract operation `ToBoolean()` as defined in Section ToBoolean of the ECMAScript Language Specification. #### `napi_coerce_to_number`# Added in: v8.0.0 N-API version: 1 napi_status napi_coerce_to_number(napi_env env, napi_value value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to coerce. * `[out] result`: `napi_value` representing the coerced JavaScript `number`. Returns `napi_ok` if the API succeeded. This API implements the abstract operation `ToNumber()` as defined in Section ToNumber of the ECMAScript Language Specification. This function potentially runs JS code if the passed-in value is an object. #### `napi_coerce_to_object`# Added in: v8.0.0 N-API version: 1 napi_status napi_coerce_to_object(napi_env env, napi_value value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to coerce. * `[out] result`: `napi_value` representing the coerced JavaScript `Object`. Returns `napi_ok` if the API succeeded. This API implements the abstract operation `ToObject()` as defined in Section ToObject of the ECMAScript Language Specification. #### `napi_coerce_to_string`# Added in: v8.0.0 N-API version: 1 napi_status napi_coerce_to_string(napi_env env, napi_value value, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to coerce. * `[out] result`: `napi_value` representing the coerced JavaScript `string`. Returns `napi_ok` if the API succeeded. This API implements the abstract operation `ToString()` as defined in Section ToString of the ECMAScript Language Specification. This function potentially runs JS code if the passed-in value is an object. #### `napi_typeof`# Added in: v8.0.0 N-API version: 1 napi_status napi_typeof(napi_env env, napi_value value, napi_valuetype* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value whose type to query. * `[out] result`: The type of the JavaScript value. Returns `napi_ok` if the API succeeded. * `napi_invalid_arg` if the type of `value` is not a known ECMAScript type and `value` is not an External value. This API represents behavior similar to invoking the `typeof` Operator on the object as defined in Section typeof operator of the ECMAScript Language Specification. However, there are some differences: 1. It has support for detecting an External value. 2. It detects `null` as a separate type, while ECMAScript `typeof` would detect `object`. If `value` has a type that is invalid, an error is returned. #### `napi_instanceof`# Added in: v8.0.0 N-API version: 1 napi_status napi_instanceof(napi_env env, napi_value object, napi_value constructor, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] object`: The JavaScript value to check. * `[in] constructor`: The JavaScript function object of the constructor function to check against. * `[out] result`: Boolean that is set to true if `object instanceof constructor` is true. Returns `napi_ok` if the API succeeded. This API represents invoking the `instanceof` Operator on the object as defined in Section instanceof operator of the ECMAScript Language Specification. #### `napi_is_array`# Added in: v8.0.0 N-API version: 1 napi_status napi_is_array(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given object is an array. Returns `napi_ok` if the API succeeded. This API represents invoking the `IsArray` operation on the object as defined in Section IsArray of the ECMAScript Language Specification. #### `napi_is_arraybuffer`# Added in: v8.0.0 N-API version: 1 napi_status napi_is_arraybuffer(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given object is an `ArrayBuffer`. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in is an array buffer. #### `napi_is_buffer`# Added in: v8.0.0 N-API version: 1 napi_status napi_is_buffer(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given `napi_value` represents a `node::Buffer` or `Uint8Array` object. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in is a buffer or Uint8Array. `napi_is_typedarray` should be preferred if the caller needs to check if the value is a Uint8Array. #### `napi_is_date`# Added in: v11.11.0, v10.17.0 N-API version: 5 napi_status napi_is_date(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given `napi_value` represents a JavaScript `Date` object. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in is a date. #### `napi_is_error`# Added in: v8.0.0 N-API version: 1 napi_status napi_is_error(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given `napi_value` represents an `Error` object. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in is an `Error`. #### `napi_is_typedarray`# Added in: v8.0.0 N-API version: 1 napi_status napi_is_typedarray(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given `napi_value` represents a `TypedArray`. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in is a typed array. #### `napi_is_dataview`# Added in: v8.3.0 N-API version: 1 napi_status napi_is_dataview(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given `napi_value` represents a `DataView`. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in is a `DataView`. #### `napi_strict_equals`# Added in: v8.0.0 N-API version: 1 napi_status napi_strict_equals(napi_env env, napi_value lhs, napi_value rhs, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] lhs`: The JavaScript value to check. * `[in] rhs`: The JavaScript value to check against. * `[out] result`: Whether the two `napi_value` objects are equal. Returns `napi_ok` if the API succeeded. This API represents the invocation of the Strict Equality algorithm as defined in Section IsStrctEqual of the ECMAScript Language Specification. #### `napi_detach_arraybuffer`# Added in: v13.0.0, v12.16.0, v10.22.0 N-API version: 7 napi_status napi_detach_arraybuffer(napi_env env, napi_value arraybuffer) * `[in] env`: The environment that the API is invoked under. * `[in] arraybuffer`: The JavaScript `ArrayBuffer` to be detached. Returns `napi_ok` if the API succeeded. If a non-detachable `ArrayBuffer` is passed in it returns `napi_detachable_arraybuffer_expected`. Generally, an `ArrayBuffer` is non-detachable if it has been detached before. The engine may impose additional conditions on whether an `ArrayBuffer` is detachable. For example, V8 requires that the `ArrayBuffer` be external, that is, created with `napi_create_external_arraybuffer`. This API represents the invocation of the `ArrayBuffer` detach operation as defined in Section detachArrayBuffer of the ECMAScript Language Specification. #### `napi_is_detached_arraybuffer`# Added in: v13.3.0, v12.16.0, v10.22.0 N-API version: 7 napi_status napi_is_detached_arraybuffer(napi_env env, napi_value arraybuffer, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] arraybuffer`: The JavaScript `ArrayBuffer` to be checked. * `[out] result`: Whether the `arraybuffer` is detached. Returns `napi_ok` if the API succeeded. The `ArrayBuffer` is considered detached if its internal data is `null`. This API represents the invocation of the `ArrayBuffer` `IsDetachedBuffer` operation as defined in Section isDetachedBuffer of the ECMAScript Language Specification. #### `node_api_is_sharedarraybuffer`# Added in: v24.9.0 Stability: 1 \- Experimental napi_status node_api_is_sharedarraybuffer(napi_env env, napi_value value, bool* result) * `[in] env`: The environment that the API is invoked under. * `[in] value`: The JavaScript value to check. * `[out] result`: Whether the given `napi_value` represents a `SharedArrayBuffer`. Returns `napi_ok` if the API succeeded. This API checks if the Object passed in is a `SharedArrayBuffer`. #### `node_api_create_sharedarraybuffer`# Added in: v24.9.0 Stability: 1 \- Experimental napi_status node_api_create_sharedarraybuffer(napi_env env, size_t byte_length, void** data, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] byte_length`: The length in bytes of the shared array buffer to create. * `[out] data`: Pointer to the underlying byte buffer of the `SharedArrayBuffer`. `data` can optionally be ignored by passing `NULL`. * `[out] result`: A `napi_value` representing a JavaScript `SharedArrayBuffer`. Returns `napi_ok` if the API succeeded. This API returns a Node-API value corresponding to a JavaScript `SharedArrayBuffer`. `SharedArrayBuffer`s are used to represent fixed-length binary data buffers that can be shared across multiple workers. The `SharedArrayBuffer` allocated will have an underlying byte buffer whose size is determined by the `byte_length` parameter that's passed in. The underlying buffer is optionally returned back to the caller in case the caller wants to directly manipulate the buffer. This buffer can only be written to directly from native code. To write to this buffer from JavaScript, a typed array or `DataView` object would need to be created. JavaScript `SharedArrayBuffer` objects are described in Section SharedArrayBuffer objects of the ECMAScript Language Specification. ### Working with JavaScript properties# Node-API exposes a set of APIs to get and set properties on JavaScript objects. Properties in JavaScript are represented as a tuple of a key and a value. Fundamentally, all property keys in Node-API can be represented in one of the following forms: * Named: a simple UTF8-encoded string * Integer-Indexed: an index value represented by `uint32_t` * JavaScript value: these are represented in Node-API by `napi_value`. This can be a `napi_value` representing a `string`, `number`, or `symbol`. Node-API values are represented by the type `napi_value`. Any Node-API call that requires a JavaScript value takes in a `napi_value`. However, it's the caller's responsibility to make sure that the `napi_value` in question is of the JavaScript type expected by the API. The APIs documented in this section provide a simple interface to get and set properties on arbitrary JavaScript objects represented by `napi_value`. For instance, consider the following JavaScript code snippet: const obj = {}; obj.myProp = 123; The equivalent can be done using Node-API values with the following snippet: napi_status status = napi_generic_failure; // const obj = {} napi_value obj, value; status = napi_create_object(env, &obj); if (status != napi_ok) return status; // Create a napi_value for 123 status = napi_create_int32(env, 123, &value); if (status != napi_ok) return status; // obj.myProp = 123 status = napi_set_named_property(env, obj, "myProp", value); if (status != napi_ok) return status; Indexed properties can be set in a similar manner. Consider the following JavaScript snippet: const arr = []; arr[123] = 'hello'; The equivalent can be done using Node-API values with the following snippet: napi_status status = napi_generic_failure; // const arr = []; napi_value arr, value; status = napi_create_array(env, &arr); if (status != napi_ok) return status; // Create a napi_value for 'hello' status = napi_create_string_utf8(env, "hello", NAPI_AUTO_LENGTH, &value); if (status != napi_ok) return status; // arr[123] = 'hello'; status = napi_set_element(env, arr, 123, value); if (status != napi_ok) return status; Properties can be retrieved using the APIs described in this section. Consider the following JavaScript snippet: const arr = []; const value = arr[123]; The following is the approximate equivalent of the Node-API counterpart: napi_status status = napi_generic_failure; // const arr = [] napi_value arr, value; status = napi_create_array(env, &arr); if (status != napi_ok) return status; // const value = arr[123] status = napi_get_element(env, arr, 123, &value); if (status != napi_ok) return status; Finally, multiple properties can also be defined on an object for performance reasons. Consider the following JavaScript: const obj = {}; Object.defineProperties(obj, { 'foo': { value: 123, writable: true, configurable: true, enumerable: true }, 'bar': { value: 456, writable: true, configurable: true, enumerable: true }, }); The following is the approximate equivalent of the Node-API counterpart: napi_status status = napi_status_generic_failure; // const obj = {}; napi_value obj; status = napi_create_object(env, &obj); if (status != napi_ok) return status; // Create napi_values for 123 and 456 napi_value fooValue, barValue; status = napi_create_int32(env, 123, &fooValue); if (status != napi_ok) return status; status = napi_create_int32(env, 456, &barValue); if (status != napi_ok) return status; // Set the properties napi_property_descriptor descriptors[] = { { "foo", NULL, NULL, NULL, NULL, fooValue, napi_writable | napi_configurable, NULL }, { "bar", NULL, NULL, NULL, NULL, barValue, napi_writable | napi_configurable, NULL } } status = napi_define_properties(env, obj, sizeof(descriptors) / sizeof(descriptors[0]), descriptors); if (status != napi_ok) return status; #### Structures# ##### `napi_property_attributes`# History VersionChanges v14.12.0 added `napi_default_method` and `napi_default_property`. typedef enum { napi_default = 0, napi_writable = 1 << 0, napi_enumerable = 1 << 1, napi_configurable = 1 << 2, // Used with napi_define_class to distinguish static properties // from instance properties. Ignored by napi_define_properties. napi_static = 1 << 10, // Default for class methods. napi_default_method = napi_writable | napi_configurable, // Default for object properties, like in JS obj[prop]. napi_default_jsproperty = napi_writable | napi_enumerable | napi_configurable, } napi_property_attributes; `napi_property_attributes` are bit flags used to control the behavior of properties set on a JavaScript object. Other than `napi_static` they correspond to the attributes listed in Section property attributes of the ECMAScript Language Specification. They can be one or more of the following bit flags: * `napi_default`: No explicit attributes are set on the property. By default, a property is read only, not enumerable and not configurable. * `napi_writable`: The property is writable. * `napi_enumerable`: The property is enumerable. * `napi_configurable`: The property is configurable as defined in Section property attributes of the ECMAScript Language Specification. * `napi_static`: The property will be defined as a static property on a class as opposed to an instance property, which is the default. This is used only by `napi_define_class`. It is ignored by `napi_define_properties`. * `napi_default_method`: Like a method in a JS class, the property is configurable and writeable, but not enumerable. * `napi_default_jsproperty`: Like a property set via assignment in JavaScript, the property is writable, enumerable, and configurable. ##### `napi_property_descriptor`# typedef struct { // One of utf8name or name should be NULL. const char* utf8name; napi_value name; napi_callback method; napi_callback getter; napi_callback setter; napi_value value; napi_property_attributes attributes; void* data; } napi_property_descriptor; * `utf8name`: Optional string describing the key for the property, encoded as UTF8. One of `utf8name` or `name` must be provided for the property. * `name`: Optional `napi_value` that points to a JavaScript string or symbol to be used as the key for the property. One of `utf8name` or `name` must be provided for the property. * `value`: The value that's retrieved by a get access of the property if the property is a data property. If this is passed in, set `getter`, `setter`, `method` and `data` to `NULL` (since these members won't be used). * `getter`: A function to call when a get access of the property is performed. If this is passed in, set `value` and `method` to `NULL` (since these members won't be used). The given function is called implicitly by the runtime when the property is accessed from JavaScript code (or if a get on the property is performed using a Node-API call). `napi_callback` provides more details. * `setter`: A function to call when a set access of the property is performed. If this is passed in, set `value` and `method` to `NULL` (since these members won't be used). The given function is called implicitly by the runtime when the property is set from JavaScript code (or if a set on the property is performed using a Node-API call). `napi_callback` provides more details. * `method`: Set this to make the property descriptor object's `value` property to be a JavaScript function represented by `method`. If this is passed in, set `value`, `getter` and `setter` to `NULL` (since these members won't be used). `napi_callback` provides more details. * `attributes`: The attributes associated with the particular property. See `napi_property_attributes`. * `data`: The callback data passed into `method`, `getter` and `setter` if this function is invoked. #### Functions# ##### `napi_get_property_names`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_property_names(napi_env env, napi_value object, napi_value* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object from which to retrieve the properties. * `[out] result`: A `napi_value` representing an array of JavaScript values that represent the property names of the object. The API can be used to iterate over `result` using `napi_get_array_length` and `napi_get_element`. Returns `napi_ok` if the API succeeded. This API returns the names of the enumerable properties of `object` as an array of strings. The properties of `object` whose key is a symbol will not be included. ##### `napi_get_all_property_names`# Added in: v13.7.0, v12.17.0, v10.20.0 N-API version: 6 napi_get_all_property_names(napi_env env, napi_value object, napi_key_collection_mode key_mode, napi_key_filter key_filter, napi_key_conversion key_conversion, napi_value* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object from which to retrieve the properties. * `[in] key_mode`: Whether to retrieve prototype properties as well. * `[in] key_filter`: Which properties to retrieve (enumerable/readable/writable). * `[in] key_conversion`: Whether to convert numbered property keys to strings. * `[out] result`: A `napi_value` representing an array of JavaScript values that represent the property names of the object. `napi_get_array_length` and `napi_get_element` can be used to iterate over `result`. Returns `napi_ok` if the API succeeded. This API returns an array containing the names of the available properties of this object. ##### `napi_set_property`# Added in: v8.0.0 N-API version: 1 napi_status napi_set_property(napi_env env, napi_value object, napi_value key, napi_value value); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object on which to set the property. * `[in] key`: The name of the property to set. * `[in] value`: The property value. Returns `napi_ok` if the API succeeded. This API set a property on the `Object` passed in. ##### `napi_get_property`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_property(napi_env env, napi_value object, napi_value key, napi_value* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object from which to retrieve the property. * `[in] key`: The name of the property to retrieve. * `[out] result`: The value of the property. Returns `napi_ok` if the API succeeded. This API gets the requested property from the `Object` passed in. ##### `napi_has_property`# Added in: v8.0.0 N-API version: 1 napi_status napi_has_property(napi_env env, napi_value object, napi_value key, bool* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to query. * `[in] key`: The name of the property whose existence to check. * `[out] result`: Whether the property exists on the object or not. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in has the named property. ##### `napi_delete_property`# Added in: v8.2.0 N-API version: 1 napi_status napi_delete_property(napi_env env, napi_value object, napi_value key, bool* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to query. * `[in] key`: The name of the property to delete. * `[out] result`: Whether the property deletion succeeded or not. `result` can optionally be ignored by passing `NULL`. Returns `napi_ok` if the API succeeded. This API attempts to delete the `key` own property from `object`. ##### `napi_has_own_property`# Added in: v8.2.0 N-API version: 1 napi_status napi_has_own_property(napi_env env, napi_value object, napi_value key, bool* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to query. * `[in] key`: The name of the own property whose existence to check. * `[out] result`: Whether the own property exists on the object or not. Returns `napi_ok` if the API succeeded. This API checks if the `Object` passed in has the named own property. `key` must be a `string` or a `symbol`, or an error will be thrown. Node-API will not perform any conversion between data types. ##### `napi_set_named_property`# Added in: v8.0.0 N-API version: 1 napi_status napi_set_named_property(napi_env env, napi_value object, const char* utf8Name, napi_value value); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object on which to set the property. * `[in] utf8Name`: The name of the property to set. * `[in] value`: The property value. Returns `napi_ok` if the API succeeded. This method is equivalent to calling `napi_set_property` with a `napi_value` created from the string passed in as `utf8Name`. ##### `napi_get_named_property`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_named_property(napi_env env, napi_value object, const char* utf8Name, napi_value* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object from which to retrieve the property. * `[in] utf8Name`: The name of the property to get. * `[out] result`: The value of the property. Returns `napi_ok` if the API succeeded. This method is equivalent to calling `napi_get_property` with a `napi_value` created from the string passed in as `utf8Name`. ##### `napi_has_named_property`# Added in: v8.0.0 N-API version: 1 napi_status napi_has_named_property(napi_env env, napi_value object, const char* utf8Name, bool* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to query. * `[in] utf8Name`: The name of the property whose existence to check. * `[out] result`: Whether the property exists on the object or not. Returns `napi_ok` if the API succeeded. This method is equivalent to calling `napi_has_property` with a `napi_value` created from the string passed in as `utf8Name`. ##### `napi_set_element`# Added in: v8.0.0 N-API version: 1 napi_status napi_set_element(napi_env env, napi_value object, uint32_t index, napi_value value); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object from which to set the properties. * `[in] index`: The index of the property to set. * `[in] value`: The property value. Returns `napi_ok` if the API succeeded. This API sets an element on the `Object` passed in. ##### `napi_get_element`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_element(napi_env env, napi_value object, uint32_t index, napi_value* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object from which to retrieve the property. * `[in] index`: The index of the property to get. * `[out] result`: The value of the property. Returns `napi_ok` if the API succeeded. This API gets the element at the requested index. ##### `napi_has_element`# Added in: v8.0.0 N-API version: 1 napi_status napi_has_element(napi_env env, napi_value object, uint32_t index, bool* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to query. * `[in] index`: The index of the property whose existence to check. * `[out] result`: Whether the property exists on the object or not. Returns `napi_ok` if the API succeeded. This API returns if the `Object` passed in has an element at the requested index. ##### `napi_delete_element`# Added in: v8.2.0 N-API version: 1 napi_status napi_delete_element(napi_env env, napi_value object, uint32_t index, bool* result); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to query. * `[in] index`: The index of the property to delete. * `[out] result`: Whether the element deletion succeeded or not. `result` can optionally be ignored by passing `NULL`. Returns `napi_ok` if the API succeeded. This API attempts to delete the specified `index` from `object`. ##### `napi_define_properties`# Added in: v8.0.0 N-API version: 1 napi_status napi_define_properties(napi_env env, napi_value object, size_t property_count, const napi_property_descriptor* properties); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object from which to retrieve the properties. * `[in] property_count`: The number of elements in the `properties` array. * `[in] properties`: The array of property descriptors. Returns `napi_ok` if the API succeeded. This method allows the efficient definition of multiple properties on a given object. The properties are defined using property descriptors (see `napi_property_descriptor`). Given an array of such property descriptors, this API will set the properties on the object one at a time, as defined by `DefineOwnProperty()` (described in Section DefineOwnProperty of the ECMA-262 specification). ##### `napi_object_freeze`# Added in: v14.14.0, v12.20.0 N-API version: 8 napi_status napi_object_freeze(napi_env env, napi_value object); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to freeze. Returns `napi_ok` if the API succeeded. This method freezes a given object. This prevents new properties from being added to it, existing properties from being removed, prevents changing the enumerability, configurability, or writability of existing properties, and prevents the values of existing properties from being changed. It also prevents the object's prototype from being changed. This is described in Section 19.1.2.6 of the ECMA-262 specification. ##### `napi_object_seal`# Added in: v14.14.0, v12.20.0 N-API version: 8 napi_status napi_object_seal(napi_env env, napi_value object); * `[in] env`: The environment that the Node-API call is invoked under. * `[in] object`: The object to seal. Returns `napi_ok` if the API succeeded. This method seals a given object. This prevents new properties from being added to it, as well as marking all existing properties as non-configurable. This is described in Section 19.1.2.20 of the ECMA-262 specification. ### Working with JavaScript functions# Node-API provides a set of APIs that allow JavaScript code to call back into native code. Node-APIs that support calling back into native code take in a callback functions represented by the `napi_callback` type. When the JavaScript VM calls back to native code, the `napi_callback` function provided is invoked. The APIs documented in this section allow the callback function to do the following: * Get information about the context in which the callback was invoked. * Get the arguments passed into the callback. * Return a `napi_value` back from the callback. Additionally, Node-API provides a set of functions which allow calling JavaScript functions from native code. One can either call a function like a regular JavaScript function call, or as a constructor function. Any non-`NULL` data which is passed to this API via the `data` field of the `napi_property_descriptor` items can be associated with `object` and freed whenever `object` is garbage-collected by passing both `object` and the data to `napi_add_finalizer`. #### `napi_call_function`# Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_call_function(napi_env env, napi_value recv, napi_value func, size_t argc, const napi_value* argv, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] recv`: The `this` value passed to the called function. * `[in] func`: `napi_value` representing the JavaScript function to be invoked. * `[in] argc`: The count of elements in the `argv` array. * `[in] argv`: Array of `napi_values` representing JavaScript values passed in as arguments to the function. * `[out] result`: `napi_value` representing the JavaScript object returned. Returns `napi_ok` if the API succeeded. This method allows a JavaScript function object to be called from a native add-on. This is the primary mechanism of calling back from the add-on's native code into JavaScript. For the special case of calling into JavaScript after an async operation, see `napi_make_callback`. A sample use case might look as follows. Consider the following JavaScript snippet: function AddTwo(num) { return num + 2; } global.AddTwo = AddTwo; Then, the above function can be invoked from a native add-on using the following code: // Get the function named "AddTwo" on the global object napi_value global, add_two, arg; napi_status status = napi_get_global(env, &global); if (status != napi_ok) return; status = napi_get_named_property(env, global, "AddTwo", &add_two); if (status != napi_ok) return; // const arg = 1337 status = napi_create_int32(env, 1337, &arg); if (status != napi_ok) return; napi_value* argv = &arg; size_t argc = 1; // AddTwo(arg); napi_value return_val; status = napi_call_function(env, global, add_two, argc, argv, &return_val); if (status != napi_ok) return; // Convert the result back to a native type int32_t result; status = napi_get_value_int32(env, return_val, &result); if (status != napi_ok) return; #### `napi_create_function`# Added in: v8.0.0 N-API version: 1 napi_status napi_create_function(napi_env env, const char* utf8name, size_t length, napi_callback cb, void* data, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] utf8Name`: Optional name of the function encoded as UTF8. This is visible within JavaScript as the new function object's `name` property. * `[in] length`: The length of the `utf8name` in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[in] cb`: The native function which should be called when this function object is invoked. `napi_callback` provides more details. * `[in] data`: User-provided data context. This will be passed back into the function when invoked later. * `[out] result`: `napi_value` representing the JavaScript function object for the newly created function. Returns `napi_ok` if the API succeeded. This API allows an add-on author to create a function object in native code. This is the primary mechanism to allow calling into the add-on's native code from JavaScript. The newly created function is not automatically visible from script after this call. Instead, a property must be explicitly set on any object that is visible to JavaScript, in order for the function to be accessible from script. In order to expose a function as part of the add-on's module exports, set the newly created function on the exports object. A sample module might look as follows: napi_value SayHello(napi_env env, napi_callback_info info) { printf("Hello\n"); return NULL; } napi_value Init(napi_env env, napi_value exports) { napi_status status; napi_value fn; status = napi_create_function(env, NULL, 0, SayHello, NULL, &fn); if (status != napi_ok) return NULL; status = napi_set_named_property(env, exports, "sayHello", fn); if (status != napi_ok) return NULL; return exports; } NAPI_MODULE(NODE_GYP_MODULE_NAME, Init) Given the above code, the add-on can be used from JavaScript as follows: const myaddon = require('./addon'); myaddon.sayHello(); The string passed to `require()` is the name of the target in `binding.gyp` responsible for creating the `.node` file. Any non-`NULL` data which is passed to this API via the `data` parameter can be associated with the resulting JavaScript function (which is returned in the `result` parameter) and freed whenever the function is garbage-collected by passing both the JavaScript function and the data to `napi_add_finalizer`. JavaScript `Function`s are described in Section Function objects of the ECMAScript Language Specification. #### `napi_get_cb_info`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_cb_info(napi_env env, napi_callback_info cbinfo, size_t* argc, napi_value* argv, napi_value* thisArg, void** data) * `[in] env`: The environment that the API is invoked under. * `[in] cbinfo`: The callback info passed into the callback function. * `[in-out] argc`: Specifies the length of the provided `argv` array and receives the actual count of arguments. `argc` can optionally be ignored by passing `NULL`. * `[out] argv`: C array of `napi_value`s to which the arguments will be copied. If there are more arguments than the provided count, only the requested number of arguments are copied. If there are fewer arguments provided than claimed, the rest of `argv` is filled with `napi_value` values that represent `undefined`. `argv` can optionally be ignored by passing `NULL`. * `[out] thisArg`: Receives the JavaScript `this` argument for the call. `thisArg` can optionally be ignored by passing `NULL`. * `[out] data`: Receives the data pointer for the callback. `data` can optionally be ignored by passing `NULL`. Returns `napi_ok` if the API succeeded. This method is used within a callback function to retrieve details about the call like the arguments and the `this` pointer from a given callback info. #### `napi_get_new_target`# Added in: v8.6.0 N-API version: 1 napi_status napi_get_new_target(napi_env env, napi_callback_info cbinfo, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] cbinfo`: The callback info passed into the callback function. * `[out] result`: The `new.target` of the constructor call. Returns `napi_ok` if the API succeeded. This API returns the `new.target` of the constructor call. If the current callback is not a constructor call, the result is `NULL`. #### `napi_new_instance`# Added in: v8.0.0 N-API version: 1 napi_status napi_new_instance(napi_env env, napi_value cons, size_t argc, napi_value* argv, napi_value* result) * `[in] env`: The environment that the API is invoked under. * `[in] cons`: `napi_value` representing the JavaScript function to be invoked as a constructor. * `[in] argc`: The count of elements in the `argv` array. * `[in] argv`: Array of JavaScript values as `napi_value` representing the arguments to the constructor. If `argc` is zero this parameter may be omitted by passing in `NULL`. * `[out] result`: `napi_value` representing the JavaScript object returned, which in this case is the constructed object. This method is used to instantiate a new JavaScript value using a given `napi_value` that represents the constructor for the object. For example, consider the following snippet: function MyObject(param) { this.param = param; } const arg = 'hello'; const value = new MyObject(arg); The following can be approximated in Node-API using the following snippet: // Get the constructor function MyObject napi_value global, constructor, arg, value; napi_status status = napi_get_global(env, &global); if (status != napi_ok) return; status = napi_get_named_property(env, global, "MyObject", &constructor); if (status != napi_ok) return; // const arg = "hello" status = napi_create_string_utf8(env, "hello", NAPI_AUTO_LENGTH, &arg); if (status != napi_ok) return; napi_value* argv = &arg; size_t argc = 1; // const value = new MyObject(arg) status = napi_new_instance(env, constructor, argc, argv, &value); Returns `napi_ok` if the API succeeded. ### Object wrap# Node-API offers a way to "wrap" C++ classes and instances so that the class constructor and methods can be called from JavaScript. 1. The `napi_define_class` API defines a JavaScript class with constructor, static properties and methods, and instance properties and methods that correspond to the C++ class. 2. When JavaScript code invokes the constructor, the constructor callback uses `napi_wrap` to wrap a new C++ instance in a JavaScript object, then returns the wrapper object. 3. When JavaScript code invokes a method or property accessor on the class, the corresponding `napi_callback` C++ function is invoked. For an instance callback, `napi_unwrap` obtains the C++ instance that is the target of the call. For wrapped objects it may be difficult to distinguish between a function called on a class prototype and a function called on an instance of a class. A common pattern used to address this problem is to save a persistent reference to the class constructor for later `instanceof` checks. napi_value MyClass_constructor = NULL; status = napi_get_reference_value(env, MyClass::es_constructor, &MyClass_constructor); assert(napi_ok == status); bool is_instance = false; status = napi_instanceof(env, es_this, MyClass_constructor, &is_instance); assert(napi_ok == status); if (is_instance) { // napi_unwrap() ... } else { // otherwise... } The reference must be freed once it is no longer needed. There are occasions where `napi_instanceof()` is insufficient for ensuring that a JavaScript object is a wrapper for a certain native type. This is the case especially when wrapped JavaScript objects are passed back into the addon via static methods rather than as the `this` value of prototype methods. In such cases there is a chance that they may be unwrapped incorrectly. const myAddon = require('./build/Release/my_addon.node'); // `openDatabase()` returns a JavaScript object that wraps a native database // handle. const dbHandle = myAddon.openDatabase(); // `query()` returns a JavaScript object that wraps a native query handle. const queryHandle = myAddon.query(dbHandle, 'Gimme ALL the things!'); // There is an accidental error in the line below. The first parameter to // `myAddon.queryHasRecords()` should be the database handle (`dbHandle`), not // the query handle (`query`), so the correct condition for the while-loop // should be // // myAddon.queryHasRecords(dbHandle, queryHandle) // while (myAddon.queryHasRecords(queryHandle, dbHandle)) { // retrieve records } In the above example `myAddon.queryHasRecords()` is a method that accepts two arguments. The first is a database handle and the second is a query handle. Internally, it unwraps the first argument and casts the resulting pointer to a native database handle. It then unwraps the second argument and casts the resulting pointer to a query handle. If the arguments are passed in the wrong order, the casts will work, however, there is a good chance that the underlying database operation will fail, or will even cause an invalid memory access. To ensure that the pointer retrieved from the first argument is indeed a pointer to a database handle and, similarly, that the pointer retrieved from the second argument is indeed a pointer to a query handle, the implementation of `queryHasRecords()` has to perform a type validation. Retaining the JavaScript class constructor from which the database handle was instantiated and the constructor from which the query handle was instantiated in `napi_ref`s can help, because `napi_instanceof()` can then be used to ensure that the instances passed into `queryHashRecords()` are indeed of the correct type. Unfortunately, `napi_instanceof()` does not protect against prototype manipulation. For example, the prototype of the database handle instance can be set to the prototype of the constructor for query handle instances. In this case, the database handle instance can appear as a query handle instance, and it will pass the `napi_instanceof()` test for a query handle instance, while still containing a pointer to a database handle. To this end, Node-API provides type-tagging capabilities. A type tag is a 128-bit integer unique to the addon. Node-API provides the `napi_type_tag` structure for storing a type tag. When such a value is passed along with a JavaScript object or external stored in a `napi_value` to `napi_type_tag_object()`, the JavaScript object will be "marked" with the type tag. The "mark" is invisible on the JavaScript side. When a JavaScript object arrives into a native binding, `napi_check_object_type_tag()` can be used along with the original type tag to determine whether the JavaScript object was previously "marked" with the type tag. This creates a type-checking capability of a higher fidelity than `napi_instanceof()` can provide, because such type- tagging survives prototype manipulation and addon unloading/reloading. Continuing the above example, the following skeleton addon implementation illustrates the use of `napi_type_tag_object()` and `napi_check_object_type_tag()`. // This value is the type tag for a database handle. The command // // uuidgen | sed -r -e 's/-//g' -e 's/(.{16})(.*)/0x\1, 0x\2/' // // can be used to obtain the two values with which to initialize the structure. static const napi_type_tag DatabaseHandleTypeTag = { 0x1edf75a38336451d, 0xa5ed9ce2e4c00c38 }; // This value is the type tag for a query handle. static const napi_type_tag QueryHandleTypeTag = { 0x9c73317f9fad44a3, 0x93c3920bf3b0ad6a }; static napi_value openDatabase(napi_env env, napi_callback_info info) { napi_status status; napi_value result; // Perform the underlying action which results in a database handle. DatabaseHandle* dbHandle = open_database(); // Create a new, empty JS object. status = napi_create_object(env, &result); if (status != napi_ok) return NULL; // Tag the object to indicate that it holds a pointer to a `DatabaseHandle`. status = napi_type_tag_object(env, result, &DatabaseHandleTypeTag); if (status != napi_ok) return NULL; // Store the pointer to the `DatabaseHandle` structure inside the JS object. status = napi_wrap(env, result, dbHandle, NULL, NULL, NULL); if (status != napi_ok) return NULL; return result; } // Later when we receive a JavaScript object purporting to be a database handle // we can use `napi_check_object_type_tag()` to ensure that it is indeed such a // handle. static napi_value query(napi_env env, napi_callback_info info) { napi_status status; size_t argc = 2; napi_value argv[2]; bool is_db_handle; status = napi_get_cb_info(env, info, &argc, argv, NULL, NULL); if (status != napi_ok) return NULL; // Check that the object passed as the first parameter has the previously // applied tag. status = napi_check_object_type_tag(env, argv[0], &DatabaseHandleTypeTag, &is_db_handle); if (status != napi_ok) return NULL; // Throw a `TypeError` if it doesn't. if (!is_db_handle) { // Throw a TypeError. return NULL; } } #### `napi_define_class`# Added in: v8.0.0 N-API version: 1 napi_status napi_define_class(napi_env env, const char* utf8name, size_t length, napi_callback constructor, void* data, size_t property_count, const napi_property_descriptor* properties, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] utf8name`: Name of the JavaScript constructor function. For clarity, it is recommended to use the C++ class name when wrapping a C++ class. * `[in] length`: The length of the `utf8name` in bytes, or `NAPI_AUTO_LENGTH` if it is null-terminated. * `[in] constructor`: Callback function that handles constructing instances of the class. When wrapping a C++ class, this method must be a static member with the `napi_callback` signature. A C++ class constructor cannot be used. `napi_callback` provides more details. * `[in] data`: Optional data to be passed to the constructor callback as the `data` property of the callback info. * `[in] property_count`: Number of items in the `properties` array argument. * `[in] properties`: Array of property descriptors describing static and instance data properties, accessors, and methods on the class See `napi_property_descriptor`. * `[out] result`: A `napi_value` representing the constructor function for the class. Returns `napi_ok` if the API succeeded. Defines a JavaScript class, including: * A JavaScript constructor function that has the class name. When wrapping a corresponding C++ class, the callback passed via `constructor` can be used to instantiate a new C++ class instance, which can then be placed inside the JavaScript object instance being constructed using `napi_wrap`. * Properties on the constructor function whose implementation can call corresponding static data properties, accessors, and methods of the C++ class (defined by property descriptors with the `napi_static` attribute). * Properties on the constructor function's `prototype` object. When wrapping a C++ class, non-static data properties, accessors, and methods of the C++ class can be called from the static functions given in the property descriptors without the `napi_static` attribute after retrieving the C++ class instance placed inside the JavaScript object instance by using `napi_unwrap`. When wrapping a C++ class, the C++ constructor callback passed via `constructor` should be a static method on the class that calls the actual class constructor, then wraps the new C++ instance in a JavaScript object, and returns the wrapper object. See `napi_wrap` for details. The JavaScript constructor function returned from `napi_define_class` is often saved and used later to construct new instances of the class from native code, and/or to check whether provided values are instances of the class. In that case, to prevent the function value from being garbage-collected, a strong persistent reference to it can be created using `napi_create_reference`, ensuring that the reference count is kept >= 1. Any non-`NULL` data which is passed to this API via the `data` parameter or via the `data` field of the `napi_property_descriptor` array items can be associated with the resulting JavaScript constructor (which is returned in the `result` parameter) and freed whenever the class is garbage-collected by passing both the JavaScript function and the data to `napi_add_finalizer`. #### `napi_wrap`# Added in: v8.0.0 N-API version: 1 napi_status napi_wrap(napi_env env, napi_value js_object, void* native_object, napi_finalize finalize_cb, void* finalize_hint, napi_ref* result); * `[in] env`: The environment that the API is invoked under. * `[in] js_object`: The JavaScript object that will be the wrapper for the native object. * `[in] native_object`: The native instance that will be wrapped in the JavaScript object. * `[in] finalize_cb`: Optional native callback that can be used to free the native instance when the JavaScript object has been garbage-collected. `napi_finalize` provides more details. * `[in] finalize_hint`: Optional contextual hint that is passed to the finalize callback. * `[out] result`: Optional reference to the wrapped object. Returns `napi_ok` if the API succeeded. Wraps a native instance in a JavaScript object. The native instance can be retrieved later using `napi_unwrap()`. When JavaScript code invokes a constructor for a class that was defined using `napi_define_class()`, the `napi_callback` for the constructor is invoked. After constructing an instance of the native class, the callback must then call `napi_wrap()` to wrap the newly constructed instance in the already-created JavaScript object that is the `this` argument to the constructor callback. (That `this` object was created from the constructor function's `prototype`, so it already has definitions of all the instance properties and methods.) Typically when wrapping a class instance, a finalize callback should be provided that simply deletes the native instance that is received as the `data` argument to the finalize callback. The optional returned reference is initially a weak reference, meaning it has a reference count of 0. Typically this reference count would be incremented temporarily during async operations that require the instance to remain valid. Caution: The optional returned reference (if obtained) should be deleted via `napi_delete_reference` ONLY in response to the finalize callback invocation. If it is deleted before then, then the finalize callback may never be invoked. Therefore, when obtaining a reference a finalize callback is also required in order to enable correct disposal of the reference. Finalizer callbacks may be deferred, leaving a window where the object has been garbage collected (and the weak reference is invalid) but the finalizer hasn't been called yet. When using `napi_get_reference_value()` on weak references returned by `napi_wrap()`, you should still handle an empty result. Calling `napi_wrap()` a second time on an object will return an error. To associate another native instance with the object, use `napi_remove_wrap()` first. #### `napi_unwrap`# Added in: v8.0.0 N-API version: 1 napi_status napi_unwrap(napi_env env, napi_value js_object, void** result); * `[in] env`: The environment that the API is invoked under. * `[in] js_object`: The object associated with the native instance. * `[out] result`: Pointer to the wrapped native instance. Returns `napi_ok` if the API succeeded. Retrieves a native instance that was previously wrapped in a JavaScript object using `napi_wrap()`. When JavaScript code invokes a method or property accessor on the class, the corresponding `napi_callback` is invoked. If the callback is for an instance method or accessor, then the `this` argument to the callback is the wrapper object; the wrapped C++ instance that is the target of the call can be obtained then by calling `napi_unwrap()` on the wrapper object. #### `napi_remove_wrap`# Added in: v8.5.0 N-API version: 1 napi_status napi_remove_wrap(napi_env env, napi_value js_object, void** result); * `[in] env`: The environment that the API is invoked under. * `[in] js_object`: The object associated with the native instance. * `[out] result`: Pointer to the wrapped native instance. Returns `napi_ok` if the API succeeded. Retrieves a native instance that was previously wrapped in the JavaScript object `js_object` using `napi_wrap()` and removes the wrapping. If a finalize callback was associated with the wrapping, it will no longer be called when the JavaScript object becomes garbage-collected. #### `napi_type_tag_object`# Added in: v14.8.0, v12.19.0 N-API version: 8 napi_status napi_type_tag_object(napi_env env, napi_value js_object, const napi_type_tag* type_tag); * `[in] env`: The environment that the API is invoked under. * `[in] js_object`: The JavaScript object or external to be marked. * `[in] type_tag`: The tag with which the object is to be marked. Returns `napi_ok` if the API succeeded. Associates the value of the `type_tag` pointer with the JavaScript object or external. `napi_check_object_type_tag()` can then be used to compare the tag that was attached to the object with one owned by the addon to ensure that the object has the right type. If the object already has an associated type tag, this API will return `napi_invalid_arg`. #### `napi_check_object_type_tag`# Added in: v14.8.0, v12.19.0 N-API version: 8 napi_status napi_check_object_type_tag(napi_env env, napi_value js_object, const napi_type_tag* type_tag, bool* result); * `[in] env`: The environment that the API is invoked under. * `[in] js_object`: The JavaScript object or external whose type tag to examine. * `[in] type_tag`: The tag with which to compare any tag found on the object. * `[out] result`: Whether the type tag given matched the type tag on the object. `false` is also returned if no type tag was found on the object. Returns `napi_ok` if the API succeeded. Compares the pointer given as `type_tag` with any that can be found on `js_object`. If no tag is found on `js_object` or, if a tag is found but it does not match `type_tag`, then `result` is set to `false`. If a tag is found and it matches `type_tag`, then `result` is set to `true`. #### `napi_add_finalizer`# Added in: v8.0.0 N-API version: 5 napi_status napi_add_finalizer(napi_env env, napi_value js_object, void* finalize_data, node_api_basic_finalize finalize_cb, void* finalize_hint, napi_ref* result); * `[in] env`: The environment that the API is invoked under. * `[in] js_object`: The JavaScript object to which the native data will be attached. * `[in] finalize_data`: Optional data to be passed to `finalize_cb`. * `[in] finalize_cb`: Native callback that will be used to free the native data when the JavaScript object has been garbage-collected. `napi_finalize` provides more details. * `[in] finalize_hint`: Optional contextual hint that is passed to the finalize callback. * `[out] result`: Optional reference to the JavaScript object. Returns `napi_ok` if the API succeeded. Adds a `napi_finalize` callback which will be called when the JavaScript object in `js_object` has been garbage-collected. This API can be called multiple times on a single JavaScript object. Caution: The optional returned reference (if obtained) should be deleted via `napi_delete_reference` ONLY in response to the finalize callback invocation. If it is deleted before then, then the finalize callback may never be invoked. Therefore, when obtaining a reference a finalize callback is also required in order to enable correct disposal of the reference. ##### `node_api_post_finalizer`# Added in: v21.0.0, v20.10.0, v18.19.0 Stability: 1 \- Experimental napi_status node_api_post_finalizer(node_api_basic_env env, napi_finalize finalize_cb, void* finalize_data, void* finalize_hint); * `[in] env`: The environment that the API is invoked under. * `[in] finalize_cb`: Native callback that will be used to free the native data when the JavaScript object has been garbage-collected. `napi_finalize` provides more details. * `[in] finalize_data`: Optional data to be passed to `finalize_cb`. * `[in] finalize_hint`: Optional contextual hint that is passed to the finalize callback. Returns `napi_ok` if the API succeeded. Schedules a `napi_finalize` callback to be called asynchronously in the event loop. Normally, finalizers are called while the GC (garbage collector) collects objects. At that point calling any Node-API that may cause changes in the GC state will be disabled and will crash Node.js. `node_api_post_finalizer` helps to work around this limitation by allowing the add-on to defer calls to such Node-APIs to a point in time outside of the GC finalization. ### Simple asynchronous operations# Addon modules often need to leverage async helpers from libuv as part of their implementation. This allows them to schedule work to be executed asynchronously so that their methods can return in advance of the work being completed. This allows them to avoid blocking overall execution of the Node.js application. Node-API provides an ABI-stable interface for these supporting functions which covers the most common asynchronous use cases. Node-API defines the `napi_async_work` structure which is used to manage asynchronous workers. Instances are created/deleted with `napi_create_async_work` and `napi_delete_async_work`. The `execute` and `complete` callbacks are functions that will be invoked when the executor is ready to execute and when it completes its task respectively. The `execute` function should avoid making any Node-API calls that could result in the execution of JavaScript or interaction with JavaScript objects. Most often, any code that needs to make Node-API calls should be made in `complete` callback instead. Avoid using the `napi_env` parameter in the execute callback as it will likely execute JavaScript. These functions implement the following interfaces: typedef void (*napi_async_execute_callback)(napi_env env, void* data); typedef void (*napi_async_complete_callback)(napi_env env, napi_status status, void* data); When these methods are invoked, the `data` parameter passed will be the addon-provided `void*` data that was passed into the `napi_create_async_work` call. Once created the async worker can be queued for execution using the `napi_queue_async_work` function: napi_status napi_queue_async_work(node_api_basic_env env, napi_async_work work); `napi_cancel_async_work` can be used if the work needs to be cancelled before the work has started execution. After calling `napi_cancel_async_work`, the `complete` callback will be invoked with a status value of `napi_cancelled`. The work should not be deleted before the `complete` callback invocation, even when it was cancelled. #### `napi_create_async_work`# History VersionChanges v8.6.0 Added `async_resource` and `async_resource_name` parameters. v8.0.0 Added in: v8.0.0 N-API version: 1 napi_status napi_create_async_work(napi_env env, napi_value async_resource, napi_value async_resource_name, napi_async_execute_callback execute, napi_async_complete_callback complete, void* data, napi_async_work* result); * `[in] env`: The environment that the API is invoked under. * `[in] async_resource`: An optional object associated with the async work that will be passed to possible `async_hooks` `init` hooks. * `[in] async_resource_name`: Identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API. * `[in] execute`: The native function which should be called to execute the logic asynchronously. The given function is called from a worker pool thread and can execute in parallel with the main event loop thread. * `[in] complete`: The native function which will be called when the asynchronous logic is completed or is cancelled. The given function is called from the main event loop thread. `napi_async_complete_callback` provides more details. * `[in] data`: User-provided data context. This will be passed back into the execute and complete functions. * `[out] result`: `napi_async_work*` which is the handle to the newly created async work. Returns `napi_ok` if the API succeeded. This API allocates a work object that is used to execute logic asynchronously. It should be freed using `napi_delete_async_work` once the work is no longer required. `async_resource_name` should be a null-terminated, UTF-8-encoded string. The `async_resource_name` identifier is provided by the user and should be representative of the type of async work being performed. It is also recommended to apply namespacing to the identifier, e.g. by including the module name. See the `async_hooks` documentation for more information. #### `napi_delete_async_work`# Added in: v8.0.0 N-API version: 1 napi_status napi_delete_async_work(napi_env env, napi_async_work work); * `[in] env`: The environment that the API is invoked under. * `[in] work`: The handle returned by the call to `napi_create_async_work`. Returns `napi_ok` if the API succeeded. This API frees a previously allocated work object. This API can be called even if there is a pending JavaScript exception. #### `napi_queue_async_work`# Added in: v8.0.0 N-API version: 1 napi_status napi_queue_async_work(node_api_basic_env env, napi_async_work work); * `[in] env`: The environment that the API is invoked under. * `[in] work`: The handle returned by the call to `napi_create_async_work`. Returns `napi_ok` if the API succeeded. This API requests that the previously allocated work be scheduled for execution. Once it returns successfully, this API must not be called again with the same `napi_async_work` item or the result will be undefined. #### `napi_cancel_async_work`# Added in: v8.0.0 N-API version: 1 napi_status napi_cancel_async_work(node_api_basic_env env, napi_async_work work); * `[in] env`: The environment that the API is invoked under. * `[in] work`: The handle returned by the call to `napi_create_async_work`. Returns `napi_ok` if the API succeeded. This API cancels queued work if it has not yet been started. If it has already started executing, it cannot be cancelled and `napi_generic_failure` will be returned. If successful, the `complete` callback will be invoked with a status value of `napi_cancelled`. The work should not be deleted before the `complete` callback invocation, even if it has been successfully cancelled. This API can be called even if there is a pending JavaScript exception. ### Custom asynchronous operations# The simple asynchronous work APIs above may not be appropriate for every scenario. When using any other asynchronous mechanism, the following APIs are necessary to ensure an asynchronous operation is properly tracked by the runtime. #### `napi_async_init`# Added in: v8.6.0 N-API version: 1 napi_status napi_async_init(napi_env env, napi_value async_resource, napi_value async_resource_name, napi_async_context* result) * `[in] env`: The environment that the API is invoked under. * `[in] async_resource`: Object associated with the async work that will be passed to possible `async_hooks` `init` hooks and can be accessed by `async_hooks.executionAsyncResource()`. * `[in] async_resource_name`: Identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API. * `[out] result`: The initialized async context. Returns `napi_ok` if the API succeeded. The `async_resource` object needs to be kept alive until `napi_async_destroy` to keep `async_hooks` related API acts correctly. In order to retain ABI compatibility with previous versions, `napi_async_context`s are not maintaining the strong reference to the `async_resource` objects to avoid introducing causing memory leaks. However, if the `async_resource` is garbage collected by JavaScript engine before the `napi_async_context` was destroyed by `napi_async_destroy`, calling `napi_async_context` related APIs like `napi_open_callback_scope` and `napi_make_callback` can cause problems like loss of async context when using the `AsyncLocalStorage` API. In order to retain ABI compatibility with previous versions, passing `NULL` for `async_resource` does not result in an error. However, this is not recommended as this will result in undesirable behavior with `async_hooks` `init` hooks and `async_hooks.executionAsyncResource()` as the resource is now required by the underlying `async_hooks` implementation in order to provide the linkage between async callbacks. #### `napi_async_destroy`# Added in: v8.6.0 N-API version: 1 napi_status napi_async_destroy(napi_env env, napi_async_context async_context); * `[in] env`: The environment that the API is invoked under. * `[in] async_context`: The async context to be destroyed. Returns `napi_ok` if the API succeeded. This API can be called even if there is a pending JavaScript exception. #### `napi_make_callback`# History VersionChanges v8.6.0 Added `async_context` parameter. v8.0.0 Added in: v8.0.0 N-API version: 1 NAPI_EXTERN napi_status napi_make_callback(napi_env env, napi_async_context async_context, napi_value recv, napi_value func, size_t argc, const napi_value* argv, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] async_context`: Context for the async operation that is invoking the callback. This should normally be a value previously obtained from `napi_async_init`. In order to retain ABI compatibility with previous versions, passing `NULL` for `async_context` does not result in an error. However, this results in incorrect operation of async hooks. Potential issues include loss of async context when using the `AsyncLocalStorage` API. * `[in] recv`: The `this` value passed to the called function. * `[in] func`: `napi_value` representing the JavaScript function to be invoked. * `[in] argc`: The count of elements in the `argv` array. * `[in] argv`: Array of JavaScript values as `napi_value` representing the arguments to the function. If `argc` is zero this parameter may be omitted by passing in `NULL`. * `[out] result`: `napi_value` representing the JavaScript object returned. Returns `napi_ok` if the API succeeded. This method allows a JavaScript function object to be called from a native add-on. This API is similar to `napi_call_function`. However, it is used to call from native code back into JavaScript after returning from an async operation (when there is no other script on the stack). It is a fairly simple wrapper around `node::MakeCallback`. Note it is not necessary to use `napi_make_callback` from within a `napi_async_complete_callback`; in that situation the callback's async context has already been set up, so a direct call to `napi_call_function` is sufficient and appropriate. Use of the `napi_make_callback` function may be required when implementing custom async behavior that does not use `napi_create_async_work`. Any `process.nextTick`s or Promises scheduled on the microtask queue by JavaScript during the callback are ran before returning back to C/C++. #### `napi_open_callback_scope`# Added in: v9.6.0 N-API version: 3 NAPI_EXTERN napi_status napi_open_callback_scope(napi_env env, napi_value resource_object, napi_async_context context, napi_callback_scope* result) * `[in] env`: The environment that the API is invoked under. * `[in] resource_object`: An object associated with the async work that will be passed to possible `async_hooks` `init` hooks. This parameter has been deprecated and is ignored at runtime. Use the `async_resource` parameter in `napi_async_init` instead. * `[in] context`: Context for the async operation that is invoking the callback. This should be a value previously obtained from `napi_async_init`. * `[out] result`: The newly created scope. There are cases (for example, resolving promises) where it is necessary to have the equivalent of the scope associated with a callback in place when making certain Node-API calls. If there is no other script on the stack the `napi_open_callback_scope` and `napi_close_callback_scope` functions can be used to open/close the required scope. #### `napi_close_callback_scope`# Added in: v9.6.0 N-API version: 3 NAPI_EXTERN napi_status napi_close_callback_scope(napi_env env, napi_callback_scope scope) * `[in] env`: The environment that the API is invoked under. * `[in] scope`: The scope to be closed. This API can be called even if there is a pending JavaScript exception. ### Version management# #### `napi_get_node_version`# Added in: v8.4.0 N-API version: 1 typedef struct { uint32_t major; uint32_t minor; uint32_t patch; const char* release; } napi_node_version; napi_status napi_get_node_version(node_api_basic_env env, const napi_node_version** version); * `[in] env`: The environment that the API is invoked under. * `[out] version`: A pointer to version information for Node.js itself. Returns `napi_ok` if the API succeeded. This function fills the `version` struct with the major, minor, and patch version of Node.js that is currently running, and the `release` field with the value of `process.release.name`. The returned buffer is statically allocated and does not need to be freed. #### `napi_get_version`# Added in: v8.0.0 N-API version: 1 napi_status napi_get_version(node_api_basic_env env, uint32_t* result); * `[in] env`: The environment that the API is invoked under. * `[out] result`: The highest version of Node-API supported. Returns `napi_ok` if the API succeeded. This API returns the highest Node-API version supported by the Node.js runtime. Node-API is planned to be additive such that newer releases of Node.js may support additional API functions. In order to allow an addon to use a newer function when running with versions of Node.js that support it, while providing fallback behavior when running with Node.js versions that don't support it: * Call `napi_get_version()` to determine if the API is available. * If available, dynamically load a pointer to the function using `uv_dlsym()`. * Use the dynamically loaded pointer to invoke the function. * If the function is not available, provide an alternate implementation that does not use the function. ### Memory management# #### `napi_adjust_external_memory`# Added in: v8.5.0 N-API version: 1 NAPI_EXTERN napi_status napi_adjust_external_memory(node_api_basic_env env, int64_t change_in_bytes, int64_t* result); * `[in] env`: The environment that the API is invoked under. * `[in] change_in_bytes`: The change in externally allocated memory that is kept alive by JavaScript objects. * `[out] result`: The adjusted value. This value should reflect the total amount of external memory with the given `change_in_bytes` included. The absolute value of the returned value should not be depended on. For example, implementations may use a single counter for all addons, or a counter for each addon. Returns `napi_ok` if the API succeeded. This function gives the runtime an indication of the amount of externally allocated memory that is kept alive by JavaScript objects (i.e. a JavaScript object that points to its own memory allocated by a native addon). Registering externally allocated memory may, but is not guaranteed to, trigger global garbage collections more often than it would otherwise. This function is expected to be called in a manner such that an addon does not decrease the external memory more than it has increased the external memory. ### Promises# Node-API provides facilities for creating `Promise` objects as described in Section Promise objects of the ECMA specification. It implements promises as a pair of objects. When a promise is created by `napi_create_promise()`, a "deferred" object is created and returned alongside the `Promise`. The deferred object is bound to the created `Promise` and is the only means to resolve or reject the `Promise` using `napi_resolve_deferred()` or `napi_reject_deferred()`. The deferred object that is created by `napi_create_promise()` is freed by `napi_resolve_deferred()` or `napi_reject_deferred()`. The `Promise` object may be returned to JavaScript where it can be used in the usual fashion. For example, to create a promise and pass it to an asynchronous worker: napi_deferred deferred; napi_value promise; napi_status status; // Create the promise. status = napi_create_promise(env, &deferred, &promise); if (status != napi_ok) return NULL; // Pass the deferred to a function that performs an asynchronous action. do_something_asynchronous(deferred); // Return the promise to JS return promise; The above function `do_something_asynchronous()` would perform its asynchronous action and then it would resolve or reject the deferred, thereby concluding the promise and freeing the deferred: napi_deferred deferred; napi_value undefined; napi_status status; // Create a value with which to conclude the deferred. status = napi_get_undefined(env, &undefined); if (status != napi_ok) return NULL; // Resolve or reject the promise associated with the deferred depending on // whether the asynchronous action succeeded. if (asynchronous_action_succeeded) { status = napi_resolve_deferred(env, deferred, undefined); } else { status = napi_reject_deferred(env, deferred, undefined); } if (status != napi_ok) return NULL; // At this point the deferred has been freed, so we should assign NULL to it. deferred = NULL; #### `napi_create_promise`# Added in: v8.5.0 N-API version: 1 napi_status napi_create_promise(napi_env env, napi_deferred* deferred, napi_value* promise); * `[in] env`: The environment that the API is invoked under. * `[out] deferred`: A newly created deferred object which can later be passed to `napi_resolve_deferred()` or `napi_reject_deferred()` to resolve resp. reject the associated promise. * `[out] promise`: The JavaScript promise associated with the deferred object. Returns `napi_ok` if the API succeeded. This API creates a deferred object and a JavaScript promise. #### `napi_resolve_deferred`# Added in: v8.5.0 N-API version: 1 napi_status napi_resolve_deferred(napi_env env, napi_deferred deferred, napi_value resolution); * `[in] env`: The environment that the API is invoked under. * `[in] deferred`: The deferred object whose associated promise to resolve. * `[in] resolution`: The value with which to resolve the promise. This API resolves a JavaScript promise by way of the deferred object with which it is associated. Thus, it can only be used to resolve JavaScript promises for which the corresponding deferred object is available. This effectively means that the promise must have been created using `napi_create_promise()` and the deferred object returned from that call must have been retained in order to be passed to this API. The deferred object is freed upon successful completion. #### `napi_reject_deferred`# Added in: v8.5.0 N-API version: 1 napi_status napi_reject_deferred(napi_env env, napi_deferred deferred, napi_value rejection); * `[in] env`: The environment that the API is invoked under. * `[in] deferred`: The deferred object whose associated promise to resolve. * `[in] rejection`: The value with which to reject the promise. This API rejects a JavaScript promise by way of the deferred object with which it is associated. Thus, it can only be used to reject JavaScript promises for which the corresponding deferred object is available. This effectively means that the promise must have been created using `napi_create_promise()` and the deferred object returned from that call must have been retained in order to be passed to this API. The deferred object is freed upon successful completion. #### `napi_is_promise`# Added in: v8.5.0 N-API version: 1 napi_status napi_is_promise(napi_env env, napi_value value, bool* is_promise); * `[in] env`: The environment that the API is invoked under. * `[in] value`: The value to examine * `[out] is_promise`: Flag indicating whether `promise` is a native promise object (that is, a promise object created by the underlying engine). ### Script execution# Node-API provides an API for executing a string containing JavaScript using the underlying JavaScript engine. #### `napi_run_script`# Added in: v8.5.0 N-API version: 1 NAPI_EXTERN napi_status napi_run_script(napi_env env, napi_value script, napi_value* result); * `[in] env`: The environment that the API is invoked under. * `[in] script`: A JavaScript string containing the script to execute. * `[out] result`: The value resulting from having executed the script. This function executes a string of JavaScript code and returns its result with the following caveats: * Unlike `eval`, this function does not allow the script to access the current lexical scope, and therefore also does not allow to access the module scope, meaning that pseudo-globals such as `require` will not be available. * The script can access the global scope. Function and `var` declarations in the script will be added to the `global` object. Variable declarations made using `let` and `const` will be visible globally, but will not be added to the `global` object. * The value of `this` is `global` within the script. ### libuv event loop# Node-API provides a function for getting the current event loop associated with a specific `napi_env`. #### `napi_get_uv_event_loop`# Added in: v9.3.0, v8.10.0 N-API version: 2 NAPI_EXTERN napi_status napi_get_uv_event_loop(node_api_basic_env env, struct uv_loop_s** loop); * `[in] env`: The environment that the API is invoked under. * `[out] loop`: The current libuv loop instance. Note: While libuv has been relatively stable over time, it does not provide an ABI stability guarantee. Use of this function should be avoided. Its use may result in an addon that does not work across Node.js versions. asynchronous-thread-safe-function-calls are an alternative for many use cases. ### Asynchronous thread-safe function calls# JavaScript functions can normally only be called from a native addon's main thread. If an addon creates additional threads, then Node-API functions that require a `napi_env`, `napi_value`, or `napi_ref` must not be called from those threads. When an addon has additional threads and JavaScript functions need to be invoked based on the processing completed by those threads, those threads must communicate with the addon's main thread so that the main thread can invoke the JavaScript function on their behalf. The thread-safe function APIs provide an easy way to do this. These APIs provide the type `napi_threadsafe_function` as well as APIs to create, destroy, and call objects of this type. `napi_create_threadsafe_function()` creates a persistent reference to a `napi_value` that holds a JavaScript function which can be called from multiple threads. The calls happen asynchronously. This means that values with which the JavaScript callback is to be called will be placed in a queue, and, for each value in the queue, a call will eventually be made to the JavaScript function. Upon creation of a `napi_threadsafe_function` a `napi_finalize` callback can be provided. This callback will be invoked on the main thread when the thread-safe function is about to be destroyed. It receives the context and the finalize data given during construction, and provides an opportunity for cleaning up after the threads e.g. by calling `uv_thread_join()`. Aside from the main loop thread, no threads should be using the thread-safe function after the finalize callback completes. The `context` given during the call to `napi_create_threadsafe_function()` can be retrieved from any thread with a call to `napi_get_threadsafe_function_context()`. #### Calling a thread-safe function# `napi_call_threadsafe_function()` can be used for initiating a call into JavaScript. `napi_call_threadsafe_function()` accepts a parameter which controls whether the API behaves blockingly. If set to `napi_tsfn_nonblocking`, the API behaves non-blockingly, returning `napi_queue_full` if the queue was full, preventing data from being successfully added to the queue. If set to `napi_tsfn_blocking`, the API blocks until space becomes available in the queue. `napi_call_threadsafe_function()` never blocks if the thread-safe function was created with a maximum queue size of 0. `napi_call_threadsafe_function()` should not be called with `napi_tsfn_blocking` from a JavaScript thread, because, if the queue is full, it may cause the JavaScript thread to deadlock. The actual call into JavaScript is controlled by the callback given via the `call_js_cb` parameter. `call_js_cb` is invoked on the main thread once for each value that was placed into the queue by a successful call to `napi_call_threadsafe_function()`. If such a callback is not given, a default callback will be used, and the resulting JavaScript call will have no arguments. The `call_js_cb` callback receives the JavaScript function to call as a `napi_value` in its parameters, as well as the `void*` context pointer used when creating the `napi_threadsafe_function`, and the next data pointer that was created by one of the secondary threads. The callback can then use an API such as `napi_call_function()` to call into JavaScript. The callback may also be invoked with `env` and `call_js_cb` both set to `NULL` to indicate that calls into JavaScript are no longer possible, while items remain in the queue that may need to be freed. This normally occurs when the Node.js process exits while there is a thread-safe function still active. It is not necessary to call into JavaScript via `napi_make_callback()` because Node-API runs `call_js_cb` in a context appropriate for callbacks. Zero or more queued items may be invoked in each tick of the event loop. Applications should not depend on a specific behavior other than progress in invoking callbacks will be made and events will be invoked as time moves forward. #### Reference counting of thread-safe functions# Threads can be added to and removed from a `napi_threadsafe_function` object during its existence. Thus, in addition to specifying an initial number of threads upon creation, `napi_acquire_threadsafe_function` can be called to indicate that a new thread will start making use of the thread-safe function. Similarly, `napi_release_threadsafe_function` can be called to indicate that an existing thread will stop making use of the thread-safe function. `napi_threadsafe_function` objects are destroyed when every thread which uses the object has called `napi_release_threadsafe_function()` or has received a return status of `napi_closing` in response to a call to `napi_call_threadsafe_function`. The queue is emptied before the `napi_threadsafe_function` is destroyed. `napi_release_threadsafe_function()` should be the last API call made in conjunction with a given `napi_threadsafe_function`, because after the call completes, there is no guarantee that the `napi_threadsafe_function` is still allocated. For the same reason, do not use a thread-safe function after receiving a return value of `napi_closing` in response to a call to `napi_call_threadsafe_function`. Data associated with the `napi_threadsafe_function` can be freed in its `napi_finalize` callback which was passed to `napi_create_threadsafe_function()`. The parameter `initial_thread_count` of `napi_create_threadsafe_function` marks the initial number of acquisitions of the thread-safe functions, instead of calling `napi_acquire_threadsafe_function` multiple times at creation. Once the number of threads making use of a `napi_threadsafe_function` reaches zero, no further threads can start making use of it by calling `napi_acquire_threadsafe_function()`. In fact, all subsequent API calls associated with it, except `napi_release_threadsafe_function()`, will return an error value of `napi_closing`. The thread-safe function can be "aborted" by giving a value of `napi_tsfn_abort` to `napi_release_threadsafe_function()`. This will cause all subsequent APIs associated with the thread-safe function except `napi_release_threadsafe_function()` to return `napi_closing` even before its reference count reaches zero. In particular, `napi_call_threadsafe_function()` will return `napi_closing`, thus informing the threads that it is no longer possible to make asynchronous calls to the thread-safe function. This can be used as a criterion for terminating the thread. Upon receiving a return value of `napi_closing` from `napi_call_threadsafe_function()` a thread must not use the thread-safe function anymore because it is no longer guaranteed to be allocated. #### Deciding whether to keep the process running# Similarly to libuv handles, thread-safe functions can be "referenced" and "unreferenced". A "referenced" thread-safe function will cause the event loop on the thread on which it is created to remain alive until the thread-safe function is destroyed. In contrast, an "unreferenced" thread-safe function will not prevent the event loop from exiting. The APIs `napi_ref_threadsafe_function` and `napi_unref_threadsafe_function` exist for this purpose. Neither does `napi_unref_threadsafe_function` mark the thread-safe functions as able to be destroyed nor does `napi_ref_threadsafe_function` prevent it from being destroyed. #### `napi_create_threadsafe_function`# History VersionChanges v12.6.0, v10.17.0 Made `func` parameter optional with custom `call_js_cb`. v10.6.0 Added in: v10.6.0 N-API version: 4 NAPI_EXTERN napi_status napi_create_threadsafe_function(napi_env env, napi_value func, napi_value async_resource, napi_value async_resource_name, size_t max_queue_size, size_t initial_thread_count, void* thread_finalize_data, napi_finalize thread_finalize_cb, void* context, napi_threadsafe_function_call_js call_js_cb, napi_threadsafe_function* result); * `[in] env`: The environment that the API is invoked under. * `[in] func`: An optional JavaScript function to call from another thread. It must be provided if `NULL` is passed to `call_js_cb`. * `[in] async_resource`: An optional object associated with the async work that will be passed to possible `async_hooks` `init` hooks. * `[in] async_resource_name`: A JavaScript string to provide an identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API. * `[in] max_queue_size`: Maximum size of the queue. `0` for no limit. * `[in] initial_thread_count`: The initial number of acquisitions, i.e. the initial number of threads, including the main thread, which will be making use of this function. * `[in] thread_finalize_data`: Optional data to be passed to `thread_finalize_cb`. * `[in] thread_finalize_cb`: Optional function to call when the `napi_threadsafe_function` is being destroyed. * `[in] context`: Optional data to attach to the resulting `napi_threadsafe_function`. * `[in] call_js_cb`: Optional callback which calls the JavaScript function in response to a call on a different thread. This callback will be called on the main thread. If not given, the JavaScript function will be called with no parameters and with `undefined` as its `this` value. `napi_threadsafe_function_call_js` provides more details. * `[out] result`: The asynchronous thread-safe JavaScript function. Change History: * Version 10 (`NAPI_VERSION` is defined as `10` or higher): Uncaught exceptions thrown in `call_js_cb` are handled with the `'uncaughtException'` event, instead of being ignored. #### `napi_get_threadsafe_function_context`# Added in: v10.6.0 N-API version: 4 NAPI_EXTERN napi_status napi_get_threadsafe_function_context(napi_threadsafe_function func, void** result); * `[in] func`: The thread-safe function for which to retrieve the context. * `[out] result`: The location where to store the context. This API may be called from any thread which makes use of `func`. #### `napi_call_threadsafe_function`# History VersionChanges v14.5.0 Support for `napi_would_deadlock` has been reverted. v14.1.0 Return `napi_would_deadlock` when called with `napi_tsfn_blocking` from the main thread or a worker thread and the queue is full. v10.6.0 Added in: v10.6.0 N-API version: 4 NAPI_EXTERN napi_status napi_call_threadsafe_function(napi_threadsafe_function func, void* data, napi_threadsafe_function_call_mode is_blocking); * `[in] func`: The asynchronous thread-safe JavaScript function to invoke. * `[in] data`: Data to send into JavaScript via the callback `call_js_cb` provided during the creation of the thread-safe JavaScript function. * `[in] is_blocking`: Flag whose value can be either `napi_tsfn_blocking` to indicate that the call should block if the queue is full or `napi_tsfn_nonblocking` to indicate that the call should return immediately with a status of `napi_queue_full` whenever the queue is full. This API should not be called with `napi_tsfn_blocking` from a JavaScript thread, because, if the queue is full, it may cause the JavaScript thread to deadlock. This API will return `napi_closing` if `napi_release_threadsafe_function()` was called with `abort` set to `napi_tsfn_abort` from any thread. The value is only added to the queue if the API returns `napi_ok`. This API may be called from any thread which makes use of `func`. #### `napi_acquire_threadsafe_function`# Added in: v10.6.0 N-API version: 4 NAPI_EXTERN napi_status napi_acquire_threadsafe_function(napi_threadsafe_function func); * `[in] func`: The asynchronous thread-safe JavaScript function to start making use of. A thread should call this API before passing `func` to any other thread-safe function APIs to indicate that it will be making use of `func`. This prevents `func` from being destroyed when all other threads have stopped making use of it. This API may be called from any thread which will start making use of `func`. #### `napi_release_threadsafe_function`# Added in: v10.6.0 N-API version: 4 NAPI_EXTERN napi_status napi_release_threadsafe_function(napi_threadsafe_function func, napi_threadsafe_function_release_mode mode); * `[in] func`: The asynchronous thread-safe JavaScript function whose reference count to decrement. * `[in] mode`: Flag whose value can be either `napi_tsfn_release` to indicate that the current thread will make no further calls to the thread-safe function, or `napi_tsfn_abort` to indicate that in addition to the current thread, no other thread should make any further calls to the thread-safe function. If set to `napi_tsfn_abort`, further calls to `napi_call_threadsafe_function()` will return `napi_closing`, and no further values will be placed in the queue. A thread should call this API when it stops making use of `func`. Passing `func` to any thread-safe APIs after having called this API has undefined results, as `func` may have been destroyed. This API may be called from any thread which will stop making use of `func`. #### `napi_ref_threadsafe_function`# Added in: v10.6.0 N-API version: 4 NAPI_EXTERN napi_status napi_ref_threadsafe_function(node_api_basic_env env, napi_threadsafe_function func); * `[in] env`: The environment that the API is invoked under. * `[in] func`: The thread-safe function to reference. This API is used to indicate that the event loop running on the main thread should not exit until `func` has been destroyed. Similar to `uv_ref` it is also idempotent. Neither does `napi_unref_threadsafe_function` mark the thread-safe functions as able to be destroyed nor does `napi_ref_threadsafe_function` prevent it from being destroyed. `napi_acquire_threadsafe_function` and `napi_release_threadsafe_function` are available for that purpose. This API may only be called from the main thread. #### `napi_unref_threadsafe_function`# Added in: v10.6.0 N-API version: 4 NAPI_EXTERN napi_status napi_unref_threadsafe_function(node_api_basic_env env, napi_threadsafe_function func); * `[in] env`: The environment that the API is invoked under. * `[in] func`: The thread-safe function to unreference. This API is used to indicate that the event loop running on the main thread may exit before `func` is destroyed. Similar to `uv_unref` it is also idempotent. This API may only be called from the main thread. ### Miscellaneous utilities# #### `node_api_get_module_file_name`# Added in: v15.9.0, v14.18.0, v12.22.0 N-API version: 9 NAPI_EXTERN napi_status node_api_get_module_file_name(node_api_basic_env env, const char** result); * `[in] env`: The environment that the API is invoked under. * `[out] result`: A URL containing the absolute path of the location from which the add-on was loaded. For a file on the local file system it will start with `file://`. The string is null-terminated and owned by `env` and must thus not be modified or freed. `result` may be an empty string if the add-on loading process fails to establish the add-on's file name during loading. ## C++ embedder API# Node.js provides a number of C++ APIs that can be used to execute JavaScript in a Node.js environment from other C++ software. The documentation for these APIs can be found in src/node.h in the Node.js source tree. In addition to the APIs exposed by Node.js, some required concepts are provided by the V8 embedder API. Because using Node.js as an embedded library is different from writing code that is executed by Node.js, breaking changes do not follow typical Node.js deprecation policy and may occur on each semver-major release without prior warning. ### Example embedding application# The following sections will provide an overview over how to use these APIs to create an application from scratch that will perform the equivalent of `node -e `, i.e. that will take a piece of JavaScript and run it in a Node.js-specific environment. The full code can be found in the Node.js source tree. #### Setting up a per-process state# Node.js requires some per-process state management in order to run: * Arguments parsing for Node.js CLI options, * V8 per-process requirements, such as a `v8::Platform` instance. The following example shows how these can be set up. Some class names are from the `node` and `v8` C++ namespaces, respectively. int main(int argc, char** argv) { argv = uv_setup_args(argc, argv); std::vector args(argv, argv + argc); // Parse Node.js CLI options, and print any errors that have occurred while // trying to parse them. std::unique_ptr result = node::InitializeOncePerProcess(args, { node::ProcessInitializationFlags::kNoInitializeV8, node::ProcessInitializationFlags::kNoInitializeNodeV8Platform }); for (const std::string& error : result->errors()) fprintf(stderr, "%s: %s\n", args[0].c_str(), error.c_str()); if (result->early_return() != 0) { return result->exit_code(); } // Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way // to create a v8::Platform instance that Node.js can use when creating // Worker threads. When no `MultiIsolatePlatform` instance is present, // Worker threads are disabled. std::unique_ptr platform = MultiIsolatePlatform::Create(4); V8::InitializePlatform(platform.get()); V8::Initialize(); // See below for the contents of this function. int ret = RunNodeInstance( platform.get(), result->args(), result->exec_args()); V8::Dispose(); V8::DisposePlatform(); node::TearDownOncePerProcess(); return ret; } #### Setting up a per-instance state# History VersionChanges v15.0.0 The `CommonEnvironmentSetup` and `SpinEventLoop` utilities were added. Node.js has a concept of a “Node.js instance”, that is commonly being referred to as `node::Environment`. Each `node::Environment` is associated with: * Exactly one `v8::Isolate`, i.e. one JS Engine instance, * Exactly one `uv_loop_t`, i.e. one event loop, * A number of `v8::Context`s, but exactly one main `v8::Context`, and * One `node::IsolateData` instance that contains information that could be shared by multiple `node::Environment`s. The embedder should make sure that `node::IsolateData` is shared only among `node::Environment`s that use the same `v8::Isolate`, Node.js does not perform this check. In order to set up a `v8::Isolate`, an `v8::ArrayBuffer::Allocator` needs to be provided. One possible choice is the default Node.js allocator, which can be created through `node::ArrayBufferAllocator::Create()`. Using the Node.js allocator allows minor performance optimizations when addons use the Node.js C++ `Buffer` API, and is required in order to track `ArrayBuffer` memory in `process.memoryUsage()`. Additionally, each `v8::Isolate` that is used for a Node.js instance needs to be registered and unregistered with the `MultiIsolatePlatform` instance, if one is being used, in order for the platform to know which event loop to use for tasks scheduled by the `v8::Isolate`. The `node::NewIsolate()` helper function creates a `v8::Isolate`, sets it up with some Node.js-specific hooks (e.g. the Node.js error handler), and registers it with the platform automatically. int RunNodeInstance(MultiIsolatePlatform* platform, const std::vector& args, const std::vector& exec_args) { int exit_code = 0; // Setup up a libuv event loop, v8::Isolate, and Node.js Environment. std::vector errors; std::unique_ptr setup = CommonEnvironmentSetup::Create(platform, &errors, args, exec_args); if (!setup) { for (const std::string& err : errors) fprintf(stderr, "%s: %s\n", args[0].c_str(), err.c_str()); return 1; } Isolate* isolate = setup->isolate(); Environment* env = setup->env(); { Locker locker(isolate); Isolate::Scope isolate_scope(isolate); HandleScope handle_scope(isolate); // The v8::Context needs to be entered when node::CreateEnvironment() and // node::LoadEnvironment() are being called. Context::Scope context_scope(setup->context()); // Set up the Node.js instance for execution, and run code inside of it. // There is also a variant that takes a callback and provides it with // the `require` and `process` objects, so that it can manually compile // and run scripts as needed. // The `require` function inside this script does *not* access the file // system, and can only load built-in Node.js modules. // `module.createRequire()` is being used to create one that is able to // load files from the disk, and uses the standard CommonJS file loader // instead of the internal-only `require` function. MaybeLocal loadenv_ret = node::LoadEnvironment( env, "const publicRequire =" " require('node:module').createRequire(process.cwd() + '/');" "globalThis.require = publicRequire;" "require('node:vm').runInThisContext(process.argv[1]);"); if (loadenv_ret.IsEmpty()) // There has been a JS exception. return 1; exit_code = node::SpinEventLoop(env).FromMaybe(1); // node::Stop() can be used to explicitly stop the event loop and keep // further JavaScript from running. It can be called from any thread, // and will act like worker.terminate() if called from another thread. node::Stop(env); } return exit_code; } ## Child process# Stability: 2 \- Stable Source Code: lib/child_process.js The `node:child_process` module provides the ability to spawn subprocesses in a manner that is similar, but not identical, to `popen(3)`. This capability is primarily provided by the `child_process.spawn()` function: import { spawn } from 'node:child_process'; const ls = spawn('ls', ['-lh', '/usr']); ls.stdout.on('data', (data) => { console.log(`stdout: ${data}`); }); ls.stderr.on('data', (data) => { console.error(`stderr: ${data}`); }); ls.on('close', (code) => { console.log(`child process exited with code ${code}`); }); By default, pipes for `stdin`, `stdout`, and `stderr` are established between the parent Node.js process and the spawned subprocess. These pipes have limited (and platform-specific) capacity. If the subprocess writes to stdout in excess of that limit without the output being captured, the subprocess blocks, waiting for the pipe buffer to accept more data. This is identical to the behavior of pipes in the shell. Use the `{ stdio: 'ignore' }` option if the output will not be consumed. The command lookup is performed using the `options.env.PATH` environment variable if `env` is in the `options` object. Otherwise, `process.env.PATH` is used. If `options.env` is set without `PATH`, lookup on Unix is performed on a default search path search of `/usr/bin:/bin` (see your operating system's manual for execvpe/execvp), on Windows the current processes environment variable `PATH` is used. On Windows, environment variables are case-insensitive. Node.js lexicographically sorts the `env` keys and uses the first one that case-insensitively matches. Only first (in lexicographic order) entry will be passed to the subprocess. This might lead to issues on Windows when passing objects to the `env` option that have multiple variants of the same key, such as `PATH` and `Path`. The `child_process.spawn()` method spawns the child process asynchronously, without blocking the Node.js event loop. The `child_process.spawnSync()` function provides equivalent functionality in a synchronous manner that blocks the event loop until the spawned process either exits or is terminated. For convenience, the `node:child_process` module provides a handful of synchronous and asynchronous alternatives to `child_process.spawn()` and `child_process.spawnSync()`. Each of these alternatives are implemented on top of `child_process.spawn()` or `child_process.spawnSync()`. * `child_process.exec()`: spawns a shell and runs a command within that shell, passing the `stdout` and `stderr` to a callback function when complete. * `child_process.execFile()`: similar to `child_process.exec()` except that it spawns the command directly without first spawning a shell by default. * `child_process.fork()`: spawns a new Node.js process and invokes a specified module with an IPC communication channel established that allows sending messages between parent and child. * `child_process.execSync()`: a synchronous version of `child_process.exec()` that will block the Node.js event loop. * `child_process.execFileSync()`: a synchronous version of `child_process.execFile()` that will block the Node.js event loop. For certain use cases, such as automating shell scripts, the synchronous counterparts may be more convenient. In many cases, however, the synchronous methods can have significant impact on performance due to stalling the event loop while spawned processes complete. ### Asynchronous process creation# The `child_process.spawn()`, `child_process.fork()`, `child_process.exec()`, and `child_process.execFile()` methods all follow the idiomatic asynchronous programming pattern typical of other Node.js APIs. Each of the methods returns a `ChildProcess` instance. These objects implement the Node.js `EventEmitter` API, allowing the parent process to register listener functions that are called when certain events occur during the life cycle of the child process. The `child_process.exec()` and `child_process.execFile()` methods additionally allow for an optional `callback` function to be specified that is invoked when the child process terminates. #### Spawning `.bat` and `.cmd` files on Windows# The importance of the distinction between `child_process.exec()` and `child_process.execFile()` can vary based on platform. On Unix-type operating systems (Unix, Linux, macOS) `child_process.execFile()` can be more efficient because it does not spawn a shell by default. On Windows, however, `.bat` and `.cmd` files are not executable on their own without a terminal, and therefore cannot be launched using `child_process.execFile()`. When running on Windows, `.bat` and `.cmd` files can be invoked using `child_process.spawn()` with the `shell` option set, with `child_process.exec()`, or by spawning `cmd.exe` and passing the `.bat` or `.cmd` file as an argument (which is what the `shell` option and `child_process.exec()` do). In any case, if the script filename contains spaces it needs to be quoted. // OR... import { exec, spawn } from 'node:child_process'; exec('my.bat', (err, stdout, stderr) => { if (err) { console.error(err); return; } console.log(stdout); }); // Script with spaces in the filename: const bat = spawn('"my script.cmd" a b', { shell: true }); // or: exec('"my script.cmd" a b', (err, stdout, stderr) => { // ... }); #### `child_process.exec(command[, options][, callback])`# History VersionChanges v15.4.0 AbortSignal support was added. v16.4.0, v14.18.0 The `cwd` option can be a WHATWG `URL` object using `file:` protocol. v8.8.0 The `windowsHide` option is supported now. v0.1.90 Added in: v0.1.90 * `command` The command to run, with space-separated arguments. * `options` * `cwd` | Current working directory of the child process. Default: `process.cwd()`. * `env` Environment key-value pairs. Default: `process.env`. * `encoding` Default: `'utf8'` * `shell` Shell to execute the command with. See Shell requirements and Default Windows shell. Default: `'/bin/sh'` on Unix, `process.env.ComSpec` on Windows. * `signal` allows aborting the child process using an AbortSignal. * `timeout` Default: `0` * `maxBuffer` Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at `maxBuffer` and Unicode. Default: `1024 * 1024`. * `killSignal` | Default: `'SIGTERM'` * `uid` Sets the user identity of the process (see `setuid(2)`). * `gid` Sets the group identity of the process (see `setgid(2)`). * `windowsHide` Hide the subprocess console window that would normally be created on Windows systems. Default: `false`. * `callback` called with the output when process terminates. * `error` * `stdout` | * `stderr` | * Returns: Spawns a shell then executes the `command` within that shell, buffering any generated output. The `command` string passed to the exec function is processed directly by the shell and special characters (vary based on shell) need to be dealt with accordingly: import { exec } from 'node:child_process'; exec('"/path/to/test file/test.sh" arg1 arg2'); // Double quotes are used so that the space in the path is not interpreted as // a delimiter of multiple arguments. exec('echo "The \\$HOME variable is $HOME"'); // The $HOME variable is escaped in the first instance, but not in the second. Never pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution. If a `callback` function is provided, it is called with the arguments `(error, stdout, stderr)`. On success, `error` will be `null`. On error, `error` will be an instance of `Error`. The `error.code` property will be the exit code of the process. By convention, any exit code other than `0` indicates an error. `error.signal` will be the signal that terminated the process. The `stdout` and `stderr` arguments passed to the callback will contain the stdout and stderr output of the child process. By default, Node.js will decode the output as UTF-8 and pass strings to the callback. The `encoding` option can be used to specify the character encoding used to decode the stdout and stderr output. If `encoding` is `'buffer'`, or an unrecognized character encoding, `Buffer` objects will be passed to the callback instead. import { exec } from 'node:child_process'; exec('cat *.js missing_file | wc -l', (error, stdout, stderr) => { if (error) { console.error(`exec error: ${error}`); return; } console.log(`stdout: ${stdout}`); console.error(`stderr: ${stderr}`); }); If `timeout` is greater than `0`, the parent process will send the signal identified by the `killSignal` property (the default is `'SIGTERM'`) if the child process runs longer than `timeout` milliseconds. Unlike the `exec(3)` POSIX system call, `child_process.exec()` does not replace the existing process and uses a shell to execute the command. If this method is invoked as its `util.promisify()`ed version, it returns a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned `ChildProcess` instance is attached to the `Promise` as a `child` property. In case of an error (including any error resulting in an exit code other than 0), a rejected promise is returned, with the same `error` object given in the callback, but with two additional properties `stdout` and `stderr`. import { promisify } from 'node:util'; import child_process from 'node:child_process'; const exec = promisify(child_process.exec); async function lsExample() { const { stdout, stderr } = await exec('ls'); console.log('stdout:', stdout); console.error('stderr:', stderr); } lsExample(); If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`: import { exec } from 'node:child_process'; const controller = new AbortController(); const { signal } = controller; const child = exec('grep ssh', { signal }, (error) => { console.error(error); // an AbortError }); controller.abort(); #### `child_process.execFile(file[, args][, options][, callback])`# History VersionChanges v23.11.0, v22.15.0 Passing `args` when `shell` is set to `true` is deprecated. v16.4.0, v14.18.0 The `cwd` option can be a WHATWG `URL` object using `file:` protocol. v15.4.0, v14.17.0 AbortSignal support was added. v8.8.0 The `windowsHide` option is supported now. v0.1.91 Added in: v0.1.91 * `file` The name or path of the executable file to run. * `args` List of string arguments. * `options` * `cwd` | Current working directory of the child process. * `env` Environment key-value pairs. Default: `process.env`. * `encoding` Default: `'utf8'` * `timeout` Default: `0` * `maxBuffer` Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at `maxBuffer` and Unicode. Default: `1024 * 1024`. * `killSignal` | Default: `'SIGTERM'` * `uid` Sets the user identity of the process (see `setuid(2)`). * `gid` Sets the group identity of the process (see `setgid(2)`). * `windowsHide` Hide the subprocess console window that would normally be created on Windows systems. Default: `false`. * `windowsVerbatimArguments` No quoting or escaping of arguments is done on Windows. Ignored on Unix. Default: `false`. * `shell` | If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See Shell requirements and Default Windows shell. Default: `false` (no shell). * `signal` allows aborting the child process using an AbortSignal. * `callback` Called with the output when process terminates. * `error` * `stdout` | * `stderr` | * Returns: The `child_process.execFile()` function is similar to `child_process.exec()` except that it does not spawn a shell by default. Rather, the specified executable `file` is spawned directly as a new process making it slightly more efficient than `child_process.exec()`. The same options as `child_process.exec()` are supported. Since a shell is not spawned, behaviors such as I/O redirection and file globbing are not supported. import { execFile } from 'node:child_process'; const child = execFile('node', ['--version'], (error, stdout, stderr) => { if (error) { throw error; } console.log(stdout); }); The `stdout` and `stderr` arguments passed to the callback will contain the stdout and stderr output of the child process. By default, Node.js will decode the output as UTF-8 and pass strings to the callback. The `encoding` option can be used to specify the character encoding used to decode the stdout and stderr output. If `encoding` is `'buffer'`, or an unrecognized character encoding, `Buffer` objects will be passed to the callback instead. If this method is invoked as its `util.promisify()`ed version, it returns a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned `ChildProcess` instance is attached to the `Promise` as a `child` property. In case of an error (including any error resulting in an exit code other than 0), a rejected promise is returned, with the same `error` object given in the callback, but with two additional properties `stdout` and `stderr`. import { promisify } from 'node:util'; import child_process from 'node:child_process'; const execFile = promisify(child_process.execFile); async function getVersion() { const { stdout } = await execFile('node', ['--version']); console.log(stdout); } getVersion(); If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution. If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`: import { execFile } from 'node:child_process'; const controller = new AbortController(); const { signal } = controller; const child = execFile('node', ['--version'], { signal }, (error) => { console.error(error); // an AbortError }); controller.abort(); #### `child_process.fork(modulePath[, args][, options])`# History VersionChanges v17.4.0, v16.14.0 The `modulePath` parameter can be a WHATWG `URL` object using `file:` protocol. v16.4.0, v14.18.0 The `cwd` option can be a WHATWG `URL` object using `file:` protocol. v15.13.0, v14.18.0 timeout was added. v15.11.0, v14.18.0 killSignal for AbortSignal was added. v15.6.0, v14.17.0 AbortSignal support was added. v13.2.0, v12.16.0 The `serialization` option is supported now. v8.0.0 The `stdio` option can now be a string. v6.4.0 The `stdio` option is supported now. v0.5.0 Added in: v0.5.0 * `modulePath` | The module to run in the child. * `args` List of string arguments. * `options` * `cwd` | Current working directory of the child process. * `detached` Prepare child process to run independently of its parent process. Specific behavior depends on the platform (see `options.detached`). * `env` Environment key-value pairs. Default: `process.env`. * `execPath` Executable used to create the child process. * `execArgv` List of string arguments passed to the executable. Default: `process.execArgv`. * `gid` Sets the group identity of the process (see `setgid(2)`). * `serialization` Specify the kind of serialization used for sending messages between processes. Possible values are `'json'` and `'advanced'`. See Advanced serialization for more details. Default: `'json'`. * `signal` Allows closing the child process using an AbortSignal. * `killSignal` | The signal value to be used when the spawned process will be killed by timeout or abort signal. Default: `'SIGTERM'`. * `silent` If `true`, stdin, stdout, and stderr of the child process will be piped to the parent process, otherwise they will be inherited from the parent process, see the `'pipe'` and `'inherit'` options for `child_process.spawn()`'s `stdio` for more details. Default: `false`. * `stdio` | See `child_process.spawn()`'s `stdio`. When this option is provided, it overrides `silent`. If the array variant is used, it must contain exactly one item with value `'ipc'` or an error will be thrown. For instance `[0, 1, 2, 'ipc']`. * `uid` Sets the user identity of the process (see `setuid(2)`). * `windowsVerbatimArguments` No quoting or escaping of arguments is done on Windows. Ignored on Unix. Default: `false`. * `timeout` In milliseconds the maximum amount of time the process is allowed to run. Default: `undefined`. * Returns: The `child_process.fork()` method is a special case of `child_process.spawn()` used specifically to spawn new Node.js processes. Like `child_process.spawn()`, a `ChildProcess` object is returned. The returned `ChildProcess` will have an additional communication channel built-in that allows messages to be passed back and forth between the parent and child. See `subprocess.send()` for details. Keep in mind that spawned Node.js child processes are independent of the parent with exception of the IPC communication channel that is established between the two. Each process has its own memory, with their own V8 instances. Because of the additional resource allocations required, spawning a large number of child Node.js processes is not recommended. By default, `child_process.fork()` will spawn new Node.js instances using the `process.execPath` of the parent process. The `execPath` property in the `options` object allows for an alternative execution path to be used. Node.js processes launched with a custom `execPath` will communicate with the parent process using the file descriptor (fd) identified using the environment variable `NODE_CHANNEL_FD` on the child process. Unlike the `fork(2)` POSIX system call, `child_process.fork()` does not clone the current process. The `shell` option available in `child_process.spawn()` is not supported by `child_process.fork()` and will be ignored if set. If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`: import { fork } from 'node:child_process'; import process from 'node:process'; if (process.argv[2] === 'child') { setTimeout(() => { console.log(`Hello from ${process.argv[2]}!`); }, 1_000); } else { const controller = new AbortController(); const { signal } = controller; const child = fork(import.meta.url, ['child'], { signal }); child.on('error', (err) => { // This will be called with err being an AbortError if the controller aborts }); controller.abort(); // Stops the child process } #### `child_process.spawn(command[, args][, options])`# History VersionChanges v23.11.0, v22.15.0 Passing `args` when `shell` is set to `true` is deprecated. v16.4.0, v14.18.0 The `cwd` option can be a WHATWG `URL` object using `file:` protocol. v15.13.0, v14.18.0 timeout was added. v15.11.0, v14.18.0 killSignal for AbortSignal was added. v15.5.0, v14.17.0 AbortSignal support was added. v13.2.0, v12.16.0 The `serialization` option is supported now. v8.8.0 The `windowsHide` option is supported now. v6.4.0 The `argv0` option is supported now. v5.7.0 The `shell` option is supported now. v0.1.90 Added in: v0.1.90 * `command` The command to run. * `args` List of string arguments. * `options` * `cwd` | Current working directory of the child process. * `env` Environment key-value pairs. Default: `process.env`. * `argv0` Explicitly set the value of `argv[0]` sent to the child process. This will be set to `command` if not specified. * `stdio` | Child's stdio configuration (see `options.stdio`). * `detached` Prepare child process to run independently of its parent process. Specific behavior depends on the platform (see `options.detached`). * `uid` Sets the user identity of the process (see `setuid(2)`). * `gid` Sets the group identity of the process (see `setgid(2)`). * `serialization` Specify the kind of serialization used for sending messages between processes. Possible values are `'json'` and `'advanced'`. See Advanced serialization for more details. Default: `'json'`. * `shell` | If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See Shell requirements and Default Windows shell. Default: `false` (no shell). * `windowsVerbatimArguments` No quoting or escaping of arguments is done on Windows. Ignored on Unix. This is set to `true` automatically when `shell` is specified and is CMD. Default: `false`. * `windowsHide` Hide the subprocess console window that would normally be created on Windows systems. Default: `false`. * `signal` allows aborting the child process using an AbortSignal. * `timeout` In milliseconds the maximum amount of time the process is allowed to run. Default: `undefined`. * `killSignal` | The signal value to be used when the spawned process will be killed by timeout or abort signal. Default: `'SIGTERM'`. * Returns: The `child_process.spawn()` method spawns a new process using the given `command`, with command-line arguments in `args`. If omitted, `args` defaults to an empty array. If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution. A third argument may be used to specify additional options, with these defaults: const defaults = { cwd: undefined, env: process.env, }; Use `cwd` to specify the working directory from which the process is spawned. If not given, the default is to inherit the current working directory. If given, but the path does not exist, the child process emits an `ENOENT` error and exits immediately. `ENOENT` is also emitted when the command does not exist. Use `env` to specify environment variables that will be visible to the new process, the default is `process.env`. `undefined` values in `env` will be ignored. Example of running `ls -lh /usr`, capturing `stdout`, `stderr`, and the exit code: import { spawn } from 'node:child_process'; const ls = spawn('ls', ['-lh', '/usr']); ls.stdout.on('data', (data) => { console.log(`stdout: ${data}`); }); ls.stderr.on('data', (data) => { console.error(`stderr: ${data}`); }); ls.on('close', (code) => { console.log(`child process exited with code ${code}`); }); Example: A very elaborate way to run `ps ax | grep ssh` import { spawn } from 'node:child_process'; const ps = spawn('ps', ['ax']); const grep = spawn('grep', ['ssh']); ps.stdout.on('data', (data) => { grep.stdin.write(data); }); ps.stderr.on('data', (data) => { console.error(`ps stderr: ${data}`); }); ps.on('close', (code) => { if (code !== 0) { console.log(`ps process exited with code ${code}`); } grep.stdin.end(); }); grep.stdout.on('data', (data) => { console.log(data.toString()); }); grep.stderr.on('data', (data) => { console.error(`grep stderr: ${data}`); }); grep.on('close', (code) => { if (code !== 0) { console.log(`grep process exited with code ${code}`); } }); Example of checking for failed `spawn`: import { spawn } from 'node:child_process'; const subprocess = spawn('bad_command'); subprocess.on('error', (err) => { console.error('Failed to start subprocess.'); }); Certain platforms (macOS, Linux) will use the value of `argv[0]` for the process title while others (Windows, SunOS) will use `command`. Node.js overwrites `argv[0]` with `process.execPath` on startup, so `process.argv[0]` in a Node.js child process will not match the `argv0` parameter passed to `spawn` from the parent. Retrieve it with the `process.argv0` property instead. If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.kill()` on the child process except the error passed to the callback will be an `AbortError`: import { spawn } from 'node:child_process'; const controller = new AbortController(); const { signal } = controller; const grep = spawn('grep', ['ssh'], { signal }); grep.on('error', (err) => { // This will be called with err being an AbortError if the controller aborts }); controller.abort(); // Stops the child process ##### `options.detached`# Added in: v0.7.10 On Windows, setting `options.detached` to `true` makes it possible for the child process to continue running after the parent exits. The child process will have its own console window. Once enabled for a child process, it cannot be disabled. On non-Windows platforms, if `options.detached` is set to `true`, the child process will be made the leader of a new process group and session. Child processes may continue running after the parent exits regardless of whether they are detached or not. See `setsid(2)` for more information. By default, the parent will wait for the detached child process to exit. To prevent the parent process from waiting for a given `subprocess` to exit, use the `subprocess.unref()` method. Doing so will cause the parent process' event loop to not include the child process in its reference count, allowing the parent process to exit independently of the child process, unless there is an established IPC channel between the child and the parent processes. When using the `detached` option to start a long-running process, the process will not stay running in the background after the parent exits unless it is provided with a `stdio` configuration that is not connected to the parent. If the parent process' `stdio` is inherited, the child process will remain attached to the controlling terminal. Example of a long-running process, by detaching and also ignoring its parent `stdio` file descriptors, in order to ignore the parent's termination: import { spawn } from 'node:child_process'; import process from 'node:process'; const subprocess = spawn(process.argv[0], ['child_program.js'], { detached: true, stdio: 'ignore', }); subprocess.unref(); Alternatively one can redirect the child process' output into files: import { openSync } from 'node:fs'; import { spawn } from 'node:child_process'; const out = openSync('./out.log', 'a'); const err = openSync('./out.log', 'a'); const subprocess = spawn('prg', [], { detached: true, stdio: [ 'ignore', out, err ], }); subprocess.unref(); ##### `options.stdio`# History VersionChanges v15.6.0, v14.18.0 Added the `overlapped` stdio flag. v3.3.1 The value `0` is now accepted as a file descriptor. v0.7.10 Added in: v0.7.10 The `options.stdio` option is used to configure the pipes that are established between the parent and child process. By default, the child's stdin, stdout, and stderr are redirected to corresponding `subprocess.stdin`, `subprocess.stdout`, and `subprocess.stderr` streams on the `ChildProcess` object. This is equivalent to setting the `options.stdio` equal to `['pipe', 'pipe', 'pipe']`. For convenience, `options.stdio` may be one of the following strings: * `'pipe'`: equivalent to `['pipe', 'pipe', 'pipe']` (the default) * `'overlapped'`: equivalent to `['overlapped', 'overlapped', 'overlapped']` * `'ignore'`: equivalent to `['ignore', 'ignore', 'ignore']` * `'inherit'`: equivalent to `['inherit', 'inherit', 'inherit']` or `[0, 1, 2]` Otherwise, the value of `options.stdio` is an array where each index corresponds to an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout, and stderr, respectively. Additional fds can be specified to create additional pipes between the parent and child. The value is one of the following: 1. `'pipe'`: Create a pipe between the child process and the parent process. The parent end of the pipe is exposed to the parent as a property on the `child_process` object as `subprocess.stdio[fd]`. Pipes created for fds 0, 1, and 2 are also available as `subprocess.stdin`, `subprocess.stdout` and `subprocess.stderr`, respectively. These are not actual Unix pipes and therefore the child process can not use them by their descriptor files, e.g. `/dev/fd/2` or `/dev/stdout`. 2. `'overlapped'`: Same as `'pipe'` except that the `FILE_FLAG_OVERLAPPED` flag is set on the handle. This is necessary for overlapped I/O on the child process's stdio handles. See the docs for more details. This is exactly the same as `'pipe'` on non-Windows systems. 3. `'ipc'`: Create an IPC channel for passing messages/file descriptors between parent and child. A `ChildProcess` may have at most one IPC stdio file descriptor. Setting this option enables the `subprocess.send()` method. If the child process is a Node.js instance, the presence of an IPC channel will enable `process.send()` and `process.disconnect()` methods, as well as `'disconnect'` and `'message'` events within the child process. Accessing the IPC channel fd in any way other than `process.send()` or using the IPC channel with a child process that is not a Node.js instance is not supported. 4. `'ignore'`: Instructs Node.js to ignore the fd in the child. While Node.js will always open fds 0, 1, and 2 for the processes it spawns, setting the fd to `'ignore'` will cause Node.js to open `/dev/null` and attach it to the child's fd. 5. `'inherit'`: Pass through the corresponding stdio stream to/from the parent process. In the first three positions, this is equivalent to `process.stdin`, `process.stdout`, and `process.stderr`, respectively. In any other position, equivalent to `'ignore'`. 6. object: Share a readable or writable stream that refers to a tty, file, socket, or a pipe with the child process. The stream's underlying file descriptor is duplicated in the child process to the fd that corresponds to the index in the `stdio` array. The stream must have an underlying descriptor (file streams do not start until the `'open'` event has occurred). NOTE: While it is technically possible to pass `stdin` as a writable or `stdout`/`stderr` as readable, it is not recommended. Readable and writable streams are designed with distinct behaviors, and using them incorrectly (e.g., passing a readable stream where a writable stream is expected) can lead to unexpected results or errors. This practice is discouraged as it may result in undefined behavior or dropped callbacks if the stream encounters errors. Always ensure that `stdin` is used as writable and `stdout`/`stderr` as readable to maintain the intended flow of data between the parent and child processes. 7. Positive integer: The integer value is interpreted as a file descriptor that is open in the parent process. It is shared with the child process, similar to how objects can be shared. Passing sockets is not supported on Windows. 8. `null`, `undefined`: Use default value. For stdio fds 0, 1, and 2 (in other words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the default is `'ignore'`. import { spawn } from 'node:child_process'; import process from 'node:process'; // Child will use parent's stdios. spawn('prg', [], { stdio: 'inherit' }); // Spawn child sharing only stderr. spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] }); // Open an extra fd=4, to interact with programs presenting a // startd-style interface. spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] }); It is worth noting that when an IPC channel is established between the parent and child processes, and the child process is a Node.js instance, the child process is launched with the IPC channel unreferenced (using `unref()`) until the child process registers an event handler for the `'disconnect'` event or the `'message'` event. This allows the child process to exit normally without the process being held open by the open IPC channel. See also: `child_process.exec()` and `child_process.fork()`. ### Synchronous process creation# The `child_process.spawnSync()`, `child_process.execSync()`, and `child_process.execFileSync()` methods are synchronous and will block the Node.js event loop, pausing execution of any additional code until the spawned process exits. Blocking calls like these are mostly useful for simplifying general-purpose scripting tasks and for simplifying the loading/processing of application configuration at startup. #### `child_process.execFileSync(file[, args][, options])`# History VersionChanges v16.4.0, v14.18.0 The `cwd` option can be a WHATWG `URL` object using `file:` protocol. v10.10.0 The `input` option can now be any `TypedArray` or a `DataView`. v8.8.0 The `windowsHide` option is supported now. v8.0.0 The `input` option can now be a `Uint8Array`. v6.2.1, v4.5.0 The `encoding` option can now explicitly be set to `buffer`. v0.11.12 Added in: v0.11.12 * `file` The name or path of the executable file to run. * `args` List of string arguments. * `options` * `cwd` | Current working directory of the child process. * `input` | | | The value which will be passed as stdin to the spawned process. If `stdio[0]` is set to `'pipe'`, Supplying this value will override `stdio[0]`. * `stdio` | Child's stdio configuration. See `child_process.spawn()`'s `stdio`. `stderr` by default will be output to the parent process' stderr unless `stdio` is specified. Default: `'pipe'`. * `env` Environment key-value pairs. Default: `process.env`. * `uid` Sets the user identity of the process (see `setuid(2)`). * `gid` Sets the group identity of the process (see `setgid(2)`). * `timeout` In milliseconds the maximum amount of time the process is allowed to run. Default: `undefined`. * `killSignal` | The signal value to be used when the spawned process will be killed. Default: `'SIGTERM'`. * `maxBuffer` Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated. See caveat at `maxBuffer` and Unicode. Default: `1024 * 1024`. * `encoding` The encoding used for all stdio inputs and outputs. Default: `'buffer'`. * `windowsHide` Hide the subprocess console window that would normally be created on Windows systems. Default: `false`. * `shell` | If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See Shell requirements and Default Windows shell. Default: `false` (no shell). * Returns: | The stdout from the command. The `child_process.execFileSync()` method is generally identical to `child_process.execFile()` with the exception that the method will not return until the child process has fully closed. When a timeout has been encountered and `killSignal` is sent, the method won't return until the process has completely exited. If the child process intercepts and handles the `SIGTERM` signal and does not exit, the parent process will still wait until the child process has exited. If the process times out or has a non-zero exit code, this method will throw an `Error` that will include the full result of the underlying `child_process.spawnSync()`. If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution. import { execFileSync } from 'node:child_process'; try { const stdout = execFileSync('my-script.sh', ['my-arg'], { // Capture stdout and stderr from child process. Overrides the // default behavior of streaming child stderr to the parent stderr stdio: 'pipe', // Use utf8 encoding for stdio pipes encoding: 'utf8', }); console.log(stdout); } catch (err) { if (err.code) { // Spawning child process failed console.error(err.code); } else { // Child was spawned but exited with non-zero exit code // Error contains any stdout and stderr from the child const { stdout, stderr } = err; console.error({ stdout, stderr }); } } #### `child_process.execSync(command[, options])`# History VersionChanges v16.4.0, v14.18.0 The `cwd` option can be a WHATWG `URL` object using `file:` protocol. v10.10.0 The `input` option can now be any `TypedArray` or a `DataView`. v8.8.0 The `windowsHide` option is supported now. v8.0.0 The `input` option can now be a `Uint8Array`. v0.11.12 Added in: v0.11.12 * `command` The command to run. * `options` * `cwd` | Current working directory of the child process. * `input` | | | The value which will be passed as stdin to the spawned process. If `stdio[0]` is set to `'pipe'`, Supplying this value will override `stdio[0]`. * `stdio` | Child's stdio configuration. See `child_process.spawn()`'s `stdio`. `stderr` by default will be output to the parent process' stderr unless `stdio` is specified. Default: `'pipe'`. * `env` Environment key-value pairs. Default: `process.env`. * `shell` Shell to execute the command with. See Shell requirements and Default Windows shell. Default: `'/bin/sh'` on Unix, `process.env.ComSpec` on Windows. * `uid` Sets the user identity of the process. (See `setuid(2)`). * `gid` Sets the group identity of the process. (See `setgid(2)`). * `timeout` In milliseconds the maximum amount of time the process is allowed to run. Default: `undefined`. * `killSignal` | The signal value to be used when the spawned process will be killed. Default: `'SIGTERM'`. * `maxBuffer` Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at `maxBuffer` and Unicode. Default: `1024 * 1024`. * `encoding` The encoding used for all stdio inputs and outputs. Default: `'buffer'`. * `windowsHide` Hide the subprocess console window that would normally be created on Windows systems. Default: `false`. * Returns: | The stdout from the command. The `child_process.execSync()` method is generally identical to `child_process.exec()` with the exception that the method will not return until the child process has fully closed. When a timeout has been encountered and `killSignal` is sent, the method won't return until the process has completely exited. If the child process intercepts and handles the `SIGTERM` signal and doesn't exit, the parent process will wait until the child process has exited. If the process times out or has a non-zero exit code, this method will throw. The `Error` object will contain the entire result from `child_process.spawnSync()`. Never pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution. #### `child_process.spawnSync(command[, args][, options])`# History VersionChanges v16.4.0, v14.18.0 The `cwd` option can be a WHATWG `URL` object using `file:` protocol. v10.10.0 The `input` option can now be any `TypedArray` or a `DataView`. v8.8.0 The `windowsHide` option is supported now. v8.0.0 The `input` option can now be a `Uint8Array`. v5.7.0 The `shell` option is supported now. v6.2.1, v4.5.0 The `encoding` option can now explicitly be set to `buffer`. v0.11.12 Added in: v0.11.12 * `command` The command to run. * `args` List of string arguments. * `options` * `cwd` | Current working directory of the child process. * `input` | | | The value which will be passed as stdin to the spawned process. If `stdio[0]` is set to `'pipe'`, Supplying this value will override `stdio[0]`. * `argv0` Explicitly set the value of `argv[0]` sent to the child process. This will be set to `command` if not specified. * `stdio` | Child's stdio configuration. See `child_process.spawn()`'s `stdio`. Default: `'pipe'`. * `env` Environment key-value pairs. Default: `process.env`. * `uid` Sets the user identity of the process (see `setuid(2)`). * `gid` Sets the group identity of the process (see `setgid(2)`). * `timeout` In milliseconds the maximum amount of time the process is allowed to run. Default: `undefined`. * `killSignal` | The signal value to be used when the spawned process will be killed. Default: `'SIGTERM'`. * `maxBuffer` Largest amount of data in bytes allowed on stdout or stderr. If exceeded, the child process is terminated and any output is truncated. See caveat at `maxBuffer` and Unicode. Default: `1024 * 1024`. * `encoding` The encoding used for all stdio inputs and outputs. Default: `'buffer'`. * `shell` | If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See Shell requirements and Default Windows shell. Default: `false` (no shell). * `windowsVerbatimArguments` No quoting or escaping of arguments is done on Windows. Ignored on Unix. This is set to `true` automatically when `shell` is specified and is CMD. Default: `false`. * `windowsHide` Hide the subprocess console window that would normally be created on Windows systems. Default: `false`. * Returns: * `pid` Pid of the child process. * `output` Array of results from stdio output. * `stdout` | The contents of `output[1]`. * `stderr` | The contents of `output[2]`. * `status` | The exit code of the subprocess, or `null` if the subprocess terminated due to a signal. * `signal` | The signal used to kill the subprocess, or `null` if the subprocess did not terminate due to a signal. * `error` The error object if the child process failed or timed out. The `child_process.spawnSync()` method is generally identical to `child_process.spawn()` with the exception that the function will not return until the child process has fully closed. When a timeout has been encountered and `killSignal` is sent, the method won't return until the process has completely exited. If the process intercepts and handles the `SIGTERM` signal and doesn't exit, the parent process will wait until the child process has exited. If the `shell` option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution. ### Class: `ChildProcess`# Added in: v2.2.0 * Extends: Instances of the `ChildProcess` represent spawned child processes. Instances of `ChildProcess` are not intended to be created directly. Rather, use the `child_process.spawn()`, `child_process.exec()`, `child_process.execFile()`, or `child_process.fork()` methods to create instances of `ChildProcess`. #### Event: `'close'`# Added in: v0.7.7 * `code` The exit code if the child process exited on its own, or `null` if the child process terminated due to a signal. * `signal` The signal by which the child process was terminated, or `null` if the child process did not terminated due to a signal. The `'close'` event is emitted after a process has ended and the stdio streams of a child process have been closed. This is distinct from the `'exit'` event, since multiple processes might share the same stdio streams. The `'close'` event will always emit after `'exit'` was already emitted, or `'error'` if the child process failed to spawn. If the process exited, `code` is the final exit code of the process, otherwise `null`. If the process terminated due to receipt of a signal, `signal` is the string name of the signal, otherwise `null`. One of the two will always be non-`null`. import { spawn } from 'node:child_process'; const ls = spawn('ls', ['-lh', '/usr']); ls.stdout.on('data', (data) => { console.log(`stdout: ${data}`); }); ls.on('close', (code) => { console.log(`child process close all stdio with code ${code}`); }); ls.on('exit', (code) => { console.log(`child process exited with code ${code}`); }); #### Event: `'disconnect'`# Added in: v0.7.2 The `'disconnect'` event is emitted after calling the `subprocess.disconnect()` method in parent process or `process.disconnect()` in child process. After disconnecting it is no longer possible to send or receive messages, and the `subprocess.connected` property is `false`. #### Event: `'error'`# * `err` The error. The `'error'` event is emitted whenever: * The process could not be spawned. * The process could not be killed. * Sending a message to the child process failed. * The child process was aborted via the `signal` option. The `'exit'` event may or may not fire after an error has occurred. When listening to both the `'exit'` and `'error'` events, guard against accidentally invoking handler functions multiple times. See also `subprocess.kill()` and `subprocess.send()`. #### Event: `'exit'`# Added in: v0.1.90 * `code` The exit code if the child process exited on its own, or `null` if the child process terminated due to a signal. * `signal` The signal by which the child process was terminated, or `null` if the child process did not terminated due to a signal. The `'exit'` event is emitted after the child process ends. If the process exited, `code` is the final exit code of the process, otherwise `null`. If the process terminated due to receipt of a signal, `signal` is the string name of the signal, otherwise `null`. One of the two will always be non-`null`. When the `'exit'` event is triggered, child process stdio streams might still be open. Node.js establishes signal handlers for `SIGINT` and `SIGTERM` and Node.js processes will not terminate immediately due to receipt of those signals. Rather, Node.js will perform a sequence of cleanup actions and then will re-raise the handled signal. See `waitpid(2)`. #### Event: `'message'`# Added in: v0.5.9 * `message` A parsed JSON object or primitive value. * `sendHandle` | `undefined` or a `net.Socket`, `net.Server`, or `dgram.Socket` object. The `'message'` event is triggered when a child process uses `process.send()` to send messages. The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent. If the `serialization` option was set to `'advanced'` used when spawning the child process, the `message` argument can contain data that JSON is not able to represent. See Advanced serialization for more details. #### Event: `'spawn'`# Added in: v15.1.0, v14.17.0 The `'spawn'` event is emitted once the child process has spawned successfully. If the child process does not spawn successfully, the `'spawn'` event is not emitted and the `'error'` event is emitted instead. If emitted, the `'spawn'` event comes before all other events and before any data is received via `stdout` or `stderr`. The `'spawn'` event will fire regardless of whether an error occurs within the spawned process. For example, if `bash some-command` spawns successfully, the `'spawn'` event will fire, though `bash` may fail to spawn `some-command`. This caveat also applies when using `{ shell: true }`. #### `subprocess.channel`# History VersionChanges v14.0.0 The object no longer accidentally exposes native C++ bindings. v7.1.0 Added in: v7.1.0 * Type: A pipe representing the IPC channel to the child process. The `subprocess.channel` property is a reference to the child's IPC channel. If no IPC channel exists, this property is `undefined`. ##### `subprocess.channel.ref()`# Added in: v7.1.0 This method makes the IPC channel keep the event loop of the parent process running if `.unref()` has been called before. ##### `subprocess.channel.unref()`# Added in: v7.1.0 This method makes the IPC channel not keep the event loop of the parent process running, and lets it finish even while the channel is open. #### `subprocess.connected`# Added in: v0.7.2 * Type: Set to `false` after `subprocess.disconnect()` is called. The `subprocess.connected` property indicates whether it is still possible to send and receive messages from a child process. When `subprocess.connected` is `false`, it is no longer possible to send or receive messages. #### `subprocess.disconnect()`# Added in: v0.7.2 Closes the IPC channel between parent and child processes, allowing the child process to exit gracefully once there are no other connections keeping it alive. After calling this method the `subprocess.connected` and `process.connected` properties in both the parent and child processes (respectively) will be set to `false`, and it will be no longer possible to pass messages between the processes. The `'disconnect'` event will be emitted when there are no messages in the process of being received. This will most often be triggered immediately after calling `subprocess.disconnect()`. When the child process is a Node.js instance (e.g. spawned using `child_process.fork()`), the `process.disconnect()` method can be invoked within the child process to close the IPC channel as well. #### `subprocess.exitCode`# * Type: The `subprocess.exitCode` property indicates the exit code of the child process. If the child process is still running, the field will be `null`. #### `subprocess.kill([signal])`# Added in: v0.1.90 * `signal` | * Returns: The `subprocess.kill()` method sends a signal to the child process. If no argument is given, the process will be sent the `'SIGTERM'` signal. See `signal(7)` for a list of available signals. This function returns `true` if `kill(2)` succeeds, and `false` otherwise. import { spawn } from 'node:child_process'; const grep = spawn('grep', ['ssh']); grep.on('close', (code, signal) => { console.log( `child process terminated due to receipt of signal ${signal}`); }); // Send SIGHUP to process. grep.kill('SIGHUP'); The `ChildProcess` object may emit an `'error'` event if the signal cannot be delivered. Sending a signal to a child process that has already exited is not an error but may have unforeseen consequences. Specifically, if the process identifier (PID) has been reassigned to another process, the signal will be delivered to that process instead which can have unexpected results. While the function is called `kill`, the signal delivered to the child process may not actually terminate the process. See `kill(2)` for reference. On Windows, where POSIX signals do not exist, the `signal` argument will be ignored except for `'SIGKILL'`, `'SIGTERM'`, `'SIGINT'` and `'SIGQUIT'`, and the process will always be killed forcefully and abruptly (similar to `'SIGKILL'`). See Signal Events for more details. On Linux, child processes of child processes will not be terminated when attempting to kill their parent. This is likely to happen when running a new process in a shell or with the use of the `shell` option of `ChildProcess`: import { spawn } from 'node:child_process'; const subprocess = spawn( 'sh', [ '-c', `node -e "setInterval(() => { console.log(process.pid, 'is alive') }, 500);"`, ], { stdio: ['inherit', 'inherit', 'inherit'], }, ); setTimeout(() => { subprocess.kill(); // Does not terminate the Node.js process in the shell. }, 2000); #### `subprocess[Symbol.dispose]()`# History VersionChanges v24.2.0 No longer experimental. v20.5.0, v18.18.0 Added in: v20.5.0, v18.18.0 Calls `subprocess.kill()` with `'SIGTERM'`. #### `subprocess.killed`# Added in: v0.5.10 * Type: Set to `true` after `subprocess.kill()` is used to successfully send a signal to the child process. The `subprocess.killed` property indicates whether the child process successfully received a signal from `subprocess.kill()`. The `killed` property does not indicate that the child process has been terminated. #### `subprocess.pid`# Added in: v0.1.90 * Type: | Returns the process identifier (PID) of the child process. If the child process fails to spawn due to errors, then the value is `undefined` and `error` is emitted. import { spawn } from 'node:child_process'; const grep = spawn('grep', ['ssh']); console.log(`Spawned child pid: ${grep.pid}`); grep.stdin.end(); #### `subprocess.ref()`# Added in: v0.7.10 Calling `subprocess.ref()` after making a call to `subprocess.unref()` will restore the removed reference count for the child process, forcing the parent process to wait for the child process to exit before exiting itself. import { spawn } from 'node:child_process'; import process from 'node:process'; const subprocess = spawn(process.argv[0], ['child_program.js'], { detached: true, stdio: 'ignore', }); subprocess.unref(); subprocess.ref(); #### `subprocess.send(message[, sendHandle[, options]][, callback])`# History VersionChanges v5.8.0 The `options` parameter, and the `keepOpen` option in particular, is supported now. v5.0.0 This method returns a boolean for flow control now. v4.0.0 The `callback` parameter is supported now. v0.5.9 Added in: v0.5.9 * `message` * `sendHandle` | `undefined`, or a `net.Socket`, `net.Server`, or `dgram.Socket` object. * `options` The `options` argument, if present, is an object used to parameterize the sending of certain types of handles. `options` supports the following properties: * `keepOpen` A value that can be used when passing instances of `net.Socket`. When `true`, the socket is kept open in the sending process. Default: `false`. * `callback` * Returns: When an IPC channel has been established between the parent and child processes ( i.e. when using `child_process.fork()`), the `subprocess.send()` method can be used to send messages to the child process. When the child process is a Node.js instance, these messages can be received via the `'message'` event. The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent. For example, in the parent script: import { fork } from 'node:child_process'; const forkedProcess = fork(`${import.meta.dirname}/sub.js`); forkedProcess.on('message', (message) => { console.log('PARENT got message:', message); }); // Causes the child to print: CHILD got message: { hello: 'world' } forkedProcess.send({ hello: 'world' }); And then the child script, `'sub.js'` might look like this: process.on('message', (message) => { console.log('CHILD got message:', message); }); // Causes the parent to print: PARENT got message: { foo: 'bar', baz: null } process.send({ foo: 'bar', baz: NaN }); Child Node.js processes will have a `process.send()` method of their own that allows the child process to send messages back to the parent process. There is a special case when sending a `{cmd: 'NODE_foo'}` message. Messages containing a `NODE_` prefix in the `cmd` property are reserved for use within Node.js core and will not be emitted in the child's `'message'` event. Rather, such messages are emitted using the `'internalMessage'` event and are consumed internally by Node.js. Applications should avoid using such messages or listening for `'internalMessage'` events as it is subject to change without notice. The optional `sendHandle` argument that may be passed to `subprocess.send()` is for passing a TCP server or socket object to the child process. The child process will receive the object as the second argument passed to the callback function registered on the `'message'` event. Any data that is received and buffered in the socket will not be sent to the child. Sending IPC sockets is not supported on Windows. The optional `callback` is a function that is invoked after the message is sent but before the child process may have received it. The function is called with a single argument: `null` on success, or an `Error` object on failure. If no `callback` function is provided and the message cannot be sent, an `'error'` event will be emitted by the `ChildProcess` object. This can happen, for instance, when the child process has already exited. `subprocess.send()` will return `false` if the channel has closed or when the backlog of unsent messages exceeds a threshold that makes it unwise to send more. Otherwise, the method returns `true`. The `callback` function can be used to implement flow control. ##### Example: sending a server object# The `sendHandle` argument can be used, for instance, to pass the handle of a TCP server object to the child process as illustrated in the example below: import { fork } from 'node:child_process'; import { createServer } from 'node:net'; const subprocess = fork('subprocess.js'); // Open up the server object and send the handle. const server = createServer(); server.on('connection', (socket) => { socket.end('handled by parent'); }); server.listen(1337, () => { subprocess.send('server', server); }); The child process would then receive the server object as: process.on('message', (m, server) => { if (m === 'server') { server.on('connection', (socket) => { socket.end('handled by child'); }); } }); Once the server is now shared between the parent and child, some connections can be handled by the parent and some by the child. While the example above uses a server created using the `node:net` module, `node:dgram` module servers use exactly the same workflow with the exceptions of listening on a `'message'` event instead of `'connection'` and using `server.bind()` instead of `server.listen()`. This is, however, only supported on Unix platforms. ##### Example: sending a socket object# Similarly, the `sendHandler` argument can be used to pass the handle of a socket to the child process. The example below spawns two children that each handle connections with "normal" or "special" priority: import { fork } from 'node:child_process'; import { createServer } from 'node:net'; const normal = fork('subprocess.js', ['normal']); const special = fork('subprocess.js', ['special']); // Open up the server and send sockets to child. Use pauseOnConnect to prevent // the sockets from being read before they are sent to the child process. const server = createServer({ pauseOnConnect: true }); server.on('connection', (socket) => { // If this is special priority... if (socket.remoteAddress === '74.125.127.100') { special.send('socket', socket); return; } // This is normal priority. normal.send('socket', socket); }); server.listen(1337); The `subprocess.js` would receive the socket handle as the second argument passed to the event callback function: process.on('message', (m, socket) => { if (m === 'socket') { if (socket) { // Check that the client socket exists. // It is possible for the socket to be closed between the time it is // sent and the time it is received in the child process. socket.end(`Request handled with ${process.argv[2]} priority`); } } }); Do not use `.maxConnections` on a socket that has been passed to a subprocess. The parent cannot track when the socket is destroyed. Any `'message'` handlers in the subprocess should verify that `socket` exists, as the connection may have been closed during the time it takes to send the connection to the child. #### `subprocess.signalCode`# * Type: | The `subprocess.signalCode` property indicates the signal received by the child process if any, else `null`. #### `subprocess.spawnargs`# * Type: The `subprocess.spawnargs` property represents the full list of command-line arguments the child process was launched with. #### `subprocess.spawnfile`# * Type: The `subprocess.spawnfile` property indicates the executable file name of the child process that is launched. For `child_process.fork()`, its value will be equal to `process.execPath`. For `child_process.spawn()`, its value will be the name of the executable file. For `child_process.exec()`, its value will be the name of the shell in which the child process is launched. #### `subprocess.stderr`# Added in: v0.1.90 * Type: | | A `Readable Stream` that represents the child process's `stderr`. If the child process was spawned with `stdio[2]` set to anything other than `'pipe'`, then this will be `null`. `subprocess.stderr` is an alias for `subprocess.stdio[2]`. Both properties will refer to the same value. The `subprocess.stderr` property can be `null` or `undefined` if the child process could not be successfully spawned. #### `subprocess.stdin`# Added in: v0.1.90 * Type: | | A `Writable Stream` that represents the child process's `stdin`. If a child process waits to read all of its input, the child process will not continue until this stream has been closed via `end()`. If the child process was spawned with `stdio[0]` set to anything other than `'pipe'`, then this will be `null`. `subprocess.stdin` is an alias for `subprocess.stdio[0]`. Both properties will refer to the same value. The `subprocess.stdin` property can be `null` or `undefined` if the child process could not be successfully spawned. #### `subprocess.stdio`# Added in: v0.7.10 * Type: A sparse array of pipes to the child process, corresponding with positions in the `stdio` option passed to `child_process.spawn()` that have been set to the value `'pipe'`. `subprocess.stdio[0]`, `subprocess.stdio[1]`, and `subprocess.stdio[2]` are also available as `subprocess.stdin`, `subprocess.stdout`, and `subprocess.stderr`, respectively. In the following example, only the child's fd `1` (stdout) is configured as a pipe, so only the parent's `subprocess.stdio[1]` is a stream, all other values in the array are `null`. import assert from 'node:assert'; import fs from 'node:fs'; import child_process from 'node:child_process'; const subprocess = child_process.spawn('ls', { stdio: [ 0, // Use parent's stdin for child. 'pipe', // Pipe child's stdout to parent. fs.openSync('err.out', 'w'), // Direct child's stderr to a file. ], }); assert.strictEqual(subprocess.stdio[0], null); assert.strictEqual(subprocess.stdio[0], subprocess.stdin); assert(subprocess.stdout); assert.strictEqual(subprocess.stdio[1], subprocess.stdout); assert.strictEqual(subprocess.stdio[2], null); assert.strictEqual(subprocess.stdio[2], subprocess.stderr); The `subprocess.stdio` property can be `undefined` if the child process could not be successfully spawned. #### `subprocess.stdout`# Added in: v0.1.90 * Type: | | A `Readable Stream` that represents the child process's `stdout`. If the child process was spawned with `stdio[1]` set to anything other than `'pipe'`, then this will be `null`. `subprocess.stdout` is an alias for `subprocess.stdio[1]`. Both properties will refer to the same value. import { spawn } from 'node:child_process'; const subprocess = spawn('ls'); subprocess.stdout.on('data', (data) => { console.log(`Received chunk ${data}`); }); The `subprocess.stdout` property can be `null` or `undefined` if the child process could not be successfully spawned. #### `subprocess.unref()`# Added in: v0.7.10 By default, the parent process will wait for the detached child process to exit. To prevent the parent process from waiting for a given `subprocess` to exit, use the `subprocess.unref()` method. Doing so will cause the parent's event loop to not include the child process in its reference count, allowing the parent to exit independently of the child, unless there is an established IPC channel between the child and the parent processes. import { spawn } from 'node:child_process'; import process from 'node:process'; const subprocess = spawn(process.argv[0], ['child_program.js'], { detached: true, stdio: 'ignore', }); subprocess.unref(); ### `maxBuffer` and Unicode# The `maxBuffer` option specifies the largest number of bytes allowed on `stdout` or `stderr`. If this value is exceeded, then the child process is terminated. This impacts output that includes multibyte character encodings such as UTF-8 or UTF-16. For instance, `console.log('中文测试')` will send 13 UTF-8 encoded bytes to `stdout` although there are only 4 characters. ### Shell requirements# The shell should understand the `-c` switch. If the shell is `'cmd.exe'`, it should understand the `/d /s /c` switches and command-line parsing should be compatible. ### Default Windows shell# Although Microsoft specifies `%COMSPEC%` must contain the path to `'cmd.exe'` in the root environment, child processes are not always subject to the same requirement. Thus, in `child_process` functions where a shell can be spawned, `'cmd.exe'` is used as a fallback if `process.env.ComSpec` is unavailable. ### Advanced serialization# Added in: v13.2.0, v12.16.0 Child processes support a serialization mechanism for IPC that is based on the serialization API of the `node:v8` module, based on the HTML structured clone algorithm. This is generally more powerful and supports more built-in JavaScript object types, such as `BigInt`, `Map` and `Set`, `ArrayBuffer` and `TypedArray`, `Buffer`, `Error`, `RegExp` etc. However, this format is not a full superset of JSON, and e.g. properties set on objects of such built-in types will not be passed on through the serialization step. Additionally, performance may not be equivalent to that of JSON, depending on the structure of the passed data. Therefore, this feature requires opting in by setting the `serialization` option to `'advanced'` when calling `child_process.spawn()` or `child_process.fork()`. ## Cluster# Stability: 2 \- Stable Source Code: lib/cluster.js Clusters of Node.js processes can be used to run multiple instances of Node.js that can distribute workloads among their application threads. When process isolation is not needed, use the `worker_threads` module instead, which allows running multiple application threads within a single Node.js instance. The cluster module allows easy creation of child processes that all share server ports. import cluster from 'node:cluster'; import http from 'node:http'; import { availableParallelism } from 'node:os'; import process from 'node:process'; const numCPUs = availableParallelism(); if (cluster.isPrimary) { console.log(`Primary ${process.pid} is running`); // Fork workers. for (let i = 0; i < numCPUs; i++) { cluster.fork(); } cluster.on('exit', (worker, code, signal) => { console.log(`worker ${worker.process.pid} died`); }); } else { // Workers can share any TCP connection // In this case it is an HTTP server http.createServer((req, res) => { res.writeHead(200); res.end('hello world\n'); }).listen(8000); console.log(`Worker ${process.pid} started`); } Running Node.js will now share port 8000 between the workers: $ node server.js Primary 3596 is running Worker 4324 started Worker 4520 started Worker 6056 started Worker 5644 started On Windows, it is not yet possible to set up a named pipe server in a worker. ### How it works# The worker processes are spawned using the `child_process.fork()` method, so that they can communicate with the parent via IPC and pass server handles back and forth. The cluster module supports two methods of distributing incoming connections. The first one (and the default one on all platforms except Windows) is the round-robin approach, where the primary process listens on a port, accepts new connections and distributes them across the workers in a round-robin fashion, with some built-in smarts to avoid overloading a worker process. The second approach is where the primary process creates the listen socket and sends it to interested workers. The workers then accept incoming connections directly. The second approach should, in theory, give the best performance. In practice however, distribution tends to be very unbalanced due to operating system scheduler vagaries. Loads have been observed where over 70% of all connections ended up in just two processes, out of a total of eight. Because `server.listen()` hands off most of the work to the primary process, there are three cases where the behavior between a normal Node.js process and a cluster worker differs: 1. `server.listen({fd: 7})` Because the message is passed to the primary, file descriptor 7 in the parent will be listened on, and the handle passed to the worker, rather than listening to the worker's idea of what the number 7 file descriptor references. 2. `server.listen(handle)` Listening on handles explicitly will cause the worker to use the supplied handle, rather than talk to the primary process. 3. `server.listen(0)` Normally, this will cause servers to listen on a random port. However, in a cluster, each worker will receive the same "random" port each time they do `listen(0)`. In essence, the port is random the first time, but predictable thereafter. To listen on a unique port, generate a port number based on the cluster worker ID. Node.js does not provide routing logic. It is therefore important to design an application such that it does not rely too heavily on in-memory data objects for things like sessions and login. Because workers are all separate processes, they can be killed or re-spawned depending on a program's needs, without affecting other workers. As long as there are some workers still alive, the server will continue to accept connections. If no workers are alive, existing connections will be dropped and new connections will be refused. Node.js does not automatically manage the number of workers, however. It is the application's responsibility to manage the worker pool based on its own needs. Although a primary use case for the `node:cluster` module is networking, it can also be used for other use cases requiring worker processes. ### Class: `Worker`# Added in: v0.7.0 * Extends: A `Worker` object contains all public information and method about a worker. In the primary it can be obtained using `cluster.workers`. In a worker it can be obtained using `cluster.worker`. #### Event: `'disconnect'`# Added in: v0.7.7 Similar to the `cluster.on('disconnect')` event, but specific to this worker. cluster.fork().on('disconnect', () => { // Worker has disconnected }); #### Event: `'error'`# Added in: v0.7.3 This event is the same as the one provided by `child_process.fork()`. Within a worker, `process.on('error')` may also be used. #### Event: `'exit'`# Added in: v0.11.2 * `code` The exit code, if it exited normally. * `signal` The name of the signal (e.g. `'SIGHUP'`) that caused the process to be killed. Similar to the `cluster.on('exit')` event, but specific to this worker. import cluster from 'node:cluster'; if (cluster.isPrimary) { const worker = cluster.fork(); worker.on('exit', (code, signal) => { if (signal) { console.log(`worker was killed by signal: ${signal}`); } else if (code !== 0) { console.log(`worker exited with error code: ${code}`); } else { console.log('worker success!'); } }); } #### Event: `'listening'`# Added in: v0.7.0 * `address` Similar to the `cluster.on('listening')` event, but specific to this worker. cluster.fork().on('listening', (address) => { // Worker is listening }); It is not emitted in the worker. #### Event: `'message'`# Added in: v0.7.0 * `message` * `handle` | Similar to the `'message'` event of `cluster`, but specific to this worker. Within a worker, `process.on('message')` may also be used. See `process` event: `'message'`. Here is an example using the message system. It keeps a count in the primary process of the number of HTTP requests received by the workers: import cluster from 'node:cluster'; import http from 'node:http'; import { availableParallelism } from 'node:os'; import process from 'node:process'; if (cluster.isPrimary) { // Keep track of http requests let numReqs = 0; setInterval(() => { console.log(`numReqs = ${numReqs}`); }, 1000); // Count requests function messageHandler(msg) { if (msg.cmd && msg.cmd === 'notifyRequest') { numReqs += 1; } } // Start workers and listen for messages containing notifyRequest const numCPUs = availableParallelism(); for (let i = 0; i < numCPUs; i++) { cluster.fork(); } for (const id in cluster.workers) { cluster.workers[id].on('message', messageHandler); } } else { // Worker processes have a http server. http.Server((req, res) => { res.writeHead(200); res.end('hello world\n'); // Notify primary about the request process.send({ cmd: 'notifyRequest' }); }).listen(8000); } #### Event: `'online'`# Added in: v0.7.0 Similar to the `cluster.on('online')` event, but specific to this worker. cluster.fork().on('online', () => { // Worker is online }); It is not emitted in the worker. #### `worker.disconnect()`# History VersionChanges v7.3.0 This method now returns a reference to `worker`. v0.7.7 Added in: v0.7.7 * Returns: A reference to `worker`. In a worker, this function will close all servers, wait for the `'close'` event on those servers, and then disconnect the IPC channel. In the primary, an internal message is sent to the worker causing it to call `.disconnect()` on itself. Causes `.exitedAfterDisconnect` to be set. After a server is closed, it will no longer accept new connections, but connections may be accepted by any other listening worker. Existing connections will be allowed to close as usual. When no more connections exist, see `server.close()`, the IPC channel to the worker will close allowing it to die gracefully. The above applies only to server connections, client connections are not automatically closed by workers, and disconnect does not wait for them to close before exiting. In a worker, `process.disconnect` exists, but it is not this function; it is `disconnect()`. Because long living server connections may block workers from disconnecting, it may be useful to send a message, so application specific actions may be taken to close them. It also may be useful to implement a timeout, killing a worker if the `'disconnect'` event has not been emitted after some time. if (cluster.isPrimary) { const worker = cluster.fork(); let timeout; worker.on('listening', (address) => { worker.send('shutdown'); worker.disconnect(); timeout = setTimeout(() => { worker.kill(); }, 2000); }); worker.on('disconnect', () => { clearTimeout(timeout); }); } else if (cluster.isWorker) { const net = require('node:net'); const server = net.createServer((socket) => { // Connections never end }); server.listen(8000); process.on('message', (msg) => { if (msg === 'shutdown') { // Initiate graceful close of any connections to server } }); } #### `worker.exitedAfterDisconnect`# Added in: v6.0.0 * Type: This property is `true` if the worker exited due to `.disconnect()`. If the worker exited any other way, it is `false`. If the worker has not exited, it is `undefined`. The boolean `worker.exitedAfterDisconnect` allows distinguishing between voluntary and accidental exit, the primary may choose not to respawn a worker based on this value. cluster.on('exit', (worker, code, signal) => { if (worker.exitedAfterDisconnect === true) { console.log('Oh, it was just voluntary – no need to worry'); } }); // kill worker worker.kill(); #### `worker.id`# Added in: v0.8.0 * Type: Each new worker is given its own unique id, this id is stored in the `id`. While a worker is alive, this is the key that indexes it in `cluster.workers`. #### `worker.isConnected()`# Added in: v0.11.14 This function returns `true` if the worker is connected to its primary via its IPC channel, `false` otherwise. A worker is connected to its primary after it has been created. It is disconnected after the `'disconnect'` event is emitted. #### `worker.isDead()`# Added in: v0.11.14 This function returns `true` if the worker's process has terminated (either because of exiting or being signaled). Otherwise, it returns `false`. import cluster from 'node:cluster'; import http from 'node:http'; import { availableParallelism } from 'node:os'; import process from 'node:process'; const numCPUs = availableParallelism(); if (cluster.isPrimary) { console.log(`Primary ${process.pid} is running`); // Fork workers. for (let i = 0; i < numCPUs; i++) { cluster.fork(); } cluster.on('fork', (worker) => { console.log('worker is dead:', worker.isDead()); }); cluster.on('exit', (worker, code, signal) => { console.log('worker is dead:', worker.isDead()); }); } else { // Workers can share any TCP connection. In this case, it is an HTTP server. http.createServer((req, res) => { res.writeHead(200); res.end(`Current process\n ${process.pid}`); process.kill(process.pid); }).listen(8000); } #### `worker.kill([signal])`# Added in: v0.9.12 * `signal` Name of the kill signal to send to the worker process. Default: `'SIGTERM'` This function will kill the worker. In the primary worker, it does this by disconnecting the `worker.process`, and once disconnected, killing with `signal`. In the worker, it does it by killing the process with `signal`. The `kill()` function kills the worker process without waiting for a graceful disconnect, it has the same behavior as `worker.process.kill()`. This method is aliased as `worker.destroy()` for backwards compatibility. In a worker, `process.kill()` exists, but it is not this function; it is `kill()`. #### `worker.process`# Added in: v0.7.0 * Type: All workers are created using `child_process.fork()`, the returned object from this function is stored as `.process`. In a worker, the global `process` is stored. See: Child Process module. Workers will call `process.exit(0)` if the `'disconnect'` event occurs on `process` and `.exitedAfterDisconnect` is not `true`. This protects against accidental disconnection. #### `worker.send(message[, sendHandle[, options]][, callback])`# History VersionChanges v4.0.0 The `callback` parameter is supported now. v0.7.0 Added in: v0.7.0 * `message` * `sendHandle` * `options` The `options` argument, if present, is an object used to parameterize the sending of certain types of handles. `options` supports the following properties: * `keepOpen` A value that can be used when passing instances of `net.Socket`. When `true`, the socket is kept open in the sending process. Default: `false`. * `callback` * Returns: Send a message to a worker or primary, optionally with a handle. In the primary, this sends a message to a specific worker. It is identical to `ChildProcess.send()`. In a worker, this sends a message to the primary. It is identical to `process.send()`. This example will echo back all messages from the primary: if (cluster.isPrimary) { const worker = cluster.fork(); worker.send('hi there'); } else if (cluster.isWorker) { process.on('message', (msg) => { process.send(msg); }); } ### Event: `'disconnect'`# Added in: v0.7.9 * `worker` Emitted after the worker IPC channel has disconnected. This can occur when a worker exits gracefully, is killed, or is disconnected manually (such as with `worker.disconnect()`). There may be a delay between the `'disconnect'` and `'exit'` events. These events can be used to detect if the process is stuck in a cleanup or if there are long-living connections. cluster.on('disconnect', (worker) => { console.log(`The worker #${worker.id} has disconnected`); }); ### Event: `'exit'`# Added in: v0.7.9 * `worker` * `code` The exit code, if it exited normally. * `signal` The name of the signal (e.g. `'SIGHUP'`) that caused the process to be killed. When any of the workers die the cluster module will emit the `'exit'` event. This can be used to restart the worker by calling `.fork()` again. cluster.on('exit', (worker, code, signal) => { console.log('worker %d died (%s). restarting...', worker.process.pid, signal || code); cluster.fork(); }); See `child_process` event: `'exit'`. ### Event: `'fork'`# Added in: v0.7.0 * `worker` When a new worker is forked the cluster module will emit a `'fork'` event. This can be used to log worker activity, and create a custom timeout. const timeouts = []; function errorMsg() { console.error('Something must be wrong with the connection ...'); } cluster.on('fork', (worker) => { timeouts[worker.id] = setTimeout(errorMsg, 2000); }); cluster.on('listening', (worker, address) => { clearTimeout(timeouts[worker.id]); }); cluster.on('exit', (worker, code, signal) => { clearTimeout(timeouts[worker.id]); errorMsg(); }); ### Event: `'listening'`# Added in: v0.7.0 * `worker` * `address` After calling `listen()` from a worker, when the `'listening'` event is emitted on the server, a `'listening'` event will also be emitted on `cluster` in the primary. The event handler is executed with two arguments, the `worker` contains the worker object and the `address` object contains the following connection properties: `address`, `port`, and `addressType`. This is very useful if the worker is listening on more than one address. cluster.on('listening', (worker, address) => { console.log( `A worker is now connected to ${address.address}:${address.port}`); }); The `addressType` is one of: * `4` (TCPv4) * `6` (TCPv6) * `-1` (Unix domain socket) * `'udp4'` or `'udp6'` (UDPv4 or UDPv6) ### Event: `'message'`# History VersionChanges v6.0.0 The `worker` parameter is passed now; see below for details. v2.5.0 Added in: v2.5.0 * `worker` * `message` * `handle` | Emitted when the cluster primary receives a message from any worker. See `child_process` event: `'message'`. ### Event: `'online'`# Added in: v0.7.0 * `worker` After forking a new worker, the worker should respond with an online message. When the primary receives an online message it will emit this event. The difference between `'fork'` and `'online'` is that fork is emitted when the primary forks a worker, and `'online'` is emitted when the worker is running. cluster.on('online', (worker) => { console.log('Yay, the worker responded after it was forked'); }); ### Event: `'setup'`# Added in: v0.7.1 * `settings` Emitted every time `.setupPrimary()` is called. The `settings` object is the `cluster.settings` object at the time `.setupPrimary()` was called and is advisory only, since multiple calls to `.setupPrimary()` can be made in a single tick. If accuracy is important, use `cluster.settings`. ### `cluster.disconnect([callback])`# Added in: v0.7.7 * `callback` Called when all workers are disconnected and handles are closed. Calls `.disconnect()` on each worker in `cluster.workers`. When they are disconnected all internal handles will be closed, allowing the primary process to die gracefully if no other event is waiting. The method takes an optional callback argument which will be called when finished. This can only be called from the primary process. ### `cluster.fork([env])`# Added in: v0.6.0 * `env` Key/value pairs to add to worker process environment. * Returns: Spawn a new worker process. This can only be called from the primary process. ### `cluster.isMaster`# Added in: v0.8.1Deprecated since: v16.0.0 Stability: 0 \- Deprecated Deprecated alias for `cluster.isPrimary`. ### `cluster.isPrimary`# Added in: v16.0.0 * Type: True if the process is a primary. This is determined by the `process.env.NODE_UNIQUE_ID`. If `process.env.NODE_UNIQUE_ID` is undefined, then `isPrimary` is `true`. ### `cluster.isWorker`# Added in: v0.6.0 * Type: True if the process is not a primary (it is the negation of `cluster.isPrimary`). ### `cluster.schedulingPolicy`# Added in: v0.11.2 The scheduling policy, either `cluster.SCHED_RR` for round-robin or `cluster.SCHED_NONE` to leave it to the operating system. This is a global setting and effectively frozen once either the first worker is spawned, or `.setupPrimary()` is called, whichever comes first. `SCHED_RR` is the default on all operating systems except Windows. Windows will change to `SCHED_RR` once libuv is able to effectively distribute IOCP handles without incurring a large performance hit. `cluster.schedulingPolicy` can also be set through the `NODE_CLUSTER_SCHED_POLICY` environment variable. Valid values are `'rr'` and `'none'`. ### `cluster.settings`# History VersionChanges v13.2.0, v12.16.0 The `serialization` option is supported now. v9.5.0 The `cwd` option is supported now. v9.4.0 The `windowsHide` option is supported now. v8.2.0 The `inspectPort` option is supported now. v6.4.0 The `stdio` option is supported now. v0.7.1 Added in: v0.7.1 * Type: * `execArgv` List of string arguments passed to the Node.js executable. Default: `process.execArgv`. * `exec` File path to worker file. Default: `process.argv[1]`. * `args` String arguments passed to worker. Default: `process.argv.slice(2)`. * `cwd` Current working directory of the worker process. Default: `undefined` (inherits from parent process). * `serialization` Specify the kind of serialization used for sending messages between processes. Possible values are `'json'` and `'advanced'`. See Advanced serialization for `child_process` for more details. Default: `false`. * `silent` Whether or not to send output to parent's stdio. Default: `false`. * `stdio` Configures the stdio of forked processes. Because the cluster module relies on IPC to function, this configuration must contain an `'ipc'` entry. When this option is provided, it overrides `silent`. See `child_process.spawn()`'s `stdio`. * `uid` Sets the user identity of the process. (See `setuid(2)`.) * `gid` Sets the group identity of the process. (See `setgid(2)`.) * `inspectPort` | Sets inspector port of worker. This can be a number, or a function that takes no arguments and returns a number. By default each worker gets its own port, incremented from the primary's `process.debugPort`. * `windowsHide` Hide the forked processes console window that would normally be created on Windows systems. Default: `false`. After calling `.setupPrimary()` (or `.fork()`) this settings object will contain the settings, including the default values. This object is not intended to be changed or set manually. ### `cluster.setupMaster([settings])`# History VersionChanges v16.0.0 Deprecated since: v16.0.0 v6.4.0 The `stdio` option is supported now. v0.7.1 Added in: v0.7.1 Stability: 0 \- Deprecated Deprecated alias for `.setupPrimary()`. ### `cluster.setupPrimary([settings])`# Added in: v16.0.0 * `settings` See `cluster.settings`. `setupPrimary` is used to change the default 'fork' behavior. Once called, the settings will be present in `cluster.settings`. Any settings changes only affect future calls to `.fork()` and have no effect on workers that are already running. The only attribute of a worker that cannot be set via `.setupPrimary()` is the `env` passed to `.fork()`. The defaults above apply to the first call only; the defaults for later calls are the current values at the time of `cluster.setupPrimary()` is called. import cluster from 'node:cluster'; cluster.setupPrimary({ exec: 'worker.js', args: ['--use', 'https'], silent: true, }); cluster.fork(); // https worker cluster.setupPrimary({ exec: 'worker.js', args: ['--use', 'http'], }); cluster.fork(); // http worker This can only be called from the primary process. ### `cluster.worker`# Added in: v0.7.0 * Type: A reference to the current worker object. Not available in the primary process. import cluster from 'node:cluster'; if (cluster.isPrimary) { console.log('I am primary'); cluster.fork(); cluster.fork(); } else if (cluster.isWorker) { console.log(`I am worker #${cluster.worker.id}`); } ### `cluster.workers`# Added in: v0.7.0 * Type: A hash that stores the active worker objects, keyed by `id` field. This makes it easy to loop through all the workers. It is only available in the primary process. A worker is removed from `cluster.workers` after the worker has disconnected and exited. The order between these two events cannot be determined in advance. However, it is guaranteed that the removal from the `cluster.workers` list happens before the last `'disconnect'` or `'exit'` event is emitted. import cluster from 'node:cluster'; for (const worker of Object.values(cluster.workers)) { worker.send('big announcement to all workers'); } ## Command-line API# Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options. To view this documentation as a manual page in a terminal, run `man node`. ### Synopsis# `node [options] [V8 options] [ | -e "script" | -] [--] [arguments]` `node inspect [ | -e "script" | :] …` `node --v8-options` Execute without arguments to start the REPL. For more info about `node inspect`, see the debugger documentation. ### Program entry point# The program entry point is a specifier-like string. If the string is not an absolute path, it's resolved as a relative path from the current working directory. That path is then resolved by CommonJS module loader. If no corresponding file is found, an error is thrown. If a file is found, its path will be passed to the ES module loader under any of the following conditions: * The program was started with a command-line flag that forces the entry point to be loaded with ECMAScript module loader, such as `--import`. * The file has an `.mjs` or `.wasm` extension. * The file does not have a `.cjs` extension, and the nearest parent `package.json` file contains a top-level `"type"` field with a value of `"module"`. Otherwise, the file is loaded using the CommonJS module loader. See Modules loaders for more details. #### ECMAScript modules loader entry point caveat# When loading, the ES module loader loads the program entry point, the `node` command will accept as input only files with `.js`, `.mjs`, or `.cjs` extensions. With the following flags, additional file extensions are enabled: * `--experimental-addon-modules` for files with `.node` extension. ### Options# History VersionChanges v10.12.0 Underscores instead of dashes are now allowed for Node.js options as well, in addition to V8 options. Stability: 2 \- Stable All options, including V8 options, allow words to be separated by both dashes (`-`) or underscores (`_`). For example, `--pending-deprecation` is equivalent to `--pending_deprecation`. If an option that takes a single value (such as `--max-http-header-size`) is passed more than once, then the last passed value is used. Options from the command line take precedence over options passed through the `NODE_OPTIONS` environment variable. #### `-`# Added in: v8.0.0 Alias for stdin. Analogous to the use of `-` in other command-line utilities, meaning that the script is read from stdin, and the rest of the options are passed to that script. #### `--`# Added in: v6.11.0 Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument is used as a script filename. #### `--abort-on-uncaught-exception`# Added in: v0.10.8 Aborting instead of exiting causes a core file to be generated for post-mortem analysis using a debugger (such as `lldb`, `gdb`, and `mdb`). If this flag is passed, the behavior can still be set to not abort through `process.setUncaughtExceptionCaptureCallback()` (and through usage of the `node:domain` module that uses it). #### `--allow-addons`# Added in: v21.6.0, v20.12.0 Stability: 1.1 \- Active development When using the Permission Model, the process will not be able to use native addons by default. Attempts to do so will throw an `ERR_DLOPEN_DISABLED` unless the user explicitly passes the `--allow-addons` flag when starting Node.js. Example: $ node --permission --allow-fs-read=* index.js node:internal/modules/cjs/loader:1319 return process.dlopen(module, path.toNamespacedPath(filename)); ^ Error: Cannot load native addon because loading addons is disabled. at Module._extensions..node (node:internal/modules/cjs/loader:1319:18) at Module.load (node:internal/modules/cjs/loader:1091:32) at Module._load (node:internal/modules/cjs/loader:938:12) at Module.require (node:internal/modules/cjs/loader:1115:19) at require (node:internal/modules/helpers:130:18) at Object. (/home/index.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1233:14) at Module._extensions..js (node:internal/modules/cjs/loader:1287:10) at Module.load (node:internal/modules/cjs/loader:1091:32) at Module._load (node:internal/modules/cjs/loader:938:12) { code: 'ERR_DLOPEN_DISABLED' } #### `--allow-child-process`# History VersionChanges v24.4.0 When spawning process with the permission model enabled. The flags are inherit to the child Node.js process through NODE_OPTIONS environment variable. v20.0.0 Added in: v20.0.0 Stability: 1.1 \- Active development When using the Permission Model, the process will not be able to spawn any child process by default. Attempts to do so will throw an `ERR_ACCESS_DENIED` unless the user explicitly passes the `--allow-child-process` flag when starting Node.js. Example: const childProcess = require('node:child_process'); // Attempt to bypass the permission childProcess.spawn('node', ['-e', 'require("fs").writeFileSync("/new-file", "example")']); $ node --permission --allow-fs-read=* index.js node:internal/child_process:388 const err = this._handle.spawn(options); ^ Error: Access to this API has been restricted at ChildProcess.spawn (node:internal/child_process:388:28) at node:internal/main/run_main_module:17:47 { code: 'ERR_ACCESS_DENIED', permission: 'ChildProcess' } The `child_process.fork()` API inherits the execution arguments from the parent process. This means that if Node.js is started with the Permission Model enabled and the `--allow-child-process` flag is set, any child process created using `child_process.fork()` will automatically receive all relevant Permission Model flags. This behavior also applies to `child_process.spawn()`, but in that case, the flags are propagated via the `NODE_OPTIONS` environment variable rather than directly through the process arguments. #### `--allow-fs-read`# History VersionChanges v24.2.0 Entrypoints of your application are allowed to be read implicitly. v23.5.0, v22.13.0 Permission Model and --allow-fs flags are stable. v20.7.0 Paths delimited by comma (`,`) are no longer allowed. v20.0.0 Added in: v20.0.0 This flag configures file system read permissions using the Permission Model. The valid arguments for the `--allow-fs-read` flag are: * `*` \- To allow all `FileSystemRead` operations. * Multiple paths can be allowed using multiple `--allow-fs-read` flags. Example `--allow-fs-read=/folder1/ --allow-fs-read=/folder1/` Examples can be found in the File System Permissions documentation. The initializer module and custom `--require` modules has a implicit read permission. $ node --permission -r custom-require.js -r custom-require-2.js index.js * The `custom-require.js`, `custom-require-2.js`, and `index.js` will be by default in the allowed read list. process.has('fs.read', 'index.js'); // true process.has('fs.read', 'custom-require.js'); // true process.has('fs.read', 'custom-require-2.js'); // true #### `--allow-fs-write`# History VersionChanges v23.5.0, v22.13.0 Permission Model and --allow-fs flags are stable. v20.7.0 Paths delimited by comma (`,`) are no longer allowed. v20.0.0 Added in: v20.0.0 This flag configures file system write permissions using the Permission Model. The valid arguments for the `--allow-fs-write` flag are: * `*` \- To allow all `FileSystemWrite` operations. * Multiple paths can be allowed using multiple `--allow-fs-write` flags. Example `--allow-fs-write=/folder1/ --allow-fs-write=/folder1/` Paths delimited by comma (`,`) are no longer allowed. When passing a single flag with a comma a warning will be displayed. Examples can be found in the File System Permissions documentation. #### `--allow-wasi`# Added in: v22.3.0, v20.16.0 Stability: 1.1 \- Active development When using the Permission Model, the process will not be capable of creating any WASI instances by default. For security reasons, the call will throw an `ERR_ACCESS_DENIED` unless the user explicitly passes the flag `--allow-wasi` in the main Node.js process. Example: const { WASI } = require('node:wasi'); // Attempt to bypass the permission new WASI({ version: 'preview1', // Attempt to mount the whole filesystem preopens: { '/': '/', }, }); $ node --permission --allow-fs-read=* index.js Error: Access to this API has been restricted at node:internal/main/run_main_module:30:49 { code: 'ERR_ACCESS_DENIED', permission: 'WASI', } #### `--allow-worker`# Added in: v20.0.0 Stability: 1.1 \- Active development When using the Permission Model, the process will not be able to create any worker threads by default. For security reasons, the call will throw an `ERR_ACCESS_DENIED` unless the user explicitly pass the flag `--allow-worker` in the main Node.js process. Example: const { Worker } = require('node:worker_threads'); // Attempt to bypass the permission new Worker(__filename); $ node --permission --allow-fs-read=* index.js Error: Access to this API has been restricted at node:internal/main/run_main_module:17:47 { code: 'ERR_ACCESS_DENIED', permission: 'WorkerThreads' } #### `--build-snapshot`# Added in: v18.8.0 Stability: 1 \- Experimental Generates a snapshot blob when the process exits and writes it to disk, which can be loaded later with `--snapshot-blob`. When building the snapshot, if `--snapshot-blob` is not specified, the generated blob will be written, by default, to `snapshot.blob` in the current working directory. Otherwise it will be written to the path specified by `--snapshot-blob`. $ echo "globalThis.foo = 'I am from the snapshot'" > snapshot.js # Run snapshot.js to initialize the application and snapshot the # state of it into snapshot.blob. $ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js $ echo "console.log(globalThis.foo)" > index.js # Load the generated snapshot and start the application from index.js. $ node --snapshot-blob snapshot.blob index.js I am from the snapshot The `v8.startupSnapshot` API can be used to specify an entry point at snapshot building time, thus avoiding the need of an additional entry script at deserialization time: $ echo "require('v8').startupSnapshot.setDeserializeMainFunction(() => console.log('I am from the snapshot'))" > snapshot.js $ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js $ node --snapshot-blob snapshot.blob I am from the snapshot For more information, check out the `v8.startupSnapshot` API documentation. Currently the support for run-time snapshot is experimental in that: 1. User-land modules are not yet supported in the snapshot, so only one single file can be snapshotted. Users can bundle their applications into a single script with their bundler of choice before building a snapshot, however. 2. Only a subset of the built-in modules work in the snapshot, though the Node.js core test suite checks that a few fairly complex applications can be snapshotted. Support for more modules are being added. If any crashes or buggy behaviors occur when building a snapshot, please file a report in the Node.js issue tracker and link to it in the tracking issue for user-land snapshots. #### `--build-snapshot-config`# Added in: v21.6.0, v20.12.0 Stability: 1 \- Experimental Specifies the path to a JSON configuration file which configures snapshot creation behavior. The following options are currently supported: * `builder` Required. Provides the name to the script that is executed before building the snapshot, as if `--build-snapshot` had been passed with `builder` as the main script name. * `withoutCodeCache` Optional. Including the code cache reduces the time spent on compiling functions included in the snapshot at the expense of a bigger snapshot size and potentially breaking portability of the snapshot. When using this flag, additional script files provided on the command line will not be executed and instead be interpreted as regular command line arguments. #### `-c`, `--check`# History VersionChanges v10.0.0 The `--require` option is now supported when checking a file. v5.0.0, v4.2.0 Added in: v5.0.0, v4.2.0 Syntax check the script without executing. #### `--completion-bash`# Added in: v10.12.0 Print source-able bash completion script for Node.js. node --completion-bash > node_bash_completion source node_bash_completion #### `-C condition`, `--conditions=condition`# History VersionChanges v22.9.0, v20.18.0 The flag is no longer experimental. v14.9.0, v12.19.0 Added in: v14.9.0, v12.19.0 Provide custom conditional exports resolution conditions. Any number of custom string condition names are permitted. The default Node.js conditions of `"node"`, `"default"`, `"import"`, and `"require"` will always apply as defined. For example, to run a module with "development" resolutions: node -C development app.js #### `--cpu-prof`# History VersionChanges v22.4.0, v20.16.0 The `--cpu-prof` flags are now stable. v12.0.0 Added in: v12.0.0 Starts the V8 CPU profiler on start up, and writes the CPU profile to disk before exit. If `--cpu-prof-dir` is not specified, the generated profile is placed in the current working directory. If `--cpu-prof-name` is not specified, the generated profile is named `CPU.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.cpuprofile`. $ node --cpu-prof index.js $ ls *.cpuprofile CPU.20190409.202950.15293.0.0.cpuprofile If `--cpu-prof-name` is specified, the provided value is used as a template for the file name. The following placeholder is supported and will be substituted at runtime: * `${pid}` — the current process ID $ node --cpu-prof --cpu-prof-name 'CPU.${pid}.cpuprofile' index.js $ ls *.cpuprofile CPU.15293.cpuprofile #### `--cpu-prof-dir`# History VersionChanges v22.4.0, v20.16.0 The `--cpu-prof` flags are now stable. v12.0.0 Added in: v12.0.0 Specify the directory where the CPU profiles generated by `--cpu-prof` will be placed. The default value is controlled by the `--diagnostic-dir` command-line option. #### `--cpu-prof-interval`# History VersionChanges v22.4.0, v20.16.0 The `--cpu-prof` flags are now stable. v12.2.0 Added in: v12.2.0 Specify the sampling interval in microseconds for the CPU profiles generated by `--cpu-prof`. The default is 1000 microseconds. #### `--cpu-prof-name`# History VersionChanges v22.4.0, v20.16.0 The `--cpu-prof` flags are now stable. v12.0.0 Added in: v12.0.0 Specify the file name of the CPU profile generated by `--cpu-prof`. #### `--diagnostic-dir=directory`# Set the directory to which all diagnostic output files are written. Defaults to current working directory. Affects the default output directory of: * `--cpu-prof-dir` * `--heap-prof-dir` * `--redirect-warnings` #### `--disable-proto=mode`# Added in: v13.12.0, v12.17.0 Disable the `Object.prototype.__proto__` property. If `mode` is `delete`, the property is removed entirely. If `mode` is `throw`, accesses to the property throw an exception with the code `ERR_PROTO_ACCESS`. #### `--disable-sigusr1`# History VersionChanges v24.8.0 The option is no longer experimental. v23.7.0, v22.14.0 Added in: v23.7.0, v22.14.0 Disable the ability of starting a debugging session by sending a `SIGUSR1` signal to the process. #### `--disable-warning=code-or-type`# Added in: v21.3.0, v20.11.0 Stability: 1.1 \- Active development Disable specific process warnings by `code` or `type`. Warnings emitted from `process.emitWarning()` may contain a `code` and a `type`. This option will not-emit warnings that have a matching `code` or `type`. List of deprecation warnings. The Node.js core warning types are: `DeprecationWarning` and `ExperimentalWarning` For example, the following script will not emit DEP0025 `require('node:sys')` when executed with `node --disable-warning=DEP0025`: import sys from 'node:sys'; For example, the following script will emit the DEP0025 `require('node:sys')`, but not any Experimental Warnings (such as ExperimentalWarning: `vm.measureMemory` is an experimental feature in <=v21) when executed with `node --disable-warning=ExperimentalWarning`: import sys from 'node:sys'; import vm from 'node:vm'; vm.measureMemory(); #### `--disable-wasm-trap-handler`# Added in: v22.2.0, v20.15.0 By default, Node.js enables trap-handler-based WebAssembly bound checks. As a result, V8 does not need to insert inline bound checks int the code compiled from WebAssembly which may speedup WebAssembly execution significantly, but this optimization requires allocating a big virtual memory cage (currently 10GB). If the Node.js process does not have access to a large enough virtual memory address space due to system configurations or hardware limitations, users won't be able to run any WebAssembly that involves allocation in this virtual memory cage and will see an out-of-memory error. $ ulimit -v 5000000 $ node -p "new WebAssembly.Memory({ initial: 10, maximum: 100 });" [eval]:1 new WebAssembly.Memory({ initial: 10, maximum: 100 }); ^ RangeError: WebAssembly.Memory(): could not allocate memory at [eval]:1:1 at runScriptInThisContext (node:internal/vm:209:10) at node:internal/process/execution:118:14 at [eval]-wrapper:6:24 at runScript (node:internal/process/execution:101:62) at evalScript (node:internal/process/execution:136:3) at node:internal/main/eval_string:49:3 `--disable-wasm-trap-handler` disables this optimization so that users can at least run WebAssembly (with less optimal performance) when the virtual memory address space available to their Node.js process is lower than what the V8 WebAssembly memory cage needs. #### `--disallow-code-generation-from-strings`# Added in: v9.8.0 Make built-in language features like `eval` and `new Function` that generate code from strings throw an exception instead. This does not affect the Node.js `node:vm` module. #### `--dns-result-order=order`# History VersionChanges v22.1.0, v20.13.0 The `ipv6first` is supported now. v17.0.0 Changed default value to `verbatim`. v16.4.0, v14.18.0 Added in: v16.4.0, v14.18.0 Set the default value of `order` in `dns.lookup()` and `dnsPromises.lookup()`. The value could be: * `ipv4first`: sets default `order` to `ipv4first`. * `ipv6first`: sets default `order` to `ipv6first`. * `verbatim`: sets default `order` to `verbatim`. The default is `verbatim` and `dns.setDefaultResultOrder()` have higher priority than `--dns-result-order`. #### `--enable-fips`# Added in: v6.0.0 Enable FIPS-compliant crypto at startup. (Requires Node.js to be built against FIPS-compatible OpenSSL.) #### `--enable-network-family-autoselection`# Added in: v18.18.0 Enables the family autoselection algorithm unless connection options explicitly disables it. #### `--enable-source-maps`# History VersionChanges v15.11.0, v14.18.0 This API is no longer experimental. v12.12.0 Added in: v12.12.0 Enable Source Map support for stack traces. When using a transpiler, such as TypeScript, stack traces thrown by an application reference the transpiled code, not the original source position. `--enable-source-maps` enables caching of Source Maps and makes a best effort to report stack traces relative to the original source file. Overriding `Error.prepareStackTrace` may prevent `--enable-source-maps` from modifying the stack trace. Call and return the results of the original `Error.prepareStackTrace` in the overriding function to modify the stack trace with source maps. const originalPrepareStackTrace = Error.prepareStackTrace; Error.prepareStackTrace = (error, trace) => { // Modify error and trace and format stack trace with // original Error.prepareStackTrace. return originalPrepareStackTrace(error, trace); }; Note, enabling source maps can introduce latency to your application when `Error.stack` is accessed. If you access `Error.stack` frequently in your application, take into account the performance implications of `--enable-source-maps`. #### `--entry-url`# Added in: v23.0.0, v22.10.0 Stability: 1 \- Experimental When present, Node.js will interpret the entry point as a URL, rather than a path. Follows ECMAScript module resolution rules. Any query parameter or hash in the URL will be accessible via `import.meta.url`. node --entry-url 'file:///path/to/file.js?queryparams=work#and-hashes-too' node --entry-url 'file.ts?query#hash' node --entry-url 'data:text/javascript,console.log("Hello")' #### `--env-file-if-exists=file`# Added in: v22.9.0 Stability: 1.1 \- Active development Behavior is the same as `--env-file`, but an error is not thrown if the file does not exist. #### `--env-file=file`# History VersionChanges v21.7.0, v20.12.0 Add support to multi-line values. v20.6.0 Added in: v20.6.0 Stability: 1.1 \- Active development Loads environment variables from a file relative to the current directory, making them available to applications on `process.env`. The environment variables which configure Node.js, such as `NODE_OPTIONS`, are parsed and applied. If the same variable is defined in the environment and in the file, the value from the environment takes precedence. You can pass multiple `--env-file` arguments. Subsequent files override pre-existing variables defined in previous files. An error is thrown if the file does not exist. node --env-file=.env --env-file=.development.env index.js The format of the file should be one line per key-value pair of environment variable name and value separated by `=`: PORT=3000 Any text after a `#` is treated as a comment: # This is a comment PORT=3000 # This is also a comment Values can start and end with the following quotes: ```, `"` or `'`. They are omitted from the values. USERNAME="nodejs" # will result in `nodejs` as the value. Multi-line values are supported: MULTI_LINE="THIS IS A MULTILINE" # will result in `THIS IS\nA MULTILINE` as the value. Export keyword before a key is ignored: export USERNAME="nodejs" # will result in `nodejs` as the value. If you want to load environment variables from a file that may not exist, you can use the `--env-file-if-exists` flag instead. #### `-e`, `--eval "script"`# History VersionChanges v22.6.0 Eval now supports experimental type-stripping. v5.11.0 Built-in libraries are now available as predefined variables. v0.5.2 Added in: v0.5.2 Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in `script`. On Windows, using `cmd.exe` a single quote will not work correctly because it only recognizes double `"` for quoting. In Powershell or Git bash, both `'` and `"` are usable. It is possible to run code containing inline types unless the `--no-experimental-strip-types` flag is provided. #### `--experimental-addon-modules`# Added in: v23.6.0 Stability: 1.0 \- Early development Enable experimental import support for `.node` addons. #### `--experimental-config-file=config`# Added in: v23.10.0 Stability: 1.0 \- Early development If present, Node.js will look for a configuration file at the specified path. Node.js will read the configuration file and apply the settings. The configuration file should be a JSON file with the following structure. `vX.Y.Z` in the `$schema` must be replaced with the version of Node.js you are using. { "$schema": "https://nodejs.org/dist/vX.Y.Z/docs/node-config-schema.json", "nodeOptions": { "import": [ "amaro/strip" ], "watch-path": "src", "watch-preserve-output": true }, "testRunner": { "test-isolation": "process" } } The configuration file supports namespace-specific options: * The `nodeOptions` field contains CLI flags that are allowed in `NODE_OPTIONS`. * Namespace fields like `testRunner` contain configuration specific to that subsystem. No-op flags are not supported. Not all V8 flags are currently supported. It is possible to use the official JSON schema to validate the configuration file, which may vary depending on the Node.js version. Each key in the configuration file corresponds to a flag that can be passed as a command-line argument. The value of the key is the value that would be passed to the flag. For example, the configuration file above is equivalent to the following command-line arguments: node --import amaro/strip --watch-path=src --watch-preserve-output --test-isolation=process The priority in configuration is as follows: 1. NODE_OPTIONS and command-line options 2. Configuration file 3. Dotenv NODE_OPTIONS Values in the configuration file will not override the values in the environment variables and command-line options, but will override the values in the `NODE_OPTIONS` env file parsed by the `--env-file` flag. Keys cannot be duplicated within the same or different namespaces. The configuration parser will throw an error if the configuration file contains unknown keys or keys that cannot be used in a namespace. Node.js will not sanitize or perform validation on the user-provided configuration, so NEVER use untrusted configuration files. #### `--experimental-default-config-file`# Added in: v23.10.0 Stability: 1.0 \- Early development If the `--experimental-default-config-file` flag is present, Node.js will look for a `node.config.json` file in the current working directory and load it as a as configuration file. #### `--experimental-eventsource`# Added in: v22.3.0, v20.18.0 Enable exposition of EventSource Web API on the global scope. #### `--experimental-import-meta-resolve`# History VersionChanges v20.6.0, v18.19.0 synchronous import.meta.resolve made available by default, with the flag retained for enabling the experimental second argument as previously supported. v13.9.0, v12.16.2 Added in: v13.9.0, v12.16.2 Enable experimental `import.meta.resolve()` parent URL support, which allows passing a second `parentURL` argument for contextual resolution. Previously gated the entire `import.meta.resolve` feature. #### `--experimental-inspector-network-resource`# Added in: v24.5.0 Stability: 1.1 \- Active Development Enable experimental support for inspector network resources. #### `--experimental-loader=module`# History VersionChanges v23.6.1, v22.13.1, v20.18.2 Using this feature with the permission model enabled requires passing `--allow-worker`. v12.11.1 This flag was renamed from `--loader` to `--experimental-loader`. v8.8.0 Added in: v8.8.0 > This flag is discouraged and may be removed in a future version of Node.js. Please use `--import` with `register()` instead. Specify the `module` containing exported module customization hooks. `module` may be any string accepted as an `import` specifier. This feature requires `--allow-worker` if used with the Permission Model. #### `--experimental-network-inspection`# Added in: v22.6.0, v20.18.0 Stability: 1 \- Experimental Enable experimental support for the network inspection with Chrome DevTools. #### `--experimental-print-required-tla`# Added in: v22.0.0, v20.17.0 If the ES module being `require()`'d contains top-level `await`, this flag allows Node.js to evaluate the module, try to locate the top-level awaits, and print their location to help users find them. #### `--experimental-require-module`# History VersionChanges v23.0.0, v22.12.0, v20.19.0 This is now true by default. v22.0.0, v20.17.0 Added in: v22.0.0, v20.17.0 Stability: 1.1 \- Active Development Supports loading a synchronous ES module graph in `require()`. See Loading ECMAScript modules using `require()`. #### `--experimental-sea-config`# Added in: v20.0.0 Stability: 1 \- Experimental Use this flag to generate a blob that can be injected into the Node.js binary to produce a single executable application. See the documentation about this configuration for details. #### `--experimental-shadow-realm`# Added in: v19.0.0, v18.13.0 Use this flag to enable ShadowRealm support. #### `--experimental-test-coverage`# History VersionChanges v20.1.0, v18.17.0 This option can be used with `--test`. v19.7.0, v18.15.0 Added in: v19.7.0, v18.15.0 When used in conjunction with the `node:test` module, a code coverage report is generated as part of the test runner output. If no tests are run, a coverage report is not generated. See the documentation on collecting code coverage from tests for more details. #### `--experimental-test-module-mocks`# History VersionChanges v23.6.1, v22.13.1, v20.18.2 Using this feature with the permission model enabled requires passing `--allow-worker`. v22.3.0, v20.18.0 Added in: v22.3.0, v20.18.0 Stability: 1.0 \- Early development Enable module mocking in the test runner. This feature requires `--allow-worker` if used with the Permission Model. #### `--experimental-transform-types`# Added in: v22.7.0 Stability: 1.2 \- Release candidate Enables the transformation of TypeScript-only syntax into JavaScript code. Implies `--enable-source-maps`. #### `--experimental-vm-modules`# Added in: v9.6.0 Enable experimental ES Module support in the `node:vm` module. #### `--experimental-wasi-unstable-preview1`# History VersionChanges v20.0.0, v18.17.0 This option is no longer required as WASI is enabled by default, but can still be passed. v13.6.0 changed from `--experimental-wasi-unstable-preview0` to `--experimental-wasi-unstable-preview1`. v13.3.0, v12.16.0 Added in: v13.3.0, v12.16.0 Enable experimental WebAssembly System Interface (WASI) support. #### `--experimental-webstorage`# Added in: v22.4.0 Enable experimental `Web Storage` support. #### `--experimental-worker-inspection`# Added in: v24.1.0 Stability: 1.1 \- Active Development Enable experimental support for the worker inspection with Chrome DevTools. #### `--expose-gc`# Added in: v22.3.0, v20.18.0 Stability: 1 \- Experimental. This flag is inherited from V8 and is subject to change upstream. This flag will expose the gc extension from V8. if (globalThis.gc) { globalThis.gc(); } #### `--force-context-aware`# Added in: v12.12.0 Disable loading native addons that are not context-aware. #### `--force-fips`# Added in: v6.0.0 Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.) (Same requirements as `--enable-fips`.) #### `--force-node-api-uncaught-exceptions-policy`# Added in: v18.3.0, v16.17.0 Enforces `uncaughtException` event on Node-API asynchronous callbacks. To prevent from an existing add-on from crashing the process, this flag is not enabled by default. In the future, this flag will be enabled by default to enforce the correct behavior. #### `--frozen-intrinsics`# Added in: v11.12.0 Stability: 1 \- Experimental Enable experimental frozen intrinsics like `Array` and `Object`. Only the root context is supported. There is no guarantee that `globalThis.Array` is indeed the default intrinsic reference. Code may break under this flag. To allow polyfills to be added, `--require` and `--import` both run before freezing intrinsics. #### `--heap-prof`# History VersionChanges v22.4.0, v20.16.0 The `--heap-prof` flags are now stable. v12.4.0 Added in: v12.4.0 Starts the V8 heap profiler on start up, and writes the heap profile to disk before exit. If `--heap-prof-dir` is not specified, the generated profile is placed in the current working directory. If `--heap-prof-name` is not specified, the generated profile is named `Heap.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.heapprofile`. $ node --heap-prof index.js $ ls *.heapprofile Heap.20190409.202950.15293.0.001.heapprofile #### `--heap-prof-dir`# History VersionChanges v22.4.0, v20.16.0 The `--heap-prof` flags are now stable. v12.4.0 Added in: v12.4.0 Specify the directory where the heap profiles generated by `--heap-prof` will be placed. The default value is controlled by the `--diagnostic-dir` command-line option. #### `--heap-prof-interval`# History VersionChanges v22.4.0, v20.16.0 The `--heap-prof` flags are now stable. v12.4.0 Added in: v12.4.0 Specify the average sampling interval in bytes for the heap profiles generated by `--heap-prof`. The default is 512 * 1024 bytes. #### `--heap-prof-name`# History VersionChanges v22.4.0, v20.16.0 The `--heap-prof` flags are now stable. v12.4.0 Added in: v12.4.0 Specify the file name of the heap profile generated by `--heap-prof`. #### `--heapsnapshot-near-heap-limit=max_count`# Added in: v15.1.0, v14.18.0 Stability: 1 \- Experimental Writes a V8 heap snapshot to disk when the V8 heap usage is approaching the heap limit. `count` should be a non-negative integer (in which case Node.js will write no more than `max_count` snapshots to disk). When generating snapshots, garbage collection may be triggered and bring the heap usage down. Therefore multiple snapshots may be written to disk before the Node.js instance finally runs out of memory. These heap snapshots can be compared to determine what objects are being allocated during the time consecutive snapshots are taken. It's not guaranteed that Node.js will write exactly `max_count` snapshots to disk, but it will try its best to generate at least one and up to `max_count` snapshots before the Node.js instance runs out of memory when `max_count` is greater than `0`. Generating V8 snapshots takes time and memory (both memory managed by the V8 heap and native memory outside the V8 heap). The bigger the heap is, the more resources it needs. Node.js will adjust the V8 heap to accommodate the additional V8 heap memory overhead, and try its best to avoid using up all the memory available to the process. When the process uses more memory than the system deems appropriate, the process may be terminated abruptly by the system, depending on the system configuration. $ node --max-old-space-size=100 --heapsnapshot-near-heap-limit=3 index.js Wrote snapshot to Heap.20200430.100036.49580.0.001.heapsnapshot Wrote snapshot to Heap.20200430.100037.49580.0.002.heapsnapshot Wrote snapshot to Heap.20200430.100038.49580.0.003.heapsnapshot <--- Last few GCs ---> [49580:0x110000000] 4826 ms: Mark-sweep 130.6 (147.8) -> 130.5 (147.8) MB, 27.4 / 0.0 ms (average mu = 0.126, current mu = 0.034) allocation failure scavenge might not succeed [49580:0x110000000] 4845 ms: Mark-sweep 130.6 (147.8) -> 130.6 (147.8) MB, 18.8 / 0.0 ms (average mu = 0.088, current mu = 0.031) allocation failure scavenge might not succeed <--- JS stacktrace ---> FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory .... #### `--heapsnapshot-signal=signal`# Added in: v12.0.0 Enables a signal handler that causes the Node.js process to write a heap dump when the specified signal is received. `signal` must be a valid signal name. Disabled by default. $ node --heapsnapshot-signal=SIGUSR2 index.js & $ ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND node 1 5.5 6.1 787252 247004 ? Ssl 16:43 0:02 node --heapsnapshot-signal=SIGUSR2 index.js $ kill -USR2 1 $ ls Heap.20190718.133405.15554.0.001.heapsnapshot #### `-h`, `--help`# Added in: v0.1.3 Print node command-line options. The output of this option is less detailed than this document. #### `--icu-data-dir=file`# Added in: v0.11.15 Specify ICU data load path. (Overrides `NODE_ICU_DATA`.) #### `--import=module`# Added in: v19.0.0, v18.18.0 Stability: 1 \- Experimental Preload the specified module at startup. If the flag is provided several times, each module will be executed sequentially in the order they appear, starting with the ones provided in `NODE_OPTIONS`. Follows ECMAScript module resolution rules. Use `--require` to load a CommonJS module. Modules preloaded with `--require` will run before modules preloaded with `--import`. Modules are preloaded into the main thread as well as any worker threads, forked processes, or clustered processes. #### `--input-type=type`# History VersionChanges v23.6.0 Add support for `-typescript` values. v22.7.0, v20.19.0 ESM syntax detection is enabled by default. v12.0.0 Added in: v12.0.0 This configures Node.js to interpret `--eval` or `STDIN` input as CommonJS or as an ES module. Valid values are `"commonjs"`, `"module"`, `"module-typescript"` and `"commonjs-typescript"`. The `"-typescript"` values are not available with the flag `--no-experimental-strip-types`. The default is no value, or `"commonjs"` if `--no-experimental-detect-module` is passed. If `--input-type` is not provided, Node.js will try to detect the syntax with the following steps: 1. Run the input as CommonJS. 2. If step 1 fails, run the input as an ES module. 3. If step 2 fails with a SyntaxError, strip the types. 4. If step 3 fails with an error code `ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX` or `ERR_INVALID_TYPESCRIPT_SYNTAX`, throw the error from step 2, including the TypeScript error in the message, else run as CommonJS. 5. If step 4 fails, run the input as an ES module. To avoid the delay of multiple syntax detection passes, the `--input-type=type` flag can be used to specify how the `--eval` input should be interpreted. The REPL does not support this option. Usage of `--input-type=module` with `--print` will throw an error, as `--print` does not support ES module syntax. #### `--insecure-http-parser`# Added in: v13.4.0, v12.15.0, v10.19.0 Enable leniency flags on the HTTP parser. This may allow interoperability with non-conformant HTTP implementations. When enabled, the parser will accept the following: * Invalid HTTP headers values. * Invalid HTTP versions. * Allow message containing both `Transfer-Encoding` and `Content-Length` headers. * Allow extra data after message when `Connection: close` is present. * Allow extra transfer encodings after `chunked` has been provided. * Allow `\n` to be used as token separator instead of `\r\n`. * Allow `\r\n` not to be provided after a chunk. * Allow spaces to be present after a chunk size and before `\r\n`. All the above will expose your application to request smuggling or poisoning attack. Avoid using this option. ##### Warning: binding inspector to a public IP:port combination is insecure# Binding the inspector to a public IP (including `0.0.0.0`) with an open port is insecure, as it allows external hosts to connect to the inspector and perform a remote code execution attack. If specifying a host, make sure that either: * The host is not accessible from public networks. * A firewall disallows unwanted connections on the port. More specifically, `--inspect=0.0.0.0` is insecure if the port (`9229` by default) is not firewall-protected. See the debugging security implications section for more information. #### `--inspect-brk[=[host:]port]`# Added in: v7.6.0 Activate inspector on `host:port` and break at start of user script. Default `host:port` is `127.0.0.1:9229`. If port `0` is specified, a random available port will be used. See V8 Inspector integration for Node.js for further explanation on Node.js debugger. #### `--inspect-port=[host:]port`# Added in: v7.6.0 Set the `host:port` to be used when the inspector is activated. Useful when activating the inspector by sending the `SIGUSR1` signal. Except when `--disable-sigusr1` is passed. Default host is `127.0.0.1`. If port `0` is specified, a random available port will be used. See the security warning below regarding the `host` parameter usage. #### `--inspect-publish-uid=stderr,http`# Specify ways of the inspector web socket url exposure. By default inspector websocket url is available in stderr and under `/json/list` endpoint on `http://host:port/json/list`. #### `--inspect-wait[=[host:]port]`# Added in: v22.2.0, v20.15.0 Activate inspector on `host:port` and wait for debugger to be attached. Default `host:port` is `127.0.0.1:9229`. If port `0` is specified, a random available port will be used. See V8 Inspector integration for Node.js for further explanation on Node.js debugger. #### `--inspect[=[host:]port]`# Added in: v6.3.0 Activate inspector on `host:port`. Default is `127.0.0.1:9229`. If port `0` is specified, a random available port will be used. V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the Chrome DevTools Protocol. See V8 Inspector integration for Node.js for further explanation on Node.js debugger. #### `-i`, `--interactive`# Added in: v0.7.7 Opens the REPL even if stdin does not appear to be a terminal. #### `--jitless`# Added in: v12.0.0 Stability: 1 \- Experimental. This flag is inherited from V8 and is subject to change upstream. Disable runtime allocation of executable memory. This may be required on some platforms for security reasons. It can also reduce attack surface on other platforms, but the performance impact may be severe. #### `--localstorage-file=file`# Added in: v22.4.0 The file used to store `localStorage` data. If the file does not exist, it is created the first time `localStorage` is accessed. The same file may be shared between multiple Node.js processes concurrently. This flag is a no-op unless Node.js is started with the `--experimental-webstorage` flag. #### `--max-http-header-size=size`# History VersionChanges v13.13.0 Change maximum default size of HTTP headers from 8 KiB to 16 KiB. v11.6.0, v10.15.0 Added in: v11.6.0, v10.15.0 Specify the maximum size, in bytes, of HTTP headers. Defaults to 16 KiB. #### `--max-old-space-size-percentage=PERCENTAGE`# Sets the max memory size of V8's old memory section as a percentage of available system memory. This flag takes precedence over `--max-old-space-size` when both are specified. The `PERCENTAGE` parameter must be a number greater than 0 and up to 100. representing the percentage of available system memory to allocate to the V8 heap. # Using 50% of available system memory node --max-old-space-size-percentage=50 index.js # Using 75% of available system memory node --max-old-space-size-percentage=75 index.js #### `--napi-modules`# Added in: v7.10.0 This option is a no-op. It is kept for compatibility. #### `--network-family-autoselection-attempt-timeout`# Added in: v22.1.0, v20.13.0 Sets the default value for the network family autoselection attempt timeout. For more information, see `net.getDefaultAutoSelectFamilyAttemptTimeout()`. #### `--no-addons`# Added in: v16.10.0, v14.19.0 Disable the `node-addons` exports condition as well as disable loading native addons. When `--no-addons` is specified, calling `process.dlopen` or requiring a native C++ addon will fail and throw an exception. #### `--no-async-context-frame`# Added in: v24.0.0 Disables the use of `AsyncLocalStorage` backed by `AsyncContextFrame` and uses the prior implementation which relied on async_hooks. The previous model is retained for compatibility with Electron and for cases where the context flow may differ. However, if a difference in flow is found please report it. #### `--no-deprecation`# Added in: v0.8.0 Silence deprecation warnings. #### `--no-experimental-detect-module`# History VersionChanges v22.7.0, v20.19.0 Syntax detection is enabled by default. v21.1.0, v20.10.0 Added in: v21.1.0, v20.10.0 Disable using syntax detection to determine module type. #### `--no-experimental-global-navigator`# Added in: v21.2.0 Stability: 1 \- Experimental Disable exposition of Navigator API on the global scope. #### `--no-experimental-repl-await`# Added in: v16.6.0 Use this flag to disable top-level await in REPL. #### `--no-experimental-require-module`# History VersionChanges v23.0.0, v22.12.0, v20.19.0 This is now false by default. v22.0.0, v20.17.0 Added in: v22.0.0, v20.17.0 Stability: 1.1 \- Active Development Disable support for loading a synchronous ES module graph in `require()`. See Loading ECMAScript modules using `require()`. #### `--no-experimental-sqlite`# History VersionChanges v23.4.0, v22.13.0 SQLite is unflagged but still experimental. v22.5.0 Added in: v22.5.0 Disable the experimental `node:sqlite` module. #### `--no-experimental-strip-types`# History VersionChanges v23.6.0 Type stripping is enabled by default. v22.6.0 Added in: v22.6.0 Stability: 1.2 \- Release candidate Disable experimental type-stripping for TypeScript files. For more information, see the TypeScript type-stripping documentation. #### `--no-experimental-websocket`# Added in: v22.0.0 Disable exposition of on the global scope. #### `--no-extra-info-on-fatal-exception`# Added in: v17.0.0 Hide extra information on fatal exception that causes exit. #### `--no-force-async-hooks-checks`# Added in: v9.0.0 Disables runtime checks for `async_hooks`. These will still be enabled dynamically when `async_hooks` is enabled. #### `--no-global-search-paths`# Added in: v16.10.0 Do not search modules from global paths like `$HOME/.node_modules` and `$NODE_PATH`. #### `--no-network-family-autoselection`# History VersionChanges v20.0.0 The flag was renamed from `--no-enable-network-family-autoselection` to `--no-network-family-autoselection`. The old name can still work as an alias. v19.4.0 Added in: v19.4.0 Disables the family autoselection algorithm unless connection options explicitly enables it. #### `--no-warnings`# Added in: v6.0.0 Silence all process warnings (including deprecations). #### `--node-memory-debug`# Added in: v15.0.0, v14.18.0 Enable extra debug checks for memory leaks in Node.js internals. This is usually only useful for developers debugging Node.js itself. #### `--openssl-config=file`# Added in: v6.9.0 Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built against FIPS-enabled OpenSSL. #### `--openssl-legacy-provider`# Added in: v17.0.0, v16.17.0 Enable OpenSSL 3.0 legacy provider. For more information please see OSSL_PROVIDER-legacy. #### `--openssl-shared-config`# Added in: v18.5.0, v16.17.0, v14.21.0 Enable OpenSSL default configuration section, `openssl_conf` to be read from the OpenSSL configuration file. The default configuration file is named `openssl.cnf` but this can be changed using the environment variable `OPENSSL_CONF`, or by using the command line option `--openssl-config`. The location of the default OpenSSL configuration file depends on how OpenSSL is being linked to Node.js. Sharing the OpenSSL configuration may have unwanted implications and it is recommended to use a configuration section specific to Node.js which is `nodejs_conf` and is default when this option is not used. #### `--pending-deprecation`# Added in: v8.0.0 Emit pending deprecation warnings. Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the `--pending-deprecation` command-line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage. #### `--permission`# History VersionChanges v23.5.0, v22.13.0 Permission Model is now stable. v20.0.0 Added in: v20.0.0 Enable the Permission Model for current process. When enabled, the following permissions are restricted: * File System - manageable through `--allow-fs-read`, `--allow-fs-write` flags * Child Process - manageable through `--allow-child-process` flag * Worker Threads - manageable through `--allow-worker` flag * WASI - manageable through `--allow-wasi` flag * Addons - manageable through `--allow-addons` flag #### `--preserve-symlinks`# Added in: v6.3.0 Instructs the module loader to preserve symbolic links when resolving and caching modules. By default, when Node.js loads a module from a path that is symbolically linked to a different on-disk location, Node.js will dereference the link and use the actual on-disk "real path" of the module as both an identifier and as a root path to locate other dependency modules. In most cases, this default behavior is acceptable. However, when using symbolically linked peer dependencies, as illustrated in the example below, the default behavior causes an exception to be thrown if `moduleA` attempts to require `moduleB` as a peer dependency: {appDir} ├── app │ ├── index.js │ └── node_modules │ ├── moduleA -> {appDir}/moduleA │ └── moduleB │ ├── index.js │ └── package.json └── moduleA ├── index.js └── package.json The `--preserve-symlinks` command-line flag instructs Node.js to use the symlink path for modules as opposed to the real path, allowing symbolically linked peer dependencies to be found. Note, however, that using `--preserve-symlinks` can have other side effects. Specifically, symbolically linked native modules can fail to load if those are linked from more than one location in the dependency tree (Node.js would see those as two separate modules and would attempt to load the module multiple times, causing an exception to be thrown). The `--preserve-symlinks` flag does not apply to the main module, which allows `node --preserve-symlinks node_module/.bin/` to work. To apply the same behavior for the main module, also use `--preserve-symlinks-main`. #### `--preserve-symlinks-main`# Added in: v10.2.0 Instructs the module loader to preserve symbolic links when resolving and caching the main module (`require.main`). This flag exists so that the main module can be opted-in to the same behavior that `--preserve-symlinks` gives to all other imports; they are separate flags, however, for backward compatibility with older Node.js versions. `--preserve-symlinks-main` does not imply `--preserve-symlinks`; use `--preserve-symlinks-main` in addition to `--preserve-symlinks` when it is not desirable to follow symlinks before resolving relative paths. See `--preserve-symlinks` for more information. #### `-p`, `--print "script"`# History VersionChanges v5.11.0 Built-in libraries are now available as predefined variables. v0.6.4 Added in: v0.6.4 Identical to `-e` but prints the result. #### `--prof`# Added in: v2.0.0 Generate V8 profiler output. #### `--prof-process`# Added in: v5.2.0 Process V8 profiler output generated using the V8 option `--prof`. #### `--redirect-warnings=file`# Added in: v8.0.0 Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. The `file` name may be an absolute path. If it is not, the default directory it will be written to is controlled by the `--diagnostic-dir` command-line option. #### `--report-compact`# Added in: v13.12.0, v12.17.0 Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption. #### `--report-dir=directory`, `report-directory=directory`# History VersionChanges v13.12.0, v12.17.0 This option is no longer experimental. v12.0.0 Changed from `--diagnostic-report-directory` to `--report-directory`. v11.8.0 Added in: v11.8.0 Location at which the report will be generated. #### `--report-exclude-env`# Added in: v23.3.0, v22.13.0 When `--report-exclude-env` is passed the diagnostic report generated will not contain the `environmentVariables` data. #### `--report-exclude-network`# Added in: v22.0.0, v20.13.0 Exclude `header.networkInterfaces` from the diagnostic report. By default this is not set and the network interfaces are included. #### `--report-filename=filename`# History VersionChanges v13.12.0, v12.17.0 This option is no longer experimental. v12.0.0 changed from `--diagnostic-report-filename` to `--report-filename`. v11.8.0 Added in: v11.8.0 Name of the file to which the report will be written. If the filename is set to `'stdout'` or `'stderr'`, the report is written to the stdout or stderr of the process respectively. #### `--report-on-fatalerror`# History VersionChanges v14.0.0, v13.14.0, v12.17.0 This option is no longer experimental. v12.0.0 changed from `--diagnostic-report-on-fatalerror` to `--report-on-fatalerror`. v11.8.0 Added in: v11.8.0 Enables the report to be triggered on fatal errors (internal errors within the Node.js runtime such as out of memory) that lead to termination of the application. Useful to inspect various diagnostic data elements such as heap, stack, event loop state, resource consumption etc. to reason about the fatal error. #### `--report-on-signal`# History VersionChanges v13.12.0, v12.17.0 This option is no longer experimental. v12.0.0 changed from `--diagnostic-report-on-signal` to `--report-on-signal`. v11.8.0 Added in: v11.8.0 Enables report to be generated upon receiving the specified (or predefined) signal to the running Node.js process. The signal to trigger the report is specified through `--report-signal`. #### `--report-signal=signal`# History VersionChanges v13.12.0, v12.17.0 This option is no longer experimental. v12.0.0 changed from `--diagnostic-report-signal` to `--report-signal`. v11.8.0 Added in: v11.8.0 Sets or resets the signal for report generation (not supported on Windows). Default signal is `SIGUSR2`. #### `--report-uncaught-exception`# History VersionChanges v18.8.0, v16.18.0 Report is not generated if the uncaught exception is handled. v13.12.0, v12.17.0 This option is no longer experimental. v12.0.0 changed from `--diagnostic-report-uncaught-exception` to `--report-uncaught-exception`. v11.8.0 Added in: v11.8.0 Enables report to be generated when the process exits due to an uncaught exception. Useful when inspecting the JavaScript stack in conjunction with native stack and other runtime environment data. #### `-r`, `--require module`# History VersionChanges v23.0.0, v22.12.0, v20.19.0 This option also supports ECMAScript module. v1.6.0 Added in: v1.6.0 Preload the specified module at startup. Follows `require()`'s module resolution rules. `module` may be either a path to a file, or a node module name. Modules preloaded with `--require` will run before modules preloaded with `--import`. Modules are preloaded into the main thread as well as any worker threads, forked processes, or clustered processes. #### `--run`# History VersionChanges v22.3.0 NODE_RUN_SCRIPT_NAME environment variable is added. v22.3.0 NODE_RUN_PACKAGE_JSON_PATH environment variable is added. v22.3.0 Traverses up to the root directory and finds a `package.json` file to run the command from, and updates `PATH` environment variable accordingly. v22.0.0 Added in: v22.0.0 This runs a specified command from a package.json's `"scripts"` object. If a missing `"command"` is provided, it will list the available scripts. `--run` will traverse up to the root directory and finds a `package.json` file to run the command from. `--run` prepends `./node_modules/.bin` for each ancestor of the current directory, to the `PATH` in order to execute the binaries from different folders where multiple `node_modules` directories are present, if `ancestor-folder/node_modules/.bin` is a directory. `--run` executes the command in the directory containing the related `package.json`. For example, the following command will run the `test` script of the `package.json` in the current folder: $ node --run test You can also pass arguments to the command. Any argument after `--` will be appended to the script: $ node --run test -- --verbose ##### Intentional limitations# `node --run` is not meant to match the behaviors of `npm run` or of the `run` commands of other package managers. The Node.js implementation is intentionally more limited, in order to focus on top performance for the most common use cases. Some features of other `run` implementations that are intentionally excluded are: * Running `pre` or `post` scripts in addition to the specified script. * Defining package manager-specific environment variables. ##### Environment variables# The following environment variables are set when running a script with `--run`: * `NODE_RUN_SCRIPT_NAME`: The name of the script being run. For example, if `--run` is used to run `test`, the value of this variable will be `test`. * `NODE_RUN_PACKAGE_JSON_PATH`: The path to the `package.json` that is being processed. #### `--secure-heap-min=n`# Added in: v15.6.0 When using `--secure-heap`, the `--secure-heap-min` flag specifies the minimum allocation from the secure heap. The minimum value is `2`. The maximum value is the lesser of `--secure-heap` or `2147483647`. The value given must be a power of two. #### `--secure-heap=n`# Added in: v15.6.0 Initializes an OpenSSL secure heap of `n` bytes. When initialized, the secure heap is used for selected types of allocations within OpenSSL during key generation and other operations. This is useful, for instance, to prevent sensitive information from leaking due to pointer overruns or underruns. The secure heap is a fixed size and cannot be resized at runtime so, if used, it is important to select a large enough heap to cover all application uses. The heap size given must be a power of two. Any value less than 2 will disable the secure heap. The secure heap is disabled by default. The secure heap is not available on Windows. See `CRYPTO_secure_malloc_init` for more details. #### `--snapshot-blob=path`# Added in: v18.8.0 Stability: 1 \- Experimental When used with `--build-snapshot`, `--snapshot-blob` specifies the path where the generated snapshot blob is written to. If not specified, the generated blob is written to `snapshot.blob` in the current working directory. When used without `--build-snapshot`, `--snapshot-blob` specifies the path to the blob that is used to restore the application state. When loading a snapshot, Node.js checks that: 1. The version, architecture, and platform of the running Node.js binary are exactly the same as that of the binary that generates the snapshot. 2. The V8 flags and CPU features are compatible with that of the binary that generates the snapshot. If they don't match, Node.js refuses to load the snapshot and exits with status code 1. #### `--test`# History VersionChanges v20.0.0 The test runner is now stable. v19.2.0, v18.13.0 Test runner now supports running in watch mode. v18.1.0, v16.17.0 Added in: v18.1.0, v16.17.0 Starts the Node.js command line test runner. This flag cannot be combined with `--watch-path`, `--check`, `--eval`, `--interactive`, or the inspector. See the documentation on running tests from the command line for more details. #### `--test-concurrency`# Added in: v21.0.0, v20.10.0, v18.19.0 The maximum number of test files that the test runner CLI will execute concurrently. If `--test-isolation` is set to `'none'`, this flag is ignored and concurrency is one. Otherwise, concurrency defaults to `os.availableParallelism() - 1`. #### `--test-coverage-branches=threshold`# Added in: v22.8.0 Stability: 1 \- Experimental Require a minimum percent of covered branches. If code coverage does not reach the threshold specified, the process will exit with code `1`. #### `--test-coverage-exclude`# Added in: v22.5.0 Stability: 1 \- Experimental Excludes specific files from code coverage using a glob pattern, which can match both absolute and relative file paths. This option may be specified multiple times to exclude multiple glob patterns. If both `--test-coverage-exclude` and `--test-coverage-include` are provided, files must meet both criteria to be included in the coverage report. By default all the matching test files are excluded from the coverage report. Specifying this option will override the default behavior. #### `--test-coverage-functions=threshold`# Added in: v22.8.0 Stability: 1 \- Experimental Require a minimum percent of covered functions. If code coverage does not reach the threshold specified, the process will exit with code `1`. #### `--test-coverage-include`# Added in: v22.5.0 Stability: 1 \- Experimental Includes specific files in code coverage using a glob pattern, which can match both absolute and relative file paths. This option may be specified multiple times to include multiple glob patterns. If both `--test-coverage-exclude` and `--test-coverage-include` are provided, files must meet both criteria to be included in the coverage report. #### `--test-coverage-lines=threshold`# Added in: v22.8.0 Stability: 1 \- Experimental Require a minimum percent of covered lines. If code coverage does not reach the threshold specified, the process will exit with code `1`. #### `--test-force-exit`# Added in: v22.0.0, v20.14.0 Configures the test runner to exit the process once all known tests have finished executing even if the event loop would otherwise remain active. #### `--test-global-setup=module`# Added in: v24.0.0 Stability: 1.0 \- Early development Specify a module that will be evaluated before all tests are executed and can be used to setup global state or fixtures for tests. See the documentation on global setup and teardown for more details. #### `--test-isolation=mode`# History VersionChanges v23.6.0 This flag was renamed from `--experimental-test-isolation` to `--test-isolation`. v22.8.0 Added in: v22.8.0 Configures the type of test isolation used in the test runner. When `mode` is `'process'`, each test file is run in a separate child process. When `mode` is `'none'`, all test files run in the same process as the test runner. The default isolation mode is `'process'`. This flag is ignored if the `--test` flag is not present. See the test runner execution model section for more information. #### `--test-name-pattern`# History VersionChanges v20.0.0 The test runner is now stable. v18.11.0 Added in: v18.11.0 A regular expression that configures the test runner to only execute tests whose name matches the provided pattern. See the documentation on filtering tests by name for more details. If both `--test-name-pattern` and `--test-skip-pattern` are supplied, tests must satisfy both requirements in order to be executed. #### `--test-only`# History VersionChanges v20.0.0 The test runner is now stable. v18.0.0, v16.17.0 Added in: v18.0.0, v16.17.0 Configures the test runner to only execute top level tests that have the `only` option set. This flag is not necessary when test isolation is disabled. #### `--test-reporter`# History VersionChanges v20.0.0 The test runner is now stable. v19.6.0, v18.15.0 Added in: v19.6.0, v18.15.0 A test reporter to use when running tests. See the documentation on test reporters for more details. #### `--test-reporter-destination`# History VersionChanges v20.0.0 The test runner is now stable. v19.6.0, v18.15.0 Added in: v19.6.0, v18.15.0 The destination for the corresponding test reporter. See the documentation on test reporters for more details. #### `--test-rerun-failures`# Added in: v24.7.0 A path to a file allowing the test runner to persist the state of the test suite between runs. The test runner will use this file to determine which tests have already succeeded or failed, allowing for re-running of failed tests without having to re-run the entire test suite. The test runner will create this file if it does not exist. See the documentation on test reruns for more details. #### `--test-shard`# Added in: v20.5.0, v18.19.0 Test suite shard to execute in a format of `/`, where * `index` is a positive integer, index of divided parts. * `total` is a positive integer, total of divided part. This command will divide all tests files into `total` equal parts, and will run only those that happen to be in an `index` part. For example, to split your tests suite into three parts, use this: node --test --test-shard=1/3 node --test --test-shard=2/3 node --test --test-shard=3/3 #### `--test-skip-pattern`# Added in: v22.1.0 A regular expression that configures the test runner to skip tests whose name matches the provided pattern. See the documentation on filtering tests by name for more details. If both `--test-name-pattern` and `--test-skip-pattern` are supplied, tests must satisfy both requirements in order to be executed. #### `--test-timeout`# Added in: v21.2.0, v20.11.0 A number of milliseconds the test execution will fail after. If unspecified, subtests inherit this value from their parent. The default value is `Infinity`. #### `--test-update-snapshots`# History VersionChanges v23.4.0, v22.13.0 Snapshot testing is no longer experimental. v22.3.0 Added in: v22.3.0 Regenerates the snapshot files used by the test runner for snapshot testing. #### `--throw-deprecation`# Added in: v0.11.14 Throw errors for deprecations. #### `--title=title`# Added in: v10.7.0 Set `process.title` on startup. #### `--tls-cipher-list=list`# Added in: v4.0.0 Specify an alternative default TLS cipher list. Requires Node.js to be built with crypto support (default). #### `--tls-keylog=file`# Added in: v13.2.0, v12.16.0 Log TLS key material to a file. The key material is in NSS `SSLKEYLOGFILE` format and can be used by software (such as Wireshark) to decrypt the TLS traffic. #### `--tls-max-v1.2`# Added in: v12.0.0, v10.20.0 Set `tls.DEFAULT_MAX_VERSION` to 'TLSv1.2'. Use to disable support for TLSv1.3. #### `--tls-max-v1.3`# Added in: v12.0.0 Set default `tls.DEFAULT_MAX_VERSION` to 'TLSv1.3'. Use to enable support for TLSv1.3. #### `--tls-min-v1.0`# Added in: v12.0.0, v10.20.0 Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1'. Use for compatibility with old TLS clients or servers. #### `--tls-min-v1.1`# Added in: v12.0.0, v10.20.0 Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1.1'. Use for compatibility with old TLS clients or servers. #### `--tls-min-v1.2`# Added in: v12.2.0, v10.20.0 Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1.2'. This is the default for 12.x and later, but the option is supported for compatibility with older Node.js versions. #### `--tls-min-v1.3`# Added in: v12.0.0 Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1.3'. Use to disable support for TLSv1.2, which is not as secure as TLSv1.3. #### `--trace-deprecation`# Added in: v0.8.0 Print stack traces for deprecations. #### `--trace-env`# Added in: v23.4.0, v22.13.0 Print information about any access to environment variables done in the current Node.js instance to stderr, including: * The environment variable reads that Node.js does internally. * Writes in the form of `process.env.KEY = "SOME VALUE"`. * Reads in the form of `process.env.KEY`. * Definitions in the form of `Object.defineProperty(process.env, 'KEY', {...})`. * Queries in the form of `Object.hasOwn(process.env, 'KEY')`, `process.env.hasOwnProperty('KEY')` or `'KEY' in process.env`. * Deletions in the form of `delete process.env.KEY`. * Enumerations inf the form of `...process.env` or `Object.keys(process.env)`. Only the names of the environment variables being accessed are printed. The values are not printed. To print the stack trace of the access, use `--trace-env-js-stack` and/or `--trace-env-native-stack`. #### `--trace-env-js-stack`# Added in: v23.4.0, v22.13.0 In addition to what `--trace-env` does, this prints the JavaScript stack trace of the access. #### `--trace-env-native-stack`# Added in: v23.4.0, v22.13.0 In addition to what `--trace-env` does, this prints the native stack trace of the access. #### `--trace-event-categories`# Added in: v7.7.0 A comma separated list of categories that should be traced when trace event tracing is enabled using `--trace-events-enabled`. #### `--trace-event-file-pattern`# Added in: v9.8.0 Template string specifying the filepath for the trace event data, it supports `${rotation}` and `${pid}`. #### `--trace-events-enabled`# Added in: v7.7.0 Enables the collection of trace event tracing information. #### `--trace-exit`# Added in: v13.5.0, v12.16.0 Prints a stack trace whenever an environment is exited proactively, i.e. invoking `process.exit()`. #### `--trace-require-module=mode`# Added in: v23.5.0, v22.13.0, v20.19.0 Prints information about usage of Loading ECMAScript modules using `require()`. When `mode` is `all`, all usage is printed. When `mode` is `no-node-modules`, usage from the `node_modules` folder is excluded. #### `--trace-sigint`# Added in: v13.9.0, v12.17.0 Prints a stack trace on SIGINT. #### `--trace-sync-io`# Added in: v2.1.0 Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop. #### `--trace-tls`# Added in: v12.2.0 Prints TLS packet trace information to `stderr`. This can be used to debug TLS connection problems. #### `--trace-uncaught`# Added in: v13.1.0 Print stack traces for uncaught exceptions; usually, the stack trace associated with the creation of an `Error` is printed, whereas this makes Node.js also print the stack trace associated with throwing the value (which does not need to be an `Error` instance). Enabling this option may affect garbage collection behavior negatively. #### `--trace-warnings`# Added in: v6.0.0 Print stack traces for process warnings (including deprecations). #### `--track-heap-objects`# Added in: v2.4.0 Track heap object allocations for heap snapshots. #### `--unhandled-rejections=mode`# History VersionChanges v15.0.0 Changed default mode to `throw`. Previously, a warning was emitted. v12.0.0, v10.17.0 Added in: v12.0.0, v10.17.0 Using this flag allows to change what should happen when an unhandled rejection occurs. One of the following modes can be chosen: * `throw`: Emit `unhandledRejection`. If this hook is not set, raise the unhandled rejection as an uncaught exception. This is the default. * `strict`: Raise the unhandled rejection as an uncaught exception. If the exception is handled, `unhandledRejection` is emitted. * `warn`: Always trigger a warning, no matter if the `unhandledRejection` hook is set or not but do not print the deprecation warning. * `warn-with-error-code`: Emit `unhandledRejection`. If this hook is not set, trigger a warning, and set the process exit code to 1. * `none`: Silence all warnings. If a rejection happens during the command line entry point's ES module static loading phase, it will always raise it as an uncaught exception. #### `--use-bundled-ca`, `--use-openssl-ca`# Added in: v6.11.0 Use bundled Mozilla CA store as supplied by current Node.js version or use OpenSSL's default CA store. The default store is selectable at build-time. The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms. Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables. See `SSL_CERT_DIR` and `SSL_CERT_FILE`. #### `--use-env-proxy`# Added in: v24.5.0 Stability: 1.1 \- Active Development When enabled, Node.js parses the `HTTP_PROXY`, `HTTPS_PROXY` and `NO_PROXY` environment variables during startup, and tunnels requests over the specified proxy. This is equivalent to setting the `NODE_USE_ENV_PROXY=1` environment variable. When both are set, `--use-env-proxy` takes precedence. #### `--use-largepages=mode`# Added in: v13.6.0, v12.17.0 Re-map the Node.js static code to large memory pages at startup. If supported on the target system, this will cause the Node.js static code to be moved onto 2 MiB pages instead of 4 KiB pages. The following values are valid for `mode`: * `off`: No mapping will be attempted. This is the default. * `on`: If supported by the OS, mapping will be attempted. Failure to map will be ignored and a message will be printed to standard error. * `silent`: If supported by the OS, mapping will be attempted. Failure to map will be ignored and will not be reported. #### `--use-system-ca`# History VersionChanges v23.9.0 Added support on non-Windows and non-macOS. v23.8.0 Added in: v23.8.0 Node.js uses the trusted CA certificates present in the system store along with the `--use-bundled-ca` option and the `NODE_EXTRA_CA_CERTS` environment variable. On platforms other than Windows and macOS, this loads certificates from the directory and file trusted by OpenSSL, similar to `--use-openssl-ca`, with the difference being that it caches the certificates after first load. On Windows and macOS, the certificate trust policy is planned to follow Chromium's policy for locally trusted certificates: On macOS, the following settings are respected: * Default and System Keychains * Trust: * Any certificate where the “When using this certificate” flag is set to “Always Trust” or * Any certificate where the “Secure Sockets Layer (SSL)” flag is set to “Always Trust.” * Distrust: * Any certificate where the “When using this certificate” flag is set to “Never Trust” or * Any certificate where the “Secure Sockets Layer (SSL)” flag is set to “Never Trust.” On Windows, the following settings are respected (unlike Chromium's policy, distrust and intermediate CA are not currently supported): * Local Machine (accessed via `certlm.msc`) * Trust: * Trusted Root Certification Authorities * Trusted People * Enterprise Trust -> Enterprise -> Trusted Root Certification Authorities * Enterprise Trust -> Enterprise -> Trusted People * Enterprise Trust -> Group Policy -> Trusted Root Certification Authorities * Enterprise Trust -> Group Policy -> Trusted People * Current User (accessed via `certmgr.msc`) * Trust: * Trusted Root Certification Authorities * Enterprise Trust -> Group Policy -> Trusted Root Certification Authorities On Windows and macOS, Node.js would check that the user settings for the certificates do not forbid them for TLS server authentication before using them. On other systems, Node.js loads certificates from the default certificate file (typically `/etc/ssl/cert.pem`) and default certificate directory (typically `/etc/ssl/certs`) that the version of OpenSSL that Node.js links to respects. This typically works with the convention on major Linux distributions and other Unix-like systems. If the overriding OpenSSL environment variables (typically `SSL_CERT_FILE` and `SSL_CERT_DIR`, depending on the configuration of the OpenSSL that Node.js links to) are set, the specified paths will be used to load certificates instead. These environment variables can be used as workarounds if the conventional paths used by the version of OpenSSL Node.js links to are not consistent with the system configuration that the users have for some reason. #### `--v8-options`# Added in: v0.1.3 Print V8 command-line options. #### `--v8-pool-size=num`# Added in: v5.10.0 Set V8's thread pool size which will be used to allocate background jobs. If set to `0` then Node.js will choose an appropriate size of the thread pool based on an estimate of the amount of parallelism. The amount of parallelism refers to the number of computations that can be carried out simultaneously in a given machine. In general, it's the same as the amount of CPUs, but it may diverge in environments such as VMs or containers. #### `-v`, `--version`# Added in: v0.1.3 Print node's version. #### `--watch`# History VersionChanges v22.0.0, v20.13.0 Watch mode is now stable. v19.2.0, v18.13.0 Test runner now supports running in watch mode. v18.11.0, v16.19.0 Added in: v18.11.0, v16.19.0 Starts Node.js in watch mode. When in watch mode, changes in the watched files cause the Node.js process to restart. By default, watch mode will watch the entry point and any required or imported module. Use `--watch-path` to specify what paths to watch. This flag cannot be combined with `--check`, `--eval`, `--interactive`, or the REPL. Note: The `--watch` flag requires a file path as an argument and is incompatible with `--run` or inline script input, as `--run` takes precedence and ignores watch mode. If no file is provided, Node.js will exit with status code `9`. node --watch index.js #### `--watch-kill-signal`# Added in: v24.4.0 Stability: 1.1 \- Active Development Customizes the signal sent to the process on watch mode restarts. node --watch --watch-kill-signal SIGINT test.js #### `--watch-path`# History VersionChanges v22.0.0, v20.13.0 Watch mode is now stable. v18.11.0, v16.19.0 Added in: v18.11.0, v16.19.0 Starts Node.js in watch mode and specifies what paths to watch. When in watch mode, changes in the watched paths cause the Node.js process to restart. This will turn off watching of required or imported modules, even when used in combination with `--watch`. This flag cannot be combined with `--check`, `--eval`, `--interactive`, `--test`, or the REPL. Note: Using `--watch-path` implicitly enables `--watch`, which requires a file path and is incompatible with `--run`, as `--run` takes precedence and ignores watch mode. node --watch-path=./src --watch-path=./tests index.js This option is only supported on macOS and Windows. An `ERR_FEATURE_UNAVAILABLE_ON_PLATFORM` exception will be thrown when the option is used on a platform that does not support it. #### `--watch-preserve-output`# Added in: v19.3.0, v18.13.0 Disable the clearing of the console when watch mode restarts the process. node --watch --watch-preserve-output test.js #### `--zero-fill-buffers`# Added in: v6.0.0 Automatically zero-fills all newly allocated `Buffer` and `SlowBuffer` instances. ### Environment variables# Stability: 2 \- Stable #### `FORCE_COLOR=[1, 2, 3]`# The `FORCE_COLOR` environment variable is used to enable ANSI colorized output. The value may be: * `1`, `true`, or the empty string `''` indicate 16-color support, * `2` to indicate 256-color support, or * `3` to indicate 16 million-color support. When `FORCE_COLOR` is used and set to a supported value, both the `NO_COLOR`, and `NODE_DISABLE_COLORS` environment variables are ignored. Any other value will result in colorized output being disabled. #### `NODE_COMPILE_CACHE=dir`# Added in: v22.1.0 Stability: 1.1 \- Active Development Enable the module compile cache for the Node.js instance. See the documentation of module compile cache for details. #### `NODE_DEBUG=module[,…]`# Added in: v0.1.32 `','`-separated list of core modules that should print debug information. #### `NODE_DEBUG_NATIVE=module[,…]`# `','`-separated list of core C++ modules that should print debug information. #### `NODE_DISABLE_COLORS=1`# Added in: v0.3.0 When set, colors will not be used in the REPL. #### `NODE_DISABLE_COMPILE_CACHE=1`# Added in: v22.8.0 Stability: 1.1 \- Active Development Disable the module compile cache for the Node.js instance. See the documentation of module compile cache for details. #### `NODE_EXTRA_CA_CERTS=file`# Added in: v7.3.0 When set, the well known "root" CAs (like VeriSign) will be extended with the extra certificates in `file`. The file should consist of one or more trusted certificates in PEM format. A message will be emitted (once) with `process.emitWarning()` if the file is missing or malformed, but any errors are otherwise ignored. Neither the well known nor extra certificates are used when the `ca` options property is explicitly specified for a TLS or HTTPS client or server. This environment variable is ignored when `node` runs as setuid root or has Linux file capabilities set. The `NODE_EXTRA_CA_CERTS` environment variable is only read when the Node.js process is first launched. Changing the value at runtime using `process.env.NODE_EXTRA_CA_CERTS` has no effect on the current process. #### `NODE_ICU_DATA=file`# Added in: v0.11.15 Data path for ICU (`Intl` object) data. Will extend linked-in data when compiled with small-icu support. #### `NODE_NO_WARNINGS=1`# Added in: v6.11.0 When set to `1`, process warnings are silenced. #### `NODE_OPTIONS=options...`# Added in: v8.0.0 A space-separated list of command-line options. `options...` are interpreted before command-line options, so command-line options will override or compound after anything in `options...`. Node.js will exit with an error if an option that is not allowed in the environment is used, such as `-p` or a script file. If an option value contains a space, it can be escaped using double quotes: NODE_OPTIONS='--require "./my path/file.js"' A singleton flag passed as a command-line option will override the same flag passed into `NODE_OPTIONS`: # The inspector will be available on port 5555 NODE_OPTIONS='--inspect=localhost:4444' node --inspect=localhost:5555 A flag that can be passed multiple times will be treated as if its `NODE_OPTIONS` instances were passed first, and then its command-line instances afterwards: NODE_OPTIONS='--require "./a.js"' node --require "./b.js" # is equivalent to: node --require "./a.js" --require "./b.js" Node.js options that are allowed are in the following list. If an option supports both --XX and --no-XX variants, they are both supported but only one is included in the list below. * `--allow-addons` * `--allow-child-process` * `--allow-fs-read` * `--allow-fs-write` * `--allow-wasi` * `--allow-worker` * `--conditions`, `-C` * `--cpu-prof-dir` * `--cpu-prof-interval` * `--cpu-prof-name` * `--cpu-prof` * `--diagnostic-dir` * `--disable-proto` * `--disable-sigusr1` * `--disable-warning` * `--disable-wasm-trap-handler` * `--dns-result-order` * `--enable-fips` * `--enable-network-family-autoselection` * `--enable-source-maps` * `--entry-url` * `--experimental-abortcontroller` * `--experimental-addon-modules` * `--experimental-detect-module` * `--experimental-eventsource` * `--experimental-import-meta-resolve` * `--experimental-json-modules` * `--experimental-loader` * `--experimental-modules` * `--experimental-print-required-tla` * `--experimental-require-module` * `--experimental-shadow-realm` * `--experimental-specifier-resolution` * `--experimental-test-isolation` * `--experimental-top-level-await` * `--experimental-transform-types` * `--experimental-vm-modules` * `--experimental-wasi-unstable-preview1` * `--experimental-webstorage` * `--force-context-aware` * `--force-fips` * `--force-node-api-uncaught-exceptions-policy` * `--frozen-intrinsics` * `--heap-prof-dir` * `--heap-prof-interval` * `--heap-prof-name` * `--heap-prof` * `--heapsnapshot-near-heap-limit` * `--heapsnapshot-signal` * `--http-parser` * `--icu-data-dir` * `--import` * `--input-type` * `--insecure-http-parser` * `--inspect-brk` * `--inspect-port`, `--debug-port` * `--inspect-publish-uid` * `--inspect-wait` * `--inspect` * `--localstorage-file` * `--max-http-header-size` * `--max-old-space-size-percentage` * `--napi-modules` * `--network-family-autoselection-attempt-timeout` * `--no-addons` * `--no-async-context-frame` * `--no-deprecation` * `--no-experimental-global-navigator` * `--no-experimental-repl-await` * `--no-experimental-sqlite` * `--no-experimental-strip-types` * `--no-experimental-websocket` * `--no-extra-info-on-fatal-exception` * `--no-force-async-hooks-checks` * `--no-global-search-paths` * `--no-network-family-autoselection` * `--no-warnings` * `--node-memory-debug` * `--openssl-config` * `--openssl-legacy-provider` * `--openssl-shared-config` * `--pending-deprecation` * `--permission` * `--preserve-symlinks-main` * `--preserve-symlinks` * `--prof-process` * `--redirect-warnings` * `--report-compact` * `--report-dir`, `--report-directory` * `--report-exclude-env` * `--report-exclude-network` * `--report-filename` * `--report-on-fatalerror` * `--report-on-signal` * `--report-signal` * `--report-uncaught-exception` * `--require`, `-r` * `--secure-heap-min` * `--secure-heap` * `--snapshot-blob` * `--test-coverage-branches` * `--test-coverage-exclude` * `--test-coverage-functions` * `--test-coverage-include` * `--test-coverage-lines` * `--test-global-setup` * `--test-isolation` * `--test-name-pattern` * `--test-only` * `--test-reporter-destination` * `--test-reporter` * `--test-rerun-failures` * `--test-shard` * `--test-skip-pattern` * `--throw-deprecation` * `--title` * `--tls-cipher-list` * `--tls-keylog` * `--tls-max-v1.2` * `--tls-max-v1.3` * `--tls-min-v1.0` * `--tls-min-v1.1` * `--tls-min-v1.2` * `--tls-min-v1.3` * `--trace-deprecation` * `--trace-env-js-stack` * `--trace-env-native-stack` * `--trace-env` * `--trace-event-categories` * `--trace-event-file-pattern` * `--trace-events-enabled` * `--trace-exit` * `--trace-require-module` * `--trace-sigint` * `--trace-sync-io` * `--trace-tls` * `--trace-uncaught` * `--trace-warnings` * `--track-heap-objects` * `--unhandled-rejections` * `--use-bundled-ca` * `--use-env-proxy` * `--use-largepages` * `--use-openssl-ca` * `--use-system-ca` * `--v8-pool-size` * `--watch-kill-signal` * `--watch-path` * `--watch-preserve-output` * `--watch` * `--zero-fill-buffers` V8 options that are allowed are: * `--abort-on-uncaught-exception` * `--disallow-code-generation-from-strings` * `--enable-etw-stack-walking` * `--expose-gc` * `--interpreted-frames-native-stack` * `--jitless` * `--max-old-space-size` * `--max-semi-space-size` * `--perf-basic-prof-only-functions` * `--perf-basic-prof` * `--perf-prof-unwinding-info` * `--perf-prof` * `--stack-trace-limit` `--perf-basic-prof-only-functions`, `--perf-basic-prof`, `--perf-prof-unwinding-info`, and `--perf-prof` are only available on Linux. `--enable-etw-stack-walking` is only available on Windows. #### `NODE_PATH=path[:…]`# Added in: v0.1.32 `':'`-separated list of directories prefixed to the module search path. On Windows, this is a `';'`-separated list instead. #### `NODE_PENDING_DEPRECATION=1`# Added in: v8.0.0 When set to `1`, emit pending deprecation warnings. Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the `--pending-deprecation` command-line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage. #### `NODE_PENDING_PIPE_INSTANCES=instances`# Set the number of pending pipe instance handles when the pipe server is waiting for connections. This setting applies to Windows only. #### `NODE_PRESERVE_SYMLINKS=1`# Added in: v7.1.0 When set to `1`, instructs the module loader to preserve symbolic links when resolving and caching modules. #### `NODE_REDIRECT_WARNINGS=file`# Added in: v8.0.0 When set, process warnings will be emitted to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. This is equivalent to using the `--redirect-warnings=file` command-line flag. #### `NODE_REPL_EXTERNAL_MODULE=file`# History VersionChanges v22.3.0, v20.16.0 Remove the possibility to use this env var with kDisableNodeOptionsEnv for embedders. v13.0.0, v12.16.0 Added in: v13.0.0, v12.16.0 Path to a Node.js module which will be loaded in place of the built-in REPL. Overriding this value to an empty string (`''`) will use the built-in REPL. #### `NODE_REPL_HISTORY=file`# Added in: v3.0.0 Path to the file used to store the persistent REPL history. The default path is `~/.node_repl_history`, which is overridden by this variable. Setting the value to an empty string (`''` or `' '`) disables persistent REPL history. #### `NODE_SKIP_PLATFORM_CHECK=value`# Added in: v14.5.0 If `value` equals `'1'`, the check for a supported platform is skipped during Node.js startup. Node.js might not execute correctly. Any issues encountered on unsupported platforms will not be fixed. #### `NODE_TEST_CONTEXT=value`# If `value` equals `'child'`, test reporter options will be overridden and test output will be sent to stdout in the TAP format. If any other value is provided, Node.js makes no guarantees about the reporter format used or its stability. #### `NODE_TLS_REJECT_UNAUTHORIZED=value`# If `value` equals `'0'`, certificate validation is disabled for TLS connections. This makes TLS, and HTTPS by extension, insecure. The use of this environment variable is strongly discouraged. #### `NODE_USE_ENV_PROXY=1`# Added in: v24.0.0 Stability: 1.1 \- Active Development When enabled, Node.js parses the `HTTP_PROXY`, `HTTPS_PROXY` and `NO_PROXY` environment variables during startup, and tunnels requests over the specified proxy. This can also be enabled using the `--use-env-proxy` command-line flag. When both are set, `--use-env-proxy` takes precedence. #### `NODE_USE_SYSTEM_CA=1`# Added in: v24.6.0 Node.js uses the trusted CA certificates present in the system store along with the `--use-bundled-ca` option and the `NODE_EXTRA_CA_CERTS` environment variable. This can also be enabled using the `--use-system-ca` command-line flag. When both are set, `--use-system-ca` takes precedence. #### `NODE_V8_COVERAGE=dir`# When set, Node.js will begin outputting V8 JavaScript code coverage and Source Map data to the directory provided as an argument (coverage information is written as JSON to files with a `coverage` prefix). `NODE_V8_COVERAGE` will automatically propagate to subprocesses, making it easier to instrument applications that call the `child_process.spawn()` family of functions. `NODE_V8_COVERAGE` can be set to an empty string, to prevent propagation. ##### Coverage output# Coverage is output as an array of ScriptCoverage objects on the top-level key `result`: { "result": [ { "scriptId": "67", "url": "internal/tty.js", "functions": [] } ] } ##### Source map cache# Stability: 1 \- Experimental If found, source map data is appended to the top-level key `source-map-cache` on the JSON coverage object. `source-map-cache` is an object with keys representing the files source maps were extracted from, and values which include the raw source-map URL (in the key `url`), the parsed Source Map v3 information (in the key `data`), and the line lengths of the source file (in the key `lineLengths`). { "result": [ { "scriptId": "68", "url": "file:///absolute/path/to/source.js", "functions": [] } ], "source-map-cache": { "file:///absolute/path/to/source.js": { "url": "./path-to-map.json", "data": { "version": 3, "sources": [ "file:///absolute/path/to/original.js" ], "names": [ "Foo", "console", "info" ], "mappings": "MAAMA,IACJC,YAAaC", "sourceRoot": "./" }, "lineLengths": [ 13, 62, 38, 27 ] } } } #### `NO_COLOR=`# `NO_COLOR` is an alias for `NODE_DISABLE_COLORS`. The value of the environment variable is arbitrary. #### `OPENSSL_CONF=file`# Added in: v6.11.0 Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with `./configure --openssl-fips`. If the `--openssl-config` command-line option is used, the environment variable is ignored. #### `SSL_CERT_DIR=dir`# Added in: v7.7.0 If `--use-openssl-ca` is enabled, or if `--use-system-ca` is enabled on platforms other than macOS and Windows, this overrides and sets OpenSSL's directory containing trusted certificates. Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node. #### `SSL_CERT_FILE=file`# Added in: v7.7.0 If `--use-openssl-ca` is enabled, or if `--use-system-ca` is enabled on platforms other than macOS and Windows, this overrides and sets OpenSSL's file containing trusted certificates. Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node. #### `TZ`# History VersionChanges v16.2.0 Changing the TZ variable using process.env.TZ = changes the timezone on Windows as well. v13.0.0 Changing the TZ variable using process.env.TZ = changes the timezone on POSIX systems. v0.0.1 Added in: v0.0.1 The `TZ` environment variable is used to specify the timezone configuration. While Node.js does not support all of the various ways that `TZ` is handled in other environments, it does support basic timezone IDs (such as `'Etc/UTC'`, `'Europe/Paris'`, or `'America/New_York'`). It may support a few other abbreviations or aliases, but these are strongly discouraged and not guaranteed. $ TZ=Europe/Dublin node -pe "new Date().toString()" Wed May 12 2021 20:30:48 GMT+0100 (Irish Standard Time) #### `UV_THREADPOOL_SIZE=size`# Set the number of threads used in libuv's threadpool to `size` threads. Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv's threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are: * all `fs` APIs, other than the file watcher APIs and those that are explicitly synchronous * asynchronous crypto APIs such as `crypto.pbkdf2()`, `crypto.scrypt()`, `crypto.randomBytes()`, `crypto.randomFill()`, `crypto.generateKeyPair()` * `dns.lookup()` * all `zlib` APIs, other than those that are explicitly synchronous Because libuv's threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv's threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv's threadpool by setting the `'UV_THREADPOOL_SIZE'` environment variable to a value greater than `4` (its current default value). However, setting this from inside the process using `process.env.UV_THREADPOOL_SIZE=size` is not guranteed to work as the threadpool would have been created as part of the runtime initialisation much before user code is run. For more information, see the libuv threadpool documentation. ### Useful V8 options# V8 has its own set of CLI options. Any V8 CLI option that is provided to `node` will be passed on to V8 to handle. V8's options have no stability guarantee. The V8 team themselves don't consider them to be part of their formal API, and reserve the right to change them at any time. Likewise, they are not covered by the Node.js stability guarantees. Many of the V8 options are of interest only to V8 developers. Despite this, there is a small set of V8 options that are widely applicable to Node.js, and they are documented here: #### `--abort-on-uncaught-exception`# #### `--disallow-code-generation-from-strings`# #### `--enable-etw-stack-walking`# #### `--expose-gc`# #### `--harmony-shadow-realm`# #### `--interpreted-frames-native-stack`# #### `--jitless`# #### `--max-old-space-size=SIZE` (in MiB)# Sets the max memory size of V8's old memory section. As memory consumption approaches the limit, V8 will spend more time on garbage collection in an effort to free unused memory. On a machine with 2 GiB of memory, consider setting this to 1536 (1.5 GiB) to leave some memory for other uses and avoid swapping. node --max-old-space-size=1536 index.js #### `--max-semi-space-size=SIZE` (in MiB)# Sets the maximum semi-space size for V8's scavenge garbage collector in MiB (mebibytes). Increasing the max size of a semi-space may improve throughput for Node.js at the cost of more memory consumption. Since the young generation size of the V8 heap is three times (see `YoungGenerationSizeFromSemiSpaceSize` in V8) the size of the semi-space, an increase of 1 MiB to semi-space applies to each of the three individual semi-spaces and causes the heap size to increase by 3 MiB. The throughput improvement depends on your workload (see #42511). The default value depends on the memory limit. For example, on 64-bit systems with a memory limit of 512 MiB, the max size of a semi-space defaults to 1 MiB. For memory limits up to and including 2GiB, the default max size of a semi-space will be less than 16 MiB on 64-bit systems. To get the best configuration for your application, you should try different max-semi-space-size values when running benchmarks for your application. For example, benchmark on a 64-bit systems: for MiB in 16 32 64 128; do node --max-semi-space-size=$MiB index.js done #### `--perf-basic-prof`# #### `--perf-basic-prof-only-functions`# #### `--perf-prof`# #### `--perf-prof-unwinding-info`# #### `--prof`# #### `--security-revert`# #### `--stack-trace-limit=limit`# The maximum number of stack frames to collect in an error's stack trace. Setting it to 0 disables stack trace collection. The default value is 10. node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12 ## Console# Stability: 2 \- Stable Source Code: lib/console.js The `node:console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()`, and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to `process.stdout` and `process.stderr`. The global `console` can be used without calling `require('node:console')`. Warning: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. Programs that desire to depend on the synchronous / asynchronous behavior of the console functions should first figure out the nature of console's backing stream. This is because the stream is dependent on the underlying platform and standard stream configuration of the current process. See the note on process I/O for more information. Example using the global `console`: console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr Example using the `Console` class: const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ### Class: `Console`# History VersionChanges v8.0.0 Errors that occur while writing to the underlying streams will now be ignored by default. The `Console` class can be used to create a simple logger with configurable output streams and can be accessed using either `require('node:console').Console` or `console.Console` (or their destructured counterparts): import { Console } from 'node:console'; const { Console } = console; #### `new Console(stdout[, stderr][, ignoreErrors])`# #### `new Console(options)`# History VersionChanges v14.2.0, v12.17.0 The `groupIndentation` option was introduced. v11.7.0 The `inspectOptions` option is introduced. v10.0.0 The `Console` constructor now supports an `options` argument, and the `colorMode` option was introduced. v8.0.0 The `ignoreErrors` option was introduced. * `options` * `stdout` * `stderr` * `ignoreErrors` Ignore errors when writing to the underlying streams. Default: `true`. * `colorMode` | Set color support for this `Console` instance. Setting to `true` enables coloring while inspecting values. Setting to `false` disables coloring while inspecting values. Setting to `'auto'` makes color support depend on the value of the `isTTY` property and the value returned by `getColorDepth()` on the respective stream. This option can not be used, if `inspectOptions.colors` is set as well. Default: `'auto'`. * `inspectOptions` Specifies options that are passed along to `util.inspect()`. * `groupIndentation` Set group indentation. Default: `2`. Creates a new `Console` with one or two writable stream instances. `stdout` is a writable stream to print log or info output. `stderr` is used for warning or error output. If `stderr` is not provided, `stdout` is used for `stderr`. import { createWriteStream } from 'node:fs'; import { Console } from 'node:console'; // Alternatively // const { Console } = console; const output = createWriteStream('./stdout.log'); const errorOutput = createWriteStream('./stderr.log'); // Custom simple logger const logger = new Console({ stdout: output, stderr: errorOutput }); // use it like console const count = 5; logger.log('count: %d', count); // In stdout.log: count 5 The global `console` is a special `Console` whose output is sent to `process.stdout` and `process.stderr`. It is equivalent to calling: new Console({ stdout: process.stdout, stderr: process.stderr }); #### `console.assert(value[, ...message])`# History VersionChanges v10.0.0 The implementation is now spec compliant and does not throw anymore. v0.1.101 Added in: v0.1.101 * `value` The value tested for being truthy. * `...message` All arguments besides `value` are used as error message. `console.assert()` writes a message if `value` is falsy or omitted. It only writes a message and does not otherwise affect execution. The output always starts with `"Assertion failed"`. If provided, `message` is formatted using `util.format()`. If `value` is truthy, nothing happens. console.assert(true, 'does nothing'); console.assert(false, 'Whoops %s work', 'didn\'t'); // Assertion failed: Whoops didn't work console.assert(); // Assertion failed #### `console.clear()`# Added in: v8.3.0 When `stdout` is a TTY, calling `console.clear()` will attempt to clear the TTY. When `stdout` is not a TTY, this method does nothing. The specific operation of `console.clear()` can vary across operating systems and terminal types. For most Linux operating systems, `console.clear()` operates similarly to the `clear` shell command. On Windows, `console.clear()` will clear only the output in the current terminal viewport for the Node.js binary. #### `console.count([label])`# Added in: v8.3.0 * `label` The display label for the counter. Default: `'default'`. Maintains an internal counter specific to `label` and outputs to `stdout` the number of times `console.count()` has been called with the given `label`. > console.count() default: 1 undefined > console.count('default') default: 2 undefined > console.count('abc') abc: 1 undefined > console.count('xyz') xyz: 1 undefined > console.count('abc') abc: 2 undefined > console.count() default: 3 undefined > #### `console.countReset([label])`# Added in: v8.3.0 * `label` The display label for the counter. Default: `'default'`. Resets the internal counter specific to `label`. > console.count('abc'); abc: 1 undefined > console.countReset('abc'); undefined > console.count('abc'); abc: 1 undefined > #### `console.debug(data[, ...args])`# History VersionChanges v8.10.0 `console.debug` is now an alias for `console.log`. v8.0.0 Added in: v8.0.0 * `data` * `...args` The `console.debug()` function is an alias for `console.log()`. #### `console.dir(obj[, options])`# Added in: v0.1.101 * `obj` * `options` * `showHidden` If `true` then the object's non-enumerable and symbol properties will be shown too. Default: `false`. * `depth` Tells `util.inspect()` how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. To make it recurse indefinitely, pass `null`. Default: `2`. * `colors` If `true`, then the output will be styled with ANSI color codes. Colors are customizable; see customizing `util.inspect()` colors. Default: `false`. Uses `util.inspect()` on `obj` and prints the resulting string to `stdout`. This function bypasses any custom `inspect()` function defined on `obj`. #### `console.dirxml(...data)`# History VersionChanges v9.3.0 `console.dirxml` now calls `console.log` for its arguments. v8.0.0 Added in: v8.0.0 * `...data` This method calls `console.log()` passing it the arguments received. This method does not produce any XML formatting. #### `console.error([data][, ...args])`# Added in: v0.1.100 * `data` * `...args` Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to `printf(3)` (the arguments are all passed to `util.format()`). const code = 5; console.error('error #%d', code); // Prints: error #5, to stderr console.error('error', code); // Prints: error 5, to stderr If formatting elements (e.g. `%d`) are not found in the first string then `util.inspect()` is called on each argument and the resulting string values are concatenated. See `util.format()` for more information. #### `console.group([...label])`# Added in: v8.5.0 * `...label` Increases indentation of subsequent lines by spaces for `groupIndentation` length. If one or more `label`s are provided, those are printed first without the additional indentation. #### `console.groupCollapsed()`# Added in: v8.5.0 An alias for `console.group()`. #### `console.groupEnd()`# Added in: v8.5.0 Decreases indentation of subsequent lines by spaces for `groupIndentation` length. #### `console.info([data][, ...args])`# Added in: v0.1.100 * `data` * `...args` The `console.info()` function is an alias for `console.log()`. #### `console.log([data][, ...args])`# Added in: v0.1.100 * `data` * `...args` Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to `printf(3)` (the arguments are all passed to `util.format()`). const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout See `util.format()` for more information. #### `console.table(tabularData[, properties])`# Added in: v10.0.0 * `tabularData` * `properties` Alternate properties for constructing the table. Try to construct a table with the columns of the properties of `tabularData` (or use `properties`) and rows of `tabularData` and log it. Falls back to just logging the argument if it can't be parsed as tabular. // These can't be parsed as tabular data console.table(Symbol()); // Symbol() console.table(undefined); // undefined console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }]); // ┌─────────┬─────┬─────┐ // │ (index) │ a │ b │ // ├─────────┼─────┼─────┤ // │ 0 │ 1 │ 'Y' │ // │ 1 │ 'Z' │ 2 │ // └─────────┴─────┴─────┘ console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }], ['a']); // ┌─────────┬─────┐ // │ (index) │ a │ // ├─────────┼─────┤ // │ 0 │ 1 │ // │ 1 │ 'Z' │ // └─────────┴─────┘ #### `console.time([label])`# Added in: v0.1.104 * `label` Default: `'default'` Starts a timer that can be used to compute the duration of an operation. Timers are identified by a unique `label`. Use the same `label` when calling `console.timeEnd()` to stop the timer and output the elapsed time in suitable time units to `stdout`. For example, if the elapsed time is 3869ms, `console.timeEnd()` displays "3.869s". #### `console.timeEnd([label])`# History VersionChanges v13.0.0 The elapsed time is displayed with a suitable time unit. v6.0.0 This method no longer supports multiple calls that don't map to individual `console.time()` calls; see below for details. v0.1.104 Added in: v0.1.104 * `label` Default: `'default'` Stops a timer that was previously started by calling `console.time()` and prints the result to `stdout`: console.time('bunch-of-stuff'); // Do a bunch of stuff. console.timeEnd('bunch-of-stuff'); // Prints: bunch-of-stuff: 225.438ms #### `console.timeLog([label][, ...data])`# Added in: v10.7.0 * `label` Default: `'default'` * `...data` For a timer that was previously started by calling `console.time()`, prints the elapsed time and other `data` arguments to `stdout`: console.time('process'); const value = expensiveProcess1(); // Returns 42 console.timeLog('process', value); // Prints "process: 365.227ms 42". doExpensiveProcess2(value); console.timeEnd('process'); #### `console.trace([message][, ...args])`# Added in: v0.1.104 * `message` * `...args` Prints to `stderr` the string `'Trace: '`, followed by the `util.format()` formatted message and stack trace to the current position in the code. console.trace('Show me'); // Prints: (stack trace will vary based on where trace is called) // Trace: Show me // at repl:2:9 // at REPLServer.defaultEval (repl.js:248:27) // at bound (domain.js:287:14) // at REPLServer.runBound [as eval] (domain.js:300:12) // at REPLServer. (repl.js:412:12) // at emitOne (events.js:82:20) // at REPLServer.emit (events.js:169:7) // at REPLServer.Interface._onLine (readline.js:210:10) // at REPLServer.Interface._line (readline.js:549:8) // at REPLServer.Interface._ttyWrite (readline.js:826:14) #### `console.warn([data][, ...args])`# Added in: v0.1.100 * `data` * `...args` The `console.warn()` function is an alias for `console.error()`. ### Inspector only methods# The following methods are exposed by the V8 engine in the general API but do not display anything unless used in conjunction with the inspector (`--inspect` flag). #### `console.profile([label])`# Added in: v8.0.0 * `label` This method does not display anything unless used in the inspector. The `console.profile()` method starts a JavaScript CPU profile with an optional label until `console.profileEnd()` is called. The profile is then added to the Profile panel of the inspector. console.profile('MyLabel'); // Some code console.profileEnd('MyLabel'); // Adds the profile 'MyLabel' to the Profiles panel of the inspector. #### `console.profileEnd([label])`# Added in: v8.0.0 * `label` This method does not display anything unless used in the inspector. Stops the current JavaScript CPU profiling session if one has been started and prints the report to the Profiles panel of the inspector. See `console.profile()` for an example. If this method is called without a label, the most recently started profile is stopped. #### `console.timeStamp([label])`# Added in: v8.0.0 * `label` This method does not display anything unless used in the inspector. The `console.timeStamp()` method adds an event with the label `'label'` to the Timeline panel of the inspector. ## Crypto# Stability: 2 \- Stable Source Code: lib/crypto.js The `node:crypto` module provides cryptographic functionality that includes a set of wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign, and verify functions. const { createHmac } = await import('node:crypto'); const secret = 'abcdefg'; const hash = createHmac('sha256', secret) .update('I love cupcakes') .digest('hex'); console.log(hash); // Prints: // c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e ### Determining if crypto support is unavailable# It is possible for Node.js to be built without including support for the `node:crypto` module. In such cases, attempting to `import` from `crypto` or calling `require('node:crypto')` will result in an error being thrown. When using CommonJS, the error thrown can be caught using try/catch: When using the lexical ESM `import` keyword, the error can only be caught if a handler for `process.on('uncaughtException')` is registered before any attempt to load the module is made (using, for instance, a preload module). When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the `import()` function instead of the lexical `import` keyword: let crypto; try { crypto = await import('node:crypto'); } catch (err) { console.error('crypto support is disabled!'); } ### Asymmetric key types# The following table lists the asymmetric key types recognized by the `KeyObject` API: Key TypeDescriptionOID `'dh'`Diffie-Hellman1.2.840.113549.1.3.1 `'dsa'`DSA1.2.840.10040.4.1 `'ec'`Elliptic curve1.2.840.10045.2.1 `'ed25519'`Ed255191.3.101.112 `'ed448'`Ed4481.3.101.113 `'ml-dsa-44'`1ML-DSA-442.16.840.1.101.3.4.3.17 `'ml-dsa-65'`1ML-DSA-652.16.840.1.101.3.4.3.18 `'ml-dsa-87'`1ML-DSA-872.16.840.1.101.3.4.3.19 `'ml-kem-1024'`1ML-KEM-10242.16.840.1.101.3.4.4.3 `'ml-kem-512'`1ML-KEM-5122.16.840.1.101.3.4.4.1 `'ml-kem-768'`1ML-KEM-7682.16.840.1.101.3.4.4.2 `'rsa-pss'`RSA PSS1.2.840.113549.1.1.10 `'rsa'`RSA1.2.840.113549.1.1.1 `'slh-dsa-sha2-128f'`1SLH-DSA-SHA2-128f2.16.840.1.101.3.4.3.21 `'slh-dsa-sha2-128s'`1SLH-DSA-SHA2-128s2.16.840.1.101.3.4.3.22 `'slh-dsa-sha2-192f'`1SLH-DSA-SHA2-192f2.16.840.1.101.3.4.3.23 `'slh-dsa-sha2-192s'`1SLH-DSA-SHA2-192s2.16.840.1.101.3.4.3.24 `'slh-dsa-sha2-256f'`1SLH-DSA-SHA2-256f2.16.840.1.101.3.4.3.25 `'slh-dsa-sha2-256s'`1SLH-DSA-SHA2-256s2.16.840.1.101.3.4.3.26 `'slh-dsa-shake-128f'`1SLH-DSA-SHAKE-128f2.16.840.1.101.3.4.3.27 `'slh-dsa-shake-128s'`1SLH-DSA-SHAKE-128s2.16.840.1.101.3.4.3.28 `'slh-dsa-shake-192f'`1SLH-DSA-SHAKE-192f2.16.840.1.101.3.4.3.29 `'slh-dsa-shake-192s'`1SLH-DSA-SHAKE-192s2.16.840.1.101.3.4.3.30 `'slh-dsa-shake-256f'`1SLH-DSA-SHAKE-256f2.16.840.1.101.3.4.3.31 `'slh-dsa-shake-256s'`1SLH-DSA-SHAKE-256s2.16.840.1.101.3.4.3.32 `'x25519'`X255191.3.101.110 `'x448'`X4481.3.101.111 ### Class: `Certificate`# Added in: v0.11.8 SPKAC is a Certificate Signing Request mechanism originally implemented by Netscape and was specified formally as part of HTML5's `keygen` element. `` is deprecated since HTML 5.2 and new projects should not use this element anymore. The `node:crypto` module provides the `Certificate` class for working with SPKAC data. The most common usage is handling output generated by the HTML5 `` element. Node.js uses OpenSSL's SPKAC implementation internally. #### Static method: `Certificate.exportChallenge(spkac[, encoding])`# History VersionChanges v15.0.0 The spkac argument can be an ArrayBuffer. Limited the size of the spkac argument to a maximum of 2**31 - 1 bytes. v9.0.0 Added in: v9.0.0 * `spkac` | | | | * `encoding` The encoding of the `spkac` string. * Returns: The challenge component of the `spkac` data structure, which includes a public key and a challenge. const { Certificate } = await import('node:crypto'); const spkac = getSpkacSomehow(); const challenge = Certificate.exportChallenge(spkac); console.log(challenge.toString('utf8')); // Prints: the challenge as a UTF8 string #### Static method: `Certificate.exportPublicKey(spkac[, encoding])`# History VersionChanges v15.0.0 The spkac argument can be an ArrayBuffer. Limited the size of the spkac argument to a maximum of 2**31 - 1 bytes. v9.0.0 Added in: v9.0.0 * `spkac` | | | | * `encoding` The encoding of the `spkac` string. * Returns: The public key component of the `spkac` data structure, which includes a public key and a challenge. const { Certificate } = await import('node:crypto'); const spkac = getSpkacSomehow(); const publicKey = Certificate.exportPublicKey(spkac); console.log(publicKey); // Prints: the public key as #### Static method: `Certificate.verifySpkac(spkac[, encoding])`# History VersionChanges v15.0.0 The spkac argument can be an ArrayBuffer. Added encoding. Limited the size of the spkac argument to a maximum of 2**31 - 1 bytes. v9.0.0 Added in: v9.0.0 * `spkac` | | | | * `encoding` The encoding of the `spkac` string. * Returns: `true` if the given `spkac` data structure is valid, `false` otherwise. import { Buffer } from 'node:buffer'; const { Certificate } = await import('node:crypto'); const spkac = getSpkacSomehow(); console.log(Certificate.verifySpkac(Buffer.from(spkac))); // Prints: true or false #### Legacy API# Stability: 0 \- Deprecated As a legacy interface, it is possible to create new instances of the `crypto.Certificate` class as illustrated in the examples below. ##### `new crypto.Certificate()`# Instances of the `Certificate` class can be created using the `new` keyword or by calling `crypto.Certificate()` as a function: const { Certificate } = await import('node:crypto'); const cert1 = new Certificate(); const cert2 = Certificate(); ##### `certificate.exportChallenge(spkac[, encoding])`# Added in: v0.11.8 * `spkac` | | | | * `encoding` The encoding of the `spkac` string. * Returns: The challenge component of the `spkac` data structure, which includes a public key and a challenge. const { Certificate } = await import('node:crypto'); const cert = Certificate(); const spkac = getSpkacSomehow(); const challenge = cert.exportChallenge(spkac); console.log(challenge.toString('utf8')); // Prints: the challenge as a UTF8 string ##### `certificate.exportPublicKey(spkac[, encoding])`# Added in: v0.11.8 * `spkac` | | | | * `encoding` The encoding of the `spkac` string. * Returns: The public key component of the `spkac` data structure, which includes a public key and a challenge. const { Certificate } = await import('node:crypto'); const cert = Certificate(); const spkac = getSpkacSomehow(); const publicKey = cert.exportPublicKey(spkac); console.log(publicKey); // Prints: the public key as ##### `certificate.verifySpkac(spkac[, encoding])`# Added in: v0.11.8 * `spkac` | | | | * `encoding` The encoding of the `spkac` string. * Returns: `true` if the given `spkac` data structure is valid, `false` otherwise. import { Buffer } from 'node:buffer'; const { Certificate } = await import('node:crypto'); const cert = Certificate(); const spkac = getSpkacSomehow(); console.log(cert.verifySpkac(Buffer.from(spkac))); // Prints: true or false ### Class: `Cipheriv`# Added in: v0.1.94 * Extends: Instances of the `Cipheriv` class are used to encrypt data. The class can be used in one of two ways: * As a stream that is both readable and writable, where plain unencrypted data is written to produce encrypted data on the readable side, or * Using the `cipher.update()` and `cipher.final()` methods to produce the encrypted data. The `crypto.createCipheriv()` method is used to create `Cipheriv` instances. `Cipheriv` objects are not to be created directly using the `new` keyword. Example: Using `Cipheriv` objects as streams: const { scrypt, randomFill, createCipheriv, } = await import('node:crypto'); const algorithm = 'aes-192-cbc'; const password = 'Password used to generate key'; // First, we'll generate the key. The key length is dependent on the algorithm. // In this case for aes192, it is 24 bytes (192 bits). scrypt(password, 'salt', 24, (err, key) => { if (err) throw err; // Then, we'll generate a random initialization vector randomFill(new Uint8Array(16), (err, iv) => { if (err) throw err; // Once we have the key and iv, we can create and use the cipher... const cipher = createCipheriv(algorithm, key, iv); let encrypted = ''; cipher.setEncoding('hex'); cipher.on('data', (chunk) => encrypted += chunk); cipher.on('end', () => console.log(encrypted)); cipher.write('some clear text data'); cipher.end(); }); }); Example: Using `Cipheriv` and piped streams: import { createReadStream, createWriteStream, } from 'node:fs'; import { pipeline, } from 'node:stream'; const { scrypt, randomFill, createCipheriv, } = await import('node:crypto'); const algorithm = 'aes-192-cbc'; const password = 'Password used to generate key'; // First, we'll generate the key. The key length is dependent on the algorithm. // In this case for aes192, it is 24 bytes (192 bits). scrypt(password, 'salt', 24, (err, key) => { if (err) throw err; // Then, we'll generate a random initialization vector randomFill(new Uint8Array(16), (err, iv) => { if (err) throw err; const cipher = createCipheriv(algorithm, key, iv); const input = createReadStream('test.js'); const output = createWriteStream('test.enc'); pipeline(input, cipher, output, (err) => { if (err) throw err; }); }); }); Example: Using the `cipher.update()` and `cipher.final()` methods: const { scrypt, randomFill, createCipheriv, } = await import('node:crypto'); const algorithm = 'aes-192-cbc'; const password = 'Password used to generate key'; // First, we'll generate the key. The key length is dependent on the algorithm. // In this case for aes192, it is 24 bytes (192 bits). scrypt(password, 'salt', 24, (err, key) => { if (err) throw err; // Then, we'll generate a random initialization vector randomFill(new Uint8Array(16), (err, iv) => { if (err) throw err; const cipher = createCipheriv(algorithm, key, iv); let encrypted = cipher.update('some clear text data', 'utf8', 'hex'); encrypted += cipher.final('hex'); console.log(encrypted); }); }); #### `cipher.final([outputEncoding])`# Added in: v0.1.94 * `outputEncoding` The encoding of the return value. * Returns: | Any remaining enciphered contents. If `outputEncoding` is specified, a string is returned. If an `outputEncoding` is not provided, a `Buffer` is returned. Once the `cipher.final()` method has been called, the `Cipheriv` object can no longer be used to encrypt data. Attempts to call `cipher.final()` more than once will result in an error being thrown. #### `cipher.getAuthTag()`# Added in: v1.0.0 * Returns: When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `cipher.getAuthTag()` method returns a `Buffer` containing the authentication tag that has been computed from the given data. The `cipher.getAuthTag()` method should only be called after encryption has been completed using the `cipher.final()` method. If the `authTagLength` option was set during the `cipher` instance's creation, this function will return exactly `authTagLength` bytes. #### `cipher.setAAD(buffer[, options])`# Added in: v1.0.0 * `buffer` | | | | * `options` `stream.transform` options * `plaintextLength` * `encoding` The string encoding to use when `buffer` is a string. * Returns: The same `Cipheriv` instance for method chaining. When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `cipher.setAAD()` method sets the value used for the additional authenticated data (AAD) input parameter. The `plaintextLength` option is optional for `GCM` and `OCB`. When using `CCM`, the `plaintextLength` option must be specified and its value must match the length of the plaintext in bytes. See CCM mode. The `cipher.setAAD()` method must be called before `cipher.update()`. #### `cipher.setAutoPadding([autoPadding])`# Added in: v0.7.1 * `autoPadding` Default: `true` * Returns: The same `Cipheriv` instance for method chaining. When using block encryption algorithms, the `Cipheriv` class will automatically add padding to the input data to the appropriate block size. To disable the default padding call `cipher.setAutoPadding(false)`. When `autoPadding` is `false`, the length of the entire input data must be a multiple of the cipher's block size or `cipher.final()` will throw an error. Disabling automatic padding is useful for non-standard padding, for instance using `0x0` instead of PKCS padding. The `cipher.setAutoPadding()` method must be called before `cipher.final()`. #### `cipher.update(data[, inputEncoding][, outputEncoding])`# History VersionChanges v6.0.0 The default `inputEncoding` changed from `binary` to `utf8`. v0.1.94 Added in: v0.1.94 * `data` | | | * `inputEncoding` The encoding of the data. * `outputEncoding` The encoding of the return value. * Returns: | Updates the cipher with `data`. If the `inputEncoding` argument is given, the `data` argument is a string using the specified encoding. If the `inputEncoding` argument is not given, `data` must be a `Buffer`, `TypedArray`, or `DataView`. If `data` is a `Buffer`, `TypedArray`, or `DataView`, then `inputEncoding` is ignored. The `outputEncoding` specifies the output format of the enciphered data. If the `outputEncoding` is specified, a string using the specified encoding is returned. If no `outputEncoding` is provided, a `Buffer` is returned. The `cipher.update()` method can be called multiple times with new data until `cipher.final()` is called. Calling `cipher.update()` after `cipher.final()` will result in an error being thrown. ### Class: `Decipheriv`# Added in: v0.1.94 * Extends: Instances of the `Decipheriv` class are used to decrypt data. The class can be used in one of two ways: * As a stream that is both readable and writable, where plain encrypted data is written to produce unencrypted data on the readable side, or * Using the `decipher.update()` and `decipher.final()` methods to produce the unencrypted data. The `crypto.createDecipheriv()` method is used to create `Decipheriv` instances. `Decipheriv` objects are not to be created directly using the `new` keyword. Example: Using `Decipheriv` objects as streams: import { Buffer } from 'node:buffer'; const { scryptSync, createDecipheriv, } = await import('node:crypto'); const algorithm = 'aes-192-cbc'; const password = 'Password used to generate key'; // Key length is dependent on the algorithm. In this case for aes192, it is // 24 bytes (192 bits). // Use the async `crypto.scrypt()` instead. const key = scryptSync(password, 'salt', 24); // The IV is usually passed along with the ciphertext. const iv = Buffer.alloc(16, 0); // Initialization vector. const decipher = createDecipheriv(algorithm, key, iv); let decrypted = ''; decipher.on('readable', () => { let chunk; while (null !== (chunk = decipher.read())) { decrypted += chunk.toString('utf8'); } }); decipher.on('end', () => { console.log(decrypted); // Prints: some clear text data }); // Encrypted with same algorithm, key and iv. const encrypted = 'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa'; decipher.write(encrypted, 'hex'); decipher.end(); Example: Using `Decipheriv` and piped streams: import { createReadStream, createWriteStream, } from 'node:fs'; import { Buffer } from 'node:buffer'; const { scryptSync, createDecipheriv, } = await import('node:crypto'); const algorithm = 'aes-192-cbc'; const password = 'Password used to generate key'; // Use the async `crypto.scrypt()` instead. const key = scryptSync(password, 'salt', 24); // The IV is usually passed along with the ciphertext. const iv = Buffer.alloc(16, 0); // Initialization vector. const decipher = createDecipheriv(algorithm, key, iv); const input = createReadStream('test.enc'); const output = createWriteStream('test.js'); input.pipe(decipher).pipe(output); Example: Using the `decipher.update()` and `decipher.final()` methods: import { Buffer } from 'node:buffer'; const { scryptSync, createDecipheriv, } = await import('node:crypto'); const algorithm = 'aes-192-cbc'; const password = 'Password used to generate key'; // Use the async `crypto.scrypt()` instead. const key = scryptSync(password, 'salt', 24); // The IV is usually passed along with the ciphertext. const iv = Buffer.alloc(16, 0); // Initialization vector. const decipher = createDecipheriv(algorithm, key, iv); // Encrypted using same algorithm, key and iv. const encrypted = 'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa'; let decrypted = decipher.update(encrypted, 'hex', 'utf8'); decrypted += decipher.final('utf8'); console.log(decrypted); // Prints: some clear text data #### `decipher.final([outputEncoding])`# Added in: v0.1.94 * `outputEncoding` The encoding of the return value. * Returns: | Any remaining deciphered contents. If `outputEncoding` is specified, a string is returned. If an `outputEncoding` is not provided, a `Buffer` is returned. Once the `decipher.final()` method has been called, the `Decipheriv` object can no longer be used to decrypt data. Attempts to call `decipher.final()` more than once will result in an error being thrown. #### `decipher.setAAD(buffer[, options])`# History VersionChanges v15.0.0 The buffer argument can be a string or ArrayBuffer and is limited to no more than 2 ** 31 - 1 bytes. v7.2.0 This method now returns a reference to `decipher`. v1.0.0 Added in: v1.0.0 * `buffer` | | | | * `options` `stream.transform` options * `plaintextLength` * `encoding` String encoding to use when `buffer` is a string. * Returns: The same Decipher for method chaining. When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `decipher.setAAD()` method sets the value used for the additional authenticated data (AAD) input parameter. The `options` argument is optional for `GCM`. When using `CCM`, the `plaintextLength` option must be specified and its value must match the length of the ciphertext in bytes. See CCM mode. The `decipher.setAAD()` method must be called before `decipher.update()`. When passing a string as the `buffer`, please consider caveats when using strings as inputs to cryptographic APIs. #### `decipher.setAuthTag(buffer[, encoding])`# History VersionChanges v22.0.0, v20.13.0 Using GCM tag lengths other than 128 bits without specifying the `authTagLength` option when creating `decipher` is deprecated. v15.0.0 The buffer argument can be a string or ArrayBuffer and is limited to no more than 2 ** 31 - 1 bytes. v11.0.0 This method now throws if the GCM tag length is invalid. v7.2.0 This method now returns a reference to `decipher`. v1.0.0 Added in: v1.0.0 * `buffer` | | | | * `encoding` String encoding to use when `buffer` is a string. * Returns: The same Decipher for method chaining. When using an authenticated encryption mode (`GCM`, `CCM`, `OCB`, and `chacha20-poly1305` are currently supported), the `decipher.setAuthTag()` method is used to pass in the received authentication tag. If no tag is provided, or if the cipher text has been tampered with, `decipher.final()` will throw, indicating that the cipher text should be discarded due to failed authentication. If the tag length is invalid according to NIST SP 800-38D or does not match the value of the `authTagLength` option, `decipher.setAuthTag()` will throw an error. The `decipher.setAuthTag()` method must be called before `decipher.update()` for `CCM` mode or before `decipher.final()` for `GCM` and `OCB` modes and `chacha20-poly1305`. `decipher.setAuthTag()` can only be called once. When passing a string as the authentication tag, please consider caveats when using strings as inputs to cryptographic APIs. #### `decipher.setAutoPadding([autoPadding])`# Added in: v0.7.1 * `autoPadding` Default: `true` * Returns: The same Decipher for method chaining. When data has been encrypted without standard block padding, calling `decipher.setAutoPadding(false)` will disable automatic padding to prevent `decipher.final()` from checking for and removing padding. Turning auto padding off will only work if the input data's length is a multiple of the ciphers block size. The `decipher.setAutoPadding()` method must be called before `decipher.final()`. #### `decipher.update(data[, inputEncoding][, outputEncoding])`# History VersionChanges v6.0.0 The default `inputEncoding` changed from `binary` to `utf8`. v0.1.94 Added in: v0.1.94 * `data` | | | * `inputEncoding` The encoding of the `data` string. * `outputEncoding` The encoding of the return value. * Returns: | Updates the decipher with `data`. If the `inputEncoding` argument is given, the `data` argument is a string using the specified encoding. If the `inputEncoding` argument is not given, `data` must be a `Buffer`. If `data` is a `Buffer` then `inputEncoding` is ignored. The `outputEncoding` specifies the output format of the enciphered data. If the `outputEncoding` is specified, a string using the specified encoding is returned. If no `outputEncoding` is provided, a `Buffer` is returned. The `decipher.update()` method can be called multiple times with new data until `decipher.final()` is called. Calling `decipher.update()` after `decipher.final()` will result in an error being thrown. Even if the underlying cipher implements authentication, the authenticity and integrity of the plaintext returned from this function may be uncertain at this time. For authenticated encryption algorithms, authenticity is generally only established when the application calls `decipher.final()`. ### Class: `DiffieHellman`# Added in: v0.5.0 The `DiffieHellman` class is a utility for creating Diffie-Hellman key exchanges. Instances of the `DiffieHellman` class can be created using the `crypto.createDiffieHellman()` function. import assert from 'node:assert'; const { createDiffieHellman, } = await import('node:crypto'); // Generate Alice's keys... const alice = createDiffieHellman(2048); const aliceKey = alice.generateKeys(); // Generate Bob's keys... const bob = createDiffieHellman(alice.getPrime(), alice.getGenerator()); const bobKey = bob.generateKeys(); // Exchange and generate the secret... const aliceSecret = alice.computeSecret(bobKey); const bobSecret = bob.computeSecret(aliceKey); // OK assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex')); #### `diffieHellman.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])`# Added in: v0.5.0 * `otherPublicKey` | | | | * `inputEncoding` The encoding of an `otherPublicKey` string. * `outputEncoding` The encoding of the return value. * Returns: | Computes the shared secret using `otherPublicKey` as the other party's public key and returns the computed shared secret. The supplied key is interpreted using the specified `inputEncoding`, and secret is encoded using specified `outputEncoding`. If the `inputEncoding` is not provided, `otherPublicKey` is expected to be a `Buffer`, `TypedArray`, or `DataView`. If `outputEncoding` is given a string is returned; otherwise, a `Buffer` is returned. #### `diffieHellman.generateKeys([encoding])`# Added in: v0.5.0 * `encoding` The encoding of the return value. * Returns: | Generates private and public Diffie-Hellman key values unless they have been generated or computed already, and returns the public key in the specified `encoding`. This key should be transferred to the other party. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned. This function is a thin wrapper around `DH_generate_key()`. In particular, once a private key has been generated or set, calling this function only updates the public key but does not generate a new private key. #### `diffieHellman.getGenerator([encoding])`# Added in: v0.5.0 * `encoding` The encoding of the return value. * Returns: | Returns the Diffie-Hellman generator in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned. #### `diffieHellman.getPrime([encoding])`# Added in: v0.5.0 * `encoding` The encoding of the return value. * Returns: | Returns the Diffie-Hellman prime in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned. #### `diffieHellman.getPrivateKey([encoding])`# Added in: v0.5.0 * `encoding` The encoding of the return value. * Returns: | Returns the Diffie-Hellman private key in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned. #### `diffieHellman.getPublicKey([encoding])`# Added in: v0.5.0 * `encoding` The encoding of the return value. * Returns: | Returns the Diffie-Hellman public key in the specified `encoding`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned. #### `diffieHellman.setPrivateKey(privateKey[, encoding])`# Added in: v0.5.0 * `privateKey` | | | | * `encoding` The encoding of the `privateKey` string. Sets the Diffie-Hellman private key. If the `encoding` argument is provided, `privateKey` is expected to be a string. If no `encoding` is provided, `privateKey` is expected to be a `Buffer`, `TypedArray`, or `DataView`. This function does not automatically compute the associated public key. Either `diffieHellman.setPublicKey()` or `diffieHellman.generateKeys()` can be used to manually provide the public key or to automatically derive it. #### `diffieHellman.setPublicKey(publicKey[, encoding])`# Added in: v0.5.0 * `publicKey` | | | | * `encoding` The encoding of the `publicKey` string. Sets the Diffie-Hellman public key. If the `encoding` argument is provided, `publicKey` is expected to be a string. If no `encoding` is provided, `publicKey` is expected to be a `Buffer`, `TypedArray`, or `DataView`. #### `diffieHellman.verifyError`# Added in: v0.11.12 A bit field containing any warnings and/or errors resulting from a check performed during initialization of the `DiffieHellman` object. The following values are valid for this property (as defined in `node:constants` module): * `DH_CHECK_P_NOT_SAFE_PRIME` * `DH_CHECK_P_NOT_PRIME` * `DH_UNABLE_TO_CHECK_GENERATOR` * `DH_NOT_SUITABLE_GENERATOR` ### Class: `DiffieHellmanGroup`# Added in: v0.7.5 The `DiffieHellmanGroup` class takes a well-known modp group as its argument. It works the same as `DiffieHellman`, except that it does not allow changing its keys after creation. In other words, it does not implement `setPublicKey()` or `setPrivateKey()` methods. const { createDiffieHellmanGroup } = await import('node:crypto'); const dh = createDiffieHellmanGroup('modp16'); The following groups are supported: * `'modp14'` (2048 bits, RFC 3526 Section 3) * `'modp15'` (3072 bits, RFC 3526 Section 4) * `'modp16'` (4096 bits, RFC 3526 Section 5) * `'modp17'` (6144 bits, RFC 3526 Section 6) * `'modp18'` (8192 bits, RFC 3526 Section 7) The following groups are still supported but deprecated (see Caveats): * `'modp1'` (768 bits, RFC 2409 Section 6.1) * `'modp2'` (1024 bits, RFC 2409 Section 6.2) * `'modp5'` (1536 bits, RFC 3526 Section 2) These deprecated groups might be removed in future versions of Node.js. ### Class: `ECDH`# Added in: v0.11.14 The `ECDH` class is a utility for creating Elliptic Curve Diffie-Hellman (ECDH) key exchanges. Instances of the `ECDH` class can be created using the `crypto.createECDH()` function. import assert from 'node:assert'; const { createECDH, } = await import('node:crypto'); // Generate Alice's keys... const alice = createECDH('secp521r1'); const aliceKey = alice.generateKeys(); // Generate Bob's keys... const bob = createECDH('secp521r1'); const bobKey = bob.generateKeys(); // Exchange and generate the secret... const aliceSecret = alice.computeSecret(bobKey); const bobSecret = bob.computeSecret(aliceKey); assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex')); // OK #### Static method: `ECDH.convertKey(key, curve[, inputEncoding[, outputEncoding[, format]]])`# Added in: v10.0.0 * `key` | | | | * `curve` * `inputEncoding` The encoding of the `key` string. * `outputEncoding` The encoding of the return value. * `format` Default: `'uncompressed'` * Returns: | Converts the EC Diffie-Hellman public key specified by `key` and `curve` to the format specified by `format`. The `format` argument specifies point encoding and can be `'compressed'`, `'uncompressed'` or `'hybrid'`. The supplied key is interpreted using the specified `inputEncoding`, and the returned key is encoded using the specified `outputEncoding`. Use `crypto.getCurves()` to obtain a list of available curve names. On recent OpenSSL releases, `openssl ecparam -list_curves` will also display the name and description of each available elliptic curve. If `format` is not specified the point will be returned in `'uncompressed'` format. If the `inputEncoding` is not provided, `key` is expected to be a `Buffer`, `TypedArray`, or `DataView`. Example (uncompressing a key): const { createECDH, ECDH, } = await import('node:crypto'); const ecdh = createECDH('secp256k1'); ecdh.generateKeys(); const compressedKey = ecdh.getPublicKey('hex', 'compressed'); const uncompressedKey = ECDH.convertKey(compressedKey, 'secp256k1', 'hex', 'hex', 'uncompressed'); // The converted key and the uncompressed public key should be the same console.log(uncompressedKey === ecdh.getPublicKey('hex')); #### `ecdh.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])`# History VersionChanges v10.0.0 Changed error format to better support invalid public key error. v6.0.0 The default `inputEncoding` changed from `binary` to `utf8`. v0.11.14 Added in: v0.11.14 * `otherPublicKey` | | | | * `inputEncoding` The encoding of the `otherPublicKey` string. * `outputEncoding` The encoding of the return value. * Returns: | Computes the shared secret using `otherPublicKey` as the other party's public key and returns the computed shared secret. The supplied key is interpreted using specified `inputEncoding`, and the returned secret is encoded using the specified `outputEncoding`. If the `inputEncoding` is not provided, `otherPublicKey` is expected to be a `Buffer`, `TypedArray`, or `DataView`. If `outputEncoding` is given a string will be returned; otherwise a `Buffer` is returned. `ecdh.computeSecret` will throw an `ERR_CRYPTO_ECDH_INVALID_PUBLIC_KEY` error when `otherPublicKey` lies outside of the elliptic curve. Since `otherPublicKey` is usually supplied from a remote user over an insecure network, be sure to handle this exception accordingly. #### `ecdh.generateKeys([encoding[, format]])`# Added in: v0.11.14 * `encoding` The encoding of the return value. * `format` Default: `'uncompressed'` * Returns: | Generates private and public EC Diffie-Hellman key values, and returns the public key in the specified `format` and `encoding`. This key should be transferred to the other party. The `format` argument specifies point encoding and can be `'compressed'` or `'uncompressed'`. If `format` is not specified, the point will be returned in `'uncompressed'` format. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned. #### `ecdh.getPrivateKey([encoding])`# Added in: v0.11.14 * `encoding` The encoding of the return value. * Returns: | The EC Diffie-Hellman in the specified `encoding`. If `encoding` is specified, a string is returned; otherwise a `Buffer` is returned. #### `ecdh.getPublicKey([encoding][, format])`# Added in: v0.11.14 * `encoding` The encoding of the return value. * `format` Default: `'uncompressed'` * Returns: | The EC Diffie-Hellman public key in the specified `encoding` and `format`. The `format` argument specifies point encoding and can be `'compressed'` or `'uncompressed'`. If `format` is not specified the point will be returned in `'uncompressed'` format. If `encoding` is specified, a string is returned; otherwise a `Buffer` is returned. #### `ecdh.setPrivateKey(privateKey[, encoding])`# Added in: v0.11.14 * `privateKey` | | | | * `encoding` The encoding of the `privateKey` string. Sets the EC Diffie-Hellman private key. If `encoding` is provided, `privateKey` is expected to be a string; otherwise `privateKey` is expected to be a `Buffer`, `TypedArray`, or `DataView`. If `privateKey` is not valid for the curve specified when the `ECDH` object was created, an error is thrown. Upon setting the private key, the associated public point (key) is also generated and set in the `ECDH` object. #### `ecdh.setPublicKey(publicKey[, encoding])`# Added in: v0.11.14Deprecated since: v5.2.0 Stability: 0 \- Deprecated * `publicKey` | | | | * `encoding` The encoding of the `publicKey` string. Sets the EC Diffie-Hellman public key. If `encoding` is provided `publicKey` is expected to be a string; otherwise a `Buffer`, `TypedArray`, or `DataView` is expected. There is not normally a reason to call this method because `ECDH` only requires a private key and the other party's public key to compute the shared secret. Typically either `ecdh.generateKeys()` or `ecdh.setPrivateKey()` will be called. The `ecdh.setPrivateKey()` method attempts to generate the public point/key associated with the private key being set. Example (obtaining a shared secret): const { createECDH, createHash, } = await import('node:crypto'); const alice = createECDH('secp256k1'); const bob = createECDH('secp256k1'); // This is a shortcut way of specifying one of Alice's previous private // keys. It would be unwise to use such a predictable private key in a real // application. alice.setPrivateKey( createHash('sha256').update('alice', 'utf8').digest(), ); // Bob uses a newly generated cryptographically strong // pseudorandom key pair bob.generateKeys(); const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex'); const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex'); // aliceSecret and bobSecret should be the same shared secret value console.log(aliceSecret === bobSecret); ### Class: `Hash`# Added in: v0.1.92 * Extends: The `Hash` class is a utility for creating hash digests of data. It can be used in one of two ways: * As a stream that is both readable and writable, where data is written to produce a computed hash digest on the readable side, or * Using the `hash.update()` and `hash.digest()` methods to produce the computed hash. The `crypto.createHash()` method is used to create `Hash` instances. `Hash` objects are not to be created directly using the `new` keyword. Example: Using `Hash` objects as streams: const { createHash, } = await import('node:crypto'); const hash = createHash('sha256'); hash.on('readable', () => { // Only one element is going to be produced by the // hash stream. const data = hash.read(); if (data) { console.log(data.toString('hex')); // Prints: // 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50 } }); hash.write('some data to hash'); hash.end(); Example: Using `Hash` and piped streams: import { createReadStream } from 'node:fs'; import { stdout } from 'node:process'; const { createHash } = await import('node:crypto'); const hash = createHash('sha256'); const input = createReadStream('test.js'); input.pipe(hash).setEncoding('hex').pipe(stdout); Example: Using the `hash.update()` and `hash.digest()` methods: const { createHash, } = await import('node:crypto'); const hash = createHash('sha256'); hash.update('some data to hash'); console.log(hash.digest('hex')); // Prints: // 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50 #### `hash.copy([options])`# Added in: v13.1.0 * `options` `stream.transform` options * Returns: Creates a new `Hash` object that contains a deep copy of the internal state of the current `Hash` object. The optional `options` argument controls stream behavior. For XOF hash functions such as `'shake256'`, the `outputLength` option can be used to specify the desired output length in bytes. An error is thrown when an attempt is made to copy the `Hash` object after its `hash.digest()` method has been called. // Calculate a rolling hash. const { createHash, } = await import('node:crypto'); const hash = createHash('sha256'); hash.update('one'); console.log(hash.copy().digest('hex')); hash.update('two'); console.log(hash.copy().digest('hex')); hash.update('three'); console.log(hash.copy().digest('hex')); // Etc. #### `hash.digest([encoding])`# Added in: v0.1.92 * `encoding` The encoding of the return value. * Returns: | Calculates the digest of all of the data passed to be hashed (using the `hash.update()` method). If `encoding` is provided a string will be returned; otherwise a `Buffer` is returned. The `Hash` object can not be used again after `hash.digest()` method has been called. Multiple calls will cause an error to be thrown. #### `hash.update(data[, inputEncoding])`# History VersionChanges v6.0.0 The default `inputEncoding` changed from `binary` to `utf8`. v0.1.92 Added in: v0.1.92 * `data` | | | * `inputEncoding` The encoding of the `data` string. Updates the hash content with the given `data`, the encoding of which is given in `inputEncoding`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a `Buffer`, `TypedArray`, or `DataView`, then `inputEncoding` is ignored. This can be called many times with new data as it is streamed. ### Class: `Hmac`# Added in: v0.1.94 * Extends: The `Hmac` class is a utility for creating cryptographic HMAC digests. It can be used in one of two ways: * As a stream that is both readable and writable, where data is written to produce a computed HMAC digest on the readable side, or * Using the `hmac.update()` and `hmac.digest()` methods to produce the computed HMAC digest. The `crypto.createHmac()` method is used to create `Hmac` instances. `Hmac` objects are not to be created directly using the `new` keyword. Example: Using `Hmac` objects as streams: const { createHmac, } = await import('node:crypto'); const hmac = createHmac('sha256', 'a secret'); hmac.on('readable', () => { // Only one element is going to be produced by the // hash stream. const data = hmac.read(); if (data) { console.log(data.toString('hex')); // Prints: // 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e } }); hmac.write('some data to hash'); hmac.end(); Example: Using `Hmac` and piped streams: import { createReadStream } from 'node:fs'; import { stdout } from 'node:process'; const { createHmac, } = await import('node:crypto'); const hmac = createHmac('sha256', 'a secret'); const input = createReadStream('test.js'); input.pipe(hmac).pipe(stdout); Example: Using the `hmac.update()` and `hmac.digest()` methods: const { createHmac, } = await import('node:crypto'); const hmac = createHmac('sha256', 'a secret'); hmac.update('some data to hash'); console.log(hmac.digest('hex')); // Prints: // 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e #### `hmac.digest([encoding])`# Added in: v0.1.94 * `encoding` The encoding of the return value. * Returns: | Calculates the HMAC digest of all of the data passed using `hmac.update()`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned; The `Hmac` object can not be used again after `hmac.digest()` has been called. Multiple calls to `hmac.digest()` will result in an error being thrown. #### `hmac.update(data[, inputEncoding])`# History VersionChanges v6.0.0 The default `inputEncoding` changed from `binary` to `utf8`. v0.1.94 Added in: v0.1.94 * `data` | | | * `inputEncoding` The encoding of the `data` string. Updates the `Hmac` content with the given `data`, the encoding of which is given in `inputEncoding`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a `Buffer`, `TypedArray`, or `DataView`, then `inputEncoding` is ignored. This can be called many times with new data as it is streamed. ### Class: `KeyObject`# History VersionChanges v24.6.0 Add support for ML-DSA keys. v14.5.0, v12.19.0 Instances of this class can now be passed to worker threads using `postMessage`. v11.13.0 This class is now exported. v11.6.0 Added in: v11.6.0 Node.js uses a `KeyObject` class to represent a symmetric or asymmetric key, and each kind of key exposes different functions. The `crypto.createSecretKey()`, `crypto.createPublicKey()` and `crypto.createPrivateKey()` methods are used to create `KeyObject` instances. `KeyObject` objects are not to be created directly using the `new` keyword. Most applications should consider using the new `KeyObject` API instead of passing keys as strings or `Buffer`s due to improved security features. `KeyObject` instances can be passed to other threads via `postMessage()`. The receiver obtains a cloned `KeyObject`, and the `KeyObject` does not need to be listed in the `transferList` argument. #### Static method: `KeyObject.from(key)`# Added in: v15.0.0 * `key` * Returns: Example: Converting a `CryptoKey` instance to a `KeyObject`: const { KeyObject } = await import('node:crypto'); const { subtle } = globalThis.crypto; const key = await subtle.generateKey({ name: 'HMAC', hash: 'SHA-256', length: 256, }, true, ['sign', 'verify']); const keyObject = KeyObject.from(key); console.log(keyObject.symmetricKeySize); // Prints: 32 (symmetric key size in bytes) #### `keyObject.asymmetricKeyDetails`# History VersionChanges v16.9.0 Expose `RSASSA-PSS-params` sequence parameters for RSA-PSS keys. v15.7.0 Added in: v15.7.0 * Type: * `modulusLength` Key size in bits (RSA, DSA). * `publicExponent` Public exponent (RSA). * `hashAlgorithm` Name of the message digest (RSA-PSS). * `mgf1HashAlgorithm` Name of the message digest used by MGF1 (RSA-PSS). * `saltLength` Minimal salt length in bytes (RSA-PSS). * `divisorLength` Size of `q` in bits (DSA). * `namedCurve` Name of the curve (EC). This property exists only on asymmetric keys. Depending on the type of the key, this object contains information about the key. None of the information obtained through this property can be used to uniquely identify a key or to compromise the security of the key. For RSA-PSS keys, if the key material contains a `RSASSA-PSS-params` sequence, the `hashAlgorithm`, `mgf1HashAlgorithm`, and `saltLength` properties will be set. Other key details might be exposed via this API using additional attributes. #### `keyObject.asymmetricKeyType`# History VersionChanges v24.8.0 Add support for SLH-DSA keys. v24.7.0 Add support for ML-KEM keys. v24.6.0 Add support for ML-DSA keys. v13.9.0, v12.17.0 Added support for `'dh'`. v12.0.0 Added support for `'rsa-pss'`. v12.0.0 This property now returns `undefined` for KeyObject instances of unrecognized type instead of aborting. v12.0.0 Added support for `'x25519'` and `'x448'`. v12.0.0 Added support for `'ed25519'` and `'ed448'`. v11.6.0 Added in: v11.6.0 * Type: For asymmetric keys, this property represents the type of the key. See the supported asymmetric key types. This property is `undefined` for unrecognized `KeyObject` types and symmetric keys. #### `keyObject.equals(otherKeyObject)`# Added in: v17.7.0, v16.15.0 * `otherKeyObject` A `KeyObject` with which to compare `keyObject`. * Returns: Returns `true` or `false` depending on whether the keys have exactly the same type, value, and parameters. This method is not constant time. #### `keyObject.export([options])`# History VersionChanges v15.9.0 Added support for `'jwk'` format. v11.6.0 Added in: v11.6.0 * `options` * Returns: | | For symmetric keys, the following encoding options can be used: * `format` Must be `'buffer'` (default) or `'jwk'`. For public keys, the following encoding options can be used: * `type` Must be one of `'pkcs1'` (RSA only) or `'spki'`. * `format` Must be `'pem'`, `'der'`, or `'jwk'`. For private keys, the following encoding options can be used: * `type` Must be one of `'pkcs1'` (RSA only), `'pkcs8'` or `'sec1'` (EC only). * `format` Must be `'pem'`, `'der'`, or `'jwk'`. * `cipher` If specified, the private key will be encrypted with the given `cipher` and `passphrase` using PKCS#5 v2.0 password based encryption. * `passphrase` | The passphrase to use for encryption, see `cipher`. The result type depends on the selected encoding format, when PEM the result is a string, when DER it will be a buffer containing the data encoded as DER, when JWK it will be an object. When JWK encoding format was selected, all other encoding options are ignored. PKCS#1, SEC1, and PKCS#8 type keys can be encrypted by using a combination of the `cipher` and `format` options. The PKCS#8 `type` can be used with any `format` to encrypt any key algorithm (RSA, EC, or DH) by specifying a `cipher`. PKCS#1 and SEC1 can only be encrypted by specifying a `cipher` when the PEM `format` is used. For maximum compatibility, use PKCS#8 for encrypted private keys. Since PKCS#8 defines its own encryption mechanism, PEM-level encryption is not supported when encrypting a PKCS#8 key. See RFC 5208 for PKCS#8 encryption and RFC 1421 for PKCS#1 and SEC1 encryption. #### `keyObject.symmetricKeySize`# Added in: v11.6.0 * Type: For secret keys, this property represents the size of the key in bytes. This property is `undefined` for asymmetric keys. #### `keyObject.toCryptoKey(algorithm, extractable, keyUsages)`# Added in: v23.0.0, v22.10.0 * `algorithm` | | | | * `extractable` * `keyUsages` See Key usages. * Returns: Converts a `KeyObject` instance to a `CryptoKey`. #### `keyObject.type`# Added in: v11.6.0 * Type: Depending on the type of this `KeyObject`, this property is either `'secret'` for secret (symmetric) keys, `'public'` for public (asymmetric) keys or `'private'` for private (asymmetric) keys. ### Class: `Sign`# Added in: v0.1.92 * Extends: The `Sign` class is a utility for generating signatures. It can be used in one of two ways: * As a writable stream, where data to be signed is written and the `sign.sign()` method is used to generate and return the signature, or * Using the `sign.update()` and `sign.sign()` methods to produce the signature. The `crypto.createSign()` method is used to create `Sign` instances. The argument is the string name of the hash function to use. `Sign` objects are not to be created directly using the `new` keyword. Example: Using `Sign` and `Verify` objects as streams: const { generateKeyPairSync, createSign, createVerify, } = await import('node:crypto'); const { privateKey, publicKey } = generateKeyPairSync('ec', { namedCurve: 'sect239k1', }); const sign = createSign('SHA256'); sign.write('some data to sign'); sign.end(); const signature = sign.sign(privateKey, 'hex'); const verify = createVerify('SHA256'); verify.write('some data to sign'); verify.end(); console.log(verify.verify(publicKey, signature, 'hex')); // Prints: true Example: Using the `sign.update()` and `verify.update()` methods: const { generateKeyPairSync, createSign, createVerify, } = await import('node:crypto'); const { privateKey, publicKey } = generateKeyPairSync('rsa', { modulusLength: 2048, }); const sign = createSign('SHA256'); sign.update('some data to sign'); sign.end(); const signature = sign.sign(privateKey); const verify = createVerify('SHA256'); verify.update('some data to sign'); verify.end(); console.log(verify.verify(publicKey, signature)); // Prints: true #### `sign.sign(privateKey[, outputEncoding])`# History VersionChanges v15.0.0 The privateKey can also be an ArrayBuffer and CryptoKey. v13.2.0, v12.16.0 This function now supports IEEE-P1363 DSA and ECDSA signatures. v12.0.0 This function now supports RSA-PSS keys. v11.6.0 This function now supports key objects. v8.0.0 Support for RSASSA-PSS and additional options was added. v0.1.92 Added in: v0.1.92 * `privateKey` | | | | | | | * `dsaEncoding` * `padding` * `saltLength` * `outputEncoding` The encoding of the return value. * Returns: | Calculates the signature on all the data passed through using either `sign.update()` or `sign.write()`. If `privateKey` is not a `KeyObject`, this function behaves as if `privateKey` had been passed to `crypto.createPrivateKey()`. If it is an object, the following additional properties can be passed: * `dsaEncoding` For DSA and ECDSA, this option specifies the format of the generated signature. It can be one of the following: * `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`. * `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363. * `padding` Optional padding value for RSA, one of the following: * `crypto.constants.RSA_PKCS1_PADDING` (default) * `crypto.constants.RSA_PKCS1_PSS_PADDING` `RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of RFC 4055, unless an MGF1 hash function has been specified as part of the key in compliance with section 3.3 of RFC 4055. * `saltLength` Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN` (default) sets it to the maximum permissible value. If `outputEncoding` is provided a string is returned; otherwise a `Buffer` is returned. The `Sign` object can not be again used after `sign.sign()` method has been called. Multiple calls to `sign.sign()` will result in an error being thrown. #### `sign.update(data[, inputEncoding])`# History VersionChanges v6.0.0 The default `inputEncoding` changed from `binary` to `utf8`. v0.1.92 Added in: v0.1.92 * `data` | | | * `inputEncoding` The encoding of the `data` string. Updates the `Sign` content with the given `data`, the encoding of which is given in `inputEncoding`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a `Buffer`, `TypedArray`, or `DataView`, then `inputEncoding` is ignored. This can be called many times with new data as it is streamed. ### Class: `Verify`# Added in: v0.1.92 * Extends: The `Verify` class is a utility for verifying signatures. It can be used in one of two ways: * As a writable stream where written data is used to validate against the supplied signature, or * Using the `verify.update()` and `verify.verify()` methods to verify the signature. The `crypto.createVerify()` method is used to create `Verify` instances. `Verify` objects are not to be created directly using the `new` keyword. See `Sign` for examples. #### `verify.update(data[, inputEncoding])`# History VersionChanges v6.0.0 The default `inputEncoding` changed from `binary` to `utf8`. v0.1.92 Added in: v0.1.92 * `data` | | | * `inputEncoding` The encoding of the `data` string. Updates the `Verify` content with the given `data`, the encoding of which is given in `inputEncoding`. If `inputEncoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a `Buffer`, `TypedArray`, or `DataView`, then `inputEncoding` is ignored. This can be called many times with new data as it is streamed. #### `verify.verify(object, signature[, signatureEncoding])`# History VersionChanges v15.0.0 The object can also be an ArrayBuffer and CryptoKey. v13.2.0, v12.16.0 This function now supports IEEE-P1363 DSA and ECDSA signatures. v12.0.0 This function now supports RSA-PSS keys. v11.7.0 The key can now be a private key. v8.0.0 Support for RSASSA-PSS and additional options was added. v0.1.92 Added in: v0.1.92 * `object` | | | | | | | * `dsaEncoding` * `padding` * `saltLength` * `signature` | | | | * `signatureEncoding` The encoding of the `signature` string. * Returns: `true` or `false` depending on the validity of the signature for the data and public key. Verifies the provided data using the given `object` and `signature`. If `object` is not a `KeyObject`, this function behaves as if `object` had been passed to `crypto.createPublicKey()`. If it is an object, the following additional properties can be passed: * `dsaEncoding` For DSA and ECDSA, this option specifies the format of the signature. It can be one of the following: * `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`. * `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363. * `padding` Optional padding value for RSA, one of the following: * `crypto.constants.RSA_PKCS1_PADDING` (default) * `crypto.constants.RSA_PKCS1_PSS_PADDING` `RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to verify the message as specified in section 3.1 of RFC 4055, unless an MGF1 hash function has been specified as part of the key in compliance with section 3.3 of RFC 4055. * `saltLength` Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_AUTO` (default) causes it to be determined automatically. The `signature` argument is the previously calculated signature for the data, in the `signatureEncoding`. If a `signatureEncoding` is specified, the `signature` is expected to be a string; otherwise `signature` is expected to be a `Buffer`, `TypedArray`, or `DataView`. The `verify` object can not be used again after `verify.verify()` has been called. Multiple calls to `verify.verify()` will result in an error being thrown. Because public keys can be derived from private keys, a private key may be passed instead of a public key. ### Class: `X509Certificate`# Added in: v15.6.0 Encapsulates an X509 certificate and provides read-only access to its information. const { X509Certificate } = await import('node:crypto'); const x509 = new X509Certificate('{... pem encoded cert ...}'); console.log(x509.subject); #### `new X509Certificate(buffer)`# Added in: v15.6.0 * `buffer` | | | A PEM or DER encoded X509 Certificate. #### `x509.ca`# Added in: v15.6.0 * Type: Will be `true` if this is a Certificate Authority (CA) certificate. #### `x509.checkEmail(email[, options])`# History VersionChanges v18.0.0 The subject option now defaults to `'default'`. v17.5.0, v16.15.0 The subject option can now be set to `'default'`. v17.5.0, v16.14.1 The `wildcards`, `partialWildcards`, `multiLabelWildcards`, and `singleLabelSubdomains` options have been removed since they had no effect. v15.6.0 Added in: v15.6.0 * `email` * `options` * `subject` `'default'`, `'always'`, or `'never'`. Default: `'default'`. * Returns: | Returns `email` if the certificate matches, `undefined` if it does not. Checks whether the certificate matches the given email address. If the `'subject'` option is undefined or set to `'default'`, the certificate subject is only considered if the subject alternative name extension either does not exist or does not contain any email addresses. If the `'subject'` option is set to `'always'` and if the subject alternative name extension either does not exist or does not contain a matching email address, the certificate subject is considered. If the `'subject'` option is set to `'never'`, the certificate subject is never considered, even if the certificate contains no subject alternative names. #### `x509.checkHost(name[, options])`# History VersionChanges v18.0.0 The subject option now defaults to `'default'`. v17.5.0, v16.15.0 The subject option can now be set to `'default'`. v15.6.0 Added in: v15.6.0 * `name` * `options` * `subject` `'default'`, `'always'`, or `'never'`. Default: `'default'`. * `wildcards` Default: `true`. * `partialWildcards` Default: `true`. * `multiLabelWildcards` Default: `false`. * `singleLabelSubdomains` Default: `false`. * Returns: | Returns a subject name that matches `name`, or `undefined` if no subject name matches `name`. Checks whether the certificate matches the given host name. If the certificate matches the given host name, the matching subject name is returned. The returned name might be an exact match (e.g., `foo.example.com`) or it might contain wildcards (e.g., `*.example.com`). Because host name comparisons are case-insensitive, the returned subject name might also differ from the given `name` in capitalization. If the `'subject'` option is undefined or set to `'default'`, the certificate subject is only considered if the subject alternative name extension either does not exist or does not contain any DNS names. This behavior is consistent with RFC 2818 ("HTTP Over TLS"). If the `'subject'` option is set to `'always'` and if the subject alternative name extension either does not exist or does not contain a matching DNS name, the certificate subject is considered. If the `'subject'` option is set to `'never'`, the certificate subject is never considered, even if the certificate contains no subject alternative names. #### `x509.checkIP(ip)`# History VersionChanges v17.5.0, v16.14.1 The `options` argument has been removed since it had no effect. v15.6.0 Added in: v15.6.0 * `ip` * Returns: | Returns `ip` if the certificate matches, `undefined` if it does not. Checks whether the certificate matches the given IP address (IPv4 or IPv6). Only RFC 5280 `iPAddress` subject alternative names are considered, and they must match the given `ip` address exactly. Other subject alternative names as well as the subject field of the certificate are ignored. #### `x509.checkIssued(otherCert)`# Added in: v15.6.0 * `otherCert` * Returns: Checks whether this certificate was potentially issued by the given `otherCert` by comparing the certificate metadata. This is useful for pruning a list of possible issuer certificates which have been selected using a more rudimentary filtering routine, i.e. just based on subject and issuer names. Finally, to verify that this certificate's signature was produced by a private key corresponding to `otherCert`'s public key use `x509.verify(publicKey)` with `otherCert`'s public key represented as a `KeyObject` like so if (!x509.verify(otherCert.publicKey)) { throw new Error('otherCert did not issue x509'); } #### `x509.checkPrivateKey(privateKey)`# Added in: v15.6.0 * `privateKey` A private key. * Returns: Checks whether the public key for this certificate is consistent with the given private key. #### `x509.fingerprint`# Added in: v15.6.0 * Type: The SHA-1 fingerprint of this certificate. Because SHA-1 is cryptographically broken and because the security of SHA-1 is significantly worse than that of algorithms that are commonly used to sign certificates, consider using `x509.fingerprint256` instead. #### `x509.fingerprint256`# Added in: v15.6.0 * Type: The SHA-256 fingerprint of this certificate. #### `x509.fingerprint512`# Added in: v17.2.0, v16.14.0 * Type: The SHA-512 fingerprint of this certificate. Because computing the SHA-256 fingerprint is usually faster and because it is only half the size of the SHA-512 fingerprint, `x509.fingerprint256` may be a better choice. While SHA-512 presumably provides a higher level of security in general, the security of SHA-256 matches that of most algorithms that are commonly used to sign certificates. #### `x509.infoAccess`# History VersionChanges v17.3.1, v16.13.2 Parts of this string may be encoded as JSON string literals in response to CVE-2021-44532. v15.6.0 Added in: v15.6.0 * Type: A textual representation of the certificate's authority information access extension. This is a line feed separated list of access descriptions. Each line begins with the access method and the kind of the access location, followed by a colon and the value associated with the access location. After the prefix denoting the access method and the kind of the access location, the remainder of each line might be enclosed in quotes to indicate that the value is a JSON string literal. For backward compatibility, Node.js only uses JSON string literals within this property when necessary to avoid ambiguity. Third-party code should be prepared to handle both possible entry formats. #### `x509.issuer`# Added in: v15.6.0 * Type: The issuer identification included in this certificate. #### `x509.issuerCertificate`# Added in: v15.9.0 * Type: The issuer certificate or `undefined` if the issuer certificate is not available. #### `x509.keyUsage`# Added in: v15.6.0 * Type: An array detailing the key extended usages for this certificate. #### `x509.publicKey`# Added in: v15.6.0 * Type: The public key for this certificate. #### `x509.raw`# Added in: v15.6.0 * Type: A `Buffer` containing the DER encoding of this certificate. #### `x509.serialNumber`# Added in: v15.6.0 * Type: The serial number of this certificate. Serial numbers are assigned by certificate authorities and do not uniquely identify certificates. Consider using `x509.fingerprint256` as a unique identifier instead. #### `x509.subject`# Added in: v15.6.0 * Type: The complete subject of this certificate. #### `x509.subjectAltName`# History VersionChanges v17.3.1, v16.13.2 Parts of this string may be encoded as JSON string literals in response to CVE-2021-44532. v15.6.0 Added in: v15.6.0 * Type: The subject alternative name specified for this certificate. This is a comma-separated list of subject alternative names. Each entry begins with a string identifying the kind of the subject alternative name followed by a colon and the value associated with the entry. Earlier versions of Node.js incorrectly assumed that it is safe to split this property at the two-character sequence `', '` (see CVE-2021-44532). However, both malicious and legitimate certificates can contain subject alternative names that include this sequence when represented as a string. After the prefix denoting the type of the entry, the remainder of each entry might be enclosed in quotes to indicate that the value is a JSON string literal. For backward compatibility, Node.js only uses JSON string literals within this property when necessary to avoid ambiguity. Third-party code should be prepared to handle both possible entry formats. #### `x509.toJSON()`# Added in: v15.6.0 * Type: There is no standard JSON encoding for X509 certificates. The `toJSON()` method returns a string containing the PEM encoded certificate. #### `x509.toLegacyObject()`# Added in: v15.6.0 * Type: Returns information about this certificate using the legacy certificate object encoding. #### `x509.toString()`# Added in: v15.6.0 * Type: Returns the PEM-encoded certificate. #### `x509.validFrom`# Added in: v15.6.0 * Type: The date/time from which this certificate is valid. #### `x509.validFromDate`# Added in: v23.0.0, v22.10.0 * Type: The date/time from which this certificate is valid, encapsulated in a `Date` object. #### `x509.validTo`# Added in: v15.6.0 * Type: The date/time until which this certificate is valid. #### `x509.validToDate`# Added in: v23.0.0, v22.10.0 * Type: The date/time until which this certificate is valid, encapsulated in a `Date` object. #### `x509.signatureAlgorithm`# Added in: v24.9.0 * Type: | The algorithm used to sign the certificate or `undefined` if the signature algorithm is unknown by OpenSSL. #### `x509.signatureAlgorithmOid`# Added in: v24.9.0 * Type: The OID of the algorithm used to sign the certificate. #### `x509.verify(publicKey)`# Added in: v15.6.0 * `publicKey` A public key. * Returns: Verifies that this certificate was signed by the given public key. Does not perform any other validation checks on the certificate. ### `node:crypto` module methods and properties# #### `crypto.argon2(algorithm, parameters, callback)`# Added in: v24.7.0 Stability: 1.2 \- Release candidate * `algorithm` Variant of Argon2, one of `"argon2d"`, `"argon2i"` or `"argon2id"`. * `parameters` * `message` | | | | REQUIRED, this is the password for password hashing applications of Argon2. * `nonce` | | | | REQUIRED, must be at least 8 bytes long. This is the salt for password hashing applications of Argon2. * `parallelism` REQUIRED, degree of parallelism determines how many computational chains (lanes) can be run. Must be greater than 1 and less than `2**24-1`. * `tagLength` REQUIRED, the length of the key to generate. Must be greater than 4 and less than `2**32-1`. * `memory` REQUIRED, memory cost in 1KiB blocks. Must be greater than `8 * parallelism` and less than `2**32-1`. The actual number of blocks is rounded down to the nearest multiple of `4 * parallelism`. * `passes` REQUIRED, number of passes (iterations). Must be greater than 1 and less than `2**32-1`. * `secret` | | | | | OPTIONAL, Random additional input, similar to the salt, that should NOT be stored with the derived key. This is known as pepper in password hashing applications. If used, must have a length not greater than `2**32-1` bytes. * `associatedData` | | | | | OPTIONAL, Additional data to be added to the hash, functionally equivalent to salt or secret, but meant for non-random data. If used, must have a length not greater than `2**32-1` bytes. * `callback` * `err` * `derivedKey` Provides an asynchronous Argon2 implementation. Argon2 is a password-based key derivation function that is designed to be expensive computationally and memory-wise in order to make brute-force attacks unrewarding. The `nonce` should be as unique as possible. It is recommended that a nonce is random and at least 16 bytes long. See NIST SP 800-132 for details. When passing strings for `message`, `nonce`, `secret` or `associatedData`, please consider caveats when using strings as inputs to cryptographic APIs. The `callback` function is called with two arguments: `err` and `derivedKey`. `err` is an exception object when key derivation fails, otherwise `err` is `null`. `derivedKey` is passed to the callback as a `Buffer`. An exception is thrown when any of the input arguments specify invalid values or types. const { argon2, randomBytes } = await import('node:crypto'); const parameters = { message: 'password', nonce: randomBytes(16), parallelism: 4, tagLength: 64, memory: 65536, passes: 3, }; argon2('argon2id', parameters, (err, derivedKey) => { if (err) throw err; console.log(derivedKey.toString('hex')); // 'af91dad...9520f15' }); #### `crypto.argon2Sync(algorithm, parameters)`# Added in: v24.7.0 Stability: 1.2 \- Release candidate * `algorithm` Variant of Argon2, one of `"argon2d"`, `"argon2i"` or `"argon2id"`. * `parameters` * `message` | | | | REQUIRED, this is the password for password hashing applications of Argon2. * `nonce` | | | | REQUIRED, must be at least 8 bytes long. This is the salt for password hashing applications of Argon2. * `parallelism` REQUIRED, degree of parallelism determines how many computational chains (lanes) can be run. Must be greater than 1 and less than `2**24-1`. * `tagLength` REQUIRED, the length of the key to generate. Must be greater than 4 and less than `2**32-1`. * `memory` REQUIRED, memory cost in 1KiB blocks. Must be greater than `8 * parallelism` and less than `2**32-1`. The actual number of blocks is rounded down to the nearest multiple of `4 * parallelism`. * `passes` REQUIRED, number of passes (iterations). Must be greater than 1 and less than `2**32-1`. * `secret` | | | | | OPTIONAL, Random additional input, similar to the salt, that should NOT be stored with the derived key. This is known as pepper in password hashing applications. If used, must have a length not greater than `2**32-1` bytes. * `associatedData` | | | | | OPTIONAL, Additional data to be added to the hash, functionally equivalent to salt or secret, but meant for non-random data. If used, must have a length not greater than `2**32-1` bytes. * Returns: Provides a synchronous Argon2 implementation. Argon2 is a password-based key derivation function that is designed to be expensive computationally and memory-wise in order to make brute-force attacks unrewarding. The `nonce` should be as unique as possible. It is recommended that a nonce is random and at least 16 bytes long. See NIST SP 800-132 for details. When passing strings for `message`, `nonce`, `secret` or `associatedData`, please consider caveats when using strings as inputs to cryptographic APIs. An exception is thrown when key derivation fails, otherwise the derived key is returned as a `Buffer`. An exception is thrown when any of the input arguments specify invalid values or types. const { argon2Sync, randomBytes } = await import('node:crypto'); const parameters = { message: 'password', nonce: randomBytes(16), parallelism: 4, tagLength: 64, memory: 65536, passes: 3, }; const derivedKey = argon2Sync('argon2id', parameters); console.log(derivedKey.toString('hex')); // 'af91dad...9520f15' #### `crypto.checkPrime(candidate[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.8.0 Added in: v15.8.0 * `candidate` | | | | | A possible prime encoded as a sequence of big endian octets of arbitrary length. * `options` * `checks` The number of Miller-Rabin probabilistic primality iterations to perform. When the value is `0` (zero), a number of checks is used that yields a false positive rate of at most 2-64 for random input. Care must be used when selecting a number of checks. Refer to the OpenSSL documentation for the `BN_is_prime_ex` function `nchecks` options for more details. Default: `0` * `callback` * `err` Set to an object if an error occurred during check. * `result` `true` if the candidate is a prime with an error probability less than `0.25 ** options.checks`. Checks the primality of the `candidate`. #### `crypto.checkPrimeSync(candidate[, options])`# Added in: v15.8.0 * `candidate` | | | | | A possible prime encoded as a sequence of big endian octets of arbitrary length. * `options` * `checks` The number of Miller-Rabin probabilistic primality iterations to perform. When the value is `0` (zero), a number of checks is used that yields a false positive rate of at most 2-64 for random input. Care must be used when selecting a number of checks. Refer to the OpenSSL documentation for the `BN_is_prime_ex` function `nchecks` options for more details. Default: `0` * Returns: `true` if the candidate is a prime with an error probability less than `0.25 ** options.checks`. Checks the primality of the `candidate`. #### `crypto.constants`# Added in: v6.3.0 * Type: An object containing commonly used constants for crypto and security related operations. The specific constants currently defined are described in Crypto constants. #### `crypto.createCipheriv(algorithm, key, iv[, options])`# History VersionChanges v17.9.0, v16.17.0 The `authTagLength` option is now optional when using the `chacha20-poly1305` cipher and defaults to 16 bytes. v15.0.0 The password and iv arguments can be an ArrayBuffer and are each limited to a maximum of 2 ** 31 - 1 bytes. v11.6.0 The `key` argument can now be a `KeyObject`. v11.2.0, v10.17.0 The cipher `chacha20-poly1305` (the IETF variant of ChaCha20-Poly1305) is now supported. v10.10.0 Ciphers in OCB mode are now supported. v10.2.0 The `authTagLength` option can now be used to produce shorter authentication tags in GCM mode and defaults to 16 bytes. v9.9.0 The `iv` parameter may now be `null` for ciphers which do not need an initialization vector. v0.1.94 Added in: v0.1.94 * `algorithm` * `key` | | | | | | * `iv` | | | | | * `options` `stream.transform` options * Returns: Creates and returns a `Cipheriv` object, with the given `algorithm`, `key` and initialization vector (`iv`). The `options` argument controls stream behavior and is optional except when a cipher in CCM or OCB mode (e.g. `'aes-128-ccm'`) is used. In that case, the `authTagLength` option is required and specifies the length of the authentication tag in bytes, see CCM mode. In GCM mode, the `authTagLength` option is not required but can be used to set the length of the authentication tag that will be returned by `getAuthTag()` and defaults to 16 bytes. For `chacha20-poly1305`, the `authTagLength` option defaults to 16 bytes. The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On recent OpenSSL releases, `openssl list -cipher-algorithms` will display the available cipher algorithms. The `key` is the raw key used by the `algorithm` and `iv` is an initialization vector. Both arguments must be `'utf8'` encoded strings, Buffers, `TypedArray`, or `DataView`s. The `key` may optionally be a `KeyObject` of type `secret`. If the cipher does not need an initialization vector, `iv` may be `null`. When passing strings for `key` or `iv`, please consider caveats when using strings as inputs to cryptographic APIs. Initialization vectors should be unpredictable and unique; ideally, they will be cryptographically random. They do not have to be secret: IVs are typically just added to ciphertext messages unencrypted. It may sound contradictory that something has to be unpredictable and unique, but does not have to be secret; remember that an attacker must not be able to predict ahead of time what a given IV will be. #### `crypto.createDecipheriv(algorithm, key, iv[, options])`# History VersionChanges v17.9.0, v16.17.0 The `authTagLength` option is now optional when using the `chacha20-poly1305` cipher and defaults to 16 bytes. v11.6.0 The `key` argument can now be a `KeyObject`. v11.2.0, v10.17.0 The cipher `chacha20-poly1305` (the IETF variant of ChaCha20-Poly1305) is now supported. v10.10.0 Ciphers in OCB mode are now supported. v10.2.0 The `authTagLength` option can now be used to restrict accepted GCM authentication tag lengths. v9.9.0 The `iv` parameter may now be `null` for ciphers which do not need an initialization vector. v0.1.94 Added in: v0.1.94 * `algorithm` * `key` | | | | | | * `iv` | | | | | * `options` `stream.transform` options * Returns: Creates and returns a `Decipheriv` object that uses the given `algorithm`, `key` and initialization vector (`iv`). The `options` argument controls stream behavior and is optional except when a cipher in CCM or OCB mode (e.g. `'aes-128-ccm'`) is used. In that case, the `authTagLength` option is required and specifies the length of the authentication tag in bytes, see CCM mode. For AES-GCM and `chacha20-poly1305`, the `authTagLength` option defaults to 16 bytes and must be set to a different value if a different length is used. The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On recent OpenSSL releases, `openssl list -cipher-algorithms` will display the available cipher algorithms. The `key` is the raw key used by the `algorithm` and `iv` is an initialization vector. Both arguments must be `'utf8'` encoded strings, Buffers, `TypedArray`, or `DataView`s. The `key` may optionally be a `KeyObject` of type `secret`. If the cipher does not need an initialization vector, `iv` may be `null`. When passing strings for `key` or `iv`, please consider caveats when using strings as inputs to cryptographic APIs. Initialization vectors should be unpredictable and unique; ideally, they will be cryptographically random. They do not have to be secret: IVs are typically just added to ciphertext messages unencrypted. It may sound contradictory that something has to be unpredictable and unique, but does not have to be secret; remember that an attacker must not be able to predict ahead of time what a given IV will be. #### `crypto.createDiffieHellman(prime[, primeEncoding][, generator][, generatorEncoding])`# History VersionChanges v8.0.0 The `prime` argument can be any `TypedArray` or `DataView` now. v8.0.0 The `prime` argument can be a `Uint8Array` now. v6.0.0 The default for the encoding parameters changed from `binary` to `utf8`. v0.11.12 Added in: v0.11.12 * `prime` | | | | * `primeEncoding` The encoding of the `prime` string. * `generator` | | | | | Default: `2` * `generatorEncoding` The encoding of the `generator` string. * Returns: Creates a `DiffieHellman` key exchange object using the supplied `prime` and an optional specific `generator`. The `generator` argument can be a number, string, or `Buffer`. If `generator` is not specified, the value `2` is used. If `primeEncoding` is specified, `prime` is expected to be a string; otherwise a `Buffer`, `TypedArray`, or `DataView` is expected. If `generatorEncoding` is specified, `generator` is expected to be a string; otherwise a number, `Buffer`, `TypedArray`, or `DataView` is expected. #### `crypto.createDiffieHellman(primeLength[, generator])`# Added in: v0.5.0 * `primeLength` * `generator` Default: `2` * Returns: Creates a `DiffieHellman` key exchange object and generates a prime of `primeLength` bits using an optional specific numeric `generator`. If `generator` is not specified, the value `2` is used. #### `crypto.createDiffieHellmanGroup(name)`# Added in: v0.9.3 * `name` * Returns: An alias for `crypto.getDiffieHellman()` #### `crypto.createECDH(curveName)`# Added in: v0.11.14 * `curveName` * Returns: Creates an Elliptic Curve Diffie-Hellman (`ECDH`) key exchange object using a predefined curve specified by the `curveName` string. Use `crypto.getCurves()` to obtain a list of available curve names. On recent OpenSSL releases, `openssl ecparam -list_curves` will also display the name and description of each available elliptic curve. #### `crypto.createHash(algorithm[, options])`# History VersionChanges v12.8.0 The `outputLength` option was added for XOF hash functions. v0.1.92 Added in: v0.1.92 * `algorithm` * `options` `stream.transform` options * Returns: Creates and returns a `Hash` object that can be used to generate hash digests using the given `algorithm`. Optional `options` argument controls stream behavior. For XOF hash functions such as `'shake256'`, the `outputLength` option can be used to specify the desired output length in bytes. The `algorithm` is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are `'sha256'`, `'sha512'`, etc. On recent releases of OpenSSL, `openssl list -digest-algorithms` will display the available digest algorithms. Example: generating the sha256 sum of a file import { createReadStream, } from 'node:fs'; import { argv } from 'node:process'; const { createHash, } = await import('node:crypto'); const filename = argv[2]; const hash = createHash('sha256'); const input = createReadStream(filename); input.on('readable', () => { // Only one element is going to be produced by the // hash stream. const data = input.read(); if (data) hash.update(data); else { console.log(`${hash.digest('hex')} ${filename}`); } }); #### `crypto.createHmac(algorithm, key[, options])`# History VersionChanges v15.0.0 The key can also be an ArrayBuffer or CryptoKey. The encoding option was added. The key cannot contain more than 2 ** 32 - 1 bytes. v11.6.0 The `key` argument can now be a `KeyObject`. v0.1.94 Added in: v0.1.94 * `algorithm` * `key` | | | | | | * `options` `stream.transform` options * `encoding` The string encoding to use when `key` is a string. * Returns: Creates and returns an `Hmac` object that uses the given `algorithm` and `key`. Optional `options` argument controls stream behavior. The `algorithm` is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are `'sha256'`, `'sha512'`, etc. On recent releases of OpenSSL, `openssl list -digest-algorithms` will display the available digest algorithms. The `key` is the HMAC key used to generate the cryptographic HMAC hash. If it is a `KeyObject`, its type must be `secret`. If it is a string, please consider caveats when using strings as inputs to cryptographic APIs. If it was obtained from a cryptographically secure source of entropy, such as `crypto.randomBytes()` or `crypto.generateKey()`, its length should not exceed the block size of `algorithm` (e.g., 512 bits for SHA-256). Example: generating the sha256 HMAC of a file import { createReadStream, } from 'node:fs'; import { argv } from 'node:process'; const { createHmac, } = await import('node:crypto'); const filename = argv[2]; const hmac = createHmac('sha256', 'a secret'); const input = createReadStream(filename); input.on('readable', () => { // Only one element is going to be produced by the // hash stream. const data = input.read(); if (data) hmac.update(data); else { console.log(`${hmac.digest('hex')} ${filename}`); } }); #### `crypto.createPrivateKey(key)`# History VersionChanges v24.6.0 Add support for ML-DSA keys. v15.12.0 The key can also be a JWK object. v15.0.0 The key can also be an ArrayBuffer. The encoding option was added. The key cannot contain more than 2 ** 32 - 1 bytes. v11.6.0 Added in: v11.6.0 * `key` | | | | | * `key` | | | | | The key material, either in PEM, DER, or JWK format. * `format` Must be `'pem'`, `'der'`, or '`'jwk'`. Default: `'pem'`. * `type` Must be `'pkcs1'`, `'pkcs8'` or `'sec1'`. This option is required only if the `format` is `'der'` and ignored otherwise. * `passphrase` | The passphrase to use for decryption. * `encoding` The string encoding to use when `key` is a string. * Returns: Creates and returns a new key object containing a private key. If `key` is a string or `Buffer`, `format` is assumed to be `'pem'`; otherwise, `key` must be an object with the properties described above. If the private key is encrypted, a `passphrase` must be specified. The length of the passphrase is limited to 1024 bytes. #### `crypto.createPublicKey(key)`# History VersionChanges v24.6.0 Add support for ML-DSA keys. v15.12.0 The key can also be a JWK object. v15.0.0 The key can also be an ArrayBuffer. The encoding option was added. The key cannot contain more than 2 ** 32 - 1 bytes. v11.13.0 The `key` argument can now be a `KeyObject` with type `private`. v11.7.0 The `key` argument can now be a private key. v11.6.0 Added in: v11.6.0 * `key` | | | | | * `key` | | | | | The key material, either in PEM, DER, or JWK format. * `format` Must be `'pem'`, `'der'`, or `'jwk'`. Default: `'pem'`. * `type` Must be `'pkcs1'` or `'spki'`. This option is required only if the `format` is `'der'` and ignored otherwise. * `encoding` The string encoding to use when `key` is a string. * Returns: Creates and returns a new key object containing a public key. If `key` is a string or `Buffer`, `format` is assumed to be `'pem'`; if `key` is a `KeyObject` with type `'private'`, the public key is derived from the given private key; otherwise, `key` must be an object with the properties described above. If the format is `'pem'`, the `'key'` may also be an X.509 certificate. Because public keys can be derived from private keys, a private key may be passed instead of a public key. In that case, this function behaves as if `crypto.createPrivateKey()` had been called, except that the type of the returned `KeyObject` will be `'public'` and that the private key cannot be extracted from the returned `KeyObject`. Similarly, if a `KeyObject` with type `'private'` is given, a new `KeyObject` with type `'public'` will be returned and it will be impossible to extract the private key from the returned object. #### `crypto.createSecretKey(key[, encoding])`# History VersionChanges v18.8.0, v16.18.0 The key can now be zero-length. v15.0.0 The key can also be an ArrayBuffer or string. The encoding argument was added. The key cannot contain more than 2 ** 32 - 1 bytes. v11.6.0 Added in: v11.6.0 * `key` | | | | * `encoding` The string encoding when `key` is a string. * Returns: Creates and returns a new key object containing a secret key for symmetric encryption or `Hmac`. #### `crypto.createSign(algorithm[, options])`# Added in: v0.1.92 * `algorithm` * `options` `stream.Writable` options * Returns: Creates and returns a `Sign` object that uses the given `algorithm`. Use `crypto.getHashes()` to obtain the names of the available digest algorithms. Optional `options` argument controls the `stream.Writable` behavior. In some cases, a `Sign` instance can be created using the name of a signature algorithm, such as `'RSA-SHA256'`, instead of a digest algorithm. This will use the corresponding digest algorithm. This does not work for all signature algorithms, such as `'ecdsa-with-SHA256'`, so it is best to always use digest algorithm names. #### `crypto.createVerify(algorithm[, options])`# Added in: v0.1.92 * `algorithm` * `options` `stream.Writable` options * Returns: Creates and returns a `Verify` object that uses the given algorithm. Use `crypto.getHashes()` to obtain an array of names of the available signing algorithms. Optional `options` argument controls the `stream.Writable` behavior. In some cases, a `Verify` instance can be created using the name of a signature algorithm, such as `'RSA-SHA256'`, instead of a digest algorithm. This will use the corresponding digest algorithm. This does not work for all signature algorithms, such as `'ecdsa-with-SHA256'`, so it is best to always use digest algorithm names. #### `crypto.decapsulate(key, ciphertext[, callback])`# Added in: v24.7.0 Stability: 1.2 \- Release candidate * `key` | | | | | | Private Key * `ciphertext` | | | * `callback` * `err` * `sharedKey` * Returns: if the `callback` function is not provided. Key decapsulation using a KEM algorithm with a private key. Supported key types and their KEM algorithms are: * `'rsa'`2 RSA Secret Value Encapsulation * `'ec'`3 DHKEM(P-256, HKDF-SHA256), DHKEM(P-384, HKDF-SHA256), DHKEM(P-521, HKDF-SHA256) * `'x25519'`3 DHKEM(X25519, HKDF-SHA256) * `'x448'`3 DHKEM(X448, HKDF-SHA512) * `'ml-kem-512'`1 ML-KEM * `'ml-kem-768'`1 ML-KEM * `'ml-kem-1024'`1 ML-KEM If `key` is not a `KeyObject`, this function behaves as if `key` had been passed to `crypto.createPrivateKey()`. If the `callback` function is provided this function uses libuv's threadpool. #### `crypto.diffieHellman(options[, callback])`# History VersionChanges v23.11.0 Optional callback argument added. v13.9.0, v12.17.0 Added in: v13.9.0, v12.17.0 * `options` * `privateKey` * `publicKey` * `callback` * `err` * `secret` * Returns: if the `callback` function is not provided. Computes the Diffie-Hellman shared secret based on a `privateKey` and a `publicKey`. Both keys must have the same `asymmetricKeyType` and must support either the DH or ECDH operation. If the `callback` function is provided this function uses libuv's threadpool. #### `crypto.encapsulate(key[, callback])`# Added in: v24.7.0 Stability: 1.2 \- Release candidate * `key` | | | | | | Public Key * `callback` * `err` * `result` * `sharedKey` * `ciphertext` * Returns: if the `callback` function is not provided. * `sharedKey` * `ciphertext` Key encapsulation using a KEM algorithm with a public key. Supported key types and their KEM algorithms are: * `'rsa'`2 RSA Secret Value Encapsulation * `'ec'`3 DHKEM(P-256, HKDF-SHA256), DHKEM(P-384, HKDF-SHA256), DHKEM(P-521, HKDF-SHA256) * `'x25519'`3 DHKEM(X25519, HKDF-SHA256) * `'x448'`3 DHKEM(X448, HKDF-SHA512) * `'ml-kem-512'`1 ML-KEM * `'ml-kem-768'`1 ML-KEM * `'ml-kem-1024'`1 ML-KEM If `key` is not a `KeyObject`, this function behaves as if `key` had been passed to `crypto.createPublicKey()`. If the `callback` function is provided this function uses libuv's threadpool. #### `crypto.fips`# Added in: v6.0.0Deprecated since: v10.0.0 Stability: 0 \- Deprecated Property for checking and controlling whether a FIPS compliant crypto provider is currently in use. Setting to true requires a FIPS build of Node.js. This property is deprecated. Please use `crypto.setFips()` and `crypto.getFips()` instead. #### `crypto.generateKey(type, options, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.0.0 Added in: v15.0.0 * `type` The intended use of the generated secret key. Currently accepted values are `'hmac'` and `'aes'`. * `options` * `length` The bit length of the key to generate. This must be a value greater than 0. * If `type` is `'hmac'`, the minimum is 8, and the maximum length is 231-1. If the value is not a multiple of 8, the generated key will be truncated to `Math.floor(length / 8)`. * If `type` is `'aes'`, the length must be one of `128`, `192`, or `256`. * `callback` * `err` * `key` Asynchronously generates a new random secret key of the given `length`. The `type` will determine which validations will be performed on the `length`. const { generateKey, } = await import('node:crypto'); generateKey('hmac', { length: 512 }, (err, key) => { if (err) throw err; console.log(key.export().toString('hex')); // 46e..........620 }); The size of a generated HMAC key should not exceed the block size of the underlying hash function. See `crypto.createHmac()` for more information. #### `crypto.generateKeyPair(type, options, callback)`# History VersionChanges v24.8.0 Add support for SLH-DSA key pairs. v24.7.0 Add support for ML-KEM key pairs. v24.6.0 Add support for ML-DSA key pairs. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v16.10.0 Add ability to define `RSASSA-PSS-params` sequence parameters for RSA-PSS keys pairs. v13.9.0, v12.17.0 Add support for Diffie-Hellman. v12.0.0 Add support for RSA-PSS key pairs. v12.0.0 Add ability to generate X25519 and X448 key pairs. v12.0.0 Add ability to generate Ed25519 and Ed448 key pairs. v11.6.0 The `generateKeyPair` and `generateKeyPairSync` functions now produce key objects if no encoding was specified. v10.12.0 Added in: v10.12.0 * `type` The asymmetric key type to generate. See the supported asymmetric key types. * `options` * `modulusLength` Key size in bits (RSA, DSA). * `publicExponent` Public exponent (RSA). Default: `0x10001`. * `hashAlgorithm` Name of the message digest (RSA-PSS). * `mgf1HashAlgorithm` Name of the message digest used by MGF1 (RSA-PSS). * `saltLength` Minimal salt length in bytes (RSA-PSS). * `divisorLength` Size of `q` in bits (DSA). * `namedCurve` Name of the curve to use (EC). * `prime` The prime parameter (DH). * `primeLength` Prime length in bits (DH). * `generator` Custom generator (DH). Default: `2`. * `groupName` Diffie-Hellman group name (DH). See `crypto.getDiffieHellman()`. * `paramEncoding` Must be `'named'` or `'explicit'` (EC). Default: `'named'`. * `publicKeyEncoding` See `keyObject.export()`. * `privateKeyEncoding` See `keyObject.export()`. * `callback` * `err` * `publicKey` | | * `privateKey` | | Generates a new asymmetric key pair of the given `type`. RSA, RSA-PSS, DSA, EC, Ed25519, Ed448, X25519, X448, and DH are currently supported. If a `publicKeyEncoding` or `privateKeyEncoding` was specified, this function behaves as if `keyObject.export()` had been called on its result. Otherwise, the respective part of the key is returned as a `KeyObject`. It is recommended to encode public keys as `'spki'` and private keys as `'pkcs8'` with encryption for long-term storage: const { generateKeyPair, } = await import('node:crypto'); generateKeyPair('rsa', { modulusLength: 4096, publicKeyEncoding: { type: 'spki', format: 'pem', }, privateKeyEncoding: { type: 'pkcs8', format: 'pem', cipher: 'aes-256-cbc', passphrase: 'top secret', }, }, (err, publicKey, privateKey) => { // Handle errors and use the generated key pair. }); On completion, `callback` will be called with `err` set to `undefined` and `publicKey` / `privateKey` representing the generated key pair. If this method is invoked as its `util.promisify()`ed version, it returns a `Promise` for an `Object` with `publicKey` and `privateKey` properties. #### `crypto.generateKeyPairSync(type, options)`# History VersionChanges v24.8.0 Add support for SLH-DSA key pairs. v24.7.0 Add support for ML-KEM key pairs. v24.6.0 Add support for ML-DSA key pairs. v16.10.0 Add ability to define `RSASSA-PSS-params` sequence parameters for RSA-PSS keys pairs. v13.9.0, v12.17.0 Add support for Diffie-Hellman. v12.0.0 Add support for RSA-PSS key pairs. v12.0.0 Add ability to generate X25519 and X448 key pairs. v12.0.0 Add ability to generate Ed25519 and Ed448 key pairs. v11.6.0 The `generateKeyPair` and `generateKeyPairSync` functions now produce key objects if no encoding was specified. v10.12.0 Added in: v10.12.0 * `type` The asymmetric key type to generate. See the supported asymmetric key types. * `options` * `modulusLength` Key size in bits (RSA, DSA). * `publicExponent` Public exponent (RSA). Default: `0x10001`. * `hashAlgorithm` Name of the message digest (RSA-PSS). * `mgf1HashAlgorithm` Name of the message digest used by MGF1 (RSA-PSS). * `saltLength` Minimal salt length in bytes (RSA-PSS). * `divisorLength` Size of `q` in bits (DSA). * `namedCurve` Name of the curve to use (EC). * `prime` The prime parameter (DH). * `primeLength` Prime length in bits (DH). * `generator` Custom generator (DH). Default: `2`. * `groupName` Diffie-Hellman group name (DH). See `crypto.getDiffieHellman()`. * `paramEncoding` Must be `'named'` or `'explicit'` (EC). Default: `'named'`. * `publicKeyEncoding` See `keyObject.export()`. * `privateKeyEncoding` See `keyObject.export()`. * Returns: * `publicKey` | | * `privateKey` | | Generates a new asymmetric key pair of the given `type`. RSA, RSA-PSS, DSA, EC, Ed25519, Ed448, X25519, X448, DH, and ML-DSA1 are currently supported. If a `publicKeyEncoding` or `privateKeyEncoding` was specified, this function behaves as if `keyObject.export()` had been called on its result. Otherwise, the respective part of the key is returned as a `KeyObject`. When encoding public keys, it is recommended to use `'spki'`. When encoding private keys, it is recommended to use `'pkcs8'` with a strong passphrase, and to keep the passphrase confidential. const { generateKeyPairSync, } = await import('node:crypto'); const { publicKey, privateKey, } = generateKeyPairSync('rsa', { modulusLength: 4096, publicKeyEncoding: { type: 'spki', format: 'pem', }, privateKeyEncoding: { type: 'pkcs8', format: 'pem', cipher: 'aes-256-cbc', passphrase: 'top secret', }, }); The return value `{ publicKey, privateKey }` represents the generated key pair. When PEM encoding was selected, the respective key will be a string, otherwise it will be a buffer containing the data encoded as DER. #### `crypto.generateKeySync(type, options)`# Added in: v15.0.0 * `type` The intended use of the generated secret key. Currently accepted values are `'hmac'` and `'aes'`. * `options` * `length` The bit length of the key to generate. * If `type` is `'hmac'`, the minimum is 8, and the maximum length is 231-1. If the value is not a multiple of 8, the generated key will be truncated to `Math.floor(length / 8)`. * If `type` is `'aes'`, the length must be one of `128`, `192`, or `256`. * Returns: Synchronously generates a new random secret key of the given `length`. The `type` will determine which validations will be performed on the `length`. const { generateKeySync, } = await import('node:crypto'); const key = generateKeySync('hmac', { length: 512 }); console.log(key.export().toString('hex')); // e89..........41e The size of a generated HMAC key should not exceed the block size of the underlying hash function. See `crypto.createHmac()` for more information. #### `crypto.generatePrime(size[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.8.0 Added in: v15.8.0 * `size` The size (in bits) of the prime to generate. * `options` * `add` | | | | | * `rem` | | | | | * `safe` Default: `false`. * `bigint` When `true`, the generated prime is returned as a `bigint`. * `callback` * `err` * `prime` | Generates a pseudorandom prime of `size` bits. If `options.safe` is `true`, the prime will be a safe prime -- that is, `(prime - 1) / 2` will also be a prime. The `options.add` and `options.rem` parameters can be used to enforce additional requirements, e.g., for Diffie-Hellman: * If `options.add` and `options.rem` are both set, the prime will satisfy the condition that `prime % add = rem`. * If only `options.add` is set and `options.safe` is not `true`, the prime will satisfy the condition that `prime % add = 1`. * If only `options.add` is set and `options.safe` is set to `true`, the prime will instead satisfy the condition that `prime % add = 3`. This is necessary because `prime % add = 1` for `options.add > 2` would contradict the condition enforced by `options.safe`. * `options.rem` is ignored if `options.add` is not given. Both `options.add` and `options.rem` must be encoded as big-endian sequences if given as an `ArrayBuffer`, `SharedArrayBuffer`, `TypedArray`, `Buffer`, or `DataView`. By default, the prime is encoded as a big-endian sequence of octets in an . If the `bigint` option is `true`, then a is provided. The `size` of the prime will have a direct impact on how long it takes to generate the prime. The larger the size, the longer it will take. Because we use OpenSSL's `BN_generate_prime_ex` function, which provides only minimal control over our ability to interrupt the generation process, it is not recommended to generate overly large primes, as doing so may make the process unresponsive. #### `crypto.generatePrimeSync(size[, options])`# Added in: v15.8.0 * `size` The size (in bits) of the prime to generate. * `options` * `add` | | | | | * `rem` | | | | | * `safe` Default: `false`. * `bigint` When `true`, the generated prime is returned as a `bigint`. * Returns: | Generates a pseudorandom prime of `size` bits. If `options.safe` is `true`, the prime will be a safe prime -- that is, `(prime - 1) / 2` will also be a prime. The `options.add` and `options.rem` parameters can be used to enforce additional requirements, e.g., for Diffie-Hellman: * If `options.add` and `options.rem` are both set, the prime will satisfy the condition that `prime % add = rem`. * If only `options.add` is set and `options.safe` is not `true`, the prime will satisfy the condition that `prime % add = 1`. * If only `options.add` is set and `options.safe` is set to `true`, the prime will instead satisfy the condition that `prime % add = 3`. This is necessary because `prime % add = 1` for `options.add > 2` would contradict the condition enforced by `options.safe`. * `options.rem` is ignored if `options.add` is not given. Both `options.add` and `options.rem` must be encoded as big-endian sequences if given as an `ArrayBuffer`, `SharedArrayBuffer`, `TypedArray`, `Buffer`, or `DataView`. By default, the prime is encoded as a big-endian sequence of octets in an . If the `bigint` option is `true`, then a is provided. The `size` of the prime will have a direct impact on how long it takes to generate the prime. The larger the size, the longer it will take. Because we use OpenSSL's `BN_generate_prime_ex` function, which provides only minimal control over our ability to interrupt the generation process, it is not recommended to generate overly large primes, as doing so may make the process unresponsive. #### `crypto.getCipherInfo(nameOrNid[, options])`# Added in: v15.0.0 * `nameOrNid` | The name or nid of the cipher to query. * `options` * `keyLength` A test key length. * `ivLength` A test IV length. * Returns: * `name` The name of the cipher * `nid` The nid of the cipher * `blockSize` The block size of the cipher in bytes. This property is omitted when `mode` is `'stream'`. * `ivLength` The expected or default initialization vector length in bytes. This property is omitted if the cipher does not use an initialization vector. * `keyLength` The expected or default key length in bytes. * `mode` The cipher mode. One of `'cbc'`, `'ccm'`, `'cfb'`, `'ctr'`, `'ecb'`, `'gcm'`, `'ocb'`, `'ofb'`, `'stream'`, `'wrap'`, `'xts'`. Returns information about a given cipher. Some ciphers accept variable length keys and initialization vectors. By default, the `crypto.getCipherInfo()` method will return the default values for these ciphers. To test if a given key length or iv length is acceptable for given cipher, use the `keyLength` and `ivLength` options. If the given values are unacceptable, `undefined` will be returned. #### `crypto.getCiphers()`# Added in: v0.9.3 * Returns: An array with the names of the supported cipher algorithms. const { getCiphers, } = await import('node:crypto'); console.log(getCiphers()); // ['aes-128-cbc', 'aes-128-ccm', ...] #### `crypto.getCurves()`# Added in: v2.3.0 * Returns: An array with the names of the supported elliptic curves. const { getCurves, } = await import('node:crypto'); console.log(getCurves()); // ['Oakley-EC2N-3', 'Oakley-EC2N-4', ...] #### `crypto.getDiffieHellman(groupName)`# Added in: v0.7.5 * `groupName` * Returns: Creates a predefined `DiffieHellmanGroup` key exchange object. The supported groups are listed in the documentation for `DiffieHellmanGroup`. The returned object mimics the interface of objects created by `crypto.createDiffieHellman()`, but will not allow changing the keys (with `diffieHellman.setPublicKey()`, for example). The advantage of using this method is that the parties do not have to generate nor exchange a group modulus beforehand, saving both processor and communication time. Example (obtaining a shared secret): const { getDiffieHellman, } = await import('node:crypto'); const alice = getDiffieHellman('modp14'); const bob = getDiffieHellman('modp14'); alice.generateKeys(); bob.generateKeys(); const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex'); const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex'); /* aliceSecret and bobSecret should be the same */ console.log(aliceSecret === bobSecret); #### `crypto.getFips()`# Added in: v10.0.0 * Returns: `1` if and only if a FIPS compliant crypto provider is currently in use, `0` otherwise. A future semver-major release may change the return type of this API to a . #### `crypto.getHashes()`# Added in: v0.9.3 * Returns: An array of the names of the supported hash algorithms, such as `'RSA-SHA256'`. Hash algorithms are also called "digest" algorithms. const { getHashes, } = await import('node:crypto'); console.log(getHashes()); // ['DSA', 'DSA-SHA', 'DSA-SHA1', ...] #### `crypto.getRandomValues(typedArray)`# Added in: v17.4.0 * `typedArray` | | | * Returns: | | | Returns `typedArray`. A convenient alias for `crypto.webcrypto.getRandomValues()`. This implementation is not compliant with the Web Crypto spec, to write web-compatible code use `crypto.webcrypto.getRandomValues()` instead. #### `crypto.hash(algorithm, data[, options])`# History VersionChanges v24.4.0 The `outputLength` option was added for XOF hash functions. v21.7.0, v20.12.0 Added in: v21.7.0, v20.12.0 Stability: 1.2 \- Release candidate * `algorithm` | * `data` | | | When `data` is a string, it will be encoded as UTF-8 before being hashed. If a different input encoding is desired for a string input, user could encode the string into a `TypedArray` using either `TextEncoder` or `Buffer.from()` and passing the encoded `TypedArray` into this API instead. * `options` | * `outputEncoding` Encoding used to encode the returned digest. Default: `'hex'`. * `outputLength` For XOF hash functions such as 'shake256', the outputLength option can be used to specify the desired output length in bytes. * Returns: | A utility for creating one-shot hash digests of data. It can be faster than the object-based `crypto.createHash()` when hashing a smaller amount of data (<= 5MB) that's readily available. If the data can be big or if it is streamed, it's still recommended to use `crypto.createHash()` instead. The `algorithm` is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are `'sha256'`, `'sha512'`, etc. On recent releases of OpenSSL, `openssl list -digest-algorithms` will display the available digest algorithms. If `options` is a string, then it specifies the `outputEncoding`. Example: import crypto from 'node:crypto'; import { Buffer } from 'node:buffer'; // Hashing a string and return the result as a hex-encoded string. const string = 'Node.js'; // 10b3493287f831e81a438811a1ffba01f8cec4b7 console.log(crypto.hash('sha1', string)); // Encode a base64-encoded string into a Buffer, hash it and return // the result as a buffer. const base64 = 'Tm9kZS5qcw=='; // console.log(crypto.hash('sha1', Buffer.from(base64, 'base64'), 'buffer')); #### `crypto.hkdf(digest, ikm, salt, info, keylen, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v18.8.0, v16.18.0 The input keying material can now be zero-length. v15.0.0 Added in: v15.0.0 * `digest` The digest algorithm to use. * `ikm` | | | | | The input keying material. Must be provided but can be zero-length. * `salt` | | | | The salt value. Must be provided but can be zero-length. * `info` | | | | Additional info value. Must be provided but can be zero-length, and cannot be more than 1024 bytes. * `keylen` The length of the key to generate. Must be greater than 0. The maximum allowable value is `255` times the number of bytes produced by the selected digest function (e.g. `sha512` generates 64-byte hashes, making the maximum HKDF output 16320 bytes). * `callback` * `err` * `derivedKey` HKDF is a simple key derivation function defined in RFC 5869. The given `ikm`, `salt` and `info` are used with the `digest` to derive a key of `keylen` bytes. The supplied `callback` function is called with two arguments: `err` and `derivedKey`. If an errors occurs while deriving the key, `err` will be set; otherwise `err` will be `null`. The successfully generated `derivedKey` will be passed to the callback as an . An error will be thrown if any of the input arguments specify invalid values or types. import { Buffer } from 'node:buffer'; const { hkdf, } = await import('node:crypto'); hkdf('sha512', 'key', 'salt', 'info', 64, (err, derivedKey) => { if (err) throw err; console.log(Buffer.from(derivedKey).toString('hex')); // '24156e2...5391653' }); #### `crypto.hkdfSync(digest, ikm, salt, info, keylen)`# History VersionChanges v18.8.0, v16.18.0 The input keying material can now be zero-length. v15.0.0 Added in: v15.0.0 * `digest` The digest algorithm to use. * `ikm` | | | | | The input keying material. Must be provided but can be zero-length. * `salt` | | | | The salt value. Must be provided but can be zero-length. * `info` | | | | Additional info value. Must be provided but can be zero-length, and cannot be more than 1024 bytes. * `keylen` The length of the key to generate. Must be greater than 0. The maximum allowable value is `255` times the number of bytes produced by the selected digest function (e.g. `sha512` generates 64-byte hashes, making the maximum HKDF output 16320 bytes). * Returns: Provides a synchronous HKDF key derivation function as defined in RFC 5869. The given `ikm`, `salt` and `info` are used with the `digest` to derive a key of `keylen` bytes. The successfully generated `derivedKey` will be returned as an . An error will be thrown if any of the input arguments specify invalid values or types, or if the derived key cannot be generated. import { Buffer } from 'node:buffer'; const { hkdfSync, } = await import('node:crypto'); const derivedKey = hkdfSync('sha512', 'key', 'salt', 'info', 64); console.log(Buffer.from(derivedKey).toString('hex')); // '24156e2...5391653' #### `crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.0.0 The password and salt arguments can also be ArrayBuffer instances. v14.0.0 The `iterations` parameter is now restricted to positive values. Earlier releases treated other values as one. v8.0.0 The `digest` parameter is always required now. v6.0.0 Calling this function without passing the `digest` parameter is deprecated now and will emit a warning. v6.0.0 The default encoding for `password` if it is a string changed from `binary` to `utf8`. v0.5.5 Added in: v0.5.5 * `password` | | | | * `salt` | | | | * `iterations` * `keylen` * `digest` * `callback` * `err` * `derivedKey` Provides an asynchronous Password-Based Key Derivation Function 2 (PBKDF2) implementation. A selected HMAC digest algorithm specified by `digest` is applied to derive a key of the requested byte length (`keylen`) from the `password`, `salt` and `iterations`. The supplied `callback` function is called with two arguments: `err` and `derivedKey`. If an error occurs while deriving the key, `err` will be set; otherwise `err` will be `null`. By default, the successfully generated `derivedKey` will be passed to the callback as a `Buffer`. An error will be thrown if any of the input arguments specify invalid values or types. The `iterations` argument must be a number set as high as possible. The higher the number of iterations, the more secure the derived key will be, but will take a longer amount of time to complete. The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See NIST SP 800-132 for details. When passing strings for `password` or `salt`, please consider caveats when using strings as inputs to cryptographic APIs. const { pbkdf2, } = await import('node:crypto'); pbkdf2('secret', 'salt', 100000, 64, 'sha512', (err, derivedKey) => { if (err) throw err; console.log(derivedKey.toString('hex')); // '3745e48...08d59ae' }); An array of supported digest functions can be retrieved using `crypto.getHashes()`. This API uses libuv's threadpool, which can have surprising and negative performance implications for some applications; see the `UV_THREADPOOL_SIZE` documentation for more information. #### `crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)`# History VersionChanges v14.0.0 The `iterations` parameter is now restricted to positive values. Earlier releases treated other values as one. v6.0.0 Calling this function without passing the `digest` parameter is deprecated now and will emit a warning. v6.0.0 The default encoding for `password` if it is a string changed from `binary` to `utf8`. v0.9.3 Added in: v0.9.3 * `password` | | | * `salt` | | | * `iterations` * `keylen` * `digest` * Returns: Provides a synchronous Password-Based Key Derivation Function 2 (PBKDF2) implementation. A selected HMAC digest algorithm specified by `digest` is applied to derive a key of the requested byte length (`keylen`) from the `password`, `salt` and `iterations`. If an error occurs an `Error` will be thrown, otherwise the derived key will be returned as a `Buffer`. The `iterations` argument must be a number set as high as possible. The higher the number of iterations, the more secure the derived key will be, but will take a longer amount of time to complete. The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See NIST SP 800-132 for details. When passing strings for `password` or `salt`, please consider caveats when using strings as inputs to cryptographic APIs. const { pbkdf2Sync, } = await import('node:crypto'); const key = pbkdf2Sync('secret', 'salt', 100000, 64, 'sha512'); console.log(key.toString('hex')); // '3745e48...08d59ae' An array of supported digest functions can be retrieved using `crypto.getHashes()`. #### `crypto.privateDecrypt(privateKey, buffer)`# History VersionChanges v21.6.2, v20.11.1, v18.19.1 The `RSA_PKCS1_PADDING` padding was disabled unless the OpenSSL build supports implicit rejection. v15.0.0 Added string, ArrayBuffer, and CryptoKey as allowable key types. The oaepLabel can be an ArrayBuffer. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 ** 31 - 1 bytes. v12.11.0 The `oaepLabel` option was added. v12.9.0 The `oaepHash` option was added. v11.6.0 This function now supports key objects. v0.11.14 Added in: v0.11.14 * `privateKey` | | | | | | | * `oaepHash` The hash function to use for OAEP padding and MGF1. Default: `'sha1'` * `oaepLabel` | | | | The label to use for OAEP padding. If not specified, no label is used. * `padding` An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`, `crypto.constants.RSA_PKCS1_PADDING`, or `crypto.constants.RSA_PKCS1_OAEP_PADDING`. * `buffer` | | | | * Returns: A new `Buffer` with the decrypted content. Decrypts `buffer` with `privateKey`. `buffer` was previously encrypted using the corresponding public key, for example using `crypto.publicEncrypt()`. If `privateKey` is not a `KeyObject`, this function behaves as if `privateKey` had been passed to `crypto.createPrivateKey()`. If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_OAEP_PADDING`. Using `crypto.constants.RSA_PKCS1_PADDING` in `crypto.privateDecrypt()` requires OpenSSL to support implicit rejection (`rsa_pkcs1_implicit_rejection`). If the version of OpenSSL used by Node.js does not support this feature, attempting to use `RSA_PKCS1_PADDING` will fail. #### `crypto.privateEncrypt(privateKey, buffer)`# History VersionChanges v15.0.0 Added string, ArrayBuffer, and CryptoKey as allowable key types. The passphrase can be an ArrayBuffer. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 ** 31 - 1 bytes. v11.6.0 This function now supports key objects. v1.1.0 Added in: v1.1.0 * `privateKey` | | | | | | | * `key` | | | | | | A PEM encoded private key. * `passphrase` | | | | An optional passphrase for the private key. * `padding` An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or `crypto.constants.RSA_PKCS1_PADDING`. * `encoding` The string encoding to use when `buffer`, `key`, or `passphrase` are strings. * `buffer` | | | | * Returns: A new `Buffer` with the encrypted content. Encrypts `buffer` with `privateKey`. The returned data can be decrypted using the corresponding public key, for example using `crypto.publicDecrypt()`. If `privateKey` is not a `KeyObject`, this function behaves as if `privateKey` had been passed to `crypto.createPrivateKey()`. If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_PADDING`. #### `crypto.publicDecrypt(key, buffer)`# History VersionChanges v15.0.0 Added string, ArrayBuffer, and CryptoKey as allowable key types. The passphrase can be an ArrayBuffer. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 ** 31 - 1 bytes. v11.6.0 This function now supports key objects. v1.1.0 Added in: v1.1.0 * `key` | | | | | | | * `passphrase` | | | | An optional passphrase for the private key. * `padding` An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or `crypto.constants.RSA_PKCS1_PADDING`. * `encoding` The string encoding to use when `buffer`, `key`, or `passphrase` are strings. * `buffer` | | | | * Returns: A new `Buffer` with the decrypted content. Decrypts `buffer` with `key`.`buffer` was previously encrypted using the corresponding private key, for example using `crypto.privateEncrypt()`. If `key` is not a `KeyObject`, this function behaves as if `key` had been passed to `crypto.createPublicKey()`. If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_PADDING`. Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key. #### `crypto.publicEncrypt(key, buffer)`# History VersionChanges v15.0.0 Added string, ArrayBuffer, and CryptoKey as allowable key types. The oaepLabel and passphrase can be ArrayBuffers. The buffer can be a string or ArrayBuffer. All types that accept buffers are limited to a maximum of 2 ** 31 - 1 bytes. v12.11.0 The `oaepLabel` option was added. v12.9.0 The `oaepHash` option was added. v11.6.0 This function now supports key objects. v0.11.14 Added in: v0.11.14 * `key` | | | | | | | * `key` | | | | | | A PEM encoded public or private key, , or . * `oaepHash` The hash function to use for OAEP padding and MGF1. Default: `'sha1'` * `oaepLabel` | | | | The label to use for OAEP padding. If not specified, no label is used. * `passphrase` | | | | An optional passphrase for the private key. * `padding` An optional padding value defined in `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`, `crypto.constants.RSA_PKCS1_PADDING`, or `crypto.constants.RSA_PKCS1_OAEP_PADDING`. * `encoding` The string encoding to use when `buffer`, `key`, `oaepLabel`, or `passphrase` are strings. * `buffer` | | | | * Returns: A new `Buffer` with the encrypted content. Encrypts the content of `buffer` with `key` and returns a new `Buffer` with encrypted content. The returned data can be decrypted using the corresponding private key, for example using `crypto.privateDecrypt()`. If `key` is not a `KeyObject`, this function behaves as if `key` had been passed to `crypto.createPublicKey()`. If it is an object, the `padding` property can be passed. Otherwise, this function uses `RSA_PKCS1_OAEP_PADDING`. Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key. #### `crypto.randomBytes(size[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v9.0.0 Passing `null` as the `callback` argument now throws `ERR_INVALID_CALLBACK`. v0.5.8 Added in: v0.5.8 * `size` The number of bytes to generate. The `size` must not be larger than `2**31 - 1`. * `callback` * `err` * `buf` * Returns: if the `callback` function is not provided. Generates cryptographically strong pseudorandom data. The `size` argument is a number indicating the number of bytes to generate. If a `callback` function is provided, the bytes are generated asynchronously and the `callback` function is invoked with two arguments: `err` and `buf`. If an error occurs, `err` will be an `Error` object; otherwise it is `null`. The `buf` argument is a `Buffer` containing the generated bytes. // Asynchronous const { randomBytes, } = await import('node:crypto'); randomBytes(256, (err, buf) => { if (err) throw err; console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`); }); If the `callback` function is not provided, the random bytes are generated synchronously and returned as a `Buffer`. An error will be thrown if there is a problem generating the bytes. // Synchronous const { randomBytes, } = await import('node:crypto'); const buf = randomBytes(256); console.log( `${buf.length} bytes of random data: ${buf.toString('hex')}`); The `crypto.randomBytes()` method will not complete until there is sufficient entropy available. This should normally never take longer than a few milliseconds. The only time when generating the random bytes may conceivably block for a longer period of time is right after boot, when the whole system is still low on entropy. This API uses libuv's threadpool, which can have surprising and negative performance implications for some applications; see the `UV_THREADPOOL_SIZE` documentation for more information. The asynchronous version of `crypto.randomBytes()` is carried out in a single threadpool request. To minimize threadpool task length variation, partition large `randomBytes` requests when doing so as part of fulfilling a client request. #### `crypto.randomFill(buffer[, offset][, size], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v9.0.0 The `buffer` argument may be any `TypedArray` or `DataView`. v7.10.0, v6.13.0 Added in: v7.10.0, v6.13.0 * `buffer` | | | Must be supplied. The size of the provided `buffer` must not be larger than `2**31 - 1`. * `offset` Default: `0` * `size` Default: `buffer.length - offset`. The `size` must not be larger than `2**31 - 1`. * `callback` `function(err, buf) {}`. This function is similar to `crypto.randomBytes()` but requires the first argument to be a `Buffer` that will be filled. It also requires that a callback is passed in. If the `callback` function is not provided, an error will be thrown. import { Buffer } from 'node:buffer'; const { randomFill } = await import('node:crypto'); const buf = Buffer.alloc(10); randomFill(buf, (err, buf) => { if (err) throw err; console.log(buf.toString('hex')); }); randomFill(buf, 5, (err, buf) => { if (err) throw err; console.log(buf.toString('hex')); }); // The above is equivalent to the following: randomFill(buf, 5, 5, (err, buf) => { if (err) throw err; console.log(buf.toString('hex')); }); Any `ArrayBuffer`, `TypedArray`, or `DataView` instance may be passed as `buffer`. While this includes instances of `Float32Array` and `Float64Array`, this function should not be used to generate random floating-point numbers. The result may contain `+Infinity`, `-Infinity`, and `NaN`, and even if the array contains finite numbers only, they are not drawn from a uniform random distribution and have no meaningful lower or upper bounds. import { Buffer } from 'node:buffer'; const { randomFill } = await import('node:crypto'); const a = new Uint32Array(10); randomFill(a, (err, buf) => { if (err) throw err; console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength) .toString('hex')); }); const b = new DataView(new ArrayBuffer(10)); randomFill(b, (err, buf) => { if (err) throw err; console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength) .toString('hex')); }); const c = new ArrayBuffer(10); randomFill(c, (err, buf) => { if (err) throw err; console.log(Buffer.from(buf).toString('hex')); }); This API uses libuv's threadpool, which can have surprising and negative performance implications for some applications; see the `UV_THREADPOOL_SIZE` documentation for more information. The asynchronous version of `crypto.randomFill()` is carried out in a single threadpool request. To minimize threadpool task length variation, partition large `randomFill` requests when doing so as part of fulfilling a client request. #### `crypto.randomFillSync(buffer[, offset][, size])`# History VersionChanges v9.0.0 The `buffer` argument may be any `TypedArray` or `DataView`. v7.10.0, v6.13.0 Added in: v7.10.0, v6.13.0 * `buffer` | | | Must be supplied. The size of the provided `buffer` must not be larger than `2**31 - 1`. * `offset` Default: `0` * `size` Default: `buffer.length - offset`. The `size` must not be larger than `2**31 - 1`. * Returns: | | | The object passed as `buffer` argument. Synchronous version of `crypto.randomFill()`. import { Buffer } from 'node:buffer'; const { randomFillSync } = await import('node:crypto'); const buf = Buffer.alloc(10); console.log(randomFillSync(buf).toString('hex')); randomFillSync(buf, 5); console.log(buf.toString('hex')); // The above is equivalent to the following: randomFillSync(buf, 5, 5); console.log(buf.toString('hex')); Any `ArrayBuffer`, `TypedArray` or `DataView` instance may be passed as `buffer`. import { Buffer } from 'node:buffer'; const { randomFillSync } = await import('node:crypto'); const a = new Uint32Array(10); console.log(Buffer.from(randomFillSync(a).buffer, a.byteOffset, a.byteLength).toString('hex')); const b = new DataView(new ArrayBuffer(10)); console.log(Buffer.from(randomFillSync(b).buffer, b.byteOffset, b.byteLength).toString('hex')); const c = new ArrayBuffer(10); console.log(Buffer.from(randomFillSync(c)).toString('hex')); #### `crypto.randomInt([min, ]max[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v14.10.0, v12.19.0 Added in: v14.10.0, v12.19.0 * `min` Start of random range (inclusive). Default: `0`. * `max` End of random range (exclusive). * `callback` `function(err, n) {}`. Return a random integer `n` such that `min <= n < max`. This implementation avoids modulo bias. The range (`max - min`) must be less than 248. `min` and `max` must be safe integers. If the `callback` function is not provided, the random integer is generated synchronously. // Asynchronous const { randomInt, } = await import('node:crypto'); randomInt(3, (err, n) => { if (err) throw err; console.log(`Random number chosen from (0, 1, 2): ${n}`); }); // Synchronous const { randomInt, } = await import('node:crypto'); const n = randomInt(3); console.log(`Random number chosen from (0, 1, 2): ${n}`); // With `min` argument const { randomInt, } = await import('node:crypto'); const n = randomInt(1, 7); console.log(`The dice rolled: ${n}`); #### `crypto.randomUUID([options])`# Added in: v15.6.0, v14.17.0 * `options` * `disableEntropyCache` By default, to improve performance, Node.js generates and caches enough random data to generate up to 128 random UUIDs. To generate a UUID without using the cache, set `disableEntropyCache` to `true`. Default: `false`. * Returns: Generates a random RFC 4122 version 4 UUID. The UUID is generated using a cryptographic pseudorandom number generator. #### `crypto.scrypt(password, salt, keylen[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.0.0 The password and salt arguments can also be ArrayBuffer instances. v12.8.0, v10.17.0 The `maxmem` value can now be any safe integer. v10.9.0 The `cost`, `blockSize` and `parallelization` option names have been added. v10.5.0 Added in: v10.5.0 * `password` | | | | * `salt` | | | | * `keylen` * `options` * `cost` CPU/memory cost parameter. Must be a power of two greater than one. Default: `16384`. * `blockSize` Block size parameter. Default: `8`. * `parallelization` Parallelization parameter. Default: `1`. * `N` Alias for `cost`. Only one of both may be specified. * `r` Alias for `blockSize`. Only one of both may be specified. * `p` Alias for `parallelization`. Only one of both may be specified. * `maxmem` Memory upper bound. It is an error when (approximately) `128 * N * r > maxmem`. Default: `32 * 1024 * 1024`. * `callback` * `err` * `derivedKey` Provides an asynchronous scrypt implementation. Scrypt is a password-based key derivation function that is designed to be expensive computationally and memory-wise in order to make brute-force attacks unrewarding. The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See NIST SP 800-132 for details. When passing strings for `password` or `salt`, please consider caveats when using strings as inputs to cryptographic APIs. The `callback` function is called with two arguments: `err` and `derivedKey`. `err` is an exception object when key derivation fails, otherwise `err` is `null`. `derivedKey` is passed to the callback as a `Buffer`. An exception is thrown when any of the input arguments specify invalid values or types. const { scrypt, } = await import('node:crypto'); // Using the factory defaults. scrypt('password', 'salt', 64, (err, derivedKey) => { if (err) throw err; console.log(derivedKey.toString('hex')); // '3745e48...08d59ae' }); // Using a custom N parameter. Must be a power of two. scrypt('password', 'salt', 64, { N: 1024 }, (err, derivedKey) => { if (err) throw err; console.log(derivedKey.toString('hex')); // '3745e48...aa39b34' }); #### `crypto.scryptSync(password, salt, keylen[, options])`# History VersionChanges v12.8.0, v10.17.0 The `maxmem` value can now be any safe integer. v10.9.0 The `cost`, `blockSize` and `parallelization` option names have been added. v10.5.0 Added in: v10.5.0 * `password` | | | * `salt` | | | * `keylen` * `options` * `cost` CPU/memory cost parameter. Must be a power of two greater than one. Default: `16384`. * `blockSize` Block size parameter. Default: `8`. * `parallelization` Parallelization parameter. Default: `1`. * `N` Alias for `cost`. Only one of both may be specified. * `r` Alias for `blockSize`. Only one of both may be specified. * `p` Alias for `parallelization`. Only one of both may be specified. * `maxmem` Memory upper bound. It is an error when (approximately) `128 * N * r > maxmem`. Default: `32 * 1024 * 1024`. * Returns: Provides a synchronous scrypt implementation. Scrypt is a password-based key derivation function that is designed to be expensive computationally and memory-wise in order to make brute-force attacks unrewarding. The `salt` should be as unique as possible. It is recommended that a salt is random and at least 16 bytes long. See NIST SP 800-132 for details. When passing strings for `password` or `salt`, please consider caveats when using strings as inputs to cryptographic APIs. An exception is thrown when key derivation fails, otherwise the derived key is returned as a `Buffer`. An exception is thrown when any of the input arguments specify invalid values or types. const { scryptSync, } = await import('node:crypto'); // Using the factory defaults. const key1 = scryptSync('password', 'salt', 64); console.log(key1.toString('hex')); // '3745e48...08d59ae' // Using a custom N parameter. Must be a power of two. const key2 = scryptSync('password', 'salt', 64, { N: 1024 }); console.log(key2.toString('hex')); // '3745e48...aa39b34' #### `crypto.secureHeapUsed()`# Added in: v15.6.0 * Returns: * `total` The total allocated secure heap size as specified using the `--secure-heap=n` command-line flag. * `min` The minimum allocation from the secure heap as specified using the `--secure-heap-min` command-line flag. * `used` The total number of bytes currently allocated from the secure heap. * `utilization` The calculated ratio of `used` to `total` allocated bytes. #### `crypto.setEngine(engine[, flags])`# History VersionChanges v22.4.0, v20.16.0 Custom engine support in OpenSSL 3 is deprecated. v0.11.11 Added in: v0.11.11 * `engine` * `flags` Default: `crypto.constants.ENGINE_METHOD_ALL` Load and set the `engine` for some or all OpenSSL functions (selected by flags). Support for custom engines in OpenSSL is deprecated from OpenSSL 3. `engine` could be either an id or a path to the engine's shared library. The optional `flags` argument uses `ENGINE_METHOD_ALL` by default. The `flags` is a bit field taking one of or a mix of the following flags (defined in `crypto.constants`): * `crypto.constants.ENGINE_METHOD_RSA` * `crypto.constants.ENGINE_METHOD_DSA` * `crypto.constants.ENGINE_METHOD_DH` * `crypto.constants.ENGINE_METHOD_RAND` * `crypto.constants.ENGINE_METHOD_EC` * `crypto.constants.ENGINE_METHOD_CIPHERS` * `crypto.constants.ENGINE_METHOD_DIGESTS` * `crypto.constants.ENGINE_METHOD_PKEY_METHS` * `crypto.constants.ENGINE_METHOD_PKEY_ASN1_METHS` * `crypto.constants.ENGINE_METHOD_ALL` * `crypto.constants.ENGINE_METHOD_NONE` #### `crypto.setFips(bool)`# Added in: v10.0.0 * `bool` `true` to enable FIPS mode. Enables the FIPS compliant crypto provider in a FIPS-enabled Node.js build. Throws an error if FIPS mode is not available. #### `crypto.sign(algorithm, data, key[, callback])`# History VersionChanges v24.8.0 Add support for ML-DSA, Ed448, and SLH-DSA context parameter. v24.8.0 Add support for SLH-DSA signing. v24.6.0 Add support for ML-DSA signing. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.12.0 Optional callback argument added. v13.2.0, v12.16.0 This function now supports IEEE-P1363 DSA and ECDSA signatures. v12.0.0 Added in: v12.0.0 * `algorithm` | | * `data` | | | * `key` | | | | | | | * `callback` * `err` * `signature` * Returns: if the `callback` function is not provided. Calculates and returns the signature for `data` using the given private key and algorithm. If `algorithm` is `null` or `undefined`, then the algorithm is dependent upon the key type. `algorithm` is required to be `null` or `undefined` for Ed25519, Ed448, and ML-DSA. If `key` is not a `KeyObject`, this function behaves as if `key` had been passed to `crypto.createPrivateKey()`. If it is an object, the following additional properties can be passed: * `dsaEncoding` For DSA and ECDSA, this option specifies the format of the generated signature. It can be one of the following: * `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`. * `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363. * `padding` Optional padding value for RSA, one of the following: * `crypto.constants.RSA_PKCS1_PADDING` (default) * `crypto.constants.RSA_PKCS1_PSS_PADDING` `RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of RFC 4055. * `saltLength` Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN` (default) sets it to the maximum permissible value. * `context` | | | For Ed448, ML-DSA, and SLH-DSA, this option specifies the optional context to differentiate signatures generated for different purposes with the same key. If the `callback` function is provided this function uses libuv's threadpool. #### `crypto.subtle`# Added in: v17.4.0 * Type: A convenient alias for `crypto.webcrypto.subtle`. #### `crypto.timingSafeEqual(a, b)`# History VersionChanges v15.0.0 The a and b arguments can also be ArrayBuffer. v6.6.0 Added in: v6.6.0 * `a` | | | * `b` | | | * Returns: This function compares the underlying bytes that represent the given `ArrayBuffer`, `TypedArray`, or `DataView` instances using a constant-time algorithm. This function does not leak timing information that would allow an attacker to guess one of the values. This is suitable for comparing HMAC digests or secret values like authentication cookies or capability urls. `a` and `b` must both be `Buffer`s, `TypedArray`s, or `DataView`s, and they must have the same byte length. An error is thrown if `a` and `b` have different byte lengths. If at least one of `a` and `b` is a `TypedArray` with more than one byte per entry, such as `Uint16Array`, the result will be computed using the platform byte order. When both of the inputs are `Float32Array`s or `Float64Array`s, this function might return unexpected results due to IEEE 754 encoding of floating-point numbers. In particular, neither `x === y` nor `Object.is(x, y)` implies that the byte representations of two floating-point numbers `x` and `y` are equal. Use of `crypto.timingSafeEqual` does not guarantee that the surrounding code is timing-safe. Care should be taken to ensure that the surrounding code does not introduce timing vulnerabilities. #### `crypto.verify(algorithm, data, key, signature[, callback])`# History VersionChanges v24.8.0 Add support for ML-DSA, Ed448, and SLH-DSA context parameter. v24.8.0 Add support for SLH-DSA signature verification. v24.6.0 Add support for ML-DSA signature verification. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.12.0 Optional callback argument added. v15.0.0 The data, key, and signature arguments can also be ArrayBuffer. v13.2.0, v12.16.0 This function now supports IEEE-P1363 DSA and ECDSA signatures. v12.0.0 Added in: v12.0.0 * `algorithm` | | * `data` | | | * `key` | | | | | | | * `signature` | | | * `callback` * `err` * `result` * Returns: `true` or `false` depending on the validity of the signature for the data and public key if the `callback` function is not provided. Verifies the given signature for `data` using the given key and algorithm. If `algorithm` is `null` or `undefined`, then the algorithm is dependent upon the key type. `algorithm` is required to be `null` or `undefined` for Ed25519, Ed448, and ML-DSA. If `key` is not a `KeyObject`, this function behaves as if `key` had been passed to `crypto.createPublicKey()`. If it is an object, the following additional properties can be passed: * `dsaEncoding` For DSA and ECDSA, this option specifies the format of the signature. It can be one of the following: * `'der'` (default): DER-encoded ASN.1 signature structure encoding `(r, s)`. * `'ieee-p1363'`: Signature format `r || s` as proposed in IEEE-P1363. * `padding` Optional padding value for RSA, one of the following: * `crypto.constants.RSA_PKCS1_PADDING` (default) * `crypto.constants.RSA_PKCS1_PSS_PADDING` `RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of RFC 4055. * `saltLength` Salt length for when padding is `RSA_PKCS1_PSS_PADDING`. The special value `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest size, `crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN` (default) sets it to the maximum permissible value. * `context` | | | For Ed448, ML-DSA, and SLH-DSA, this option specifies the optional context to differentiate signatures generated for different purposes with the same key. The `signature` argument is the previously calculated signature for the `data`. Because public keys can be derived from private keys, a private key or a public key may be passed for `key`. If the `callback` function is provided this function uses libuv's threadpool. #### `crypto.webcrypto`# Added in: v15.0.0 Type: An implementation of the Web Crypto API standard. See the Web Crypto API documentation for details. ### Notes# #### Using strings as inputs to cryptographic APIs# For historical reasons, many cryptographic APIs provided by Node.js accept strings as inputs where the underlying cryptographic algorithm works on byte sequences. These instances include plaintexts, ciphertexts, symmetric keys, initialization vectors, passphrases, salts, authentication tags, and additional authenticated data. When passing strings to cryptographic APIs, consider the following factors. * Not all byte sequences are valid UTF-8 strings. Therefore, when a byte sequence of length `n` is derived from a string, its entropy is generally lower than the entropy of a random or pseudorandom `n` byte sequence. For example, no UTF-8 string will result in the byte sequence `c0 af`. Secret keys should almost exclusively be random or pseudorandom byte sequences. * Similarly, when converting random or pseudorandom byte sequences to UTF-8 strings, subsequences that do not represent valid code points may be replaced by the Unicode replacement character (`U+FFFD`). The byte representation of the resulting Unicode string may, therefore, not be equal to the byte sequence that the string was created from. const original = [0xc0, 0xaf]; const bytesAsString = Buffer.from(original).toString('utf8'); const stringAsBytes = Buffer.from(bytesAsString, 'utf8'); console.log(stringAsBytes); // Prints ''. The outputs of ciphers, hash functions, signature algorithms, and key derivation functions are pseudorandom byte sequences and should not be used as Unicode strings. * When strings are obtained from user input, some Unicode characters can be represented in multiple equivalent ways that result in different byte sequences. For example, when passing a user passphrase to a key derivation function, such as PBKDF2 or scrypt, the result of the key derivation function depends on whether the string uses composed or decomposed characters. Node.js does not normalize character representations. Developers should consider using `String.prototype.normalize()` on user inputs before passing them to cryptographic APIs. #### Legacy streams API (prior to Node.js 0.10)# The Crypto module was added to Node.js before there was the concept of a unified Stream API, and before there were `Buffer` objects for handling binary data. As such, many `crypto` classes have methods not typically found on other Node.js classes that implement the streams API (e.g. `update()`, `final()`, or `digest()`). Also, many methods accepted and returned `'latin1'` encoded strings by default rather than `Buffer`s. This default was changed after Node.js v0.8 to use `Buffer` objects by default instead. #### Support for weak or compromised algorithms# The `node:crypto` module still supports some algorithms which are already compromised and are not recommended for use. The API also allows the use of ciphers and hashes with a small key size that are too weak for safe use. Users should take full responsibility for selecting the crypto algorithm and key size according to their security requirements. Based on the recommendations of NIST SP 800-131A: * MD5 and SHA-1 are no longer acceptable where collision resistance is required such as digital signatures. * The key used with RSA, DSA, and DH algorithms is recommended to have at least 2048 bits and that of the curve of ECDSA and ECDH at least 224 bits, to be safe to use for several years. * The DH groups of `modp1`, `modp2` and `modp5` have a key size smaller than 2048 bits and are not recommended. See the reference for other recommendations and details. Some algorithms that have known weaknesses and are of little relevance in practice are only available through the legacy provider, which is not enabled by default. #### CCM mode# CCM is one of the supported AEAD algorithms. Applications which use this mode must adhere to certain restrictions when using the cipher API: * The authentication tag length must be specified during cipher creation by setting the `authTagLength` option and must be one of 4, 6, 8, 10, 12, 14 or 16 bytes. * The length of the initialization vector (nonce) `N` must be between 7 and 13 bytes (`7 ≤ N ≤ 13`). * The length of the plaintext is limited to `2 ** (8 * (15 - N))` bytes. * When decrypting, the authentication tag must be set via `setAuthTag()` before calling `update()`. Otherwise, decryption will fail and `final()` will throw an error in compliance with section 2.6 of RFC 3610. * Using stream methods such as `write(data)`, `end(data)` or `pipe()` in CCM mode might fail as CCM cannot handle more than one chunk of data per instance. * When passing additional authenticated data (AAD), the length of the actual message in bytes must be passed to `setAAD()` via the `plaintextLength` option. Many crypto libraries include the authentication tag in the ciphertext, which means that they produce ciphertexts of the length `plaintextLength + authTagLength`. Node.js does not include the authentication tag, so the ciphertext length is always `plaintextLength`. This is not necessary if no AAD is used. * As CCM processes the whole message at once, `update()` must be called exactly once. * Even though calling `update()` is sufficient to encrypt/decrypt the message, applications must call `final()` to compute or verify the authentication tag. import { Buffer } from 'node:buffer'; const { createCipheriv, createDecipheriv, randomBytes, } = await import('node:crypto'); const key = 'keykeykeykeykeykeykeykey'; const nonce = randomBytes(12); const aad = Buffer.from('0123456789', 'hex'); const cipher = createCipheriv('aes-192-ccm', key, nonce, { authTagLength: 16, }); const plaintext = 'Hello world'; cipher.setAAD(aad, { plaintextLength: Buffer.byteLength(plaintext), }); const ciphertext = cipher.update(plaintext, 'utf8'); cipher.final(); const tag = cipher.getAuthTag(); // Now transmit { ciphertext, nonce, tag }. const decipher = createDecipheriv('aes-192-ccm', key, nonce, { authTagLength: 16, }); decipher.setAuthTag(tag); decipher.setAAD(aad, { plaintextLength: ciphertext.length, }); const receivedPlaintext = decipher.update(ciphertext, null, 'utf8'); try { decipher.final(); } catch (err) { throw new Error('Authentication failed!', { cause: err }); } console.log(receivedPlaintext); #### FIPS mode# When using OpenSSL 3, Node.js supports FIPS 140-2 when used with an appropriate OpenSSL 3 provider, such as the FIPS provider from OpenSSL 3 which can be installed by following the instructions in OpenSSL's FIPS README file. For FIPS support in Node.js you will need: * A correctly installed OpenSSL 3 FIPS provider. * An OpenSSL 3 FIPS module configuration file. * An OpenSSL 3 configuration file that references the FIPS module configuration file. Node.js will need to be configured with an OpenSSL configuration file that points to the FIPS provider. An example configuration file looks like this: nodejs_conf = nodejs_init .include //fipsmodule.cnf [nodejs_init] providers = provider_sect [provider_sect] default = default_sect # The fips section name should match the section name inside the # included fipsmodule.cnf. fips = fips_sect [default_sect] activate = 1 where `fipsmodule.cnf` is the FIPS module configuration file generated from the FIPS provider installation step: openssl fipsinstall Set the `OPENSSL_CONF` environment variable to point to your configuration file and `OPENSSL_MODULES` to the location of the FIPS provider dynamic library. e.g. export OPENSSL_CONF=//nodejs.cnf export OPENSSL_MODULES=//ossl-modules FIPS mode can then be enabled in Node.js either by: * Starting Node.js with `--enable-fips` or `--force-fips` command line flags. * Programmatically calling `crypto.setFips(true)`. Optionally FIPS mode can be enabled in Node.js via the OpenSSL configuration file. e.g. nodejs_conf = nodejs_init .include //fipsmodule.cnf [nodejs_init] providers = provider_sect alg_section = algorithm_sect [provider_sect] default = default_sect # The fips section name should match the section name inside the # included fipsmodule.cnf. fips = fips_sect [default_sect] activate = 1 [algorithm_sect] default_properties = fips=yes ### Crypto constants# The following constants exported by `crypto.constants` apply to various uses of the `node:crypto`, `node:tls`, and `node:https` modules and are generally specific to OpenSSL. #### OpenSSL options# See the list of SSL OP Flags for details. Constant Description `SSL_OP_ALL` Applies multiple bug workarounds within OpenSSL. See https://www.openssl.org/docs/man3.0/man3/SSL_CTX_set_options.html for detail. `SSL_OP_ALLOW_NO_DHE_KEX` Instructs OpenSSL to allow a non-[EC]DHE-based key exchange mode for TLS v1.3 `SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION` Allows legacy insecure renegotiation between OpenSSL and unpatched clients or servers. See https://www.openssl.org/docs/man3.0/man3/SSL_CTX_set_options.html. `SSL_OP_CIPHER_SERVER_PREFERENCE` Attempts to use the server's preferences instead of the client's when selecting a cipher. Behavior depends on protocol version. See https://www.openssl.org/docs/man3.0/man3/SSL_CTX_set_options.html. `SSL_OP_CISCO_ANYCONNECT` Instructs OpenSSL to use Cisco's version identifier of DTLS_BAD_VER. `SSL_OP_COOKIE_EXCHANGE` Instructs OpenSSL to turn on cookie exchange. `SSL_OP_CRYPTOPRO_TLSEXT_BUG` Instructs OpenSSL to add server-hello extension from an early version of the cryptopro draft. `SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS` Instructs OpenSSL to disable a SSL 3.0/TLS 1.0 vulnerability workaround added in OpenSSL 0.9.6d. `SSL_OP_LEGACY_SERVER_CONNECT` Allows initial connection to servers that do not support RI. `SSL_OP_NO_COMPRESSION` Instructs OpenSSL to disable support for SSL/TLS compression. `SSL_OP_NO_ENCRYPT_THEN_MAC` Instructs OpenSSL to disable encrypt-then-MAC. `SSL_OP_NO_QUERY_MTU` `SSL_OP_NO_RENEGOTIATION` Instructs OpenSSL to disable renegotiation. `SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION` Instructs OpenSSL to always start a new session when performing renegotiation. `SSL_OP_NO_SSLv2` Instructs OpenSSL to turn off SSL v2 `SSL_OP_NO_SSLv3` Instructs OpenSSL to turn off SSL v3 `SSL_OP_NO_TICKET` Instructs OpenSSL to disable use of RFC4507bis tickets. `SSL_OP_NO_TLSv1` Instructs OpenSSL to turn off TLS v1 `SSL_OP_NO_TLSv1_1` Instructs OpenSSL to turn off TLS v1.1 `SSL_OP_NO_TLSv1_2` Instructs OpenSSL to turn off TLS v1.2 `SSL_OP_NO_TLSv1_3` Instructs OpenSSL to turn off TLS v1.3 `SSL_OP_PRIORITIZE_CHACHA` Instructs OpenSSL server to prioritize ChaCha20-Poly1305 when the client does. This option has no effect if `SSL_OP_CIPHER_SERVER_PREFERENCE` is not enabled. `SSL_OP_TLS_ROLLBACK_BUG` Instructs OpenSSL to disable version rollback attack detection. #### OpenSSL engine constants# Constant Description `ENGINE_METHOD_RSA` Limit engine usage to RSA `ENGINE_METHOD_DSA` Limit engine usage to DSA `ENGINE_METHOD_DH` Limit engine usage to DH `ENGINE_METHOD_RAND` Limit engine usage to RAND `ENGINE_METHOD_EC` Limit engine usage to EC `ENGINE_METHOD_CIPHERS` Limit engine usage to CIPHERS `ENGINE_METHOD_DIGESTS` Limit engine usage to DIGESTS `ENGINE_METHOD_PKEY_METHS` Limit engine usage to PKEY_METHS `ENGINE_METHOD_PKEY_ASN1_METHS` Limit engine usage to PKEY_ASN1_METHS `ENGINE_METHOD_ALL` `ENGINE_METHOD_NONE` #### Other OpenSSL constants# Constant Description `DH_CHECK_P_NOT_SAFE_PRIME` `DH_CHECK_P_NOT_PRIME` `DH_UNABLE_TO_CHECK_GENERATOR` `DH_NOT_SUITABLE_GENERATOR` `RSA_PKCS1_PADDING` `RSA_SSLV23_PADDING` `RSA_NO_PADDING` `RSA_PKCS1_OAEP_PADDING` `RSA_X931_PADDING` `RSA_PKCS1_PSS_PADDING` `RSA_PSS_SALTLEN_DIGEST` Sets the salt length for `RSA_PKCS1_PSS_PADDING` to the digest size when signing or verifying. `RSA_PSS_SALTLEN_MAX_SIGN` Sets the salt length for `RSA_PKCS1_PSS_PADDING` to the maximum permissible value when signing data. `RSA_PSS_SALTLEN_AUTO` Causes the salt length for `RSA_PKCS1_PSS_PADDING` to be determined automatically when verifying a signature. `POINT_CONVERSION_COMPRESSED` `POINT_CONVERSION_UNCOMPRESSED` `POINT_CONVERSION_HYBRID` #### Node.js crypto constants# Constant Description `defaultCoreCipherList` Specifies the built-in default cipher list used by Node.js. `defaultCipherList` Specifies the active default cipher list used by the current Node.js process. ### Footnotes 1. Requires OpenSSL >= 3.5 ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8 ↩9 ↩10 ↩11 ↩12 ↩13 ↩14 ↩15 ↩16 ↩17 ↩18 ↩19 ↩20 ↩21 ↩22 ↩23 ↩24 ↩25 2. Requires OpenSSL >= 3.0 ↩ ↩2 3. Requires OpenSSL >= 3.2 ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ## Debugger# Stability: 2 \- Stable Node.js includes a command-line debugging utility. The Node.js debugger client is not a full-featured debugger, but simple stepping and inspection are possible. To use it, start Node.js with the `inspect` argument followed by the path to the script to debug. $ node inspect myscript.js < Debugger listening on ws://127.0.0.1:9229/621111f9-ffcb-4e82-b718-48a145fa5db8 < For help, see: https://nodejs.org/en/docs/inspector < connecting to 127.0.0.1:9229 ... ok < Debugger attached. < ok Break on start in myscript.js:2 1 // myscript.js > 2 global.x = 5; 3 setTimeout(() => { 4 debugger; debug> The debugger automatically breaks on the first executable line. To instead run until the first breakpoint (specified by a `debugger` statement), set the `NODE_INSPECT_RESUME_ON_START` environment variable to `1`. $ cat myscript.js // myscript.js global.x = 5; setTimeout(() => { debugger; console.log('world'); }, 1000); console.log('hello'); $ NODE_INSPECT_RESUME_ON_START=1 node inspect myscript.js < Debugger listening on ws://127.0.0.1:9229/f1ed133e-7876-495b-83ae-c32c6fc319c2 < For help, see: https://nodejs.org/en/docs/inspector < connecting to 127.0.0.1:9229 ... ok < Debugger attached. < < hello < break in myscript.js:4 2 global.x = 5; 3 setTimeout(() => { > 4 debugger; 5 console.log('world'); 6 }, 1000); debug> next break in myscript.js:5 3 setTimeout(() => { 4 debugger; > 5 console.log('world'); 6 }, 1000); 7 console.log('hello'); debug> repl Press Ctrl+C to leave debug repl > x 5 > 2 + 2 4 debug> next < world < break in myscript.js:6 4 debugger; 5 console.log('world'); > 6 }, 1000); 7 console.log('hello'); 8 debug> .exit $ The `repl` command allows code to be evaluated remotely. The `next` command steps to the next line. Type `help` to see what other commands are available. Pressing `enter` without typing a command will repeat the previous debugger command. ### Watchers# It is possible to watch expression and variable values while debugging. On every breakpoint, each expression from the watchers list will be evaluated in the current context and displayed immediately before the breakpoint's source code listing. To begin watching an expression, type `watch('my_expression')`. The command `watchers` will print the active watchers. To remove a watcher, type `unwatch('my_expression')`. ### Command reference# #### Stepping# * `cont`, `c`: Continue execution * `next`, `n`: Step next * `step`, `s`: Step in * `out`, `o`: Step out * `pause`: Pause running code (like pause button in Developer Tools) #### Breakpoints# * `setBreakpoint()`, `sb()`: Set breakpoint on current line * `setBreakpoint(line)`, `sb(line)`: Set breakpoint on specific line * `setBreakpoint('fn()')`, `sb(...)`: Set breakpoint on a first statement in function's body * `setBreakpoint('script.js', 1)`, `sb(...)`: Set breakpoint on first line of `script.js` * `setBreakpoint('script.js', 1, 'num < 4')`, `sb(...)`: Set conditional breakpoint on first line of `script.js` that only breaks when `num < 4` evaluates to `true` * `clearBreakpoint('script.js', 1)`, `cb(...)`: Clear breakpoint in `script.js` on line 1 It is also possible to set a breakpoint in a file (module) that is not loaded yet: $ node inspect main.js < Debugger listening on ws://127.0.0.1:9229/48a5b28a-550c-471b-b5e1-d13dd7165df9 < For help, see: https://nodejs.org/en/docs/inspector < connecting to 127.0.0.1:9229 ... ok < Debugger attached. < Break on start in main.js:1 > 1 const mod = require('./mod.js'); 2 mod.hello(); 3 mod.hello(); debug> setBreakpoint('mod.js', 22) Warning: script 'mod.js' was not loaded yet. debug> c break in mod.js:22 20 // USE OR OTHER DEALINGS IN THE SOFTWARE. 21 >22 exports.hello = function() { 23 return 'hello from module'; 24 }; debug> It is also possible to set a conditional breakpoint that only breaks when a given expression evaluates to `true`: $ node inspect main.js < Debugger listening on ws://127.0.0.1:9229/ce24daa8-3816-44d4-b8ab-8273c8a66d35 < For help, see: https://nodejs.org/en/docs/inspector < connecting to 127.0.0.1:9229 ... ok < Debugger attached. Break on start in main.js:7 5 } 6 > 7 addOne(10); 8 addOne(-1); 9 debug> setBreakpoint('main.js', 4, 'num < 0') 1 'use strict'; 2 3 function addOne(num) { > 4 return num + 1; 5 } 6 7 addOne(10); 8 addOne(-1); 9 debug> cont break in main.js:4 2 3 function addOne(num) { > 4 return num + 1; 5 } 6 debug> exec('num') -1 debug> #### Information# * `backtrace`, `bt`: Print backtrace of current execution frame * `list(5)`: List scripts source code with 5 line context (5 lines before and after) * `watch(expr)`: Add expression to watch list * `unwatch(expr)`: Remove expression from watch list * `unwatch(index)`: Remove expression at specific index from watch list * `watchers`: List all watchers and their values (automatically listed on each breakpoint) * `repl`: Open debugger's repl for evaluation in debugging script's context * `exec expr`, `p expr`: Execute an expression in debugging script's context and print its value * `profile`: Start CPU profiling session * `profileEnd`: Stop current CPU profiling session * `profiles`: List all completed CPU profiling sessions * `profiles[n].save(filepath = 'node.cpuprofile')`: Save CPU profiling session to disk as JSON * `takeHeapSnapshot(filepath = 'node.heapsnapshot')`: Take a heap snapshot and save to disk as JSON #### Execution control# * `run`: Run script (automatically runs on debugger's start) * `restart`: Restart script * `kill`: Kill script #### Various# * `scripts`: List all loaded scripts * `version`: Display V8's version ### Advanced usage# #### V8 inspector integration for Node.js# V8 Inspector integration allows attaching Chrome DevTools to Node.js instances for debugging and profiling. It uses the Chrome DevTools Protocol. V8 Inspector can be enabled by passing the `--inspect` flag when starting a Node.js application. It is also possible to supply a custom port with that flag, e.g. `--inspect=9222` will accept DevTools connections on port 9222. Using the `--inspect` flag will execute the code immediately before debugger is connected. This means that the code will start running before you can start debugging, which might not be ideal if you want to debug from the very beginning. In such cases, you have two alternatives: 1. `--inspect-wait` flag: This flag will wait for debugger to be attached before executing the code. This allows you to start debugging right from the beginning of the execution. 2. `--inspect-brk` flag: Unlike `--inspect`, this flag will break on the first line of the code as soon as debugger is attached. This is useful when you want to debug the code step by step from the very beginning, without any code execution prior to debugging. So, when deciding between `--inspect`, `--inspect-wait`, and `--inspect-brk`, consider whether you want the code to start executing immediately, wait for debugger to be attached before execution, or break on the first line for step-by-step debugging. $ node --inspect index.js Debugger listening on ws://127.0.0.1:9229/dc9010dd-f8b8-4ac5-a510-c1a114ec7d29 For help, see: https://nodejs.org/en/docs/inspector (In the example above, the UUID dc9010dd-f8b8-4ac5-a510-c1a114ec7d29 at the end of the URL is generated on the fly, it varies in different debugging sessions.) If the Chrome browser is older than 66.0.3345.0, use `inspector.html` instead of `js_app.html` in the above URL. Chrome DevTools doesn't support debugging worker threads yet. ndb can be used to debug them. ## Deprecated APIs# Node.js APIs might be deprecated for any of the following reasons: * Use of the API is unsafe. * An improved alternative API is available. * Breaking changes to the API are expected in a future major release. Node.js uses four kinds of deprecations: * Documentation-only * Application (non-`node_modules` code only) * Runtime (all code) * End-of-Life A Documentation-only deprecation is one that is expressed only within the Node.js API docs. These generate no side-effects while running Node.js. Some Documentation-only deprecations trigger a runtime warning when launched with `--pending-deprecation` flag (or its alternative, `NODE_PENDING_DEPRECATION=1` environment variable), similarly to Runtime deprecations below. Documentation-only deprecations that support that flag are explicitly labeled as such in the list of Deprecated APIs. An Application deprecation for only non-`node_modules` code will, by default, generate a process warning that will be printed to `stderr` the first time the deprecated API is used in code that's not loaded from `node_modules`. When the `--throw-deprecation` command-line flag is used, a Runtime deprecation will cause an error to be thrown. When `--pending-deprecation` is used, warnings will also be emitted for code loaded from `node_modules`. A runtime deprecation for all code is similar to the runtime deprecation for non-`node_modules` code, except that it also emits a warning for code loaded from `node_modules`. An End-of-Life deprecation is used when functionality is or will soon be removed from Node.js. ### Revoking deprecations# Occasionally, the deprecation of an API might be reversed. In such situations, this document will be updated with information relevant to the decision. However, the deprecation identifier will not be modified. ### List of deprecated APIs# #### DEP0001: `http.OutgoingMessage.prototype.flush`# History VersionChanges v14.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v1.6.0 Runtime deprecation. Type: End-of-Life `OutgoingMessage.prototype.flush()` has been removed. Use `OutgoingMessage.prototype.flushHeaders()` instead. #### DEP0002: `require('_linklist')`# History VersionChanges v8.0.0 End-of-Life. v6.12.0 A deprecation code has been assigned. v5.0.0 Runtime deprecation. Type: End-of-Life The `_linklist` module is deprecated. Please use a userland alternative. #### DEP0003: `_writableState.buffer`# History VersionChanges v14.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.15 Runtime deprecation. Type: End-of-Life The `_writableState.buffer` has been removed. Use `_writableState.getBuffer()` instead. #### DEP0004: `CryptoStream.prototype.readyState`# History VersionChanges v10.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.4.0 Documentation-only deprecation. Type: End-of-Life The `CryptoStream.prototype.readyState` property was removed. #### DEP0005: `Buffer()` constructor# History VersionChanges v10.0.0 Runtime deprecation. v6.12.0 A deprecation code has been assigned. v6.0.0 Documentation-only deprecation. Type: Application (non-`node_modules` code only) The `Buffer()` function and `new Buffer()` constructor are deprecated due to API usability issues that can lead to accidental security issues. As an alternative, use one of the following methods of constructing `Buffer` objects: * `Buffer.alloc(size[, fill[, encoding]])`: Create a `Buffer` with initialized memory. * `Buffer.allocUnsafe(size)`: Create a `Buffer` with uninitialized memory. * `Buffer.allocUnsafeSlow(size)`: Create a `Buffer` with uninitialized memory. * `Buffer.from(array)`: Create a `Buffer` with a copy of `array` * `Buffer.from(arrayBuffer[, byteOffset[, length]])` \- Create a `Buffer` that wraps the given `arrayBuffer`. * `Buffer.from(buffer)`: Create a `Buffer` that copies `buffer`. * `Buffer.from(string[, encoding])`: Create a `Buffer` that copies `string`. Without `--pending-deprecation`, runtime warnings occur only for code not in `node_modules`. This means there will not be deprecation warnings for `Buffer()` usage in dependencies. With `--pending-deprecation`, a runtime warning results no matter where the `Buffer()` usage occurs. #### DEP0006: `child_process` `options.customFds`# History VersionChanges v12.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.14 Runtime deprecation. v0.5.10 Documentation-only deprecation. Type: End-of-Life Within the `child_process` module's `spawn()`, `fork()`, and `exec()` methods, the `options.customFds` option is deprecated. The `options.stdio` option should be used instead. #### DEP0007: Replace `cluster` `worker.suicide` with `worker.exitedAfterDisconnect`# History VersionChanges v9.0.0 End-of-Life. v7.0.0 Runtime deprecation. v6.12.0 A deprecation code has been assigned. v6.0.0 Documentation-only deprecation. Type: End-of-Life In an earlier version of the Node.js `cluster`, a boolean property with the name `suicide` was added to the `Worker` object. The intent of this property was to provide an indication of how and why the `Worker` instance exited. In Node.js 6.0.0, the old property was deprecated and replaced with a new `worker.exitedAfterDisconnect` property. The old property name did not precisely describe the actual semantics and was unnecessarily emotion-laden. #### DEP0008: `require('node:constants')`# History VersionChanges v6.12.0 A deprecation code has been assigned. v6.3.0 Documentation-only deprecation. Type: Documentation-only The `node:constants` module is deprecated. When requiring access to constants relevant to specific Node.js builtin modules, developers should instead refer to the `constants` property exposed by the relevant module. For instance, `require('node:fs').constants` and `require('node:os').constants`. #### DEP0009: `crypto.pbkdf2` without digest# History VersionChanges v14.0.0 End-of-Life (for `digest === null`). v11.0.0 Runtime deprecation (for `digest === null`). v8.0.0 End-of-Life (for `digest === undefined`). v6.12.0 A deprecation code has been assigned. v6.0.0 Runtime deprecation (for `digest === undefined`). Type: End-of-Life Use of the `crypto.pbkdf2()` API without specifying a digest was deprecated in Node.js 6.0 because the method defaulted to using the non-recommended `'SHA1'` digest. Previously, a deprecation warning was printed. Starting in Node.js 8.0.0, calling `crypto.pbkdf2()` or `crypto.pbkdf2Sync()` with `digest` set to `undefined` will throw a `TypeError`. Beginning in Node.js v11.0.0, calling these functions with `digest` set to `null` would print a deprecation warning to align with the behavior when `digest` is `undefined`. Now, however, passing either `undefined` or `null` will throw a `TypeError`. #### DEP0010: `crypto.createCredentials`# History VersionChanges v11.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.13 Runtime deprecation. Type: End-of-Life The `crypto.createCredentials()` API was removed. Please use `tls.createSecureContext()` instead. #### DEP0011: `crypto.Credentials`# History VersionChanges v11.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.13 Runtime deprecation. Type: End-of-Life The `crypto.Credentials` class was removed. Please use `tls.SecureContext` instead. #### DEP0012: `Domain.dispose`# History VersionChanges v9.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.7 Runtime deprecation. Type: End-of-Life `Domain.dispose()` has been removed. Recover from failed I/O actions explicitly via error event handlers set on the domain instead. #### DEP0013: `fs` asynchronous function without callback# History VersionChanges v10.0.0 End-of-Life. v7.0.0 Runtime deprecation. Type: End-of-Life Calling an asynchronous function without a callback throws a `TypeError` in Node.js 10.0.0 onwards. See https://github.com/nodejs/node/pull/12562. #### DEP0014: `fs.read` legacy String interface# History VersionChanges v8.0.0 End-of-Life. v6.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.1.96 Documentation-only deprecation. Type: End-of-Life The `fs.read()` legacy `String` interface is deprecated. Use the `Buffer` API as mentioned in the documentation instead. #### DEP0015: `fs.readSync` legacy String interface# History VersionChanges v8.0.0 End-of-Life. v6.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.1.96 Documentation-only deprecation. Type: End-of-Life The `fs.readSync()` legacy `String` interface is deprecated. Use the `Buffer` API as mentioned in the documentation instead. #### DEP0016: `GLOBAL`/`root`# History VersionChanges v14.0.0 End-of-Life. v6.12.0 A deprecation code has been assigned. v6.0.0 Runtime deprecation. Type: End-of-Life The `GLOBAL` and `root` aliases for the `global` property were deprecated in Node.js 6.0.0 and have since been removed. #### DEP0017: `Intl.v8BreakIterator`# History VersionChanges v9.0.0 End-of-Life. v7.0.0 Runtime deprecation. Type: End-of-Life `Intl.v8BreakIterator` was a non-standard extension and has been removed. See `Intl.Segmenter`. #### DEP0018: Unhandled promise rejections# History VersionChanges v15.0.0 End-of-Life. v7.0.0 Runtime deprecation. Type: End-of-Life Unhandled promise rejections are deprecated. By default, promise rejections that are not handled terminate the Node.js process with a non-zero exit code. To change the way Node.js treats unhandled rejections, use the `--unhandled-rejections` command-line option. #### DEP0019: `require('.')` resolved outside directory# History VersionChanges v12.0.0 Removed functionality. v6.12.0, v4.8.6 A deprecation code has been assigned. v1.8.1 Runtime deprecation. Type: End-of-Life In certain cases, `require('.')` could resolve outside the package directory. This behavior has been removed. #### DEP0020: `Server.connections`# History VersionChanges v15.0.0 Server.connections has been removed. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.9.7 Runtime deprecation. Type: End-of-Life The `Server.connections` property was deprecated in Node.js v0.9.7 and has been removed. Please use the `Server.getConnections()` method instead. #### DEP0021: `Server.listenFD`# History VersionChanges v12.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.7.12 Runtime deprecation. Type: End-of-Life The `Server.listenFD()` method was deprecated and removed. Please use `Server.listen({fd: })` instead. #### DEP0022: `os.tmpDir()`# History VersionChanges v14.0.0 End-of-Life. v7.0.0 Runtime deprecation. Type: End-of-Life The `os.tmpDir()` API was deprecated in Node.js 7.0.0 and has since been removed. Please use `os.tmpdir()` instead. #### DEP0023: `os.getNetworkInterfaces()`# History VersionChanges v12.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.6.0 Runtime deprecation. Type: End-of-Life The `os.getNetworkInterfaces()` method is deprecated. Please use the `os.networkInterfaces()` method instead. #### DEP0024: `REPLServer.prototype.convertToContext()`# History VersionChanges v9.0.0 End-of-Life. v7.0.0 Runtime deprecation. Type: End-of-Life The `REPLServer.prototype.convertToContext()` API has been removed. #### DEP0025: `require('node:sys')`# History VersionChanges v6.12.0, v4.8.6 A deprecation code has been assigned. v1.0.0 Runtime deprecation. Type: Runtime The `node:sys` module is deprecated. Please use the `util` module instead. #### DEP0026: `util.print()`# History VersionChanges v12.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.3 Runtime deprecation. Type: End-of-Life `util.print()` has been removed. Please use `console.log()` instead. #### DEP0027: `util.puts()`# History VersionChanges v12.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.3 Runtime deprecation. Type: End-of-Life `util.puts()` has been removed. Please use `console.log()` instead. #### DEP0028: `util.debug()`# History VersionChanges v12.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.3 Runtime deprecation. Type: End-of-Life `util.debug()` has been removed. Please use `console.error()` instead. #### DEP0029: `util.error()`# History VersionChanges v12.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.3 Runtime deprecation. Type: End-of-Life `util.error()` has been removed. Please use `console.error()` instead. #### DEP0030: `SlowBuffer`# History VersionChanges v24.0.0 Runtime deprecation. v6.12.0 A deprecation code has been assigned. v6.0.0 Documentation-only deprecation. Type: Runtime The `SlowBuffer` class is deprecated. Please use `Buffer.allocUnsafeSlow(size)` instead. #### DEP0031: `ecdh.setPublicKey()`# History VersionChanges v6.12.0 A deprecation code has been assigned. v5.2.0 Documentation-only deprecation. Type: Documentation-only The `ecdh.setPublicKey()` method is now deprecated as its inclusion in the API is not useful. #### DEP0032: `node:domain` module# History VersionChanges v6.12.0, v4.8.6 A deprecation code has been assigned. v1.4.2 Documentation-only deprecation. Type: Documentation-only The `domain` module is deprecated and should not be used. #### DEP0033: `EventEmitter.listenerCount()`# History VersionChanges v6.12.0, v4.8.6 A deprecation code has been assigned. v3.2.0 Documentation-only deprecation. Type: Documentation-only The `events.listenerCount(emitter, eventName)` API is deprecated. Please use `emitter.listenerCount(eventName)` instead. #### DEP0034: `fs.exists(path, callback)`# History VersionChanges v6.12.0, v4.8.6 A deprecation code has been assigned. v1.0.0 Documentation-only deprecation. Type: Documentation-only The `fs.exists(path, callback)` API is deprecated. Please use `fs.stat()` or `fs.access()` instead. #### DEP0035: `fs.lchmod(path, mode, callback)`# History VersionChanges v6.12.0, v4.8.6 A deprecation code has been assigned. v0.4.7 Documentation-only deprecation. Type: Documentation-only The `fs.lchmod(path, mode, callback)` API is deprecated. #### DEP0036: `fs.lchmodSync(path, mode)`# History VersionChanges v6.12.0, v4.8.6 A deprecation code has been assigned. v0.4.7 Documentation-only deprecation. Type: Documentation-only The `fs.lchmodSync(path, mode)` API is deprecated. #### DEP0037: `fs.lchown(path, uid, gid, callback)`# History VersionChanges v10.6.0 Deprecation revoked. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.4.7 Documentation-only deprecation. Type: Deprecation revoked The `fs.lchown(path, uid, gid, callback)` API was deprecated. The deprecation was revoked because the requisite supporting APIs were added in libuv. #### DEP0038: `fs.lchownSync(path, uid, gid)`# History VersionChanges v10.6.0 Deprecation revoked. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.4.7 Documentation-only deprecation. Type: Deprecation revoked The `fs.lchownSync(path, uid, gid)` API was deprecated. The deprecation was revoked because the requisite supporting APIs were added in libuv. #### DEP0039: `require.extensions`# History VersionChanges v6.12.0, v4.8.6 A deprecation code has been assigned. v0.10.6 Documentation-only deprecation. Type: Documentation-only The `require.extensions` property is deprecated. #### DEP0040: `node:punycode` module# History VersionChanges v21.0.0 Runtime deprecation. v16.6.0 Added support for `--pending-deprecation`. v7.0.0 Documentation-only deprecation. Type: Runtime The `punycode` module is deprecated. Please use a userland alternative instead. #### DEP0041: `NODE_REPL_HISTORY_FILE` environment variable# History VersionChanges v10.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v3.0.0 Documentation-only deprecation. Type: End-of-Life The `NODE_REPL_HISTORY_FILE` environment variable was removed. Please use `NODE_REPL_HISTORY` instead. #### DEP0042: `tls.CryptoStream`# History VersionChanges v10.0.0 End-of-Life. v6.12.0, v4.8.6 A deprecation code has been assigned. v0.11.3 Documentation-only deprecation. Type: End-of-Life The `tls.CryptoStream` class was removed. Please use `tls.TLSSocket` instead. #### DEP0043: `tls.SecurePair`# History VersionChanges v24.0.0 End-of-Life. v8.0.0 Runtime deprecation. v6.12.0 A deprecation code has been assigned. v6.0.0 Documentation-only deprecation. v0.11.15 Deprecation revoked. v0.11.3 Runtime deprecation. Type: End-of-Life The `tls.SecurePair` class is deprecated. Please use `tls.TLSSocket` instead. #### DEP0044: `util.isArray()`# History VersionChanges v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: Runtime The `util.isArray()` API is deprecated. Please use `Array.isArray()` instead. #### DEP0045: `util.isBoolean()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isBoolean()` API has been removed. Please use `typeof arg === 'boolean'` instead. #### DEP0046: `util.isBuffer()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isBuffer()` API has been removed. Please use `Buffer.isBuffer()` instead. #### DEP0047: `util.isDate()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isDate()` API has been removed. Please use `arg instanceof Date` instead. Also for stronger approaches, consider using: `Date.prototype.toString.call(arg) === '[object Date]' && !isNaN(arg)`. This can also be used in a `try/catch` block to handle invalid date objects. #### DEP0048: `util.isError()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isError()` API has been removed. Please use `Error.isError(arg)`. #### DEP0049: `util.isFunction()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isFunction()` API has been removed. Please use `typeof arg === 'function'` instead. #### DEP0050: `util.isNull()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isNull()` API has been removed. Please use `arg === null` instead. #### DEP0051: `util.isNullOrUndefined()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isNullOrUndefined()` API has been removed. Please use `arg === null || arg === undefined` instead. #### DEP0052: `util.isNumber()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isNumber()` API has been removed. Please use `typeof arg === 'number'` instead. #### DEP0053: `util.isObject()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isObject()` API has been removed. Please use `arg && typeof arg === 'object'` instead. #### DEP0054: `util.isPrimitive()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isPrimitive()` API has been removed. Please use `Object(arg) !== arg` instead. #### DEP0055: `util.isRegExp()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isRegExp()` API has been removed. Please use `arg instanceof RegExp` instead. #### DEP0056: `util.isString()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isString()` API has been removed. Please use `typeof arg === 'string'` instead. #### DEP0057: `util.isSymbol()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isSymbol()` API has been removed. Please use `typeof arg === 'symbol'` instead. #### DEP0058: `util.isUndefined()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0, v4.8.6 A deprecation code has been assigned. v4.0.0, v3.3.1 Documentation-only deprecation. Type: End-of-Life The `util.isUndefined()` API has been removed. Please use `arg === undefined` instead. #### DEP0059: `util.log()`# History VersionChanges v23.0.0 End-of-Life deprecation. v22.0.0 Runtime deprecation. v6.12.0 A deprecation code has been assigned. v6.0.0 Documentation-only deprecation. Type: End-of-Life The `util.log()` API has been removed because it's an unmaintained legacy API that was exposed to user land by accident. Instead, consider the following alternatives based on your specific needs: * Third-Party Logging Libraries * Use `console.log(new Date().toLocaleString(), message)` By adopting one of these alternatives, you can transition away from `util.log()` and choose a logging strategy that aligns with the specific requirements and complexity of your application. #### DEP0060: `util._extend()`# History VersionChanges v22.0.0 Runtime deprecation. v6.12.0 A deprecation code has been assigned. v6.0.0 Documentation-only deprecation. Type: Runtime The `util._extend()` API is deprecated because it's an unmaintained legacy API that was exposed to user land by accident. Please use `target = Object.assign(target, source)` instead. #### DEP0061: `fs.SyncWriteStream`# History VersionChanges v11.0.0 End-of-Life. v8.0.0 Runtime deprecation. v7.0.0 Documentation-only deprecation. Type: End-of-Life The `fs.SyncWriteStream` class was never intended to be a publicly accessible API and has been removed. No alternative API is available. Please use a userland alternative. #### DEP0062: `node --debug`# History VersionChanges v12.0.0 End-of-Life. v8.0.0 Runtime deprecation. Type: End-of-Life `--debug` activates the legacy V8 debugger interface, which was removed as of V8 5.8. It is replaced by Inspector which is activated with `--inspect` instead. #### DEP0063: `ServerResponse.prototype.writeHeader()`# History VersionChanges v8.0.0 Documentation-only deprecation. Type: Documentation-only The `node:http` module `ServerResponse.prototype.writeHeader()` API is deprecated. Please use `ServerResponse.prototype.writeHead()` instead. The `ServerResponse.prototype.writeHeader()` method was never documented as an officially supported API. #### DEP0064: `tls.createSecurePair()`# History VersionChanges v24.0.0 End-of-Life. v8.0.0 Runtime deprecation. v6.12.0 A deprecation code has been assigned. v6.0.0 Documentation-only deprecation. v0.11.15 Deprecation revoked. v0.11.3 Runtime deprecation. Type: End-of-Life The `tls.createSecurePair()` API was deprecated in documentation in Node.js 0.11.3. Users should use `tls.Socket` instead. #### DEP0065: `repl.REPL_MODE_MAGIC` and `NODE_REPL_MODE=magic`# History VersionChanges v10.0.0 End-of-Life. v8.0.0 Documentation-only deprecation. Type: End-of-Life The `node:repl` module's `REPL_MODE_MAGIC` constant, used for `replMode` option, has been removed. Its behavior has been functionally identical to that of `REPL_MODE_SLOPPY` since Node.js 6.0.0, when V8 5.0 was imported. Please use `REPL_MODE_SLOPPY` instead. The `NODE_REPL_MODE` environment variable is used to set the underlying `replMode` of an interactive `node` session. Its value, `magic`, is also removed. Please use `sloppy` instead. #### DEP0066: `OutgoingMessage.prototype._headers, OutgoingMessage.prototype._headerNames`# History VersionChanges v24.0.0 End-of-Life. v12.0.0 Runtime deprecation. v8.0.0 Documentation-only deprecation. Type: End-of-Life The `node:http` module `OutgoingMessage.prototype._headers` and `OutgoingMessage.prototype._headerNames` properties are deprecated. Use one of the public methods (e.g. `OutgoingMessage.prototype.getHeader()`, `OutgoingMessage.prototype.getHeaders()`, `OutgoingMessage.prototype.getHeaderNames()`, `OutgoingMessage.prototype.getRawHeaderNames()`, `OutgoingMessage.prototype.hasHeader()`, `OutgoingMessage.prototype.removeHeader()`, `OutgoingMessage.prototype.setHeader()`) for working with outgoing headers. The `OutgoingMessage.prototype._headers` and `OutgoingMessage.prototype._headerNames` properties were never documented as officially supported properties. #### DEP0067: `OutgoingMessage.prototype._renderHeaders`# History VersionChanges v8.0.0 Documentation-only deprecation. Type: Documentation-only The `node:http` module `OutgoingMessage.prototype._renderHeaders()` API is deprecated. The `OutgoingMessage.prototype._renderHeaders` property was never documented as an officially supported API. #### DEP0068: `node debug`# History VersionChanges v15.0.0 The legacy `node debug` command was removed. v8.0.0 Runtime deprecation. Type: End-of-Life `node debug` corresponds to the legacy CLI debugger which has been replaced with a V8-inspector based CLI debugger available through `node inspect`. #### DEP0069: `vm.runInDebugContext(string)`# History VersionChanges v10.0.0 End-of-Life. v9.0.0 Runtime deprecation. v8.0.0 Documentation-only deprecation. Type: End-of-Life DebugContext has been removed in V8 and is not available in Node.js 10+. DebugContext was an experimental API. #### DEP0070: `async_hooks.currentId()`# History VersionChanges v9.0.0 End-of-Life. v8.2.0 Runtime deprecation. Type: End-of-Life `async_hooks.currentId()` was renamed to `async_hooks.executionAsyncId()` for clarity. This change was made while `async_hooks` was an experimental API. #### DEP0071: `async_hooks.triggerId()`# History VersionChanges v9.0.0 End-of-Life. v8.2.0 Runtime deprecation. Type: End-of-Life `async_hooks.triggerId()` was renamed to `async_hooks.triggerAsyncId()` for clarity. This change was made while `async_hooks` was an experimental API. #### DEP0072: `async_hooks.AsyncResource.triggerId()`# History VersionChanges v9.0.0 End-of-Life. v8.2.0 Runtime deprecation. Type: End-of-Life `async_hooks.AsyncResource.triggerId()` was renamed to `async_hooks.AsyncResource.triggerAsyncId()` for clarity. This change was made while `async_hooks` was an experimental API. #### DEP0073: Several internal properties of `net.Server`# History VersionChanges v10.0.0 End-of-Life. v9.0.0 Runtime deprecation. Type: End-of-Life Accessing several internal, undocumented properties of `net.Server` instances with inappropriate names is deprecated. As the original API was undocumented and not generally useful for non-internal code, no replacement API is provided. #### DEP0074: `REPLServer.bufferedCommand`# History VersionChanges v15.0.0 End-of-Life. v9.0.0 Runtime deprecation. Type: End-of-Life The `REPLServer.bufferedCommand` property was deprecated in favor of `REPLServer.clearBufferedCommand()`. #### DEP0075: `REPLServer.parseREPLKeyword()`# History VersionChanges v15.0.0 End-of-Life. v9.0.0 Runtime deprecation. Type: End-of-Life `REPLServer.parseREPLKeyword()` was removed from userland visibility. #### DEP0076: `tls.parseCertString()`# History VersionChanges v18.0.0 End-of-Life. v9.0.0 Runtime deprecation. v8.6.0 Documentation-only deprecation. Type: End-of-Life `tls.parseCertString()` was a trivial parsing helper that was made public by mistake. While it was supposed to parse certificate subject and issuer strings, it never handled multi-value Relative Distinguished Names correctly. Earlier versions of this document suggested using `querystring.parse()` as an alternative to `tls.parseCertString()`. However, `querystring.parse()` also does not handle all certificate subjects correctly and should not be used. #### DEP0077: `Module._debug()`# History VersionChanges v9.0.0 Runtime deprecation. Type: Runtime `Module._debug()` is deprecated. The `Module._debug()` function was never documented as an officially supported API. #### DEP0078: `REPLServer.turnOffEditorMode()`# History VersionChanges v15.0.0 End-of-Life. v9.0.0 Runtime deprecation. Type: End-of-Life `REPLServer.turnOffEditorMode()` was removed from userland visibility. #### DEP0079: Custom inspection function on objects via `.inspect()`# History VersionChanges v11.0.0 End-of-Life. v10.0.0 Runtime deprecation. v8.7.0 Documentation-only deprecation. Type: End-of-Life Using a property named `inspect` on an object to specify a custom inspection function for `util.inspect()` is deprecated. Use `util.inspect.custom` instead. For backward compatibility with Node.js prior to version 6.4.0, both can be specified. #### DEP0080: `path._makeLong()`# History VersionChanges v9.0.0 Documentation-only deprecation. Type: Documentation-only The internal `path._makeLong()` was not intended for public use. However, userland modules have found it useful. The internal API is deprecated and replaced with an identical, public `path.toNamespacedPath()` method. #### DEP0081: `fs.truncate()` using a file descriptor# History VersionChanges v24.0.0 End-of-Life. v9.0.0 Runtime deprecation. Type: End-of-Life `fs.truncate()` `fs.truncateSync()` usage with a file descriptor is deprecated. Please use `fs.ftruncate()` or `fs.ftruncateSync()` to work with file descriptors. #### DEP0082: `REPLServer.prototype.memory()`# History VersionChanges v15.0.0 End-of-Life. v9.0.0 Runtime deprecation. Type: End-of-Life `REPLServer.prototype.memory()` is only necessary for the internal mechanics of the `REPLServer` itself. Do not use this function. #### DEP0083: Disabling ECDH by setting `ecdhCurve` to `false`# History VersionChanges v10.0.0 End-of-Life. v9.2.0 Runtime deprecation. Type: End-of-Life The `ecdhCurve` option to `tls.createSecureContext()` and `tls.TLSSocket` could be set to `false` to disable ECDH entirely on the server only. This mode was deprecated in preparation for migrating to OpenSSL 1.1.0 and consistency with the client and is now unsupported. Use the `ciphers` parameter instead. #### DEP0084: requiring bundled internal dependencies# History VersionChanges v12.0.0 This functionality has been removed. v10.0.0 Runtime deprecation. Type: End-of-Life Since Node.js versions 4.4.0 and 5.2.0, several modules only intended for internal usage were mistakenly exposed to user code through `require()`. These modules were: * `v8/tools/codemap` * `v8/tools/consarray` * `v8/tools/csvparser` * `v8/tools/logreader` * `v8/tools/profile_view` * `v8/tools/profile` * `v8/tools/SourceMap` * `v8/tools/splaytree` * `v8/tools/tickprocessor-driver` * `v8/tools/tickprocessor` * `node-inspect/lib/_inspect` (from 7.6.0) * `node-inspect/lib/internal/inspect_client` (from 7.6.0) * `node-inspect/lib/internal/inspect_repl` (from 7.6.0) The `v8/*` modules do not have any exports, and if not imported in a specific order would in fact throw errors. As such there are virtually no legitimate use cases for importing them through `require()`. On the other hand, `node-inspect` can be installed locally through a package manager, as it is published on the npm registry under the same name. No source code modification is necessary if that is done. #### DEP0085: AsyncHooks sensitive API# History VersionChanges v10.0.0 End-of-Life. v9.4.0, v8.10.0 Runtime deprecation. Type: End-of-Life The AsyncHooks sensitive API was never documented and had various minor issues. Use the `AsyncResource` API instead. See https://github.com/nodejs/node/issues/15572. #### DEP0086: Remove `runInAsyncIdScope`# History VersionChanges v10.0.0 End-of-Life. v9.4.0, v8.10.0 Runtime deprecation. Type: End-of-Life `runInAsyncIdScope` doesn't emit the `'before'` or `'after'` event and can thus cause a lot of issues. See https://github.com/nodejs/node/issues/14328. #### DEP0089: `require('node:assert')`# History VersionChanges v12.8.0 Deprecation revoked. v9.9.0, v8.13.0 Documentation-only deprecation. Type: Deprecation revoked Importing assert directly was not recommended as the exposed functions use loose equality checks. The deprecation was revoked because use of the `node:assert` module is not discouraged, and the deprecation caused developer confusion. #### DEP0090: Invalid GCM authentication tag lengths# History VersionChanges v11.0.0 End-of-Life. v10.0.0 Runtime deprecation. Type: End-of-Life Node.js used to support all GCM authentication tag lengths which are accepted by OpenSSL when calling `decipher.setAuthTag()`. Beginning with Node.js v11.0.0, only authentication tag lengths of 128, 120, 112, 104, 96, 64, and 32 bits are allowed. Authentication tags of other lengths are invalid per NIST SP 800-38D. #### DEP0091: `crypto.DEFAULT_ENCODING`# History VersionChanges v20.0.0 End-of-Life. v10.0.0 Runtime deprecation. Type: End-of-Life The `crypto.DEFAULT_ENCODING` property only existed for compatibility with Node.js releases prior to versions 0.9.3 and has been removed. #### DEP0092: Top-level `this` bound to `module.exports`# History VersionChanges v10.0.0 Documentation-only deprecation. Type: Documentation-only Assigning properties to the top-level `this` as an alternative to `module.exports` is deprecated. Developers should use `exports` or `module.exports` instead. #### DEP0093: `crypto.fips` is deprecated and replaced# History VersionChanges v23.0.0 Runtime deprecation. v10.0.0 Documentation-only deprecation. Type: Runtime The `crypto.fips` property is deprecated. Please use `crypto.setFips()` and `crypto.getFips()` instead. #### DEP0094: Using `assert.fail()` with more than one argument# History VersionChanges v10.0.0 Runtime deprecation. Type: Runtime Using `assert.fail()` with more than one argument is deprecated. Use `assert.fail()` with only one argument or use a different `node:assert` module method. #### DEP0095: `timers.enroll()`# History VersionChanges v24.0.0 End-of-Life. v10.0.0 Runtime deprecation. Type: End-of-Life `timers.enroll()` has been removed. Please use the publicly documented `setTimeout()` or `setInterval()` instead. #### DEP0096: `timers.unenroll()`# History VersionChanges v24.0.0 End-of-Life. v10.0.0 Runtime deprecation. Type: End-of-Life `timers.unenroll()` has been removed. Please use the publicly documented `clearTimeout()` or `clearInterval()` instead. #### DEP0097: `MakeCallback` with `domain` property# History VersionChanges v10.0.0 Runtime deprecation. Type: Runtime Users of `MakeCallback` that add the `domain` property to carry context, should start using the `async_context` variant of `MakeCallback` or `CallbackScope`, or the high-level `AsyncResource` class. #### DEP0098: AsyncHooks embedder `AsyncResource.emitBefore` and `AsyncResource.emitAfter` APIs# History VersionChanges v12.0.0 End-of-Life. v10.0.0, v9.6.0, v8.12.0 Runtime deprecation. Type: End-of-Life The embedded API provided by AsyncHooks exposes `.emitBefore()` and `.emitAfter()` methods which are very easy to use incorrectly which can lead to unrecoverable errors. Use `asyncResource.runInAsyncScope()` API instead which provides a much safer, and more convenient, alternative. See https://github.com/nodejs/node/pull/18513. #### DEP0099: Async context-unaware `node::MakeCallback` C++ APIs# History VersionChanges v10.0.0 Compile-time deprecation. Type: Compile-time Certain versions of `node::MakeCallback` APIs available to native addons are deprecated. Please use the versions of the API that accept an `async_context` parameter. #### DEP0100: `process.assert()`# History VersionChanges v23.0.0 End-of-Life. v10.0.0 Runtime deprecation. v0.3.7 Documentation-only deprecation. Type: End-of-Life `process.assert()` is deprecated. Please use the `assert` module instead. This was never a documented feature. #### DEP0101: `--with-lttng`# History VersionChanges v10.0.0 End-of-Life. Type: End-of-Life The `--with-lttng` compile-time option has been removed. #### DEP0102: Using `noAssert` in `Buffer#(read|write)` operations# History VersionChanges v10.0.0 End-of-Life. Type: End-of-Life Using the `noAssert` argument has no functionality anymore. All input is verified regardless of the value of `noAssert`. Skipping the verification could lead to hard-to-find errors and crashes. #### DEP0103: `process.binding('util').is[...]` typechecks# History VersionChanges v10.9.0 Superseded by DEP0111. v10.0.0 Documentation-only deprecation. Type: Documentation-only (supports `--pending-deprecation`) Using `process.binding()` in general should be avoided. The type checking methods in particular can be replaced by using `util.types`. This deprecation has been superseded by the deprecation of the `process.binding()` API (DEP0111). #### DEP0104: `process.env` string coercion# History VersionChanges v10.0.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Documentation-only (supports `--pending-deprecation`) When assigning a non-string property to `process.env`, the assigned value is implicitly converted to a string. This behavior is deprecated if the assigned value is not a string, boolean, or number. In the future, such assignment might result in a thrown error. Please convert the property to a string before assigning it to `process.env`. #### DEP0105: `decipher.finaltol`# History VersionChanges v11.0.0 End-of-Life. v10.0.0 Runtime deprecation. Type: End-of-Life `decipher.finaltol()` has never been documented and was an alias for `decipher.final()`. This API has been removed, and it is recommended to use `decipher.final()` instead. #### DEP0106: `crypto.createCipher` and `crypto.createDecipher`# History VersionChanges v22.0.0 End-of-Life. v11.0.0 Runtime deprecation. v10.0.0 Documentation-only deprecation. Type: End-of-Life `crypto.createCipher()` and `crypto.createDecipher()` have been removed as they use a weak key derivation function (MD5 with no salt) and static initialization vectors. It is recommended to derive a key using `crypto.pbkdf2()` or `crypto.scrypt()` with random salts and to use `crypto.createCipheriv()` and `crypto.createDecipheriv()` to obtain the `Cipheriv` and `Decipheriv` objects respectively. #### DEP0107: `tls.convertNPNProtocols()`# History VersionChanges v11.0.0 End-of-Life. v10.0.0 Runtime deprecation. Type: End-of-Life This was an undocumented helper function not intended for use outside Node.js core and obsoleted by the removal of NPN (Next Protocol Negotiation) support. #### DEP0108: `zlib.bytesRead`# History VersionChanges v23.0.0 End-of-Life. v11.0.0 Runtime deprecation. v10.0.0 Documentation-only deprecation. Type: End-of-Life Deprecated alias for `zlib.bytesWritten`. This original name was chosen because it also made sense to interpret the value as the number of bytes read by the engine, but is inconsistent with other streams in Node.js that expose values under these names. #### DEP0109: `http`, `https`, and `tls` support for invalid URLs# History VersionChanges v16.0.0 End-of-Life. v11.0.0 Runtime deprecation. Type: End-of-Life Some previously supported (but strictly invalid) URLs were accepted through the `http.request()`, `http.get()`, `https.request()`, `https.get()`, and `tls.checkServerIdentity()` APIs because those were accepted by the legacy `url.parse()` API. The mentioned APIs now use the WHATWG URL parser that requires strictly valid URLs. Passing an invalid URL is deprecated and support will be removed in the future. #### DEP0110: `vm.Script` cached data# History VersionChanges v10.6.0 Documentation-only deprecation. Type: Documentation-only The `produceCachedData` option is deprecated. Use `script.createCachedData()` instead. #### DEP0111: `process.binding()`# History VersionChanges v11.12.0 Added support for `--pending-deprecation`. v10.9.0 Documentation-only deprecation. Type: Documentation-only (supports `--pending-deprecation`) `process.binding()` is for use by Node.js internal code only. While `process.binding()` has not reached End-of-Life status in general, it is unavailable when the permission model is enabled. #### DEP0112: `dgram` private APIs# History VersionChanges v11.0.0 Runtime deprecation. Type: Runtime The `node:dgram` module previously contained several APIs that were never meant to accessed outside of Node.js core: `Socket.prototype._handle`, `Socket.prototype._receiving`, `Socket.prototype._bindState`, `Socket.prototype._queue`, `Socket.prototype._reuseAddr`, `Socket.prototype._healthCheck()`, `Socket.prototype._stopReceiving()`, and `dgram._createSocketHandle()`. #### DEP0113: `Cipher.setAuthTag()`, `Decipher.getAuthTag()`# History VersionChanges v12.0.0 End-of-Life. v11.0.0 Runtime deprecation. Type: End-of-Life `Cipher.setAuthTag()` and `Decipher.getAuthTag()` are no longer available. They were never documented and would throw when called. #### DEP0114: `crypto._toBuf()`# History VersionChanges v12.0.0 End-of-Life. v11.0.0 Runtime deprecation. Type: End-of-Life The `crypto._toBuf()` function was not designed to be used by modules outside of Node.js core and was removed. #### DEP0115: `crypto.prng()`, `crypto.pseudoRandomBytes()`, `crypto.rng()`# History VersionChanges v11.0.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Documentation-only (supports `--pending-deprecation`) In recent versions of Node.js, there is no difference between `crypto.randomBytes()` and `crypto.pseudoRandomBytes()`. The latter is deprecated along with the undocumented aliases `crypto.prng()` and `crypto.rng()` in favor of `crypto.randomBytes()` and might be removed in a future release. #### DEP0116: Legacy URL API# History VersionChanges v19.0.0, v18.13.0 `url.parse()` is deprecated again in DEP0169. v15.13.0, v14.17.0 Deprecation revoked. Status changed to "Legacy". v11.0.0 Documentation-only deprecation. Type: Deprecation revoked The legacy URL API is deprecated. This includes `url.format()`, `url.parse()`, `url.resolve()`, and the legacy `urlObject`. Please use the WHATWG URL API instead. #### DEP0117: Native crypto handles# History VersionChanges v12.0.0 End-of-Life. v11.0.0 Runtime deprecation. Type: End-of-Life Previous versions of Node.js exposed handles to internal native objects through the `_handle` property of the `Cipher`, `Decipher`, `DiffieHellman`, `DiffieHellmanGroup`, `ECDH`, `Hash`, `Hmac`, `Sign`, and `Verify` classes. The `_handle` property has been removed because improper use of the native object can lead to crashing the application. #### DEP0118: `dns.lookup()` support for a falsy host name# History VersionChanges v11.0.0 Runtime deprecation. Type: Runtime Previous versions of Node.js supported `dns.lookup()` with a falsy host name like `dns.lookup(false)` due to backward compatibility. This behavior is undocumented and is thought to be unused in real world apps. It will become an error in future versions of Node.js. #### DEP0119: `process.binding('uv').errname()` private API# History VersionChanges v11.0.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Documentation-only (supports `--pending-deprecation`) `process.binding('uv').errname()` is deprecated. Please use `util.getSystemErrorName()` instead. #### DEP0120: Windows Performance Counter support# History VersionChanges v12.0.0 End-of-Life. v11.0.0 Runtime deprecation. Type: End-of-Life Windows Performance Counter support has been removed from Node.js. The undocumented `COUNTER_NET_SERVER_CONNECTION()`, `COUNTER_NET_SERVER_CONNECTION_CLOSE()`, `COUNTER_HTTP_SERVER_REQUEST()`, `COUNTER_HTTP_SERVER_RESPONSE()`, `COUNTER_HTTP_CLIENT_REQUEST()`, and `COUNTER_HTTP_CLIENT_RESPONSE()` functions have been deprecated. #### DEP0121: `net._setSimultaneousAccepts()`# History VersionChanges v24.0.0 End-of-Life. v12.0.0 Runtime deprecation. Type: End-of-Life The undocumented `net._setSimultaneousAccepts()` function was originally intended for debugging and performance tuning when using the `node:child_process` and `node:cluster` modules on Windows. The function is not generally useful and is being removed. See discussion here: https://github.com/nodejs/node/issues/18391 #### DEP0122: `tls` `Server.prototype.setOptions()`# History VersionChanges v24.0.0 End-of-Life. v12.0.0 Runtime deprecation. Type: End-of-Life Please use `Server.prototype.setSecureContext()` instead. #### DEP0123: setting the TLS ServerName to an IP address# History VersionChanges v12.0.0 Runtime deprecation. Type: Runtime Setting the TLS ServerName to an IP address is not permitted by RFC 6066. This will be ignored in a future version. #### DEP0124: using `REPLServer.rli`# History VersionChanges v15.0.0 End-of-Life. v12.0.0 Runtime deprecation. Type: End-of-Life This property is a reference to the instance itself. #### DEP0125: `require('node:_stream_wrap')`# History VersionChanges v12.0.0 Runtime deprecation. Type: Runtime The `node:_stream_wrap` module is deprecated. #### DEP0126: `timers.active()`# History VersionChanges v24.0.0 End-of-Life. v11.14.0 Runtime deprecation. Type: End-of-Life The previously undocumented `timers.active()` has been removed. Please use the publicly documented `timeout.refresh()` instead. If re-referencing the timeout is necessary, `timeout.ref()` can be used with no performance impact since Node.js 10. #### DEP0127: `timers._unrefActive()`# History VersionChanges v24.0.0 End-of-Life. v11.14.0 Runtime deprecation. Type: End-of-Life The previously undocumented and "private" `timers._unrefActive()` has been removed. Please use the publicly documented `timeout.refresh()` instead. If unreferencing the timeout is necessary, `timeout.unref()` can be used with no performance impact since Node.js 10. #### DEP0128: modules with an invalid `main` entry and an `index.js` file# History VersionChanges v16.0.0 Runtime deprecation. v12.0.0 Documentation-only. Type: Runtime Modules that have an invalid `main` entry (e.g., `./does-not-exist.js`) and also have an `index.js` file in the top level directory will resolve the `index.js` file. That is deprecated and is going to throw an error in future Node.js versions. #### DEP0129: `ChildProcess._channel`# History VersionChanges v13.0.0 Runtime deprecation. v11.14.0 Documentation-only. Type: Runtime The `_channel` property of child process objects returned by `spawn()` and similar functions is not intended for public use. Use `ChildProcess.channel` instead. #### DEP0130: `Module.createRequireFromPath()`# History VersionChanges v16.0.0 End-of-life. v13.0.0 Runtime deprecation. v12.2.0 Documentation-only. Type: End-of-Life Use `module.createRequire()` instead. #### DEP0131: Legacy HTTP parser# History VersionChanges v13.0.0 This feature has been removed. v12.22.0 Runtime deprecation. v12.3.0 Documentation-only. Type: End-of-Life The legacy HTTP parser, used by default in versions of Node.js prior to 12.0.0, is deprecated and has been removed in v13.0.0. Prior to v13.0.0, the `--http-parser=legacy` command-line flag could be used to revert to using the legacy parser. #### DEP0132: `worker.terminate()` with callback# History VersionChanges v12.5.0 Runtime deprecation. Type: Runtime Passing a callback to `worker.terminate()` is deprecated. Use the returned `Promise` instead, or a listener to the worker's `'exit'` event. #### DEP0133: `http` `connection`# History VersionChanges v12.12.0 Documentation-only deprecation. Type: Documentation-only Prefer `response.socket` over `response.connection` and `request.socket` over `request.connection`. #### DEP0134: `process._tickCallback`# History VersionChanges v12.12.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Documentation-only (supports `--pending-deprecation`) The `process._tickCallback` property was never documented as an officially supported API. #### DEP0135: `WriteStream.open()` and `ReadStream.open()` are internal# History VersionChanges v13.0.0 Runtime deprecation. Type: Runtime `WriteStream.open()` and `ReadStream.open()` are undocumented internal APIs that do not make sense to use in userland. File streams should always be opened through their corresponding factory methods `fs.createWriteStream()` and `fs.createReadStream()`) or by passing a file descriptor in options. #### DEP0136: `http` `finished`# History VersionChanges v13.4.0, v12.16.0 Documentation-only deprecation. Type: Documentation-only `response.finished` indicates whether `response.end()` has been called, not whether `'finish'` has been emitted and the underlying data is flushed. Use `response.writableFinished` or `response.writableEnded` accordingly instead to avoid the ambiguity. To maintain existing behavior `response.finished` should be replaced with `response.writableEnded`. #### DEP0137: Closing fs.FileHandle on garbage collection# History VersionChanges v14.0.0 Runtime deprecation. Type: Runtime Allowing a `fs.FileHandle` object to be closed on garbage collection is deprecated. In the future, doing so might result in a thrown error that will terminate the process. Please ensure that all `fs.FileHandle` objects are explicitly closed using `FileHandle.prototype.close()` when the `fs.FileHandle` is no longer needed: const fsPromises = require('node:fs').promises; async function openAndClose() { let filehandle; try { filehandle = await fsPromises.open('thefile.txt', 'r'); } finally { if (filehandle !== undefined) await filehandle.close(); } } #### DEP0138: `process.mainModule`# History VersionChanges v14.0.0 Documentation-only deprecation. Type: Documentation-only `process.mainModule` is a CommonJS-only feature while `process` global object is shared with non-CommonJS environment. Its use within ECMAScript modules is unsupported. It is deprecated in favor of `require.main`, because it serves the same purpose and is only available on CommonJS environment. #### DEP0139: `process.umask()` with no arguments# History VersionChanges v14.0.0, v12.19.0 Documentation-only deprecation. Type: Documentation-only Calling `process.umask()` with no argument causes the process-wide umask to be written twice. This introduces a race condition between threads, and is a potential security vulnerability. There is no safe, cross-platform alternative API. #### DEP0140: Use `request.destroy()` instead of `request.abort()`# History VersionChanges v14.1.0, v13.14.0 Documentation-only deprecation. Type: Documentation-only Use `request.destroy()` instead of `request.abort()`. #### DEP0141: `repl.inputStream` and `repl.outputStream`# History VersionChanges v14.3.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Documentation-only (supports `--pending-deprecation`) The `node:repl` module exported the input and output stream twice. Use `.input` instead of `.inputStream` and `.output` instead of `.outputStream`. #### DEP0142: `repl._builtinLibs`# History VersionChanges v14.3.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Documentation-only (supports `--pending-deprecation`) The `node:repl` module exports a `_builtinLibs` property that contains an array of built-in modules. It was incomplete so far and instead it's better to rely upon `require('node:module').builtinModules`. #### DEP0143: `Transform._transformState`# History VersionChanges v15.0.0 End-of-Life. v14.5.0 Runtime deprecation. Type: End-of-Life `Transform._transformState` will be removed in future versions where it is no longer required due to simplification of the implementation. #### DEP0144: `module.parent`# History VersionChanges v14.6.0, v12.19.0 Documentation-only deprecation. Type: Documentation-only (supports `--pending-deprecation`) A CommonJS module can access the first module that required it using `module.parent`. This feature is deprecated because it does not work consistently in the presence of ECMAScript modules and because it gives an inaccurate representation of the CommonJS module graph. Some modules use it to check if they are the entry point of the current process. Instead, it is recommended to compare `require.main` and `module`: if (require.main === module) { // Code section that will run only if current file is the entry point. } When looking for the CommonJS modules that have required the current one, `require.cache` and `module.children` can be used: const moduleParents = Object.values(require.cache) .filter((m) => m.children.includes(module)); #### DEP0145: `socket.bufferSize`# History VersionChanges v14.6.0 Documentation-only deprecation. Type: Documentation-only `socket.bufferSize` is just an alias for `writable.writableLength`. #### DEP0146: `new crypto.Certificate()`# History VersionChanges v14.9.0 Documentation-only deprecation. Type: Documentation-only The `crypto.Certificate()` constructor is deprecated. Use static methods of `crypto.Certificate()` instead. #### DEP0147: `fs.rmdir(path, { recursive: true })`# History VersionChanges v16.0.0 Runtime deprecation. v15.0.0 Runtime deprecation for permissive behavior. v14.14.0 Documentation-only deprecation. Type: Runtime In future versions of Node.js, `recursive` option will be ignored for `fs.rmdir`, `fs.rmdirSync`, and `fs.promises.rmdir`. Use `fs.rm(path, { recursive: true, force: true })`, `fs.rmSync(path, { recursive: true, force: true })` or `fs.promises.rm(path, { recursive: true, force: true })` instead. #### DEP0148: Folder mappings in `"exports"` (trailing `"/"`)# History VersionChanges v17.0.0 End-of-Life. v16.0.0 Runtime deprecation. v15.1.0 Runtime deprecation for self-referencing imports. v14.13.0 Documentation-only deprecation. Type: End-of-Life Using a trailing `"/"` to define subpath folder mappings in the subpath exports or subpath imports fields is no longer supported. Use subpath patterns instead. #### DEP0149: `http.IncomingMessage#connection`# History VersionChanges v16.0.0 Documentation-only deprecation. Type: Documentation-only Prefer `message.socket` over `message.connection`. #### DEP0150: Changing the value of `process.config`# History VersionChanges v19.0.0 End-of-Life. v16.0.0 Runtime deprecation. Type: End-of-Life The `process.config` property provides access to Node.js compile-time settings. However, the property is mutable and therefore subject to tampering. The ability to change the value will be removed in a future version of Node.js. #### DEP0151: Main index lookup and extension searching# History VersionChanges v16.0.0 Runtime deprecation. v15.8.0, v14.18.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Runtime Previously, `index.js` and extension searching lookups would apply to `import 'pkg'` main entry point resolution, even when resolving ES modules. With this deprecation, all ES module main entry point resolutions require an explicit `"exports"` or `"main"` entry with the exact file extension. #### DEP0152: Extension PerformanceEntry properties# History VersionChanges v16.0.0 Runtime deprecation. Type: Runtime The `'gc'`, `'http2'`, and `'http'` object types have additional properties assigned to them that provide additional information. These properties are now available within the standard `detail` property of the `PerformanceEntry` object. The existing accessors have been deprecated and should no longer be used. #### DEP0153: `dns.lookup` and `dnsPromises.lookup` options type coercion# History VersionChanges v18.0.0 End-of-Life. v17.0.0 Runtime deprecation. v16.8.0 Documentation-only deprecation. Type: End-of-Life Using a non-nullish non-integer value for `family` option, a non-nullish non-number value for `hints` option, a non-nullish non-boolean value for `all` option, or a non-nullish non-boolean value for `verbatim` option in `dns.lookup()` and `dnsPromises.lookup()` throws an `ERR_INVALID_ARG_TYPE` error. #### DEP0154: RSA-PSS generate key pair options# History VersionChanges v20.0.0 Runtime deprecation. v16.10.0 Documentation-only deprecation. Type: Runtime The `'hash'` and `'mgf1Hash'` options are replaced with `'hashAlgorithm'` and `'mgf1HashAlgorithm'`. #### DEP0155: Trailing slashes in pattern specifier resolutions# History VersionChanges v17.0.0 Runtime deprecation. v16.10.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Runtime The remapping of specifiers ending in `"/"` like `import 'pkg/x/'` is deprecated for package `"exports"` and `"imports"` pattern resolutions. #### DEP0156: `.aborted` property and `'abort'`, `'aborted'` event in `http`# History VersionChanges v17.0.0, v16.12.0 Documentation-only deprecation. Type: Documentation-only Move to API instead, as the `http.ClientRequest`, `http.ServerResponse`, and `http.IncomingMessage` are all stream-based. Check `stream.destroyed` instead of the `.aborted` property, and listen for `'close'` instead of `'abort'`, `'aborted'` event. The `.aborted` property and `'abort'` event are only useful for detecting `.abort()` calls. For closing a request early, use the Stream `.destroy([error])` then check the `.destroyed` property and `'close'` event should have the same effect. The receiving end should also check the `readable.readableEnded` value on `http.IncomingMessage` to get whether it was an aborted or graceful destroy. #### DEP0157: Thenable support in streams# History VersionChanges v18.0.0 End-of-life. v17.2.0, v16.14.0 Documentation-only deprecation. Type: End-of-Life An undocumented feature of Node.js streams was to support thenables in implementation methods. This is now deprecated, use callbacks instead and avoid use of async function for streams implementation methods. This feature caused users to encounter unexpected problems where the user implements the function in callback style but uses e.g. an async method which would cause an error since mixing promise and callback semantics is not valid. const w = new Writable({ async final(callback) { await someOp(); callback(); }, }); #### DEP0158: `buffer.slice(start, end)`# History VersionChanges v17.5.0, v16.15.0 Documentation-only deprecation. Type: Documentation-only This method was deprecated because it is not compatible with `Uint8Array.prototype.slice()`, which is a superclass of `Buffer`. Use `buffer.subarray` which does the same thing instead. #### DEP0159: `ERR_INVALID_CALLBACK`# History VersionChanges v18.0.0 End-of-Life. Type: End-of-Life This error code was removed due to adding more confusion to the errors used for value type validation. #### DEP0160: `process.on('multipleResolves', handler)`# History VersionChanges v18.0.0 Runtime deprecation. v17.6.0, v16.15.0 Documentation-only deprecation. Type: Runtime This event was deprecated because it did not work with V8 promise combinators which diminished its usefulness. #### DEP0161: `process._getActiveRequests()` and `process._getActiveHandles()`# History VersionChanges v17.6.0, v16.15.0 Documentation-only deprecation. Type: Documentation-only The `process._getActiveHandles()` and `process._getActiveRequests()` functions are not intended for public use and can be removed in future releases. Use `process.getActiveResourcesInfo()` to get a list of types of active resources and not the actual references. #### DEP0162: `fs.write()`, `fs.writeFileSync()` coercion to string# History VersionChanges v19.0.0 End-of-Life. v18.0.0 Runtime deprecation. v17.8.0, v16.15.0 Documentation-only deprecation. Type: End-of-Life Implicit coercion of objects with own `toString` property, passed as second parameter in `fs.write()`, `fs.writeFile()`, `fs.appendFile()`, `fs.writeFileSync()`, and `fs.appendFileSync()` is deprecated. Convert them to primitive strings. #### DEP0163: `channel.subscribe(onMessage)`, `channel.unsubscribe(onMessage)`# History VersionChanges v24.8.0 Deprecation revoked. v18.7.0, v16.17.0 Documentation-only deprecation. Type: Deprecation revoked These methods were deprecated because their use could leave the channel object vulnerable to being garbage-collected if not strongly referenced by the user. The deprecation was revoked because channel objects are now resistant to garbage collection when the channel has active subscribers. #### DEP0164: `process.exit(code)`, `process.exitCode` coercion to integer# History VersionChanges v20.0.0 End-of-Life. v19.0.0 Runtime deprecation. v18.10.0, v16.18.0 Documentation-only deprecation of `process.exitCode` integer coercion. v18.7.0, v16.17.0 Documentation-only deprecation of `process.exit(code)` integer coercion. Type: End-of-Life Values other than `undefined`, `null`, integer numbers, and integer strings (e.g., `'1'`) are deprecated as value for the `code` parameter in `process.exit()` and as value to assign to `process.exitCode`. #### DEP0165: `--trace-atomics-wait`# History VersionChanges v23.0.0 End-of-Life. v22.0.0 Runtime deprecation. v18.8.0, v16.18.0 Documentation-only deprecation. Type: End-of-Life The `--trace-atomics-wait` flag has been removed because it uses the V8 hook `SetAtomicsWaitCallback`, that will be removed in a future V8 release. #### DEP0166: Double slashes in imports and exports targets# History VersionChanges v19.0.0 Runtime deprecation. v18.10.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Runtime Package imports and exports targets mapping into paths including a double slash (of "/" or "\") are deprecated and will fail with a resolution validation error in a future release. This same deprecation also applies to pattern matches starting or ending in a slash. #### DEP0167: Weak `DiffieHellmanGroup` instances (`modp1`, `modp2`, `modp5`)# History VersionChanges v18.10.0, v16.18.0 Documentation-only deprecation. Type: Documentation-only The well-known MODP groups `modp1`, `modp2`, and `modp5` are deprecated because they are not secure against practical attacks. See RFC 8247 Section 2.4 for details. These groups might be removed in future versions of Node.js. Applications that rely on these groups should evaluate using stronger MODP groups instead. #### DEP0168: Unhandled exception in Node-API callbacks# History VersionChanges v18.3.0, v16.17.0 Runtime deprecation. Type: Runtime The implicit suppression of uncaught exceptions in Node-API callbacks is now deprecated. Set the flag `--force-node-api-uncaught-exceptions-policy` to force Node.js to emit an `'uncaughtException'` event if the exception is not handled in Node-API callbacks. #### DEP0169: Insecure url.parse()# History VersionChanges v24.0.0 Application deprecation. v19.9.0, v18.17.0 Added support for `--pending-deprecation`. v19.0.0, v18.13.0 Documentation-only deprecation. Type: Application (non-`node_modules` code only) `url.parse()` behavior is not standardized and prone to errors that have security implications. Use the WHATWG URL API instead. CVEs are not issued for `url.parse()` vulnerabilities. #### DEP0170: Invalid port when using `url.parse()`# History VersionChanges v20.0.0 Runtime deprecation. v19.2.0, v18.13.0 Documentation-only deprecation. Type: Runtime `url.parse()` accepts URLs with ports that are not numbers. This behavior might result in host name spoofing with unexpected input. These URLs will throw an error in future versions of Node.js, as the WHATWG URL API does already. #### DEP0171: Setters for `http.IncomingMessage` headers and trailers# History VersionChanges v19.3.0, v18.13.0 Documentation-only deprecation. Type: Documentation-only In a future version of Node.js, `message.headers`, `message.headersDistinct`, `message.trailers`, and `message.trailersDistinct` will be read-only. #### DEP0172: The `asyncResource` property of `AsyncResource` bound functions# History VersionChanges v20.0.0 Runtime-deprecation. Type: Runtime In a future version of Node.js, the `asyncResource` property will no longer be added when a function is bound to an `AsyncResource`. #### DEP0173: the `assert.CallTracker` class# History VersionChanges v20.1.0 Runtime deprecation. Type: Runtime In a future version of Node.js, `assert.CallTracker`, will be removed. Consider using alternatives such as the `mock` helper function. #### DEP0174: calling `promisify` on a function that returns a `Promise`# History VersionChanges v21.0.0 Runtime deprecation. v20.8.0 Documentation-only deprecation. Type: Runtime Calling `util.promisify` on a function that returns a `Promise` will ignore the result of said promise, which can lead to unhandled promise rejections. #### DEP0175: `util.toUSVString`# History VersionChanges v20.8.0 Documentation-only deprecation. Type: Documentation-only The `util.toUSVString()` API is deprecated. Please use `String.prototype.toWellFormed` instead. #### DEP0176: `fs.F_OK`, `fs.R_OK`, `fs.W_OK`, `fs.X_OK`# History VersionChanges v24.0.0 Runtime deprecation. v20.8.0 Documentation-only deprecation. Type: Runtime `F_OK`, `R_OK`, `W_OK` and `X_OK` getters exposed directly on `node:fs` are deprecated. Get them from `fs.constants` or `fs.promises.constants` instead. #### DEP0177: `util.types.isWebAssemblyCompiledModule`# History VersionChanges v21.7.0, v20.12.0 End-of-Life. v21.3.0, v20.11.0 A deprecation code has been assigned. v14.0.0 Documentation-only deprecation. Type: End-of-Life The `util.types.isWebAssemblyCompiledModule` API has been removed. Please use `value instanceof WebAssembly.Module` instead. #### DEP0178: `dirent.path`# History VersionChanges v24.0.0 End-of-Life. v23.0.0 Runtime deprecation. v21.5.0, v20.12.0, v18.20.0 Documentation-only deprecation. Type: End-of-Life The `dirent.path` property has been removed due to its lack of consistency across release lines. Please use `dirent.parentPath` instead. #### DEP0179: `Hash` constructor# History VersionChanges v22.0.0 Runtime deprecation. v21.5.0, v20.12.0 Documentation-only deprecation. Type: Runtime Calling `Hash` class directly with `Hash()` or `new Hash()` is deprecated due to being internals, not intended for public use. Please use the `crypto.createHash()` method to create Hash instances. #### DEP0180: `fs.Stats` constructor# History VersionChanges v22.0.0 Runtime deprecation. v20.13.0 Documentation-only deprecation. Type: Runtime Calling `fs.Stats` class directly with `Stats()` or `new Stats()` is deprecated due to being internals, not intended for public use. #### DEP0181: `Hmac` constructor# History VersionChanges v22.0.0 Runtime deprecation. v20.13.0 Documentation-only deprecation. Type: Runtime Calling `Hmac` class directly with `Hmac()` or `new Hmac()` is deprecated due to being internals, not intended for public use. Please use the `crypto.createHmac()` method to create Hmac instances. #### DEP0182: Short GCM authentication tags without explicit `authTagLength`# History VersionChanges v23.0.0 Runtime deprecation. v20.13.0 Documentation-only deprecation. Type: Runtime Applications that intend to use authentication tags that are shorter than the default authentication tag length must set the `authTagLength` option of the `crypto.createDecipheriv()` function to the appropriate length. For ciphers in GCM mode, the `decipher.setAuthTag()` function accepts authentication tags of any valid length (see DEP0090). This behavior is deprecated to better align with recommendations per NIST SP 800-38D. #### DEP0183: OpenSSL engine-based APIs# History VersionChanges v22.4.0, v20.16.0 Documentation-only deprecation. Type: Documentation-only OpenSSL 3 has deprecated support for custom engines with a recommendation to switch to its new provider model. The `clientCertEngine` option for `https.request()`, `tls.createSecureContext()`, and `tls.createServer()`; the `privateKeyEngine` and `privateKeyIdentifier` for `tls.createSecureContext()`; and `crypto.setEngine()` all depend on this functionality from OpenSSL. #### DEP0184: Instantiating `node:zlib` classes without `new`# History VersionChanges v24.0.0 Runtime deprecation. v22.9.0, v20.18.0 Documentation-only deprecation. Type: Runtime Instantiating classes without the `new` qualifier exported by the `node:zlib` module is deprecated. It is recommended to use the `new` qualifier instead. This applies to all Zlib classes, such as `Deflate`, `DeflateRaw`, `Gunzip`, `Inflate`, `InflateRaw`, `Unzip`, and `Zlib`. #### DEP0185: Instantiating `node:repl` classes without `new`# History VersionChanges v24.0.0 Runtime deprecation. v22.9.0, v20.18.0 Documentation-only deprecation. Type: Runtime Instantiating classes without the `new` qualifier exported by the `node:repl` module is deprecated. It is recommended to use the `new` qualifier instead. This applies to all REPL classes, including `REPLServer` and `Recoverable`. #### DEP0187: Passing invalid argument types to `fs.existsSync`# History VersionChanges v24.0.0 Runtime deprecation. v23.4.0, v22.13.0 Documentation-only. Type: Runtime Passing non-supported argument types is deprecated and, instead of returning `false`, will throw an error in a future version. #### DEP0188: `process.features.ipv6` and `process.features.uv`# History VersionChanges v23.4.0, v22.13.0 Documentation-only deprecation. Type: Documentation-only These properties are unconditionally `true`. Any checks based on these properties are redundant. #### DEP0189: `process.features.tls_*`# History VersionChanges v23.4.0, v22.13.0 Documentation-only deprecation. Type: Documentation-only `process.features.tls_alpn`, `process.features.tls_ocsp`, and `process.features.tls_sni` are deprecated, as their values are guaranteed to be identical to that of `process.features.tls`. #### DEP0190: Passing `args` to `node:child_process` `execFile`/`spawn` with `shell` option `true`# History VersionChanges v24.0.0 Runtime deprecation. v23.11.0, v22.15.0 Documentation-only deprecation. Type: Runtime When an `args` array is passed to `child_process.execFile` or `child_process.spawn` with the option `{ shell: true }`, the values are not escaped, only space-separated, which can lead to shell injection. #### DEP0191: `repl.builtinModules`# History VersionChanges v24.0.0 Documentation-only deprecation with `--pending-deprecation` support. Type: Documentation-only (supports `--pending-deprecation`) The `node:repl` module exports a `builtinModules` property that contains an array of built-in modules. This was incomplete and matched the already deprecated `repl._builtinLibs` (DEP0142) instead it's better to rely upon `require('node:module').builtinModules`. #### DEP0192: `require('node:_tls_common')` and `require('node:_tls_wrap')`# History VersionChanges v24.2.0 Documentation-only deprecation. Type: Documentation-only The `node:_tls_common` and `node:_tls_wrap` modules are deprecated as they should be considered an internal nodejs implementation rather than a public facing API, use `node:tls` instead. #### DEP0193: `require('node:_stream_*')`# History VersionChanges v24.2.0 Documentation-only deprecation. Type: Documentation-only The `node:_stream_duplex`, `node:_stream_passthrough`, `node:_stream_readable`, `node:_stream_transform`, `node:_stream_wrap` and `node:_stream_writable` modules are deprecated as they should be considered an internal nodejs implementation rather than a public facing API, use `node:stream` instead. #### DEP0194: HTTP/2 priority signaling# History VersionChanges v24.2.0 End-of-Life. v24.2.0 Documentation-only deprecation. Type: End-of-Life The support for priority signaling has been removed following its deprecation in the RFC 9113. #### DEP0195: Instantiating `node:http` classes without `new`# History VersionChanges v24.2.0 Documentation-only deprecation. Type: Documentation-only Instantiating classes without the `new` qualifier exported by the `node:http` module is deprecated. It is recommended to use the `new` qualifier instead. This applies to all http classes, such as `OutgoingMessage`, `IncomingMessage`, `ServerResponse` and `ClientRequest`. #### DEP0196: Calling `node:child_process` functions with `options.shell` as an empty string# History VersionChanges v24.2.0 Documentation-only deprecation. Type: Documentation-only Calling the process-spawning functions with `{ shell: '' }` is almost certainly unintentional, and can cause aberrant behavior. To make `child_process.execFile` or `child_process.spawn` invoke the default shell, use `{ shell: true }`. If the intention is not to invoke a shell (default behavior), either omit the `shell` option, or set it to `false` or a nullish value. To make `child_process.exec` invoke the default shell, either omit the `shell` option, or set it to a nullish value. If the intention is not to invoke a shell, use `child_process.execFile` instead. #### DEP0197: `util.types.isNativeError()`# History VersionChanges v24.2.0 Documentation-only deprecation. Type: Documentation-only The `util.types.isNativeError` API is deprecated. Please use `Error.isError` instead. #### DEP0198: Creating SHAKE-128 and SHAKE-256 digests without an explicit `options.outputLength`# History VersionChanges v24.4.0 Documentation-only deprecation with support for `--pending-deprecation`. Type: Documentation-only (supports `--pending-deprecation`) Creating SHAKE-128 and SHAKE-256 digests without an explicit `options.outputLength` is deprecated. #### DEP0199: `require('node:_http_*')`# History VersionChanges v24.6.0 Documentation-only deprecation. Type: Documentation-only The `node:_http_agent`, `node:_http_client`, `node:_http_common`, `node:_http_incoming`, `node:_http_outgoing` and `node:_http_server` modules are deprecated as they should be considered an internal nodejs implementation rather than a public facing API, use `node:http` instead. #### DEP0200: Closing fs.Dir on garbage collection# History VersionChanges v24.9.0 Documentation-only deprecation. Type: Documentation-only Allowing a `fs.Dir` object to be closed on garbage collection is deprecated. In the future, doing so might result in a thrown error that will terminate the process. Please ensure that all `fs.Dir` objects are explicitly closed using `Dir.prototype.close()` or `using` keyword: import { opendir } from 'node:fs/promises'; { await using dir = await opendir('/async/disposable/directory'); } // Closed by dir[Symbol.asyncDispose]() { using dir = await opendir('/sync/disposable/directory'); } // Closed by dir[Symbol.dispose]() { const dir = await opendir('/unconditionally/iterated/directory'); for await (const entry of dir) { // process an entry } // Closed by iterator } { let dir; try { dir = await opendir('/legacy/closeable/directory'); } finally { await dir?.close(); } } ## Diagnostics Channel# History VersionChanges v19.2.0, v18.13.0 diagnostics_channel is now Stable. v15.1.0, v14.17.0 Added in: v15.1.0, v14.17.0 Stability: 2 \- Stable Source Code: lib/diagnostics_channel.js The `node:diagnostics_channel` module provides an API to create named channels to report arbitrary message data for diagnostics purposes. It can be accessed using: import diagnostics_channel from 'node:diagnostics_channel'; It is intended that a module writer wanting to report diagnostics messages will create one or many top-level channels to report messages through. Channels may also be acquired at runtime but it is not encouraged due to the additional overhead of doing so. Channels may be exported for convenience, but as long as the name is known it can be acquired anywhere. If you intend for your module to produce diagnostics data for others to consume it is recommended that you include documentation of what named channels are used along with the shape of the message data. Channel names should generally include the module name to avoid collisions with data from other modules. ### Public API# #### Overview# Following is a simple overview of the public API. import diagnostics_channel from 'node:diagnostics_channel'; // Get a reusable channel object const channel = diagnostics_channel.channel('my-channel'); function onMessage(message, name) { // Received data } // Subscribe to the channel diagnostics_channel.subscribe('my-channel', onMessage); // Check if the channel has an active subscriber if (channel.hasSubscribers) { // Publish data to the channel channel.publish({ some: 'data', }); } // Unsubscribe from the channel diagnostics_channel.unsubscribe('my-channel', onMessage); ##### `diagnostics_channel.hasSubscribers(name)`# Added in: v15.1.0, v14.17.0 * `name` | The channel name * Returns: If there are active subscribers Check if there are active subscribers to the named channel. This is helpful if the message you want to send might be expensive to prepare. This API is optional but helpful when trying to publish messages from very performance-sensitive code. import diagnostics_channel from 'node:diagnostics_channel'; if (diagnostics_channel.hasSubscribers('my-channel')) { // There are subscribers, prepare and publish message } ##### `diagnostics_channel.channel(name)`# Added in: v15.1.0, v14.17.0 * `name` | The channel name * Returns: The named channel object This is the primary entry-point for anyone wanting to publish to a named channel. It produces a channel object which is optimized to reduce overhead at publish time as much as possible. import diagnostics_channel from 'node:diagnostics_channel'; const channel = diagnostics_channel.channel('my-channel'); ##### `diagnostics_channel.subscribe(name, onMessage)`# Added in: v18.7.0, v16.17.0 * `name` | The channel name * `onMessage` The handler to receive channel messages * `message` The message data * `name` | The name of the channel Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an `'uncaughtException'`. import diagnostics_channel from 'node:diagnostics_channel'; diagnostics_channel.subscribe('my-channel', (message, name) => { // Received data }); ##### `diagnostics_channel.unsubscribe(name, onMessage)`# Added in: v18.7.0, v16.17.0 * `name` | The channel name * `onMessage` The previous subscribed handler to remove * Returns: `true` if the handler was found, `false` otherwise. Remove a message handler previously registered to this channel with `diagnostics_channel.subscribe(name, onMessage)`. import diagnostics_channel from 'node:diagnostics_channel'; function onMessage(message, name) { // Received data } diagnostics_channel.subscribe('my-channel', onMessage); diagnostics_channel.unsubscribe('my-channel', onMessage); ##### `diagnostics_channel.tracingChannel(nameOrChannels)`# Added in: v19.9.0, v18.19.0 Stability: 1 \- Experimental * `nameOrChannels` | Channel name or object containing all the TracingChannel Channels * Returns: Collection of channels to trace with Creates a `TracingChannel` wrapper for the given TracingChannel Channels. If a name is given, the corresponding tracing channels will be created in the form of `tracing:${name}:${eventType}` where `eventType` corresponds to the types of TracingChannel Channels. import diagnostics_channel from 'node:diagnostics_channel'; const channelsByName = diagnostics_channel.tracingChannel('my-channel'); // or... const channelsByCollection = diagnostics_channel.tracingChannel({ start: diagnostics_channel.channel('tracing:my-channel:start'), end: diagnostics_channel.channel('tracing:my-channel:end'), asyncStart: diagnostics_channel.channel('tracing:my-channel:asyncStart'), asyncEnd: diagnostics_channel.channel('tracing:my-channel:asyncEnd'), error: diagnostics_channel.channel('tracing:my-channel:error'), }); #### Class: `Channel`# Added in: v15.1.0, v14.17.0 The class `Channel` represents an individual named channel within the data pipeline. It is used to track subscribers and to publish messages when there are subscribers present. It exists as a separate object to avoid channel lookups at publish time, enabling very fast publish speeds and allowing for heavy use while incurring very minimal cost. Channels are created with `diagnostics_channel.channel(name)`, constructing a channel directly with `new Channel(name)` is not supported. ##### `channel.hasSubscribers`# Added in: v15.1.0, v14.17.0 * Returns: If there are active subscribers Check if there are active subscribers to this channel. This is helpful if the message you want to send might be expensive to prepare. This API is optional but helpful when trying to publish messages from very performance-sensitive code. import diagnostics_channel from 'node:diagnostics_channel'; const channel = diagnostics_channel.channel('my-channel'); if (channel.hasSubscribers) { // There are subscribers, prepare and publish message } ##### `channel.publish(message)`# Added in: v15.1.0, v14.17.0 * `message` The message to send to the channel subscribers Publish a message to any subscribers to the channel. This will trigger message handlers synchronously so they will execute within the same context. import diagnostics_channel from 'node:diagnostics_channel'; const channel = diagnostics_channel.channel('my-channel'); channel.publish({ some: 'message', }); ##### `channel.subscribe(onMessage)`# History VersionChanges v24.8.0 Deprecation revoked. v18.7.0, v16.17.0 Documentation-only deprecation. v15.1.0, v14.17.0 Added in: v15.1.0, v14.17.0 * `onMessage` The handler to receive channel messages * `message` The message data * `name` | The name of the channel Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an `'uncaughtException'`. import diagnostics_channel from 'node:diagnostics_channel'; const channel = diagnostics_channel.channel('my-channel'); channel.subscribe((message, name) => { // Received data }); ##### `channel.unsubscribe(onMessage)`# History VersionChanges v24.8.0 Deprecation revoked. v18.7.0, v16.17.0 Documentation-only deprecation. v17.1.0, v16.14.0, v14.19.0 Added return value. Added to channels without subscribers. v15.1.0, v14.17.0 Added in: v15.1.0, v14.17.0 * `onMessage` The previous subscribed handler to remove * Returns: `true` if the handler was found, `false` otherwise. Remove a message handler previously registered to this channel with `channel.subscribe(onMessage)`. import diagnostics_channel from 'node:diagnostics_channel'; const channel = diagnostics_channel.channel('my-channel'); function onMessage(message, name) { // Received data } channel.subscribe(onMessage); channel.unsubscribe(onMessage); ##### `channel.bindStore(store[, transform])`# Added in: v19.9.0, v18.19.0 Stability: 1 \- Experimental * `store` The store to which to bind the context data * `transform` Transform context data before setting the store context When `channel.runStores(context, ...)` is called, the given context data will be applied to any store bound to the channel. If the store has already been bound the previous `transform` function will be replaced with the new one. The `transform` function may be omitted to set the given context data as the context directly. import diagnostics_channel from 'node:diagnostics_channel'; import { AsyncLocalStorage } from 'node:async_hooks'; const store = new AsyncLocalStorage(); const channel = diagnostics_channel.channel('my-channel'); channel.bindStore(store, (data) => { return { data }; }); ##### `channel.unbindStore(store)`# Added in: v19.9.0, v18.19.0 Stability: 1 \- Experimental * `store` The store to unbind from the channel. * Returns: `true` if the store was found, `false` otherwise. Remove a message handler previously registered to this channel with `channel.bindStore(store)`. import diagnostics_channel from 'node:diagnostics_channel'; import { AsyncLocalStorage } from 'node:async_hooks'; const store = new AsyncLocalStorage(); const channel = diagnostics_channel.channel('my-channel'); channel.bindStore(store); channel.unbindStore(store); ##### `channel.runStores(context, fn[, thisArg[, ...args]])`# Added in: v19.9.0, v18.19.0 Stability: 1 \- Experimental * `context` Message to send to subscribers and bind to stores * `fn` Handler to run within the entered storage context * `thisArg` The receiver to be used for the function call. * `...args` Optional arguments to pass to the function. Applies the given data to any AsyncLocalStorage instances bound to the channel for the duration of the given function, then publishes to the channel within the scope of that data is applied to the stores. If a transform function was given to `channel.bindStore(store)` it will be applied to transform the message data before it becomes the context value for the store. The prior storage context is accessible from within the transform function in cases where context linking is required. The context applied to the store should be accessible in any async code which continues from execution which began during the given function, however there are some situations in which context loss may occur. import diagnostics_channel from 'node:diagnostics_channel'; import { AsyncLocalStorage } from 'node:async_hooks'; const store = new AsyncLocalStorage(); const channel = diagnostics_channel.channel('my-channel'); channel.bindStore(store, (message) => { const parent = store.getStore(); return new Span(message, parent); }); channel.runStores({ some: 'message' }, () => { store.getStore(); // Span({ some: 'message' }) }); #### Class: `TracingChannel`# Added in: v19.9.0, v18.19.0 Stability: 1 \- Experimental The class `TracingChannel` is a collection of TracingChannel Channels which together express a single traceable action. It is used to formalize and simplify the process of producing events for tracing application flow. `diagnostics_channel.tracingChannel()` is used to construct a `TracingChannel`. As with `Channel` it is recommended to create and reuse a single `TracingChannel` at the top-level of the file rather than creating them dynamically. ##### `tracingChannel.subscribe(subscribers)`# Added in: v19.9.0, v18.19.0 * `subscribers` Set of TracingChannel Channels subscribers * `start` The `start` event subscriber * `end` The `end` event subscriber * `asyncStart` The `asyncStart` event subscriber * `asyncEnd` The `asyncEnd` event subscriber * `error` The `error` event subscriber Helper to subscribe a collection of functions to the corresponding channels. This is the same as calling `channel.subscribe(onMessage)` on each channel individually. import diagnostics_channel from 'node:diagnostics_channel'; const channels = diagnostics_channel.tracingChannel('my-channel'); channels.subscribe({ start(message) { // Handle start message }, end(message) { // Handle end message }, asyncStart(message) { // Handle asyncStart message }, asyncEnd(message) { // Handle asyncEnd message }, error(message) { // Handle error message }, }); ##### `tracingChannel.unsubscribe(subscribers)`# Added in: v19.9.0, v18.19.0 * `subscribers` Set of TracingChannel Channels subscribers * `start` The `start` event subscriber * `end` The `end` event subscriber * `asyncStart` The `asyncStart` event subscriber * `asyncEnd` The `asyncEnd` event subscriber * `error` The `error` event subscriber * Returns: `true` if all handlers were successfully unsubscribed, and `false` otherwise. Helper to unsubscribe a collection of functions from the corresponding channels. This is the same as calling `channel.unsubscribe(onMessage)` on each channel individually. import diagnostics_channel from 'node:diagnostics_channel'; const channels = diagnostics_channel.tracingChannel('my-channel'); channels.unsubscribe({ start(message) { // Handle start message }, end(message) { // Handle end message }, asyncStart(message) { // Handle asyncStart message }, asyncEnd(message) { // Handle asyncEnd message }, error(message) { // Handle error message }, }); ##### `tracingChannel.traceSync(fn[, context[, thisArg[, ...args]]])`# Added in: v19.9.0, v18.19.0 * `fn` Function to wrap a trace around * `context` Shared object to correlate events through * `thisArg` The receiver to be used for the function call * `...args` Optional arguments to pass to the function * Returns: The return value of the given function Trace a synchronous function call. This will always produce a `start` event and `end` event around the execution and may produce an `error` event if the given function throws an error. This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all events should have any bound stores set to match this trace context. To ensure only correct trace graphs are formed, events will only be published if subscribers are present prior to starting the trace. Subscriptions which are added after the trace begins will not receive future events from that trace, only future traces will be seen. import diagnostics_channel from 'node:diagnostics_channel'; const channels = diagnostics_channel.tracingChannel('my-channel'); channels.traceSync(() => { // Do something }, { some: 'thing', }); ##### `tracingChannel.tracePromise(fn[, context[, thisArg[, ...args]]])`# Added in: v19.9.0, v18.19.0 * `fn` Promise-returning function to wrap a trace around * `context` Shared object to correlate trace events through * `thisArg` The receiver to be used for the function call * `...args` Optional arguments to pass to the function * Returns: Chained from promise returned by the given function Trace a promise-returning function call. This will always produce a `start` event and `end` event around the synchronous portion of the function execution, and will produce an `asyncStart` event and `asyncEnd` event when a promise continuation is reached. It may also produce an `error` event if the given function throws an error or the returned promise rejects. This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all events should have any bound stores set to match this trace context. To ensure only correct trace graphs are formed, events will only be published if subscribers are present prior to starting the trace. Subscriptions which are added after the trace begins will not receive future events from that trace, only future traces will be seen. import diagnostics_channel from 'node:diagnostics_channel'; const channels = diagnostics_channel.tracingChannel('my-channel'); channels.tracePromise(async () => { // Do something }, { some: 'thing', }); ##### `tracingChannel.traceCallback(fn[, position[, context[, thisArg[, ...args]]]])`# Added in: v19.9.0, v18.19.0 * `fn` callback using function to wrap a trace around * `position` Zero-indexed argument position of expected callback (defaults to last argument if `undefined` is passed) * `context` Shared object to correlate trace events through (defaults to `{}` if `undefined` is passed) * `thisArg` The receiver to be used for the function call * `...args` arguments to pass to the function (must include the callback) * Returns: The return value of the given function Trace a callback-receiving function call. The callback is expected to follow the error as first arg convention typically used. This will always produce a `start` event and `end` event around the synchronous portion of the function execution, and will produce a `asyncStart` event and `asyncEnd` event around the callback execution. It may also produce an `error` event if the given function throws or the first argument passed to the callback is set. This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all events should have any bound stores set to match this trace context. To ensure only correct trace graphs are formed, events will only be published if subscribers are present prior to starting the trace. Subscriptions which are added after the trace begins will not receive future events from that trace, only future traces will be seen. import diagnostics_channel from 'node:diagnostics_channel'; const channels = diagnostics_channel.tracingChannel('my-channel'); channels.traceCallback((arg1, callback) => { // Do something callback(null, 'result'); }, 1, { some: 'thing', }, thisArg, arg1, callback); The callback will also be run with `channel.runStores(context, ...)` which enables context loss recovery in some cases. import diagnostics_channel from 'node:diagnostics_channel'; import { AsyncLocalStorage } from 'node:async_hooks'; const channels = diagnostics_channel.tracingChannel('my-channel'); const myStore = new AsyncLocalStorage(); // The start channel sets the initial store data to something // and stores that store data value on the trace context object channels.start.bindStore(myStore, (data) => { const span = new Span(data); data.span = span; return span; }); // Then asyncStart can restore from that data it stored previously channels.asyncStart.bindStore(myStore, (data) => { return data.span; }); ##### `tracingChannel.hasSubscribers`# Added in: v22.0.0, v20.13.0 * Returns: `true` if any of the individual channels has a subscriber, `false` if not. This is a helper method available on a `TracingChannel` instance to check if any of the TracingChannel Channels have subscribers. A `true` is returned if any of them have at least one subscriber, a `false` is returned otherwise. import diagnostics_channel from 'node:diagnostics_channel'; const channels = diagnostics_channel.tracingChannel('my-channel'); if (channels.hasSubscribers) { // Do something } #### TracingChannel Channels# A TracingChannel is a collection of several diagnostics_channels representing specific points in the execution lifecycle of a single traceable action. The behavior is split into five diagnostics_channels consisting of `start`, `end`, `asyncStart`, `asyncEnd`, and `error`. A single traceable action will share the same event object between all events, this can be helpful for managing correlation through a weakmap. These event objects will be extended with `result` or `error` values when the task "completes". In the case of a synchronous task the `result` will be the return value and the `error` will be anything thrown from the function. With callback-based async functions the `result` will be the second argument of the callback while the `error` will either be a thrown error visible in the `end` event or the first callback argument in either of the `asyncStart` or `asyncEnd` events. To ensure only correct trace graphs are formed, events should only be published if subscribers are present prior to starting the trace. Subscriptions which are added after the trace begins should not receive future events from that trace, only future traces will be seen. Tracing channels should follow a naming pattern of: * `tracing:module.class.method:start` or `tracing:module.function:start` * `tracing:module.class.method:end` or `tracing:module.function:end` * `tracing:module.class.method:asyncStart` or `tracing:module.function:asyncStart` * `tracing:module.class.method:asyncEnd` or `tracing:module.function:asyncEnd` * `tracing:module.class.method:error` or `tracing:module.function:error` ##### `start(event)`# * Name: `tracing:${name}:start` The `start` event represents the point at which a function is called. At this point the event data may contain function arguments or anything else available at the very start of the execution of the function. ##### `end(event)`# * Name: `tracing:${name}:end` The `end` event represents the point at which a function call returns a value. In the case of an async function this is when the promise returned not when the function itself makes a return statement internally. At this point, if the traced function was synchronous the `result` field will be set to the return value of the function. Alternatively, the `error` field may be present to represent any thrown errors. It is recommended to listen specifically to the `error` event to track errors as it may be possible for a traceable action to produce multiple errors. For example, an async task which fails may be started internally before the sync part of the task then throws an error. ##### `asyncStart(event)`# * Name: `tracing:${name}:asyncStart` The `asyncStart` event represents the callback or continuation of a traceable function being reached. At this point things like callback arguments may be available, or anything else expressing the "result" of the action. For callbacks-based functions, the first argument of the callback will be assigned to the `error` field, if not `undefined` or `null`, and the second argument will be assigned to the `result` field. For promises, the argument to the `resolve` path will be assigned to `result` or the argument to the `reject` path will be assign to `error`. It is recommended to listen specifically to the `error` event to track errors as it may be possible for a traceable action to produce multiple errors. For example, an async task which fails may be started internally before the sync part of the task then throws an error. ##### `asyncEnd(event)`# * Name: `tracing:${name}:asyncEnd` The `asyncEnd` event represents the callback of an asynchronous function returning. It's not likely event data will change after the `asyncStart` event, however it may be useful to see the point where the callback completes. ##### `error(event)`# * Name: `tracing:${name}:error` The `error` event represents any error produced by the traceable function either synchronously or asynchronously. If an error is thrown in the synchronous portion of the traced function the error will be assigned to the `error` field of the event and the `error` event will be triggered. If an error is received asynchronously through a callback or promise rejection it will also be assigned to the `error` field of the event and trigger the `error` event. It is possible for a single traceable function call to produce errors multiple times so this should be considered when consuming this event. For example, if another async task is triggered internally which fails and then the sync part of the function then throws and error two `error` events will be emitted, one for the sync error and one for the async error. #### Built-in Channels# ##### Console# Stability: 1 \- Experimental ###### Event: `'console.log'`# * `args` Emitted when `console.log()` is called. Receives and array of the arguments passed to `console.log()`. ###### Event: `'console.info'`# * `args` Emitted when `console.info()` is called. Receives and array of the arguments passed to `console.info()`. ###### Event: `'console.debug'`# * `args` Emitted when `console.debug()` is called. Receives and array of the arguments passed to `console.debug()`. ###### Event: `'console.warn'`# * `args` Emitted when `console.warn()` is called. Receives and array of the arguments passed to `console.warn()`. ###### Event: `'console.error'`# * `args` Emitted when `console.error()` is called. Receives and array of the arguments passed to `console.error()`. ##### HTTP# Stability: 1 \- Experimental ###### Event: `'http.client.request.created'`# * `request` Emitted when client creates a request object. Unlike `http.client.request.start`, this event is emitted before the request has been sent. ###### Event: `'http.client.request.start'`# * `request` Emitted when client starts a request. ###### Event: `'http.client.request.error'`# * `request` * `error` Emitted when an error occurs during a client request. ###### Event: `'http.client.response.finish'`# * `request` * `response` Emitted when client receives a response. ###### Event: `'http.server.request.start'`# * `request` * `response` * `socket` * `server` Emitted when server receives a request. ###### Event: `'http.server.response.created'`# * `request` * `response` Emitted when server creates a response. The event is emitted before the response is sent. ###### Event: `'http.server.response.finish'`# * `request` * `response` * `socket` * `server` Emitted when server sends a response. ##### HTTP/2# Stability: 1 \- Experimental ###### Event: `'http2.client.stream.created'`# * `stream` * `headers` Emitted when a stream is created on the client. ###### Event: `'http2.client.stream.start'`# * `stream` * `headers` Emitted when a stream is started on the client. ###### Event: `'http2.client.stream.error'`# * `stream` * `error` Emitted when an error occurs during the processing of a stream on the client. ###### Event: `'http2.client.stream.finish'`# * `stream` * `headers` * `flags` Emitted when a stream is received on the client. ###### Event: `'http2.client.stream.close'`# * `stream` Emitted when a stream is closed on the client. The HTTP/2 error code used when closing the stream can be retrieved using the `stream.rstCode` property. ###### Event: `'http2.server.stream.created'`# * `stream` * `headers` Emitted when a stream is created on the server. ###### Event: `'http2.server.stream.start'`# * `stream` * `headers` Emitted when a stream is started on the server. ###### Event: `'http2.server.stream.error'`# * `stream` * `error` Emitted when an error occurs during the processing of a stream on the server. ###### Event: `'http2.server.stream.finish'`# * `stream` * `headers` * `flags` Emitted when a stream is sent on the server. ###### Event: `'http2.server.stream.close'`# * `stream` Emitted when a stream is closed on the server. The HTTP/2 error code used when closing the stream can be retrieved using the `stream.rstCode` property. ##### Modules# Stability: 1 \- Experimental ###### Event: `'module.require.start'`# * `event` containing the following properties * `id` Argument passed to `require()`. Module name. * `parentFilename` Name of the module that attempted to require(id). Emitted when `require()` is executed. See `start` event. ###### Event: `'module.require.end'`# * `event` containing the following properties * `id` Argument passed to `require()`. Module name. * `parentFilename` Name of the module that attempted to require(id). Emitted when a `require()` call returns. See `end` event. ###### Event: `'module.require.error'`# * `event` containing the following properties * `id` Argument passed to `require()`. Module name. * `parentFilename` Name of the module that attempted to require(id). * `error` Emitted when a `require()` throws an error. See `error` event. ###### Event: `'module.import.asyncStart'`# * `event` containing the following properties * `id` Argument passed to `import()`. Module name. * `parentURL` URL object of the module that attempted to import(id). Emitted when `import()` is invoked. See `asyncStart` event. ###### Event: `'module.import.asyncEnd'`# * `event` containing the following properties * `id` Argument passed to `import()`. Module name. * `parentURL` URL object of the module that attempted to import(id). Emitted when `import()` has completed. See `asyncEnd` event. ###### Event: `'module.import.error'`# * `event` containing the following properties * `id` Argument passed to `import()`. Module name. * `parentURL` URL object of the module that attempted to import(id). * `error` Emitted when a `import()` throws an error. See `error` event. ##### NET# Stability: 1 \- Experimental ###### Event: `'net.client.socket'`# * `socket` | Emitted when a new TCP or pipe client socket connection is created. ###### Event: `'net.server.socket'`# * `socket` Emitted when a new TCP or pipe connection is received. ###### Event: `'tracing:net.server.listen:asyncStart'`# * `server` * `options` Emitted when `net.Server.listen()` is invoked, before the port or pipe is actually setup. ###### Event: `'tracing:net.server.listen:asyncEnd'`# * `server` Emitted when `net.Server.listen()` has completed and thus the server is ready to accept connection. ###### Event: `'tracing:net.server.listen:error'`# * `server` * `error` Emitted when `net.Server.listen()` is returning an error. ##### UDP# Stability: 1 \- Experimental ###### Event: `'udp.socket'`# * `socket` Emitted when a new UDP socket is created. ##### Process# Stability: 1 \- Experimental Added in: v16.18.0 ###### Event: `'child_process'`# * `process` Emitted when a new process is created. ###### Event: `'execve'`# * `execPath` * `args` * `env` Emitted when `process.execve()` is invoked. ##### Worker Thread# Stability: 1 \- Experimental Added in: v16.18.0 ###### Event: `'worker_threads'`# * `worker` Emitted when a new thread is created. ## DNS# Stability: 2 \- Stable Source Code: lib/dns.js The `node:dns` module enables name resolution. For example, use it to look up IP addresses of host names. Although named for the Domain Name System (DNS), it does not always use the DNS protocol for lookups. `dns.lookup()` uses the operating system facilities to perform name resolution. It may not need to perform any network communication. To perform name resolution the way other applications on the same system do, use `dns.lookup()`. import dns from 'node:dns'; dns.lookup('example.org', (err, address, family) => { console.log('address: %j family: IPv%s', address, family); }); // address: "2606:2800:21f:cb07:6820:80da:af6b:8b2c" family: IPv6 All other functions in the `node:dns` module connect to an actual DNS server to perform name resolution. They will always use the network to perform DNS queries. These functions do not use the same set of configuration files used by `dns.lookup()` (e.g. `/etc/hosts`). Use these functions to always perform DNS queries, bypassing other name-resolution facilities. import dns from 'node:dns'; dns.resolve4('archive.org', (err, addresses) => { if (err) throw err; console.log(`addresses: ${JSON.stringify(addresses)}`); addresses.forEach((a) => { dns.reverse(a, (err, hostnames) => { if (err) { throw err; } console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`); }); }); }); See the Implementation considerations section for more information. ### Class: `dns.Resolver`# Added in: v8.3.0 An independent resolver for DNS requests. Creating a new resolver uses the default server settings. Setting the servers used for a resolver using `resolver.setServers()` does not affect other resolvers: import { Resolver } from 'node:dns'; const resolver = new Resolver(); resolver.setServers(['4.4.4.4']); // This request will use the server at 4.4.4.4, independent of global settings. resolver.resolve4('example.org', (err, addresses) => { // ... }); The following methods from the `node:dns` module are available: * `resolver.getServers()` * `resolver.resolve()` * `resolver.resolve4()` * `resolver.resolve6()` * `resolver.resolveAny()` * `resolver.resolveCaa()` * `resolver.resolveCname()` * `resolver.resolveMx()` * `resolver.resolveNaptr()` * `resolver.resolveNs()` * `resolver.resolvePtr()` * `resolver.resolveSoa()` * `resolver.resolveSrv()` * `resolver.resolveTlsa()` * `resolver.resolveTxt()` * `resolver.reverse()` * `resolver.setServers()` #### `Resolver([options])`# History VersionChanges v16.7.0, v14.18.0 The `options` object now accepts a `tries` option. v12.18.3 The constructor now accepts an `options` object. The single supported option is `timeout`. v8.3.0 Added in: v8.3.0 Create a new resolver. * `options` * `timeout` Query timeout in milliseconds, or `-1` to use the default timeout. * `tries` The number of tries the resolver will try contacting each name server before giving up. Default: `4` * `maxTimeout` The max retry timeout, in milliseconds. Default: `0`, disabled. #### `resolver.cancel()`# Added in: v8.3.0 Cancel all outstanding DNS queries made by this resolver. The corresponding callbacks will be called with an error with code `ECANCELLED`. #### `resolver.setLocalAddress([ipv4][, ipv6])`# Added in: v15.1.0, v14.17.0 * `ipv4` A string representation of an IPv4 address. Default: `'0.0.0.0'` * `ipv6` A string representation of an IPv6 address. Default: `'::0'` The resolver instance will send its requests from the specified IP address. This allows programs to specify outbound interfaces when used on multi-homed systems. If a v4 or v6 address is not specified, it is set to the default and the operating system will choose a local address automatically. The resolver will use the v4 local address when making requests to IPv4 DNS servers, and the v6 local address when making requests to IPv6 DNS servers. The `rrtype` of resolution requests has no impact on the local address used. ### `dns.getServers()`# Added in: v0.11.3 * Returns: Returns an array of IP address strings, formatted according to RFC 5952, that are currently configured for DNS resolution. A string will include a port section if a custom port is used. [ '8.8.8.8', '2001:4860:4860::8888', '8.8.8.8:1053', '[2001:4860:4860::8888]:1053', ] ### `dns.lookup(hostname[, options], callback)`# History VersionChanges v22.1.0, v20.13.0 The `verbatim` option is now deprecated in favor of the new `order` option. v18.4.0 For compatibility with `node:net`, when passing an option object the `family` option can be the string `'IPv4'` or the string `'IPv6'`. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v17.0.0 The `verbatim` options defaults to `true` now. v8.5.0 The `verbatim` option is supported now. v1.2.0 The `all` option is supported now. v0.1.90 Added in: v0.1.90 * `hostname` * `options` | * `family` | The record family. Must be `4`, `6`, or `0`. For backward compatibility reasons,`'IPv4'` and `'IPv6'` are interpreted as `4` and `6` respectively. The value `0` indicates that either an IPv4 or IPv6 address is returned. If the value `0` is used with `{ all: true }` (see below), either one of or both IPv4 and IPv6 addresses are returned, depending on the system's DNS resolver. Default: `0`. * `hints` One or more supported `getaddrinfo` flags. Multiple flags may be passed by bitwise `OR`ing their values. * `all` When `true`, the callback returns all resolved addresses in an array. Otherwise, returns a single address. Default: `false`. * `order` When `verbatim`, the resolved addresses are return unsorted. When `ipv4first`, the resolved addresses are sorted by placing IPv4 addresses before IPv6 addresses. When `ipv6first`, the resolved addresses are sorted by placing IPv6 addresses before IPv4 addresses. Default: `verbatim` (addresses are not reordered). Default value is configurable using `dns.setDefaultResultOrder()` or `--dns-result-order`. * `verbatim` When `true`, the callback receives IPv4 and IPv6 addresses in the order the DNS resolver returned them. When `false`, IPv4 addresses are placed before IPv6 addresses. This option will be deprecated in favor of `order`. When both are specified, `order` has higher precedence. New code should only use `order`. Default: `true` (addresses are not reordered). Default value is configurable using `dns.setDefaultResultOrder()` or `--dns-result-order`. * `callback` * `err` * `address` A string representation of an IPv4 or IPv6 address. * `family` `4` or `6`, denoting the family of `address`, or `0` if the address is not an IPv4 or IPv6 address. `0` is a likely indicator of a bug in the name resolution service used by the operating system. Resolves a host name (e.g. `'nodejs.org'`) into the first found A (IPv4) or AAAA (IPv6) record. All `option` properties are optional. If `options` is an integer, then it must be `4` or `6` – if `options` is not provided, then either IPv4 or IPv6 addresses, or both, are returned if found. With the `all` option set to `true`, the arguments for `callback` change to `(err, addresses)`, with `addresses` being an array of objects with the properties `address` and `family`. On error, `err` is an `Error` object, where `err.code` is the error code. Keep in mind that `err.code` will be set to `'ENOTFOUND'` not only when the host name does not exist but also when the lookup fails in other ways such as no available file descriptors. `dns.lookup()` does not necessarily have anything to do with the DNS protocol. The implementation uses an operating system facility that can associate names with addresses and vice versa. This implementation can have subtle but important consequences on the behavior of any Node.js program. Please take some time to consult the Implementation considerations section before using `dns.lookup()`. Example usage: import dns from 'node:dns'; const options = { family: 6, hints: dns.ADDRCONFIG | dns.V4MAPPED, }; dns.lookup('example.org', options, (err, address, family) => console.log('address: %j family: IPv%s', address, family)); // address: "2606:2800:21f:cb07:6820:80da:af6b:8b2c" family: IPv6 // When options.all is true, the result will be an Array. options.all = true; dns.lookup('example.org', options, (err, addresses) => console.log('addresses: %j', addresses)); // addresses: [{"address":"2606:2800:21f:cb07:6820:80da:af6b:8b2c","family":6}] If this method is invoked as its `util.promisify()`ed version, and `all` is not set to `true`, it returns a `Promise` for an `Object` with `address` and `family` properties. #### Supported getaddrinfo flags# History VersionChanges v13.13.0, v12.17.0 Added support for the `dns.ALL` flag. The following flags can be passed as hints to `dns.lookup()`. * `dns.ADDRCONFIG`: Limits returned address types to the types of non-loopback addresses configured on the system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured. * `dns.V4MAPPED`: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. It is not supported on some operating systems (e.g. FreeBSD 10.1). * `dns.ALL`: If `dns.V4MAPPED` is specified, return resolved IPv6 addresses as well as IPv4 mapped IPv6 addresses. ### `dns.lookupService(address, port, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.11.14 Added in: v0.11.14 * `address` * `port` * `callback` * `err` * `hostname` e.g. `example.com` * `service` e.g. `http` Resolves the given `address` and `port` into a host name and service using the operating system's underlying `getnameinfo` implementation. If `address` is not a valid IP address, a `TypeError` will be thrown. The `port` will be coerced to a number. If it is not a legal port, a `TypeError` will be thrown. On an error, `err` is an `Error` object, where `err.code` is the error code. import dns from 'node:dns'; dns.lookupService('127.0.0.1', 22, (err, hostname, service) => { console.log(hostname, service); // Prints: localhost ssh }); If this method is invoked as its `util.promisify()`ed version, it returns a `Promise` for an `Object` with `hostname` and `service` properties. ### `dns.resolve(hostname[, rrtype], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.1.27 Added in: v0.1.27 * `hostname` Host name to resolve. * `rrtype` Resource record type. Default: `'A'`. * `callback` * `err` * `records` | | Uses the DNS protocol to resolve a host name (e.g. `'nodejs.org'`) into an array of the resource records. The `callback` function has arguments `(err, records)`. When successful, `records` will be an array of resource records. The type and structure of individual results varies based on `rrtype`: `rrtype``records` containsResult typeShorthand method `'A'`IPv4 addresses (default)`dns.resolve4()` `'AAAA'`IPv6 addresses`dns.resolve6()` `'ANY'`any records`dns.resolveAny()` `'CAA'`CA authorization records`dns.resolveCaa()` `'CNAME'`canonical name records`dns.resolveCname()` `'MX'`mail exchange records`dns.resolveMx()` `'NAPTR'`name authority pointer records`dns.resolveNaptr()` `'NS'`name server records`dns.resolveNs()` `'PTR'`pointer records`dns.resolvePtr()` `'SOA'`start of authority records`dns.resolveSoa()` `'SRV'`service records`dns.resolveSrv()` `'TLSA'`certificate associations`dns.resolveTlsa()` `'TXT'`text records`dns.resolveTxt()` On error, `err` is an `Error` object, where `err.code` is one of the DNS error codes. ### `dns.resolve4(hostname[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v7.2.0 This method now supports passing `options`, specifically `options.ttl`. v0.1.16 Added in: v0.1.16 * `hostname` Host name to resolve. * `options` * `ttl` Retrieves the Time-To-Live value (TTL) of each record. When `true`, the callback receives an array of `{ address: '1.2.3.4', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds. * `callback` * `err` * `addresses` | Uses the DNS protocol to resolve a IPv4 addresses (`A` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of IPv4 addresses (e.g. `['74.125.79.104', '74.125.79.105', '74.125.79.106']`). ### `dns.resolve6(hostname[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v7.2.0 This method now supports passing `options`, specifically `options.ttl`. v0.1.16 Added in: v0.1.16 * `hostname` Host name to resolve. * `options` * `ttl` Retrieve the Time-To-Live value (TTL) of each record. When `true`, the callback receives an array of `{ address: '0:1:2:3:4:5:6:7', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds. * `callback` * `err` * `addresses` | Uses the DNS protocol to resolve IPv6 addresses (`AAAA` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of IPv6 addresses. ### `dns.resolveAny(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. * `hostname` * `callback` * `err` * `ret` Uses the DNS protocol to resolve all records (also known as `ANY` or `*` query). The `ret` argument passed to the `callback` function will be an array containing various types of records. Each object has a property `type` that indicates the type of the current record. And depending on the `type`, additional properties will be present on the object: TypeProperties `'A'``address`/`ttl` `'AAAA'``address`/`ttl` `'CNAME'``value` `'MX'`Refer to `dns.resolveMx()` `'NAPTR'`Refer to `dns.resolveNaptr()` `'NS'``value` `'PTR'``value` `'SOA'`Refer to `dns.resolveSoa()` `'SRV'`Refer to `dns.resolveSrv()` `'TLSA'`Refer to `dns.resolveTlsa()` `'TXT'`This type of record contains an array property called `entries` which refers to `dns.resolveTxt()`, e.g. `{ entries: ['...'], type: 'TXT' }` Here is an example of the `ret` object passed to the callback: [ { type: 'A', address: '127.0.0.1', ttl: 299 }, { type: 'CNAME', value: 'example.com' }, { type: 'MX', exchange: 'alt4.aspmx.l.example.com', priority: 50 }, { type: 'NS', value: 'ns1.example.com' }, { type: 'TXT', entries: [ 'v=spf1 include:_spf.example.com ~all' ] }, { type: 'SOA', nsname: 'ns1.example.com', hostmaster: 'admin.example.com', serial: 156696742, refresh: 900, retry: 900, expire: 1800, minttl: 60 } ] DNS server operators may choose not to respond to `ANY` queries. It may be better to call individual methods like `dns.resolve4()`, `dns.resolveMx()`, and so on. For more details, see RFC 8482. ### `dns.resolveCname(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.3.2 Added in: v0.3.2 * `hostname` * `callback` * `err` * `addresses` Uses the DNS protocol to resolve `CNAME` records for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of canonical name records available for the `hostname` (e.g. `['bar.example.com']`). ### `dns.resolveCaa(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.0.0, v14.17.0 Added in: v15.0.0, v14.17.0 * `hostname` * `callback` * `err` * `records` Uses the DNS protocol to resolve `CAA` records for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of certification authority authorization records available for the `hostname` (e.g. `[{critical: 0, iodef: 'mailto:[email protected]'}, {critical: 128, issue: 'pki.example.com'}]`). ### `dns.resolveMx(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.1.27 Added in: v0.1.27 * `hostname` * `callback` * `err` * `addresses` Uses the DNS protocol to resolve mail exchange records (`MX` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of objects containing both a `priority` and `exchange` property (e.g. `[{priority: 10, exchange: 'mx.example.com'}, ...]`). ### `dns.resolveNaptr(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.9.12 Added in: v0.9.12 * `hostname` * `callback` * `err` * `addresses` Uses the DNS protocol to resolve regular expression-based records (`NAPTR` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of objects with the following properties: * `flags` * `service` * `regexp` * `replacement` * `order` * `preference` { flags: 's', service: 'SIP+D2U', regexp: '', replacement: '_sip._udp.example.com', order: 30, preference: 100 } ### `dns.resolveNs(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.1.90 Added in: v0.1.90 * `hostname` * `callback` * `err` * `addresses` Uses the DNS protocol to resolve name server records (`NS` records) for the `hostname`. The `addresses` argument passed to the `callback` function will contain an array of name server records available for `hostname` (e.g. `['ns1.example.com', 'ns2.example.com']`). ### `dns.resolvePtr(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v6.0.0 Added in: v6.0.0 * `hostname` * `callback` * `err` * `addresses` Uses the DNS protocol to resolve pointer records (`PTR` records) for the `hostname`. The `addresses` argument passed to the `callback` function will be an array of strings containing the reply records. ### `dns.resolveSoa(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.11.10 Added in: v0.11.10 * `hostname` * `callback` * `err` * `address` Uses the DNS protocol to resolve a start of authority record (`SOA` record) for the `hostname`. The `address` argument passed to the `callback` function will be an object with the following properties: * `nsname` * `hostmaster` * `serial` * `refresh` * `retry` * `expire` * `minttl` { nsname: 'ns.example.com', hostmaster: 'root.example.com', serial: 2013101809, refresh: 10000, retry: 2400, expire: 604800, minttl: 3600 } ### `dns.resolveSrv(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.1.27 Added in: v0.1.27 * `hostname` * `callback` * `err` * `addresses` Uses the DNS protocol to resolve service records (`SRV` records) for the `hostname`. The `addresses` argument passed to the `callback` function will be an array of objects with the following properties: * `priority` * `weight` * `port` * `name` { priority: 10, weight: 5, port: 21223, name: 'service.example.com' } ### `dns.resolveTlsa(hostname, callback)`# Added in: v23.9.0, v22.15.0 * `hostname` * `callback` * `err` * `records` Uses the DNS protocol to resolve certificate associations (`TLSA` records) for the `hostname`. The `records` argument passed to the `callback` function is an array of objects with these properties: * `certUsage` * `selector` * `match` * `data` { certUsage: 3, selector: 1, match: 1, data: [ArrayBuffer] } ### `dns.resolveTxt(hostname, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.1.27 Added in: v0.1.27 * `hostname` * `callback` * `err` * `records` Uses the DNS protocol to resolve text queries (`TXT` records) for the `hostname`. The `records` argument passed to the `callback` function is a two-dimensional array of the text records available for `hostname` (e.g. `[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]`). Each sub-array contains TXT chunks of one record. Depending on the use case, these could be either joined together or treated separately. ### `dns.reverse(ip, callback)`# Added in: v0.1.16 * `ip` * `callback` * `err` * `hostnames` Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of host names. On error, `err` is an `Error` object, where `err.code` is one of the DNS error codes. ### `dns.setDefaultResultOrder(order)`# History VersionChanges v22.1.0, v20.13.0 The `ipv6first` value is supported now. v17.0.0 Changed default value to `verbatim`. v16.4.0, v14.18.0 Added in: v16.4.0, v14.18.0 * `order` must be `'ipv4first'`, `'ipv6first'` or `'verbatim'`. Set the default value of `order` in `dns.lookup()` and `dnsPromises.lookup()`. The value could be: * `ipv4first`: sets default `order` to `ipv4first`. * `ipv6first`: sets default `order` to `ipv6first`. * `verbatim`: sets default `order` to `verbatim`. The default is `verbatim` and `dns.setDefaultResultOrder()` have higher priority than `--dns-result-order`. When using worker threads, `dns.setDefaultResultOrder()` from the main thread won't affect the default dns orders in workers. ### `dns.getDefaultResultOrder()`# History VersionChanges v22.1.0, v20.13.0 The `ipv6first` value is supported now. v20.1.0, v18.17.0 Added in: v20.1.0, v18.17.0 Get the default value for `order` in `dns.lookup()` and `dnsPromises.lookup()`. The value could be: * `ipv4first`: for `order` defaulting to `ipv4first`. * `ipv6first`: for `order` defaulting to `ipv6first`. * `verbatim`: for `order` defaulting to `verbatim`. ### `dns.setServers(servers)`# Added in: v0.11.3 * `servers` array of RFC 5952 formatted addresses Sets the IP address and port of servers to be used when performing DNS resolution. The `servers` argument is an array of RFC 5952 formatted addresses. If the port is the IANA default DNS port (53) it can be omitted. dns.setServers([ '8.8.8.8', '[2001:4860:4860::8888]', '8.8.8.8:1053', '[2001:4860:4860::8888]:1053', ]); An error will be thrown if an invalid address is provided. The `dns.setServers()` method must not be called while a DNS query is in progress. The `dns.setServers()` method affects only `dns.resolve()`, `dns.resolve*()` and `dns.reverse()` (and specifically not `dns.lookup()`). This method works much like resolve.conf. That is, if attempting to resolve with the first server provided results in a `NOTFOUND` error, the `resolve()` method will not attempt to resolve with subsequent servers provided. Fallback DNS servers will only be used if the earlier ones time out or result in some other error. ### DNS promises API# History VersionChanges v15.0.0 Exposed as `require('dns/promises')`. v11.14.0, v10.17.0 This API is no longer experimental. v10.6.0 Added in: v10.6.0 The `dns.promises` API provides an alternative set of asynchronous DNS methods that return `Promise` objects rather than using callbacks. The API is accessible via `require('node:dns').promises` or `require('node:dns/promises')`. #### Class: `dnsPromises.Resolver`# Added in: v10.6.0 An independent resolver for DNS requests. Creating a new resolver uses the default server settings. Setting the servers used for a resolver using `resolver.setServers()` does not affect other resolvers: import { Resolver } from 'node:dns/promises'; const resolver = new Resolver(); resolver.setServers(['4.4.4.4']); // This request will use the server at 4.4.4.4, independent of global settings. const addresses = await resolver.resolve4('example.org'); The following methods from the `dnsPromises` API are available: * `resolver.getServers()` * `resolver.resolve()` * `resolver.resolve4()` * `resolver.resolve6()` * `resolver.resolveAny()` * `resolver.resolveCaa()` * `resolver.resolveCname()` * `resolver.resolveMx()` * `resolver.resolveNaptr()` * `resolver.resolveNs()` * `resolver.resolvePtr()` * `resolver.resolveSoa()` * `resolver.resolveSrv()` * `resolver.resolveTlsa()` * `resolver.resolveTxt()` * `resolver.reverse()` * `resolver.setServers()` #### `resolver.cancel()`# Added in: v15.3.0, v14.17.0 Cancel all outstanding DNS queries made by this resolver. The corresponding promises will be rejected with an error with the code `ECANCELLED`. #### `dnsPromises.getServers()`# Added in: v10.6.0 * Returns: Returns an array of IP address strings, formatted according to RFC 5952, that are currently configured for DNS resolution. A string will include a port section if a custom port is used. [ '8.8.8.8', '2001:4860:4860::8888', '8.8.8.8:1053', '[2001:4860:4860::8888]:1053', ] #### `dnsPromises.lookup(hostname[, options])`# History VersionChanges v22.1.0, v20.13.0 The `verbatim` option is now deprecated in favor of the new `order` option. v10.6.0 Added in: v10.6.0 * `hostname` * `options` | * `family` The record family. Must be `4`, `6`, or `0`. The value `0` indicates that either an IPv4 or IPv6 address is returned. If the value `0` is used with `{ all: true }` (see below), either one of or both IPv4 and IPv6 addresses are returned, depending on the system's DNS resolver. Default: `0`. * `hints` One or more supported `getaddrinfo` flags. Multiple flags may be passed by bitwise `OR`ing their values. * `all` When `true`, the `Promise` is resolved with all addresses in an array. Otherwise, returns a single address. Default: `false`. * `order` When `verbatim`, the `Promise` is resolved with IPv4 and IPv6 addresses in the order the DNS resolver returned them. When `ipv4first`, IPv4 addresses are placed before IPv6 addresses. When `ipv6first`, IPv6 addresses are placed before IPv4 addresses. Default: `verbatim` (addresses are not reordered). Default value is configurable using `dns.setDefaultResultOrder()` or `--dns-result-order`. New code should use `{ order: 'verbatim' }`. * `verbatim` When `true`, the `Promise` is resolved with IPv4 and IPv6 addresses in the order the DNS resolver returned them. When `false`, IPv4 addresses are placed before IPv6 addresses. This option will be deprecated in favor of `order`. When both are specified, `order` has higher precedence. New code should only use `order`. Default: currently `false` (addresses are reordered) but this is expected to change in the not too distant future. Default value is configurable using `dns.setDefaultResultOrder()` or `--dns-result-order`. Resolves a host name (e.g. `'nodejs.org'`) into the first found A (IPv4) or AAAA (IPv6) record. All `option` properties are optional. If `options` is an integer, then it must be `4` or `6` – if `options` is not provided, then either IPv4 or IPv6 addresses, or both, are returned if found. With the `all` option set to `true`, the `Promise` is resolved with `addresses` being an array of objects with the properties `address` and `family`. On error, the `Promise` is rejected with an `Error` object, where `err.code` is the error code. Keep in mind that `err.code` will be set to `'ENOTFOUND'` not only when the host name does not exist but also when the lookup fails in other ways such as no available file descriptors. `dnsPromises.lookup()` does not necessarily have anything to do with the DNS protocol. The implementation uses an operating system facility that can associate names with addresses and vice versa. This implementation can have subtle but important consequences on the behavior of any Node.js program. Please take some time to consult the Implementation considerations section before using `dnsPromises.lookup()`. Example usage: import dns from 'node:dns'; const dnsPromises = dns.promises; const options = { family: 6, hints: dns.ADDRCONFIG | dns.V4MAPPED, }; await dnsPromises.lookup('example.org', options).then((result) => { console.log('address: %j family: IPv%s', result.address, result.family); // address: "2606:2800:21f:cb07:6820:80da:af6b:8b2c" family: IPv6 }); // When options.all is true, the result will be an Array. options.all = true; await dnsPromises.lookup('example.org', options).then((result) => { console.log('addresses: %j', result); // addresses: [{"address":"2606:2800:21f:cb07:6820:80da:af6b:8b2c","family":6}] }); #### `dnsPromises.lookupService(address, port)`# Added in: v10.6.0 * `address` * `port` Resolves the given `address` and `port` into a host name and service using the operating system's underlying `getnameinfo` implementation. If `address` is not a valid IP address, a `TypeError` will be thrown. The `port` will be coerced to a number. If it is not a legal port, a `TypeError` will be thrown. On error, the `Promise` is rejected with an `Error` object, where `err.code` is the error code. import dnsPromises from 'node:dns/promises'; const result = await dnsPromises.lookupService('127.0.0.1', 22); console.log(result.hostname, result.service); // Prints: localhost ssh #### `dnsPromises.resolve(hostname[, rrtype])`# Added in: v10.6.0 * `hostname` Host name to resolve. * `rrtype` Resource record type. Default: `'A'`. Uses the DNS protocol to resolve a host name (e.g. `'nodejs.org'`) into an array of the resource records. When successful, the `Promise` is resolved with an array of resource records. The type and structure of individual results vary based on `rrtype`: `rrtype``records` containsResult typeShorthand method `'A'`IPv4 addresses (default)`dnsPromises.resolve4()` `'AAAA'`IPv6 addresses`dnsPromises.resolve6()` `'ANY'`any records`dnsPromises.resolveAny()` `'CAA'`CA authorization records`dnsPromises.resolveCaa()` `'CNAME'`canonical name records`dnsPromises.resolveCname()` `'MX'`mail exchange records`dnsPromises.resolveMx()` `'NAPTR'`name authority pointer records`dnsPromises.resolveNaptr()` `'NS'`name server records`dnsPromises.resolveNs()` `'PTR'`pointer records`dnsPromises.resolvePtr()` `'SOA'`start of authority records`dnsPromises.resolveSoa()` `'SRV'`service records`dnsPromises.resolveSrv()` `'TLSA'`certificate associations`dnsPromises.resolveTlsa()` `'TXT'`text records`dnsPromises.resolveTxt()` On error, the `Promise` is rejected with an `Error` object, where `err.code` is one of the DNS error codes. #### `dnsPromises.resolve4(hostname[, options])`# Added in: v10.6.0 * `hostname` Host name to resolve. * `options` * `ttl` Retrieve the Time-To-Live value (TTL) of each record. When `true`, the `Promise` is resolved with an array of `{ address: '1.2.3.4', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds. Uses the DNS protocol to resolve IPv4 addresses (`A` records) for the `hostname`. On success, the `Promise` is resolved with an array of IPv4 addresses (e.g. `['74.125.79.104', '74.125.79.105', '74.125.79.106']`). #### `dnsPromises.resolve6(hostname[, options])`# Added in: v10.6.0 * `hostname` Host name to resolve. * `options` * `ttl` Retrieve the Time-To-Live value (TTL) of each record. When `true`, the `Promise` is resolved with an array of `{ address: '0:1:2:3:4:5:6:7', ttl: 60 }` objects rather than an array of strings, with the TTL expressed in seconds. Uses the DNS protocol to resolve IPv6 addresses (`AAAA` records) for the `hostname`. On success, the `Promise` is resolved with an array of IPv6 addresses. #### `dnsPromises.resolveAny(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve all records (also known as `ANY` or `*` query). On success, the `Promise` is resolved with an array containing various types of records. Each object has a property `type` that indicates the type of the current record. And depending on the `type`, additional properties will be present on the object: TypeProperties `'A'``address`/`ttl` `'AAAA'``address`/`ttl` `'CNAME'``value` `'MX'`Refer to `dnsPromises.resolveMx()` `'NAPTR'`Refer to `dnsPromises.resolveNaptr()` `'NS'``value` `'PTR'``value` `'SOA'`Refer to `dnsPromises.resolveSoa()` `'SRV'`Refer to `dnsPromises.resolveSrv()` `'TLSA'`Refer to `dnsPromises.resolveTlsa()` `'TXT'`This type of record contains an array property called `entries` which refers to `dnsPromises.resolveTxt()`, e.g. `{ entries: ['...'], type: 'TXT' }` Here is an example of the result object: [ { type: 'A', address: '127.0.0.1', ttl: 299 }, { type: 'CNAME', value: 'example.com' }, { type: 'MX', exchange: 'alt4.aspmx.l.example.com', priority: 50 }, { type: 'NS', value: 'ns1.example.com' }, { type: 'TXT', entries: [ 'v=spf1 include:_spf.example.com ~all' ] }, { type: 'SOA', nsname: 'ns1.example.com', hostmaster: 'admin.example.com', serial: 156696742, refresh: 900, retry: 900, expire: 1800, minttl: 60 } ] #### `dnsPromises.resolveCaa(hostname)`# Added in: v15.0.0, v14.17.0 * `hostname` Uses the DNS protocol to resolve `CAA` records for the `hostname`. On success, the `Promise` is resolved with an array of objects containing available certification authority authorization records available for the `hostname` (e.g. `[{critical: 0, iodef: 'mailto:[email protected]'},{critical: 128, issue: 'pki.example.com'}]`). #### `dnsPromises.resolveCname(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve `CNAME` records for the `hostname`. On success, the `Promise` is resolved with an array of canonical name records available for the `hostname` (e.g. `['bar.example.com']`). #### `dnsPromises.resolveMx(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve mail exchange records (`MX` records) for the `hostname`. On success, the `Promise` is resolved with an array of objects containing both a `priority` and `exchange` property (e.g. `[{priority: 10, exchange: 'mx.example.com'}, ...]`). #### `dnsPromises.resolveNaptr(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve regular expression-based records (`NAPTR` records) for the `hostname`. On success, the `Promise` is resolved with an array of objects with the following properties: * `flags` * `service` * `regexp` * `replacement` * `order` * `preference` { flags: 's', service: 'SIP+D2U', regexp: '', replacement: '_sip._udp.example.com', order: 30, preference: 100 } #### `dnsPromises.resolveNs(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve name server records (`NS` records) for the `hostname`. On success, the `Promise` is resolved with an array of name server records available for `hostname` (e.g. `['ns1.example.com', 'ns2.example.com']`). #### `dnsPromises.resolvePtr(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve pointer records (`PTR` records) for the `hostname`. On success, the `Promise` is resolved with an array of strings containing the reply records. #### `dnsPromises.resolveSoa(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve a start of authority record (`SOA` record) for the `hostname`. On success, the `Promise` is resolved with an object with the following properties: * `nsname` * `hostmaster` * `serial` * `refresh` * `retry` * `expire` * `minttl` { nsname: 'ns.example.com', hostmaster: 'root.example.com', serial: 2013101809, refresh: 10000, retry: 2400, expire: 604800, minttl: 3600 } #### `dnsPromises.resolveSrv(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve service records (`SRV` records) for the `hostname`. On success, the `Promise` is resolved with an array of objects with the following properties: * `priority` * `weight` * `port` * `name` { priority: 10, weight: 5, port: 21223, name: 'service.example.com' } #### `dnsPromises.resolveTlsa(hostname)`# Added in: v23.9.0, v22.15.0 * `hostname` Uses the DNS protocol to resolve certificate associations (`TLSA` records) for the `hostname`. On success, the `Promise` is resolved with an array of objects with these properties: * `certUsage` * `selector` * `match` * `data` { certUsage: 3, selector: 1, match: 1, data: [ArrayBuffer] } #### `dnsPromises.resolveTxt(hostname)`# Added in: v10.6.0 * `hostname` Uses the DNS protocol to resolve text queries (`TXT` records) for the `hostname`. On success, the `Promise` is resolved with a two-dimensional array of the text records available for `hostname` (e.g. `[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]`). Each sub-array contains TXT chunks of one record. Depending on the use case, these could be either joined together or treated separately. #### `dnsPromises.reverse(ip)`# Added in: v10.6.0 * `ip` Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of host names. On error, the `Promise` is rejected with an `Error` object, where `err.code` is one of the DNS error codes. #### `dnsPromises.setDefaultResultOrder(order)`# History VersionChanges v22.1.0, v20.13.0 The `ipv6first` value is supported now. v17.0.0 Changed default value to `verbatim`. v16.4.0, v14.18.0 Added in: v16.4.0, v14.18.0 * `order` must be `'ipv4first'`, `'ipv6first'` or `'verbatim'`. Set the default value of `order` in `dns.lookup()` and `dnsPromises.lookup()`. The value could be: * `ipv4first`: sets default `order` to `ipv4first`. * `ipv6first`: sets default `order` to `ipv6first`. * `verbatim`: sets default `order` to `verbatim`. The default is `verbatim` and `dnsPromises.setDefaultResultOrder()` have higher priority than `--dns-result-order`. When using worker threads, `dnsPromises.setDefaultResultOrder()` from the main thread won't affect the default dns orders in workers. #### `dnsPromises.getDefaultResultOrder()`# Added in: v20.1.0, v18.17.0 Get the value of `dnsOrder`. #### `dnsPromises.setServers(servers)`# Added in: v10.6.0 * `servers` array of RFC 5952 formatted addresses Sets the IP address and port of servers to be used when performing DNS resolution. The `servers` argument is an array of RFC 5952 formatted addresses. If the port is the IANA default DNS port (53) it can be omitted. dnsPromises.setServers([ '8.8.8.8', '[2001:4860:4860::8888]', '8.8.8.8:1053', '[2001:4860:4860::8888]:1053', ]); An error will be thrown if an invalid address is provided. The `dnsPromises.setServers()` method must not be called while a DNS query is in progress. This method works much like resolve.conf. That is, if attempting to resolve with the first server provided results in a `NOTFOUND` error, the `resolve()` method will not attempt to resolve with subsequent servers provided. Fallback DNS servers will only be used if the earlier ones time out or result in some other error. ### Error codes# Each DNS query can return one of the following error codes: * `dns.NODATA`: DNS server returned an answer with no data. * `dns.FORMERR`: DNS server claims query was misformatted. * `dns.SERVFAIL`: DNS server returned general failure. * `dns.NOTFOUND`: Domain name not found. * `dns.NOTIMP`: DNS server does not implement the requested operation. * `dns.REFUSED`: DNS server refused query. * `dns.BADQUERY`: Misformatted DNS query. * `dns.BADNAME`: Misformatted host name. * `dns.BADFAMILY`: Unsupported address family. * `dns.BADRESP`: Misformatted DNS reply. * `dns.CONNREFUSED`: Could not contact DNS servers. * `dns.TIMEOUT`: Timeout while contacting DNS servers. * `dns.EOF`: End of file. * `dns.FILE`: Error reading file. * `dns.NOMEM`: Out of memory. * `dns.DESTRUCTION`: Channel is being destroyed. * `dns.BADSTR`: Misformatted string. * `dns.BADFLAGS`: Illegal flags specified. * `dns.NONAME`: Given host name is not numeric. * `dns.BADHINTS`: Illegal hints flags specified. * `dns.NOTINITIALIZED`: c-ares library initialization not yet performed. * `dns.LOADIPHLPAPI`: Error loading `iphlpapi.dll`. * `dns.ADDRGETNETWORKPARAMS`: Could not find `GetNetworkParams` function. * `dns.CANCELLED`: DNS query cancelled. The `dnsPromises` API also exports the above error codes, e.g., `dnsPromises.NODATA`. ### Implementation considerations# Although `dns.lookup()` and the various `dns.resolve*()/dns.reverse()` functions have the same goal of associating a network name with a network address (or vice versa), their behavior is quite different. These differences can have subtle but significant consequences on the behavior of Node.js programs. #### `dns.lookup()`# Under the hood, `dns.lookup()` uses the same operating system facilities as most other programs. For instance, `dns.lookup()` will almost always resolve a given name the same way as the `ping` command. On most POSIX-like operating systems, the behavior of the `dns.lookup()` function can be modified by changing settings in `nsswitch.conf(5)` and/or `resolv.conf(5)`, but changing these files will change the behavior of all other programs running on the same operating system. Though the call to `dns.lookup()` will be asynchronous from JavaScript's perspective, it is implemented as a synchronous call to `getaddrinfo(3)` that runs on libuv's threadpool. This can have surprising negative performance implications for some applications, see the `UV_THREADPOOL_SIZE` documentation for more information. Various networking APIs will call `dns.lookup()` internally to resolve host names. If that is an issue, consider resolving the host name to an address using `dns.resolve()` and using the address instead of a host name. Also, some networking APIs (such as `socket.connect()` and `dgram.createSocket()`) allow the default resolver, `dns.lookup()`, to be replaced. #### `dns.resolve()`, `dns.resolve*()`, and `dns.reverse()`# These functions are implemented quite differently than `dns.lookup()`. They do not use `getaddrinfo(3)` and they always perform a DNS query on the network. This network communication is always done asynchronously and does not use libuv's threadpool. As a result, these functions cannot have the same negative impact on other processing that happens on libuv's threadpool that `dns.lookup()` can have. They do not use the same set of configuration files that `dns.lookup()` uses. For instance, they do not use the configuration from `/etc/hosts`. ## Domain# History VersionChanges v8.8.0 Any `Promise`s created in VM contexts no longer have a `.domain` property. Their handlers are still executed in the proper domain, however, and `Promise`s created in the main context still possess a `.domain` property. v8.0.0 Handlers for `Promise`s are now invoked in the domain in which the first promise of a chain was created. v1.4.2 Deprecated since: v1.4.2 Stability: 0 \- Deprecated Source Code: lib/domain.js This module is pending deprecation. Once a replacement API has been finalized, this module will be fully deprecated. Most developers should not have cause to use this module. Users who absolutely must have the functionality that domains provide may rely on it for the time being but should expect to have to migrate to a different solution in the future. Domains provide a way to handle multiple different IO operations as a single group. If any of the event emitters or callbacks registered to a domain emit an `'error'` event, or throw an error, then the domain object will be notified, rather than losing the context of the error in the `process.on('uncaughtException')` handler, or causing the program to exit immediately with an error code. ### Warning: Don't ignore errors!# Domain error handlers are not a substitute for closing down a process when an error occurs. By the very nature of how `throw` works in JavaScript, there is almost never any way to safely "pick up where it left off", without leaking references, or creating some other sort of undefined brittle state. The safest way to respond to a thrown error is to shut down the process. Of course, in a normal web server, there may be many open connections, and it is not reasonable to abruptly shut those down because an error was triggered by someone else. The better approach is to send an error response to the request that triggered the error, while letting the others finish in their normal time, and stop listening for new requests in that worker. In this way, `domain` usage goes hand-in-hand with the cluster module, since the primary process can fork a new worker when a worker encounters an error. For Node.js programs that scale to multiple machines, the terminating proxy or service registry can take note of the failure, and react accordingly. For example, this is not a good idea: // XXX WARNING! BAD IDEA! const d = require('node:domain').create(); d.on('error', (er) => { // The error won't crash the process, but what it does is worse! // Though we've prevented abrupt process restarting, we are leaking // a lot of resources if this ever happens. // This is no better than process.on('uncaughtException')! console.log(`error, but oh well ${er.message}`); }); d.run(() => { require('node:http').createServer((req, res) => { handleRequest(req, res); }).listen(PORT); }); By using the context of a domain, and the resilience of separating our program into multiple worker processes, we can react more appropriately, and handle errors with much greater safety. // Much better! const cluster = require('node:cluster'); const PORT = +process.env.PORT || 1337; if (cluster.isPrimary) { // A more realistic scenario would have more than 2 workers, // and perhaps not put the primary and worker in the same file. // // It is also possible to get a bit fancier about logging, and // implement whatever custom logic is needed to prevent DoS // attacks and other bad behavior. // // See the options in the cluster documentation. // // The important thing is that the primary does very little, // increasing our resilience to unexpected errors. cluster.fork(); cluster.fork(); cluster.on('disconnect', (worker) => { console.error('disconnect!'); cluster.fork(); }); } else { // the worker // // This is where we put our bugs! const domain = require('node:domain'); // See the cluster documentation for more details about using // worker processes to serve requests. How it works, caveats, etc. const server = require('node:http').createServer((req, res) => { const d = domain.create(); d.on('error', (er) => { console.error(`error ${er.stack}`); // We're in dangerous territory! // By definition, something unexpected occurred, // which we probably didn't want. // Anything can happen now! Be very careful! try { // Make sure we close down within 30 seconds const killtimer = setTimeout(() => { process.exit(1); }, 30000); // But don't keep the process open just for that! killtimer.unref(); // Stop taking new requests. server.close(); // Let the primary know we're dead. This will trigger a // 'disconnect' in the cluster primary, and then it will fork // a new worker. cluster.worker.disconnect(); // Try to send an error to the request that triggered the problem res.statusCode = 500; res.setHeader('content-type', 'text/plain'); res.end('Oops, there was a problem!\n'); } catch (er2) { // Oh well, not much we can do at this point. console.error(`Error sending 500! ${er2.stack}`); } }); // Because req and res were created before this domain existed, // we need to explicitly add them. // See the explanation of implicit vs explicit binding below. d.add(req); d.add(res); // Now run the handler function in the domain. d.run(() => { handleRequest(req, res); }); }); server.listen(PORT); } // This part is not important. Just an example routing thing. // Put fancy application logic here. function handleRequest(req, res) { switch (req.url) { case '/error': // We do some async stuff, and then... setTimeout(() => { // Whoops! flerb.bark(); }, timeout); break; default: res.end('ok'); } } ### Additions to `Error` objects# Any time an `Error` object is routed through a domain, a few extra fields are added to it. * `error.domain` The domain that first handled the error. * `error.domainEmitter` The event emitter that emitted an `'error'` event with the error object. * `error.domainBound` The callback function which was bound to the domain, and passed an error as its first argument. * `error.domainThrown` A boolean indicating whether the error was thrown, emitted, or passed to a bound callback function. ### Implicit binding# If domains are in use, then all new `EventEmitter` objects (including Stream objects, requests, responses, etc.) will be implicitly bound to the active domain at the time of their creation. Additionally, callbacks passed to low-level event loop requests (such as to `fs.open()`, or other callback-taking methods) will automatically be bound to the active domain. If they throw, then the domain will catch the error. In order to prevent excessive memory usage, `Domain` objects themselves are not implicitly added as children of the active domain. If they were, then it would be too easy to prevent request and response objects from being properly garbage collected. To nest `Domain` objects as children of a parent `Domain` they must be explicitly added. Implicit binding routes thrown errors and `'error'` events to the `Domain`'s `'error'` event, but does not register the `EventEmitter` on the `Domain`. Implicit binding only takes care of thrown errors and `'error'` events. ### Explicit binding# Sometimes, the domain in use is not the one that ought to be used for a specific event emitter. Or, the event emitter could have been created in the context of one domain, but ought to instead be bound to some other domain. For example, there could be one domain in use for an HTTP server, but perhaps we would like to have a separate domain to use for each request. That is possible via explicit binding. // Create a top-level domain for the server const domain = require('node:domain'); const http = require('node:http'); const serverDomain = domain.create(); serverDomain.run(() => { // Server is created in the scope of serverDomain http.createServer((req, res) => { // Req and res are also created in the scope of serverDomain // however, we'd prefer to have a separate domain for each request. // create it first thing, and add req and res to it. const reqd = domain.create(); reqd.add(req); reqd.add(res); reqd.on('error', (er) => { console.error('Error', er, req.url); try { res.writeHead(500); res.end('Error occurred, sorry.'); } catch (er2) { console.error('Error sending 500', er2, req.url); } }); }).listen(1337); }); ### `domain.create()`# * Returns: ### Class: `Domain`# * Extends: The `Domain` class encapsulates the functionality of routing errors and uncaught exceptions to the active `Domain` object. To handle the errors that it catches, listen to its `'error'` event. #### `domain.members`# * Type: An array of timers and event emitters that have been explicitly added to the domain. #### `domain.add(emitter)`# * `emitter` | emitter or timer to be added to the domain Explicitly adds an emitter to the domain. If any event handlers called by the emitter throw an error, or if the emitter emits an `'error'` event, it will be routed to the domain's `'error'` event, just like with implicit binding. This also works with timers that are returned from `setInterval()` and `setTimeout()`. If their callback function throws, it will be caught by the domain `'error'` handler. If the Timer or `EventEmitter` was already bound to a domain, it is removed from that one, and bound to this one instead. #### `domain.bind(callback)`# * `callback` The callback function * Returns: The bound function The returned function will be a wrapper around the supplied callback function. When the returned function is called, any errors that are thrown will be routed to the domain's `'error'` event. const d = domain.create(); function readSomeFile(filename, cb) { fs.readFile(filename, 'utf8', d.bind((er, data) => { // If this throws, it will also be passed to the domain. return cb(er, data ? JSON.parse(data) : null); })); } d.on('error', (er) => { // An error occurred somewhere. If we throw it now, it will crash the program // with the normal line number and stack message. }); #### `domain.enter()`# The `enter()` method is plumbing used by the `run()`, `bind()`, and `intercept()` methods to set the active domain. It sets `domain.active` and `process.domain` to the domain, and implicitly pushes the domain onto the domain stack managed by the domain module (see `domain.exit()` for details on the domain stack). The call to `enter()` delimits the beginning of a chain of asynchronous calls and I/O operations bound to a domain. Calling `enter()` changes only the active domain, and does not alter the domain itself. `enter()` and `exit()` can be called an arbitrary number of times on a single domain. #### `domain.exit()`# The `exit()` method exits the current domain, popping it off the domain stack. Any time execution is going to switch to the context of a different chain of asynchronous calls, it's important to ensure that the current domain is exited. The call to `exit()` delimits either the end of or an interruption to the chain of asynchronous calls and I/O operations bound to a domain. If there are multiple, nested domains bound to the current execution context, `exit()` will exit any domains nested within this domain. Calling `exit()` changes only the active domain, and does not alter the domain itself. `enter()` and `exit()` can be called an arbitrary number of times on a single domain. #### `domain.intercept(callback)`# * `callback` The callback function * Returns: The intercepted function This method is almost identical to `domain.bind(callback)`. However, in addition to catching thrown errors, it will also intercept `Error` objects sent as the first argument to the function. In this way, the common `if (err) return callback(err);` pattern can be replaced with a single error handler in a single place. const d = domain.create(); function readSomeFile(filename, cb) { fs.readFile(filename, 'utf8', d.intercept((data) => { // Note, the first argument is never passed to the // callback since it is assumed to be the 'Error' argument // and thus intercepted by the domain. // If this throws, it will also be passed to the domain // so the error-handling logic can be moved to the 'error' // event on the domain instead of being repeated throughout // the program. return cb(null, JSON.parse(data)); })); } d.on('error', (er) => { // An error occurred somewhere. If we throw it now, it will crash the program // with the normal line number and stack message. }); #### `domain.remove(emitter)`# * `emitter` | emitter or timer to be removed from the domain The opposite of `domain.add(emitter)`. Removes domain handling from the specified emitter. #### `domain.run(fn[, ...args])`# * `fn` * `...args` Run the supplied function in the context of the domain, implicitly binding all event emitters, timers, and low-level requests that are created in that context. Optionally, arguments can be passed to the function. This is the most basic way to use a domain. const domain = require('node:domain'); const fs = require('node:fs'); const d = domain.create(); d.on('error', (er) => { console.error('Caught error!', er); }); d.run(() => { process.nextTick(() => { setTimeout(() => { // Simulating some various async stuff fs.open('non-existent file', 'r', (er, fd) => { if (er) throw er; // proceed... }); }, 100); }); }); In this example, the `d.on('error')` handler will be triggered, rather than crashing the program. ### Domains and promises# As of Node.js 8.0.0, the handlers of promises are run inside the domain in which the call to `.then()` or `.catch()` itself was made: const d1 = domain.create(); const d2 = domain.create(); let p; d1.run(() => { p = Promise.resolve(42); }); d2.run(() => { p.then((v) => { // running in d2 }); }); A callback may be bound to a specific domain using `domain.bind(callback)`: const d1 = domain.create(); const d2 = domain.create(); let p; d1.run(() => { p = Promise.resolve(42); }); d2.run(() => { p.then(p.domain.bind((v) => { // running in d1 })); }); Domains will not interfere with the error handling mechanisms for promises. In other words, no `'error'` event will be emitted for unhandled `Promise` rejections. ## Environment Variables# Environment variables are variables associated to the environment the Node.js process runs in. ### CLI Environment Variables# There is a set of environment variables that can be defined to customize the behavior of Node.js, for more details refer to the CLI Environment Variables documentation. ### `process.env`# The basic API for interacting with environment variables is `process.env`, it consists of an object with pre-populated user environment variables that can be modified and expanded. For more details refer to the `process.env` documentation. ### DotEnv# Set of utilities for dealing with additional environment variables defined in `.env` files. Stability: 1.1 \- Active development #### .env files# `.env` files (also known as dotenv files) are files that define environment variables, which Node.js applications can then interact with (popularized by the dotenv package). The following is an example of the content of a basic `.env` file: MY_VAR_A = "my variable A" MY_VAR_B = "my variable B" This type of file is used in various different programming languages and platforms but there is no formal specification for it, therefore Node.js defines its own specification described below. A `.env` file is a file that contains key-value pairs, each pair is represented by a variable name followed by the equal sign (`=`) followed by a variable value. The name of such files is usually `.env` or it starts with `.env` (like for example `.env.dev` where `dev` indicates a specific target environment). This is the recommended naming scheme but it is not mandatory and dotenv files can have any arbitrary file name. ##### Variable Names# A valid variable name must contain only letters (uppercase or lowercase), digits and underscores (`_`) and it can't begin with a digit. More specifically a valid variable name must match the following regular expression: ^[a-zA-Z_]+[a-zA-Z0-9_]*$ The recommended convention is to use capital letters with underscores and digits when necessary, but any variable name respecting the above definition will work just fine. For example, the following are some valid variable names: `MY_VAR`, `MY_VAR_1`, `my_var`, `my_var_1`, `myVar`, `My_Var123`, while these are instead not valid: `1_VAR`, `'my-var'`, `"my var"`, `VAR_#1`. ##### Variable Values# Variable values are comprised by any arbitrary text, which can optionally be wrapped inside single (`'`) or double (`"`) quotes. Quoted variables can span across multiple lines, while non quoted ones are restricted to a single line. Noting that when parsed by Node.js all values are interpreted as text, meaning that any value will result in a JavaScript string inside Node.js. For example the following values: `0`, `true` and `{ "hello": "world" }` will result in the literal strings `'0'`, `'true'` and `'{ "hello": "world" }'` instead of the number zero, the boolean `true` and an object with the `hello` property respectively. Examples of valid variables: MY_SIMPLE_VAR = a simple single line variable MY_EQUALS_VAR = "this variable contains an = sign!" MY_HASH_VAR = 'this variable contains a # symbol!' MY_MULTILINE_VAR = ' this is a multiline variable containing two separate lines\nSorry, I meant three lines' ##### Spacing# Leading and trailing whitespace characters around variable keys and values are ignored unless they are enclosed within quotes. For example: MY_VAR_A = my variable a MY_VAR_B = ' my variable b ' will be treated identically to: MY_VAR_A = my variable a MY_VAR_B = ' my variable b ' ##### Comments# Hash-tag (`#`) characters denote the beginning of a comment, meaning that the rest of the line will be completely ignored. Hash-tags found within quotes are however treated as any other standard character. For example: # This is a comment MY_VAR = my variable # This is also a comment MY_VAR_A = "# this is NOT a comment" ##### `export` prefixes# The `export` keyword can optionally be added in front of variable declarations, such keyword will be completely ignored by all processing done on the file. This is useful so that the file can be sourced, without modifications, in shell terminals. Example: export MY_VAR = my variable #### CLI Options# `.env` files can be used to populate the `process.env` object via one the following CLI options: * `--env-file=file` * `--env-file-if-exists=file` #### Programmatic APIs# There following two functions allow you to directly interact with `.env` files: * `process.loadEnvFile` loads an `.env` file and populates `process.env` with its variables * `util.parseEnv` parses the row content of an `.env` file and returns its value in an object ## Errors# Applications running in Node.js will generally experience the following categories of errors: * Standard JavaScript errors such as , , , , , and . * Standard `DOMException`s. * System errors triggered by underlying operating system constraints such as attempting to open a file that does not exist or attempting to send data over a closed socket. * `AssertionError`s are a special class of error that can be triggered when Node.js detects an exceptional logic violation that should never occur. These are raised typically by the `node:assert` module. * User-specified errors triggered by application code. All JavaScript and system errors raised by Node.js inherit from, or are instances of, the standard JavaScript class and are guaranteed to provide at least the properties available on that class. The `error.message` property of errors raised by Node.js may be changed in any versions. Use `error.code` to identify an error instead. For a `DOMException`, use `domException.name` to identify its type. ### Error propagation and interception# Node.js supports several mechanisms for propagating and handling errors that occur while an application is running. How these errors are reported and handled depends entirely on the type of `Error` and the style of the API that is called. All JavaScript errors are handled as exceptions that immediately generate and throw an error using the standard JavaScript `throw` mechanism. These are handled using the `try…catch` construct provided by the JavaScript language. // Throws with a ReferenceError because z is not defined. try { const m = 1; const n = m + z; } catch (err) { // Handle the error here. } Any use of the JavaScript `throw` mechanism will raise an exception that must be handled or the Node.js process will exit immediately. With few exceptions, Synchronous APIs (any blocking method that does not return a nor accept a `callback` function, such as `fs.readFileSync`), will use `throw` to report errors. Errors that occur within Asynchronous APIs may be reported in multiple ways: * Some asynchronous methods returns a , you should always take into account that it might be rejected. See `--unhandled-rejections` flag for how the process will react to an unhandled promise rejection. const fs = require('node:fs/promises'); (async () => { let data; try { data = await fs.readFile('a file that does not exist'); } catch (err) { console.error('There was an error reading the file!', err); return; } // Otherwise handle the data })(); * Most asynchronous methods that accept a `callback` function will accept an `Error` object passed as the first argument to that function. If that first argument is not `null` and is an instance of `Error`, then an error occurred that should be handled. const fs = require('node:fs'); fs.readFile('a file that does not exist', (err, data) => { if (err) { console.error('There was an error reading the file!', err); return; } // Otherwise handle the data }); * When an asynchronous method is called on an object that is an `EventEmitter`, errors can be routed to that object's `'error'` event. const net = require('node:net'); const connection = net.connect('localhost'); // Adding an 'error' event handler to a stream: connection.on('error', (err) => { // If the connection is reset by the server, or if it can't // connect at all, or on any sort of error encountered by // the connection, the error will be sent here. console.error(err); }); connection.pipe(process.stdout); * A handful of typically asynchronous methods in the Node.js API may still use the `throw` mechanism to raise exceptions that must be handled using `try…catch`. There is no comprehensive list of such methods; please refer to the documentation of each method to determine the appropriate error handling mechanism required. The use of the `'error'` event mechanism is most common for stream-based and event emitter-based APIs, which themselves represent a series of asynchronous operations over time (as opposed to a single operation that may pass or fail). For all `EventEmitter` objects, if an `'error'` event handler is not provided, the error will be thrown, causing the Node.js process to report an uncaught exception and crash unless either: a handler has been registered for the `'uncaughtException'` event, or the deprecated `node:domain` module is used. const EventEmitter = require('node:events'); const ee = new EventEmitter(); setImmediate(() => { // This will crash the process because no 'error' event // handler has been added. ee.emit('error', new Error('This will crash')); }); Errors generated in this way cannot be intercepted using `try…catch` as they are thrown after the calling code has already exited. Developers must refer to the documentation for each method to determine exactly how errors raised by those methods are propagated. ### Class: `Error`# A generic JavaScript object that does not denote any specific circumstance of why the error occurred. `Error` objects capture a "stack trace" detailing the point in the code at which the `Error` was instantiated, and may provide a text description of the error. All errors generated by Node.js, including all system and JavaScript errors, will either be instances of, or inherit from, the `Error` class. #### `new Error(message[, options])`# * `message` * `options` * `cause` The error that caused the newly created error. Creates a new `Error` object and sets the `error.message` property to the provided text message. If an object is passed as `message`, the text message is generated by calling `String(message)`. If the `cause` option is provided, it is assigned to the `error.cause` property. The `error.stack` property will represent the point in the code at which `new Error()` was called. Stack traces are dependent on V8's stack trace API. Stack traces extend only to either (a) the beginning of synchronous code execution, or (b) the number of frames given by the property `Error.stackTraceLimit`, whichever is smaller. #### `Error.captureStackTrace(targetObject[, constructorOpt])`# * `targetObject` * `constructorOpt` Creates a `.stack` property on `targetObject`, which when accessed returns a string representing the location in the code at which `Error.captureStackTrace()` was called. const myObject = {}; Error.captureStackTrace(myObject); myObject.stack; // Similar to `new Error().stack` The first line of the trace will be prefixed with `${myObject.name}: ${myObject.message}`. The optional `constructorOpt` argument accepts a function. If given, all frames above `constructorOpt`, including `constructorOpt`, will be omitted from the generated stack trace. The `constructorOpt` argument is useful for hiding implementation details of error generation from the user. For instance: function a() { b(); } function b() { c(); } function c() { // Create an error without stack trace to avoid calculating the stack trace twice. const { stackTraceLimit } = Error; Error.stackTraceLimit = 0; const error = new Error(); Error.stackTraceLimit = stackTraceLimit; // Capture the stack trace above function b Error.captureStackTrace(error, b); // Neither function c, nor b is included in the stack trace throw error; } a(); #### `Error.stackTraceLimit`# * Type: The `Error.stackTraceLimit` property specifies the number of stack frames collected by a stack trace (whether generated by `new Error().stack` or `Error.captureStackTrace(obj)`). The default value is `10` but may be set to any valid JavaScript number. Changes will affect any stack trace captured after the value has been changed. If set to a non-number value, or set to a negative number, stack traces will not capture any frames. #### `error.cause`# Added in: v16.9.0 * Type: If present, the `error.cause` property is the underlying cause of the `Error`. It is used when catching an error and throwing a new one with a different message or code in order to still have access to the original error. The `error.cause` property is typically set by calling `new Error(message, { cause })`. It is not set by the constructor if the `cause` option is not provided. This property allows errors to be chained. When serializing `Error` objects, `util.inspect()` recursively serializes `error.cause` if it is set. const cause = new Error('The remote HTTP server responded with a 500 status'); const symptom = new Error('The message failed to send', { cause }); console.log(symptom); // Prints: // Error: The message failed to send // at REPL2:1:17 // at Script.runInThisContext (node:vm:130:12) // ... 7 lines matching cause stack trace ... // at [_line] [as _line] (node:internal/readline/interface:886:18) { // [cause]: Error: The remote HTTP server responded with a 500 status // at REPL1:1:15 // at Script.runInThisContext (node:vm:130:12) // at REPLServer.defaultEval (node:repl:574:29) // at bound (node:domain:426:15) // at REPLServer.runBound [as eval] (node:domain:437:12) // at REPLServer.onLine (node:repl:902:10) // at REPLServer.emit (node:events:549:35) // at REPLServer.emit (node:domain:482:12) // at [_onLine] [as _onLine] (node:internal/readline/interface:425:12) // at [_line] [as _line] (node:internal/readline/interface:886:18) #### `error.code`# * Type: The `error.code` property is a string label that identifies the kind of error. `error.code` is the most stable way to identify an error. It will only change between major versions of Node.js. In contrast, `error.message` strings may change between any versions of Node.js. See Node.js error codes for details about specific codes. #### `error.message`# * Type: The `error.message` property is the string description of the error as set by calling `new Error(message)`. The `message` passed to the constructor will also appear in the first line of the stack trace of the `Error`, however changing this property after the `Error` object is created may not change the first line of the stack trace (for example, when `error.stack` is read before this property is changed). const err = new Error('The message'); console.error(err.message); // Prints: The message #### `error.stack`# * Type: The `error.stack` property is a string describing the point in the code at which the `Error` was instantiated. Error: Things keep happening! at /home/gbusey/file.js:525:2 at Frobnicator.refrobulate (/home/gbusey/business-logic.js:424:21) at Actor. (/home/gbusey/actors.js:400:8) at increaseSynergy (/home/gbusey/actors.js:701:6) The first line is formatted as `: `, and is followed by a series of stack frames (each line beginning with "at "). Each frame describes a call site within the code that lead to the error being generated. V8 attempts to display a name for each function (by variable name, function name, or object method name), but occasionally it will not be able to find a suitable name. If V8 cannot determine a name for the function, only location information will be displayed for that frame. Otherwise, the determined function name will be displayed with location information appended in parentheses. Frames are only generated for JavaScript functions. If, for example, execution synchronously passes through a C++ addon function called `cheetahify` which itself calls a JavaScript function, the frame representing the `cheetahify` call will not be present in the stack traces: const cheetahify = require('./native-binding.node'); function makeFaster() { // `cheetahify()` *synchronously* calls speedy. cheetahify(function speedy() { throw new Error('oh no!'); }); } makeFaster(); // will throw: // /home/gbusey/file.js:6 // throw new Error('oh no!'); // ^ // Error: oh no! // at speedy (/home/gbusey/file.js:6:11) // at makeFaster (/home/gbusey/file.js:5:3) // at Object. (/home/gbusey/file.js:10:1) // at Module._compile (module.js:456:26) // at Object.Module._extensions..js (module.js:474:10) // at Module.load (module.js:356:32) // at Function.Module._load (module.js:312:12) // at Function.Module.runMain (module.js:497:10) // at startup (node.js:119:16) // at node.js:906:3 The location information will be one of: * `native`, if the frame represents a call internal to V8 (as in `[].forEach`). * `plain-filename.js:line:column`, if the frame represents a call internal to Node.js. * `/absolute/path/to/file.js:line:column`, if the frame represents a call in a user program (using CommonJS module system), or its dependencies. * `:///url/to/module/file.mjs:line:column`, if the frame represents a call in a user program (using ES module system), or its dependencies. The string representing the stack trace is lazily generated when the `error.stack` property is accessed. The number of frames captured by the stack trace is bounded by the smaller of `Error.stackTraceLimit` or the number of available frames on the current event loop tick. ### Class: `AssertionError`# * Extends: Indicates the failure of an assertion. For details, see `Class: assert.AssertionError`. ### Class: `RangeError`# * Extends: Indicates that a provided argument was not within the set or range of acceptable values for a function; whether that is a numeric range, or outside the set of options for a given function parameter. require('node:net').connect(-1); // Throws "RangeError: "port" option should be >= 0 and < 65536: -1" Node.js will generate and throw `RangeError` instances immediately as a form of argument validation. ### Class: `ReferenceError`# * Extends: Indicates that an attempt is being made to access a variable that is not defined. Such errors commonly indicate typos in code, or an otherwise broken program. While client code may generate and propagate these errors, in practice, only V8 will do so. doesNotExist; // Throws ReferenceError, doesNotExist is not a variable in this program. Unless an application is dynamically generating and running code, `ReferenceError` instances indicate a bug in the code or its dependencies. ### Class: `SyntaxError`# * Extends: Indicates that a program is not valid JavaScript. These errors may only be generated and propagated as a result of code evaluation. Code evaluation may happen as a result of `eval`, `Function`, `require`, or vm. These errors are almost always indicative of a broken program. try { require('node:vm').runInThisContext('binary ! isNotOk'); } catch (err) { // 'err' will be a SyntaxError. } `SyntaxError` instances are unrecoverable in the context that created them – they may only be caught by other contexts. ### Class: `SystemError`# * Extends: Node.js generates system errors when exceptions occur within its runtime environment. These usually occur when an application violates an operating system constraint. For example, a system error will occur if an application attempts to read a file that does not exist. * `address` If present, the address to which a network connection failed * `code` The string error code * `dest` If present, the file path destination when reporting a file system error * `errno` The system-provided error number * `info` If present, extra details about the error condition * `message` A system-provided human-readable description of the error * `path` If present, the file path when reporting a file system error * `port` If present, the network connection port that is not available * `syscall` The name of the system call that triggered the error #### `error.address`# * Type: If present, `error.address` is a string describing the address to which a network connection failed. #### `error.code`# * Type: The `error.code` property is a string representing the error code. #### `error.dest`# * Type: If present, `error.dest` is the file path destination when reporting a file system error. #### `error.errno`# * Type: The `error.errno` property is a negative number which corresponds to the error code defined in `libuv Error handling`. On Windows the error number provided by the system will be normalized by libuv. To get the string representation of the error code, use `util.getSystemErrorName(error.errno)`. #### `error.info`# * Type: If present, `error.info` is an object with details about the error condition. #### `error.message`# * Type: `error.message` is a system-provided human-readable description of the error. #### `error.path`# * Type: If present, `error.path` is a string containing a relevant invalid pathname. #### `error.port`# * Type: If present, `error.port` is the network connection port that is not available. #### `error.syscall`# * Type: The `error.syscall` property is a string describing the syscall that failed. #### Common system errors# This is a list of system errors commonly-encountered when writing a Node.js program. For a comprehensive list, see the `errno`(3) man page. * `EACCES` (Permission denied): An attempt was made to access a file in a way forbidden by its file access permissions. * `EADDRINUSE` (Address already in use): An attempt to bind a server (`net`, `http`, or `https`) to a local address failed due to another server on the local system already occupying that address. * `ECONNREFUSED` (Connection refused): No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host. * `ECONNRESET` (Connection reset by peer): A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote socket due to a timeout or reboot. Commonly encountered via the `http` and `net` modules. * `EEXIST` (File exists): An existing file was the target of an operation that required that the target not exist. * `EISDIR` (Is a directory): An operation expected a file, but the given pathname was a directory. * `EMFILE` (Too many open files in system): Maximum number of file descriptors allowable on the system has been reached, and requests for another descriptor cannot be fulfilled until at least one has been closed. This is encountered when opening many files at once in parallel, especially on systems (in particular, macOS) where there is a low file descriptor limit for processes. To remedy a low limit, run `ulimit -n 2048` in the same shell that will run the Node.js process. * `ENOENT` (No such file or directory): Commonly raised by `fs` operations to indicate that a component of the specified pathname does not exist. No entity (file or directory) could be found by the given path. * `ENOTDIR` (Not a directory): A component of the given pathname existed, but was not a directory as expected. Commonly raised by `fs.readdir`. * `ENOTEMPTY` (Directory not empty): A directory with entries was the target of an operation that requires an empty directory, usually `fs.unlink`. * `ENOTFOUND` (DNS lookup failed): Indicates a DNS failure of either `EAI_NODATA` or `EAI_NONAME`. This is not a standard POSIX error. * `EPERM` (Operation not permitted): An attempt was made to perform an operation that requires elevated privileges. * `EPIPE` (Broken pipe): A write on a pipe, socket, or FIFO for which there is no process to read the data. Commonly encountered at the `net` and `http` layers, indicative that the remote side of the stream being written to has been closed. * `ETIMEDOUT` (Operation timed out): A connect or send request failed because the connected party did not properly respond after a period of time. Usually encountered by `http` or `net`. Often a sign that a `socket.end()` was not properly called. ### Class: `TypeError`# * Extends Indicates that a provided argument is not an allowable type. For example, passing a function to a parameter which expects a string would be a `TypeError`. require('node:url').parse(() => { }); // Throws TypeError, since it expected a string. Node.js will generate and throw `TypeError` instances immediately as a form of argument validation. ### Exceptions vs. errors# A JavaScript exception is a value that is thrown as a result of an invalid operation or as the target of a `throw` statement. While it is not required that these values are instances of `Error` or classes which inherit from `Error`, all exceptions thrown by Node.js or the JavaScript runtime will be instances of `Error`. Some exceptions are unrecoverable at the JavaScript layer. Such exceptions will always cause the Node.js process to crash. Examples include `assert()` checks or `abort()` calls in the C++ layer. ### OpenSSL errors# Errors originating in `crypto` or `tls` are of class `Error`, and in addition to the standard `.code` and `.message` properties, may have some additional OpenSSL-specific properties. #### `error.opensslErrorStack`# An array of errors that can give context to where in the OpenSSL library an error originates from. #### `error.function`# The OpenSSL function the error originates in. #### `error.library`# The OpenSSL library the error originates in. #### `error.reason`# A human-readable string describing the reason for the error. ### Node.js error codes# #### `ABORT_ERR`# Added in: v15.0.0 Used when an operation has been aborted (typically using an `AbortController`). APIs not using `AbortSignal`s typically do not raise an error with this code. This code does not use the regular `ERR_*` convention Node.js errors use in order to be compatible with the web platform's `AbortError`. #### `ERR_ACCESS_DENIED`# A special type of error that is triggered whenever Node.js tries to get access to a resource restricted by the Permission Model. #### `ERR_AMBIGUOUS_ARGUMENT`# A function argument is being used in a way that suggests that the function signature may be misunderstood. This is thrown by the `node:assert` module when the `message` parameter in `assert.throws(block, message)` matches the error message thrown by `block` because that usage suggests that the user believes `message` is the expected message rather than the message the `AssertionError` will display if `block` does not throw. #### `ERR_ARG_NOT_ITERABLE`# An iterable argument (i.e. a value that works with `for...of` loops) was required, but not provided to a Node.js API. #### `ERR_ASSERTION`# A special type of error that can be triggered whenever Node.js detects an exceptional logic violation that should never occur. These are raised typically by the `node:assert` module. #### `ERR_ASYNC_CALLBACK`# An attempt was made to register something that is not a function as an `AsyncHooks` callback. #### `ERR_ASYNC_TYPE`# The type of an asynchronous resource was invalid. Users are also able to define their own types if using the public embedder API. #### `ERR_BROTLI_COMPRESSION_FAILED`# Data passed to a Brotli stream was not successfully compressed. #### `ERR_BROTLI_INVALID_PARAM`# An invalid parameter key was passed during construction of a Brotli stream. #### `ERR_BUFFER_CONTEXT_NOT_AVAILABLE`# An attempt was made to create a Node.js `Buffer` instance from addon or embedder code, while in a JS engine Context that is not associated with a Node.js instance. The data passed to the `Buffer` method will have been released by the time the method returns. When encountering this error, a possible alternative to creating a `Buffer` instance is to create a normal `Uint8Array`, which only differs in the prototype of the resulting object. `Uint8Array`s are generally accepted in all Node.js core APIs where `Buffer`s are; they are available in all Contexts. #### `ERR_BUFFER_OUT_OF_BOUNDS`# An operation outside the bounds of a `Buffer` was attempted. #### `ERR_BUFFER_TOO_LARGE`# An attempt has been made to create a `Buffer` larger than the maximum allowed size. #### `ERR_CANNOT_WATCH_SIGINT`# Node.js was unable to watch for the `SIGINT` signal. #### `ERR_CHILD_CLOSED_BEFORE_REPLY`# A child process was closed before the parent received a reply. #### `ERR_CHILD_PROCESS_IPC_REQUIRED`# Used when a child process is being forked without specifying an IPC channel. #### `ERR_CHILD_PROCESS_STDIO_MAXBUFFER`# Used when the main process is trying to read data from the child process's STDERR/STDOUT, and the data's length is longer than the `maxBuffer` option. #### `ERR_CLOSED_MESSAGE_PORT`# History VersionChanges v16.2.0, v14.17.1 The error message was reintroduced. v11.12.0 The error message was removed. v10.5.0 Added in: v10.5.0 There was an attempt to use a `MessagePort` instance in a closed state, usually after `.close()` has been called. #### `ERR_CONSOLE_WRITABLE_STREAM`# `Console` was instantiated without `stdout` stream, or `Console` has a non-writable `stdout` or `stderr` stream. #### `ERR_CONSTRUCT_CALL_INVALID`# Added in: v12.5.0 A class constructor was called that is not callable. #### `ERR_CONSTRUCT_CALL_REQUIRED`# A constructor for a class was called without `new`. #### `ERR_CONTEXT_NOT_INITIALIZED`# The vm context passed into the API is not yet initialized. This could happen when an error occurs (and is caught) during the creation of the context, for example, when the allocation fails or the maximum call stack size is reached when the context is created. #### `ERR_CPU_PROFILE_ALREADY_STARTED`# Added in: v24.8.0 The CPU profile with the given name is already started. #### `ERR_CPU_PROFILE_NOT_STARTED`# Added in: v24.8.0 The CPU profile with the given name is not started. #### `ERR_CPU_PROFILE_TOO_MANY`# Added in: v24.8.0 There are too many CPU profiles being collected. #### `ERR_CRYPTO_ARGON2_NOT_SUPPORTED`# Argon2 is not supported by the current version of OpenSSL being used. #### `ERR_CRYPTO_CUSTOM_ENGINE_NOT_SUPPORTED`# An OpenSSL engine was requested (for example, through the `clientCertEngine` or `privateKeyEngine` TLS options) that is not supported by the version of OpenSSL being used, likely due to the compile-time flag `OPENSSL_NO_ENGINE`. #### `ERR_CRYPTO_ECDH_INVALID_FORMAT`# An invalid value for the `format` argument was passed to the `crypto.ECDH()` class `getPublicKey()` method. #### `ERR_CRYPTO_ECDH_INVALID_PUBLIC_KEY`# An invalid value for the `key` argument has been passed to the `crypto.ECDH()` class `computeSecret()` method. It means that the public key lies outside of the elliptic curve. #### `ERR_CRYPTO_ENGINE_UNKNOWN`# An invalid crypto engine identifier was passed to `require('node:crypto').setEngine()`. #### `ERR_CRYPTO_FIPS_FORCED`# The `--force-fips` command-line argument was used but there was an attempt to enable or disable FIPS mode in the `node:crypto` module. #### `ERR_CRYPTO_FIPS_UNAVAILABLE`# An attempt was made to enable or disable FIPS mode, but FIPS mode was not available. #### `ERR_CRYPTO_HASH_FINALIZED`# `hash.digest()` was called multiple times. The `hash.digest()` method must be called no more than one time per instance of a `Hash` object. #### `ERR_CRYPTO_HASH_UPDATE_FAILED`# `hash.update()` failed for any reason. This should rarely, if ever, happen. #### `ERR_CRYPTO_INCOMPATIBLE_KEY`# The given crypto keys are incompatible with the attempted operation. #### `ERR_CRYPTO_INCOMPATIBLE_KEY_OPTIONS`# The selected public or private key encoding is incompatible with other options. #### `ERR_CRYPTO_INITIALIZATION_FAILED`# Added in: v15.0.0 Initialization of the crypto subsystem failed. #### `ERR_CRYPTO_INVALID_AUTH_TAG`# Added in: v15.0.0 An invalid authentication tag was provided. #### `ERR_CRYPTO_INVALID_COUNTER`# Added in: v15.0.0 An invalid counter was provided for a counter-mode cipher. #### `ERR_CRYPTO_INVALID_CURVE`# Added in: v15.0.0 An invalid elliptic-curve was provided. #### `ERR_CRYPTO_INVALID_DIGEST`# An invalid crypto digest algorithm was specified. #### `ERR_CRYPTO_INVALID_IV`# Added in: v15.0.0 An invalid initialization vector was provided. #### `ERR_CRYPTO_INVALID_JWK`# Added in: v15.0.0 An invalid JSON Web Key was provided. #### `ERR_CRYPTO_INVALID_KEYLEN`# Added in: v15.0.0 An invalid key length was provided. #### `ERR_CRYPTO_INVALID_KEYPAIR`# Added in: v15.0.0 An invalid key pair was provided. #### `ERR_CRYPTO_INVALID_KEYTYPE`# Added in: v15.0.0 An invalid key type was provided. #### `ERR_CRYPTO_INVALID_KEY_OBJECT_TYPE`# The given crypto key object's type is invalid for the attempted operation. #### `ERR_CRYPTO_INVALID_MESSAGELEN`# Added in: v15.0.0 An invalid message length was provided. #### `ERR_CRYPTO_INVALID_SCRYPT_PARAMS`# Added in: v15.0.0 One or more `crypto.scrypt()` or `crypto.scryptSync()` parameters are outside their legal range. #### `ERR_CRYPTO_INVALID_STATE`# A crypto method was used on an object that was in an invalid state. For instance, calling `cipher.getAuthTag()` before calling `cipher.final()`. #### `ERR_CRYPTO_INVALID_TAG_LENGTH`# Added in: v15.0.0 An invalid authentication tag length was provided. #### `ERR_CRYPTO_JOB_INIT_FAILED`# Added in: v15.0.0 Initialization of an asynchronous crypto operation failed. #### `ERR_CRYPTO_JWK_UNSUPPORTED_CURVE`# Key's Elliptic Curve is not registered for use in the JSON Web Key Elliptic Curve Registry. #### `ERR_CRYPTO_JWK_UNSUPPORTED_KEY_TYPE`# Key's Asymmetric Key Type is not registered for use in the JSON Web Key Types Registry. #### `ERR_CRYPTO_KEM_NOT_SUPPORTED`# Added in: v24.7.0 Attempted to use KEM operations while Node.js was not compiled with OpenSSL with KEM support. #### `ERR_CRYPTO_OPERATION_FAILED`# Added in: v15.0.0 A crypto operation failed for an otherwise unspecified reason. #### `ERR_CRYPTO_PBKDF2_ERROR`# The PBKDF2 algorithm failed for unspecified reasons. OpenSSL does not provide more details and therefore neither does Node.js. #### `ERR_CRYPTO_SCRYPT_NOT_SUPPORTED`# Node.js was compiled without `scrypt` support. Not possible with the official release binaries but can happen with custom builds, including distro builds. #### `ERR_CRYPTO_SIGN_KEY_REQUIRED`# A signing `key` was not provided to the `sign.sign()` method. #### `ERR_CRYPTO_TIMING_SAFE_EQUAL_LENGTH`# `crypto.timingSafeEqual()` was called with `Buffer`, `TypedArray`, or `DataView` arguments of different lengths. #### `ERR_CRYPTO_UNKNOWN_CIPHER`# An unknown cipher was specified. #### `ERR_CRYPTO_UNKNOWN_DH_GROUP`# An unknown Diffie-Hellman group name was given. See `crypto.getDiffieHellman()` for a list of valid group names. #### `ERR_CRYPTO_UNSUPPORTED_OPERATION`# Added in: v15.0.0, v14.18.0 An attempt to invoke an unsupported crypto operation was made. #### `ERR_DEBUGGER_ERROR`# Added in: v16.4.0, v14.17.4 An error occurred with the debugger. #### `ERR_DEBUGGER_STARTUP_ERROR`# Added in: v16.4.0, v14.17.4 The debugger timed out waiting for the required host/port to be free. #### `ERR_DIR_CLOSED`# The `fs.Dir` was previously closed. #### `ERR_DIR_CONCURRENT_OPERATION`# Added in: v14.3.0 A synchronous read or close call was attempted on an `fs.Dir` which has ongoing asynchronous operations. #### `ERR_DLOPEN_DISABLED`# Added in: v16.10.0, v14.19.0 Loading native addons has been disabled using `--no-addons`. #### `ERR_DLOPEN_FAILED`# Added in: v15.0.0 A call to `process.dlopen()` failed. #### `ERR_DNS_SET_SERVERS_FAILED`# `c-ares` failed to set the DNS server. #### `ERR_DOMAIN_CALLBACK_NOT_AVAILABLE`# The `node:domain` module was not usable since it could not establish the required error handling hooks, because `process.setUncaughtExceptionCaptureCallback()` had been called at an earlier point in time. #### `ERR_DOMAIN_CANNOT_SET_UNCAUGHT_EXCEPTION_CAPTURE`# `process.setUncaughtExceptionCaptureCallback()` could not be called because the `node:domain` module has been loaded at an earlier point in time. The stack trace is extended to include the point in time at which the `node:domain` module had been loaded. #### `ERR_DUPLICATE_STARTUP_SNAPSHOT_MAIN_FUNCTION`# `v8.startupSnapshot.setDeserializeMainFunction()` could not be called because it had already been called before. #### `ERR_ENCODING_INVALID_ENCODED_DATA`# Data provided to `TextDecoder()` API was invalid according to the encoding provided. #### `ERR_ENCODING_NOT_SUPPORTED`# Encoding provided to `TextDecoder()` API was not one of the WHATWG Supported Encodings. #### `ERR_EVAL_ESM_CANNOT_PRINT`# `--print` cannot be used with ESM input. #### `ERR_EVENT_RECURSION`# Thrown when an attempt is made to recursively dispatch an event on `EventTarget`. #### `ERR_EXECUTION_ENVIRONMENT_NOT_AVAILABLE`# The JS execution context is not associated with a Node.js environment. This may occur when Node.js is used as an embedded library and some hooks for the JS engine are not set up properly. #### `ERR_FALSY_VALUE_REJECTION`# A `Promise` that was callbackified via `util.callbackify()` was rejected with a falsy value. #### `ERR_FEATURE_UNAVAILABLE_ON_PLATFORM`# Added in: v14.0.0 Used when a feature that is not available to the current platform which is running Node.js is used. #### `ERR_FS_CP_DIR_TO_NON_DIR`# Added in: v16.7.0 An attempt was made to copy a directory to a non-directory (file, symlink, etc.) using `fs.cp()`. #### `ERR_FS_CP_EEXIST`# Added in: v16.7.0 An attempt was made to copy over a file that already existed with `fs.cp()`, with the `force` and `errorOnExist` set to `true`. #### `ERR_FS_CP_EINVAL`# Added in: v16.7.0 When using `fs.cp()`, `src` or `dest` pointed to an invalid path. #### `ERR_FS_CP_FIFO_PIPE`# Added in: v16.7.0 An attempt was made to copy a named pipe with `fs.cp()`. #### `ERR_FS_CP_NON_DIR_TO_DIR`# Added in: v16.7.0 An attempt was made to copy a non-directory (file, symlink, etc.) to a directory using `fs.cp()`. #### `ERR_FS_CP_SOCKET`# Added in: v16.7.0 An attempt was made to copy to a socket with `fs.cp()`. #### `ERR_FS_CP_SYMLINK_TO_SUBDIRECTORY`# Added in: v16.7.0 When using `fs.cp()`, a symlink in `dest` pointed to a subdirectory of `src`. #### `ERR_FS_CP_UNKNOWN`# Added in: v16.7.0 An attempt was made to copy to an unknown file type with `fs.cp()`. #### `ERR_FS_EISDIR`# Path is a directory. #### `ERR_FS_FILE_TOO_LARGE`# An attempt was made to read a file larger than the supported 2 GiB limit for `fs.readFile()`. This is not a limitation of `Buffer`, but an internal I/O constraint. For handling larger files, consider using `fs.createReadStream()` to read the file in chunks. #### `ERR_FS_WATCH_QUEUE_OVERFLOW`# The number of file system events queued without being handled exceeded the size specified in `maxQueue` in `fs.watch()`. #### `ERR_HTTP2_ALTSVC_INVALID_ORIGIN`# HTTP/2 ALTSVC frames require a valid origin. #### `ERR_HTTP2_ALTSVC_LENGTH`# HTTP/2 ALTSVC frames are limited to a maximum of 16,382 payload bytes. #### `ERR_HTTP2_CONNECT_AUTHORITY`# For HTTP/2 requests using the `CONNECT` method, the `:authority` pseudo-header is required. #### `ERR_HTTP2_CONNECT_PATH`# For HTTP/2 requests using the `CONNECT` method, the `:path` pseudo-header is forbidden. #### `ERR_HTTP2_CONNECT_SCHEME`# For HTTP/2 requests using the `CONNECT` method, the `:scheme` pseudo-header is forbidden. #### `ERR_HTTP2_ERROR`# A non-specific HTTP/2 error has occurred. #### `ERR_HTTP2_GOAWAY_SESSION`# New HTTP/2 Streams may not be opened after the `Http2Session` has received a `GOAWAY` frame from the connected peer. #### `ERR_HTTP2_HEADERS_AFTER_RESPOND`# An additional headers was specified after an HTTP/2 response was initiated. #### `ERR_HTTP2_HEADERS_SENT`# An attempt was made to send multiple response headers. #### `ERR_HTTP2_HEADER_SINGLE_VALUE`# Multiple values were provided for an HTTP/2 header field that was required to have only a single value. #### `ERR_HTTP2_INFO_STATUS_NOT_ALLOWED`# Informational HTTP status codes (`1xx`) may not be set as the response status code on HTTP/2 responses. #### `ERR_HTTP2_INVALID_CONNECTION_HEADERS`# HTTP/1 connection specific headers are forbidden to be used in HTTP/2 requests and responses. #### `ERR_HTTP2_INVALID_HEADER_VALUE`# An invalid HTTP/2 header value was specified. #### `ERR_HTTP2_INVALID_INFO_STATUS`# An invalid HTTP informational status code has been specified. Informational status codes must be an integer between `100` and `199` (inclusive). #### `ERR_HTTP2_INVALID_ORIGIN`# HTTP/2 `ORIGIN` frames require a valid origin. #### `ERR_HTTP2_INVALID_PACKED_SETTINGS_LENGTH`# Input `Buffer` and `Uint8Array` instances passed to the `http2.getUnpackedSettings()` API must have a length that is a multiple of six. #### `ERR_HTTP2_INVALID_PSEUDOHEADER`# Only valid HTTP/2 pseudoheaders (`:status`, `:path`, `:authority`, `:scheme`, and `:method`) may be used. #### `ERR_HTTP2_INVALID_SESSION`# An action was performed on an `Http2Session` object that had already been destroyed. #### `ERR_HTTP2_INVALID_SETTING_VALUE`# An invalid value has been specified for an HTTP/2 setting. #### `ERR_HTTP2_INVALID_STREAM`# An operation was performed on a stream that had already been destroyed. #### `ERR_HTTP2_MAX_PENDING_SETTINGS_ACK`# Whenever an HTTP/2 `SETTINGS` frame is sent to a connected peer, the peer is required to send an acknowledgment that it has received and applied the new `SETTINGS`. By default, a maximum number of unacknowledged `SETTINGS` frames may be sent at any given time. This error code is used when that limit has been reached. #### `ERR_HTTP2_NESTED_PUSH`# An attempt was made to initiate a new push stream from within a push stream. Nested push streams are not permitted. #### `ERR_HTTP2_NO_MEM`# Out of memory when using the `http2session.setLocalWindowSize(windowSize)` API. #### `ERR_HTTP2_NO_SOCKET_MANIPULATION`# An attempt was made to directly manipulate (read, write, pause, resume, etc.) a socket attached to an `Http2Session`. #### `ERR_HTTP2_ORIGIN_LENGTH`# HTTP/2 `ORIGIN` frames are limited to a length of 16382 bytes. #### `ERR_HTTP2_OUT_OF_STREAMS`# The number of streams created on a single HTTP/2 session reached the maximum limit. #### `ERR_HTTP2_PAYLOAD_FORBIDDEN`# A message payload was specified for an HTTP response code for which a payload is forbidden. #### `ERR_HTTP2_PING_CANCEL`# An HTTP/2 ping was canceled. #### `ERR_HTTP2_PING_LENGTH`# HTTP/2 ping payloads must be exactly 8 bytes in length. #### `ERR_HTTP2_PSEUDOHEADER_NOT_ALLOWED`# An HTTP/2 pseudo-header has been used inappropriately. Pseudo-headers are header key names that begin with the `:` prefix. #### `ERR_HTTP2_PUSH_DISABLED`# An attempt was made to create a push stream, which had been disabled by the client. #### `ERR_HTTP2_SEND_FILE`# An attempt was made to use the `Http2Stream.prototype.responseWithFile()` API to send a directory. #### `ERR_HTTP2_SEND_FILE_NOSEEK`# An attempt was made to use the `Http2Stream.prototype.responseWithFile()` API to send something other than a regular file, but `offset` or `length` options were provided. #### `ERR_HTTP2_SESSION_ERROR`# The `Http2Session` closed with a non-zero error code. #### `ERR_HTTP2_SETTINGS_CANCEL`# The `Http2Session` settings canceled. #### `ERR_HTTP2_SOCKET_BOUND`# An attempt was made to connect a `Http2Session` object to a `net.Socket` or `tls.TLSSocket` that had already been bound to another `Http2Session` object. #### `ERR_HTTP2_SOCKET_UNBOUND`# An attempt was made to use the `socket` property of an `Http2Session` that has already been closed. #### `ERR_HTTP2_STATUS_101`# Use of the `101` Informational status code is forbidden in HTTP/2. #### `ERR_HTTP2_STATUS_INVALID`# An invalid HTTP status code has been specified. Status codes must be an integer between `100` and `599` (inclusive). #### `ERR_HTTP2_STREAM_CANCEL`# An `Http2Stream` was destroyed before any data was transmitted to the connected peer. #### `ERR_HTTP2_STREAM_ERROR`# A non-zero error code was been specified in an `RST_STREAM` frame. #### `ERR_HTTP2_STREAM_SELF_DEPENDENCY`# When setting the priority for an HTTP/2 stream, the stream may be marked as a dependency for a parent stream. This error code is used when an attempt is made to mark a stream and dependent of itself. #### `ERR_HTTP2_TOO_MANY_CUSTOM_SETTINGS`# The number of supported custom settings (10) has been exceeded. #### `ERR_HTTP2_TOO_MANY_INVALID_FRAMES`# Added in: v15.14.0 The limit of acceptable invalid HTTP/2 protocol frames sent by the peer, as specified through the `maxSessionInvalidFrames` option, has been exceeded. #### `ERR_HTTP2_TRAILERS_ALREADY_SENT`# Trailing headers have already been sent on the `Http2Stream`. #### `ERR_HTTP2_TRAILERS_NOT_READY`# The `http2stream.sendTrailers()` method cannot be called until after the `'wantTrailers'` event is emitted on an `Http2Stream` object. The `'wantTrailers'` event will only be emitted if the `waitForTrailers` option is set for the `Http2Stream`. #### `ERR_HTTP2_UNSUPPORTED_PROTOCOL`# `http2.connect()` was passed a URL that uses any protocol other than `http:` or `https:`. #### `ERR_HTTP_BODY_NOT_ALLOWED`# An error is thrown when writing to an HTTP response which does not allow contents. #### `ERR_HTTP_CONTENT_LENGTH_MISMATCH`# Response body size doesn't match with the specified content-length header value. #### `ERR_HTTP_HEADERS_SENT`# An attempt was made to add more headers after the headers had already been sent. #### `ERR_HTTP_INVALID_HEADER_VALUE`# An invalid HTTP header value was specified. #### `ERR_HTTP_INVALID_STATUS_CODE`# Status code was outside the regular status code range (100-999). #### `ERR_HTTP_REQUEST_TIMEOUT`# The client has not sent the entire request within the allowed time. #### `ERR_HTTP_SOCKET_ASSIGNED`# The given `ServerResponse` was already assigned a socket. #### `ERR_HTTP_SOCKET_ENCODING`# Changing the socket encoding is not allowed per RFC 7230 Section 3. #### `ERR_HTTP_TRAILER_INVALID`# The `Trailer` header was set even though the transfer encoding does not support that. #### `ERR_ILLEGAL_CONSTRUCTOR`# An attempt was made to construct an object using a non-public constructor. #### `ERR_IMPORT_ATTRIBUTE_MISSING`# Added in: v21.1.0 An import attribute is missing, preventing the specified module to be imported. #### `ERR_IMPORT_ATTRIBUTE_TYPE_INCOMPATIBLE`# Added in: v21.1.0 An import `type` attribute was provided, but the specified module is of a different type. #### `ERR_IMPORT_ATTRIBUTE_UNSUPPORTED`# Added in: v21.0.0, v20.10.0, v18.19.0 An import attribute is not supported by this version of Node.js. #### `ERR_INCOMPATIBLE_OPTION_PAIR`# An option pair is incompatible with each other and cannot be used at the same time. #### `ERR_INPUT_TYPE_NOT_ALLOWED`# The `--input-type` flag was used to attempt to execute a file. This flag can only be used with input via `--eval`, `--print`, or `STDIN`. #### `ERR_INSPECTOR_ALREADY_ACTIVATED`# While using the `node:inspector` module, an attempt was made to activate the inspector when it already started to listen on a port. Use `inspector.close()` before activating it on a different address. #### `ERR_INSPECTOR_ALREADY_CONNECTED`# While using the `node:inspector` module, an attempt was made to connect when the inspector was already connected. #### `ERR_INSPECTOR_CLOSED`# While using the `node:inspector` module, an attempt was made to use the inspector after the session had already closed. #### `ERR_INSPECTOR_COMMAND`# An error occurred while issuing a command via the `node:inspector` module. #### `ERR_INSPECTOR_NOT_ACTIVE`# The `inspector` is not active when `inspector.waitForDebugger()` is called. #### `ERR_INSPECTOR_NOT_AVAILABLE`# The `node:inspector` module is not available for use. #### `ERR_INSPECTOR_NOT_CONNECTED`# While using the `node:inspector` module, an attempt was made to use the inspector before it was connected. #### `ERR_INSPECTOR_NOT_WORKER`# An API was called on the main thread that can only be used from the worker thread. #### `ERR_INTERNAL_ASSERTION`# There was a bug in Node.js or incorrect usage of Node.js internals. To fix the error, open an issue at https://github.com/nodejs/node/issues. #### `ERR_INVALID_ADDRESS`# The provided address is not understood by the Node.js API. #### `ERR_INVALID_ADDRESS_FAMILY`# The provided address family is not understood by the Node.js API. #### `ERR_INVALID_ARG_TYPE`# An argument of the wrong type was passed to a Node.js API. #### `ERR_INVALID_ARG_VALUE`# An invalid or unsupported value was passed for a given argument. #### `ERR_INVALID_ASYNC_ID`# An invalid `asyncId` or `triggerAsyncId` was passed using `AsyncHooks`. An id less than -1 should never happen. #### `ERR_INVALID_BUFFER_SIZE`# A swap was performed on a `Buffer` but its size was not compatible with the operation. #### `ERR_INVALID_CHAR`# Invalid characters were detected in headers. #### `ERR_INVALID_CURSOR_POS`# A cursor on a given stream cannot be moved to a specified row without a specified column. #### `ERR_INVALID_FD`# A file descriptor ('fd') was not valid (e.g. it was a negative value). #### `ERR_INVALID_FD_TYPE`# A file descriptor ('fd') type was not valid. #### `ERR_INVALID_FILE_URL_HOST`# A Node.js API that consumes `file:` URLs (such as certain functions in the `fs` module) encountered a file URL with an incompatible host. This situation can only occur on Unix-like systems where only `localhost` or an empty host is supported. #### `ERR_INVALID_FILE_URL_PATH`# A Node.js API that consumes `file:` URLs (such as certain functions in the `fs` module) encountered a file URL with an incompatible path. The exact semantics for determining whether a path can be used is platform-dependent. The thrown error object includes an `input` property that contains the URL object of the invalid `file:` URL. #### `ERR_INVALID_HANDLE_TYPE`# An attempt was made to send an unsupported "handle" over an IPC communication channel to a child process. See `subprocess.send()` and `process.send()` for more information. #### `ERR_INVALID_HTTP_TOKEN`# An invalid HTTP token was supplied. #### `ERR_INVALID_IP_ADDRESS`# An IP address is not valid. #### `ERR_INVALID_MIME_SYNTAX`# The syntax of a MIME is not valid. #### `ERR_INVALID_MODULE`# Added in: v15.0.0, v14.18.0 An attempt was made to load a module that does not exist or was otherwise not valid. #### `ERR_INVALID_MODULE_SPECIFIER`# The imported module string is an invalid URL, package name, or package subpath specifier. #### `ERR_INVALID_OBJECT_DEFINE_PROPERTY`# An error occurred while setting an invalid attribute on the property of an object. #### `ERR_INVALID_PACKAGE_CONFIG`# An invalid `package.json` file failed parsing. #### `ERR_INVALID_PACKAGE_TARGET`# The `package.json` `"exports"` field contains an invalid target mapping value for the attempted module resolution. #### `ERR_INVALID_PROTOCOL`# An invalid `options.protocol` was passed to `http.request()`. #### `ERR_INVALID_REPL_EVAL_CONFIG`# Both `breakEvalOnSigint` and `eval` options were set in the `REPL` config, which is not supported. #### `ERR_INVALID_REPL_INPUT`# The input may not be used in the `REPL`. The conditions under which this error is used are described in the `REPL` documentation. #### `ERR_INVALID_RETURN_PROPERTY`# Thrown in case a function option does not provide a valid value for one of its returned object properties on execution. #### `ERR_INVALID_RETURN_PROPERTY_VALUE`# Thrown in case a function option does not provide an expected value type for one of its returned object properties on execution. #### `ERR_INVALID_RETURN_VALUE`# Thrown in case a function option does not return an expected value type on execution, such as when a function is expected to return a promise. #### `ERR_INVALID_STATE`# Added in: v15.0.0 Indicates that an operation cannot be completed due to an invalid state. For instance, an object may have already been destroyed, or may be performing another operation. #### `ERR_INVALID_SYNC_FORK_INPUT`# A `Buffer`, `TypedArray`, `DataView`, or `string` was provided as stdio input to an asynchronous fork. See the documentation for the `child_process` module for more information. #### `ERR_INVALID_THIS`# A Node.js API function was called with an incompatible `this` value. const urlSearchParams = new URLSearchParams('foo=bar&baz=new'); const buf = Buffer.alloc(1); urlSearchParams.has.call(buf, 'foo'); // Throws a TypeError with code 'ERR_INVALID_THIS' #### `ERR_INVALID_TUPLE`# An element in the `iterable` provided to the WHATWG `URLSearchParams` constructor did not represent a `[name, value]` tuple – that is, if an element is not iterable, or does not consist of exactly two elements. #### `ERR_INVALID_TYPESCRIPT_SYNTAX`# History VersionChanges v23.7.0, v22.14.0 This error is no longer thrown on valid yet unsupported syntax. v23.0.0, v22.10.0 Added in: v23.0.0, v22.10.0 The provided TypeScript syntax is not valid. #### `ERR_INVALID_URI`# An invalid URI was passed. #### `ERR_INVALID_URL`# An invalid URL was passed to the WHATWG `URL` constructor or the legacy `url.parse()` to be parsed. The thrown error object typically has an additional property `'input'` that contains the URL that failed to parse. #### `ERR_INVALID_URL_PATTERN`# An invalid URLPattern was passed to the WHATWG `URLPattern` constructor to be parsed. #### `ERR_INVALID_URL_SCHEME`# An attempt was made to use a URL of an incompatible scheme (protocol) for a specific purpose. It is only used in the WHATWG URL API support in the `fs` module (which only accepts URLs with `'file'` scheme), but may be used in other Node.js APIs as well in the future. #### `ERR_IPC_CHANNEL_CLOSED`# An attempt was made to use an IPC communication channel that was already closed. #### `ERR_IPC_DISCONNECTED`# An attempt was made to disconnect an IPC communication channel that was already disconnected. See the documentation for the `child_process` module for more information. #### `ERR_IPC_ONE_PIPE`# An attempt was made to create a child Node.js process using more than one IPC communication channel. See the documentation for the `child_process` module for more information. #### `ERR_IPC_SYNC_FORK`# An attempt was made to open an IPC communication channel with a synchronously forked Node.js process. See the documentation for the `child_process` module for more information. #### `ERR_IP_BLOCKED`# IP is blocked by `net.BlockList`. #### `ERR_LOADER_CHAIN_INCOMPLETE`# Added in: v18.6.0, v16.17.0 An ESM loader hook returned without calling `next()` and without explicitly signaling a short circuit. #### `ERR_LOAD_SQLITE_EXTENSION`# Added in: v23.5.0, v22.13.0 An error occurred while loading a SQLite extension. #### `ERR_MEMORY_ALLOCATION_FAILED`# An attempt was made to allocate memory (usually in the C++ layer) but it failed. #### `ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE`# Added in: v14.5.0, v12.19.0 A message posted to a `MessagePort` could not be deserialized in the target vm `Context`. Not all Node.js objects can be successfully instantiated in any context at this time, and attempting to transfer them using `postMessage()` can fail on the receiving side in that case. #### `ERR_METHOD_NOT_IMPLEMENTED`# A method is required but not implemented. #### `ERR_MISSING_ARGS`# A required argument of a Node.js API was not passed. This is only used for strict compliance with the API specification (which in some cases may accept `func(undefined)` but not `func()`). In most native Node.js APIs, `func(undefined)` and `func()` are treated identically, and the `ERR_INVALID_ARG_TYPE` error code may be used instead. #### `ERR_MISSING_OPTION`# For APIs that accept options objects, some options might be mandatory. This code is thrown if a required option is missing. #### `ERR_MISSING_PASSPHRASE`# An attempt was made to read an encrypted key without specifying a passphrase. #### `ERR_MISSING_PLATFORM_FOR_WORKER`# The V8 platform used by this instance of Node.js does not support creating Workers. This is caused by lack of embedder support for Workers. In particular, this error will not occur with standard builds of Node.js. #### `ERR_MODULE_LINK_MISMATCH`# A module can not be linked because the same module requests in it are not resolved to the same module. #### `ERR_MODULE_NOT_FOUND`# A module file could not be resolved by the ECMAScript modules loader while attempting an `import` operation or when loading the program entry point. #### `ERR_MULTIPLE_CALLBACK`# A callback was called more than once. A callback is almost always meant to only be called once as the query can either be fulfilled or rejected but not both at the same time. The latter would be possible by calling a callback more than once. #### `ERR_NAPI_CONS_FUNCTION`# While using `Node-API`, a constructor passed was not a function. #### `ERR_NAPI_INVALID_DATAVIEW_ARGS`# While calling `napi_create_dataview()`, a given `offset` was outside the bounds of the dataview or `offset + length` was larger than a length of given `buffer`. #### `ERR_NAPI_INVALID_TYPEDARRAY_ALIGNMENT`# While calling `napi_create_typedarray()`, the provided `offset` was not a multiple of the element size. #### `ERR_NAPI_INVALID_TYPEDARRAY_LENGTH`# While calling `napi_create_typedarray()`, `(length * size_of_element) + byte_offset` was larger than the length of given `buffer`. #### `ERR_NAPI_TSFN_CALL_JS`# An error occurred while invoking the JavaScript portion of the thread-safe function. #### `ERR_NAPI_TSFN_GET_UNDEFINED`# An error occurred while attempting to retrieve the JavaScript `undefined` value. #### `ERR_NON_CONTEXT_AWARE_DISABLED`# A non-context-aware native addon was loaded in a process that disallows them. #### `ERR_NOT_BUILDING_SNAPSHOT`# An attempt was made to use operations that can only be used when building V8 startup snapshot even though Node.js isn't building one. #### `ERR_NOT_IN_SINGLE_EXECUTABLE_APPLICATION`# Added in: v21.7.0, v20.12.0 The operation cannot be performed when it's not in a single-executable application. #### `ERR_NOT_SUPPORTED_IN_SNAPSHOT`# An attempt was made to perform operations that are not supported when building a startup snapshot. #### `ERR_NO_CRYPTO`# An attempt was made to use crypto features while Node.js was not compiled with OpenSSL crypto support. #### `ERR_NO_ICU`# An attempt was made to use features that require ICU, but Node.js was not compiled with ICU support. #### `ERR_NO_TYPESCRIPT`# Added in: v23.0.0, v22.12.0 An attempt was made to use features that require Native TypeScript support, but Node.js was not compiled with TypeScript support. #### `ERR_OPERATION_FAILED`# Added in: v15.0.0 An operation failed. This is typically used to signal the general failure of an asynchronous operation. #### `ERR_OPTIONS_BEFORE_BOOTSTRAPPING`# Added in: v23.10.0 An attempt was made to get options before the bootstrapping was completed. #### `ERR_OUT_OF_RANGE`# A given value is out of the accepted range. #### `ERR_PACKAGE_IMPORT_NOT_DEFINED`# The `package.json` `"imports"` field does not define the given internal package specifier mapping. #### `ERR_PACKAGE_PATH_NOT_EXPORTED`# The `package.json` `"exports"` field does not export the requested subpath. Because exports are encapsulated, private internal modules that are not exported cannot be imported through the package resolution, unless using an absolute URL. #### `ERR_PARSE_ARGS_INVALID_OPTION_VALUE`# Added in: v18.3.0, v16.17.0 When `strict` set to `true`, thrown by `util.parseArgs()` if a value is provided for an option of type , or if a value is provided for an option of type . #### `ERR_PARSE_ARGS_UNEXPECTED_POSITIONAL`# Added in: v18.3.0, v16.17.0 Thrown by `util.parseArgs()`, when a positional argument is provided and `allowPositionals` is set to `false`. #### `ERR_PARSE_ARGS_UNKNOWN_OPTION`# Added in: v18.3.0, v16.17.0 When `strict` set to `true`, thrown by `util.parseArgs()` if an argument is not configured in `options`. #### `ERR_PERFORMANCE_INVALID_TIMESTAMP`# An invalid timestamp value was provided for a performance mark or measure. #### `ERR_PERFORMANCE_MEASURE_INVALID_OPTIONS`# Invalid options were provided for a performance measure. #### `ERR_PROTO_ACCESS`# Accessing `Object.prototype.__proto__` has been forbidden using `--disable-proto=throw`. `Object.getPrototypeOf` and `Object.setPrototypeOf` should be used to get and set the prototype of an object. #### `ERR_PROXY_INVALID_CONFIG`# Failed to proxy a request because the proxy configuration is invalid. #### `ERR_PROXY_TUNNEL`# Failed to establish proxy tunnel when `NODE_USE_ENV_PROXY` or `--use-env-proxy` is enabled. #### `ERR_QUIC_APPLICATION_ERROR`# Added in: v23.4.0, v22.13.0 Stability: 1 \- Experimental A QUIC application error occurred. #### `ERR_QUIC_CONNECTION_FAILED`# Added in: v23.0.0, v22.10.0 Stability: 1 \- Experimental Establishing a QUIC connection failed. #### `ERR_QUIC_ENDPOINT_CLOSED`# Added in: v23.0.0, v22.10.0 Stability: 1 \- Experimental A QUIC Endpoint closed with an error. #### `ERR_QUIC_OPEN_STREAM_FAILED`# Added in: v23.0.0, v22.10.0 Stability: 1 \- Experimental Opening a QUIC stream failed. #### `ERR_QUIC_TRANSPORT_ERROR`# Added in: v23.4.0, v22.13.0 Stability: 1 \- Experimental A QUIC transport error occurred. #### `ERR_QUIC_VERSION_NEGOTIATION_ERROR`# Added in: v23.4.0, v22.13.0 Stability: 1 \- Experimental A QUIC session failed because version negotiation is required. #### `ERR_REQUIRE_ASYNC_MODULE`# Stability: 1 \- Experimental When trying to `require()` a ES Module, the module turns out to be asynchronous. That is, it contains top-level await. To see where the top-level await is, use `--experimental-print-required-tla` (this would execute the modules before looking for the top-level awaits). #### `ERR_REQUIRE_CYCLE_MODULE`# Stability: 1 \- Experimental When trying to `require()` a ES Module, a CommonJS to ESM or ESM to CommonJS edge participates in an immediate cycle. This is not allowed because ES Modules cannot be evaluated while they are already being evaluated. To avoid the cycle, the `require()` call involved in a cycle should not happen at the top-level of either an ES Module (via `createRequire()`) or a CommonJS module, and should be done lazily in an inner function. #### `ERR_REQUIRE_ESM`# History VersionChanges v23.0.0, v22.12.0, v20.19.0 require() now supports loading synchronous ES modules by default. Stability: 0 \- Deprecated An attempt was made to `require()` an ES Module. This error has been deprecated since `require()` now supports loading synchronous ES modules. When `require()` encounters an ES module that contains top-level `await`, it will throw `ERR_REQUIRE_ASYNC_MODULE` instead. #### `ERR_SCRIPT_EXECUTION_INTERRUPTED`# Script execution was interrupted by `SIGINT` (For example, `Ctrl`+`C` was pressed.) #### `ERR_SCRIPT_EXECUTION_TIMEOUT`# Script execution timed out, possibly due to bugs in the script being executed. #### `ERR_SERVER_ALREADY_LISTEN`# The `server.listen()` method was called while a `net.Server` was already listening. This applies to all instances of `net.Server`, including HTTP, HTTPS, and HTTP/2 `Server` instances. #### `ERR_SERVER_NOT_RUNNING`# The `server.close()` method was called when a `net.Server` was not running. This applies to all instances of `net.Server`, including HTTP, HTTPS, and HTTP/2 `Server` instances. #### `ERR_SINGLE_EXECUTABLE_APPLICATION_ASSET_NOT_FOUND`# Added in: v21.7.0, v20.12.0 A key was passed to single executable application APIs to identify an asset, but no match could be found. #### `ERR_SOCKET_ALREADY_BOUND`# An attempt was made to bind a socket that has already been bound. #### `ERR_SOCKET_BAD_BUFFER_SIZE`# An invalid (negative) size was passed for either the `recvBufferSize` or `sendBufferSize` options in `dgram.createSocket()`. #### `ERR_SOCKET_BAD_PORT`# An API function expecting a port >= 0 and < 65536 received an invalid value. #### `ERR_SOCKET_BAD_TYPE`# An API function expecting a socket type (`udp4` or `udp6`) received an invalid value. #### `ERR_SOCKET_BUFFER_SIZE`# While using `dgram.createSocket()`, the size of the receive or send `Buffer` could not be determined. #### `ERR_SOCKET_CLOSED`# An attempt was made to operate on an already closed socket. #### `ERR_SOCKET_CLOSED_BEFORE_CONNECTION`# When calling `net.Socket.write()` on a connecting socket and the socket was closed before the connection was established. #### `ERR_SOCKET_CONNECTION_TIMEOUT`# The socket was unable to connect to any address returned by the DNS within the allowed timeout when using the family autoselection algorithm. #### `ERR_SOCKET_DGRAM_IS_CONNECTED`# A `dgram.connect()` call was made on an already connected socket. #### `ERR_SOCKET_DGRAM_NOT_CONNECTED`# A `dgram.disconnect()` or `dgram.remoteAddress()` call was made on a disconnected socket. #### `ERR_SOCKET_DGRAM_NOT_RUNNING`# A call was made and the UDP subsystem was not running. #### `ERR_SOURCE_MAP_CORRUPT`# The source map could not be parsed because it does not exist, or is corrupt. #### `ERR_SOURCE_MAP_MISSING_SOURCE`# A file imported from a source map was not found. #### `ERR_SOURCE_PHASE_NOT_DEFINED`# Added in: v24.0.0 The provided module import does not provide a source phase imports representation for source phase import syntax `import source x from 'x'` or `import.source(x)`. #### `ERR_SQLITE_ERROR`# Added in: v22.5.0 An error was returned from SQLite. #### `ERR_SRI_PARSE`# A string was provided for a Subresource Integrity check, but was unable to be parsed. Check the format of integrity attributes by looking at the Subresource Integrity specification. #### `ERR_STREAM_ALREADY_FINISHED`# A stream method was called that cannot complete because the stream was finished. #### `ERR_STREAM_CANNOT_PIPE`# An attempt was made to call `stream.pipe()` on a `Writable` stream. #### `ERR_STREAM_DESTROYED`# A stream method was called that cannot complete because the stream was destroyed using `stream.destroy()`. #### `ERR_STREAM_NULL_VALUES`# An attempt was made to call `stream.write()` with a `null` chunk. #### `ERR_STREAM_PREMATURE_CLOSE`# An error returned by `stream.finished()` and `stream.pipeline()`, when a stream or a pipeline ends non gracefully with no explicit error. #### `ERR_STREAM_PUSH_AFTER_EOF`# An attempt was made to call `stream.push()` after a `null`(EOF) had been pushed to the stream. #### `ERR_STREAM_UNABLE_TO_PIPE`# An attempt was made to pipe to a closed or destroyed stream in a pipeline. #### `ERR_STREAM_UNSHIFT_AFTER_END_EVENT`# An attempt was made to call `stream.unshift()` after the `'end'` event was emitted. #### `ERR_STREAM_WRAP`# Prevents an abort if a string decoder was set on the Socket or if the decoder is in `objectMode`. const Socket = require('node:net').Socket; const instance = new Socket(); instance.setEncoding('utf8'); #### `ERR_STREAM_WRITE_AFTER_END`# An attempt was made to call `stream.write()` after `stream.end()` has been called. #### `ERR_STRING_TOO_LONG`# An attempt has been made to create a string longer than the maximum allowed length. #### `ERR_SYNTHETIC`# An artificial error object used to capture the call stack for diagnostic reports. #### `ERR_SYSTEM_ERROR`# An unspecified or non-specific system error has occurred within the Node.js process. The error object will have an `err.info` object property with additional details. #### `ERR_TEST_FAILURE`# This error represents a failed test. Additional information about the failure is available via the `cause` property. The `failureType` property specifies what the test was doing when the failure occurred. #### `ERR_TLS_ALPN_CALLBACK_INVALID_RESULT`# This error is thrown when an `ALPNCallback` returns a value that is not in the list of ALPN protocols offered by the client. #### `ERR_TLS_ALPN_CALLBACK_WITH_PROTOCOLS`# This error is thrown when creating a `TLSServer` if the TLS options include both `ALPNProtocols` and `ALPNCallback`. These options are mutually exclusive. #### `ERR_TLS_CERT_ALTNAME_FORMAT`# This error is thrown by `checkServerIdentity` if a user-supplied `subjectaltname` property violates encoding rules. Certificate objects produced by Node.js itself always comply with encoding rules and will never cause this error. #### `ERR_TLS_CERT_ALTNAME_INVALID`# While using TLS, the host name/IP of the peer did not match any of the `subjectAltNames` in its certificate. #### `ERR_TLS_DH_PARAM_SIZE`# While using TLS, the parameter offered for the Diffie-Hellman (`DH`) key-agreement protocol is too small. By default, the key length must be greater than or equal to 1024 bits to avoid vulnerabilities, even though it is strongly recommended to use 2048 bits or larger for stronger security. #### `ERR_TLS_HANDSHAKE_TIMEOUT`# A TLS/SSL handshake timed out. In this case, the server must also abort the connection. #### `ERR_TLS_INVALID_CONTEXT`# Added in: v13.3.0 The context must be a `SecureContext`. #### `ERR_TLS_INVALID_PROTOCOL_METHOD`# The specified `secureProtocol` method is invalid. It is either unknown, or disabled because it is insecure. #### `ERR_TLS_INVALID_PROTOCOL_VERSION`# Valid TLS protocol versions are `'TLSv1'`, `'TLSv1.1'`, or `'TLSv1.2'`. #### `ERR_TLS_INVALID_STATE`# Added in: v13.10.0, v12.17.0 The TLS socket must be connected and securely established. Ensure the 'secure' event is emitted before continuing. #### `ERR_TLS_PROTOCOL_VERSION_CONFLICT`# Attempting to set a TLS protocol `minVersion` or `maxVersion` conflicts with an attempt to set the `secureProtocol` explicitly. Use one mechanism or the other. #### `ERR_TLS_PSK_SET_IDENTITY_HINT_FAILED`# Failed to set PSK identity hint. Hint may be too long. #### `ERR_TLS_RENEGOTIATION_DISABLED`# An attempt was made to renegotiate TLS on a socket instance with renegotiation disabled. #### `ERR_TLS_REQUIRED_SERVER_NAME`# While using TLS, the `server.addContext()` method was called without providing a host name in the first parameter. #### `ERR_TLS_SESSION_ATTACK`# An excessive amount of TLS renegotiations is detected, which is a potential vector for denial-of-service attacks. #### `ERR_TLS_SNI_FROM_SERVER`# An attempt was made to issue Server Name Indication from a TLS server-side socket, which is only valid from a client. #### `ERR_TRACE_EVENTS_CATEGORY_REQUIRED`# The `trace_events.createTracing()` method requires at least one trace event category. #### `ERR_TRACE_EVENTS_UNAVAILABLE`# The `node:trace_events` module could not be loaded because Node.js was compiled with the `--without-v8-platform` flag. #### `ERR_TRAILING_JUNK_AFTER_STREAM_END`# Trailing junk found after the end of the compressed stream. This error is thrown when extra, unexpected data is detected after the end of a compressed stream (for example, in zlib or gzip decompression). #### `ERR_TRANSFORM_ALREADY_TRANSFORMING`# A `Transform` stream finished while it was still transforming. #### `ERR_TRANSFORM_WITH_LENGTH_0`# A `Transform` stream finished with data still in the write buffer. #### `ERR_TTY_INIT_FAILED`# The initialization of a TTY failed due to a system error. #### `ERR_UNAVAILABLE_DURING_EXIT`# Function was called within a `process.on('exit')` handler that shouldn't be called within `process.on('exit')` handler. #### `ERR_UNCAUGHT_EXCEPTION_CAPTURE_ALREADY_SET`# `process.setUncaughtExceptionCaptureCallback()` was called twice, without first resetting the callback to `null`. This error is designed to prevent accidentally overwriting a callback registered from another module. #### `ERR_UNESCAPED_CHARACTERS`# A string that contained unescaped characters was received. #### `ERR_UNHANDLED_ERROR`# An unhandled error occurred (for instance, when an `'error'` event is emitted by an `EventEmitter` but an `'error'` handler is not registered). #### `ERR_UNKNOWN_BUILTIN_MODULE`# Used to identify a specific kind of internal Node.js error that should not typically be triggered by user code. Instances of this error point to an internal bug within the Node.js binary itself. #### `ERR_UNKNOWN_CREDENTIAL`# A Unix group or user identifier that does not exist was passed. #### `ERR_UNKNOWN_ENCODING`# An invalid or unknown encoding option was passed to an API. #### `ERR_UNKNOWN_FILE_EXTENSION`# An attempt was made to load a module with an unknown or unsupported file extension. #### `ERR_UNKNOWN_MODULE_FORMAT`# An attempt was made to load a module with an unknown or unsupported format. #### `ERR_UNKNOWN_SIGNAL`# An invalid or unknown process signal was passed to an API expecting a valid signal (such as `subprocess.kill()`). #### `ERR_UNSUPPORTED_DIR_IMPORT`# `import` a directory URL is unsupported. Instead, self-reference a package using its name and define a custom subpath in the `"exports"` field of the `package.json` file. import './'; // unsupported import './index.js'; // supported import 'package-name'; // supported #### `ERR_UNSUPPORTED_ESM_URL_SCHEME`# `import` with URL schemes other than `file` and `data` is unsupported. #### `ERR_UNSUPPORTED_NODE_MODULES_TYPE_STRIPPING`# Added in: v22.6.0 Type stripping is not supported for files descendent of a `node_modules` directory. #### `ERR_UNSUPPORTED_RESOLVE_REQUEST`# An attempt was made to resolve an invalid module referrer. This can happen when importing or calling `import.meta.resolve()` with either: * a bare specifier that is not a builtin module from a module whose URL scheme is not `file`. * a relative URL from a module whose URL scheme is not a special scheme. try { // Trying to import the package 'bare-specifier' from a `data:` URL module: await import('data:text/javascript,import "bare-specifier"'); } catch (e) { console.log(e.code); // ERR_UNSUPPORTED_RESOLVE_REQUEST } #### `ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX`# Added in: v23.7.0, v22.14.0 The provided TypeScript syntax is unsupported. This could happen when using TypeScript syntax that requires transformation with type-stripping. #### `ERR_USE_AFTER_CLOSE`# An attempt was made to use something that was already closed. #### `ERR_VALID_PERFORMANCE_ENTRY_TYPE`# While using the Performance Timing API (`perf_hooks`), no valid performance entry types are found. #### `ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`# A dynamic import callback was not specified. #### `ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING_FLAG`# A dynamic import callback was invoked without `--experimental-vm-modules`. #### `ERR_VM_MODULE_ALREADY_LINKED`# The module attempted to be linked is not eligible for linking, because of one of the following reasons: * It has already been linked (`linkingStatus` is `'linked'`) * It is being linked (`linkingStatus` is `'linking'`) * Linking has failed for this module (`linkingStatus` is `'errored'`) #### `ERR_VM_MODULE_CACHED_DATA_REJECTED`# The `cachedData` option passed to a module constructor is invalid. #### `ERR_VM_MODULE_CANNOT_CREATE_CACHED_DATA`# Cached data cannot be created for modules which have already been evaluated. #### `ERR_VM_MODULE_DIFFERENT_CONTEXT`# The module being returned from the linker function is from a different context than the parent module. Linked modules must share the same context. #### `ERR_VM_MODULE_LINK_FAILURE`# The module was unable to be linked due to a failure. #### `ERR_VM_MODULE_NOT_MODULE`# The fulfilled value of a linking promise is not a `vm.Module` object. #### `ERR_VM_MODULE_STATUS`# The current module's status does not allow for this operation. The specific meaning of the error depends on the specific function. #### `ERR_WASI_ALREADY_STARTED`# The WASI instance has already started. #### `ERR_WASI_NOT_STARTED`# The WASI instance has not been started. #### `ERR_WEBASSEMBLY_RESPONSE`# Added in: v18.1.0 The `Response` that has been passed to `WebAssembly.compileStreaming` or to `WebAssembly.instantiateStreaming` is not a valid WebAssembly response. #### `ERR_WORKER_INIT_FAILED`# The `Worker` initialization failed. #### `ERR_WORKER_INVALID_EXEC_ARGV`# The `execArgv` option passed to the `Worker` constructor contains invalid flags. #### `ERR_WORKER_MESSAGING_ERRORED`# Added in: v22.5.0 Stability: 1.1 \- Active development The destination thread threw an error while processing a message sent via `postMessageToThread()`. #### `ERR_WORKER_MESSAGING_FAILED`# Added in: v22.5.0 Stability: 1.1 \- Active development The thread requested in `postMessageToThread()` is invalid or has no `workerMessage` listener. #### `ERR_WORKER_MESSAGING_SAME_THREAD`# Added in: v22.5.0 Stability: 1.1 \- Active development The thread id requested in `postMessageToThread()` is the current thread id. #### `ERR_WORKER_MESSAGING_TIMEOUT`# Added in: v22.5.0 Stability: 1.1 \- Active development Sending a message via `postMessageToThread()` timed out. #### `ERR_WORKER_NOT_RUNNING`# An operation failed because the `Worker` instance is not currently running. #### `ERR_WORKER_OUT_OF_MEMORY`# The `Worker` instance terminated because it reached its memory limit. #### `ERR_WORKER_PATH`# The path for the main script of a worker is neither an absolute path nor a relative path starting with `./` or `../`. #### `ERR_WORKER_UNSERIALIZABLE_ERROR`# All attempts at serializing an uncaught exception from a worker thread failed. #### `ERR_WORKER_UNSUPPORTED_OPERATION`# The requested functionality is not supported in worker threads. #### `ERR_ZLIB_INITIALIZATION_FAILED`# Creation of a `zlib` object failed due to incorrect configuration. #### `ERR_ZSTD_INVALID_PARAM`# An invalid parameter key was passed during construction of a Zstd stream. #### `HPE_CHUNK_EXTENSIONS_OVERFLOW`# Added in: v21.6.2, v20.11.1, v18.19.1 Too much data was received for a chunk extensions. In order to protect against malicious or malconfigured clients, if more than 16 KiB of data is received then an `Error` with this code will be emitted. #### `HPE_HEADER_OVERFLOW`# History VersionChanges v11.4.0, v10.15.0 Max header size in `http_parser` was set to 8 KiB. Too much HTTP header data was received. In order to protect against malicious or malconfigured clients, if more than `maxHeaderSize` of HTTP header data is received then HTTP parsing will abort without a request or response object being created, and an `Error` with this code will be emitted. #### `HPE_UNEXPECTED_CONTENT_LENGTH`# Server is sending both a `Content-Length` header and `Transfer-Encoding: chunked`. `Transfer-Encoding: chunked` allows the server to maintain an HTTP persistent connection for dynamically generated content. In this case, the `Content-Length` HTTP header cannot be used. Use `Content-Length` or `Transfer-Encoding: chunked`. #### `MODULE_NOT_FOUND`# History VersionChanges v12.0.0 Added `requireStack` property. A module file could not be resolved by the CommonJS modules loader while attempting a `require()` operation or when loading the program entry point. ### Legacy Node.js error codes# Stability: 0 \- Deprecated. These error codes are either inconsistent, or have been removed. #### `ERR_CANNOT_TRANSFER_OBJECT`# Added in: v10.5.0Removed in: v12.5.0 The value passed to `postMessage()` contained an object that is not supported for transferring. #### `ERR_CPU_USAGE`# Removed in: v15.0.0 The native call from `process.cpuUsage` could not be processed. #### `ERR_CRYPTO_HASH_DIGEST_NO_UTF16`# Added in: v9.0.0Removed in: v12.12.0 The UTF-16 encoding was used with `hash.digest()`. While the `hash.digest()` method does allow an `encoding` argument to be passed in, causing the method to return a string rather than a `Buffer`, the UTF-16 encoding (e.g. `ucs` or `utf16le`) is not supported. #### `ERR_CRYPTO_SCRYPT_INVALID_PARAMETER`# Removed in: v23.0.0 An incompatible combination of options was passed to `crypto.scrypt()` or `crypto.scryptSync()`. New versions of Node.js use the error code `ERR_INCOMPATIBLE_OPTION_PAIR` instead, which is consistent with other APIs. #### `ERR_FS_INVALID_SYMLINK_TYPE`# Removed in: v23.0.0 An invalid symlink type was passed to the `fs.symlink()` or `fs.symlinkSync()` methods. #### `ERR_HTTP2_FRAME_ERROR`# Added in: v9.0.0Removed in: v10.0.0 Used when a failure occurs sending an individual frame on the HTTP/2 session. #### `ERR_HTTP2_HEADERS_OBJECT`# Added in: v9.0.0Removed in: v10.0.0 Used when an HTTP/2 Headers Object is expected. #### `ERR_HTTP2_HEADER_REQUIRED`# Added in: v9.0.0Removed in: v10.0.0 Used when a required header is missing in an HTTP/2 message. #### `ERR_HTTP2_INFO_HEADERS_AFTER_RESPOND`# Added in: v9.0.0Removed in: v10.0.0 HTTP/2 informational headers must only be sent prior to calling the `Http2Stream.prototype.respond()` method. #### `ERR_HTTP2_STREAM_CLOSED`# Added in: v9.0.0Removed in: v10.0.0 Used when an action has been performed on an HTTP/2 Stream that has already been closed. #### `ERR_HTTP_INVALID_CHAR`# Added in: v9.0.0Removed in: v10.0.0 Used when an invalid character is found in an HTTP response status message (reason phrase). #### `ERR_IMPORT_ASSERTION_TYPE_FAILED`# Added in: v17.1.0, v16.14.0Removed in: v21.1.0 An import assertion has failed, preventing the specified module to be imported. #### `ERR_IMPORT_ASSERTION_TYPE_MISSING`# Added in: v17.1.0, v16.14.0Removed in: v21.1.0 An import assertion is missing, preventing the specified module to be imported. #### `ERR_IMPORT_ASSERTION_TYPE_UNSUPPORTED`# Added in: v17.1.0, v16.14.0Removed in: v21.1.0 An import attribute is not supported by this version of Node.js. #### `ERR_INDEX_OUT_OF_RANGE`# Added in: v10.0.0Removed in: v11.0.0 A given index was out of the accepted range (e.g. negative offsets). #### `ERR_INVALID_OPT_VALUE`# Added in: v8.0.0Removed in: v15.0.0 An invalid or unexpected value was passed in an options object. #### `ERR_INVALID_OPT_VALUE_ENCODING`# Added in: v9.0.0Removed in: v15.0.0 An invalid or unknown file encoding was passed. #### `ERR_INVALID_PERFORMANCE_MARK`# Added in: v8.5.0Removed in: v16.7.0 While using the Performance Timing API (`perf_hooks`), a performance mark is invalid. #### `ERR_INVALID_TRANSFER_OBJECT`# History VersionChanges v21.0.0 A `DOMException` is thrown instead. v21.0.0 Removed in: v21.0.0 An invalid transfer object was passed to `postMessage()`. #### `ERR_MANIFEST_ASSERT_INTEGRITY`# Removed in: v22.2.0 An attempt was made to load a resource, but the resource did not match the integrity defined by the policy manifest. See the documentation for policy manifests for more information. #### `ERR_MANIFEST_DEPENDENCY_MISSING`# Removed in: v22.2.0 An attempt was made to load a resource, but the resource was not listed as a dependency from the location that attempted to load it. See the documentation for policy manifests for more information. #### `ERR_MANIFEST_INTEGRITY_MISMATCH`# Removed in: v22.2.0 An attempt was made to load a policy manifest, but the manifest had multiple entries for a resource which did not match each other. Update the manifest entries to match in order to resolve this error. See the documentation for policy manifests for more information. #### `ERR_MANIFEST_INVALID_RESOURCE_FIELD`# Removed in: v22.2.0 A policy manifest resource had an invalid value for one of its fields. Update the manifest entry to match in order to resolve this error. See the documentation for policy manifests for more information. #### `ERR_MANIFEST_INVALID_SPECIFIER`# Removed in: v22.2.0 A policy manifest resource had an invalid value for one of its dependency mappings. Update the manifest entry to match to resolve this error. See the documentation for policy manifests for more information. #### `ERR_MANIFEST_PARSE_POLICY`# Removed in: v22.2.0 An attempt was made to load a policy manifest, but the manifest was unable to be parsed. See the documentation for policy manifests for more information. #### `ERR_MANIFEST_TDZ`# Removed in: v22.2.0 An attempt was made to read from a policy manifest, but the manifest initialization has not yet taken place. This is likely a bug in Node.js. #### `ERR_MANIFEST_UNKNOWN_ONERROR`# Removed in: v22.2.0 A policy manifest was loaded, but had an unknown value for its "onerror" behavior. See the documentation for policy manifests for more information. #### `ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`# Removed in: v15.0.0 This error code was replaced by `ERR_MISSING_TRANSFERABLE_IN_TRANSFER_LIST` in Node.js v15.0.0, because it is no longer accurate as other types of transferable objects also exist now. #### `ERR_MISSING_TRANSFERABLE_IN_TRANSFER_LIST`# History VersionChanges v21.0.0 A `DOMException` is thrown instead. v21.0.0 Removed in: v21.0.0 v15.0.0 Added in: v15.0.0 An object that needs to be explicitly listed in the `transferList` argument is in the object passed to a `postMessage()` call, but is not provided in the `transferList` for that call. Usually, this is a `MessagePort`. In Node.js versions prior to v15.0.0, the error code being used here was `ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`. However, the set of transferable object types has been expanded to cover more types than `MessagePort`. #### `ERR_NAPI_CONS_PROTOTYPE_OBJECT`# Added in: v9.0.0Removed in: v10.0.0 Used by the `Node-API` when `Constructor.prototype` is not an object. #### `ERR_NAPI_TSFN_START_IDLE_LOOP`# Added in: v10.6.0, v8.16.0Removed in: v14.2.0, v12.17.0 On the main thread, values are removed from the queue associated with the thread-safe function in an idle loop. This error indicates that an error has occurred when attempting to start the loop. #### `ERR_NAPI_TSFN_STOP_IDLE_LOOP`# Added in: v10.6.0, v8.16.0Removed in: v14.2.0, v12.17.0 Once no more items are left in the queue, the idle loop must be suspended. This error indicates that the idle loop has failed to stop. #### `ERR_NO_LONGER_SUPPORTED`# A Node.js API was called in an unsupported manner, such as `Buffer.write(string, encoding, offset[, length])`. #### `ERR_OUTOFMEMORY`# Added in: v9.0.0Removed in: v10.0.0 Used generically to identify that an operation caused an out of memory condition. #### `ERR_PARSE_HISTORY_DATA`# Added in: v9.0.0Removed in: v10.0.0 The `node:repl` module was unable to parse data from the REPL history file. #### `ERR_SOCKET_CANNOT_SEND`# Added in: v9.0.0Removed in: v14.0.0 Data could not be sent on a socket. #### `ERR_STDERR_CLOSE`# History VersionChanges v10.12.0 Rather than emitting an error, `process.stderr.end()` now only closes the stream side but not the underlying resource, making this error obsolete. v10.12.0 Removed in: v10.12.0 An attempt was made to close the `process.stderr` stream. By design, Node.js does not allow `stdout` or `stderr` streams to be closed by user code. #### `ERR_STDOUT_CLOSE`# History VersionChanges v10.12.0 Rather than emitting an error, `process.stderr.end()` now only closes the stream side but not the underlying resource, making this error obsolete. v10.12.0 Removed in: v10.12.0 An attempt was made to close the `process.stdout` stream. By design, Node.js does not allow `stdout` or `stderr` streams to be closed by user code. #### `ERR_STREAM_READ_NOT_IMPLEMENTED`# Added in: v9.0.0Removed in: v10.0.0 Used when an attempt is made to use a readable stream that has not implemented `readable._read()`. #### `ERR_TAP_LEXER_ERROR`# An error representing a failing lexer state. #### `ERR_TAP_PARSER_ERROR`# An error representing a failing parser state. Additional information about the token causing the error is available via the `cause` property. #### `ERR_TAP_VALIDATION_ERROR`# This error represents a failed TAP validation. #### `ERR_TLS_RENEGOTIATION_FAILED`# Added in: v9.0.0Removed in: v10.0.0 Used when a TLS renegotiation request has failed in a non-specific way. #### `ERR_TRANSFERRING_EXTERNALIZED_SHAREDARRAYBUFFER`# Added in: v10.5.0Removed in: v14.0.0 A `SharedArrayBuffer` whose memory is not managed by the JavaScript engine or by Node.js was encountered during serialization. Such a `SharedArrayBuffer` cannot be serialized. This can only happen when native addons create `SharedArrayBuffer`s in "externalized" mode, or put existing `SharedArrayBuffer` into externalized mode. #### `ERR_UNKNOWN_STDIN_TYPE`# Added in: v8.0.0Removed in: v11.7.0 An attempt was made to launch a Node.js process with an unknown `stdin` file type. This error is usually an indication of a bug within Node.js itself, although it is possible for user code to trigger it. #### `ERR_UNKNOWN_STREAM_TYPE`# Added in: v8.0.0Removed in: v11.7.0 An attempt was made to launch a Node.js process with an unknown `stdout` or `stderr` file type. This error is usually an indication of a bug within Node.js itself, although it is possible for user code to trigger it. #### `ERR_V8BREAKITERATOR`# The V8 `BreakIterator` API was used but the full ICU data set is not installed. #### `ERR_VALUE_OUT_OF_RANGE`# Added in: v9.0.0Removed in: v10.0.0 Used when a given value is out of the accepted range. #### `ERR_VM_MODULE_LINKING_ERRORED`# Added in: v10.0.0Removed in: v18.1.0, v16.17.0 The linker function returned a module for which linking has failed. #### `ERR_VM_MODULE_NOT_LINKED`# The module must be successfully linked before instantiation. #### `ERR_WORKER_UNSUPPORTED_EXTENSION`# Added in: v11.0.0Removed in: v16.9.0 The pathname used for the main script of a worker has an unknown file extension. #### `ERR_ZLIB_BINDING_CLOSED`# Added in: v9.0.0Removed in: v10.0.0 Used when an attempt is made to use a `zlib` object after it has already been closed. ### OpenSSL Error Codes# #### Time Validity Errors# ##### `CERT_NOT_YET_VALID`# The certificate is not yet valid: the notBefore date is after the current time. ##### `CERT_HAS_EXPIRED`# The certificate has expired: the notAfter date is before the current time. ##### `CRL_NOT_YET_VALID`# The certificate revocation list (CRL) has a future issue date. ##### `CRL_HAS_EXPIRED`# The certificate revocation list (CRL) has expired. ##### `CERT_REVOKED`# The certificate has been revoked; it is on a certificate revocation list (CRL). #### Trust or Chain Related Errors# ##### `UNABLE_TO_GET_ISSUER_CERT`# The issuer certificate of a looked up certificate could not be found. This normally means the list of trusted certificates is not complete. ##### `UNABLE_TO_GET_ISSUER_CERT_LOCALLY`# The certificate’s issuer is not known. This is the case if the issuer is not included in the trusted certificate list. ##### `DEPTH_ZERO_SELF_SIGNED_CERT`# The passed certificate is self-signed and the same certificate cannot be found in the list of trusted certificates. ##### `SELF_SIGNED_CERT_IN_CHAIN`# The certificate’s issuer is not known. This is the case if the issuer is not included in the trusted certificate list. ##### `CERT_CHAIN_TOO_LONG`# The certificate chain length is greater than the maximum depth. ##### `UNABLE_TO_GET_CRL`# The CRL reference by the certificate could not be found. ##### `UNABLE_TO_VERIFY_LEAF_SIGNATURE`# No signatures could be verified because the chain contains only one certificate and it is not self signed. ##### `CERT_UNTRUSTED`# The root certificate authority (CA) is not marked as trusted for the specified purpose. #### Basic Extension Errors# ##### `INVALID_CA`# A CA certificate is invalid. Either it is not a CA or its extensions are not consistent with the supplied purpose. ##### `PATH_LENGTH_EXCEEDED`# The basicConstraints pathlength parameter has been exceeded. #### Name Related Errors# ##### `HOSTNAME_MISMATCH`# Certificate does not match provided name. #### Usage and Policy Errors# ##### `INVALID_PURPOSE`# The supplied certificate cannot be used for the specified purpose. ##### `CERT_REJECTED`# The root CA is marked to reject the specified purpose. #### Formatting Errors# ##### `CERT_SIGNATURE_FAILURE`# The signature of the certificate is invalid. ##### `CRL_SIGNATURE_FAILURE`# The signature of the certificate revocation list (CRL) is invalid. ##### `ERROR_IN_CERT_NOT_BEFORE_FIELD`# The certificate notBefore field contains an invalid time. ##### `ERROR_IN_CERT_NOT_AFTER_FIELD`# The certificate notAfter field contains an invalid time. ##### `ERROR_IN_CRL_LAST_UPDATE_FIELD`# The CRL lastUpdate field contains an invalid time. ##### `ERROR_IN_CRL_NEXT_UPDATE_FIELD`# The CRL nextUpdate field contains an invalid time. ##### `UNABLE_TO_DECRYPT_CERT_SIGNATURE`# The certificate signature could not be decrypted. This means that the actual signature value could not be determined rather than it not matching the expected value, this is only meaningful for RSA keys. ##### `UNABLE_TO_DECRYPT_CRL_SIGNATURE`# The certificate revocation list (CRL) signature could not be decrypted: this means that the actual signature value could not be determined rather than it not matching the expected value. ##### `UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY`# The public key in the certificate SubjectPublicKeyInfo could not be read. #### Other OpenSSL Errors# ##### `OUT_OF_MEM`# An error occurred trying to allocate memory. This should never happen. ## Events# Stability: 2 \- Stable Source Code: lib/events.js Much of the Node.js core API is built around an idiomatic asynchronous event-driven architecture in which certain kinds of objects (called "emitters") emit named events that cause `Function` objects ("listeners") to be called. For instance: a `net.Server` object emits an event each time a peer connects to it; a `fs.ReadStream` emits an event when the file is opened; a stream emits an event whenever data is available to be read. All objects that emit events are instances of the `EventEmitter` class. These objects expose an `eventEmitter.on()` function that allows one or more functions to be attached to named events emitted by the object. Typically, event names are camel-cased strings but any valid JavaScript property key can be used. When the `EventEmitter` object emits an event, all of the functions attached to that specific event are called synchronously. Any values returned by the called listeners are ignored and discarded. The following example shows a simple `EventEmitter` instance with a single listener. The `eventEmitter.on()` method is used to register listeners, while the `eventEmitter.emit()` method is used to trigger the event. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); myEmitter.on('event', () => { console.log('an event occurred!'); }); myEmitter.emit('event'); ### Passing arguments and `this` to listeners# The `eventEmitter.emit()` method allows an arbitrary set of arguments to be passed to the listener functions. Keep in mind that when an ordinary listener function is called, the standard `this` keyword is intentionally set to reference the `EventEmitter` instance to which the listener is attached. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); myEmitter.on('event', function(a, b) { console.log(a, b, this, this === myEmitter); // Prints: // a b MyEmitter { // _events: [Object: null prototype] { event: [Function (anonymous)] }, // _eventsCount: 1, // _maxListeners: undefined, // Symbol(shapeMode): false, // Symbol(kCapture): false // } true }); myEmitter.emit('event', 'a', 'b'); It is possible to use ES6 Arrow Functions as listeners, however, when doing so, the `this` keyword will no longer reference the `EventEmitter` instance: import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); myEmitter.on('event', (a, b) => { console.log(a, b, this); // Prints: a b undefined }); myEmitter.emit('event', 'a', 'b'); ### Asynchronous vs. synchronous# The `EventEmitter` calls all listeners synchronously in the order in which they were registered. This ensures the proper sequencing of events and helps avoid race conditions and logic errors. When appropriate, listener functions can switch to an asynchronous mode of operation using the `setImmediate()` or `process.nextTick()` methods: import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); myEmitter.on('event', (a, b) => { setImmediate(() => { console.log('this happens asynchronously'); }); }); myEmitter.emit('event', 'a', 'b'); ### Handling events only once# When a listener is registered using the `eventEmitter.on()` method, that listener is invoked every time the named event is emitted. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); let m = 0; myEmitter.on('event', () => { console.log(++m); }); myEmitter.emit('event'); // Prints: 1 myEmitter.emit('event'); // Prints: 2 Using the `eventEmitter.once()` method, it is possible to register a listener that is called at most once for a particular event. Once the event is emitted, the listener is unregistered and then called. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); let m = 0; myEmitter.once('event', () => { console.log(++m); }); myEmitter.emit('event'); // Prints: 1 myEmitter.emit('event'); // Ignored ### Error events# When an error occurs within an `EventEmitter` instance, the typical action is for an `'error'` event to be emitted. These are treated as special cases within Node.js. If an `EventEmitter` does not have at least one listener registered for the `'error'` event, and an `'error'` event is emitted, the error is thrown, a stack trace is printed, and the Node.js process exits. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); myEmitter.emit('error', new Error('whoops!')); // Throws and crashes Node.js To guard against crashing the Node.js process the `domain` module can be used. (Note, however, that the `node:domain` module is deprecated.) As a best practice, listeners should always be added for the `'error'` events. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); myEmitter.on('error', (err) => { console.error('whoops! there was an error'); }); myEmitter.emit('error', new Error('whoops!')); // Prints: whoops! there was an error It is possible to monitor `'error'` events without consuming the emitted error by installing a listener using the symbol `events.errorMonitor`. import { EventEmitter, errorMonitor } from 'node:events'; const myEmitter = new EventEmitter(); myEmitter.on(errorMonitor, (err) => { MyMonitoringTool.log(err); }); myEmitter.emit('error', new Error('whoops!')); // Still throws and crashes Node.js ### Capture rejections of promises# Using `async` functions with event handlers is problematic, because it can lead to an unhandled rejection in case of a thrown exception: import { EventEmitter } from 'node:events'; const ee = new EventEmitter(); ee.on('something', async (value) => { throw new Error('kaboom'); }); The `captureRejections` option in the `EventEmitter` constructor or the global setting change this behavior, installing a `.then(undefined, handler)` handler on the `Promise`. This handler routes the exception asynchronously to the `Symbol.for('nodejs.rejection')` method if there is one, or to `'error'` event handler if there is none. import { EventEmitter } from 'node:events'; const ee1 = new EventEmitter({ captureRejections: true }); ee1.on('something', async (value) => { throw new Error('kaboom'); }); ee1.on('error', console.log); const ee2 = new EventEmitter({ captureRejections: true }); ee2.on('something', async (value) => { throw new Error('kaboom'); }); ee2[Symbol.for('nodejs.rejection')] = console.log; Setting `events.captureRejections = true` will change the default for all new instances of `EventEmitter`. import { EventEmitter } from 'node:events'; EventEmitter.captureRejections = true; const ee1 = new EventEmitter(); ee1.on('something', async (value) => { throw new Error('kaboom'); }); ee1.on('error', console.log); The `'error'` events that are generated by the `captureRejections` behavior do not have a catch handler to avoid infinite error loops: the recommendation is to not use `async` functions as `'error'` event handlers. ### Class: `EventEmitter`# History VersionChanges v13.4.0, v12.16.0 Added captureRejections option. v0.1.26 Added in: v0.1.26 The `EventEmitter` class is defined and exposed by the `node:events` module: import { EventEmitter } from 'node:events'; All `EventEmitter`s emit the event `'newListener'` when new listeners are added and `'removeListener'` when existing listeners are removed. It supports the following option: * `captureRejections` It enables automatic capturing of promise rejection. Default: `false`. #### Event: `'newListener'`# Added in: v0.1.26 * `eventName` | The name of the event being listened for * `listener` The event handler function The `EventEmitter` instance will emit its own `'newListener'` event before a listener is added to its internal array of listeners. Listeners registered for the `'newListener'` event are passed the event name and a reference to the listener being added. The fact that the event is triggered before adding the listener has a subtle but important side effect: any additional listeners registered to the same `name` within the `'newListener'` callback are inserted before the listener that is in the process of being added. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); // Only do this once so we don't loop forever myEmitter.once('newListener', (event, listener) => { if (event === 'event') { // Insert a new listener in front myEmitter.on('event', () => { console.log('B'); }); } }); myEmitter.on('event', () => { console.log('A'); }); myEmitter.emit('event'); // Prints: // B // A #### Event: `'removeListener'`# History VersionChanges v6.1.0, v4.7.0 For listeners attached using `.once()`, the `listener` argument now yields the original listener function. v0.9.3 Added in: v0.9.3 * `eventName` | The event name * `listener` The event handler function The `'removeListener'` event is emitted after the `listener` is removed. #### `emitter.addListener(eventName, listener)`# Added in: v0.1.26 * `eventName` | * `listener` Alias for `emitter.on(eventName, listener)`. #### `emitter.emit(eventName[, ...args])`# Added in: v0.1.26 * `eventName` | * `...args` * Returns: Synchronously calls each of the listeners registered for the event named `eventName`, in the order they were registered, passing the supplied arguments to each. Returns `true` if the event had listeners, `false` otherwise. import { EventEmitter } from 'node:events'; const myEmitter = new EventEmitter(); // First listener myEmitter.on('event', function firstListener() { console.log('Helloooo! first listener'); }); // Second listener myEmitter.on('event', function secondListener(arg1, arg2) { console.log(`event with parameters ${arg1}, ${arg2} in second listener`); }); // Third listener myEmitter.on('event', function thirdListener(...args) { const parameters = args.join(', '); console.log(`event with parameters ${parameters} in third listener`); }); console.log(myEmitter.listeners('event')); myEmitter.emit('event', 1, 2, 3, 4, 5); // Prints: // [ // [Function: firstListener], // [Function: secondListener], // [Function: thirdListener] // ] // Helloooo! first listener // event with parameters 1, 2 in second listener // event with parameters 1, 2, 3, 4, 5 in third listener #### `emitter.eventNames()`# Added in: v6.0.0 * Returns: | Returns an array listing the events for which the emitter has registered listeners. import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => {}); myEE.on('bar', () => {}); const sym = Symbol('symbol'); myEE.on(sym, () => {}); console.log(myEE.eventNames()); // Prints: [ 'foo', 'bar', Symbol(symbol) ] #### `emitter.getMaxListeners()`# Added in: v1.0.0 * Returns: Returns the current max listener value for the `EventEmitter` which is either set by `emitter.setMaxListeners(n)` or defaults to `events.defaultMaxListeners`. #### `emitter.listenerCount(eventName[, listener])`# History VersionChanges v19.8.0, v18.16.0 Added the `listener` argument. v3.2.0 Added in: v3.2.0 * `eventName` | The name of the event being listened for * `listener` The event handler function * Returns: Returns the number of listeners listening for the event named `eventName`. If `listener` is provided, it will return how many times the listener is found in the list of the listeners of the event. #### `emitter.listeners(eventName)`# History VersionChanges v7.0.0 For listeners attached using `.once()` this returns the original listeners instead of wrapper functions now. v0.1.26 Added in: v0.1.26 * `eventName` | * Returns: Returns a copy of the array of listeners for the event named `eventName`. server.on('connection', (stream) => { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ] #### `emitter.off(eventName, listener)`# Added in: v10.0.0 * `eventName` | * `listener` * Returns: Alias for `emitter.removeListener()`. #### `emitter.on(eventName, listener)`# Added in: v0.1.101 * `eventName` | The name of the event. * `listener` The callback function * Returns: Adds the `listener` function to the end of the listeners array for the event named `eventName`. No checks are made to see if the `listener` has already been added. Multiple calls passing the same combination of `eventName` and `listener` will result in the `listener` being added, and called, multiple times. server.on('connection', (stream) => { console.log('someone connected!'); }); Returns a reference to the `EventEmitter`, so that calls can be chained. By default, event listeners are invoked in the order they are added. The `emitter.prependListener()` method can be used as an alternative to add the event listener to the beginning of the listeners array. import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a #### `emitter.once(eventName, listener)`# Added in: v0.3.0 * `eventName` | The name of the event. * `listener` The callback function * Returns: Adds a one-time `listener` function for the event named `eventName`. The next time `eventName` is triggered, this listener is removed and then invoked. server.once('connection', (stream) => { console.log('Ah, we have our first user!'); }); Returns a reference to the `EventEmitter`, so that calls can be chained. By default, event listeners are invoked in the order they are added. The `emitter.prependOnceListener()` method can be used as an alternative to add the event listener to the beginning of the listeners array. import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.once('foo', () => console.log('a')); myEE.prependOnceListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a #### `emitter.prependListener(eventName, listener)`# Added in: v6.0.0 * `eventName` | The name of the event. * `listener` The callback function * Returns: Adds the `listener` function to the beginning of the listeners array for the event named `eventName`. No checks are made to see if the `listener` has already been added. Multiple calls passing the same combination of `eventName` and `listener` will result in the `listener` being added, and called, multiple times. server.prependListener('connection', (stream) => { console.log('someone connected!'); }); Returns a reference to the `EventEmitter`, so that calls can be chained. #### `emitter.prependOnceListener(eventName, listener)`# Added in: v6.0.0 * `eventName` | The name of the event. * `listener` The callback function * Returns: Adds a one-time `listener` function for the event named `eventName` to the beginning of the listeners array. The next time `eventName` is triggered, this listener is removed, and then invoked. server.prependOnceListener('connection', (stream) => { console.log('Ah, we have our first user!'); }); Returns a reference to the `EventEmitter`, so that calls can be chained. #### `emitter.removeAllListeners([eventName])`# Added in: v0.1.26 * `eventName` | * Returns: Removes all listeners, or those of the specified `eventName`. It is bad practice to remove listeners added elsewhere in the code, particularly when the `EventEmitter` instance was created by some other component or module (e.g. sockets or file streams). Returns a reference to the `EventEmitter`, so that calls can be chained. #### `emitter.removeListener(eventName, listener)`# Added in: v0.1.26 * `eventName` | * `listener` * Returns: Removes the specified `listener` from the listener array for the event named `eventName`. const callback = (stream) => { console.log('someone connected!'); }; server.on('connection', callback); // ... server.removeListener('connection', callback); `removeListener()` will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified `eventName`, then `removeListener()` must be called multiple times to remove each instance. Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any `removeListener()` or `removeAllListeners()` calls after emitting and before the last listener finishes execution will not remove them from `emit()` in progress. Subsequent events behave as expected. import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); const callbackA = () => { console.log('A'); myEmitter.removeListener('event', callbackB); }; const callbackB = () => { console.log('B'); }; myEmitter.on('event', callbackA); myEmitter.on('event', callbackB); // callbackA removes listener callbackB but it will still be called. // Internal listener array at time of emit [callbackA, callbackB] myEmitter.emit('event'); // Prints: // A // B // callbackB is now removed. // Internal listener array [callbackA] myEmitter.emit('event'); // Prints: // A Because listeners are managed using an internal array, calling this will change the position indexes of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the `emitter.listeners()` method will need to be recreated. When a single function has been added as a handler multiple times for a single event (as in the example below), `removeListener()` will remove the most recently added instance. In the example the `once('ping')` listener is removed: import { EventEmitter } from 'node:events'; const ee = new EventEmitter(); function pong() { console.log('pong'); } ee.on('ping', pong); ee.once('ping', pong); ee.removeListener('ping', pong); ee.emit('ping'); ee.emit('ping'); Returns a reference to the `EventEmitter`, so that calls can be chained. #### `emitter.setMaxListeners(n)`# Added in: v0.3.5 * `n` * Returns: By default `EventEmitter`s will print a warning if more than `10` listeners are added for a particular event. This is a useful default that helps finding memory leaks. The `emitter.setMaxListeners()` method allows the limit to be modified for this specific `EventEmitter` instance. The value can be set to `Infinity` (or `0`) to indicate an unlimited number of listeners. Returns a reference to the `EventEmitter`, so that calls can be chained. #### `emitter.rawListeners(eventName)`# Added in: v9.4.0 * `eventName` | * Returns: Returns a copy of the array of listeners for the event named `eventName`, including any wrappers (such as those created by `.once()`). import { EventEmitter } from 'node:events'; const emitter = new EventEmitter(); emitter.once('log', () => console.log('log once')); // Returns a new Array with a function `onceWrapper` which has a property // `listener` which contains the original listener bound above const listeners = emitter.rawListeners('log'); const logFnWrapper = listeners[0]; // Logs "log once" to the console and does not unbind the `once` event logFnWrapper.listener(); // Logs "log once" to the console and removes the listener logFnWrapper(); emitter.on('log', () => console.log('log persistently')); // Will return a new Array with a single function bound by `.on()` above const newListeners = emitter.rawListeners('log'); // Logs "log persistently" twice newListeners[0](); emitter.emit('log'); #### `emitter[Symbol.for('nodejs.rejection')](err, eventName[, ...args])`# History VersionChanges v17.4.0, v16.14.0 No longer experimental. v13.4.0, v12.16.0 Added in: v13.4.0, v12.16.0 * `err` * `eventName` | * `...args` The `Symbol.for('nodejs.rejection')` method is called in case a promise rejection happens when emitting an event and `captureRejections` is enabled on the emitter. It is possible to use `events.captureRejectionSymbol` in place of `Symbol.for('nodejs.rejection')`. import { EventEmitter, captureRejectionSymbol } from 'node:events'; class MyClass extends EventEmitter { constructor() { super({ captureRejections: true }); } [captureRejectionSymbol](err, event, ...args) { console.log('rejection happened for', event, 'with', err, ...args); this.destroy(err); } destroy(err) { // Tear the resource down here. } } ### `events.defaultMaxListeners`# Added in: v0.11.2 By default, a maximum of `10` listeners can be registered for any single event. This limit can be changed for individual `EventEmitter` instances using the `emitter.setMaxListeners(n)` method. To change the default for all `EventEmitter` instances, the `events.defaultMaxListeners` property can be used. If this value is not a positive number, a `RangeError` is thrown. Take caution when setting the `events.defaultMaxListeners` because the change affects all `EventEmitter` instances, including those created before the change is made. However, calling `emitter.setMaxListeners(n)` still has precedence over `events.defaultMaxListeners`. This is not a hard limit. The `EventEmitter` instance will allow more listeners to be added but will output a trace warning to stderr indicating that a "possible EventEmitter memory leak" has been detected. For any single `EventEmitter`, the `emitter.getMaxListeners()` and `emitter.setMaxListeners()` methods can be used to temporarily avoid this warning: `defaultMaxListeners` has no effect on `AbortSignal` instances. While it is still possible to use `emitter.setMaxListeners(n)` to set a warning limit for individual `AbortSignal` instances, per default `AbortSignal` instances will not warn. import { EventEmitter } from 'node:events'; const emitter = new EventEmitter(); emitter.setMaxListeners(emitter.getMaxListeners() + 1); emitter.once('event', () => { // do stuff emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0)); }); The `--trace-warnings` command-line flag can be used to display the stack trace for such warnings. The emitted warning can be inspected with `process.on('warning')` and will have the additional `emitter`, `type`, and `count` properties, referring to the event emitter instance, the event's name and the number of attached listeners, respectively. Its `name` property is set to `'MaxListenersExceededWarning'`. ### `events.errorMonitor`# Added in: v13.6.0, v12.17.0 This symbol shall be used to install a listener for only monitoring `'error'` events. Listeners installed using this symbol are called before the regular `'error'` listeners are called. Installing a listener using this symbol does not change the behavior once an `'error'` event is emitted. Therefore, the process will still crash if no regular `'error'` listener is installed. ### `events.getEventListeners(emitterOrTarget, eventName)`# Added in: v15.2.0, v14.17.0 * `emitterOrTarget` | * `eventName` | * Returns: Returns a copy of the array of listeners for the event named `eventName`. For `EventEmitter`s this behaves exactly the same as calling `.listeners` on the emitter. For `EventTarget`s this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes. import { getEventListeners, EventEmitter } from 'node:events'; { const ee = new EventEmitter(); const listener = () => console.log('Events are fun'); ee.on('foo', listener); console.log(getEventListeners(ee, 'foo')); // [ [Function: listener] ] } { const et = new EventTarget(); const listener = () => console.log('Events are fun'); et.addEventListener('foo', listener); console.log(getEventListeners(et, 'foo')); // [ [Function: listener] ] } ### `events.getMaxListeners(emitterOrTarget)`# Added in: v19.9.0, v18.17.0 * `emitterOrTarget` | * Returns: Returns the currently set max amount of listeners. For `EventEmitter`s this behaves exactly the same as calling `.getMaxListeners` on the emitter. For `EventTarget`s this is the only way to get the max event listeners for the event target. If the number of event handlers on a single EventTarget exceeds the max set, the EventTarget will print a warning. import { getMaxListeners, setMaxListeners, EventEmitter } from 'node:events'; { const ee = new EventEmitter(); console.log(getMaxListeners(ee)); // 10 setMaxListeners(11, ee); console.log(getMaxListeners(ee)); // 11 } { const et = new EventTarget(); console.log(getMaxListeners(et)); // 10 setMaxListeners(11, et); console.log(getMaxListeners(et)); // 11 } ### `events.once(emitter, name[, options])`# History VersionChanges v15.0.0 The `signal` option is supported now. v11.13.0, v10.16.0 Added in: v11.13.0, v10.16.0 * `emitter` * `name` | * `options` * `signal` Can be used to cancel waiting for the event. * Returns: Creates a `Promise` that is fulfilled when the `EventEmitter` emits the given event or that is rejected if the `EventEmitter` emits `'error'` while waiting. The `Promise` will resolve with an array of all the arguments emitted to the given event. This method is intentionally generic and works with the web platform EventTarget interface, which has no special `'error'` event semantics and does not listen to the `'error'` event. import { once, EventEmitter } from 'node:events'; import process from 'node:process'; const ee = new EventEmitter(); process.nextTick(() => { ee.emit('myevent', 42); }); const [value] = await once(ee, 'myevent'); console.log(value); const err = new Error('kaboom'); process.nextTick(() => { ee.emit('error', err); }); try { await once(ee, 'myevent'); } catch (err) { console.error('error happened', err); } The special handling of the `'error'` event is only used when `events.once()` is used to wait for another event. If `events.once()` is used to wait for the '`error'` event itself, then it is treated as any other kind of event without special handling: import { EventEmitter, once } from 'node:events'; const ee = new EventEmitter(); once(ee, 'error') .then(([err]) => console.log('ok', err.message)) .catch((err) => console.error('error', err.message)); ee.emit('error', new Error('boom')); // Prints: ok boom An can be used to cancel waiting for the event: import { EventEmitter, once } from 'node:events'; const ee = new EventEmitter(); const ac = new AbortController(); async function foo(emitter, event, signal) { try { await once(emitter, event, { signal }); console.log('event emitted!'); } catch (error) { if (error.name === 'AbortError') { console.error('Waiting for the event was canceled!'); } else { console.error('There was an error', error.message); } } } foo(ee, 'foo', ac.signal); ac.abort(); // Prints: Waiting for the event was canceled! #### Awaiting multiple events emitted on `process.nextTick()`# There is an edge case worth noting when using the `events.once()` function to await multiple events emitted on in the same batch of `process.nextTick()` operations, or whenever multiple events are emitted synchronously. Specifically, because the `process.nextTick()` queue is drained before the `Promise` microtask queue, and because `EventEmitter` emits all events synchronously, it is possible for `events.once()` to miss an event. import { EventEmitter, once } from 'node:events'; import process from 'node:process'; const myEE = new EventEmitter(); async function foo() { await once(myEE, 'bar'); console.log('bar'); // This Promise will never resolve because the 'foo' event will // have already been emitted before the Promise is created. await once(myEE, 'foo'); console.log('foo'); } process.nextTick(() => { myEE.emit('bar'); myEE.emit('foo'); }); foo().then(() => console.log('done')); To catch both events, create each of the Promises before awaiting either of them, then it becomes possible to use `Promise.all()`, `Promise.race()`, or `Promise.allSettled()`: import { EventEmitter, once } from 'node:events'; import process from 'node:process'; const myEE = new EventEmitter(); async function foo() { await Promise.all([once(myEE, 'bar'), once(myEE, 'foo')]); console.log('foo', 'bar'); } process.nextTick(() => { myEE.emit('bar'); myEE.emit('foo'); }); foo().then(() => console.log('done')); ### `events.captureRejections`# History VersionChanges v17.4.0, v16.14.0 No longer experimental. v13.4.0, v12.16.0 Added in: v13.4.0, v12.16.0 * Type: Change the default `captureRejections` option on all new `EventEmitter` objects. ### `events.captureRejectionSymbol`# History VersionChanges v17.4.0, v16.14.0 No longer experimental. v13.4.0, v12.16.0 Added in: v13.4.0, v12.16.0 * Type: `Symbol.for('nodejs.rejection')` See how to write a custom rejection handler. ### `events.listenerCount(emitter, eventName)`# Added in: v0.9.12Deprecated since: v3.2.0 Stability: 0 \- Deprecated: Use `emitter.listenerCount()` instead. * `emitter` The emitter to query * `eventName` | The event name A class method that returns the number of listeners for the given `eventName` registered on the given `emitter`. import { EventEmitter, listenerCount } from 'node:events'; const myEmitter = new EventEmitter(); myEmitter.on('event', () => {}); myEmitter.on('event', () => {}); console.log(listenerCount(myEmitter, 'event')); // Prints: 2 ### `events.on(emitter, eventName[, options])`# History VersionChanges v22.0.0, v20.13.0 Support `highWaterMark` and `lowWaterMark` options, For consistency. Old options are still supported. v20.0.0 The `close`, `highWatermark`, and `lowWatermark` options are supported now. v13.6.0, v12.16.0 Added in: v13.6.0, v12.16.0 * `emitter` * `eventName` | The name of the event being listened for * `options` * `signal` Can be used to cancel awaiting events. * `close` Names of events that will end the iteration. * `highWaterMark` Default: `Number.MAX_SAFE_INTEGER` The high watermark. The emitter is paused every time the size of events being buffered is higher than it. Supported only on emitters implementing `pause()` and `resume()` methods. * `lowWaterMark` Default: `1` The low watermark. The emitter is resumed every time the size of events being buffered is lower than it. Supported only on emitters implementing `pause()` and `resume()` methods. * Returns: that iterates `eventName` events emitted by the `emitter` import { on, EventEmitter } from 'node:events'; import process from 'node:process'; const ee = new EventEmitter(); // Emit later on process.nextTick(() => { ee.emit('foo', 'bar'); ee.emit('foo', 42); }); for await (const event of on(ee, 'foo')) { // The execution of this inner block is synchronous and it // processes one event at a time (even with await). Do not use // if concurrent execution is required. console.log(event); // prints ['bar'] [42] } // Unreachable here Returns an `AsyncIterator` that iterates `eventName` events. It will throw if the `EventEmitter` emits `'error'`. It removes all listeners when exiting the loop. The `value` returned by each iteration is an array composed of the emitted event arguments. An can be used to cancel waiting on events: import { on, EventEmitter } from 'node:events'; import process from 'node:process'; const ac = new AbortController(); (async () => { const ee = new EventEmitter(); // Emit later on process.nextTick(() => { ee.emit('foo', 'bar'); ee.emit('foo', 42); }); for await (const event of on(ee, 'foo', { signal: ac.signal })) { // The execution of this inner block is synchronous and it // processes one event at a time (even with await). Do not use // if concurrent execution is required. console.log(event); // prints ['bar'] [42] } // Unreachable here })(); process.nextTick(() => ac.abort()); ### `events.setMaxListeners(n[, ...eventTargets])`# Added in: v15.4.0 * `n` A non-negative number. The maximum number of listeners per `EventTarget` event. * `...eventsTargets` | Zero or more or instances. If none are specified, `n` is set as the default max for all newly created and objects. import { setMaxListeners, EventEmitter } from 'node:events'; const target = new EventTarget(); const emitter = new EventEmitter(); setMaxListeners(5, target, emitter); ### `events.addAbortListener(signal, listener)`# History VersionChanges v24.0.0 Change stability index for this feature from Experimental to Stable. v20.5.0, v18.18.0 Added in: v20.5.0, v18.18.0 * `signal` * `listener` | * Returns: A Disposable that removes the `abort` listener. Listens once to the `abort` event on the provided `signal`. Listening to the `abort` event on abort signals is unsafe and may lead to resource leaks since another third party with the signal can call `e.stopImmediatePropagation()`. Unfortunately Node.js cannot change this since it would violate the web standard. Additionally, the original API makes it easy to forget to remove listeners. This API allows safely using `AbortSignal`s in Node.js APIs by solving these two issues by listening to the event such that `stopImmediatePropagation` does not prevent the listener from running. Returns a disposable so that it may be unsubscribed from more easily. import { addAbortListener } from 'node:events'; function example(signal) { let disposable; try { signal.addEventListener('abort', (e) => e.stopImmediatePropagation()); disposable = addAbortListener(signal, (e) => { // Do something when signal is aborted. }); } finally { disposable?.[Symbol.dispose](); } } ### Class: `events.EventEmitterAsyncResource extends EventEmitter`# Added in: v17.4.0, v16.14.0 Integrates `EventEmitter` with for `EventEmitter`s that require manual async tracking. Specifically, all events emitted by instances of `events.EventEmitterAsyncResource` will run within its async context. import { EventEmitterAsyncResource, EventEmitter } from 'node:events'; import { notStrictEqual, strictEqual } from 'node:assert'; import { executionAsyncId, triggerAsyncId } from 'node:async_hooks'; // Async tracking tooling will identify this as 'Q'. const ee1 = new EventEmitterAsyncResource({ name: 'Q' }); // 'foo' listeners will run in the EventEmitters async context. ee1.on('foo', () => { strictEqual(executionAsyncId(), ee1.asyncId); strictEqual(triggerAsyncId(), ee1.triggerAsyncId); }); const ee2 = new EventEmitter(); // 'foo' listeners on ordinary EventEmitters that do not track async // context, however, run in the same async context as the emit(). ee2.on('foo', () => { notStrictEqual(executionAsyncId(), ee2.asyncId); notStrictEqual(triggerAsyncId(), ee2.triggerAsyncId); }); Promise.resolve().then(() => { ee1.emit('foo'); ee2.emit('foo'); }); The `EventEmitterAsyncResource` class has the same methods and takes the same options as `EventEmitter` and `AsyncResource` themselves. #### `new events.EventEmitterAsyncResource([options])`# * `options` * `captureRejections` It enables automatic capturing of promise rejection. Default: `false`. * `name` The type of async event. Default: `new.target.name`. * `triggerAsyncId` The ID of the execution context that created this async event. Default: `executionAsyncId()`. * `requireManualDestroy` If set to `true`, disables `emitDestroy` when the object is garbage collected. This usually does not need to be set (even if `emitDestroy` is called manually), unless the resource's `asyncId` is retrieved and the sensitive API's `emitDestroy` is called with it. When set to `false`, the `emitDestroy` call on garbage collection will only take place if there is at least one active `destroy` hook. Default: `false`. #### `eventemitterasyncresource.asyncId`# * Type: The unique `asyncId` assigned to the resource. #### `eventemitterasyncresource.asyncResource`# * Type: The underlying . The returned `AsyncResource` object has an additional `eventEmitter` property that provides a reference to this `EventEmitterAsyncResource`. #### `eventemitterasyncresource.emitDestroy()`# Call all `destroy` hooks. This should only ever be called once. An error will be thrown if it is called more than once. This must be manually called. If the resource is left to be collected by the GC then the `destroy` hooks will never be called. #### `eventemitterasyncresource.triggerAsyncId`# * Type: The same `triggerAsyncId` that is passed to the `AsyncResource` constructor. ### `EventTarget` and `Event` API# History VersionChanges v16.0.0 changed EventTarget error handling. v15.4.0 No longer experimental. v15.0.0 The `EventTarget` and `Event` classes are now available as globals. v14.5.0 Added in: v14.5.0 The `EventTarget` and `Event` objects are a Node.js-specific implementation of the `EventTarget` Web API that are exposed by some Node.js core APIs. const target = new EventTarget(); target.addEventListener('foo', (event) => { console.log('foo event happened!'); }); #### Node.js `EventTarget` vs. DOM `EventTarget`# There are two key differences between the Node.js `EventTarget` and the `EventTarget` Web API: 1. Whereas DOM `EventTarget` instances may be hierarchical, there is no concept of hierarchy and event propagation in Node.js. That is, an event dispatched to an `EventTarget` does not propagate through a hierarchy of nested target objects that may each have their own set of handlers for the event. 2. In the Node.js `EventTarget`, if an event listener is an async function or returns a `Promise`, and the returned `Promise` rejects, the rejection is automatically captured and handled the same way as a listener that throws synchronously (see `EventTarget` error handling for details). #### `NodeEventTarget` vs. `EventEmitter`# The `NodeEventTarget` object implements a modified subset of the `EventEmitter` API that allows it to closely emulate an `EventEmitter` in certain situations. A `NodeEventTarget` is not an instance of `EventEmitter` and cannot be used in place of an `EventEmitter` in most cases. 1. Unlike `EventEmitter`, any given `listener` can be registered at most once per event `type`. Attempts to register a `listener` multiple times are ignored. 2. The `NodeEventTarget` does not emulate the full `EventEmitter` API. Specifically the `prependListener()`, `prependOnceListener()`, `rawListeners()`, and `errorMonitor` APIs are not emulated. The `'newListener'` and `'removeListener'` events will also not be emitted. 3. The `NodeEventTarget` does not implement any special default behavior for events with type `'error'`. 4. The `NodeEventTarget` supports `EventListener` objects as well as functions as handlers for all event types. #### Event listener# Event listeners registered for an event `type` may either be JavaScript functions or objects with a `handleEvent` property whose value is a function. In either case, the handler function is invoked with the `event` argument passed to the `eventTarget.dispatchEvent()` function. Async functions may be used as event listeners. If an async handler function rejects, the rejection is captured and handled as described in `EventTarget` error handling. An error thrown by one handler function does not prevent the other handlers from being invoked. The return value of a handler function is ignored. Handlers are always invoked in the order they were added. Handler functions may mutate the `event` object. function handler1(event) { console.log(event.type); // Prints 'foo' event.a = 1; } async function handler2(event) { console.log(event.type); // Prints 'foo' console.log(event.a); // Prints 1 } const handler3 = { handleEvent(event) { console.log(event.type); // Prints 'foo' }, }; const handler4 = { async handleEvent(event) { console.log(event.type); // Prints 'foo' }, }; const target = new EventTarget(); target.addEventListener('foo', handler1); target.addEventListener('foo', handler2); target.addEventListener('foo', handler3); target.addEventListener('foo', handler4, { once: true }); #### `EventTarget` error handling# When a registered event listener throws (or returns a Promise that rejects), by default the error is treated as an uncaught exception on `process.nextTick()`. This means uncaught exceptions in `EventTarget`s will terminate the Node.js process by default. Throwing within an event listener will not stop the other registered handlers from being invoked. The `EventTarget` does not implement any special default handling for `'error'` type events like `EventEmitter`. Currently errors are first forwarded to the `process.on('error')` event before reaching `process.on('uncaughtException')`. This behavior is deprecated and will change in a future release to align `EventTarget` with other Node.js APIs. Any code relying on the `process.on('error')` event should be aligned with the new behavior. #### Class: `Event`# History VersionChanges v15.0.0 The `Event` class is now available through the global object. v14.5.0 Added in: v14.5.0 The `Event` object is an adaptation of the `Event` Web API. Instances are created internally by Node.js. ##### `event.bubbles`# Added in: v14.5.0 * Type: Always returns `false`. This is not used in Node.js and is provided purely for completeness. ##### `event.cancelBubble`# Added in: v14.5.0 Stability: 3 \- Legacy: Use `event.stopPropagation()` instead. * Type: Alias for `event.stopPropagation()` if set to `true`. This is not used in Node.js and is provided purely for completeness. ##### `event.cancelable`# Added in: v14.5.0 * Type: True if the event was created with the `cancelable` option. ##### `event.composed`# Added in: v14.5.0 * Type: Always returns `false`. This is not used in Node.js and is provided purely for completeness. ##### `event.composedPath()`# Added in: v14.5.0 Returns an array containing the current `EventTarget` as the only entry or empty if the event is not being dispatched. This is not used in Node.js and is provided purely for completeness. ##### `event.currentTarget`# Added in: v14.5.0 * Type: The `EventTarget` dispatching the event. Alias for `event.target`. ##### `event.defaultPrevented`# Added in: v14.5.0 * Type: Is `true` if `cancelable` is `true` and `event.preventDefault()` has been called. ##### `event.eventPhase`# Added in: v14.5.0 * Type: Returns `0` while an event is not being dispatched, `2` while it is being dispatched. This is not used in Node.js and is provided purely for completeness. ##### `event.initEvent(type[, bubbles[, cancelable]])`# Added in: v19.5.0 Stability: 3 \- Legacy: The WHATWG spec considers it deprecated and users shouldn't use it at all. * `type` * `bubbles` * `cancelable` Redundant with event constructors and incapable of setting `composed`. This is not used in Node.js and is provided purely for completeness. ##### `event.isTrusted`# Added in: v14.5.0 * Type: The `"abort"` event is emitted with `isTrusted` set to `true`. The value is `false` in all other cases. ##### `event.preventDefault()`# Added in: v14.5.0 Sets the `defaultPrevented` property to `true` if `cancelable` is `true`. ##### `event.returnValue`# Added in: v14.5.0 Stability: 3 \- Legacy: Use `event.defaultPrevented` instead. * Type: True if the event has not been canceled. The value of `event.returnValue` is always the opposite of `event.defaultPrevented`. This is not used in Node.js and is provided purely for completeness. ##### `event.srcElement`# Added in: v14.5.0 Stability: 3 \- Legacy: Use `event.target` instead. * Type: The `EventTarget` dispatching the event. Alias for `event.target`. ##### `event.stopImmediatePropagation()`# Added in: v14.5.0 Stops the invocation of event listeners after the current one completes. ##### `event.stopPropagation()`# Added in: v14.5.0 This is not used in Node.js and is provided purely for completeness. ##### `event.target`# Added in: v14.5.0 * Type: The `EventTarget` dispatching the event. ##### `event.timeStamp`# Added in: v14.5.0 * Type: The millisecond timestamp when the `Event` object was created. ##### `event.type`# Added in: v14.5.0 * Type: The event type identifier. #### Class: `EventTarget`# History VersionChanges v15.0.0 The `EventTarget` class is now available through the global object. v14.5.0 Added in: v14.5.0 ##### `eventTarget.addEventListener(type, listener[, options])`# History VersionChanges v15.4.0 add support for `signal` option. v14.5.0 Added in: v14.5.0 * `type` * `listener` | * `options` * `once` When `true`, the listener is automatically removed when it is first invoked. Default: `false`. * `passive` When `true`, serves as a hint that the listener will not call the `Event` object's `preventDefault()` method. Default: `false`. * `capture` Not directly used by Node.js. Added for API completeness. Default: `false`. * `signal` The listener will be removed when the given AbortSignal object's `abort()` method is called. Adds a new handler for the `type` event. Any given `listener` is added only once per `type` and per `capture` option value. If the `once` option is `true`, the `listener` is removed after the next time a `type` event is dispatched. The `capture` option is not used by Node.js in any functional way other than tracking registered event listeners per the `EventTarget` specification. Specifically, the `capture` option is used as part of the key when registering a `listener`. Any individual `listener` may be added once with `capture = false`, and once with `capture = true`. function handler(event) {} const target = new EventTarget(); target.addEventListener('foo', handler, { capture: true }); // first target.addEventListener('foo', handler, { capture: false }); // second // Removes the second instance of handler target.removeEventListener('foo', handler); // Removes the first instance of handler target.removeEventListener('foo', handler, { capture: true }); ##### `eventTarget.dispatchEvent(event)`# Added in: v14.5.0 * `event` * Returns: `true` if either event's `cancelable` attribute value is false or its `preventDefault()` method was not invoked, otherwise `false`. Dispatches the `event` to the list of handlers for `event.type`. The registered event listeners is synchronously invoked in the order they were registered. ##### `eventTarget.removeEventListener(type, listener[, options])`# Added in: v14.5.0 * `type` * `listener` | * `options` * `capture` Removes the `listener` from the list of handlers for event `type`. #### Class: `CustomEvent`# History VersionChanges v23.0.0 No longer experimental. v22.1.0, v20.13.0 CustomEvent is now stable. v19.0.0 No longer behind `--experimental-global-customevent` CLI flag. v18.7.0, v16.17.0 Added in: v18.7.0, v16.17.0 * Extends: The `CustomEvent` object is an adaptation of the `CustomEvent` Web API. Instances are created internally by Node.js. ##### `event.detail`# History VersionChanges v22.1.0, v20.13.0 CustomEvent is now stable. v18.7.0, v16.17.0 Added in: v18.7.0, v16.17.0 * Type: Returns custom data passed when initializing. Read-only. #### Class: `NodeEventTarget`# Added in: v14.5.0 * Extends: The `NodeEventTarget` is a Node.js-specific extension to `EventTarget` that emulates a subset of the `EventEmitter` API. ##### `nodeEventTarget.addListener(type, listener)`# Added in: v14.5.0 * `type` * `listener` | * Returns: this Node.js-specific extension to the `EventTarget` class that emulates the equivalent `EventEmitter` API. The only difference between `addListener()` and `addEventListener()` is that `addListener()` will return a reference to the `EventTarget`. ##### `nodeEventTarget.emit(type, arg)`# Added in: v15.2.0 * `type` * `arg` * Returns: `true` if event listeners registered for the `type` exist, otherwise `false`. Node.js-specific extension to the `EventTarget` class that dispatches the `arg` to the list of handlers for `type`. ##### `nodeEventTarget.eventNames()`# Added in: v14.5.0 * Returns: Node.js-specific extension to the `EventTarget` class that returns an array of event `type` names for which event listeners are registered. ##### `nodeEventTarget.listenerCount(type)`# Added in: v14.5.0 * `type` * Returns: Node.js-specific extension to the `EventTarget` class that returns the number of event listeners registered for the `type`. ##### `nodeEventTarget.setMaxListeners(n)`# Added in: v14.5.0 * `n` Node.js-specific extension to the `EventTarget` class that sets the number of max event listeners as `n`. ##### `nodeEventTarget.getMaxListeners()`# Added in: v14.5.0 * Returns: Node.js-specific extension to the `EventTarget` class that returns the number of max event listeners. ##### `nodeEventTarget.off(type, listener[, options])`# Added in: v14.5.0 * `type` * `listener` | * `options` * `capture` * Returns: this Node.js-specific alias for `eventTarget.removeEventListener()`. ##### `nodeEventTarget.on(type, listener)`# Added in: v14.5.0 * `type` * `listener` | * Returns: this Node.js-specific alias for `eventTarget.addEventListener()`. ##### `nodeEventTarget.once(type, listener)`# Added in: v14.5.0 * `type` * `listener` | * Returns: this Node.js-specific extension to the `EventTarget` class that adds a `once` listener for the given event `type`. This is equivalent to calling `on` with the `once` option set to `true`. ##### `nodeEventTarget.removeAllListeners([type])`# Added in: v14.5.0 * `type` * Returns: this Node.js-specific extension to the `EventTarget` class. If `type` is specified, removes all registered listeners for `type`, otherwise removes all registered listeners. ##### `nodeEventTarget.removeListener(type, listener[, options])`# Added in: v14.5.0 * `type` * `listener` | * `options` * `capture` * Returns: this Node.js-specific extension to the `EventTarget` class that removes the `listener` for the given `type`. The only difference between `removeListener()` and `removeEventListener()` is that `removeListener()` will return a reference to the `EventTarget`. ## File system# Stability: 2 \- Stable Source Code: lib/fs.js The `node:fs` module enables interacting with the file system in a way modeled on standard POSIX functions. To use the promise-based APIs: import * as fs from 'node:fs/promises'; To use the callback and sync APIs: import * as fs from 'node:fs'; All file system operations have synchronous, callback, and promise-based forms, and are accessible using both CommonJS syntax and ES6 Modules (ESM). ### Promise example# Promise-based operations return a promise that is fulfilled when the asynchronous operation is complete. import { unlink } from 'node:fs/promises'; try { await unlink('/tmp/hello'); console.log('successfully deleted /tmp/hello'); } catch (error) { console.error('there was an error:', error.message); } ### Callback example# The callback form takes a completion callback function as its last argument and invokes the operation asynchronously. The arguments passed to the completion callback depend on the method, but the first argument is always reserved for an exception. If the operation is completed successfully, then the first argument is `null` or `undefined`. import { unlink } from 'node:fs'; unlink('/tmp/hello', (err) => { if (err) throw err; console.log('successfully deleted /tmp/hello'); }); The callback-based versions of the `node:fs` module APIs are preferable over the use of the promise APIs when maximal performance (both in terms of execution time and memory allocation) is required. ### Synchronous example# The synchronous APIs block the Node.js event loop and further JavaScript execution until the operation is complete. Exceptions are thrown immediately and can be handled using `try…catch`, or can be allowed to bubble up. import { unlinkSync } from 'node:fs'; try { unlinkSync('/tmp/hello'); console.log('successfully deleted /tmp/hello'); } catch (err) { // handle the error } ### Promises API# History VersionChanges v14.0.0 Exposed as `require('fs/promises')`. v11.14.0, v10.17.0 This API is no longer experimental. v10.1.0 The API is accessible via `require('fs').promises` only. v10.0.0 Added in: v10.0.0 The `fs/promises` API provides asynchronous file system methods that return promises. The promise APIs use the underlying Node.js threadpool to perform file system operations off the event loop thread. These operations are not synchronized or threadsafe. Care must be taken when performing multiple concurrent modifications on the same file or data corruption may occur. #### Class: `FileHandle`# Added in: v10.0.0 A object is an object wrapper for a numeric file descriptor. Instances of the object are created by the `fsPromises.open()` method. All objects are s. If a is not closed using the `filehandle.close()` method, it will try to automatically close the file descriptor and emit a process warning, helping to prevent memory leaks. Please do not rely on this behavior because it can be unreliable and the file may not be closed. Instead, always explicitly close s. Node.js may change this behavior in the future. ##### Event: `'close'`# Added in: v15.4.0 The `'close'` event is emitted when the has been closed and can no longer be used. ##### `filehandle.appendFile(data[, options])`# History VersionChanges v21.1.0, v20.10.0 The `flush` option is now supported. v15.14.0, v14.18.0 The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. v14.0.0 The `data` parameter won't coerce unsupported input to strings anymore. v10.0.0 Added in: v10.0.0 * `data` | | | | | | * `options` | * `encoding` | Default: `'utf8'` * `signal` | allows aborting an in-progress writeFile. Default: `undefined` * Returns: Fulfills with `undefined` upon success. Alias of `filehandle.writeFile()`. When operating on file handles, the mode cannot be changed from what it was set to with `fsPromises.open()`. Therefore, this is equivalent to `filehandle.writeFile()`. ##### `filehandle.chmod(mode)`# Added in: v10.0.0 * `mode` the file mode bit mask. * Returns: Fulfills with `undefined` upon success. Modifies the permissions on the file. See `chmod(2)`. ##### `filehandle.chown(uid, gid)`# Added in: v10.0.0 * `uid` The file's new owner's user id. * `gid` The file's new group's group id. * Returns: Fulfills with `undefined` upon success. Changes the ownership of the file. A wrapper for `chown(2)`. ##### `filehandle.close()`# Added in: v10.0.0 * Returns: Fulfills with `undefined` upon success. Closes the file handle after waiting for any pending operation on the handle to complete. import { open } from 'node:fs/promises'; let filehandle; try { filehandle = await open('thefile.txt', 'r'); } finally { await filehandle?.close(); } ##### `filehandle.createReadStream([options])`# Added in: v16.11.0 * `options` * `encoding` Default: `null` * `autoClose` Default: `true` * `emitClose` Default: `true` * `start` * `end` Default: `Infinity` * `highWaterMark` Default: `64 * 1024` * `signal` | Default: `undefined` * Returns: `options` can include `start` and `end` values to read a range of bytes from the file instead of the entire file. Both `start` and `end` are inclusive and start counting at 0, allowed values are in the [0, `Number.MAX_SAFE_INTEGER`] range. If `start` is omitted or `undefined`, `filehandle.createReadStream()` reads sequentially from the current file position. The `encoding` can be any one of those accepted by . If the `FileHandle` points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. import { open } from 'node:fs/promises'; const fd = await open('/dev/input/event0'); // Create a stream from some character device. const stream = fd.createReadStream(); setTimeout(() => { stream.close(); // This may not close the stream. // Artificially marking end-of-stream, as if the underlying resource had // indicated end-of-file by itself, allows the stream to close. // This does not cancel pending read operations, and if there is such an // operation, the process may still not be able to exit successfully // until it finishes. stream.push(null); stream.read(0); }, 100); If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak. If `autoClose` is set to true (default behavior), on `'error'` or `'end'` the file descriptor will be closed automatically. An example to read the last 10 bytes of a file which is 100 bytes long: import { open } from 'node:fs/promises'; const fd = await open('sample.txt'); fd.createReadStream({ start: 90, end: 99 }); ##### `filehandle.createWriteStream([options])`# History VersionChanges v21.0.0, v20.10.0 The `flush` option is now supported. v16.11.0 Added in: v16.11.0 * `options` * `encoding` Default: `'utf8'` * `autoClose` Default: `true` * `emitClose` Default: `true` * `start` * `highWaterMark` Default: `16384` * `flush` If `true`, the underlying file descriptor is flushed prior to closing it. Default: `false`. * Returns: `options` may also include a `start` option to allow writing data at some position past the beginning of the file, allowed values are in the [0, `Number.MAX_SAFE_INTEGER`] range. Modifying a file rather than replacing it may require the `flags` `open` option to be set to `r+` rather than the default `r`. The `encoding` can be any one of those accepted by . If `autoClose` is set to true (default behavior) on `'error'` or `'finish'` the file descriptor will be closed automatically. If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. ##### `filehandle.datasync()`# Added in: v10.0.0 * Returns: Fulfills with `undefined` upon success. Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX `fdatasync(2)` documentation for details. Unlike `filehandle.sync` this method does not flush modified metadata. ##### `filehandle.fd`# Added in: v10.0.0 * Type: The numeric file descriptor managed by the object. ##### `filehandle.read(buffer, offset, length, position)`# History VersionChanges v21.0.0 Accepts bigint values as `position`. v10.0.0 Added in: v10.0.0 * `buffer` | | A buffer that will be filled with the file data read. * `offset` The location in the buffer at which to start filling. Default: `0` * `length` The number of bytes to read. Default: `buffer.byteLength - offset` * `position` | | The location where to begin reading data from the file. If `null` or `-1`, data will be read from the current file position, and the position will be updated. If `position` is a non-negative integer, the current file position will remain unchanged. Default: `null` * Returns: Fulfills upon success with an object with two properties: * `bytesRead` The number of bytes read * `buffer` | | A reference to the passed in `buffer` argument. Reads data from the file and stores that in the given buffer. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. ##### `filehandle.read([options])`# History VersionChanges v21.0.0 Accepts bigint values as `position`. v13.11.0, v12.17.0 Added in: v13.11.0, v12.17.0 * `options` * `buffer` | | A buffer that will be filled with the file data read. Default: `Buffer.alloc(16384)` * `offset` The location in the buffer at which to start filling. Default: `0` * `length` The number of bytes to read. Default: `buffer.byteLength - offset` * `position` | | The location where to begin reading data from the file. If `null` or `-1`, data will be read from the current file position, and the position will be updated. If `position` is a non-negative integer, the current file position will remain unchanged. Default:: `null` * Returns: Fulfills upon success with an object with two properties: * `bytesRead` The number of bytes read * `buffer` | | A reference to the passed in `buffer` argument. Reads data from the file and stores that in the given buffer. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. ##### `filehandle.read(buffer[, options])`# History VersionChanges v21.0.0 Accepts bigint values as `position`. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * `buffer` | | A buffer that will be filled with the file data read. * `options` * `offset` The location in the buffer at which to start filling. Default: `0` * `length` The number of bytes to read. Default: `buffer.byteLength - offset` * `position` | | The location where to begin reading data from the file. If `null` or `-1`, data will be read from the current file position, and the position will be updated. If `position` is a non-negative integer, the current file position will remain unchanged. Default:: `null` * Returns: Fulfills upon success with an object with two properties: * `bytesRead` The number of bytes read * `buffer` | | A reference to the passed in `buffer` argument. Reads data from the file and stores that in the given buffer. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. ##### `filehandle.readableWebStream([options])`# History VersionChanges v24.2.0 Added the `autoClose` option. v24.0.0 Marking the API stable. v23.8.0, v22.15.0 Removed option to create a 'bytes' stream. Streams are now always 'bytes' streams. v20.0.0, v18.17.0 Added option to create a 'bytes' stream. v17.0.0 Added in: v17.0.0 * `options` * `autoClose` When true, causes the to be closed when the stream is closed. Default: `false` * Returns: Returns a byte-oriented `ReadableStream` that may be used to read the file's contents. An error will be thrown if this method is called more than once or is called after the `FileHandle` is closed or closing. import { open, } from 'node:fs/promises'; const file = await open('./some/file/to/read'); for await (const chunk of file.readableWebStream()) console.log(chunk); await file.close(); While the `ReadableStream` will read the file to completion, it will not close the `FileHandle` automatically. User code must still call the `fileHandle.close()` method. ##### `filehandle.readFile(options)`# Added in: v10.0.0 * `options` | * `encoding` | Default: `null` * `signal` allows aborting an in-progress readFile * Returns: Fulfills upon a successful read with the contents of the file. If no encoding is specified (using `options.encoding`), the data is returned as a object. Otherwise, the data will be a string. Asynchronously reads the entire contents of a file. If `options` is a string, then it specifies the `encoding`. The has to support reading. If one or more `filehandle.read()` calls are made on a file handle and then a `filehandle.readFile()` call is made, the data will be read from the current position till the end of the file. It doesn't always read from the beginning of the file. ##### `filehandle.readLines([options])`# Added in: v18.11.0 * `options` * `encoding` Default: `null` * `autoClose` Default: `true` * `emitClose` Default: `true` * `start` * `end` Default: `Infinity` * `highWaterMark` Default: `64 * 1024` * Returns: Convenience method to create a `readline` interface and stream over the file. See `filehandle.createReadStream()` for the options. import { open } from 'node:fs/promises'; const file = await open('./some/file/to/read'); for await (const line of file.readLines()) { console.log(line); } ##### `filehandle.readv(buffers[, position])`# Added in: v13.13.0, v12.17.0 * `buffers` | | * `position` | The offset from the beginning of the file where the data should be read from. If `position` is not a `number`, the data will be read from the current position. Default: `null` * Returns: Fulfills upon success an object containing two properties: * `bytesRead` the number of bytes read * `buffers` | | property containing a reference to the `buffers` input. Read from a file and write to an array of s ##### `filehandle.stat([options])`# History VersionChanges v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v10.0.0 Added in: v10.0.0 * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * Returns: Fulfills with an for the file. ##### `filehandle.sync()`# Added in: v10.0.0 * Returns: Fulfills with `undefined` upon success. Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX `fsync(2)` documentation for more detail. ##### `filehandle.truncate(len)`# Added in: v10.0.0 * `len` Default: `0` * Returns: Fulfills with `undefined` upon success. Truncates the file. If the file was larger than `len` bytes, only the first `len` bytes will be retained in the file. The following example retains only the first four bytes of the file: import { open } from 'node:fs/promises'; let filehandle = null; try { filehandle = await open('temp.txt', 'r+'); await filehandle.truncate(4); } finally { await filehandle?.close(); } If the file previously was shorter than `len` bytes, it is extended, and the extended part is filled with null bytes (`'\0'`): If `len` is negative then `0` will be used. ##### `filehandle.utimes(atime, mtime)`# Added in: v10.0.0 * `atime` | | * `mtime` | | * Returns: Change the file system timestamps of the object referenced by the then fulfills the promise with no arguments upon success. ##### `filehandle.write(buffer, offset[, length[, position]])`# History VersionChanges v14.0.0 The `buffer` parameter won't coerce unsupported input to buffers anymore. v10.0.0 Added in: v10.0.0 * `buffer` | | * `offset` The start position from within `buffer` where the data to write begins. * `length` The number of bytes from `buffer` to write. Default: `buffer.byteLength - offset` * `position` | The offset from the beginning of the file where the data from `buffer` should be written. If `position` is not a `number`, the data will be written at the current position. See the POSIX `pwrite(2)` documentation for more detail. Default: `null` * Returns: Write `buffer` to the file. The promise is fulfilled with an object containing two properties: * `bytesWritten` the number of bytes written * `buffer` | | a reference to the `buffer` written. It is unsafe to use `filehandle.write()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). For this scenario, use `filehandle.createWriteStream()`. On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file. ##### `filehandle.write(buffer[, options])`# Added in: v18.3.0, v16.17.0 * `buffer` | | * `options` * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | Default: `null` * Returns: Write `buffer` to the file. Similar to the above `filehandle.write` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. ##### `filehandle.write(string[, position[, encoding]])`# History VersionChanges v14.0.0 The `string` parameter won't coerce unsupported input to strings anymore. v10.0.0 Added in: v10.0.0 * `string` * `position` | The offset from the beginning of the file where the data from `string` should be written. If `position` is not a `number` the data will be written at the current position. See the POSIX `pwrite(2)` documentation for more detail. Default: `null` * `encoding` The expected string encoding. Default: `'utf8'` * Returns: Write `string` to the file. If `string` is not a string, the promise is rejected with an error. The promise is fulfilled with an object containing two properties: * `bytesWritten` the number of bytes written * `buffer` a reference to the `string` written. It is unsafe to use `filehandle.write()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). For this scenario, use `filehandle.createWriteStream()`. On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file. ##### `filehandle.writeFile(data, options)`# History VersionChanges v15.14.0, v14.18.0 The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. v14.0.0 The `data` parameter won't coerce unsupported input to strings anymore. v10.0.0 Added in: v10.0.0 * `data` | | | | | | * `options` | * `encoding` | The expected character encoding when `data` is a string. Default: `'utf8'` * `signal` | allows aborting an in-progress writeFile. Default: `undefined` * Returns: Asynchronously writes data to a file, replacing the file if it already exists. `data` can be a string, a buffer, an , or an object. The promise is fulfilled with no arguments upon success. If `options` is a string, then it specifies the `encoding`. The has to support writing. It is unsafe to use `filehandle.writeFile()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). If one or more `filehandle.write()` calls are made on a file handle and then a `filehandle.writeFile()` call is made, the data will be written from the current position till the end of the file. It doesn't always write from the beginning of the file. ##### `filehandle.writev(buffers[, position])`# Added in: v12.9.0 * `buffers` | | * `position` | The offset from the beginning of the file where the data from `buffers` should be written. If `position` is not a `number`, the data will be written at the current position. Default: `null` * Returns: Write an array of s to the file. The promise is fulfilled with an object containing a two properties: * `bytesWritten` the number of bytes written * `buffers` | | a reference to the `buffers` input. It is unsafe to call `writev()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file. ##### `filehandle[Symbol.asyncDispose]()`# History VersionChanges v24.2.0 No longer experimental. v20.4.0, v18.18.0 Added in: v20.4.0, v18.18.0 Calls `filehandle.close()` and returns a promise that fulfills when the filehandle is closed. #### `fsPromises.access(path[, mode])`# Added in: v10.0.0 * `path` | | * `mode` Default: `fs.constants.F_OK` * Returns: Fulfills with `undefined` upon success. Tests a user's permissions for the file or directory specified by `path`. The `mode` argument is an optional integer that specifies the accessibility checks to be performed. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check File access constants for possible values of `mode`. If the accessibility check is successful, the promise is fulfilled with no value. If any of the accessibility checks fail, the promise is rejected with an object. The following example checks if the file `/etc/passwd` can be read and written by the current process. import { access, constants } from 'node:fs/promises'; try { await access('/etc/passwd', constants.R_OK | constants.W_OK); console.log('can access'); } catch { console.error('cannot access'); } Using `fsPromises.access()` to check for the accessibility of a file before calling `fsPromises.open()` is not recommended. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file is not accessible. #### `fsPromises.appendFile(path, data[, options])`# History VersionChanges v21.1.0, v20.10.0 The `flush` option is now supported. v10.0.0 Added in: v10.0.0 * `path` | | | filename or * `data` | * `options` | * `encoding` | Default: `'utf8'` * `mode` Default: `0o666` * `flag` See support of file system `flags`. Default: `'a'`. * `flush` If `true`, the underlying file descriptor is flushed prior to closing it. Default: `false`. * Returns: Fulfills with `undefined` upon success. Asynchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a . If `options` is a string, then it specifies the `encoding`. The `mode` option only affects the newly created file. See `fs.open()` for more details. The `path` may be specified as a that has been opened for appending (using `fsPromises.open()`). #### `fsPromises.chmod(path, mode)`# Added in: v10.0.0 * `path` | | * `mode` | * Returns: Fulfills with `undefined` upon success. Changes the permissions of a file. #### `fsPromises.chown(path, uid, gid)`# Added in: v10.0.0 * `path` | | * `uid` * `gid` * Returns: Fulfills with `undefined` upon success. Changes the ownership of a file. #### `fsPromises.copyFile(src, dest[, mode])`# History VersionChanges v14.0.0 Changed `flags` argument to `mode` and imposed stricter type validation. v10.0.0 Added in: v10.0.0 * `src` | | source filename to copy * `dest` | | destination filename of the copy operation * `mode` Optional modifiers that specify the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`) Default: `0`. * `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists. * `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used. * `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail. * Returns: Fulfills with `undefined` upon success. Asynchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. No guarantees are made about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, an attempt will be made to remove the destination. import { copyFile, constants } from 'node:fs/promises'; try { await copyFile('source.txt', 'destination.txt'); console.log('source.txt was copied to destination.txt'); } catch { console.error('The file could not be copied'); } // By using COPYFILE_EXCL, the operation will fail if destination.txt exists. try { await copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL); console.log('source.txt was copied to destination.txt'); } catch { console.error('The file could not be copied'); } #### `fsPromises.cp(src, dest[, options])`# History VersionChanges v22.3.0 This API is no longer experimental. v20.1.0, v18.17.0 Accept an additional `mode` option to specify the copy behavior as the `mode` argument of `fs.copyFile()`. v17.6.0, v16.15.0 Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. v16.7.0 Added in: v16.7.0 * `src` | source path to copy. * `dest` | destination path to copy to. * `options` * `dereference` dereference symlinks. Default: `false`. * `errorOnExist` when `force` is `false`, and the destination exists, throw an error. Default: `false`. * `filter` Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. When ignoring a directory, all of its contents will be skipped as well. Can also return a `Promise` that resolves to `true` or `false` Default: `undefined`. * `src` source path to copy. * `dest` destination path to copy to. * Returns: | A value that is coercible to `boolean` or a `Promise` that fulfils with such value. * `force` overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. Default: `true`. * `mode` modifiers for copy operation. Default: `0`. See `mode` flag of `fsPromises.copyFile()`. * `preserveTimestamps` When `true` timestamps from `src` will be preserved. Default: `false`. * `recursive` copy directories recursively Default: `false` * `verbatimSymlinks` When `true`, path resolution for symlinks will be skipped. Default: `false` * Returns: Fulfills with `undefined` upon success. Asynchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files. When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`. #### `fsPromises.glob(pattern[, options])`# History VersionChanges v24.1.0 Add support for `URL` instances for `cwd` option. v24.0.0 Marking the API stable. v23.7.0, v22.14.0 Add support for `exclude` option to accept glob patterns. v22.2.0 Add support for `withFileTypes` as an option. v22.0.0 Added in: v22.0.0 * `pattern` | * `options` * `cwd` | current working directory. Default: `process.cwd()` * `exclude` | Function to filter out files/directories or a list of glob patterns to be excluded. If a function is provided, return `true` to exclude the item, `false` to include it. Default: `undefined`. If a string array is provided, each string should be a glob pattern that specifies paths to exclude. Note: Negation patterns (e.g., '!foo.js') are not supported. * `withFileTypes` `true` if the glob should return paths as Dirents, `false` otherwise. Default: `false`. * Returns: An AsyncIterator that yields the paths of files that match the pattern. import { glob } from 'node:fs/promises'; for await (const entry of glob('**/*.js')) console.log(entry); #### `fsPromises.lchmod(path, mode)`# Deprecated since: v10.0.0 Stability: 0 \- Deprecated * `path` | | * `mode` * Returns: Fulfills with `undefined` upon success. Changes the permissions on a symbolic link. This method is only implemented on macOS. #### `fsPromises.lchown(path, uid, gid)`# History VersionChanges v10.6.0 This API is no longer deprecated. v10.0.0 Added in: v10.0.0 * `path` | | * `uid` * `gid` * Returns: Fulfills with `undefined` upon success. Changes the ownership on a symbolic link. #### `fsPromises.lutimes(path, atime, mtime)`# Added in: v14.5.0, v12.19.0 * `path` | | * `atime` | | * `mtime` | | * Returns: Fulfills with `undefined` upon success. Changes the access and modification times of a file in the same way as `fsPromises.utimes()`, with the difference that if the path refers to a symbolic link, then the link is not dereferenced: instead, the timestamps of the symbolic link itself are changed. #### `fsPromises.link(existingPath, newPath)`# Added in: v10.0.0 * `existingPath` | | * `newPath` | | * Returns: Fulfills with `undefined` upon success. Creates a new link from the `existingPath` to the `newPath`. See the POSIX `link(2)` documentation for more detail. #### `fsPromises.lstat(path[, options])`# History VersionChanges v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v10.0.0 Added in: v10.0.0 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * Returns: Fulfills with the object for the given symbolic link `path`. Equivalent to `fsPromises.stat()` unless `path` refers to a symbolic link, in which case the link itself is stat-ed, not the file that it refers to. Refer to the POSIX `lstat(2)` document for more detail. #### `fsPromises.mkdir(path[, options])`# Added in: v10.0.0 * `path` | | * `options` | * `recursive` Default: `false` * `mode` | Not supported on Windows. Default: `0o777`. * Returns: Upon success, fulfills with `undefined` if `recursive` is `false`, or the first directory path created if `recursive` is `true`. Asynchronously creates a directory. The optional `options` argument can be an integer specifying `mode` (permission and sticky bits), or an object with a `mode` property and a `recursive` property indicating whether parent directories should be created. Calling `fsPromises.mkdir()` when `path` is a directory that exists results in a rejection only when `recursive` is false. import { mkdir } from 'node:fs/promises'; try { const projectFolder = new URL('./test/project/', import.meta.url); const createDir = await mkdir(projectFolder, { recursive: true }); console.log(`created ${createDir}`); } catch (err) { console.error(err.message); } #### `fsPromises.mkdtemp(prefix[, options])`# History VersionChanges v20.6.0, v18.19.0 The `prefix` parameter now accepts buffers and URL. v16.5.0, v14.18.0 The `prefix` parameter now accepts an empty string. v10.0.0 Added in: v10.0.0 * `prefix` | | * `options` | * `encoding` Default: `'utf8'` * Returns: Fulfills with a string containing the file system path of the newly created temporary directory. Creates a unique temporary directory. A unique directory name is generated by appending six random characters to the end of the provided `prefix`. Due to platform inconsistencies, avoid trailing `X` characters in `prefix`. Some platforms, notably the BSDs, can return more than six random characters, and replace trailing `X` characters in `prefix` with random characters. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use. import { mkdtemp } from 'node:fs/promises'; import { join } from 'node:path'; import { tmpdir } from 'node:os'; try { await mkdtemp(join(tmpdir(), 'foo-')); } catch (err) { console.error(err); } The `fsPromises.mkdtemp()` method will append the six randomly selected characters directly to the `prefix` string. For instance, given a directory `/tmp`, if the intention is to create a temporary directory within `/tmp`, the `prefix` must end with a trailing platform-specific path separator (`require('node:path').sep`). #### `fsPromises.mkdtempDisposable(prefix[, options])`# Added in: v24.4.0 * `prefix` | | * `options` | * `encoding` Default: `'utf8'` * Returns: Fulfills with a Promise for an async-disposable Object: * `path` The path of the created directory. * `remove` A function which removes the created directory. * `[Symbol.asyncDispose]` The same as `remove`. The resulting Promise holds an async-disposable object whose `path` property holds the created directory path. When the object is disposed, the directory and its contents will be removed asynchronously if it still exists. If the directory cannot be deleted, disposal will throw an error. The object has an async `remove()` method which will perform the same task. Both this function and the disposal function on the resulting object are async, so it should be used with `await` \+ `await using` as in `await using dir = await fsPromises.mkdtempDisposable('prefix')`. For detailed information, see the documentation of `fsPromises.mkdtemp()`. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use. #### `fsPromises.open(path, flags[, mode])`# History VersionChanges v11.1.0 The `flags` argument is now optional and defaults to `'r'`. v10.0.0 Added in: v10.0.0 * `path` | | * `flags` | See support of file system `flags`. Default: `'r'`. * `mode` | Sets the file mode (permission and sticky bits) if the file is created. Default: `0o666` (readable and writable) * Returns: Fulfills with a object. Opens a . Refer to the POSIX `open(2)` documentation for more detail. Some characters (`< > : " / \ | ? *`) are reserved under Windows as documented by Naming Files, Paths, and Namespaces. Under NTFS, if the filename contains a colon, Node.js will open a file system stream, as described by this MSDN page. #### `fsPromises.opendir(path[, options])`# History VersionChanges v20.1.0, v18.17.0 Added `recursive` option. v13.1.0, v12.16.0 The `bufferSize` option was introduced. v12.12.0 Added in: v12.12.0 * `path` | | * `options` * `encoding` | Default: `'utf8'` * `bufferSize` Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. Default: `32` * `recursive` Resolved `Dir` will be an containing all sub files and directories. Default: `false` * Returns: Fulfills with an . Asynchronously open a directory for iterative scanning. See the POSIX `opendir(3)` documentation for more detail. Creates an , which contains all further functions for reading from and cleaning up the directory. The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations. Example using async iteration: import { opendir } from 'node:fs/promises'; try { const dir = await opendir('./'); for await (const dirent of dir) console.log(dirent.name); } catch (err) { console.error(err); } When using the async iterator, the object will be automatically closed after the iterator exits. #### `fsPromises.readdir(path[, options])`# History VersionChanges v20.1.0, v18.17.0 Added `recursive` option. v10.11.0 New option `withFileTypes` was added. v10.0.0 Added in: v10.0.0 * `path` | | * `options` | * `encoding` Default: `'utf8'` * `withFileTypes` Default: `false` * `recursive` If `true`, reads the contents of a directory recursively. In recursive mode, it will list all files, sub files, and directories. Default: `false`. * Returns: Fulfills with an array of the names of the files in the directory excluding `'.'` and `'..'`. Reads the contents of a directory. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the filenames. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as objects. If `options.withFileTypes` is set to `true`, the returned array will contain objects. import { readdir } from 'node:fs/promises'; try { const files = await readdir(path); for (const file of files) console.log(file); } catch (err) { console.error(err); } #### `fsPromises.readFile(path[, options])`# History VersionChanges v15.2.0, v14.17.0 The options argument may include an AbortSignal to abort an ongoing readFile request. v10.0.0 Added in: v10.0.0 * `path` | | | filename or `FileHandle` * `options` | * `encoding` | Default: `null` * `flag` See support of file system `flags`. Default: `'r'`. * `signal` allows aborting an in-progress readFile * Returns: Fulfills with the contents of the file. Asynchronously reads the entire contents of a file. If no encoding is specified (using `options.encoding`), the data is returned as a object. Otherwise, the data will be a string. If `options` is a string, then it specifies the encoding. When the `path` is a directory, the behavior of `fsPromises.readFile()` is platform-specific. On macOS, Linux, and Windows, the promise will be rejected with an error. On FreeBSD, a representation of the directory's contents will be returned. An example of reading a `package.json` file located in the same directory of the running code: import { readFile } from 'node:fs/promises'; try { const filePath = new URL('./package.json', import.meta.url); const contents = await readFile(filePath, { encoding: 'utf8' }); console.log(contents); } catch (err) { console.error(err.message); } It is possible to abort an ongoing `readFile` using an . If a request is aborted the promise returned is rejected with an `AbortError`: import { readFile } from 'node:fs/promises'; try { const controller = new AbortController(); const { signal } = controller; const promise = readFile(fileName, { signal }); // Abort the request before the promise settles. controller.abort(); await promise; } catch (err) { // When a request is aborted - err is an AbortError console.error(err); } Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.readFile` performs. Any specified has to support reading. #### `fsPromises.readlink(path[, options])`# Added in: v10.0.0 * `path` | | * `options` | * `encoding` Default: `'utf8'` * Returns: Fulfills with the `linkString` upon success. Reads the contents of the symbolic link referred to by `path`. See the POSIX `readlink(2)` documentation for more detail. The promise is fulfilled with the `linkString` upon success. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the link path returned. If the `encoding` is set to `'buffer'`, the link path returned will be passed as a object. #### `fsPromises.realpath(path[, options])`# Added in: v10.0.0 * `path` | | * `options` | * `encoding` Default: `'utf8'` * Returns: Fulfills with the resolved path upon success. Determines the actual location of `path` using the same semantics as the `fs.realpath.native()` function. Only paths that can be converted to UTF8 strings are supported. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path. If the `encoding` is set to `'buffer'`, the path returned will be passed as a object. On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction. #### `fsPromises.rename(oldPath, newPath)`# Added in: v10.0.0 * `oldPath` | | * `newPath` | | * Returns: Fulfills with `undefined` upon success. Renames `oldPath` to `newPath`. #### `fsPromises.rmdir(path[, options])`# History VersionChanges v16.0.0 Using `fsPromises.rmdir(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. v16.0.0 Using `fsPromises.rmdir(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error. v16.0.0 The `recursive` option is deprecated, using it triggers a deprecation warning. v14.14.0 The `recursive` option is deprecated, use `fsPromises.rm` instead. v13.3.0, v12.16.0 The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. v12.10.0 The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. v10.0.0 Added in: v10.0.0 * `path` | | * `options` * `maxRetries` If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. Default: `0`. * `recursive` If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. Default: `false`. Deprecated. * `retryDelay` The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. Default: `100`. * Returns: Fulfills with `undefined` upon success. Removes the directory identified by `path`. Using `fsPromises.rmdir()` on a file (not a directory) results in the promise being rejected with an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. To get a behavior similar to the `rm -rf` Unix command, use `fsPromises.rm()` with options `{ recursive: true, force: true }`. #### `fsPromises.rm(path[, options])`# Added in: v14.14.0 * `path` | | * `options` * `force` When `true`, exceptions will be ignored if `path` does not exist. Default: `false`. * `maxRetries` If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. Default: `0`. * `recursive` If `true`, perform a recursive directory removal. In recursive mode operations are retried on failure. Default: `false`. * `retryDelay` The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. Default: `100`. * Returns: Fulfills with `undefined` upon success. Removes files and directories (modeled on the standard POSIX `rm` utility). #### `fsPromises.stat(path[, options])`# History VersionChanges v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v10.0.0 Added in: v10.0.0 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * Returns: Fulfills with the object for the given `path`. #### `fsPromises.statfs(path[, options])`# Added in: v19.6.0, v18.15.0 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * Returns: Fulfills with the object for the given `path`. #### `fsPromises.symlink(target, path[, type])`# History VersionChanges v19.0.0 If the `type` argument is `null` or omitted, Node.js will autodetect `target` type and automatically select `dir` or `file`. v10.0.0 Added in: v10.0.0 * `target` | | * `path` | | * `type` | Default: `null` * Returns: Fulfills with `undefined` upon success. Creates a symbolic link. The `type` argument is only used on Windows platforms and can be one of `'dir'`, `'file'`, or `'junction'`. If the `type` argument is `null`, Node.js will autodetect `target` type and use `'file'` or `'dir'`. If the `target` does not exist, `'file'` will be used. Windows junction points require the destination path to be absolute. When using `'junction'`, the `target` argument will automatically be normalized to absolute path. Junction points on NTFS volumes can only point to directories. #### `fsPromises.truncate(path[, len])`# Added in: v10.0.0 * `path` | | * `len` Default: `0` * Returns: Fulfills with `undefined` upon success. Truncates (shortens or extends the length) of the content at `path` to `len` bytes. #### `fsPromises.unlink(path)`# Added in: v10.0.0 * `path` | | * Returns: Fulfills with `undefined` upon success. If `path` refers to a symbolic link, then the link is removed without affecting the file or directory to which that link refers. If the `path` refers to a file path that is not a symbolic link, the file is deleted. See the POSIX `unlink(2)` documentation for more detail. #### `fsPromises.utimes(path, atime, mtime)`# Added in: v10.0.0 * `path` | | * `atime` | | * `mtime` | | * Returns: Fulfills with `undefined` upon success. Change the file system timestamps of the object referenced by `path`. The `atime` and `mtime` arguments follow these rules: * Values can be either numbers representing Unix epoch time, `Date`s, or a numeric string like `'123456789.0'`. * If the value can not be converted to a number, or is `NaN`, `Infinity`, or `-Infinity`, an `Error` will be thrown. #### `fsPromises.watch(filename[, options])`# Added in: v15.9.0, v14.18.0 * `filename` | | * `options` | * `persistent` Indicates whether the process should continue to run as long as files are being watched. Default: `true`. * `recursive` Indicates whether all subdirectories should be watched, or only the current directory. This applies when a directory is specified, and only on supported platforms (See caveats). Default: `false`. * `encoding` Specifies the character encoding to be used for the filename passed to the listener. Default: `'utf8'`. * `signal` An used to signal when the watcher should stop. * `maxQueue` Specifies the number of events to queue between iterations of the returned. Default: `2048`. * `overflow` Either `'ignore'` or `'throw'` when there are more events to be queued than `maxQueue` allows. `'ignore'` means overflow events are dropped and a warning is emitted, while `'throw'` means to throw an exception. Default: `'ignore'`. * Returns: of objects with the properties: * `eventType` The type of change * `filename` | | The name of the file changed. Returns an async iterator that watches for changes on `filename`, where `filename` is either a file or a directory. const { watch } = require('node:fs/promises'); const ac = new AbortController(); const { signal } = ac; setTimeout(() => ac.abort(), 10000); (async () => { try { const watcher = watch(__filename, { signal }); for await (const event of watcher) console.log(event); } catch (err) { if (err.name === 'AbortError') return; throw err; } })(); On most platforms, `'rename'` is emitted whenever a filename appears or disappears in the directory. All the caveats for `fs.watch()` also apply to `fsPromises.watch()`. #### `fsPromises.writeFile(file, data[, options])`# History VersionChanges v21.0.0, v20.10.0 The `flush` option is now supported. v15.14.0, v14.18.0 The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. v15.2.0, v14.17.0 The options argument may include an AbortSignal to abort an ongoing writeFile request. v14.0.0 The `data` parameter won't coerce unsupported input to strings anymore. v10.0.0 Added in: v10.0.0 * `file` | | | filename or `FileHandle` * `data` | | | | | | * `options` | * `encoding` | Default: `'utf8'` * `mode` Default: `0o666` * `flag` See support of file system `flags`. Default: `'w'`. * `flush` If all data is successfully written to the file, and `flush` is `true`, `filehandle.sync()` is used to flush the data. Default: `false`. * `signal` allows aborting an in-progress writeFile * Returns: Fulfills with `undefined` upon success. Asynchronously writes data to a file, replacing the file if it already exists. `data` can be a string, a buffer, an , or an object. The `encoding` option is ignored if `data` is a buffer. If `options` is a string, then it specifies the encoding. The `mode` option only affects the newly created file. See `fs.open()` for more details. Any specified has to support writing. It is unsafe to use `fsPromises.writeFile()` multiple times on the same file without waiting for the promise to be settled. Similarly to `fsPromises.readFile` \- `fsPromises.writeFile` is a convenience method that performs multiple `write` calls internally to write the buffer passed to it. For performance sensitive code consider using `fs.createWriteStream()` or `filehandle.createWriteStream()`. It is possible to use an to cancel an `fsPromises.writeFile()`. Cancelation is "best effort", and some amount of data is likely still to be written. import { writeFile } from 'node:fs/promises'; import { Buffer } from 'node:buffer'; try { const controller = new AbortController(); const { signal } = controller; const data = new Uint8Array(Buffer.from('Hello Node.js')); const promise = writeFile('message.txt', data, { signal }); // Abort the request before the promise settles. controller.abort(); await promise; } catch (err) { // When a request is aborted - err is an AbortError console.error(err); } Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.writeFile` performs. #### `fsPromises.constants`# Added in: v18.4.0, v16.17.0 * Type: Returns an object containing commonly used constants for file system operations. The object is the same as `fs.constants`. See FS constants for more details. ### Callback API# The callback APIs perform all operations asynchronously, without blocking the event loop, then invoke a callback function upon completion or error. The callback APIs use the underlying Node.js threadpool to perform file system operations off the event loop thread. These operations are not synchronized or threadsafe. Care must be taken when performing multiple concurrent modifications on the same file or data corruption may occur. #### `fs.access(path[, mode], callback)`# History VersionChanges v20.8.0 The constants `fs.F_OK`, `fs.R_OK`, `fs.W_OK` and `fs.X_OK` which were present directly on `fs` are deprecated. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v6.3.0 The constants like `fs.R_OK`, etc which were present directly on `fs` were moved into `fs.constants` as a soft deprecation. Thus for Node.js `< v6.3.0` use `fs` to access those constants, or do something like `(fs.constants || fs).R_OK` to work with all versions. v0.11.15 Added in: v0.11.15 * `path` | | * `mode` Default: `fs.constants.F_OK` * `callback` * `err` Tests a user's permissions for the file or directory specified by `path`. The `mode` argument is an optional integer that specifies the accessibility checks to be performed. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check File access constants for possible values of `mode`. The final argument, `callback`, is a callback function that is invoked with a possible error argument. If any of the accessibility checks fail, the error argument will be an `Error` object. The following examples check if `package.json` exists, and if it is readable or writable. import { access, constants } from 'node:fs'; const file = 'package.json'; // Check if the file exists in the current directory. access(file, constants.F_OK, (err) => { console.log(`${file} ${err ? 'does not exist' : 'exists'}`); }); // Check if the file is readable. access(file, constants.R_OK, (err) => { console.log(`${file} ${err ? 'is not readable' : 'is readable'}`); }); // Check if the file is writable. access(file, constants.W_OK, (err) => { console.log(`${file} ${err ? 'is not writable' : 'is writable'}`); }); // Check if the file is readable and writable. access(file, constants.R_OK | constants.W_OK, (err) => { console.log(`${file} ${err ? 'is not' : 'is'} readable and writable`); }); Do not use `fs.access()` to check for the accessibility of a file before calling `fs.open()`, `fs.readFile()`, or `fs.writeFile()`. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file is not accessible. write (NOT RECOMMENDED) import { access, open, close } from 'node:fs'; access('myfile', (err) => { if (!err) { console.error('myfile already exists'); return; } open('myfile', 'wx', (err, fd) => { if (err) throw err; try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); }); write (RECOMMENDED) import { open, close } from 'node:fs'; open('myfile', 'wx', (err, fd) => { if (err) { if (err.code === 'EEXIST') { console.error('myfile already exists'); return; } throw err; } try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); read (NOT RECOMMENDED) import { access, open, close } from 'node:fs'; access('myfile', (err) => { if (err) { if (err.code === 'ENOENT') { console.error('myfile does not exist'); return; } throw err; } open('myfile', 'r', (err, fd) => { if (err) throw err; try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); }); read (RECOMMENDED) import { open, close } from 'node:fs'; open('myfile', 'r', (err, fd) => { if (err) { if (err.code === 'ENOENT') { console.error('myfile does not exist'); return; } throw err; } try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); The "not recommended" examples above check for accessibility and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any. In general, check for the accessibility of a file only if the file will not be used directly, for example when its accessibility is a signal from another process. On Windows, access-control policies (ACLs) on a directory may limit access to a file or directory. The `fs.access()` function, however, does not check the ACL and therefore may report that a path is accessible even if the ACL restricts the user from reading or writing to it. #### `fs.appendFile(path, data[, options], callback)`# History VersionChanges v21.1.0, v20.10.0 The `flush` option is now supported. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v7.0.0 The passed `options` object will never be modified. v5.0.0 The `file` parameter can be a file descriptor now. v0.6.7 Added in: v0.6.7 * `path` | | | filename or file descriptor * `data` | * `options` | * `encoding` | Default: `'utf8'` * `mode` Default: `0o666` * `flag` See support of file system `flags`. Default: `'a'`. * `flush` If `true`, the underlying file descriptor is flushed prior to closing it. Default: `false`. * `callback` * `err` Asynchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a . The `mode` option only affects the newly created file. See `fs.open()` for more details. import { appendFile } from 'node:fs'; appendFile('message.txt', 'data to append', (err) => { if (err) throw err; console.log('The "data to append" was appended to file!'); }); If `options` is a string, then it specifies the encoding: import { appendFile } from 'node:fs'; appendFile('message.txt', 'data to append', 'utf8', callback); The `path` may be specified as a numeric file descriptor that has been opened for appending (using `fs.open()` or `fs.openSync()`). The file descriptor will not be closed automatically. import { open, close, appendFile } from 'node:fs'; function closeFd(fd) { close(fd, (err) => { if (err) throw err; }); } open('message.txt', 'a', (err, fd) => { if (err) throw err; try { appendFile(fd, 'data to append', 'utf8', (err) => { closeFd(fd); if (err) throw err; }); } catch (err) { closeFd(fd); throw err; } }); #### `fs.chmod(path, mode, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.30 Added in: v0.1.30 * `path` | | * `mode` | * `callback` * `err` Asynchronously changes the permissions of a file. No arguments other than a possible exception are given to the completion callback. See the POSIX `chmod(2)` documentation for more detail. import { chmod } from 'node:fs'; chmod('my_file.txt', 0o775, (err) => { if (err) throw err; console.log('The permissions for file "my_file.txt" have been changed!'); }); ##### File modes# The `mode` argument used in both the `fs.chmod()` and `fs.chmodSync()` methods is a numeric bitmask created using a logical OR of the following constants: ConstantOctalDescription `fs.constants.S_IRUSR``0o400`read by owner `fs.constants.S_IWUSR``0o200`write by owner `fs.constants.S_IXUSR``0o100`execute/search by owner `fs.constants.S_IRGRP``0o40`read by group `fs.constants.S_IWGRP``0o20`write by group `fs.constants.S_IXGRP``0o10`execute/search by group `fs.constants.S_IROTH``0o4`read by others `fs.constants.S_IWOTH``0o2`write by others `fs.constants.S_IXOTH``0o1`execute/search by others An easier method of constructing the `mode` is to use a sequence of three octal digits (e.g. `765`). The left-most digit (`7` in the example), specifies the permissions for the file owner. The middle digit (`6` in the example), specifies permissions for the group. The right-most digit (`5` in the example), specifies the permissions for others. NumberDescription `7`read, write, and execute `6`read and write `5`read and execute `4`read only `3`write and execute `2`write only `1`execute only `0`no permission For example, the octal value `0o765` means: * The owner may read, write, and execute the file. * The group may read and write the file. * Others may read and execute the file. When using raw numbers where file modes are expected, any value larger than `0o777` may result in platform-specific behaviors that are not supported to work consistently. Therefore constants like `S_ISVTX`, `S_ISGID`, or `S_ISUID` are not exposed in `fs.constants`. Caveats: on Windows only the write permission can be changed, and the distinction among the permissions of group, owner, or others is not implemented. #### `fs.chown(path, uid, gid, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.97 Added in: v0.1.97 * `path` | | * `uid` * `gid` * `callback` * `err` Asynchronously changes owner and group of a file. No arguments other than a possible exception are given to the completion callback. See the POSIX `chown(2)` documentation for more detail. #### `fs.close(fd[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v15.9.0, v14.17.0 A default callback is now used if one is not provided. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.0.2 Added in: v0.0.2 * `fd` * `callback` * `err` Closes the file descriptor. No arguments other than a possible exception are given to the completion callback. Calling `fs.close()` on any file descriptor (`fd`) that is currently in use through any other `fs` operation may lead to undefined behavior. See the POSIX `close(2)` documentation for more detail. #### `fs.copyFile(src, dest[, mode], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v14.0.0 Changed `flags` argument to `mode` and imposed stricter type validation. v8.5.0 Added in: v8.5.0 * `src` | | source filename to copy * `dest` | | destination filename of the copy operation * `mode` modifiers for copy operation. Default: `0`. * `callback` * `err` Asynchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. No arguments other than a possible exception are given to the callback function. Node.js makes no guarantees about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, Node.js will attempt to remove the destination. `mode` is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`). * `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists. * `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used. * `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail. import { copyFile, constants } from 'node:fs'; function callback(err) { if (err) throw err; console.log('source.txt was copied to destination.txt'); } // destination.txt will be created or overwritten by default. copyFile('source.txt', 'destination.txt', callback); // By using COPYFILE_EXCL, the operation will fail if destination.txt exists. copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL, callback); #### `fs.cp(src, dest[, options], callback)`# History VersionChanges v22.3.0 This API is no longer experimental. v20.1.0, v18.17.0 Accept an additional `mode` option to specify the copy behavior as the `mode` argument of `fs.copyFile()`. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v17.6.0, v16.15.0 Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. v16.7.0 Added in: v16.7.0 * `src` | source path to copy. * `dest` | destination path to copy to. * `options` * `dereference` dereference symlinks. Default: `false`. * `errorOnExist` when `force` is `false`, and the destination exists, throw an error. Default: `false`. * `filter` Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. When ignoring a directory, all of its contents will be skipped as well. Can also return a `Promise` that resolves to `true` or `false` Default: `undefined`. * `src` source path to copy. * `dest` destination path to copy to. * Returns: | A value that is coercible to `boolean` or a `Promise` that fulfils with such value. * `force` overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. Default: `true`. * `mode` modifiers for copy operation. Default: `0`. See `mode` flag of `fs.copyFile()`. * `preserveTimestamps` When `true` timestamps from `src` will be preserved. Default: `false`. * `recursive` copy directories recursively Default: `false` * `verbatimSymlinks` When `true`, path resolution for symlinks will be skipped. Default: `false` * `callback` * `err` Asynchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files. When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`. #### `fs.createReadStream(path[, options])`# History VersionChanges v16.10.0 The `fs` option does not need `open` method if an `fd` was provided. v16.10.0 The `fs` option does not need `close` method if `autoClose` is `false`. v15.5.0 Add support for `AbortSignal`. v15.4.0 The `fd` option accepts FileHandle arguments. v14.0.0 Change `emitClose` default to `true`. v13.6.0, v12.17.0 The `fs` options allow overriding the used `fs` implementation. v12.10.0 Enable `emitClose` option. v11.0.0 Impose new restrictions on `start` and `end`, throwing more appropriate errors in cases when we cannot reasonably handle the input values. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The passed `options` object will never be modified. v2.3.0 The passed `options` object can be a string now. v0.1.31 Added in: v0.1.31 * `path` | | * `options` | * `flags` See support of file system `flags`. Default: `'r'`. * `encoding` Default: `null` * `fd` | Default: `null` * `mode` Default: `0o666` * `autoClose` Default: `true` * `emitClose` Default: `true` * `start` * `end` Default: `Infinity` * `highWaterMark` Default: `64 * 1024` * `fs` | Default: `null` * `signal` | Default: `null` * Returns: `options` can include `start` and `end` values to read a range of bytes from the file instead of the entire file. Both `start` and `end` are inclusive and start counting at 0, allowed values are in the [0, `Number.MAX_SAFE_INTEGER`] range. If `fd` is specified and `start` is omitted or `undefined`, `fs.createReadStream()` reads sequentially from the current file position. The `encoding` can be any one of those accepted by . If `fd` is specified, `ReadStream` will ignore the `path` argument and will use the specified file descriptor. This means that no `'open'` event will be emitted. `fd` should be blocking; non-blocking `fd`s should be passed to . If `fd` points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. By providing the `fs` option, it is possible to override the corresponding `fs` implementations for `open`, `read`, and `close`. When providing the `fs` option, an override for `read` is required. If no `fd` is provided, an override for `open` is also required. If `autoClose` is `true`, an override for `close` is also required. import { createReadStream } from 'node:fs'; // Create a stream from some character device. const stream = createReadStream('/dev/input/event0'); setTimeout(() => { stream.close(); // This may not close the stream. // Artificially marking end-of-stream, as if the underlying resource had // indicated end-of-file by itself, allows the stream to close. // This does not cancel pending read operations, and if there is such an // operation, the process may still not be able to exit successfully // until it finishes. stream.push(null); stream.read(0); }, 100); If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak. If `autoClose` is set to true (default behavior), on `'error'` or `'end'` the file descriptor will be closed automatically. `mode` sets the file mode (permission and sticky bits), but only if the file was created. An example to read the last 10 bytes of a file which is 100 bytes long: import { createReadStream } from 'node:fs'; createReadStream('sample.txt', { start: 90, end: 99 }); If `options` is a string, then it specifies the encoding. #### `fs.createWriteStream(path[, options])`# History VersionChanges v21.0.0, v20.10.0 The `flush` option is now supported. v16.10.0 The `fs` option does not need `open` method if an `fd` was provided. v16.10.0 The `fs` option does not need `close` method if `autoClose` is `false`. v15.5.0 Add support for `AbortSignal`. v15.4.0 The `fd` option accepts FileHandle arguments. v14.0.0 Change `emitClose` default to `true`. v13.6.0, v12.17.0 The `fs` options allow overriding the used `fs` implementation. v12.10.0 Enable `emitClose` option. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The passed `options` object will never be modified. v5.5.0 The `autoClose` option is supported now. v2.3.0 The passed `options` object can be a string now. v0.1.31 Added in: v0.1.31 * `path` | | * `options` | * `flags` See support of file system `flags`. Default: `'w'`. * `encoding` Default: `'utf8'` * `fd` | Default: `null` * `mode` Default: `0o666` * `autoClose` Default: `true` * `emitClose` Default: `true` * `start` * `fs` | Default: `null` * `signal` | Default: `null` * `highWaterMark` Default: `16384` * `flush` If `true`, the underlying file descriptor is flushed prior to closing it. Default: `false`. * Returns: `options` may also include a `start` option to allow writing data at some position past the beginning of the file, allowed values are in the [0, `Number.MAX_SAFE_INTEGER`] range. Modifying a file rather than replacing it may require the `flags` option to be set to `r+` rather than the default `w`. The `encoding` can be any one of those accepted by . If `autoClose` is set to true (default behavior) on `'error'` or `'finish'` the file descriptor will be closed automatically. If `autoClose` is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. By providing the `fs` option it is possible to override the corresponding `fs` implementations for `open`, `write`, `writev`, and `close`. Overriding `write()` without `writev()` can reduce performance as some optimizations (`_writev()`) will be disabled. When providing the `fs` option, overrides for at least one of `write` and `writev` are required. If no `fd` option is supplied, an override for `open` is also required. If `autoClose` is `true`, an override for `close` is also required. Like , if `fd` is specified, will ignore the `path` argument and will use the specified file descriptor. This means that no `'open'` event will be emitted. `fd` should be blocking; non-blocking `fd`s should be passed to . If `options` is a string, then it specifies the encoding. #### `fs.exists(path, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v1.0.0 Deprecated since: v1.0.0 v0.0.2 Added in: v0.0.2 Stability: 0 \- Deprecated: Use `fs.stat()` or `fs.access()` instead. * `path` | | * `callback` * `exists` Test whether or not the element at the given `path` exists by checking with the file system. Then call the `callback` argument with either true or false: import { exists } from 'node:fs'; exists('/etc/passwd', (e) => { console.log(e ? 'it exists' : 'no passwd!'); }); The parameters for this callback are not consistent with other Node.js callbacks. Normally, the first parameter to a Node.js callback is an `err` parameter, optionally followed by other parameters. The `fs.exists()` callback has only one boolean parameter. This is one reason `fs.access()` is recommended instead of `fs.exists()`. If `path` is a symbolic link, it is followed. Thus, if `path` exists but points to a non-existent element, the callback will receive the value `false`. Using `fs.exists()` to check for the existence of a file before calling `fs.open()`, `fs.readFile()`, or `fs.writeFile()` is not recommended. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file does not exist. write (NOT RECOMMENDED) import { exists, open, close } from 'node:fs'; exists('myfile', (e) => { if (e) { console.error('myfile already exists'); } else { open('myfile', 'wx', (err, fd) => { if (err) throw err; try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); } }); write (RECOMMENDED) import { open, close } from 'node:fs'; open('myfile', 'wx', (err, fd) => { if (err) { if (err.code === 'EEXIST') { console.error('myfile already exists'); return; } throw err; } try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); read (NOT RECOMMENDED) import { open, close, exists } from 'node:fs'; exists('myfile', (e) => { if (e) { open('myfile', 'r', (err, fd) => { if (err) throw err; try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); } else { console.error('myfile does not exist'); } }); read (RECOMMENDED) import { open, close } from 'node:fs'; open('myfile', 'r', (err, fd) => { if (err) { if (err.code === 'ENOENT') { console.error('myfile does not exist'); return; } throw err; } try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); The "not recommended" examples above check for existence and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any. In general, check for the existence of a file only if the file won't be used directly, for example when its existence is a signal from another process. #### `fs.fchmod(fd, mode, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.4.7 Added in: v0.4.7 * `fd` * `mode` | * `callback` * `err` Sets the permissions on the file. No arguments other than a possible exception are given to the completion callback. See the POSIX `fchmod(2)` documentation for more detail. #### `fs.fchown(fd, uid, gid, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.4.7 Added in: v0.4.7 * `fd` * `uid` * `gid` * `callback` * `err` Sets the owner of the file. No arguments other than a possible exception are given to the completion callback. See the POSIX `fchown(2)` documentation for more detail. #### `fs.fdatasync(fd, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.96 Added in: v0.1.96 * `fd` * `callback` * `err` Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX `fdatasync(2)` documentation for details. No arguments other than a possible exception are given to the completion callback. #### `fs.fstat(fd[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.95 Added in: v0.1.95 * `fd` * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * `callback` * `err` * `stats` Invokes the callback with the for the file descriptor. See the POSIX `fstat(2)` documentation for more detail. #### `fs.fsync(fd, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.96 Added in: v0.1.96 * `fd` * `callback` * `err` Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX `fsync(2)` documentation for more detail. No arguments other than a possible exception are given to the completion callback. #### `fs.ftruncate(fd[, len], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.8.6 Added in: v0.8.6 * `fd` * `len` Default: `0` * `callback` * `err` Truncates the file descriptor. No arguments other than a possible exception are given to the completion callback. See the POSIX `ftruncate(2)` documentation for more detail. If the file referred to by the file descriptor was larger than `len` bytes, only the first `len` bytes will be retained in the file. For example, the following program retains only the first four bytes of the file: import { open, close, ftruncate } from 'node:fs'; function closeFd(fd) { close(fd, (err) => { if (err) throw err; }); } open('temp.txt', 'r+', (err, fd) => { if (err) throw err; try { ftruncate(fd, 4, (err) => { closeFd(fd); if (err) throw err; }); } catch (err) { closeFd(fd); if (err) throw err; } }); If the file previously was shorter than `len` bytes, it is extended, and the extended part is filled with null bytes (`'\0'`): If `len` is negative then `0` will be used. #### `fs.futimes(fd, atime, mtime, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v4.1.0 Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. v0.4.2 Added in: v0.4.2 * `fd` * `atime` | | * `mtime` | | * `callback` * `err` Change the file system timestamps of the object referenced by the supplied file descriptor. See `fs.utimes()`. #### `fs.glob(pattern[, options], callback)`# History VersionChanges v24.1.0 Add support for `URL` instances for `cwd` option. v24.0.0 Marking the API stable. v23.7.0, v22.14.0 Add support for `exclude` option to accept glob patterns. v22.2.0 Add support for `withFileTypes` as an option. v22.0.0 Added in: v22.0.0 * `pattern` | * `options` * `cwd` | current working directory. Default: `process.cwd()` * `exclude` | Function to filter out files/directories or a list of glob patterns to be excluded. If a function is provided, return `true` to exclude the item, `false` to include it. Default: `undefined`. * `withFileTypes` `true` if the glob should return paths as Dirents, `false` otherwise. Default: `false`. * `callback` * `err` * Retrieves the files matching the specified pattern. import { glob } from 'node:fs'; glob('**/*.js', (err, matches) => { if (err) throw err; console.log(matches); }); #### `fs.lchmod(path, mode, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v16.0.0 The error returned may be an `AggregateError` if more than one error is returned. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.4.7 Deprecated since: v0.4.7 Stability: 0 \- Deprecated * `path` | | * `mode` * `callback` * `err` | Changes the permissions on a symbolic link. No arguments other than a possible exception are given to the completion callback. This method is only implemented on macOS. See the POSIX `lchmod(2)` documentation for more detail. #### `fs.lchown(path, uid, gid, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.6.0 This API is no longer deprecated. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.4.7 Documentation-only deprecation. * `path` | | * `uid` * `gid` * `callback` * `err` Set the owner of the symbolic link. No arguments other than a possible exception are given to the completion callback. See the POSIX `lchown(2)` documentation for more detail. #### `fs.lutimes(path, atime, mtime, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v14.5.0, v12.19.0 Added in: v14.5.0, v12.19.0 * `path` | | * `atime` | | * `mtime` | | * `callback` * `err` Changes the access and modification times of a file in the same way as `fs.utimes()`, with the difference that if the path refers to a symbolic link, then the link is not dereferenced: instead, the timestamps of the symbolic link itself are changed. No arguments other than a possible exception are given to the completion callback. #### `fs.link(existingPath, newPath, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `existingPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still experimental. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.31 Added in: v0.1.31 * `existingPath` | | * `newPath` | | * `callback` * `err` Creates a new link from the `existingPath` to the `newPath`. See the POSIX `link(2)` documentation for more detail. No arguments other than a possible exception are given to the completion callback. #### `fs.lstat(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.30 Added in: v0.1.30 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * `callback` * `err` * `stats` Retrieves the for the symbolic link referred to by the path. The callback gets two arguments `(err, stats)` where `stats` is a object. `lstat()` is identical to `stat()`, except that if `path` is a symbolic link, then the link itself is stat-ed, not the file that it refers to. See the POSIX `lstat(2)` documentation for more details. #### `fs.mkdir(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v13.11.0, v12.17.0 In `recursive` mode, the callback now receives the first created path as an argument. v10.12.0 The second argument can now be an `options` object with `recursive` and `mode` properties. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.8 Added in: v0.1.8 * `path` | | * `options` | * `recursive` Default: `false` * `mode` | Not supported on Windows. Default: `0o777`. * `callback` * `err` * `path` | Present only if a directory is created with `recursive` set to `true`. Asynchronously creates a directory. The callback is given a possible exception and, if `recursive` is `true`, the first directory path created, `(err[, path])`. `path` can still be `undefined` when `recursive` is `true`, if no directory was created (for instance, if it was previously created). The optional `options` argument can be an integer specifying `mode` (permission and sticky bits), or an object with a `mode` property and a `recursive` property indicating whether parent directories should be created. Calling `fs.mkdir()` when `path` is a directory that exists results in an error only when `recursive` is false. If `recursive` is false and the directory exists, an `EEXIST` error occurs. import { mkdir } from 'node:fs'; // Create ./tmp/a/apple, regardless of whether ./tmp and ./tmp/a exist. mkdir('./tmp/a/apple', { recursive: true }, (err) => { if (err) throw err; }); On Windows, using `fs.mkdir()` on the root directory even with recursion will result in an error: import { mkdir } from 'node:fs'; mkdir('/', { recursive: true }, (err) => { // => [Error: EPERM: operation not permitted, mkdir 'C:\'] }); See the POSIX `mkdir(2)` documentation for more details. #### `fs.mkdtemp(prefix[, options], callback)`# History VersionChanges v20.6.0, v18.19.0 The `prefix` parameter now accepts buffers and URL. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v16.5.0, v14.18.0 The `prefix` parameter now accepts an empty string. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v6.2.1 The `callback` parameter is optional now. v5.10.0 Added in: v5.10.0 * `prefix` | | * `options` | * `encoding` Default: `'utf8'` * `callback` * `err` * `directory` Creates a unique temporary directory. Generates six random characters to be appended behind a required `prefix` to create a unique temporary directory. Due to platform inconsistencies, avoid trailing `X` characters in `prefix`. Some platforms, notably the BSDs, can return more than six random characters, and replace trailing `X` characters in `prefix` with random characters. The created directory path is passed as a string to the callback's second parameter. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use. import { mkdtemp } from 'node:fs'; import { join } from 'node:path'; import { tmpdir } from 'node:os'; mkdtemp(join(tmpdir(), 'foo-'), (err, directory) => { if (err) throw err; console.log(directory); // Prints: /tmp/foo-itXde2 or C:\Users\...\AppData\Local\Temp\foo-itXde2 }); The `fs.mkdtemp()` method will append the six randomly selected characters directly to the `prefix` string. For instance, given a directory `/tmp`, if the intention is to create a temporary directory within `/tmp`, the `prefix` must end with a trailing platform-specific path separator (`require('node:path').sep`). import { tmpdir } from 'node:os'; import { mkdtemp } from 'node:fs'; // The parent directory for the new temporary directory const tmpDir = tmpdir(); // This method is *INCORRECT*: mkdtemp(tmpDir, (err, directory) => { if (err) throw err; console.log(directory); // Will print something similar to `/tmpabc123`. // A new temporary directory is created at the file system root // rather than *within* the /tmp directory. }); // This method is *CORRECT*: import { sep } from 'node:path'; mkdtemp(`${tmpDir}${sep}`, (err, directory) => { if (err) throw err; console.log(directory); // Will print something similar to `/tmp/abc123`. // A new temporary directory is created within // the /tmp directory. }); #### `fs.open(path[, flags[, mode]], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v11.1.0 The `flags` argument is now optional and defaults to `'r'`. v9.9.0 The `as` and `as+` flags are supported now. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.0.2 Added in: v0.0.2 * `path` | | * `flags` | See support of file system `flags`. Default: `'r'`. * `mode` | Default: `0o666` (readable and writable) * `callback` * `err` * `fd` Asynchronous file open. See the POSIX `open(2)` documentation for more details. `mode` sets the file mode (permission and sticky bits), but only if the file was created. On Windows, only the write permission can be manipulated; see `fs.chmod()`. The callback gets two arguments `(err, fd)`. Some characters (`< > : " / \ | ? *`) are reserved under Windows as documented by Naming Files, Paths, and Namespaces. Under NTFS, if the filename contains a colon, Node.js will open a file system stream, as described by this MSDN page. Functions based on `fs.open()` exhibit this behavior as well: `fs.writeFile()`, `fs.readFile()`, etc. #### `fs.openAsBlob(path[, options])`# History VersionChanges v24.0.0 Marking the API stable. v19.8.0 Added in: v19.8.0 * `path` | | * `options` * `type` An optional mime type for the blob. * Returns: Fulfills with a upon success. Returns a whose data is backed by the given file. The file must not be modified after the is created. Any modifications will cause reading the data to fail with a `DOMException` error. Synchronous stat operations on the file when the `Blob` is created, and before each read in order to detect whether the file data has been modified on disk. import { openAsBlob } from 'node:fs'; const blob = await openAsBlob('the.file.txt'); const ab = await blob.arrayBuffer(); blob.stream(); #### `fs.opendir(path[, options], callback)`# History VersionChanges v20.1.0, v18.17.0 Added `recursive` option. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v13.1.0, v12.16.0 The `bufferSize` option was introduced. v12.12.0 Added in: v12.12.0 * `path` | | * `options` * `encoding` | Default: `'utf8'` * `bufferSize` Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. Default: `32` * `recursive` Default: `false` * `callback` * `err` * `dir` Asynchronously open a directory. See the POSIX `opendir(3)` documentation for more details. Creates an , which contains all further functions for reading from and cleaning up the directory. The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations. #### `fs.read(fd, buffer, offset, length, position, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.10.0 The `buffer` parameter can now be any `TypedArray`, or a `DataView`. v7.4.0 The `buffer` parameter can now be a `Uint8Array`. v6.0.0 The `length` parameter can now be `0`. v0.0.2 Added in: v0.0.2 * `fd` * `buffer` | | The buffer that the data will be written to. * `offset` The position in `buffer` to write the data to. * `length` The number of bytes to read. * `position` | | Specifies where to begin reading from in the file. If `position` is `null` or `-1 `, data will be read from the current file position, and the file position will be updated. If `position` is a non-negative integer, the file position will be unchanged. * `callback` * `err` * `bytesRead` * `buffer` Read data from the file specified by `fd`. The callback is given the three arguments, `(err, bytesRead, buffer)`. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. If this method is invoked as its `util.promisify()`ed version, it returns a promise for an `Object` with `bytesRead` and `buffer` properties. The `fs.read()` method reads data from the file specified by the file descriptor (`fd`). The `length` argument indicates the maximum number of bytes that Node.js will attempt to read from the kernel. However, the actual number of bytes read (`bytesRead`) can be lower than the specified `length` for various reasons. For example: * If the file is shorter than the specified `length`, `bytesRead` will be set to the actual number of bytes read. * If the file encounters EOF (End of File) before the buffer could be filled, Node.js will read all available bytes until EOF is encountered, and the `bytesRead` parameter in the callback will indicate the actual number of bytes read, which may be less than the specified `length`. * If the file is on a slow network `filesystem` or encounters any other issue during reading, `bytesRead` can be lower than the specified `length`. Therefore, when using `fs.read()`, it's important to check the `bytesRead` value to determine how many bytes were actually read from the file. Depending on your application logic, you may need to handle cases where `bytesRead` is lower than the specified `length`, such as by wrapping the read call in a loop if you require a minimum amount of bytes. This behavior is similar to the POSIX `preadv2` function. #### `fs.read(fd[, options], callback)`# History VersionChanges v13.11.0, v12.17.0 Options object can be passed in to make buffer, offset, length, and position optional. v13.11.0, v12.17.0 Added in: v13.11.0, v12.17.0 * `fd` * `options` * `buffer` | | Default: `Buffer.alloc(16384)` * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | | Default: `null` * `callback` * `err` * `bytesRead` * `buffer` Similar to the `fs.read()` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. #### `fs.read(fd, buffer[, options], callback)`# Added in: v18.2.0, v16.17.0 * `fd` * `buffer` | | The buffer that the data will be written to. * `options` * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | Default: `null` * `callback` * `err` * `bytesRead` * `buffer` Similar to the `fs.read()` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. #### `fs.readdir(path[, options], callback)`# History VersionChanges v20.1.0, v18.17.0 Added `recursive` option. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.10.0 New option `withFileTypes` was added. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v6.0.0 The `options` parameter was added. v0.1.8 Added in: v0.1.8 * `path` | | * `options` | * `encoding` Default: `'utf8'` * `withFileTypes` Default: `false` * `recursive` If `true`, reads the contents of a directory recursively. In recursive mode, it will list all files, sub files and directories. Default: `false`. * `callback` * `err` * `files` | | Reads the contents of a directory. The callback gets two arguments `(err, files)` where `files` is an array of the names of the files in the directory excluding `'.'` and `'..'`. See the POSIX `readdir(3)` documentation for more details. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the filenames passed to the callback. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as objects. If `options.withFileTypes` is set to `true`, the `files` array will contain objects. #### `fs.readFile(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v16.0.0 The error returned may be an `AggregateError` if more than one error is returned. v15.2.0, v14.17.0 The options argument may include an AbortSignal to abort an ongoing readFile request. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v5.1.0 The `callback` will always be called with `null` as the `error` parameter in case of success. v5.0.0 The `path` parameter can be a file descriptor now. v0.1.29 Added in: v0.1.29 * `path` | | | filename or file descriptor * `options` | * `encoding` | Default: `null` * `flag` See support of file system `flags`. Default: `'r'`. * `signal` allows aborting an in-progress readFile * `callback` * `err` | * `data` | Asynchronously reads the entire contents of a file. import { readFile } from 'node:fs'; readFile('/etc/passwd', (err, data) => { if (err) throw err; console.log(data); }); The callback is passed two arguments `(err, data)`, where `data` is the contents of the file. If no encoding is specified, then the raw buffer is returned. If `options` is a string, then it specifies the encoding: import { readFile } from 'node:fs'; readFile('/etc/passwd', 'utf8', callback); When the path is a directory, the behavior of `fs.readFile()` and `fs.readFileSync()` is platform-specific. On macOS, Linux, and Windows, an error will be returned. On FreeBSD, a representation of the directory's contents will be returned. import { readFile } from 'node:fs'; // macOS, Linux, and Windows readFile('', (err, data) => { // => [Error: EISDIR: illegal operation on a directory, read ] }); // FreeBSD readFile('', (err, data) => { // => null, }); It is possible to abort an ongoing request using an `AbortSignal`. If a request is aborted the callback is called with an `AbortError`: import { readFile } from 'node:fs'; const controller = new AbortController(); const signal = controller.signal; readFile(fileInfo[0].name, { signal }, (err, buf) => { // ... }); // When you want to abort the request controller.abort(); The `fs.readFile()` function buffers the entire file. To minimize memory costs, when possible prefer streaming via `fs.createReadStream()`. Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.readFile` performs. ##### File descriptors# 1. Any specified file descriptor has to support reading. 2. If a file descriptor is specified as the `path`, it will not be closed automatically. 3. The reading will begin at the current position. For example, if the file already had `'Hello World'` and six bytes are read with the file descriptor, the call to `fs.readFile()` with the same file descriptor, would give `'World'`, rather than `'Hello World'`. ##### Performance Considerations# The `fs.readFile()` method asynchronously reads the contents of a file into memory one chunk at a time, allowing the event loop to turn between each chunk. This allows the read operation to have less impact on other activity that may be using the underlying libuv thread pool but means that it will take longer to read a complete file into memory. The additional read overhead can vary broadly on different systems and depends on the type of file being read. If the file type is not a regular file (a pipe for instance) and Node.js is unable to determine an actual file size, each read operation will load on 64 KiB of data. For regular files, each read will process 512 KiB of data. For applications that require as-fast-as-possible reading of file contents, it is better to use `fs.read()` directly and for application code to manage reading the full contents of the file itself. The Node.js GitHub issue #25741 provides more information and a detailed analysis on the performance of `fs.readFile()` for multiple file sizes in different Node.js versions. #### `fs.readlink(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.1.31 Added in: v0.1.31 * `path` | | * `options` | * `encoding` Default: `'utf8'` * `callback` * `err` * `linkString` | Reads the contents of the symbolic link referred to by `path`. The callback gets two arguments `(err, linkString)`. See the POSIX `readlink(2)` documentation for more details. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the link path passed to the callback. If the `encoding` is set to `'buffer'`, the link path returned will be passed as a object. #### `fs.readv(fd, buffers[, position], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v13.13.0, v12.17.0 Added in: v13.13.0, v12.17.0 * `fd` * `buffers` * `position` | Default: `null` * `callback` * `err` * `bytesRead` * `buffers` Read from a file specified by `fd` and write to an array of `ArrayBufferView`s using `readv()`. `position` is the offset from the beginning of the file from where data should be read. If `typeof position !== 'number'`, the data will be read from the current position. The callback will be given three arguments: `err`, `bytesRead`, and `buffers`. `bytesRead` is how many bytes were read from the file. If this method is invoked as its `util.promisify()`ed version, it returns a promise for an `Object` with `bytesRead` and `buffers` properties. #### `fs.realpath(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v8.0.0 Pipe/Socket resolve support was added. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v6.4.0 Calling `realpath` now works again for various edge cases on Windows. v6.0.0 The `cache` parameter was removed. v0.1.31 Added in: v0.1.31 * `path` | | * `options` | * `encoding` Default: `'utf8'` * `callback` * `err` * `resolvedPath` | Asynchronously computes the canonical pathname by resolving `.`, `..`, and symbolic links. A canonical pathname is not necessarily unique. Hard links and bind mounts can expose a file system entity through many pathnames. This function behaves like `realpath(3)`, with some exceptions: 1. No case conversion is performed on case-insensitive file systems. 2. The maximum number of symbolic links is platform-independent and generally (much) higher than what the native `realpath(3)` implementation supports. The `callback` gets two arguments `(err, resolvedPath)`. May use `process.cwd` to resolve relative paths. Only paths that can be converted to UTF8 strings are supported. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path passed to the callback. If the `encoding` is set to `'buffer'`, the path returned will be passed as a object. If `path` resolves to a socket or a pipe, the function will return a system dependent name for that object. A path that does not exist results in an ENOENT error. `error.path` is the absolute file path. #### `fs.realpath.native(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v9.2.0 Added in: v9.2.0 * `path` | | * `options` | * `encoding` Default: `'utf8'` * `callback` * `err` * `resolvedPath` | Asynchronous `realpath(3)`. The `callback` gets two arguments `(err, resolvedPath)`. Only paths that can be converted to UTF8 strings are supported. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path passed to the callback. If the `encoding` is set to `'buffer'`, the path returned will be passed as a object. On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction. #### `fs.rename(oldPath, newPath, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `oldPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still experimental. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.0.2 Added in: v0.0.2 * `oldPath` | | * `newPath` | | * `callback` * `err` Asynchronously rename file at `oldPath` to the pathname provided as `newPath`. In the case that `newPath` already exists, it will be overwritten. If there is a directory at `newPath`, an error will be raised instead. No arguments other than a possible exception are given to the completion callback. See also: `rename(2)`. import { rename } from 'node:fs'; rename('oldFile.txt', 'newFile.txt', (err) => { if (err) throw err; console.log('Rename complete!'); }); #### `fs.rmdir(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v16.0.0 Using `fs.rmdir(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. v16.0.0 Using `fs.rmdir(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error. v16.0.0 The `recursive` option is deprecated, using it triggers a deprecation warning. v14.14.0 The `recursive` option is deprecated, use `fs.rm` instead. v13.3.0, v12.16.0 The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. v12.10.0 The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameters can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.0.2 Added in: v0.0.2 * `path` | | * `options` * `maxRetries` If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. Default: `0`. * `recursive` If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. Default: `false`. Deprecated. * `retryDelay` The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. Default: `100`. * `callback` * `err` Asynchronous `rmdir(2)`. No arguments other than a possible exception are given to the completion callback. Using `fs.rmdir()` on a file (not a directory) results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. To get a behavior similar to the `rm -rf` Unix command, use `fs.rm()` with options `{ recursive: true, force: true }`. #### `fs.rm(path[, options], callback)`# History VersionChanges v17.3.0, v16.14.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v14.14.0 Added in: v14.14.0 * `path` | | * `options` * `force` When `true`, exceptions will be ignored if `path` does not exist. Default: `false`. * `maxRetries` If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. Default: `0`. * `recursive` If `true`, perform a recursive removal. In recursive mode operations are retried on failure. Default: `false`. * `retryDelay` The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. Default: `100`. * `callback` * `err` Asynchronously removes files and directories (modeled on the standard POSIX `rm` utility). No arguments other than a possible exception are given to the completion callback. #### `fs.stat(path[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.0.2 Added in: v0.0.2 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * `callback` * `err` * `stats` Asynchronous `stat(2)`. The callback gets two arguments `(err, stats)` where `stats` is an object. In case of an error, the `err.code` will be one of Common System Errors. `fs.stat()` follows symbolic links. Use `fs.lstat()` to look at the links themselves. Using `fs.stat()` to check for the existence of a file before calling `fs.open()`, `fs.readFile()`, or `fs.writeFile()` is not recommended. Instead, user code should open/read/write the file directly and handle the error raised if the file is not available. To check if a file exists without manipulating it afterwards, `fs.access()` is recommended. For example, given the following directory structure: - txtDir -- file.txt - app.js The next program will check for the stats of the given paths: import { stat } from 'node:fs'; const pathsToCheck = ['./txtDir', './txtDir/file.txt']; for (let i = 0; i < pathsToCheck.length; i++) { stat(pathsToCheck[i], (err, stats) => { console.log(stats.isDirectory()); console.log(stats); }); } The resulting output will resemble: true Stats { dev: 16777220, mode: 16877, nlink: 3, uid: 501, gid: 20, rdev: 0, blksize: 4096, ino: 14214262, size: 96, blocks: 0, atimeMs: 1561174653071.963, mtimeMs: 1561174614583.3518, ctimeMs: 1561174626623.5366, birthtimeMs: 1561174126937.2893, atime: 2019-06-22T03:37:33.072Z, mtime: 2019-06-22T03:36:54.583Z, ctime: 2019-06-22T03:37:06.624Z, birthtime: 2019-06-22T03:28:46.937Z } false Stats { dev: 16777220, mode: 33188, nlink: 1, uid: 501, gid: 20, rdev: 0, blksize: 4096, ino: 14214074, size: 8, blocks: 8, atimeMs: 1561174616618.8555, mtimeMs: 1561174614584, ctimeMs: 1561174614583.8145, birthtimeMs: 1561174007710.7478, atime: 2019-06-22T03:36:56.619Z, mtime: 2019-06-22T03:36:54.584Z, ctime: 2019-06-22T03:36:54.584Z, birthtime: 2019-06-22T03:26:47.711Z } #### `fs.statfs(path[, options], callback)`# Added in: v19.6.0, v18.15.0 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * `callback` * `err` * `stats` Asynchronous `statfs(2)`. Returns information about the mounted file system which contains `path`. The callback gets two arguments `(err, stats)` where `stats` is an object. In case of an error, the `err.code` will be one of Common System Errors. #### `fs.symlink(target, path[, type], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v12.0.0 If the `type` argument is left undefined, Node will autodetect `target` type and automatically select `dir` or `file`. v7.6.0 The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still experimental. v0.1.31 Added in: v0.1.31 * `target` | | * `path` | | * `type` | Default: `null` * `callback` * `err` Creates the link called `path` pointing to `target`. No arguments other than a possible exception are given to the completion callback. See the POSIX `symlink(2)` documentation for more details. The `type` argument is only available on Windows and ignored on other platforms. It can be set to `'dir'`, `'file'`, or `'junction'`. If the `type` argument is `null`, Node.js will autodetect `target` type and use `'file'` or `'dir'`. If the `target` does not exist, `'file'` will be used. Windows junction points require the destination path to be absolute. When using `'junction'`, the `target` argument will automatically be normalized to absolute path. Junction points on NTFS volumes can only point to directories. Relative targets are relative to the link's parent directory. import { symlink } from 'node:fs'; symlink('./mew', './mewtwo', callback); The above example creates a symbolic link `mewtwo` which points to `mew` in the same directory: $ tree . . ├── mew └── mewtwo -> ./mew #### `fs.truncate(path[, len], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v16.0.0 The error returned may be an `AggregateError` if more than one error is returned. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.8.6 Added in: v0.8.6 * `path` | | * `len` Default: `0` * `callback` * `err` | Truncates the file. No arguments other than a possible exception are given to the completion callback. A file descriptor can also be passed as the first argument. In this case, `fs.ftruncate()` is called. import { truncate } from 'node:fs'; // Assuming that 'path/file.txt' is a regular file. truncate('path/file.txt', (err) => { if (err) throw err; console.log('path/file.txt was truncated'); }); Passing a file descriptor is deprecated and may result in an error being thrown in the future. See the POSIX `truncate(2)` documentation for more details. #### `fs.unlink(path, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.0.2 Added in: v0.0.2 * `path` | | * `callback` * `err` Asynchronously removes a file or symbolic link. No arguments other than a possible exception are given to the completion callback. import { unlink } from 'node:fs'; // Assuming that 'path/file.txt' is a regular file. unlink('path/file.txt', (err) => { if (err) throw err; console.log('path/file.txt was deleted'); }); `fs.unlink()` will not work on a directory, empty or otherwise. To remove a directory, use `fs.rmdir()`. See the POSIX `unlink(2)` documentation for more details. #### `fs.unwatchFile(filename[, listener])`# Added in: v0.1.31 * `filename` | | * `listener` Optional, a listener previously attached using `fs.watchFile()` Stop watching for changes on `filename`. If `listener` is specified, only that particular listener is removed. Otherwise, all listeners are removed, effectively stopping watching of `filename`. Calling `fs.unwatchFile()` with a filename that is not being watched is a no-op, not an error. Using `fs.watch()` is more efficient than `fs.watchFile()` and `fs.unwatchFile()`. `fs.watch()` should be used instead of `fs.watchFile()` and `fs.unwatchFile()` when possible. #### `fs.utimes(path, atime, mtime, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v8.0.0 `NaN`, `Infinity`, and `-Infinity` are no longer valid time specifiers. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v4.1.0 Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. v0.4.2 Added in: v0.4.2 * `path` | | * `atime` | | * `mtime` | | * `callback` * `err` Change the file system timestamps of the object referenced by `path`. The `atime` and `mtime` arguments follow these rules: * Values can be either numbers representing Unix epoch time in seconds, `Date`s, or a numeric string like `'123456789.0'`. * If the value can not be converted to a number, or is `NaN`, `Infinity`, or `-Infinity`, an `Error` will be thrown. #### `fs.watch(filename[, options][, listener])`# History VersionChanges v19.1.0 Added recursive support for Linux, AIX and IBMi. v15.9.0, v14.17.0 Added support for closing the watcher with an AbortSignal. v7.6.0 The `filename` parameter can be a WHATWG `URL` object using `file:` protocol. v7.0.0 The passed `options` object will never be modified. v0.5.10 Added in: v0.5.10 * `filename` | | * `options` | * `persistent` Indicates whether the process should continue to run as long as files are being watched. Default: `true`. * `recursive` Indicates whether all subdirectories should be watched, or only the current directory. This applies when a directory is specified, and only on supported platforms (See caveats). Default: `false`. * `encoding` Specifies the character encoding to be used for the filename passed to the listener. Default: `'utf8'`. * `signal` allows closing the watcher with an AbortSignal. * `listener` | Default: `undefined` * `eventType` * `filename` | | * Returns: Watch for changes on `filename`, where `filename` is either a file or a directory. The second argument is optional. If `options` is provided as a string, it specifies the `encoding`. Otherwise `options` should be passed as an object. The listener callback gets two arguments `(eventType, filename)`. `eventType` is either `'rename'` or `'change'`, and `filename` is the name of the file which triggered the event. On most platforms, `'rename'` is emitted whenever a filename appears or disappears in the directory. The listener callback is attached to the `'change'` event fired by , but it is not the same thing as the `'change'` value of `eventType`. If a `signal` is passed, aborting the corresponding AbortController will close the returned . ##### Caveats# The `fs.watch` API is not 100% consistent across platforms, and is unavailable in some situations. On Windows, no events will be emitted if the watched directory is moved or renamed. An `EPERM` error is reported when the watched directory is deleted. The `fs.watch` API does not provide any protection with respect to malicious actions on the file system. For example, on Windows it is implemented by monitoring changes in a directory versus specific files. This allows substitution of a file and fs reporting changes on the new file with the same filename. ###### Availability# This feature depends on the underlying operating system providing a way to be notified of file system changes. * On Linux systems, this uses `inotify(7)`. * On BSD systems, this uses `kqueue(2)`. * On macOS, this uses `kqueue(2)` for files and `FSEvents` for directories. * On SunOS systems (including Solaris and SmartOS), this uses `event ports`. * On Windows systems, this feature depends on `ReadDirectoryChangesW`. * On AIX systems, this feature depends on `AHAFS`, which must be enabled. * On IBM i systems, this feature is not supported. If the underlying functionality is not available for some reason, then `fs.watch()` will not be able to function and may throw an exception. For example, watching files or directories can be unreliable, and in some cases impossible, on network file systems (NFS, SMB, etc) or host file systems when using virtualization software such as Vagrant or Docker. It is still possible to use `fs.watchFile()`, which uses stat polling, but this method is slower and less reliable. ###### Inodes# On Linux and macOS systems, `fs.watch()` resolves the path to an inode and watches the inode. If the watched path is deleted and recreated, it is assigned a new inode. The watch will emit an event for the delete but will continue watching the original inode. Events for the new inode will not be emitted. This is expected behavior. AIX files retain the same inode for the lifetime of a file. Saving and closing a watched file on AIX will result in two notifications (one for adding new content, and one for truncation). ###### Filename argument# Providing `filename` argument in the callback is only supported on Linux, macOS, Windows, and AIX. Even on supported platforms, `filename` is not always guaranteed to be provided. Therefore, don't assume that `filename` argument is always provided in the callback, and have some fallback logic if it is `null`. import { watch } from 'node:fs'; watch('somedir', (eventType, filename) => { console.log(`event type is: ${eventType}`); if (filename) { console.log(`filename provided: ${filename}`); } else { console.log('filename not provided'); } }); #### `fs.watchFile(filename[, options], listener)`# History VersionChanges v10.5.0 The `bigint` option is now supported. v7.6.0 The `filename` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.31 Added in: v0.1.31 * `filename` | | * `options` * `bigint` Default: `false` * `persistent` Default: `true` * `interval` Default: `5007` * `listener` * `current` * `previous` * Returns: Watch for changes on `filename`. The callback `listener` will be called each time the file is accessed. The `options` argument may be omitted. If provided, it should be an object. The `options` object may contain a boolean named `persistent` that indicates whether the process should continue to run as long as files are being watched. The `options` object may specify an `interval` property indicating how often the target should be polled in milliseconds. The `listener` gets two arguments the current stat object and the previous stat object: import { watchFile } from 'node:fs'; watchFile('message.text', (curr, prev) => { console.log(`the current mtime is: ${curr.mtime}`); console.log(`the previous mtime was: ${prev.mtime}`); }); These stat objects are instances of `fs.Stat`. If the `bigint` option is `true`, the numeric values in these objects are specified as `BigInt`s. To be notified when the file was modified, not just accessed, it is necessary to compare `curr.mtimeMs` and `prev.mtimeMs`. When an `fs.watchFile` operation results in an `ENOENT` error, it will invoke the listener once, with all the fields zeroed (or, for dates, the Unix Epoch). If the file is created later on, the listener will be called again, with the latest stat objects. This is a change in functionality since v0.10. Using `fs.watch()` is more efficient than `fs.watchFile` and `fs.unwatchFile`. `fs.watch` should be used instead of `fs.watchFile` and `fs.unwatchFile` when possible. When a file being watched by `fs.watchFile()` disappears and reappears, then the contents of `previous` in the second callback event (the file's reappearance) will be the same as the contents of `previous` in the first callback event (its disappearance). This happens when: * the file is deleted, followed by a restore * the file is renamed and then renamed a second time back to its original name #### `fs.write(fd, buffer, offset[, length[, position]], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v14.0.0 The `buffer` parameter won't coerce unsupported input to strings anymore. v10.10.0 The `buffer` parameter can now be any `TypedArray` or a `DataView`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.4.0 The `buffer` parameter can now be a `Uint8Array`. v7.2.0 The `offset` and `length` parameters are optional now. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.0.2 Added in: v0.0.2 * `fd` * `buffer` | | * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | Default: `null` * `callback` * `err` * `bytesWritten` * `buffer` | | Write `buffer` to the file specified by `fd`. `offset` determines the part of the buffer to be written, and `length` is an integer specifying the number of bytes to write. `position` refers to the offset from the beginning of the file where this data should be written. If `typeof position !== 'number'`, the data will be written at the current position. See `pwrite(2)`. The callback will be given three arguments `(err, bytesWritten, buffer)` where `bytesWritten` specifies how many bytes were written from `buffer`. If this method is invoked as its `util.promisify()`ed version, it returns a promise for an `Object` with `bytesWritten` and `buffer` properties. It is unsafe to use `fs.write()` multiple times on the same file without waiting for the callback. For this scenario, `fs.createWriteStream()` is recommended. On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file. #### `fs.write(fd, buffer[, options], callback)`# Added in: v18.3.0, v16.17.0 * `fd` * `buffer` | | * `options` * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | Default: `null` * `callback` * `err` * `bytesWritten` * `buffer` | | Write `buffer` to the file specified by `fd`. Similar to the above `fs.write` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. #### `fs.write(fd, string[, position[, encoding]], callback)`# History VersionChanges v19.0.0 Passing to the `string` parameter an object with an own `toString` function is no longer supported. v17.8.0 Passing to the `string` parameter an object with an own `toString` function is deprecated. v14.12.0 The `string` parameter will stringify an object with an explicit `toString` function. v14.0.0 The `string` parameter won't coerce unsupported input to strings anymore. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.2.0 The `position` parameter is optional now. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v0.11.5 Added in: v0.11.5 * `fd` * `string` * `position` | Default: `null` * `encoding` Default: `'utf8'` * `callback` * `err` * `written` * `string` Write `string` to the file specified by `fd`. If `string` is not a string, an exception is thrown. `position` refers to the offset from the beginning of the file where this data should be written. If `typeof position !== 'number'` the data will be written at the current position. See `pwrite(2)`. `encoding` is the expected string encoding. The callback will receive the arguments `(err, written, string)` where `written` specifies how many bytes the passed string required to be written. Bytes written is not necessarily the same as string characters written. See `Buffer.byteLength`. It is unsafe to use `fs.write()` multiple times on the same file without waiting for the callback. For this scenario, `fs.createWriteStream()` is recommended. On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file. On Windows, if the file descriptor is connected to the console (e.g. `fd == 1` or `stdout`) a string containing non-ASCII characters will not be rendered properly by default, regardless of the encoding used. It is possible to configure the console to render UTF-8 properly by changing the active codepage with the `chcp 65001` command. See the chcp docs for more details. #### `fs.writeFile(file, data[, options], callback)`# History VersionChanges v21.0.0, v20.10.0 The `flush` option is now supported. v19.0.0 Passing to the `string` parameter an object with an own `toString` function is no longer supported. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v17.8.0 Passing to the `string` parameter an object with an own `toString` function is deprecated. v16.0.0 The error returned may be an `AggregateError` if more than one error is returned. v15.2.0, v14.17.0 The options argument may include an AbortSignal to abort an ongoing writeFile request. v14.12.0 The `data` parameter will stringify an object with an explicit `toString` function. v14.0.0 The `data` parameter won't coerce unsupported input to strings anymore. v10.10.0 The `data` parameter can now be any `TypedArray` or a `DataView`. v10.0.0 The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. v7.4.0 The `data` parameter can now be a `Uint8Array`. v7.0.0 The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. v5.0.0 The `file` parameter can be a file descriptor now. v0.1.29 Added in: v0.1.29 * `file` | | | filename or file descriptor * `data` | | | * `options` | * `encoding` | Default: `'utf8'` * `mode` Default: `0o666` * `flag` See support of file system `flags`. Default: `'w'`. * `flush` If all data is successfully written to the file, and `flush` is `true`, `fs.fsync()` is used to flush the data. Default: `false`. * `signal` allows aborting an in-progress writeFile * `callback` * `err` | When `file` is a filename, asynchronously writes data to the file, replacing the file if it already exists. `data` can be a string or a buffer. When `file` is a file descriptor, the behavior is similar to calling `fs.write()` directly (which is recommended). See the notes below on using a file descriptor. The `encoding` option is ignored if `data` is a buffer. The `mode` option only affects the newly created file. See `fs.open()` for more details. import { writeFile } from 'node:fs'; import { Buffer } from 'node:buffer'; const data = new Uint8Array(Buffer.from('Hello Node.js')); writeFile('message.txt', data, (err) => { if (err) throw err; console.log('The file has been saved!'); }); If `options` is a string, then it specifies the encoding: import { writeFile } from 'node:fs'; writeFile('message.txt', 'Hello Node.js', 'utf8', callback); It is unsafe to use `fs.writeFile()` multiple times on the same file without waiting for the callback. For this scenario, `fs.createWriteStream()` is recommended. Similarly to `fs.readFile` \- `fs.writeFile` is a convenience method that performs multiple `write` calls internally to write the buffer passed to it. For performance sensitive code consider using `fs.createWriteStream()`. It is possible to use an to cancel an `fs.writeFile()`. Cancelation is "best effort", and some amount of data is likely still to be written. import { writeFile } from 'node:fs'; import { Buffer } from 'node:buffer'; const controller = new AbortController(); const { signal } = controller; const data = new Uint8Array(Buffer.from('Hello Node.js')); writeFile('message.txt', data, { signal }, (err) => { // When a request is aborted - the callback is called with an AbortError }); // When the request should be aborted controller.abort(); Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.writeFile` performs. ##### Using `fs.writeFile()` with file descriptors# When `file` is a file descriptor, the behavior is almost identical to directly calling `fs.write()` like: import { write } from 'node:fs'; import { Buffer } from 'node:buffer'; write(fd, Buffer.from(data, options.encoding), callback); The difference from directly calling `fs.write()` is that under some unusual conditions, `fs.write()` might write only part of the buffer and need to be retried to write the remaining data, whereas `fs.writeFile()` retries until the data is entirely written (or an error occurs). The implications of this are a common source of confusion. In the file descriptor case, the file is not replaced! The data is not necessarily written to the beginning of the file, and the file's original data may remain before and/or after the newly written data. For example, if `fs.writeFile()` is called twice in a row, first to write the string `'Hello'`, then to write the string `', World'`, the file would contain `'Hello, World'`, and might contain some of the file's original data (depending on the size of the original file, and the position of the file descriptor). If a file name had been used instead of a descriptor, the file would be guaranteed to contain only `', World'`. #### `fs.writev(fd, buffers[, position], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v12.9.0 Added in: v12.9.0 * `fd` * `buffers` * `position` | Default: `null` * `callback` * `err` * `bytesWritten` * `buffers` Write an array of `ArrayBufferView`s to the file specified by `fd` using `writev()`. `position` is the offset from the beginning of the file where this data should be written. If `typeof position !== 'number'`, the data will be written at the current position. The callback will be given three arguments: `err`, `bytesWritten`, and `buffers`. `bytesWritten` is how many bytes were written from `buffers`. If this method is `util.promisify()`ed, it returns a promise for an `Object` with `bytesWritten` and `buffers` properties. It is unsafe to use `fs.writev()` multiple times on the same file without waiting for the callback. For this scenario, use `fs.createWriteStream()`. On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file. ### Synchronous API# The synchronous APIs perform all operations synchronously, blocking the event loop until the operation completes or fails. #### `fs.accessSync(path[, mode])`# History VersionChanges v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.11.15 Added in: v0.11.15 * `path` | | * `mode` Default: `fs.constants.F_OK` Synchronously tests a user's permissions for the file or directory specified by `path`. The `mode` argument is an optional integer that specifies the accessibility checks to be performed. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check File access constants for possible values of `mode`. If any of the accessibility checks fail, an `Error` will be thrown. Otherwise, the method will return `undefined`. import { accessSync, constants } from 'node:fs'; try { accessSync('etc/passwd', constants.R_OK | constants.W_OK); console.log('can read/write'); } catch (err) { console.error('no access!'); } #### `fs.appendFileSync(path, data[, options])`# History VersionChanges v21.1.0, v20.10.0 The `flush` option is now supported. v7.0.0 The passed `options` object will never be modified. v5.0.0 The `file` parameter can be a file descriptor now. v0.6.7 Added in: v0.6.7 * `path` | | | filename or file descriptor * `data` | * `options` | * `encoding` | Default: `'utf8'` * `mode` Default: `0o666` * `flag` See support of file system `flags`. Default: `'a'`. * `flush` If `true`, the underlying file descriptor is flushed prior to closing it. Default: `false`. Synchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a . The `mode` option only affects the newly created file. See `fs.open()` for more details. import { appendFileSync } from 'node:fs'; try { appendFileSync('message.txt', 'data to append'); console.log('The "data to append" was appended to file!'); } catch (err) { /* Handle the error */ } If `options` is a string, then it specifies the encoding: import { appendFileSync } from 'node:fs'; appendFileSync('message.txt', 'data to append', 'utf8'); The `path` may be specified as a numeric file descriptor that has been opened for appending (using `fs.open()` or `fs.openSync()`). The file descriptor will not be closed automatically. import { openSync, closeSync, appendFileSync } from 'node:fs'; let fd; try { fd = openSync('message.txt', 'a'); appendFileSync(fd, 'data to append', 'utf8'); } catch (err) { /* Handle the error */ } finally { if (fd !== undefined) closeSync(fd); } #### `fs.chmodSync(path, mode)`# History VersionChanges v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.6.7 Added in: v0.6.7 * `path` | | * `mode` | For detailed information, see the documentation of the asynchronous version of this API: `fs.chmod()`. See the POSIX `chmod(2)` documentation for more detail. #### `fs.chownSync(path, uid, gid)`# History VersionChanges v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.97 Added in: v0.1.97 * `path` | | * `uid` * `gid` Synchronously changes owner and group of a file. Returns `undefined`. This is the synchronous version of `fs.chown()`. See the POSIX `chown(2)` documentation for more detail. #### `fs.closeSync(fd)`# Added in: v0.1.21 * `fd` Closes the file descriptor. Returns `undefined`. Calling `fs.closeSync()` on any file descriptor (`fd`) that is currently in use through any other `fs` operation may lead to undefined behavior. See the POSIX `close(2)` documentation for more detail. #### `fs.copyFileSync(src, dest[, mode])`# History VersionChanges v14.0.0 Changed `flags` argument to `mode` and imposed stricter type validation. v8.5.0 Added in: v8.5.0 * `src` | | source filename to copy * `dest` | | destination filename of the copy operation * `mode` modifiers for copy operation. Default: `0`. Synchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. Returns `undefined`. Node.js makes no guarantees about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, Node.js will attempt to remove the destination. `mode` is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`). * `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists. * `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used. * `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail. import { copyFileSync, constants } from 'node:fs'; // destination.txt will be created or overwritten by default. copyFileSync('source.txt', 'destination.txt'); console.log('source.txt was copied to destination.txt'); // By using COPYFILE_EXCL, the operation will fail if destination.txt exists. copyFileSync('source.txt', 'destination.txt', constants.COPYFILE_EXCL); #### `fs.cpSync(src, dest[, options])`# History VersionChanges v22.3.0 This API is no longer experimental. v20.1.0, v18.17.0 Accept an additional `mode` option to specify the copy behavior as the `mode` argument of `fs.copyFile()`. v17.6.0, v16.15.0 Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. v16.7.0 Added in: v16.7.0 * `src` | source path to copy. * `dest` | destination path to copy to. * `options` * `dereference` dereference symlinks. Default: `false`. * `errorOnExist` when `force` is `false`, and the destination exists, throw an error. Default: `false`. * `filter` Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. When ignoring a directory, all of its contents will be skipped as well. Default: `undefined` * `src` source path to copy. * `dest` destination path to copy to. * Returns: Any non-`Promise` value that is coercible to `boolean`. * `force` overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. Default: `true`. * `mode` modifiers for copy operation. Default: `0`. See `mode` flag of `fs.copyFileSync()`. * `preserveTimestamps` When `true` timestamps from `src` will be preserved. Default: `false`. * `recursive` copy directories recursively Default: `false` * `verbatimSymlinks` When `true`, path resolution for symlinks will be skipped. Default: `false` Synchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files. When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`. #### `fs.existsSync(path)`# History VersionChanges v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.21 Added in: v0.1.21 * `path` | | * Returns: Returns `true` if the path exists, `false` otherwise. For detailed information, see the documentation of the asynchronous version of this API: `fs.exists()`. `fs.exists()` is deprecated, but `fs.existsSync()` is not. The `callback` parameter to `fs.exists()` accepts parameters that are inconsistent with other Node.js callbacks. `fs.existsSync()` does not use a callback. import { existsSync } from 'node:fs'; if (existsSync('/etc/passwd')) console.log('The path exists.'); #### `fs.fchmodSync(fd, mode)`# Added in: v0.4.7 * `fd` * `mode` | Sets the permissions on the file. Returns `undefined`. See the POSIX `fchmod(2)` documentation for more detail. #### `fs.fchownSync(fd, uid, gid)`# Added in: v0.4.7 * `fd` * `uid` The file's new owner's user id. * `gid` The file's new group's group id. Sets the owner of the file. Returns `undefined`. See the POSIX `fchown(2)` documentation for more detail. #### `fs.fdatasyncSync(fd)`# Added in: v0.1.96 * `fd` Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX `fdatasync(2)` documentation for details. Returns `undefined`. #### `fs.fstatSync(fd[, options])`# History VersionChanges v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v0.1.95 Added in: v0.1.95 * `fd` * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * Returns: Retrieves the for the file descriptor. See the POSIX `fstat(2)` documentation for more detail. #### `fs.fsyncSync(fd)`# Added in: v0.1.96 * `fd` Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX `fsync(2)` documentation for more detail. Returns `undefined`. #### `fs.ftruncateSync(fd[, len])`# Added in: v0.8.6 * `fd` * `len` Default: `0` Truncates the file descriptor. Returns `undefined`. For detailed information, see the documentation of the asynchronous version of this API: `fs.ftruncate()`. #### `fs.futimesSync(fd, atime, mtime)`# History VersionChanges v4.1.0 Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. v0.4.2 Added in: v0.4.2 * `fd` * `atime` | | * `mtime` | | Synchronous version of `fs.futimes()`. Returns `undefined`. #### `fs.globSync(pattern[, options])`# History VersionChanges v24.1.0 Add support for `URL` instances for `cwd` option. v24.0.0 Marking the API stable. v23.7.0, v22.14.0 Add support for `exclude` option to accept glob patterns. v22.2.0 Add support for `withFileTypes` as an option. v22.0.0 Added in: v22.0.0 * `pattern` | * `options` * `cwd` | current working directory. Default: `process.cwd()` * `exclude` | Function to filter out files/directories or a list of glob patterns to be excluded. If a function is provided, return `true` to exclude the item, `false` to include it. Default: `undefined`. * `withFileTypes` `true` if the glob should return paths as Dirents, `false` otherwise. Default: `false`. * Returns: paths of files that match the pattern. import { globSync } from 'node:fs'; console.log(globSync('**/*.js')); #### `fs.lchmodSync(path, mode)`# Deprecated since: v0.4.7 Stability: 0 \- Deprecated * `path` | | * `mode` Changes the permissions on a symbolic link. Returns `undefined`. This method is only implemented on macOS. See the POSIX `lchmod(2)` documentation for more detail. #### `fs.lchownSync(path, uid, gid)`# History VersionChanges v10.6.0 This API is no longer deprecated. v0.4.7 Documentation-only deprecation. * `path` | | * `uid` The file's new owner's user id. * `gid` The file's new group's group id. Set the owner for the path. Returns `undefined`. See the POSIX `lchown(2)` documentation for more details. #### `fs.lutimesSync(path, atime, mtime)`# Added in: v14.5.0, v12.19.0 * `path` | | * `atime` | | * `mtime` | | Change the file system timestamps of the symbolic link referenced by `path`. Returns `undefined`, or throws an exception when parameters are incorrect or the operation fails. This is the synchronous version of `fs.lutimes()`. #### `fs.linkSync(existingPath, newPath)`# History VersionChanges v7.6.0 The `existingPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still experimental. v0.1.31 Added in: v0.1.31 * `existingPath` | | * `newPath` | | Creates a new link from the `existingPath` to the `newPath`. See the POSIX `link(2)` documentation for more detail. Returns `undefined`. #### `fs.lstatSync(path[, options])`# History VersionChanges v15.3.0, v14.17.0 Accepts a `throwIfNoEntry` option to specify whether an exception should be thrown if the entry does not exist. v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.30 Added in: v0.1.30 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * `throwIfNoEntry` Whether an exception will be thrown if no file system entry exists, rather than returning `undefined`. Default: `true`. * Returns: Retrieves the for the symbolic link referred to by `path`. See the POSIX `lstat(2)` documentation for more details. #### `fs.mkdirSync(path[, options])`# History VersionChanges v13.11.0, v12.17.0 In `recursive` mode, the first created path is returned now. v10.12.0 The second argument can now be an `options` object with `recursive` and `mode` properties. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.21 Added in: v0.1.21 * `path` | | * `options` | * `recursive` Default: `false` * `mode` | Not supported on Windows. Default: `0o777`. * Returns: | Synchronously creates a directory. Returns `undefined`, or if `recursive` is `true`, the first directory path created. This is the synchronous version of `fs.mkdir()`. See the POSIX `mkdir(2)` documentation for more details. #### `fs.mkdtempSync(prefix[, options])`# History VersionChanges v20.6.0, v18.19.0 The `prefix` parameter now accepts buffers and URL. v16.5.0, v14.18.0 The `prefix` parameter now accepts an empty string. v5.10.0 Added in: v5.10.0 * `prefix` | | * `options` | * `encoding` Default: `'utf8'` * Returns: Returns the created directory path. For detailed information, see the documentation of the asynchronous version of this API: `fs.mkdtemp()`. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use. #### `fs.mkdtempDisposableSync(prefix[, options])`# Added in: v24.4.0 * `prefix` | | * `options` | * `encoding` Default: `'utf8'` * Returns: A disposable object: * `path` The path of the created directory. * `remove` A function which removes the created directory. * `[Symbol.dispose]` The same as `remove`. Returns a disposable object whose `path` property holds the created directory path. When the object is disposed, the directory and its contents will be removed if it still exists. If the directory cannot be deleted, disposal will throw an error. The object has a `remove()` method which will perform the same task. For detailed information, see the documentation of `fs.mkdtemp()`. There is no callback-based version of this API because it is designed for use with the `using` syntax. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use. #### `fs.opendirSync(path[, options])`# History VersionChanges v20.1.0, v18.17.0 Added `recursive` option. v13.1.0, v12.16.0 The `bufferSize` option was introduced. v12.12.0 Added in: v12.12.0 * `path` | | * `options` * `encoding` | Default: `'utf8'` * `bufferSize` Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. Default: `32` * `recursive` Default: `false` * Returns: Synchronously open a directory. See `opendir(3)`. Creates an , which contains all further functions for reading from and cleaning up the directory. The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations. #### `fs.openSync(path[, flags[, mode]])`# History VersionChanges v11.1.0 The `flags` argument is now optional and defaults to `'r'`. v9.9.0 The `as` and `as+` flags are supported now. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.21 Added in: v0.1.21 * `path` | | * `flags` | Default: `'r'`. See support of file system `flags`. * `mode` | Default: `0o666` * Returns: Returns an integer representing the file descriptor. For detailed information, see the documentation of the asynchronous version of this API: `fs.open()`. #### `fs.readdirSync(path[, options])`# History VersionChanges v20.1.0, v18.17.0 Added `recursive` option. v10.10.0 New option `withFileTypes` was added. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.21 Added in: v0.1.21 * `path` | | * `options` | * `encoding` Default: `'utf8'` * `withFileTypes` Default: `false` * `recursive` If `true`, reads the contents of a directory recursively. In recursive mode, it will list all files, sub files, and directories. Default: `false`. * Returns: | | Reads the contents of the directory. See the POSIX `readdir(3)` documentation for more details. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the filenames returned. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as objects. If `options.withFileTypes` is set to `true`, the result will contain objects. #### `fs.readFileSync(path[, options])`# History VersionChanges v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v5.0.0 The `path` parameter can be a file descriptor now. v0.1.8 Added in: v0.1.8 * `path` | | | filename or file descriptor * `options` | * `encoding` | Default: `null` * `flag` See support of file system `flags`. Default: `'r'`. * Returns: | Returns the contents of the `path`. For detailed information, see the documentation of the asynchronous version of this API: `fs.readFile()`. If the `encoding` option is specified then this function returns a string. Otherwise it returns a buffer. Similar to `fs.readFile()`, when the path is a directory, the behavior of `fs.readFileSync()` is platform-specific. import { readFileSync } from 'node:fs'; // macOS, Linux, and Windows readFileSync(''); // => [Error: EISDIR: illegal operation on a directory, read ] // FreeBSD readFileSync(''); // => #### `fs.readlinkSync(path[, options])`# History VersionChanges v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.31 Added in: v0.1.31 * `path` | | * `options` | * `encoding` Default: `'utf8'` * Returns: | Returns the symbolic link's string value. See the POSIX `readlink(2)` documentation for more details. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the link path returned. If the `encoding` is set to `'buffer'`, the link path returned will be passed as a object. #### `fs.readSync(fd, buffer, offset, length[, position])`# History VersionChanges v10.10.0 The `buffer` parameter can now be any `TypedArray` or a `DataView`. v6.0.0 The `length` parameter can now be `0`. v0.1.21 Added in: v0.1.21 * `fd` * `buffer` | | * `offset` * `length` * `position` | | Default: `null` * Returns: Returns the number of `bytesRead`. For detailed information, see the documentation of the asynchronous version of this API: `fs.read()`. #### `fs.readSync(fd, buffer[, options])`# History VersionChanges v13.13.0, v12.17.0 Options object can be passed in to make offset, length, and position optional. v13.13.0, v12.17.0 Added in: v13.13.0, v12.17.0 * `fd` * `buffer` | | * `options` * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | | Default: `null` * Returns: Returns the number of `bytesRead`. Similar to the above `fs.readSync` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. For detailed information, see the documentation of the asynchronous version of this API: `fs.read()`. #### `fs.readvSync(fd, buffers[, position])`# Added in: v13.13.0, v12.17.0 * `fd` * `buffers` * `position` | Default: `null` * Returns: The number of bytes read. For detailed information, see the documentation of the asynchronous version of this API: `fs.readv()`. #### `fs.realpathSync(path[, options])`# History VersionChanges v8.0.0 Pipe/Socket resolve support was added. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v6.4.0 Calling `realpathSync` now works again for various edge cases on Windows. v6.0.0 The `cache` parameter was removed. v0.1.31 Added in: v0.1.31 * `path` | | * `options` | * `encoding` Default: `'utf8'` * Returns: | Returns the resolved pathname. For detailed information, see the documentation of the asynchronous version of this API: `fs.realpath()`. #### `fs.realpathSync.native(path[, options])`# Added in: v9.2.0 * `path` | | * `options` | * `encoding` Default: `'utf8'` * Returns: | Synchronous `realpath(3)`. Only paths that can be converted to UTF8 strings are supported. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use for the path returned. If the `encoding` is set to `'buffer'`, the path returned will be passed as a object. On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction. #### `fs.renameSync(oldPath, newPath)`# History VersionChanges v7.6.0 The `oldPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still experimental. v0.1.21 Added in: v0.1.21 * `oldPath` | | * `newPath` | | Renames the file from `oldPath` to `newPath`. Returns `undefined`. See the POSIX `rename(2)` documentation for more details. #### `fs.rmdirSync(path[, options])`# History VersionChanges v16.0.0 Using `fs.rmdirSync(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. v16.0.0 Using `fs.rmdirSync(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error. v16.0.0 The `recursive` option is deprecated, using it triggers a deprecation warning. v14.14.0 The `recursive` option is deprecated, use `fs.rmSync` instead. v13.3.0, v12.16.0 The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. v12.10.0 The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. v7.6.0 The `path` parameters can be a WHATWG `URL` object using `file:` protocol. v0.1.21 Added in: v0.1.21 * `path` | | * `options` * `maxRetries` If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. Default: `0`. * `recursive` If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. Default: `false`. Deprecated. * `retryDelay` The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. Default: `100`. Synchronous `rmdir(2)`. Returns `undefined`. Using `fs.rmdirSync()` on a file (not a directory) results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. To get a behavior similar to the `rm -rf` Unix command, use `fs.rmSync()` with options `{ recursive: true, force: true }`. #### `fs.rmSync(path[, options])`# History VersionChanges v17.3.0, v16.14.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v14.14.0 Added in: v14.14.0 * `path` | | * `options` * `force` When `true`, exceptions will be ignored if `path` does not exist. Default: `false`. * `maxRetries` If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. Default: `0`. * `recursive` If `true`, perform a recursive directory removal. In recursive mode operations are retried on failure. Default: `false`. * `retryDelay` The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. Default: `100`. Synchronously removes files and directories (modeled on the standard POSIX `rm` utility). Returns `undefined`. #### `fs.statSync(path[, options])`# History VersionChanges v15.3.0, v14.17.0 Accepts a `throwIfNoEntry` option to specify whether an exception should be thrown if the entry does not exist. v10.5.0 Accepts an additional `options` object to specify whether the numeric values returned should be bigint. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.21 Added in: v0.1.21 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * `throwIfNoEntry` Whether an exception will be thrown if no file system entry exists, rather than returning `undefined`. Default: `true`. * Returns: Retrieves the for the path. #### `fs.statfsSync(path[, options])`# Added in: v19.6.0, v18.15.0 * `path` | | * `options` * `bigint` Whether the numeric values in the returned object should be `bigint`. Default: `false`. * Returns: Synchronous `statfs(2)`. Returns information about the mounted file system which contains `path`. In case of an error, the `err.code` will be one of Common System Errors. #### `fs.symlinkSync(target, path[, type])`# History VersionChanges v12.0.0 If the `type` argument is left undefined, Node will autodetect `target` type and automatically select `dir` or `file`. v7.6.0 The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still experimental. v0.1.31 Added in: v0.1.31 * `target` | | * `path` | | * `type` | Default: `null` * Returns: `undefined`. For detailed information, see the documentation of the asynchronous version of this API: `fs.symlink()`. #### `fs.truncateSync(path[, len])`# Added in: v0.8.6 * `path` | | * `len` Default: `0` Truncates the file. Returns `undefined`. A file descriptor can also be passed as the first argument. In this case, `fs.ftruncateSync()` is called. Passing a file descriptor is deprecated and may result in an error being thrown in the future. #### `fs.unlinkSync(path)`# History VersionChanges v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v0.1.21 Added in: v0.1.21 * `path` | | Synchronous `unlink(2)`. Returns `undefined`. #### `fs.utimesSync(path, atime, mtime)`# History VersionChanges v8.0.0 `NaN`, `Infinity`, and `-Infinity` are no longer valid time specifiers. v7.6.0 The `path` parameter can be a WHATWG `URL` object using `file:` protocol. v4.1.0 Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. v0.4.2 Added in: v0.4.2 * `path` | | * `atime` | | * `mtime` | | * Returns: `undefined`. For detailed information, see the documentation of the asynchronous version of this API: `fs.utimes()`. #### `fs.writeFileSync(file, data[, options])`# History VersionChanges v21.0.0, v20.10.0 The `flush` option is now supported. v19.0.0 Passing to the `data` parameter an object with an own `toString` function is no longer supported. v17.8.0 Passing to the `data` parameter an object with an own `toString` function is deprecated. v14.12.0 The `data` parameter will stringify an object with an explicit `toString` function. v14.0.0 The `data` parameter won't coerce unsupported input to strings anymore. v10.10.0 The `data` parameter can now be any `TypedArray` or a `DataView`. v7.4.0 The `data` parameter can now be a `Uint8Array`. v5.0.0 The `file` parameter can be a file descriptor now. v0.1.29 Added in: v0.1.29 * `file` | | | filename or file descriptor * `data` | | | * `options` | * `encoding` | Default: `'utf8'` * `mode` Default: `0o666` * `flag` See support of file system `flags`. Default: `'w'`. * `flush` If all data is successfully written to the file, and `flush` is `true`, `fs.fsyncSync()` is used to flush the data. * Returns: `undefined`. The `mode` option only affects the newly created file. See `fs.open()` for more details. For detailed information, see the documentation of the asynchronous version of this API: `fs.writeFile()`. #### `fs.writeSync(fd, buffer, offset[, length[, position]])`# History VersionChanges v14.0.0 The `buffer` parameter won't coerce unsupported input to strings anymore. v10.10.0 The `buffer` parameter can now be any `TypedArray` or a `DataView`. v7.4.0 The `buffer` parameter can now be a `Uint8Array`. v7.2.0 The `offset` and `length` parameters are optional now. v0.1.21 Added in: v0.1.21 * `fd` * `buffer` | | * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | Default: `null` * Returns: The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: `fs.write(fd, buffer...)`. #### `fs.writeSync(fd, buffer[, options])`# Added in: v18.3.0, v16.17.0 * `fd` * `buffer` | | * `options` * `offset` Default: `0` * `length` Default: `buffer.byteLength - offset` * `position` | Default: `null` * Returns: The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: `fs.write(fd, buffer...)`. #### `fs.writeSync(fd, string[, position[, encoding]])`# History VersionChanges v14.0.0 The `string` parameter won't coerce unsupported input to strings anymore. v7.2.0 The `position` parameter is optional now. v0.11.5 Added in: v0.11.5 * `fd` * `string` * `position` | Default: `null` * `encoding` Default: `'utf8'` * Returns: The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: `fs.write(fd, string...)`. #### `fs.writevSync(fd, buffers[, position])`# Added in: v12.9.0 * `fd` * `buffers` * `position` | Default: `null` * Returns: The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: `fs.writev()`. ### Common Objects# The common objects are shared by all of the file system API variants (promise, callback, and synchronous). #### Class: `fs.Dir`# Added in: v12.12.0 A class representing a directory stream. Created by `fs.opendir()`, `fs.opendirSync()`, or `fsPromises.opendir()`. import { opendir } from 'node:fs/promises'; try { const dir = await opendir('./'); for await (const dirent of dir) console.log(dirent.name); } catch (err) { console.error(err); } When using the async iterator, the object will be automatically closed after the iterator exits. ##### `dir.close()`# Added in: v12.12.0 * Returns: Asynchronously close the directory's underlying resource handle. Subsequent reads will result in errors. A promise is returned that will be fulfilled after the resource has been closed. ##### `dir.close(callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v12.12.0 Added in: v12.12.0 * `callback` * `err` Asynchronously close the directory's underlying resource handle. Subsequent reads will result in errors. The `callback` will be called after the resource handle has been closed. ##### `dir.closeSync()`# Added in: v12.12.0 Synchronously close the directory's underlying resource handle. Subsequent reads will result in errors. ##### `dir.path`# Added in: v12.12.0 * Type: The read-only path of this directory as was provided to `fs.opendir()`, `fs.opendirSync()`, or `fsPromises.opendir()`. ##### `dir.read()`# Added in: v12.12.0 * Returns: Fulfills with a | Asynchronously read the next directory entry via `readdir(3)` as an . A promise is returned that will be fulfilled with an , or `null` if there are no more directory entries to read. Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. ##### `dir.read(callback)`# Added in: v12.12.0 * `callback` * `err` * `dirent` | Asynchronously read the next directory entry via `readdir(3)` as an . After the read is completed, the `callback` will be called with an , or `null` if there are no more directory entries to read. Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. ##### `dir.readSync()`# Added in: v12.12.0 * Returns: | Synchronously read the next directory entry as an . See the POSIX `readdir(3)` documentation for more detail. If there are no more directory entries to read, `null` will be returned. Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. ##### `dir[Symbol.asyncIterator]()`# Added in: v12.12.0 * Returns: An AsyncIterator of Asynchronously iterates over the directory until all entries have been read. Refer to the POSIX `readdir(3)` documentation for more detail. Entries returned by the async iterator are always an . The `null` case from `dir.read()` is handled internally. See for an example. Directory entries returned by this iterator are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. ##### `dir[Symbol.asyncDispose]()`# History VersionChanges v24.2.0 No longer experimental. v24.1.0 Added in: v24.1.0 Calls `dir.close()` if the directory handle is open, and returns a promise that fulfills when disposal is complete. ##### `dir[Symbol.dispose]()`# History VersionChanges v24.2.0 No longer experimental. v24.1.0 Added in: v24.1.0 Calls `dir.closeSync()` if the directory handle is open, and returns `undefined`. #### Class: `fs.Dirent`# Added in: v10.10.0 A representation of a directory entry, which can be a file or a subdirectory within the directory, as returned by reading from an . The directory entry is a combination of the file name and file type pairs. Additionally, when `fs.readdir()` or `fs.readdirSync()` is called with the `withFileTypes` option set to `true`, the resulting array is filled with objects, rather than strings or s. ##### `dirent.isBlockDevice()`# Added in: v10.10.0 * Returns: Returns `true` if the object describes a block device. ##### `dirent.isCharacterDevice()`# Added in: v10.10.0 * Returns: Returns `true` if the object describes a character device. ##### `dirent.isDirectory()`# Added in: v10.10.0 * Returns: Returns `true` if the object describes a file system directory. ##### `dirent.isFIFO()`# Added in: v10.10.0 * Returns: Returns `true` if the object describes a first-in-first-out (FIFO) pipe. ##### `dirent.isFile()`# Added in: v10.10.0 * Returns: Returns `true` if the object describes a regular file. ##### `dirent.isSocket()`# Added in: v10.10.0 * Returns: Returns `true` if the object describes a socket. ##### `dirent.isSymbolicLink()`# Added in: v10.10.0 * Returns: Returns `true` if the object describes a symbolic link. ##### `dirent.name`# Added in: v10.10.0 * Type: | The file name that this object refers to. The type of this value is determined by the `options.encoding` passed to `fs.readdir()` or `fs.readdirSync()`. ##### `dirent.parentPath`# History VersionChanges v24.0.0 Marking the API stable. v21.4.0, v20.12.0, v18.20.0 Added in: v21.4.0, v20.12.0, v18.20.0 * Type: The path to the parent directory of the file this object refers to. #### Class: `fs.FSWatcher`# Added in: v0.5.8 * Extends A successful call to `fs.watch()` method will return a new object. All objects emit a `'change'` event whenever a specific watched file is modified. ##### Event: `'change'`# Added in: v0.5.8 * `eventType` The type of change event that has occurred * `filename` | The filename that changed (if relevant/available) Emitted when something changes in a watched directory or file. See more details in `fs.watch()`. The `filename` argument may not be provided depending on operating system support. If `filename` is provided, it will be provided as a if `fs.watch()` is called with its `encoding` option set to `'buffer'`, otherwise `filename` will be a UTF-8 string. import { watch } from 'node:fs'; // Example when handled through fs.watch() listener watch('./tmp', { encoding: 'buffer' }, (eventType, filename) => { if (filename) { console.log(filename); // Prints: } }); ##### Event: `'close'`# Added in: v10.0.0 Emitted when the watcher stops watching for changes. The closed object is no longer usable in the event handler. ##### Event: `'error'`# Added in: v0.5.8 * `error` Emitted when an error occurs while watching the file. The errored object is no longer usable in the event handler. ##### `watcher.close()`# Added in: v0.5.8 Stop watching for changes on the given . Once stopped, the object is no longer usable. ##### `watcher.ref()`# Added in: v14.3.0, v12.20.0 * Returns: When called, requests that the Node.js event loop not exit so long as the is active. Calling `watcher.ref()` multiple times will have no effect. By default, all objects are "ref'ed", making it normally unnecessary to call `watcher.ref()` unless `watcher.unref()` had been called previously. ##### `watcher.unref()`# Added in: v14.3.0, v12.20.0 * Returns: When called, the active object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the object's callback is invoked. Calling `watcher.unref()` multiple times will have no effect. #### Class: `fs.StatWatcher`# Added in: v14.3.0, v12.20.0 * Extends A successful call to `fs.watchFile()` method will return a new object. ##### `watcher.ref()`# Added in: v14.3.0, v12.20.0 * Returns: When called, requests that the Node.js event loop not exit so long as the is active. Calling `watcher.ref()` multiple times will have no effect. By default, all objects are "ref'ed", making it normally unnecessary to call `watcher.ref()` unless `watcher.unref()` had been called previously. ##### `watcher.unref()`# Added in: v14.3.0, v12.20.0 * Returns: When called, the active object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the object's callback is invoked. Calling `watcher.unref()` multiple times will have no effect. #### Class: `fs.ReadStream`# Added in: v0.1.93 * Extends: Instances of are created and returned using the `fs.createReadStream()` function. ##### Event: `'close'`# Added in: v0.1.93 Emitted when the 's underlying file descriptor has been closed. ##### Event: `'open'`# Added in: v0.1.93 * `fd` Integer file descriptor used by the . Emitted when the 's file descriptor has been opened. ##### Event: `'ready'`# Added in: v9.11.0 Emitted when the is ready to be used. Fires immediately after `'open'`. ##### `readStream.bytesRead`# Added in: v6.4.0 * Type: The number of bytes that have been read so far. ##### `readStream.path`# Added in: v0.1.93 * Type: | The path to the file the stream is reading from as specified in the first argument to `fs.createReadStream()`. If `path` is passed as a string, then `readStream.path` will be a string. If `path` is passed as a , then `readStream.path` will be a . If `fd` is specified, then `readStream.path` will be `undefined`. ##### `readStream.pending`# Added in: v11.2.0, v10.16.0 * Type: This property is `true` if the underlying file has not been opened yet, i.e. before the `'ready'` event is emitted. #### Class: `fs.Stats`# History VersionChanges v22.0.0, v20.13.0 Public constructor is deprecated. v8.1.0 Added times as numbers. v0.1.21 Added in: v0.1.21 A object provides information about a file. Objects returned from `fs.stat()`, `fs.lstat()`, `fs.fstat()`, and their synchronous counterparts are of this type. If `bigint` in the `options` passed to those methods is true, the numeric values will be `bigint` instead of `number`, and the object will contain additional nanosecond-precision properties suffixed with `Ns`. `Stat` objects are not to be created directly using the `new` keyword. Stats { dev: 2114, ino: 48064969, mode: 33188, nlink: 1, uid: 85, gid: 100, rdev: 0, size: 527, blksize: 4096, blocks: 8, atimeMs: 1318289051000.1, mtimeMs: 1318289051000.1, ctimeMs: 1318289051000.1, birthtimeMs: 1318289051000.1, atime: Mon, 10 Oct 2011 23:24:11 GMT, mtime: Mon, 10 Oct 2011 23:24:11 GMT, ctime: Mon, 10 Oct 2011 23:24:11 GMT, birthtime: Mon, 10 Oct 2011 23:24:11 GMT } `bigint` version: BigIntStats { dev: 2114n, ino: 48064969n, mode: 33188n, nlink: 1n, uid: 85n, gid: 100n, rdev: 0n, size: 527n, blksize: 4096n, blocks: 8n, atimeMs: 1318289051000n, mtimeMs: 1318289051000n, ctimeMs: 1318289051000n, birthtimeMs: 1318289051000n, atimeNs: 1318289051000000000n, mtimeNs: 1318289051000000000n, ctimeNs: 1318289051000000000n, birthtimeNs: 1318289051000000000n, atime: Mon, 10 Oct 2011 23:24:11 GMT, mtime: Mon, 10 Oct 2011 23:24:11 GMT, ctime: Mon, 10 Oct 2011 23:24:11 GMT, birthtime: Mon, 10 Oct 2011 23:24:11 GMT } ##### `stats.isBlockDevice()`# Added in: v0.1.10 * Returns: Returns `true` if the object describes a block device. ##### `stats.isCharacterDevice()`# Added in: v0.1.10 * Returns: Returns `true` if the object describes a character device. ##### `stats.isDirectory()`# Added in: v0.1.10 * Returns: Returns `true` if the object describes a file system directory. If the object was obtained from calling `fs.lstat()` on a symbolic link which resolves to a directory, this method will return `false`. This is because `fs.lstat()` returns information about a symbolic link itself and not the path it resolves to. ##### `stats.isFIFO()`# Added in: v0.1.10 * Returns: Returns `true` if the object describes a first-in-first-out (FIFO) pipe. ##### `stats.isFile()`# Added in: v0.1.10 * Returns: Returns `true` if the object describes a regular file. ##### `stats.isSocket()`# Added in: v0.1.10 * Returns: Returns `true` if the object describes a socket. ##### `stats.isSymbolicLink()`# Added in: v0.1.10 * Returns: Returns `true` if the object describes a symbolic link. This method is only valid when using `fs.lstat()`. ##### `stats.dev`# * Type: | The numeric identifier of the device containing the file. ##### `stats.ino`# * Type: | The file system specific "Inode" number for the file. ##### `stats.mode`# * Type: | A bit-field describing the file type and mode. ##### `stats.nlink`# * Type: | The number of hard-links that exist for the file. ##### `stats.uid`# * Type: | The numeric user identifier of the user that owns the file (POSIX). ##### `stats.gid`# * Type: | The numeric group identifier of the group that owns the file (POSIX). ##### `stats.rdev`# * Type: | A numeric device identifier if the file represents a device. ##### `stats.size`# * Type: | The size of the file in bytes. If the underlying file system does not support getting the size of the file, this will be `0`. ##### `stats.blksize`# * Type: | The file system block size for i/o operations. ##### `stats.blocks`# * Type: | The number of blocks allocated for this file. ##### `stats.atimeMs`# Added in: v8.1.0 * Type: | The timestamp indicating the last time this file was accessed expressed in milliseconds since the POSIX Epoch. ##### `stats.mtimeMs`# Added in: v8.1.0 * Type: | The timestamp indicating the last time this file was modified expressed in milliseconds since the POSIX Epoch. ##### `stats.ctimeMs`# Added in: v8.1.0 * Type: | The timestamp indicating the last time the file status was changed expressed in milliseconds since the POSIX Epoch. ##### `stats.birthtimeMs`# Added in: v8.1.0 * Type: | The timestamp indicating the creation time of this file expressed in milliseconds since the POSIX Epoch. ##### `stats.atimeNs`# Added in: v12.10.0 * Type: Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time this file was accessed expressed in nanoseconds since the POSIX Epoch. ##### `stats.mtimeNs`# Added in: v12.10.0 * Type: Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time this file was modified expressed in nanoseconds since the POSIX Epoch. ##### `stats.ctimeNs`# Added in: v12.10.0 * Type: Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time the file status was changed expressed in nanoseconds since the POSIX Epoch. ##### `stats.birthtimeNs`# Added in: v12.10.0 * Type: Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the creation time of this file expressed in nanoseconds since the POSIX Epoch. ##### `stats.atime`# Added in: v0.11.13 * Type: The timestamp indicating the last time this file was accessed. ##### `stats.mtime`# Added in: v0.11.13 * Type: The timestamp indicating the last time this file was modified. ##### `stats.ctime`# Added in: v0.11.13 * Type: The timestamp indicating the last time the file status was changed. ##### `stats.birthtime`# Added in: v0.11.13 * Type: The timestamp indicating the creation time of this file. ##### Stat time values# The `atimeMs`, `mtimeMs`, `ctimeMs`, `birthtimeMs` properties are numeric values that hold the corresponding times in milliseconds. Their precision is platform specific. When `bigint: true` is passed into the method that generates the object, the properties will be bigints, otherwise they will be numbers. The `atimeNs`, `mtimeNs`, `ctimeNs`, `birthtimeNs` properties are bigints that hold the corresponding times in nanoseconds. They are only present when `bigint: true` is passed into the method that generates the object. Their precision is platform specific. `atime`, `mtime`, `ctime`, and `birthtime` are `Date` object alternate representations of the various times. The `Date` and number values are not connected. Assigning a new number value, or mutating the `Date` value, will not be reflected in the corresponding alternate representation. The times in the stat object have the following semantics: * `atime` "Access Time": Time when file data last accessed. Changed by the `mknod(2)`, `utimes(2)`, and `read(2)` system calls. * `mtime` "Modified Time": Time when file data last modified. Changed by the `mknod(2)`, `utimes(2)`, and `write(2)` system calls. * `ctime` "Change Time": Time when file status was last changed (inode data modification). Changed by the `chmod(2)`, `chown(2)`, `link(2)`, `mknod(2)`, `rename(2)`, `unlink(2)`, `utimes(2)`, `read(2)`, and `write(2)` system calls. * `birthtime` "Birth Time": Time of file creation. Set once when the file is created. On file systems where birthtime is not available, this field may instead hold either the `ctime` or `1970-01-01T00:00Z` (ie, Unix epoch timestamp `0`). This value may be greater than `atime` or `mtime` in this case. On Darwin and other FreeBSD variants, also set if the `atime` is explicitly set to an earlier value than the current `birthtime` using the `utimes(2)` system call. Prior to Node.js 0.12, the `ctime` held the `birthtime` on Windows systems. As of 0.12, `ctime` is not "creation time", and on Unix systems, it never was. #### Class: `fs.StatFs`# Added in: v19.6.0, v18.15.0 Provides information about a mounted file system. Objects returned from `fs.statfs()` and its synchronous counterpart are of this type. If `bigint` in the `options` passed to those methods is `true`, the numeric values will be `bigint` instead of `number`. StatFs { type: 1397114950, bsize: 4096, blocks: 121938943, bfree: 61058895, bavail: 61058895, files: 999, ffree: 1000000 } `bigint` version: StatFs { type: 1397114950n, bsize: 4096n, blocks: 121938943n, bfree: 61058895n, bavail: 61058895n, files: 999n, ffree: 1000000n } ##### `statfs.bavail`# Added in: v19.6.0, v18.15.0 * Type: | Free blocks available to unprivileged users. ##### `statfs.bfree`# Added in: v19.6.0, v18.15.0 * Type: | Free blocks in file system. ##### `statfs.blocks`# Added in: v19.6.0, v18.15.0 * Type: | Total data blocks in file system. ##### `statfs.bsize`# Added in: v19.6.0, v18.15.0 * Type: | Optimal transfer block size. ##### `statfs.ffree`# Added in: v19.6.0, v18.15.0 * Type: | Free file nodes in file system. ##### `statfs.files`# Added in: v19.6.0, v18.15.0 * Type: | Total file nodes in file system. ##### `statfs.type`# Added in: v19.6.0, v18.15.0 * Type: | Type of file system. #### Class: `fs.Utf8Stream`# Added in: v24.6.0 Stability: 1 \- Experimental An optimized UTF-8 stream writer that allows for flushing all the internal buffering on demand. It handles `EAGAIN` errors correctly, allowing for customization, for example, by dropping content if the disk is busy. ##### Event: `'close'`# The `'close'` event is emitted when the stream is fully closed. ##### Event: `'drain'`# The `'drain'` event is emitted when the internal buffer has drained sufficiently to allow continued writing. ##### Event: `'drop'`# The `'drop'` event is emitted when to maximal length is reached and that data will not be written. The data that was dropped is passed as the first argument to the event handle. ##### Event: `'error'`# The `'error'` event is emitted when an error occurs. ##### Event: `'finish'`# The `'finish'` event is emitted when the stream has been ended and all data has been flushed to the underlying file. ##### Event: `'ready'`# The `'ready'` event is emitted when the stream is ready to accept writes. ##### Event: `'write'`# The `'write'` event is emitted when a write operation has completed. The number of bytes written is passed as the first argument to the event handler. ##### `new fs.Utf8Stream([options])`# * `options` * `append`: Appends writes to dest file instead of truncating it. Default: `true`. * `contentMode`: Which type of data you can send to the write function, supported values are `'utf8'` or `'buffer'`. Default: `'utf8'`. * `dest`: A path to a file to be written to (mode controlled by the append option). * `fd`: A file descriptor, something that is returned by `fs.open()` or `fs.openSync()`. * `fs`: An object that has the same API as the `fs` module, useful for mocking, testing, or customizing the behavior of the stream. * `fsync`: Perform a `fs.fsyncSync()` every time a write is completed. * `maxLength`: The maximum length of the internal buffer. If a write operation would cause the buffer to exceed `maxLength`, the data written is dropped and a drop event is emitted with the dropped data * `maxWrite`: The maximum number of bytes that can be written; Default: `16384` * `minLength`: The minimum length of the internal buffer that is required to be full before flushing. * `mkdir`: Ensure directory for `dest` file exists when true. Default: `false`. * `mode`: | Specify the creating file mode (see `fs.open()`). * `periodicFlush`: Calls flush every `periodicFlush` milliseconds. * `retryEAGAIN` A function that will be called when `write()`, `writeSync()`, or `flushSync()` encounters an `EAGAIN` or `EBUSY` error. If the return value is `true` the operation will be retried, otherwise it will bubble the error. The `err` is the error that caused this function to be called, `writeBufferLen` is the length of the buffer that was written, and `remainingBufferLen` is the length of the remaining buffer that the stream did not try to write. * `err` An error or `null`. * `writeBufferLen` * `remainingBufferLen`: * `sync`: Perform writes synchronously. ##### `utf8Stream.append`# * Whether the stream is appending to the file or truncating it. ##### `utf8Stream.contentMode`# * The type of data that can be written to the stream. Supported values are `'utf8'` or `'buffer'`. Default: `'utf8'`. ##### `utf8Stream.destroy()`# Close the stream immediately, without flushing the internal buffer. ##### `utf8Stream.end()`# Close the stream gracefully, flushing the internal buffer before closing. ##### `utf8Stream.fd`# * The file descriptor that is being written to. ##### `utf8Stream.file`# * The file that is being written to. ##### `utf8Stream.flush(callback)`# * `callback` * `err` | An error if the flush failed, otherwise `null`. Writes the current buffer to the file if a write was not in progress. Do nothing if `minLength` is zero or if it is already writing. ##### `utf8Stream.flushSync()`# Flushes the buffered data synchronously. This is a costly operation. ##### `utf8Stream.fsync`# * Whether the stream is performing a `fs.fsyncSync()` after every write operation. ##### `utf8Stream.maxLength`# * The maximum length of the internal buffer. If a write operation would cause the buffer to exceed `maxLength`, the data written is dropped and a drop event is emitted with the dropped data. ##### `utf8Stream.minLength`# * The minimum length of the internal buffer that is required to be full before flushing. ##### `utf8Stream.mkdir`# * Whether the stream should ensure that the directory for the `dest` file exists. If `true`, it will create the directory if it does not exist. Default: `false`. ##### `utf8Stream.mode`# * | The mode of the file that is being written to. ##### `utf8Stream.periodicFlush`# * The number of milliseconds between flushes. If set to `0`, no periodic flushes will be performed. ##### `utf8Stream.reopen(file)`# * `file`: | | A path to a file to be written to (mode controlled by the append option). Reopen the file in place, useful for log rotation. ##### `utf8Stream.sync`# * Whether the stream is writing synchronously or asynchronously. ##### `utf8Stream.write(data)`# * `data` | The data to write. * Returns When the `options.contentMode` is set to `'utf8'` when the stream is created, the `data` argument must be a string. If the `contentMode` is set to `'buffer'`, the `data` argument must be a . ##### `utf8Stream.writing`# * Whether the stream is currently writing data to the file. ##### `utf8Stream[Symbol.dispose]()`# Calls `utf8Stream.destroy()`. #### Class: `fs.WriteStream`# Added in: v0.1.93 * Extends Instances of are created and returned using the `fs.createWriteStream()` function. ##### Event: `'close'`# Added in: v0.1.93 Emitted when the 's underlying file descriptor has been closed. ##### Event: `'open'`# Added in: v0.1.93 * `fd` Integer file descriptor used by the . Emitted when the 's file is opened. ##### Event: `'ready'`# Added in: v9.11.0 Emitted when the is ready to be used. Fires immediately after `'open'`. ##### `writeStream.bytesWritten`# Added in: v0.4.7 The number of bytes written so far. Does not include data that is still queued for writing. ##### `writeStream.close([callback])`# Added in: v0.9.4 * `callback` * `err` Closes `writeStream`. Optionally accepts a callback that will be executed once the `writeStream` is closed. ##### `writeStream.path`# Added in: v0.1.93 The path to the file the stream is writing to as specified in the first argument to `fs.createWriteStream()`. If `path` is passed as a string, then `writeStream.path` will be a string. If `path` is passed as a , then `writeStream.path` will be a . ##### `writeStream.pending`# Added in: v11.2.0 * Type: This property is `true` if the underlying file has not been opened yet, i.e. before the `'ready'` event is emitted. #### `fs.constants`# * Type: Returns an object containing commonly used constants for file system operations. ##### FS constants# The following constants are exported by `fs.constants` and `fsPromises.constants`. Not every constant will be available on every operating system; this is especially important for Windows, where many of the POSIX specific definitions are not available. For portable applications it is recommended to check for their presence before use. To use more than one constant, use the bitwise OR `|` operator. Example: import { open, constants } from 'node:fs'; const { O_RDWR, O_CREAT, O_EXCL, } = constants; open('/path/to/my/file', O_RDWR | O_CREAT | O_EXCL, (err, fd) => { // ... }); ###### File access constants# The following constants are meant for use as the `mode` parameter passed to `fsPromises.access()`, `fs.access()`, and `fs.accessSync()`. Constant Description `F_OK` Flag indicating that the file is visible to the calling process. This is useful for determining if a file exists, but says nothing about `rwx` permissions. Default if no mode is specified. `R_OK` Flag indicating that the file can be read by the calling process. `W_OK` Flag indicating that the file can be written by the calling process. `X_OK` Flag indicating that the file can be executed by the calling process. This has no effect on Windows (will behave like `fs.constants.F_OK`). The definitions are also available on Windows. ###### File copy constants# The following constants are meant for use with `fs.copyFile()`. Constant Description `COPYFILE_EXCL` If present, the copy operation will fail with an error if the destination path already exists. `COPYFILE_FICLONE` If present, the copy operation will attempt to create a copy-on-write reflink. If the underlying platform does not support copy-on-write, then a fallback copy mechanism is used. `COPYFILE_FICLONE_FORCE` If present, the copy operation will attempt to create a copy-on-write reflink. If the underlying platform does not support copy-on-write, then the operation will fail with an error. The definitions are also available on Windows. ###### File open constants# The following constants are meant for use with `fs.open()`. Constant Description `O_RDONLY` Flag indicating to open a file for read-only access. `O_WRONLY` Flag indicating to open a file for write-only access. `O_RDWR` Flag indicating to open a file for read-write access. `O_CREAT` Flag indicating to create the file if it does not already exist. `O_EXCL` Flag indicating that opening a file should fail if the `O_CREAT` flag is set and the file already exists. `O_NOCTTY` Flag indicating that if path identifies a terminal device, opening the path shall not cause that terminal to become the controlling terminal for the process (if the process does not already have one). `O_TRUNC` Flag indicating that if the file exists and is a regular file, and the file is opened successfully for write access, its length shall be truncated to zero. `O_APPEND` Flag indicating that data will be appended to the end of the file. `O_DIRECTORY` Flag indicating that the open should fail if the path is not a directory. `O_NOATIME` Flag indicating reading accesses to the file system will no longer result in an update to the `atime` information associated with the file. This flag is available on Linux operating systems only. `O_NOFOLLOW` Flag indicating that the open should fail if the path is a symbolic link. `O_SYNC` Flag indicating that the file is opened for synchronized I/O with write operations waiting for file integrity. `O_DSYNC` Flag indicating that the file is opened for synchronized I/O with write operations waiting for data integrity. `O_SYMLINK` Flag indicating to open the symbolic link itself rather than the resource it is pointing to. `O_DIRECT` When set, an attempt will be made to minimize caching effects of file I/O. `O_NONBLOCK` Flag indicating to open the file in nonblocking mode when possible. `UV_FS_O_FILEMAP` When set, a memory file mapping is used to access the file. This flag is available on Windows operating systems only. On other operating systems, this flag is ignored. On Windows, only `O_APPEND`, `O_CREAT`, `O_EXCL`, `O_RDONLY`, `O_RDWR`, `O_TRUNC`, `O_WRONLY`, and `UV_FS_O_FILEMAP` are available. ###### File type constants# The following constants are meant for use with the object's `mode` property for determining a file's type. Constant Description `S_IFMT` Bit mask used to extract the file type code. `S_IFREG` File type constant for a regular file. `S_IFDIR` File type constant for a directory. `S_IFCHR` File type constant for a character-oriented device file. `S_IFBLK` File type constant for a block-oriented device file. `S_IFIFO` File type constant for a FIFO/pipe. `S_IFLNK` File type constant for a symbolic link. `S_IFSOCK` File type constant for a socket. On Windows, only `S_IFCHR`, `S_IFDIR`, `S_IFLNK`, `S_IFMT`, and `S_IFREG`, are available. ###### File mode constants# The following constants are meant for use with the object's `mode` property for determining the access permissions for a file. Constant Description `S_IRWXU` File mode indicating readable, writable, and executable by owner. `S_IRUSR` File mode indicating readable by owner. `S_IWUSR` File mode indicating writable by owner. `S_IXUSR` File mode indicating executable by owner. `S_IRWXG` File mode indicating readable, writable, and executable by group. `S_IRGRP` File mode indicating readable by group. `S_IWGRP` File mode indicating writable by group. `S_IXGRP` File mode indicating executable by group. `S_IRWXO` File mode indicating readable, writable, and executable by others. `S_IROTH` File mode indicating readable by others. `S_IWOTH` File mode indicating writable by others. `S_IXOTH` File mode indicating executable by others. On Windows, only `S_IRUSR` and `S_IWUSR` are available. ### Notes# #### Ordering of callback and promise-based operations# Because they are executed asynchronously by the underlying thread pool, there is no guaranteed ordering when using either the callback or promise-based methods. For example, the following is prone to error because the `fs.stat()` operation might complete before the `fs.rename()` operation: const fs = require('node:fs'); fs.rename('/tmp/hello', '/tmp/world', (err) => { if (err) throw err; console.log('renamed complete'); }); fs.stat('/tmp/world', (err, stats) => { if (err) throw err; console.log(`stats: ${JSON.stringify(stats)}`); }); It is important to correctly order the operations by awaiting the results of one before invoking the other: import { rename, stat } from 'node:fs/promises'; const oldPath = '/tmp/hello'; const newPath = '/tmp/world'; try { await rename(oldPath, newPath); const stats = await stat(newPath); console.log(`stats: ${JSON.stringify(stats)}`); } catch (error) { console.error('there was an error:', error.message); } Or, when using the callback APIs, move the `fs.stat()` call into the callback of the `fs.rename()` operation: import { rename, stat } from 'node:fs'; rename('/tmp/hello', '/tmp/world', (err) => { if (err) throw err; stat('/tmp/world', (err, stats) => { if (err) throw err; console.log(`stats: ${JSON.stringify(stats)}`); }); }); #### File paths# Most `fs` operations accept file paths that may be specified in the form of a string, a , or a object using the `file:` protocol. ##### String paths# String paths are interpreted as UTF-8 character sequences identifying the absolute or relative filename. Relative paths will be resolved relative to the current working directory as determined by calling `process.cwd()`. Example using an absolute path on POSIX: import { open } from 'node:fs/promises'; let fd; try { fd = await open('/open/some/file.txt', 'r'); // Do something with the file } finally { await fd?.close(); } Example using a relative path on POSIX (relative to `process.cwd()`): import { open } from 'node:fs/promises'; let fd; try { fd = await open('file.txt', 'r'); // Do something with the file } finally { await fd?.close(); } ##### File URL paths# Added in: v7.6.0 For most `node:fs` module functions, the `path` or `filename` argument may be passed as a object using the `file:` protocol. import { readFileSync } from 'node:fs'; readFileSync(new URL('file:///tmp/hello')); `file:` URLs are always absolute paths. ###### Platform-specific considerations# On Windows, `file:` s with a host name convert to UNC paths, while `file:` s with drive letters convert to local absolute paths. `file:` s with no host name and no drive letter will result in an error: import { readFileSync } from 'node:fs'; // On Windows : // - WHATWG file URLs with hostname convert to UNC path // file://hostname/p/a/t/h/file => \\hostname\p\a\t\h\file readFileSync(new URL('file://hostname/p/a/t/h/file')); // - WHATWG file URLs with drive letters convert to absolute path // file:///C:/tmp/hello => C:\tmp\hello readFileSync(new URL('file:///C:/tmp/hello')); // - WHATWG file URLs without hostname must have a drive letters readFileSync(new URL('file:///notdriveletter/p/a/t/h/file')); readFileSync(new URL('file:///c/p/a/t/h/file')); // TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must be absolute `file:` s with drive letters must use `:` as a separator just after the drive letter. Using another separator will result in an error. On all other platforms, `file:` s with a host name are unsupported and will result in an error: import { readFileSync } from 'node:fs'; // On other platforms: // - WHATWG file URLs with hostname are unsupported // file://hostname/p/a/t/h/file => throw! readFileSync(new URL('file://hostname/p/a/t/h/file')); // TypeError [ERR_INVALID_FILE_URL_PATH]: must be absolute // - WHATWG file URLs convert to absolute path // file:///tmp/hello => /tmp/hello readFileSync(new URL('file:///tmp/hello')); A `file:` having encoded slash characters will result in an error on all platforms: import { readFileSync } from 'node:fs'; // On Windows readFileSync(new URL('file:///C:/p/a/t/h/%2F')); readFileSync(new URL('file:///C:/p/a/t/h/%2f')); /* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded \ or / characters */ // On POSIX readFileSync(new URL('file:///p/a/t/h/%2F')); readFileSync(new URL('file:///p/a/t/h/%2f')); /* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded / characters */ On Windows, `file:` s having encoded backslash will result in an error: import { readFileSync } from 'node:fs'; // On Windows readFileSync(new URL('file:///C:/path/%5C')); readFileSync(new URL('file:///C:/path/%5c')); /* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded \ or / characters */ ##### Buffer paths# Paths specified using a are useful primarily on certain POSIX operating systems that treat file paths as opaque byte sequences. On such systems, it is possible for a single file path to contain sub-sequences that use multiple character encodings. As with string paths, paths may be relative or absolute: Example using an absolute path on POSIX: import { open } from 'node:fs/promises'; import { Buffer } from 'node:buffer'; let fd; try { fd = await open(Buffer.from('/open/some/file.txt'), 'r'); // Do something with the file } finally { await fd?.close(); } ##### Per-drive working directories on Windows# On Windows, Node.js follows the concept of per-drive working directory. This behavior can be observed when using a drive path without a backslash. For example `fs.readdirSync('C:\\')` can potentially return a different result than `fs.readdirSync('C:')`. For more information, see this MSDN page. #### File descriptors# On POSIX systems, for every process, the kernel maintains a table of currently open files and resources. Each open file is assigned a simple numeric identifier called a file descriptor. At the system-level, all file system operations use these file descriptors to identify and track each specific file. Windows systems use a different but conceptually similar mechanism for tracking resources. To simplify things for users, Node.js abstracts away the differences between operating systems and assigns all open files a numeric file descriptor. The callback-based `fs.open()`, and synchronous `fs.openSync()` methods open a file and allocate a new file descriptor. Once allocated, the file descriptor may be used to read data from, write data to, or request information about the file. Operating systems limit the number of file descriptors that may be open at any given time so it is critical to close the descriptor when operations are completed. Failure to do so will result in a memory leak that will eventually cause an application to crash. import { open, close, fstat } from 'node:fs'; function closeFd(fd) { close(fd, (err) => { if (err) throw err; }); } open('/open/some/file.txt', 'r', (err, fd) => { if (err) throw err; try { fstat(fd, (err, stat) => { if (err) { closeFd(fd); throw err; } // use stat closeFd(fd); }); } catch (err) { closeFd(fd); throw err; } }); The promise-based APIs use a object in place of the numeric file descriptor. These objects are better managed by the system to ensure that resources are not leaked. However, it is still required that they are closed when operations are completed: import { open } from 'node:fs/promises'; let file; try { file = await open('/open/some/file.txt', 'r'); const stat = await file.stat(); // use stat } finally { await file.close(); } #### Threadpool usage# All callback and promise-based file system APIs (with the exception of `fs.FSWatcher()`) use libuv's threadpool. This can have surprising and negative performance implications for some applications. See the `UV_THREADPOOL_SIZE` documentation for more information. #### File system flags# The following flags are available wherever the `flag` option takes a string. * `'a'`: Open file for appending. The file is created if it does not exist. * `'ax'`: Like `'a'` but fails if the path exists. * `'a+'`: Open file for reading and appending. The file is created if it does not exist. * `'ax+'`: Like `'a+'` but fails if the path exists. * `'as'`: Open file for appending in synchronous mode. The file is created if it does not exist. * `'as+'`: Open file for reading and appending in synchronous mode. The file is created if it does not exist. * `'r'`: Open file for reading. An exception occurs if the file does not exist. * `'rs'`: Open file for reading in synchronous mode. An exception occurs if the file does not exist. * `'r+'`: Open file for reading and writing. An exception occurs if the file does not exist. * `'rs+'`: Open file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache. This is primarily useful for opening files on NFS mounts as it allows skipping the potentially stale local cache. It has a very real impact on I/O performance so using this flag is not recommended unless it is needed. This doesn't turn `fs.open()` or `fsPromises.open()` into a synchronous blocking call. If synchronous operation is desired, something like `fs.openSync()` should be used. * `'w'`: Open file for writing. The file is created (if it does not exist) or truncated (if it exists). * `'wx'`: Like `'w'` but fails if the path exists. * `'w+'`: Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists). * `'wx+'`: Like `'w+'` but fails if the path exists. `flag` can also be a number as documented by `open(2)`; commonly used constants are available from `fs.constants`. On Windows, flags are translated to their equivalent ones where applicable, e.g. `O_WRONLY` to `FILE_GENERIC_WRITE`, or `O_EXCL|O_CREAT` to `CREATE_NEW`, as accepted by `CreateFileW`. The exclusive flag `'x'` (`O_EXCL` flag in `open(2)`) causes the operation to return an error if the path already exists. On POSIX, if the path is a symbolic link, using `O_EXCL` returns an error even if the link is to a path that does not exist. The exclusive flag might not work with network file systems. On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file. Modifying a file rather than replacing it may require the `flag` option to be set to `'r+'` rather than the default `'w'`. The behavior of some flags are platform-specific. As such, opening a directory on macOS and Linux with the `'a+'` flag, as in the example below, will return an error. In contrast, on Windows and FreeBSD, a file descriptor or a `FileHandle` will be returned. // macOS and Linux fs.open('', 'a+', (err, fd) => { // => [Error: EISDIR: illegal operation on a directory, open ] }); // Windows and FreeBSD fs.open('', 'a+', (err, fd) => { // => null, }); On Windows, opening an existing hidden file using the `'w'` flag (either through `fs.open()`, `fs.writeFile()`, or `fsPromises.open()`) will fail with `EPERM`. Existing hidden files can be opened for writing with the `'r+'` flag. A call to `fs.ftruncate()` or `filehandle.truncate()` can be used to reset the file contents. ## Global objects# Stability: 2 \- Stable These objects are available in all modules. The following variables may appear to be global but are not. They exist only in the scope of CommonJS modules: * `__dirname` * `__filename` * `exports` * `module` * `require()` The objects listed here are specific to Node.js. There are built-in objects that are part of the JavaScript language itself, which are also globally accessible. ### Class: `AbortController`# History VersionChanges v15.4.0 No longer experimental. v15.0.0, v14.17.0 Added in: v15.0.0, v14.17.0 A utility class used to signal cancelation in selected `Promise`-based APIs. The API is based on the Web API . const ac = new AbortController(); ac.signal.addEventListener('abort', () => console.log('Aborted!'), { once: true }); ac.abort(); console.log(ac.signal.aborted); // Prints true #### `abortController.abort([reason])`# History VersionChanges v17.2.0, v16.14.0 Added the new optional reason argument. v15.0.0, v14.17.0 Added in: v15.0.0, v14.17.0 * `reason` An optional reason, retrievable on the `AbortSignal`'s `reason` property. Triggers the abort signal, causing the `abortController.signal` to emit the `'abort'` event. #### `abortController.signal`# Added in: v15.0.0, v14.17.0 * Type: #### Class: `AbortSignal`# Added in: v15.0.0, v14.17.0 * Extends: The `AbortSignal` is used to notify observers when the `abortController.abort()` method is called. ##### Static method: `AbortSignal.abort([reason])`# History VersionChanges v17.2.0, v16.14.0 Added the new optional reason argument. v15.12.0, v14.17.0 Added in: v15.12.0, v14.17.0 * `reason` * Returns: Returns a new already aborted `AbortSignal`. ##### Static method: `AbortSignal.timeout(delay)`# Added in: v17.3.0, v16.14.0 * `delay` The number of milliseconds to wait before triggering the AbortSignal. Returns a new `AbortSignal` which will be aborted in `delay` milliseconds. ##### Static method: `AbortSignal.any(signals)`# Added in: v20.3.0, v18.17.0 * `signals` The `AbortSignal`s of which to compose a new `AbortSignal`. Returns a new `AbortSignal` which will be aborted if any of the provided signals are aborted. Its `abortSignal.reason` will be set to whichever one of the `signals` caused it to be aborted. ##### Event: `'abort'`# Added in: v15.0.0, v14.17.0 The `'abort'` event is emitted when the `abortController.abort()` method is called. The callback is invoked with a single object argument with a single `type` property set to `'abort'`: const ac = new AbortController(); // Use either the onabort property... ac.signal.onabort = () => console.log('aborted!'); // Or the EventTarget API... ac.signal.addEventListener('abort', (event) => { console.log(event.type); // Prints 'abort' }, { once: true }); ac.abort(); The `AbortController` with which the `AbortSignal` is associated will only ever trigger the `'abort'` event once. We recommended that code check that the `abortSignal.aborted` attribute is `false` before adding an `'abort'` event listener. Any event listeners attached to the `AbortSignal` should use the `{ once: true }` option (or, if using the `EventEmitter` APIs to attach a listener, use the `once()` method) to ensure that the event listener is removed as soon as the `'abort'` event is handled. Failure to do so may result in memory leaks. ##### `abortSignal.aborted`# Added in: v15.0.0, v14.17.0 * Type: True after the `AbortController` has been aborted. ##### `abortSignal.onabort`# Added in: v15.0.0, v14.17.0 * Type: An optional callback function that may be set by user code to be notified when the `abortController.abort()` function has been called. ##### `abortSignal.reason`# Added in: v17.2.0, v16.14.0 * Type: An optional reason specified when the `AbortSignal` was triggered. const ac = new AbortController(); ac.abort(new Error('boom!')); console.log(ac.signal.reason); // Error: boom! ##### `abortSignal.throwIfAborted()`# Added in: v17.3.0, v16.17.0 If `abortSignal.aborted` is `true`, throws `abortSignal.reason`. ### Class: `Blob`# Added in: v18.0.0 See . ### Class: `Buffer`# Added in: v0.1.103 * Type: Used to handle binary data. See the buffer section. ### Class: `ByteLengthQueuingStrategy`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `ByteLengthQueuingStrategy`. ### `__dirname`# This variable may appear to be global but is not. See `__dirname`. ### `__filename`# This variable may appear to be global but is not. See `__filename`. ### `atob(data)`# Added in: v16.0.0 Stability: 3 \- Legacy. Use `Buffer.from(data, 'base64')` instead. Global alias for `buffer.atob()`. ### Class: `BroadcastChannel`# Added in: v18.0.0 See . ### `btoa(data)`# Added in: v16.0.0 Stability: 3 \- Legacy. Use `buf.toString('base64')` instead. Global alias for `buffer.btoa()`. ### `clearImmediate(immediateObject)`# Added in: v0.9.1 `clearImmediate` is described in the timers section. ### `clearInterval(intervalObject)`# Added in: v0.0.1 `clearInterval` is described in the timers section. ### `clearTimeout(timeoutObject)`# Added in: v0.0.1 `clearTimeout` is described in the timers section. ### Class: `CloseEvent`# Added in: v23.0.0 A browser-compatible implementation of . Disable this API with the `--no-experimental-websocket` CLI flag. ### Class: `CompressionStream`# History VersionChanges v24.7.0 format now accepts `brotli` value. v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `CompressionStream`. ### `console`# Added in: v0.1.100 * Type: Used to print to stdout and stderr. See the `console` section. ### Class: `CountQueuingStrategy`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `CountQueuingStrategy`. ### Class: `Crypto`# History VersionChanges v23.0.0 No longer experimental. v19.0.0 No longer behind `--experimental-global-webcrypto` CLI flag. v17.6.0, v16.15.0 Added in: v17.6.0, v16.15.0 A browser-compatible implementation of . This global is available only if the Node.js binary was compiled with including support for the `node:crypto` module. ### `crypto`# History VersionChanges v23.0.0 No longer experimental. v19.0.0 No longer behind `--experimental-global-webcrypto` CLI flag. v17.6.0, v16.15.0 Added in: v17.6.0, v16.15.0 A browser-compatible implementation of the Web Crypto API. ### Class: `CryptoKey`# History VersionChanges v23.0.0 No longer experimental. v19.0.0 No longer behind `--experimental-global-webcrypto` CLI flag. v17.6.0, v16.15.0 Added in: v17.6.0, v16.15.0 A browser-compatible implementation of . This global is available only if the Node.js binary was compiled with including support for the `node:crypto` module. ### Class: `CustomEvent`# History VersionChanges v23.0.0 No longer experimental. v22.1.0, v20.13.0 CustomEvent is now stable. v19.0.0 No longer behind `--experimental-global-customevent` CLI flag. v18.7.0, v16.17.0 Added in: v18.7.0, v16.17.0 A browser-compatible implementation of . ### Class: `DecompressionStream`# History VersionChanges v24.7.0 format now accepts `brotli` value. v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `DecompressionStream`. ### Class: `Event`# History VersionChanges v15.4.0 No longer experimental. v15.0.0 Added in: v15.0.0 A browser-compatible implementation of the `Event` class. See `EventTarget` and `Event` API for more details. ### Class: `EventSource`# Added in: v22.3.0, v20.18.0 Stability: 1 \- Experimental. Enable this API with the `--experimental-eventsource` CLI flag. A browser-compatible implementation of . ### Class: `EventTarget`# History VersionChanges v15.4.0 No longer experimental. v15.0.0 Added in: v15.0.0 A browser-compatible implementation of the `EventTarget` class. See `EventTarget` and `Event` API for more details. ### `exports`# This variable may appear to be global but is not. See `exports`. ### `fetch`# History VersionChanges v21.0.0 No longer experimental. v18.0.0 No longer behind `--experimental-fetch` CLI flag. v17.5.0, v16.15.0 Added in: v17.5.0, v16.15.0 A browser-compatible implementation of the `fetch()` function. const res = await fetch('https://nodejs.org/api/documentation.json'); if (res.ok) { const data = await res.json(); console.log(data); } The implementation is based upon undici, an HTTP/1.1 client written from scratch for Node.js. You can figure out which version of `undici` is bundled in your Node.js process reading the `process.versions.undici` property. #### Custom dispatcher# You can use a custom dispatcher to dispatch requests passing it in fetch's options object. The dispatcher must be compatible with `undici`'s `Dispatcher` class. fetch(url, { dispatcher: new MyAgent() }); It is possible to change the global dispatcher in Node.js by installing `undici` and using the `setGlobalDispatcher()` method. Calling this method will affect both `undici` and Node.js. import { setGlobalDispatcher } from 'undici'; setGlobalDispatcher(new MyAgent()); #### Related classes# The following globals are available to use with `fetch`: * `FormData` * `Headers` * `Request` * `Response`. ### Class: `File`# Added in: v20.0.0 See . ### Class: `FormData`# History VersionChanges v21.0.0 No longer experimental. v18.0.0 No longer behind `--experimental-fetch` CLI flag. v17.6.0, v16.15.0 Added in: v17.6.0, v16.15.0 A browser-compatible implementation of . ### `global`# Added in: v0.1.27 Stability: 3 \- Legacy. Use `globalThis` instead. * Type: The global namespace object. In browsers, the top-level scope has traditionally been the global scope. This means that `var something` will define a new global variable, except within ECMAScript modules. In Node.js, this is different. The top-level scope is not the global scope; `var something` inside a Node.js module will be local to that module, regardless of whether it is a CommonJS module or an ECMAScript module. ### Class: `Headers`# History VersionChanges v21.0.0 No longer experimental. v18.0.0 No longer behind `--experimental-fetch` CLI flag. v17.5.0, v16.15.0 Added in: v17.5.0, v16.15.0 A browser-compatible implementation of . ### `localStorage`# Added in: v22.4.0 Stability: 1.0 \- Early development. A browser-compatible implementation of `localStorage`. Data is stored unencrypted in the file specified by the `--localstorage-file` CLI flag. The maximum amount of data that can be stored is 10 MB. Any modification of this data outside of the Web Storage API is not supported. Enable this API with the `--experimental-webstorage` CLI flag. `localStorage` data is not stored per user or per request when used in the context of a server, it is shared across all users and requests. ### Class: `MessageChannel`# Added in: v15.0.0 The `MessageChannel` class. See `MessageChannel` for more details. ### Class: `MessageEvent`# Added in: v15.0.0 A browser-compatible implementation of . ### Class: `MessagePort`# Added in: v15.0.0 The `MessagePort` class. See `MessagePort` for more details. ### `module`# This variable may appear to be global but is not. See `module`. ### Class: `Navigator`# Added in: v21.0.0 Stability: 1.1 \- Active development. Disable this API with the `--no-experimental-global-navigator` CLI flag. A partial implementation of the Navigator API. ### `navigator`# Added in: v21.0.0 Stability: 1.1 \- Active development. Disable this API with the `--no-experimental-global-navigator` CLI flag. A partial implementation of `window.navigator`. #### `navigator.hardwareConcurrency`# Added in: v21.0.0 * Type: The `navigator.hardwareConcurrency` read-only property returns the number of logical processors available to the current Node.js instance. console.log(`This process is running on ${navigator.hardwareConcurrency} logical processors`); #### `navigator.language`# Added in: v21.2.0 * Type: The `navigator.language` read-only property returns a string representing the preferred language of the Node.js instance. The language will be determined by the ICU library used by Node.js at runtime based on the default language of the operating system. The value is representing the language version as defined in RFC 5646. The fallback value on builds without ICU is `'en-US'`. console.log(`The preferred language of the Node.js instance has the tag '${navigator.language}'`); #### `navigator.languages`# Added in: v21.2.0 * Type: {Array} The `navigator.languages` read-only property returns an array of strings representing the preferred languages of the Node.js instance. By default `navigator.languages` contains only the value of `navigator.language`, which will be determined by the ICU library used by Node.js at runtime based on the default language of the operating system. The fallback value on builds without ICU is `['en-US']`. console.log(`The preferred languages are '${navigator.languages}'`); #### `navigator.platform`# Added in: v21.2.0 * Type: The `navigator.platform` read-only property returns a string identifying the platform on which the Node.js instance is running. console.log(`This process is running on ${navigator.platform}`); #### `navigator.userAgent`# Added in: v21.1.0 * Type: The `navigator.userAgent` read-only property returns user agent consisting of the runtime name and major version number. console.log(`The user-agent is ${navigator.userAgent}`); // Prints "Node.js/21" #### `navigator.locks`# Added in: v24.5.0 Stability: 1 \- Experimental The `navigator.locks` read-only property returns a `LockManager` instance that can be used to coordinate access to resources that may be shared across multiple threads within the same process. This global implementation matches the semantics of the browser `LockManager` API. // Request an exclusive lock await navigator.locks.request('my_resource', async (lock) => { // The lock has been acquired. console.log(`Lock acquired: ${lock.name}`); // Lock is automatically released when the function returns }); // Request a shared lock await navigator.locks.request('shared_resource', { mode: 'shared' }, async (lock) => { // Multiple shared locks can be held simultaneously console.log(`Shared lock acquired: ${lock.name}`); }); See `worker.locks` for detailed API documentation. ### Class: `PerformanceEntry`# Added in: v19.0.0 The `PerformanceEntry` class. See `PerformanceEntry` for more details. ### Class: `PerformanceMark`# Added in: v19.0.0 The `PerformanceMark` class. See `PerformanceMark` for more details. ### Class: `PerformanceMeasure`# Added in: v19.0.0 The `PerformanceMeasure` class. See `PerformanceMeasure` for more details. ### Class: `PerformanceObserver`# Added in: v19.0.0 The `PerformanceObserver` class. See `PerformanceObserver` for more details. ### Class: `PerformanceObserverEntryList`# Added in: v19.0.0 The `PerformanceObserverEntryList` class. See `PerformanceObserverEntryList` for more details. ### Class: `PerformanceResourceTiming`# Added in: v19.0.0 The `PerformanceResourceTiming` class. See `PerformanceResourceTiming` for more details. ### `performance`# Added in: v16.0.0 The `perf_hooks.performance` object. ### `process`# Added in: v0.1.7 * Type: The process object. See the `process` object section. ### `queueMicrotask(callback)`# Added in: v11.0.0 * `callback` Function to be queued. The `queueMicrotask()` method queues a microtask to invoke `callback`. If `callback` throws an exception, the `process` object `'uncaughtException'` event will be emitted. The microtask queue is managed by V8 and may be used in a similar manner to the `process.nextTick()` queue, which is managed by Node.js. The `process.nextTick()` queue is always processed before the microtask queue within each turn of the Node.js event loop. // Here, `queueMicrotask()` is used to ensure the 'load' event is always // emitted asynchronously, and therefore consistently. Using // `process.nextTick()` here would result in the 'load' event always emitting // before any other promise jobs. DataHandler.prototype.load = async function load(key) { const hit = this._cache.get(key); if (hit !== undefined) { queueMicrotask(() => { this.emit('load', hit); }); return; } const data = await fetchData(key); this._cache.set(key, data); this.emit('load', data); }; ### Class: `ReadableByteStreamController`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `ReadableByteStreamController`. ### Class: `ReadableStream`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `ReadableStream`. ### Class: `ReadableStreamBYOBReader`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `ReadableStreamBYOBReader`. ### Class: `ReadableStreamBYOBRequest`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `ReadableStreamBYOBRequest`. ### Class: `ReadableStreamDefaultController`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `ReadableStreamDefaultController`. ### Class: `ReadableStreamDefaultReader`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `ReadableStreamDefaultReader`. ### `require()`# This variable may appear to be global but is not. See `require()`. ### Class: `Response`# History VersionChanges v21.0.0 No longer experimental. v18.0.0 No longer behind `--experimental-fetch` CLI flag. v17.5.0, v16.15.0 Added in: v17.5.0, v16.15.0 A browser-compatible implementation of . ### Class: `Request`# History VersionChanges v21.0.0 No longer experimental. v18.0.0 No longer behind `--experimental-fetch` CLI flag. v17.5.0, v16.15.0 Added in: v17.5.0, v16.15.0 A browser-compatible implementation of . ### `sessionStorage`# Added in: v22.4.0 Stability: 1.0 \- Early development. A browser-compatible implementation of `sessionStorage`. Data is stored in memory, with a storage quota of 10 MB. `sessionStorage` data persists only within the currently running process, and is not shared between workers. ### `setImmediate(callback[, ...args])`# Added in: v0.9.1 `setImmediate` is described in the timers section. ### `setInterval(callback, delay[, ...args])`# Added in: v0.0.1 `setInterval` is described in the timers section. ### `setTimeout(callback, delay[, ...args])`# Added in: v0.0.1 `setTimeout` is described in the timers section. ### Class: `Storage`# Added in: v22.4.0 Stability: 1.0 \- Early development. Enable this API with the `--experimental-webstorage` CLI flag. A browser-compatible implementation of . ### `structuredClone(value[, options])`# Added in: v17.0.0 The WHATWG `structuredClone` method. ### Class: `SubtleCrypto`# History VersionChanges v19.0.0 No longer behind `--experimental-global-webcrypto` CLI flag. v17.6.0, v16.15.0 Added in: v17.6.0, v16.15.0 A browser-compatible implementation of . This global is available only if the Node.js binary was compiled with including support for the `node:crypto` module. ### Class: `DOMException`# Added in: v17.0.0 The WHATWG class. ### Class: `TextDecoder`# Added in: v11.0.0 The WHATWG `TextDecoder` class. See the `TextDecoder` section. ### Class: `TextDecoderStream`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `TextDecoderStream`. ### Class: `TextEncoder`# Added in: v11.0.0 The WHATWG `TextEncoder` class. See the `TextEncoder` section. ### Class: `TextEncoderStream`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `TextEncoderStream`. ### Class: `TransformStream`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `TransformStream`. ### Class: `TransformStreamDefaultController`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `TransformStreamDefaultController`. ### Class: `URL`# Added in: v10.0.0 The WHATWG `URL` class. See the `URL` section. ### Class: `URLPattern`# Added in: v24.0.0 Stability: 1 \- Experimental The WHATWG `URLPattern` class. See the `URLPattern` section. ### Class: `URLSearchParams`# Added in: v10.0.0 The WHATWG `URLSearchParams` class. See the `URLSearchParams` section. ### Class: `WebAssembly`# Added in: v8.0.0 * Type: The object that acts as the namespace for all W3C WebAssembly related functionality. See the Mozilla Developer Network for usage and compatibility. ### Class: `WebSocket`# History VersionChanges v22.4.0 No longer experimental. v22.0.0 No longer behind `--experimental-websocket` CLI flag. v21.0.0, v20.10.0 Added in: v21.0.0, v20.10.0 A browser-compatible implementation of . Disable this API with the `--no-experimental-websocket` CLI flag. ### Class: `WritableStream`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `WritableStream`. ### Class: `WritableStreamDefaultController`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `WritableStreamDefaultController`. ### Class: `WritableStreamDefaultWriter`# History VersionChanges v23.11.0, v22.15.0 Marking the API stable. v18.0.0 Added in: v18.0.0 A browser-compatible implementation of `WritableStreamDefaultWriter`. ## HTTP# Stability: 2 \- Stable Source Code: lib/http.js This module, containing both a client and server, can be imported via `require('node:http')` (CommonJS) or `import * as http from 'node:http'` (ES module). The HTTP interfaces in Node.js are designed to support many features of the protocol which have been traditionally difficult to use. In particular, large, possibly chunk-encoded, messages. The interface is careful to never buffer entire requests or responses, so the user is able to stream data. HTTP message headers are represented by an object like this: { "content-length": "123", "content-type": "text/plain", "connection": "keep-alive", "host": "example.com", "accept": "*/*" } Keys are lowercased. Values are not modified. In order to support the full spectrum of possible HTTP applications, the Node.js HTTP API is very low-level. It deals with stream handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body. See `message.headers` for details on how duplicate headers are handled. The raw headers as they were received are retained in the `rawHeaders` property, which is an array of `[key, value, key2, value2, ...]`. For example, the previous message header object might have a `rawHeaders` list like the following: [ 'ConTent-Length', '123456', 'content-LENGTH', '123', 'content-type', 'text/plain', 'CONNECTION', 'keep-alive', 'Host', 'example.com', 'accepT', '*/*' ] ### Class: `http.Agent`# Added in: v0.3.4 An `Agent` is responsible for managing connection persistence and reuse for HTTP clients. It maintains a queue of pending requests for a given host and port, reusing a single socket connection for each until the queue is empty, at which time the socket is either destroyed or put into a pool where it is kept to be used again for requests to the same host and port. Whether it is destroyed or pooled depends on the `keepAlive` option. Pooled connections have TCP Keep-Alive enabled for them, but servers may still close idle connections, in which case they will be removed from the pool and a new connection will be made when a new HTTP request is made for that host and port. Servers may also refuse to allow multiple requests over the same connection, in which case the connection will have to be remade for every request and cannot be pooled. The `Agent` will still make the requests to that server, but each one will occur over a new connection. When a connection is closed by the client or the server, it is removed from the pool. Any unused sockets in the pool will be unrefed so as not to keep the Node.js process running when there are no outstanding requests. (see `socket.unref()`). It is good practice, to `destroy()` an `Agent` instance when it is no longer in use, because unused sockets consume OS resources. Sockets are removed from an agent when the socket emits either a `'close'` event or an `'agentRemove'` event. When intending to keep one HTTP request open for a long time without keeping it in the agent, something like the following may be done: http.get(options, (res) => { // Do stuff }).on('socket', (socket) => { socket.emit('agentRemove'); }); An agent may also be used for an individual request. By providing `{agent: false}` as an option to the `http.get()` or `http.request()` functions, a one-time use `Agent` with default options will be used for the client connection. `agent:false`: http.get({ hostname: 'localhost', port: 80, path: '/', agent: false, // Create a new agent just for this one request }, (res) => { // Do stuff with response }); #### `new Agent([options])`# History VersionChanges v24.7.0 Add support for `agentKeepAliveTimeoutBuffer`. v24.5.0 Add support for `proxyEnv`. v24.5.0 Add support for `defaultPort` and `protocol`. v15.6.0, v14.17.0 Change the default scheduling from 'fifo' to 'lifo'. v14.5.0, v12.20.0 Add `scheduling` option to specify the free socket scheduling strategy. v14.5.0, v12.19.0 Add `maxTotalSockets` option to agent constructor. v0.3.4 Added in: v0.3.4 * `options` Set of configurable options to set on the agent. Can have the following fields: * `keepAlive` Keep sockets around even when there are no outstanding requests, so they can be used for future requests without having to reestablish a TCP connection. Not to be confused with the `keep-alive` value of the `Connection` header. The `Connection: keep-alive` header is always sent when using an agent except when the `Connection` header is explicitly specified or when the `keepAlive` and `maxSockets` options are respectively set to `false` and `Infinity`, in which case `Connection: close` will be used. Default: `false`. * `keepAliveMsecs` When using the `keepAlive` option, specifies the initial delay for TCP Keep-Alive packets. Ignored when the `keepAlive` option is `false` or `undefined`. Default: `1000`. * `agentKeepAliveTimeoutBuffer` Milliseconds to subtract from the server-provided `keep-alive: timeout=...` hint when determining socket expiration time. This buffer helps ensure the agent closes the socket slightly before the server does, reducing the chance of sending a request on a socket that’s about to be closed by the server. Default: `1000`. * `maxSockets` Maximum number of sockets to allow per host. If the same host opens multiple concurrent connections, each request will use new socket until the `maxSockets` value is reached. If the host attempts to open more connections than `maxSockets`, the additional requests will enter into a pending request queue, and will enter active connection state when an existing connection terminates. This makes sure there are at most `maxSockets` active connections at any point in time, from a given host. Default: `Infinity`. * `maxTotalSockets` Maximum number of sockets allowed for all hosts in total. Each request will use a new socket until the maximum is reached. Default: `Infinity`. * `maxFreeSockets` Maximum number of sockets per host to leave open in a free state. Only relevant if `keepAlive` is set to `true`. Default: `256`. * `scheduling` Scheduling strategy to apply when picking the next free socket to use. It can be `'fifo'` or `'lifo'`. The main difference between the two scheduling strategies is that `'lifo'` selects the most recently used socket, while `'fifo'` selects the least recently used socket. In case of a low rate of request per second, the `'lifo'` scheduling will lower the risk of picking a socket that might have been closed by the server due to inactivity. In case of a high rate of request per second, the `'fifo'` scheduling will maximize the number of open sockets, while the `'lifo'` scheduling will keep it as low as possible. Default: `'lifo'`. * `timeout` Socket timeout in milliseconds. This will set the timeout when the socket is created. * `proxyEnv` | Environment variables for proxy configuration. See Built-in Proxy Support for details. Default: `undefined` * `HTTP_PROXY` | URL for the proxy server that HTTP requests should use. If undefined, no proxy is used for HTTP requests. * `HTTPS_PROXY` | URL for the proxy server that HTTPS requests should use. If undefined, no proxy is used for HTTPS requests. * `NO_PROXY` | Patterns specifying the endpoints that should not be routed through a proxy. * `http_proxy` | Same as `HTTP_PROXY`. If both are set, `http_proxy` takes precedence. * `https_proxy` | Same as `HTTPS_PROXY`. If both are set, `https_proxy` takes precedence. * `no_proxy` | Same as `NO_PROXY`. If both are set, `no_proxy` takes precedence. * `defaultPort` Default port to use when the port is not specified in requests. Default: `80`. * `protocol` The protocol to use for the agent. Default: `'http:'`. `options` in `socket.connect()` are also supported. To configure any of them, a custom `http.Agent` instance must be created. import { Agent, request } from 'node:http'; const keepAliveAgent = new Agent({ keepAlive: true }); options.agent = keepAliveAgent; request(options, onResponseCallback); #### `agent.createConnection(options[, callback])`# Added in: v0.11.4 * `options` Options containing connection details. Check `net.createConnection()` for the format of the options * `callback` Callback function that receives the created socket * Returns: Produces a socket/stream to be used for HTTP requests. By default, this function is the same as `net.createConnection()`. However, custom agents may override this method in case greater flexibility is desired. A socket/stream can be supplied in one of two ways: by returning the socket/stream from this function, or by passing the socket/stream to `callback`. This method is guaranteed to return an instance of the class, a subclass of , unless the user specifies a socket type other than . `callback` has a signature of `(err, stream)`. #### `agent.keepSocketAlive(socket)`# Added in: v8.1.0 * `socket` Called when `socket` is detached from a request and could be persisted by the `Agent`. Default behavior is to: socket.setKeepAlive(true, this.keepAliveMsecs); socket.unref(); return true; This method can be overridden by a particular `Agent` subclass. If this method returns a falsy value, the socket will be destroyed instead of persisting it for use with the next request. The `socket` argument can be an instance of , a subclass of . #### `agent.reuseSocket(socket, request)`# Added in: v8.1.0 * `socket` * `request` Called when `socket` is attached to `request` after being persisted because of the keep-alive options. Default behavior is to: socket.ref(); This method can be overridden by a particular `Agent` subclass. The `socket` argument can be an instance of , a subclass of . #### `agent.destroy()`# Added in: v0.11.4 Destroy any sockets that are currently in use by the agent. It is usually not necessary to do this. However, if using an agent with `keepAlive` enabled, then it is best to explicitly shut down the agent when it is no longer needed. Otherwise, sockets might stay open for quite a long time before the server terminates them. #### `agent.freeSockets`# History VersionChanges v16.0.0 The property now has a `null` prototype. v0.11.4 Added in: v0.11.4 * Type: An object which contains arrays of sockets currently awaiting use by the agent when `keepAlive` is enabled. Do not modify. Sockets in the `freeSockets` list will be automatically destroyed and removed from the array on `'timeout'`. #### `agent.getName([options])`# History VersionChanges v17.7.0, v16.15.0 The `options` parameter is now optional. v0.11.4 Added in: v0.11.4 * `options` A set of options providing information for name generation * `host` A domain name or IP address of the server to issue the request to * `port` Port of remote server * `localAddress` Local interface to bind for network connections when issuing the request * `family` Must be 4 or 6 if this doesn't equal `undefined`. * Returns: Get a unique name for a set of request options, to determine whether a connection can be reused. For an HTTP agent, this returns `host:port:localAddress` or `host:port:localAddress:family`. For an HTTPS agent, the name includes the CA, cert, ciphers, and other HTTPS/TLS-specific options that determine socket reusability. #### `agent.maxFreeSockets`# Added in: v0.11.7 * Type: By default set to 256. For agents with `keepAlive` enabled, this sets the maximum number of sockets that will be left open in the free state. #### `agent.maxSockets`# Added in: v0.3.6 * Type: By default set to `Infinity`. Determines how many concurrent sockets the agent can have open per origin. Origin is the returned value of `agent.getName()`. #### `agent.maxTotalSockets`# Added in: v14.5.0, v12.19.0 * Type: By default set to `Infinity`. Determines how many concurrent sockets the agent can have open. Unlike `maxSockets`, this parameter applies across all origins. #### `agent.requests`# History VersionChanges v16.0.0 The property now has a `null` prototype. v0.5.9 Added in: v0.5.9 * Type: An object which contains queues of requests that have not yet been assigned to sockets. Do not modify. #### `agent.sockets`# History VersionChanges v16.0.0 The property now has a `null` prototype. v0.3.6 Added in: v0.3.6 * Type: An object which contains arrays of sockets currently in use by the agent. Do not modify. ### Class: `http.ClientRequest`# Added in: v0.1.17 * Extends: This object is created internally and returned from `http.request()`. It represents an in-progress request whose header has already been queued. The header is still mutable using the `setHeader(name, value)`, `getHeader(name)`, `removeHeader(name)` API. The actual header will be sent along with the first data chunk or when calling `request.end()`. To get the response, add a listener for `'response'` to the request object. `'response'` will be emitted from the request object when the response headers have been received. The `'response'` event is executed with one argument which is an instance of `http.IncomingMessage`. During the `'response'` event, one can add listeners to the response object; particularly to listen for the `'data'` event. If no `'response'` handler is added, then the response will be entirely discarded. However, if a `'response'` event handler is added, then the data from the response object must be consumed, either by calling `response.read()` whenever there is a `'readable'` event, or by adding a `'data'` handler, or by calling the `.resume()` method. Until the data is consumed, the `'end'` event will not fire. Also, until the data is read it will consume memory that can eventually lead to a 'process out of memory' error. For backward compatibility, `res` will only emit `'error'` if there is an `'error'` listener registered. Set `Content-Length` header to limit the response body size. If `response.strictContentLength` is set to `true`, mismatching the `Content-Length` header value will result in an `Error` being thrown, identified by `code:` `'ERR_HTTP_CONTENT_LENGTH_MISMATCH'`. `Content-Length` value should be in bytes, not characters. Use `Buffer.byteLength()` to determine the length of the body in bytes. #### Event: `'abort'`# Added in: v1.4.1Deprecated since: v17.0.0, v16.12.0 Stability: 0 \- Deprecated. Listen for the `'close'` event instead. Emitted when the request has been aborted by the client. This event is only emitted on the first call to `abort()`. #### Event: `'close'`# Added in: v0.5.4 Indicates that the request is completed, or its underlying connection was terminated prematurely (before the response completion). #### Event: `'connect'`# Added in: v0.7.0 * `response` * `socket` * `head` Emitted each time a server responds to a request with a `CONNECT` method. If this event is not being listened for, clients receiving a `CONNECT` method will have their connections closed. This event is guaranteed to be passed an instance of the class, a subclass of , unless the user specifies a socket type other than . A client and server pair demonstrating how to listen for the `'connect'` event: import { createServer, request } from 'node:http'; import { connect } from 'node:net'; import { URL } from 'node:url'; // Create an HTTP tunneling proxy const proxy = createServer((req, res) => { res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end('okay'); }); proxy.on('connect', (req, clientSocket, head) => { // Connect to an origin server const { port, hostname } = new URL(`http://${req.url}`); const serverSocket = connect(port || 80, hostname, () => { clientSocket.write('HTTP/1.1 200 Connection Established\r\n' + 'Proxy-agent: Node.js-Proxy\r\n' + '\r\n'); serverSocket.write(head); serverSocket.pipe(clientSocket); clientSocket.pipe(serverSocket); }); }); // Now that proxy is running proxy.listen(1337, '127.0.0.1', () => { // Make a request to a tunneling proxy const options = { port: 1337, host: '127.0.0.1', method: 'CONNECT', path: 'www.google.com:80', }; const req = request(options); req.end(); req.on('connect', (res, socket, head) => { console.log('got connected!'); // Make a request over an HTTP tunnel socket.write('GET / HTTP/1.1\r\n' + 'Host: www.google.com:80\r\n' + 'Connection: close\r\n' + '\r\n'); socket.on('data', (chunk) => { console.log(chunk.toString()); }); socket.on('end', () => { proxy.close(); }); }); }); #### Event: `'continue'`# Added in: v0.3.2 Emitted when the server sends a '100 Continue' HTTP response, usually because the request contained 'Expect: 100-continue'. This is an instruction that the client should send the request body. #### Event: `'finish'`# Added in: v0.3.6 Emitted when the request has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the server has received anything yet. #### Event: `'information'`# Added in: v10.0.0 * `info` * `httpVersion` * `httpVersionMajor` * `httpVersionMinor` * `statusCode` * `statusMessage` * `headers` * `rawHeaders` Emitted when the server sends a 1xx intermediate response (excluding 101 Upgrade). The listeners of this event will receive an object containing the HTTP version, status code, status message, key-value headers object, and array with the raw header names followed by their respective values. import { request } from 'node:http'; const options = { host: '127.0.0.1', port: 8080, path: '/length_request', }; // Make a request const req = request(options); req.end(); req.on('information', (info) => { console.log(`Got information prior to main response: ${info.statusCode}`); }); 101 Upgrade statuses do not fire this event due to their break from the traditional HTTP request/response chain, such as web sockets, in-place TLS upgrades, or HTTP 2.0. To be notified of 101 Upgrade notices, listen for the `'upgrade'` event instead. #### Event: `'response'`# Added in: v0.1.0 * `response` Emitted when a response is received to this request. This event is emitted only once. #### Event: `'socket'`# Added in: v0.5.3 * `socket` This event is guaranteed to be passed an instance of the class, a subclass of , unless the user specifies a socket type other than . #### Event: `'timeout'`# Added in: v0.7.8 Emitted when the underlying socket times out from inactivity. This only notifies that the socket has been idle. The request must be destroyed manually. See also: `request.setTimeout()`. #### Event: `'upgrade'`# Added in: v0.1.94 * `response` * `socket` * `head` Emitted each time a server responds to a request with an upgrade. If this event is not being listened for and the response status code is 101 Switching Protocols, clients receiving an upgrade header will have their connections closed. This event is guaranteed to be passed an instance of the class, a subclass of , unless the user specifies a socket type other than . A client server pair demonstrating how to listen for the `'upgrade'` event. import http from 'node:http'; import process from 'node:process'; // Create an HTTP server const server = http.createServer((req, res) => { res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end('okay'); }); server.on('upgrade', (req, socket, head) => { socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' + 'Upgrade: WebSocket\r\n' + 'Connection: Upgrade\r\n' + '\r\n'); socket.pipe(socket); // echo back }); // Now that server is running server.listen(1337, '127.0.0.1', () => { // make a request const options = { port: 1337, host: '127.0.0.1', headers: { 'Connection': 'Upgrade', 'Upgrade': 'websocket', }, }; const req = http.request(options); req.end(); req.on('upgrade', (res, socket, upgradeHead) => { console.log('got upgraded!'); socket.end(); process.exit(0); }); }); #### `request.abort()`# Added in: v0.3.8Deprecated since: v14.1.0, v13.14.0 Stability: 0 \- Deprecated: Use `request.destroy()` instead. Marks the request as aborting. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed. #### `request.aborted`# History VersionChanges v17.0.0, v16.12.0 Deprecated since: v17.0.0, v16.12.0 v11.0.0 The `aborted` property is no longer a timestamp number. v0.11.14 Added in: v0.11.14 Stability: 0 \- Deprecated. Check `request.destroyed` instead. * Type: The `request.aborted` property will be `true` if the request has been aborted. #### `request.connection`# Added in: v0.3.0Deprecated since: v13.0.0 Stability: 0 \- Deprecated. Use `request.socket`. * Type: See `request.socket`. #### `request.cork()`# Added in: v13.2.0, v12.16.0 See `writable.cork()`. #### `request.end([data[, encoding]][, callback])`# History VersionChanges v15.0.0 The `data` parameter can now be a `Uint8Array`. v10.0.0 This method now returns a reference to `ClientRequest`. v0.1.90 Added in: v0.1.90 * `data` | | * `encoding` * `callback` * Returns: Finishes sending the request. If any parts of the body are unsent, it will flush them to the stream. If the request is chunked, this will send the terminating `'0\r\n\r\n'`. If `data` is specified, it is equivalent to calling `request.write(data, encoding)` followed by `request.end(callback)`. If `callback` is specified, it will be called when the request stream is finished. #### `request.destroy([error])`# History VersionChanges v14.5.0 The function returns `this` for consistency with other Readable streams. v0.3.0 Added in: v0.3.0 * `error` Optional, an error to emit with `'error'` event. * Returns: Destroy the request. Optionally emit an `'error'` event, and emit a `'close'` event. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed. See `writable.destroy()` for further details. ##### `request.destroyed`# Added in: v14.1.0, v13.14.0 * Type: Is `true` after `request.destroy()` has been called. See `writable.destroyed` for further details. #### `request.finished`# Added in: v0.0.1Deprecated since: v13.4.0, v12.16.0 Stability: 0 \- Deprecated. Use `request.writableEnded`. * Type: The `request.finished` property will be `true` if `request.end()` has been called. `request.end()` will automatically be called if the request was initiated via `http.get()`. #### `request.flushHeaders()`# Added in: v1.6.0 Flushes the request headers. For efficiency reasons, Node.js normally buffers the request headers until `request.end()` is called or the first chunk of request data is written. It then tries to pack the request headers and data into a single TCP packet. That's usually desired (it saves a TCP round-trip), but not when the first data is not sent until possibly much later. `request.flushHeaders()` bypasses the optimization and kickstarts the request. #### `request.getHeader(name)`# Added in: v1.6.0 * `name` * Returns: Reads out a header on the request. The name is case-insensitive. The type of the return value depends on the arguments provided to `request.setHeader()`. request.setHeader('content-type', 'text/html'); request.setHeader('Content-Length', Buffer.byteLength(body)); request.setHeader('Cookie', ['type=ninja', 'language=javascript']); const contentType = request.getHeader('Content-Type'); // 'contentType' is 'text/html' const contentLength = request.getHeader('Content-Length'); // 'contentLength' is of type number const cookie = request.getHeader('Cookie'); // 'cookie' is of type string[] #### `request.getHeaderNames()`# Added in: v7.7.0 * Returns: Returns an array containing the unique names of the current outgoing headers. All header names are lowercase. request.setHeader('Foo', 'bar'); request.setHeader('Cookie', ['foo=bar', 'bar=baz']); const headerNames = request.getHeaderNames(); // headerNames === ['foo', 'cookie'] #### `request.getHeaders()`# Added in: v7.7.0 * Returns: Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related http module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase. The object returned by the `request.getHeaders()` method does not prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and will not work. request.setHeader('Foo', 'bar'); request.setHeader('Cookie', ['foo=bar', 'bar=baz']); const headers = request.getHeaders(); // headers === { foo: 'bar', 'cookie': ['foo=bar', 'bar=baz'] } #### `request.getRawHeaderNames()`# Added in: v15.13.0, v14.17.0 * Returns: Returns an array containing the unique names of the current outgoing raw headers. Header names are returned with their exact casing being set. request.setHeader('Foo', 'bar'); request.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headerNames = request.getRawHeaderNames(); // headerNames === ['Foo', 'Set-Cookie'] #### `request.hasHeader(name)`# Added in: v7.7.0 * `name` * Returns: Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name matching is case-insensitive. const hasContentType = request.hasHeader('content-type'); #### `request.maxHeadersCount`# * Type: Default: `2000` Limits maximum response headers count. If set to 0, no limit will be applied. #### `request.path`# Added in: v0.4.0 * Type: The request path. #### `request.method`# Added in: v0.1.97 * Type: The request method. #### `request.host`# Added in: v14.5.0, v12.19.0 * Type: The request host. #### `request.protocol`# Added in: v14.5.0, v12.19.0 * Type: The request protocol. #### `request.removeHeader(name)`# Added in: v1.6.0 * `name` Removes a header that's already defined into headers object. request.removeHeader('Content-Type'); #### `request.reusedSocket`# Added in: v13.0.0, v12.16.0 * Type: Whether the request is send through a reused socket. When sending request through a keep-alive enabled agent, the underlying socket might be reused. But if server closes connection at unfortunate time, client may run into a 'ECONNRESET' error. import http from 'node:http'; // Server has a 5 seconds keep-alive timeout by default http .createServer((req, res) => { res.write('hello\n'); res.end(); }) .listen(3000); setInterval(() => { // Adapting a keep-alive agent http.get('http://localhost:3000', { agent }, (res) => { res.on('data', (data) => { // Do nothing }); }); }, 5000); // Sending request on 5s interval so it's easy to hit idle timeout By marking a request whether it reused socket or not, we can do automatic error retry base on it. import http from 'node:http'; const agent = new http.Agent({ keepAlive: true }); function retriableRequest() { const req = http .get('http://localhost:3000', { agent }, (res) => { // ... }) .on('error', (err) => { // Check if retry is needed if (req.reusedSocket && err.code === 'ECONNRESET') { retriableRequest(); } }); } retriableRequest(); #### `request.setHeader(name, value)`# Added in: v1.6.0 * `name` * `value` Sets a single header value for headers object. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here to send multiple headers with the same name. Non-string values will be stored without modification. Therefore, `request.getHeader()` may return non-string values. However, the non-string values will be converted to strings for network transmission. request.setHeader('Content-Type', 'application/json'); or request.setHeader('Cookie', ['type=ninja', 'language=javascript']); When the value is a string an exception will be thrown if it contains characters outside the `latin1` encoding. If you need to pass UTF-8 characters in the value please encode the value using the RFC 8187 standard. const filename = 'Rock 🎵.txt'; request.setHeader('Content-Disposition', `attachment; filename*=utf-8''${encodeURIComponent(filename)}`); #### `request.setNoDelay([noDelay])`# Added in: v0.5.9 * `noDelay` Once a socket is assigned to this request and is connected `socket.setNoDelay()` will be called. #### `request.setSocketKeepAlive([enable][, initialDelay])`# Added in: v0.5.9 * `enable` * `initialDelay` Once a socket is assigned to this request and is connected `socket.setKeepAlive()` will be called. #### `request.setTimeout(timeout[, callback])`# History VersionChanges v9.0.0 Consistently set socket timeout only when the socket connects. v0.5.9 Added in: v0.5.9 * `timeout` Milliseconds before a request times out. * `callback` Optional function to be called when a timeout occurs. Same as binding to the `'timeout'` event. * Returns: Once a socket is assigned to this request and is connected `socket.setTimeout()` will be called. #### `request.socket`# Added in: v0.3.0 * Type: Reference to the underlying socket. Usually users will not want to access this property. In particular, the socket will not emit `'readable'` events because of how the protocol parser attaches to the socket. import http from 'node:http'; const options = { host: 'www.google.com', }; const req = http.get(options); req.end(); req.once('response', (res) => { const ip = req.socket.localAddress; const port = req.socket.localPort; console.log(`Your IP address is ${ip} and your source port is ${port}.`); // Consume response object }); This property is guaranteed to be an instance of the class, a subclass of , unless the user specified a socket type other than . #### `request.uncork()`# Added in: v13.2.0, v12.16.0 See `writable.uncork()`. #### `request.writableEnded`# Added in: v12.9.0 * Type: Is `true` after `request.end()` has been called. This property does not indicate whether the data has been flushed, for this use `request.writableFinished` instead. #### `request.writableFinished`# Added in: v12.7.0 * Type: Is `true` if all data has been flushed to the underlying system, immediately before the `'finish'` event is emitted. #### `request.write(chunk[, encoding][, callback])`# History VersionChanges v15.0.0 The `chunk` parameter can now be a `Uint8Array`. v0.1.29 Added in: v0.1.29 * `chunk` | | * `encoding` * `callback` * Returns: Sends a chunk of the body. This method can be called multiple times. If no `Content-Length` is set, data will automatically be encoded in HTTP Chunked transfer encoding, so that server knows when the data ends. The `Transfer-Encoding: chunked` header is added. Calling `request.end()` is necessary to finish sending the request. The `encoding` argument is optional and only applies when `chunk` is a string. Defaults to `'utf8'`. The `callback` argument is optional and will be called when this chunk of data is flushed, but only if the chunk is non-empty. Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. `'drain'` will be emitted when the buffer is free again. When `write` function is called with empty string or buffer, it does nothing and waits for more input. ### Class: `http.Server`# Added in: v0.1.17 * Extends: #### Event: `'checkContinue'`# Added in: v0.3.0 * `request` * `response` Emitted each time a request with an HTTP `Expect: 100-continue` is received. If this event is not listened for, the server will automatically respond with a `100 Continue` as appropriate. Handling this event involves calling `response.writeContinue()` if the client should continue to send the request body, or generating an appropriate HTTP response (e.g. 400 Bad Request) if the client should not continue to send the request body. When this event is emitted and handled, the `'request'` event will not be emitted. #### Event: `'checkExpectation'`# Added in: v5.5.0 * `request` * `response` Emitted each time a request with an HTTP `Expect` header is received, where the value is not `100-continue`. If this event is not listened for, the server will automatically respond with a `417 Expectation Failed` as appropriate. When this event is emitted and handled, the `'request'` event will not be emitted. #### Event: `'clientError'`# History VersionChanges v12.0.0 The default behavior will return a 431 Request Header Fields Too Large if a HPE_HEADER_OVERFLOW error occurs. v9.4.0 The `rawPacket` is the current buffer that just parsed. Adding this buffer to the error object of `'clientError'` event is to make it possible that developers can log the broken packet. v6.0.0 The default action of calling `.destroy()` on the `socket` will no longer take place if there are listeners attached for `'clientError'`. v0.1.94 Added in: v0.1.94 * `exception` * `socket` If a client connection emits an `'error'` event, it will be forwarded here. Listener of this event is responsible for closing/destroying the underlying socket. For example, one may wish to more gracefully close the socket with a custom HTTP response instead of abruptly severing the connection. The socket must be closed or destroyed before the listener ends. This event is guaranteed to be passed an instance of the class, a subclass of , unless the user specifies a socket type other than . Default behavior is to try close the socket with a HTTP '400 Bad Request', or a HTTP '431 Request Header Fields Too Large' in the case of a `HPE_HEADER_OVERFLOW` error. If the socket is not writable or headers of the current attached `http.ServerResponse` has been sent, it is immediately destroyed. `socket` is the `net.Socket` object that the error originated from. import http from 'node:http'; const server = http.createServer((req, res) => { res.end(); }); server.on('clientError', (err, socket) => { socket.end('HTTP/1.1 400 Bad Request\r\n\r\n'); }); server.listen(8000); When the `'clientError'` event occurs, there is no `request` or `response` object, so any HTTP response sent, including response headers and payload, must be written directly to the `socket` object. Care must be taken to ensure the response is a properly formatted HTTP response message. `err` is an instance of `Error` with two extra columns: * `bytesParsed`: the bytes count of request packet that Node.js may have parsed correctly; * `rawPacket`: the raw packet of current request. In some cases, the client has already received the response and/or the socket has already been destroyed, like in case of `ECONNRESET` errors. Before trying to send data to the socket, it is better to check that it is still writable. server.on('clientError', (err, socket) => { if (err.code === 'ECONNRESET' || !socket.writable) { return; } socket.end('HTTP/1.1 400 Bad Request\r\n\r\n'); }); #### Event: `'close'`# Added in: v0.1.4 Emitted when the server closes. #### Event: `'connect'`# Added in: v0.7.0 * `request` Arguments for the HTTP request, as it is in the `'request'` event * `socket` Network socket between the server and client * `head` The first packet of the tunneling stream (may be empty) Emitted each time a client requests an HTTP `CONNECT` method. If this event is not listened for, then clients requesting a `CONNECT` method will have their connections closed. This event is guaranteed to be passed an instance of the class, a subclass of , unless the user specifies a socket type other than . After this event is emitted, the request's socket will not have a `'data'` event listener, meaning it will need to be bound in order to handle data sent to the server on that socket. #### Event: `'connection'`# Added in: v0.1.0 * `socket` This event is emitted when a new TCP stream is established. `socket` is typically an object of type `net.Socket`. Usually users will not want to access this event. In particular, the socket will not emit `'readable'` events because of how the protocol parser attaches to the socket. The `socket` can also be accessed at `request.socket`. This event can also be explicitly emitted by users to inject connections into the HTTP server. In that case, any `Duplex` stream can be passed. If `socket.setTimeout()` is called here, the timeout will be replaced with `server.keepAliveTimeout` when the socket has served a request (if `server.keepAliveTimeout` is non-zero). This event is guaranteed to be passed an instance of the class, a subclass of , unless the user specifies a socket type other than . #### Event: `'dropRequest'`# Added in: v18.7.0, v16.17.0 * `request` Arguments for the HTTP request, as it is in the `'request'` event * `socket` Network socket between the server and client When the number of requests on a socket reaches the threshold of `server.maxRequestsPerSocket`, the server will drop new requests and emit `'dropRequest'` event instead, then send `503` to client. #### Event: `'request'`# Added in: v0.1.0 * `request` * `response` Emitted each time there is a request. There may be multiple requests per connection (in the case of HTTP Keep-Alive connections). #### Event: `'upgrade'`# History VersionChanges v24.9.0 Whether this event is fired can now be controlled by the `shouldUpgradeCallback` and sockets will be destroyed if upgraded while no event handler is listening. v10.0.0 Not listening to this event no longer causes the socket to be destroyed if a client sends an Upgrade header. v0.1.94 Added in: v0.1.94 * `request` Arguments for the HTTP request, as it is in the `'request'` event * `socket` Network socket between the server and client * `head` The first packet of the upgraded stream (may be empty) Emitted each time a client's HTTP upgrade request is accepted. By default all HTTP upgrade requests are ignored (i.e. only regular `'request'` events are emitted, sticking with the normal HTTP request/response flow) unless you listen to this event, in which case they are all accepted (i.e. the `'upgrade'` event is emitted instead, and future communication must handled directly through the raw socket). You can control this more precisely by using the server `shouldUpgradeCallback` option. Listening to this event is optional and clients cannot insist on a protocol change. After this event is emitted, the request's socket will not have a `'data'` event listener, meaning it will need to be bound in order to handle data sent to the server on that socket. If an upgrade is accepted by `shouldUpgradeCallback` but no event handler is registered then the socket is destroyed, resulting in an immediate connection closure for the client. This event is guaranteed to be passed an instance of the class, a subclass of , unless the user specifies a socket type other than . #### `server.close([callback])`# History VersionChanges v19.0.0 The method closes idle connections before returning. v0.1.90 Added in: v0.1.90 * `callback` Stops the server from accepting new connections and closes all connections connected to this server which are not sending a request or waiting for a response. See `net.Server.close()`. const http = require('node:http'); const server = http.createServer({ keepAliveTimeout: 60000 }, (req, res) => { res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ data: 'Hello World!', })); }); server.listen(8000); // Close the server after 10 seconds setTimeout(() => { server.close(() => { console.log('server on port 8000 closed successfully'); }); }, 10000); #### `server.closeAllConnections()`# Added in: v18.2.0 Closes all established HTTP(S) connections connected to this server, including active connections connected to this server which are sending a request or waiting for a response. This does not destroy sockets upgraded to a different protocol, such as WebSocket or HTTP/2. > This is a forceful way of closing all connections and should be used with caution. Whenever using this in conjunction with `server.close`, calling this after `server.close` is recommended as to avoid race conditions where new connections are created between a call to this and a call to `server.close`. const http = require('node:http'); const server = http.createServer({ keepAliveTimeout: 60000 }, (req, res) => { res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ data: 'Hello World!', })); }); server.listen(8000); // Close the server after 10 seconds setTimeout(() => { server.close(() => { console.log('server on port 8000 closed successfully'); }); // Closes all connections, ensuring the server closes successfully server.closeAllConnections(); }, 10000); #### `server.closeIdleConnections()`# Added in: v18.2.0 Closes all connections connected to this server which are not sending a request or waiting for a response. > Starting with Node.js 19.0.0, there's no need for calling this method in conjunction with `server.close` to reap `keep-alive` connections. Using it won't cause any harm though, and it can be useful to ensure backwards compatibility for libraries and applications that need to support versions older than 19.0.0. Whenever using this in conjunction with `server.close`, calling this after `server.close` is recommended as to avoid race conditions where new connections are created between a call to this and a call to `server.close`. const http = require('node:http'); const server = http.createServer({ keepAliveTimeout: 60000 }, (req, res) => { res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ data: 'Hello World!', })); }); server.listen(8000); // Close the server after 10 seconds setTimeout(() => { server.close(() => { console.log('server on port 8000 closed successfully'); }); // Closes idle connections, such as keep-alive connections. Server will close // once remaining active connections are terminated server.closeIdleConnections(); }, 10000); #### `server.headersTimeout`# History VersionChanges v19.4.0, v18.14.0 The default is now set to the minimum between 60000 (60 seconds) or `requestTimeout`. v11.3.0, v10.14.0 Added in: v11.3.0, v10.14.0 * Type: Default: The minimum between `server.requestTimeout` or `60000`. Limit the amount of time the parser will wait to receive the complete HTTP headers. If the timeout expires, the server responds with status 408 without forwarding the request to the request listener and then closes the connection. It must be set to a non-zero value (e.g. 120 seconds) to protect against potential Denial-of-Service attacks in case the server is deployed without a reverse proxy in front. #### `server.listen()`# Starts the HTTP server listening for connections. This method is identical to `server.listen()` from `net.Server`. #### `server.listening`# Added in: v5.7.0 * Type: Indicates whether or not the server is listening for connections. #### `server.maxHeadersCount`# Added in: v0.7.0 * Type: Default: `2000` Limits maximum incoming headers count. If set to 0, no limit will be applied. #### `server.requestTimeout`# History VersionChanges v18.0.0 The default request timeout changed from no timeout to 300s (5 minutes). v14.11.0 Added in: v14.11.0 * Type: Default: `300000` Sets the timeout value in milliseconds for receiving the entire request from the client. If the timeout expires, the server responds with status 408 without forwarding the request to the request listener and then closes the connection. It must be set to a non-zero value (e.g. 120 seconds) to protect against potential Denial-of-Service attacks in case the server is deployed without a reverse proxy in front. #### `server.setTimeout([msecs][, callback])`# History VersionChanges v13.0.0 The default timeout changed from 120s to 0 (no timeout). v0.9.12 Added in: v0.9.12 * `msecs` Default: 0 (no timeout) * `callback` * Returns: Sets the timeout value for sockets, and emits a `'timeout'` event on the Server object, passing the socket as an argument, if a timeout occurs. If there is a `'timeout'` event listener on the Server object, then it will be called with the timed-out socket as an argument. By default, the Server does not timeout sockets. However, if a callback is assigned to the Server's `'timeout'` event, timeouts must be handled explicitly. #### `server.maxRequestsPerSocket`# Added in: v16.10.0 * Type: Requests per socket. Default: 0 (no limit) The maximum number of requests socket can handle before closing keep alive connection. A value of `0` will disable the limit. When the limit is reached it will set the `Connection` header value to `close`, but will not actually close the connection, subsequent requests sent after the limit is reached will get `503 Service Unavailable` as a response. #### `server.timeout`# History VersionChanges v13.0.0 The default timeout changed from 120s to 0 (no timeout). v0.9.12 Added in: v0.9.12 * Type: Timeout in milliseconds. Default: 0 (no timeout) The number of milliseconds of inactivity before a socket is presumed to have timed out. A value of `0` will disable the timeout behavior on incoming connections. The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections. #### `server.keepAliveTimeout`# Added in: v8.0.0 * Type: Timeout in milliseconds. Default: `5000` (5 seconds). The number of milliseconds of inactivity a server needs to wait for additional incoming data, after it has finished writing the last response, before a socket will be destroyed. This timeout value is combined with the `server.keepAliveTimeoutBuffer` option to determine the actual socket timeout, calculated as: socketTimeout = keepAliveTimeout + keepAliveTimeoutBuffer If the server receives new data before the keep-alive timeout has fired, it will reset the regular inactivity timeout, i.e., `server.timeout`. A value of `0` will disable the keep-alive timeout behavior on incoming connections. A value of `0` makes the HTTP server behave similarly to Node.js versions prior to 8.0.0, which did not have a keep-alive timeout. The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections. #### `server.keepAliveTimeoutBuffer`# Added in: v24.6.0 * Type: Timeout in milliseconds. Default: `1000` (1 second). An additional buffer time added to the `server.keepAliveTimeout` to extend the internal socket timeout. This buffer helps reduce connection reset (`ECONNRESET`) errors by increasing the socket timeout slightly beyond the advertised keep-alive timeout. This option applies only to new incoming connections. #### `server[Symbol.asyncDispose]()`# History VersionChanges v24.2.0 No longer experimental. v20.4.0 Added in: v20.4.0 Calls `server.close()` and returns a promise that fulfills when the server has closed. ### Class: `http.ServerResponse`# Added in: v0.1.17 * Extends: This object is created internally by an HTTP server, not by the user. It is passed as the second parameter to the `'request'` event. #### Event: `'close'`# Added in: v0.6.7 Indicates that the response is completed, or its underlying connection was terminated prematurely (before the response completion). #### Event: `'finish'`# Added in: v0.3.6 Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the client has received anything yet. #### `response.addTrailers(headers)`# Added in: v0.3.0 * `headers` This method adds HTTP trailing headers (a header but at the end of the message) to the response. Trailers will only be emitted if chunked encoding is used for the response; if it is not (e.g. if the request was HTTP/1.0), they will be silently discarded. HTTP requires the `Trailer` header to be sent in order to emit trailers, with a list of the header fields in its value. E.g., response.writeHead(200, { 'Content-Type': 'text/plain', 'Trailer': 'Content-MD5' }); response.write(fileData); response.addTrailers({ 'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667' }); response.end(); Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. #### `response.connection`# Added in: v0.3.0Deprecated since: v13.0.0 Stability: 0 \- Deprecated. Use `response.socket`. * Type: See `response.socket`. #### `response.cork()`# Added in: v13.2.0, v12.16.0 See `writable.cork()`. #### `response.end([data[, encoding]][, callback])`# History VersionChanges v15.0.0 The `data` parameter can now be a `Uint8Array`. v10.0.0 This method now returns a reference to `ServerResponse`. v0.1.90 Added in: v0.1.90 * `data` | | * `encoding` * `callback` * Returns: This method signals to the server that all of the response headers and body have been sent; that server should consider this message complete. The method, `response.end()`, MUST be called on each response. If `data` is specified, it is similar in effect to calling `response.write(data, encoding)` followed by `response.end(callback)`. If `callback` is specified, it will be called when the response stream is finished. #### `response.finished`# Added in: v0.0.2Deprecated since: v13.4.0, v12.16.0 Stability: 0 \- Deprecated. Use `response.writableEnded`. * Type: The `response.finished` property will be `true` if `response.end()` has been called. #### `response.flushHeaders()`# Added in: v1.6.0 Flushes the response headers. See also: `request.flushHeaders()`. #### `response.getHeader(name)`# Added in: v0.4.0 * `name` * Returns: | | | Reads out a header that's already been queued but not sent to the client. The name is case-insensitive. The type of the return value depends on the arguments provided to `response.setHeader()`. response.setHeader('Content-Type', 'text/html'); response.setHeader('Content-Length', Buffer.byteLength(body)); response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']); const contentType = response.getHeader('content-type'); // contentType is 'text/html' const contentLength = response.getHeader('Content-Length'); // contentLength is of type number const setCookie = response.getHeader('set-cookie'); // setCookie is of type string[] #### `response.getHeaderNames()`# Added in: v7.7.0 * Returns: Returns an array containing the unique names of the current outgoing headers. All header names are lowercase. response.setHeader('Foo', 'bar'); response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headerNames = response.getHeaderNames(); // headerNames === ['foo', 'set-cookie'] #### `response.getHeaders()`# Added in: v7.7.0 * Returns: Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related http module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase. The object returned by the `response.getHeaders()` method does not prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and will not work. response.setHeader('Foo', 'bar'); response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headers = response.getHeaders(); // headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] } #### `response.hasHeader(name)`# Added in: v7.7.0 * `name` * Returns: Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name matching is case-insensitive. const hasContentType = response.hasHeader('content-type'); #### `response.headersSent`# Added in: v0.9.3 * Type: Boolean (read-only). True if headers were sent, false otherwise. #### `response.removeHeader(name)`# Added in: v0.4.0 * `name` Removes a header that's queued for implicit sending. response.removeHeader('Content-Encoding'); #### `response.req`# Added in: v15.7.0 * Type: A reference to the original HTTP `request` object. #### `response.sendDate`# Added in: v0.7.5 * Type: When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true. This should only be disabled for testing; HTTP requires the Date header in responses. #### `response.setHeader(name, value)`# Added in: v0.4.0 * `name` * `value` | | * Returns: Returns the response object. Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here to send multiple headers with the same name. Non-string values will be stored without modification. Therefore, `response.getHeader()` may return non-string values. However, the non-string values will be converted to strings for network transmission. The same response object is returned to the caller, to enable call chaining. response.setHeader('Content-Type', 'text/html'); or response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']); Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. When headers have been set with `response.setHeader()`, they will be merged with any headers passed to `response.writeHead()`, with the headers passed to `response.writeHead()` given precedence. // Returns content-type = text/plain const server = http.createServer((req, res) => { res.setHeader('Content-Type', 'text/html'); res.setHeader('X-Foo', 'bar'); res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end('ok'); }); If `response.writeHead()` method is called and this method has not been called, it will directly write the supplied header values onto the network channel without caching internally, and the `response.getHeader()` on the header will not yield the expected result. If progressive population of headers is desired with potential future retrieval and modification, use `response.setHeader()` instead of `response.writeHead()`. #### `response.setTimeout(msecs[, callback])`# Added in: v0.9.12 * `msecs` * `callback` * Returns: Sets the Socket's timeout value to `msecs`. If a callback is provided, then it is added as a listener on the `'timeout'` event on the response object. If no `'timeout'` listener is added to the request, the response, or the server, then sockets are destroyed when they time out. If a handler is assigned to the request, the response, or the server's `'timeout'` events, timed out sockets must be handled explicitly. #### `response.socket`# Added in: v0.3.0 * Type: Reference to the underlying socket. Usually users will not want to access this property. In particular, the socket will not emit `'readable'` events because of how the protocol parser attaches to the socket. After `response.end()`, the property is nulled. import http from 'node:http'; const server = http.createServer((req, res) => { const ip = res.socket.remoteAddress; const port = res.socket.remotePort; res.end(`Your IP address is ${ip} and your source port is ${port}.`); }).listen(3000); This property is guaranteed to be an instance of the class, a subclass of , unless the user specified a socket type other than . #### `response.statusCode`# Added in: v0.4.0 * Type: Default: `200` When using implicit headers (not calling `response.writeHead()` explicitly), this property controls the status code that will be sent to the client when the headers get flushed. response.statusCode = 404; After response header was sent to the client, this property indicates the status code which was sent out. #### `response.statusMessage`# Added in: v0.11.8 * Type: When using implicit headers (not calling `response.writeHead()` explicitly), this property controls the status message that will be sent to the client when the headers get flushed. If this is left as `undefined` then the standard message for the status code will be used. response.statusMessage = 'Not found'; After response header was sent to the client, this property indicates the status message which was sent out. #### `response.strictContentLength`# Added in: v18.10.0, v16.18.0 * Type: Default: `false` If set to `true`, Node.js will check whether the `Content-Length` header value and the size of the body, in bytes, are equal. Mismatching the `Content-Length` header value will result in an `Error` being thrown, identified by `code:` `'ERR_HTTP_CONTENT_LENGTH_MISMATCH'`. #### `response.uncork()`# Added in: v13.2.0, v12.16.0 See `writable.uncork()`. #### `response.writableEnded`# Added in: v12.9.0 * Type: Is `true` after `response.end()` has been called. This property does not indicate whether the data has been flushed, for this use `response.writableFinished` instead. #### `response.writableFinished`# Added in: v12.7.0 * Type: Is `true` if all data has been flushed to the underlying system, immediately before the `'finish'` event is emitted. #### `response.write(chunk[, encoding][, callback])`# History VersionChanges v15.0.0 The `chunk` parameter can now be a `Uint8Array`. v0.1.29 Added in: v0.1.29 * `chunk` | | * `encoding` Default: `'utf8'` * `callback` * Returns: If this method is called and `response.writeHead()` has not been called, it will switch to implicit header mode and flush the implicit headers. This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body. If `rejectNonStandardBodyWrites` is set to true in `createServer` then writing to the body is not allowed when the request method or response status do not support content. If an attempt is made to write to the body for a HEAD request or as part of a `204` or `304`response, a synchronous `Error` with the code `ERR_HTTP_BODY_NOT_ALLOWED` is thrown. `chunk` can be a string or a buffer. If `chunk` is a string, the second parameter specifies how to encode it into a byte stream. `callback` will be called when this chunk of data is flushed. This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used. The first time `response.write()` is called, it will send the buffered header information and the first chunk of the body to the client. The second time `response.write()` is called, Node.js assumes data will be streamed, and sends the new data separately. That is, the response is buffered up to the first chunk of the body. Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. `'drain'` will be emitted when the buffer is free again. #### `response.writeContinue()`# Added in: v0.3.0 Sends an HTTP/1.1 100 Continue message to the client, indicating that the request body should be sent. See the `'checkContinue'` event on `Server`. #### `response.writeEarlyHints(hints[, callback])`# History VersionChanges v18.11.0 Allow passing hints as an object. v18.11.0 Added in: v18.11.0 * `hints` * `callback` Sends an HTTP/1.1 103 Early Hints message to the client with a Link header, indicating that the user agent can preload/preconnect the linked resources. The `hints` is an object containing the values of headers to be sent with early hints message. The optional `callback` argument will be called when the response message has been written. Example const earlyHintsLink = '; rel=preload; as=style'; response.writeEarlyHints({ 'link': earlyHintsLink, }); const earlyHintsLinks = [ '; rel=preload; as=style', '; rel=preload; as=script', ]; response.writeEarlyHints({ 'link': earlyHintsLinks, 'x-trace-id': 'id for diagnostics', }); const earlyHintsCallback = () => console.log('early hints message sent'); response.writeEarlyHints({ 'link': earlyHintsLinks, }, earlyHintsCallback); #### `response.writeHead(statusCode[, statusMessage][, headers])`# History VersionChanges v14.14.0 Allow passing headers as an array. v11.10.0, v10.17.0 Return `this` from `writeHead()` to allow chaining with `end()`. v5.11.0, v4.4.5 A `RangeError` is thrown if `statusCode` is not a number in the range `[100, 999]`. v0.1.30 Added in: v0.1.30 * `statusCode` * `statusMessage` * `headers` | * Returns: Sends a response header to the request. The status code is a 3-digit HTTP status code, like `404`. The last argument, `headers`, are the response headers. Optionally one can give a human-readable `statusMessage` as the second argument. `headers` may be an `Array` where the keys and values are in the same list. It is not a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values. The array is in the same format as `request.rawHeaders`. Returns a reference to the `ServerResponse`, so that calls can be chained. const body = 'hello world'; response .writeHead(200, { 'Content-Length': Buffer.byteLength(body), 'Content-Type': 'text/plain', }) .end(body); This method must only be called once on a message and it must be called before `response.end()` is called. If `response.write()` or `response.end()` are called before calling this, the implicit/mutable headers will be calculated and call this function. When headers have been set with `response.setHeader()`, they will be merged with any headers passed to `response.writeHead()`, with the headers passed to `response.writeHead()` given precedence. If this method is called and `response.setHeader()` has not been called, it will directly write the supplied header values onto the network channel without caching internally, and the `response.getHeader()` on the header will not yield the expected result. If progressive population of headers is desired with potential future retrieval and modification, use `response.setHeader()` instead. // Returns content-type = text/plain const server = http.createServer((req, res) => { res.setHeader('Content-Type', 'text/html'); res.setHeader('X-Foo', 'bar'); res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end('ok'); }); `Content-Length` is read in bytes, not characters. Use `Buffer.byteLength()` to determine the length of the body in bytes. Node.js will check whether `Content-Length` and the length of the body which has been transmitted are equal or not. Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. #### `response.writeProcessing()`# Added in: v10.0.0 Sends a HTTP/1.1 102 Processing message to the client, indicating that the request body should be sent. ### Class: `http.IncomingMessage`# History VersionChanges v15.5.0 The `destroyed` value returns `true` after the incoming data is consumed. v13.1.0, v12.16.0 The `readableHighWaterMark` value mirrors that of the socket. v0.1.17 Added in: v0.1.17 * Extends: An `IncomingMessage` object is created by `http.Server` or `http.ClientRequest` and passed as the first argument to the `'request'` and `'response'` event respectively. It may be used to access response status, headers, and data. Different from its `socket` value which is a subclass of , the `IncomingMessage` itself extends and is created separately to parse and emit the incoming HTTP headers and payload, as the underlying socket may be reused multiple times in case of keep-alive. #### Event: `'aborted'`# Added in: v0.3.8Deprecated since: v17.0.0, v16.12.0 Stability: 0 \- Deprecated. Listen for `'close'` event instead. Emitted when the request has been aborted. #### Event: `'close'`# History VersionChanges v16.0.0 The close event is now emitted when the request has been completed and not when the underlying socket is closed. v0.4.2 Added in: v0.4.2 Emitted when the request has been completed. #### `message.aborted`# Added in: v10.1.0Deprecated since: v17.0.0, v16.12.0 Stability: 0 \- Deprecated. Check `message.destroyed` from . * Type: The `message.aborted` property will be `true` if the request has been aborted. #### `message.complete`# Added in: v0.3.0 * Type: The `message.complete` property will be `true` if a complete HTTP message has been received and successfully parsed. This property is particularly useful as a means of determining if a client or server fully transmitted a message before a connection was terminated: const req = http.request({ host: '127.0.0.1', port: 8080, method: 'POST', }, (res) => { res.resume(); res.on('end', () => { if (!res.complete) console.error( 'The connection was terminated while the message was still being sent'); }); }); #### `message.connection`# Added in: v0.1.90Deprecated since: v16.0.0 Stability: 0 \- Deprecated. Use `message.socket`. Alias for `message.socket`. #### `message.destroy([error])`# History VersionChanges v14.5.0, v12.19.0 The function returns `this` for consistency with other Readable streams. v0.3.0 Added in: v0.3.0 * `error` * Returns: Calls `destroy()` on the socket that received the `IncomingMessage`. If `error` is provided, an `'error'` event is emitted on the socket and `error` is passed as an argument to any listeners on the event. #### `message.headers`# History VersionChanges v19.5.0, v18.14.0 The `joinDuplicateHeaders` option in the `http.request()` and `http.createServer()` functions ensures that duplicate headers are not discarded, but rather combined using a comma separator, in accordance with RFC 9110 Section 5.3. v15.1.0 `message.headers` is now lazily computed using an accessor property on the prototype and is no longer enumerable. v0.1.5 Added in: v0.1.5 * Type: The request/response headers object. Key-value pairs of header names and values. Header names are lower-cased. // Prints something like: // // { 'user-agent': 'curl/7.22.0', // host: '127.0.0.1:8000', // accept: '*/*' } console.log(request.headers); Duplicates in raw headers are handled in the following ways, depending on the header name: * Duplicates of `age`, `authorization`, `content-length`, `content-type`, `etag`, `expires`, `from`, `host`, `if-modified-since`, `if-unmodified-since`, `last-modified`, `location`, `max-forwards`, `proxy-authorization`, `referer`, `retry-after`, `server`, or `user-agent` are discarded. To allow duplicate values of the headers listed above to be joined, use the option `joinDuplicateHeaders` in `http.request()` and `http.createServer()`. See RFC 9110 Section 5.3 for more information. * `set-cookie` is always an array. Duplicates are added to the array. * For duplicate `cookie` headers, the values are joined together with `; `. * For all other headers, the values are joined together with `, `. #### `message.headersDistinct`# Added in: v18.3.0, v16.17.0 * Type: Similar to `message.headers`, but there is no join logic and the values are always arrays of strings, even for headers received just once. // Prints something like: // // { 'user-agent': ['curl/7.22.0'], // host: ['127.0.0.1:8000'], // accept: ['*/*'] } console.log(request.headersDistinct); #### `message.httpVersion`# Added in: v0.1.1 * Type: In case of server request, the HTTP version sent by the client. In the case of client response, the HTTP version of the connected-to server. Probably either `'1.1'` or `'1.0'`. Also `message.httpVersionMajor` is the first integer and `message.httpVersionMinor` is the second. #### `message.method`# Added in: v0.1.1 * Type: Only valid for request obtained from `http.Server`. The request method as a string. Read only. Examples: `'GET'`, `'DELETE'`. #### `message.rawHeaders`# Added in: v0.11.6 * Type: The raw request/response headers list exactly as they were received. The keys and values are in the same list. It is not a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values. Header names are not lowercased, and duplicates are not merged. // Prints something like: // // [ 'user-agent', // 'this is invalid because there can be only one', // 'User-Agent', // 'curl/7.22.0', // 'Host', // '127.0.0.1:8000', // 'ACCEPT', // '*/*' ] console.log(request.rawHeaders); #### `message.rawTrailers`# Added in: v0.11.6 * Type: The raw request/response trailer keys and values exactly as they were received. Only populated at the `'end'` event. #### `message.setTimeout(msecs[, callback])`# Added in: v0.5.9 * `msecs` * `callback` * Returns: Calls `message.socket.setTimeout(msecs, callback)`. #### `message.socket`# Added in: v0.3.0 * Type: The `net.Socket` object associated with the connection. With HTTPS support, use `request.socket.getPeerCertificate()` to obtain the client's authentication details. This property is guaranteed to be an instance of the class, a subclass of , unless the user specified a socket type other than or internally nulled. #### `message.statusCode`# Added in: v0.1.1 * Type: Only valid for response obtained from `http.ClientRequest`. The 3-digit HTTP response status code. E.G. `404`. #### `message.statusMessage`# Added in: v0.11.10 * Type: Only valid for response obtained from `http.ClientRequest`. The HTTP response status message (reason phrase). E.G. `OK` or `Internal Server Error`. #### `message.trailers`# Added in: v0.3.0 * Type: The request/response trailers object. Only populated at the `'end'` event. #### `message.trailersDistinct`# Added in: v18.3.0, v16.17.0 * Type: Similar to `message.trailers`, but there is no join logic and the values are always arrays of strings, even for headers received just once. Only populated at the `'end'` event. #### `message.url`# Added in: v0.1.90 * Type: Only valid for request obtained from `http.Server`. Request URL string. This contains only the URL that is present in the actual HTTP request. Take the following request: GET /status?name=ryan HTTP/1.1 Accept: text/plain To parse the URL into its parts: new URL(`http://${process.env.HOST ?? 'localhost'}${request.url}`); When `request.url` is `'/status?name=ryan'` and `process.env.HOST` is undefined: $ node > new URL(`http://${process.env.HOST ?? 'localhost'}${request.url}`); URL { href: 'http://localhost/status?name=ryan', origin: 'http://localhost', protocol: 'http:', username: '', password: '', host: 'localhost', hostname: 'localhost', port: '', pathname: '/status', search: '?name=ryan', searchParams: URLSearchParams { 'name' => 'ryan' }, hash: '' } Ensure that you set `process.env.HOST` to the server's host name, or consider replacing this part entirely. If using `req.headers.host`, ensure proper validation is used, as clients may specify a custom `Host` header. ### Class: `http.OutgoingMessage`# Added in: v0.1.17 * Extends: This class serves as the parent class of `http.ClientRequest` and `http.ServerResponse`. It is an abstract outgoing message from the perspective of the participants of an HTTP transaction. #### Event: `'drain'`# Added in: v0.3.6 Emitted when the buffer of the message is free again. #### Event: `'finish'`# Added in: v0.1.17 Emitted when the transmission is finished successfully. #### Event: `'prefinish'`# Added in: v0.11.6 Emitted after `outgoingMessage.end()` is called. When the event is emitted, all data has been processed but not necessarily completely flushed. #### `outgoingMessage.addTrailers(headers)`# Added in: v0.3.0 * `headers` Adds HTTP trailers (headers but at the end of the message) to the message. Trailers will only be emitted if the message is chunked encoded. If not, the trailers will be silently discarded. HTTP requires the `Trailer` header to be sent to emit trailers, with a list of header field names in its value, e.g. message.writeHead(200, { 'Content-Type': 'text/plain', 'Trailer': 'Content-MD5' }); message.write(fileData); message.addTrailers({ 'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667' }); message.end(); Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. #### `outgoingMessage.appendHeader(name, value)`# Added in: v18.3.0, v16.17.0 * `name` Header name * `value` | Header value * Returns: Append a single header value to the header object. If the value is an array, this is equivalent to calling this method multiple times. If there were no previous values for the header, this is equivalent to calling `outgoingMessage.setHeader(name, value)`. Depending of the value of `options.uniqueHeaders` when the client request or the server were created, this will end up in the header being sent multiple times or a single time with values joined using `; `. #### `outgoingMessage.connection`# Added in: v0.3.0Deprecated since: v15.12.0, v14.17.1 Stability: 0 \- Deprecated: Use `outgoingMessage.socket` instead. Alias of `outgoingMessage.socket`. #### `outgoingMessage.cork()`# Added in: v13.2.0, v12.16.0 See `writable.cork()`. #### `outgoingMessage.destroy([error])`# Added in: v0.3.0 * `error` Optional, an error to emit with `error` event * Returns: Destroys the message. Once a socket is associated with the message and is connected, that socket will be destroyed as well. #### `outgoingMessage.end(chunk[, encoding][, callback])`# History VersionChanges v15.0.0 The `chunk` parameter can now be a `Uint8Array`. v0.11.6 add `callback` argument. v0.1.90 Added in: v0.1.90 * `chunk` | | * `encoding` Optional, Default: `utf8` * `callback` Optional * Returns: Finishes the outgoing message. If any parts of the body are unsent, it will flush them to the underlying system. If the message is chunked, it will send the terminating chunk `0\r\n\r\n`, and send the trailers (if any). If `chunk` is specified, it is equivalent to calling `outgoingMessage.write(chunk, encoding)`, followed by `outgoingMessage.end(callback)`. If `callback` is provided, it will be called when the message is finished (equivalent to a listener of the `'finish'` event). #### `outgoingMessage.flushHeaders()`# Added in: v1.6.0 Flushes the message headers. For efficiency reason, Node.js normally buffers the message headers until `outgoingMessage.end()` is called or the first chunk of message data is written. It then tries to pack the headers and data into a single TCP packet. It is usually desired (it saves a TCP round-trip), but not when the first data is not sent until possibly much later. `outgoingMessage.flushHeaders()` bypasses the optimization and kickstarts the message. #### `outgoingMessage.getHeader(name)`# Added in: v0.4.0 * `name` Name of header * Returns: | | | Gets the value of the HTTP header with the given name. If that header is not set, the returned value will be `undefined`. #### `outgoingMessage.getHeaderNames()`# Added in: v7.7.0 * Returns: Returns an array containing the unique names of the current outgoing headers. All names are lowercase. #### `outgoingMessage.getHeaders()`# Added in: v7.7.0 * Returns: Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related HTTP module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase. The object returned by the `outgoingMessage.getHeaders()` method does not prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and will not work. outgoingMessage.setHeader('Foo', 'bar'); outgoingMessage.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headers = outgoingMessage.getHeaders(); // headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] } #### `outgoingMessage.hasHeader(name)`# Added in: v7.7.0 * `name` * Returns: Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name is case-insensitive. const hasContentType = outgoingMessage.hasHeader('content-type'); #### `outgoingMessage.headersSent`# Added in: v0.9.3 * Type: Read-only. `true` if the headers were sent, otherwise `false`. #### `outgoingMessage.pipe()`# Added in: v9.0.0 Overrides the `stream.pipe()` method inherited from the legacy `Stream` class which is the parent class of `http.OutgoingMessage`. Calling this method will throw an `Error` because `outgoingMessage` is a write-only stream. #### `outgoingMessage.removeHeader(name)`# Added in: v0.4.0 * `name` Header name Removes a header that is queued for implicit sending. outgoingMessage.removeHeader('Content-Encoding'); #### `outgoingMessage.setHeader(name, value)`# Added in: v0.4.0 * `name` Header name * `value` | | Header value * Returns: Sets a single header value. If the header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings to send multiple headers with the same name. #### `outgoingMessage.setHeaders(headers)`# Added in: v19.6.0, v18.15.0 * `headers` | * Returns: Sets multiple header values for implicit headers. `headers` must be an instance of `Headers` or `Map`, if a header already exists in the to-be-sent headers, its value will be replaced. const headers = new Headers({ foo: 'bar' }); outgoingMessage.setHeaders(headers); or const headers = new Map([['foo', 'bar']]); outgoingMessage.setHeaders(headers); When headers have been set with `outgoingMessage.setHeaders()`, they will be merged with any headers passed to `response.writeHead()`, with the headers passed to `response.writeHead()` given precedence. // Returns content-type = text/plain const server = http.createServer((req, res) => { const headers = new Headers({ 'Content-Type': 'text/html' }); res.setHeaders(headers); res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end('ok'); }); #### `outgoingMessage.setTimeout(msecs[, callback])`# Added in: v0.9.12 * `msecs` * `callback` Optional function to be called when a timeout occurs. Same as binding to the `timeout` event. * Returns: Once a socket is associated with the message and is connected, `socket.setTimeout()` will be called with `msecs` as the first parameter. #### `outgoingMessage.socket`# Added in: v0.3.0 * Type: Reference to the underlying socket. Usually, users will not want to access this property. After calling `outgoingMessage.end()`, this property will be nulled. #### `outgoingMessage.uncork()`# Added in: v13.2.0, v12.16.0 See `writable.uncork()` #### `outgoingMessage.writableCorked`# Added in: v13.2.0, v12.16.0 * Type: The number of times `outgoingMessage.cork()` has been called. #### `outgoingMessage.writableEnded`# Added in: v12.9.0 * Type: Is `true` if `outgoingMessage.end()` has been called. This property does not indicate whether the data has been flushed. For that purpose, use `message.writableFinished` instead. #### `outgoingMessage.writableFinished`# Added in: v12.7.0 * Type: Is `true` if all data has been flushed to the underlying system. #### `outgoingMessage.writableHighWaterMark`# Added in: v12.9.0 * Type: The `highWaterMark` of the underlying socket if assigned. Otherwise, the default buffer level when `writable.write()` starts returning false (`16384`). #### `outgoingMessage.writableLength`# Added in: v12.9.0 * Type: The number of buffered bytes. #### `outgoingMessage.writableObjectMode`# Added in: v12.9.0 * Type: Always `false`. #### `outgoingMessage.write(chunk[, encoding][, callback])`# History VersionChanges v15.0.0 The `chunk` parameter can now be a `Uint8Array`. v0.11.6 The `callback` argument was added. v0.1.29 Added in: v0.1.29 * `chunk` | | * `encoding` Default: `utf8` * `callback` * Returns: Sends a chunk of the body. This method can be called multiple times. The `encoding` argument is only relevant when `chunk` is a string. Defaults to `'utf8'`. The `callback` argument is optional and will be called when this chunk of data is flushed. Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in the user memory. The `'drain'` event will be emitted when the buffer is free again. ### `http.METHODS`# Added in: v0.11.8 * Type: A list of the HTTP methods that are supported by the parser. ### `http.STATUS_CODES`# Added in: v0.1.22 * Type: A collection of all the standard HTTP response status codes, and the short description of each. For example, `http.STATUS_CODES[404] === 'Not Found'`. ### `http.createServer([options][, requestListener])`# History VersionChanges v24.9.0 The `shouldUpgradeCallback` option is now supported. v20.1.0, v18.17.0 The `highWaterMark` option is supported now. v18.0.0 The `requestTimeout`, `headersTimeout`, `keepAliveTimeout`, and `connectionsCheckingInterval` options are supported now. v18.0.0 The `noDelay` option now defaults to `true`. v17.7.0, v16.15.0 The `noDelay`, `keepAlive` and `keepAliveInitialDelay` options are supported now. v13.3.0 The `maxHeaderSize` option is supported now. v13.8.0, v12.15.0, v10.19.0 The `insecureHTTPParser` option is supported now. v9.6.0, v8.12.0 The `options` argument is supported now. v0.1.13 Added in: v0.1.13 * `options` * `connectionsCheckingInterval`: Sets the interval value in milliseconds to check for request and headers timeout in incomplete requests. Default: `30000`. * `headersTimeout`: Sets the timeout value in milliseconds for receiving the complete HTTP headers from the client. See `server.headersTimeout` for more information. Default: `60000`. * `highWaterMark` Optionally overrides all `socket`s' `readableHighWaterMark` and `writableHighWaterMark`. This affects `highWaterMark` property of both `IncomingMessage` and `ServerResponse`. Default: See `stream.getDefaultHighWaterMark()`. * `insecureHTTPParser` If set to `true`, it will use a HTTP parser with leniency flags enabled. Using the insecure parser should be avoided. See `--insecure-http-parser` for more information. Default: `false`. * `IncomingMessage` Specifies the `IncomingMessage` class to be used. Useful for extending the original `IncomingMessage`. Default: `IncomingMessage`. * `joinDuplicateHeaders` If set to `true`, this option allows joining the field line values of multiple headers in a request with a comma (`, `) instead of discarding the duplicates. For more information, refer to `message.headers`. Default: `false`. * `keepAlive` If set to `true`, it enables keep-alive functionality on the socket immediately after a new incoming connection is received, similarly on what is done in [`socket.setKeepAlive([enable][, initialDelay])`][`socket.setKeepAlive(enable, initialDelay)`]. Default: `false`. * `keepAliveInitialDelay` If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket. Default: `0`. * `keepAliveTimeout`: The number of milliseconds of inactivity a server needs to wait for additional incoming data, after it has finished writing the last response, before a socket will be destroyed. See `server.keepAliveTimeout` for more information. Default: `5000`. * `maxHeaderSize` Optionally overrides the value of `--max-http-header-size` for requests received by this server, i.e. the maximum length of request headers in bytes. Default: 16384 (16 KiB). * `noDelay` If set to `true`, it disables the use of Nagle's algorithm immediately after a new incoming connection is received. Default: `true`. * `requestTimeout`: Sets the timeout value in milliseconds for receiving the entire request from the client. See `server.requestTimeout` for more information. Default: `300000`. * `requireHostHeader` If set to `true`, it forces the server to respond with a 400 (Bad Request) status code to any HTTP/1.1 request message that lacks a Host header (as mandated by the specification). Default: `true`. * `ServerResponse` Specifies the `ServerResponse` class to be used. Useful for extending the original `ServerResponse`. Default: `ServerResponse`. * `shouldUpgradeCallback(request)` A callback which receives an incoming request and returns a boolean, to control which upgrade attempts should be accepted. Accepted upgrades will fire an `'upgrade'` event (or their sockets will be destroyed, if no listener is registered) while rejected upgrades will fire a `'request'` event like any non-upgrade request. This options defaults to `() => server.listenerCount('upgrade') > 0`. * `uniqueHeaders` A list of response headers that should be sent only once. If the header's value is an array, the items will be joined using `; `. * `rejectNonStandardBodyWrites` If set to `true`, an error is thrown when writing to an HTTP response which does not have a body. Default: `false`. * `requestListener` * Returns: Returns a new instance of `http.Server`. The `requestListener` is a function which is automatically added to the `'request'` event. import http from 'node:http'; // Create a local server to receive data from const server = http.createServer((req, res) => { res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ data: 'Hello World!', })); }); server.listen(8000); import http from 'node:http'; // Create a local server to receive data from const server = http.createServer(); // Listen to the request event server.on('request', (request, res) => { res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ data: 'Hello World!', })); }); server.listen(8000); ### `http.get(options[, callback])`# ### `http.get(url[, options][, callback])`# History VersionChanges v10.9.0 The `url` parameter can now be passed along with a separate `options` object. v7.5.0 The `options` parameter can be a WHATWG `URL` object. v0.3.6 Added in: v0.3.6 * `url` | * `options` Accepts the same `options` as `http.request()`, with the method set to GET by default. * `callback` * Returns: Since most requests are GET requests without bodies, Node.js provides this convenience method. The only difference between this method and `http.request()` is that it sets the method to GET by default and calls `req.end()` automatically. The callback must take care to consume the response data for reasons stated in `http.ClientRequest` section. The `callback` is invoked with a single argument that is an instance of `http.IncomingMessage`. JSON fetching example: http.get('http://localhost:8000/', (res) => { const { statusCode } = res; const contentType = res.headers['content-type']; let error; // Any 2xx status code signals a successful response but // here we're only checking for 200. if (statusCode !== 200) { error = new Error('Request Failed.\n' + `Status Code: ${statusCode}`); } else if (!/^application\/json/.test(contentType)) { error = new Error('Invalid content-type.\n' + `Expected application/json but received ${contentType}`); } if (error) { console.error(error.message); // Consume response data to free up memory res.resume(); return; } res.setEncoding('utf8'); let rawData = ''; res.on('data', (chunk) => { rawData += chunk; }); res.on('end', () => { try { const parsedData = JSON.parse(rawData); console.log(parsedData); } catch (e) { console.error(e.message); } }); }).on('error', (e) => { console.error(`Got error: ${e.message}`); }); // Create a local server to receive data from const server = http.createServer((req, res) => { res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ data: 'Hello World!', })); }); server.listen(8000); ### `http.globalAgent`# History VersionChanges v19.0.0 The agent now uses HTTP Keep-Alive and a 5 second timeout by default. v0.5.9 Added in: v0.5.9 * Type: Global instance of `Agent` which is used as the default for all HTTP client requests. Diverges from a default `Agent` configuration by having `keepAlive` enabled and a `timeout` of 5 seconds. ### `http.maxHeaderSize`# Added in: v11.6.0, v10.15.0 * Type: Read-only property specifying the maximum allowed size of HTTP headers in bytes. Defaults to 16 KiB. Configurable using the `--max-http-header-size` CLI option. This can be overridden for servers and client requests by passing the `maxHeaderSize` option. ### `http.request(options[, callback])`# ### `http.request(url[, options][, callback])`# History VersionChanges v16.7.0, v14.18.0 When using a `URL` object parsed username and password will now be properly URI decoded. v15.3.0, v14.17.0 It is possible to abort a request with an AbortSignal. v13.3.0 The `maxHeaderSize` option is supported now. v13.8.0, v12.15.0, v10.19.0 The `insecureHTTPParser` option is supported now. v10.9.0 The `url` parameter can now be passed along with a separate `options` object. v7.5.0 The `options` parameter can be a WHATWG `URL` object. v0.3.6 Added in: v0.3.6 * `url` | * `options` * `agent` | Controls `Agent` behavior. Possible values: * `undefined` (default): use `http.globalAgent` for this host and port. * `Agent` object: explicitly use the passed in `Agent`. * `false`: causes a new `Agent` with default values to be used. * `auth` Basic authentication (`'user:password'`) to compute an Authorization header. * `createConnection` A function that produces a socket/stream to use for the request when the `agent` option is not used. This can be used to avoid creating a custom `Agent` class just to override the default `createConnection` function. See `agent.createConnection()` for more details. Any `Duplex` stream is a valid return value. * `defaultPort` Default port for the protocol. Default: `agent.defaultPort` if an `Agent` is used, else `undefined`. * `family` IP address family to use when resolving `host` or `hostname`. Valid values are `4` or `6`. When unspecified, both IP v4 and v6 will be used. * `headers` | An object or an array of strings containing request headers. The array is in the same format as `message.rawHeaders`. * `hints` Optional `dns.lookup()` hints. * `host` A domain name or IP address of the server to issue the request to. Default: `'localhost'`. * `hostname` Alias for `host`. To support `url.parse()`, `hostname` will be used if both `host` and `hostname` are specified. * `insecureHTTPParser` If set to `true`, it will use a HTTP parser with leniency flags enabled. Using the insecure parser should be avoided. See `--insecure-http-parser` for more information. Default: `false` * `joinDuplicateHeaders` It joins the field line values of multiple headers in a request with `, ` instead of discarding the duplicates. See `message.headers` for more information. Default: `false`. * `localAddress` Local interface to bind for network connections. * `localPort` Local port to connect from. * `lookup` Custom lookup function. Default: `dns.lookup()`. * `maxHeaderSize` Optionally overrides the value of `--max-http-header-size` (the maximum length of response headers in bytes) for responses received from the server. Default: 16384 (16 KiB). * `method` A string specifying the HTTP request method. Default: `'GET'`. * `path` Request path. Should include query string if any. E.G. `'/index.html?page=12'`. An exception is thrown when the request path contains illegal characters. Currently, only spaces are rejected but that may change in the future. Default: `'/'`. * `port` Port of remote server. Default: `defaultPort` if set, else `80`. * `protocol` Protocol to use. Default: `'http:'`. * `setDefaultHeaders` : Specifies whether or not to automatically add default headers such as `Connection`, `Content-Length`, `Transfer-Encoding`, and `Host`. If set to `false` then all necessary headers must be added manually. Defaults to `true`. * `setHost` : Specifies whether or not to automatically add the `Host` header. If provided, this overrides `setDefaultHeaders`. Defaults to `true`. * `signal` : An AbortSignal that may be used to abort an ongoing request. * `socketPath` Unix domain socket. Cannot be used if one of `host` or `port` is specified, as those specify a TCP Socket. * `timeout` : A number specifying the socket timeout in milliseconds. This will set the timeout before the socket is connected. * `uniqueHeaders` A list of request headers that should be sent only once. If the header's value is an array, the items will be joined using `; `. * `callback` * Returns: `options` in `socket.connect()` are also supported. Node.js maintains several connections per server to make HTTP requests. This function allows one to transparently issue requests. `url` can be a string or a `URL` object. If `url` is a string, it is automatically parsed with `new URL()`. If it is a `URL` object, it will be automatically converted to an ordinary `options` object. If both `url` and `options` are specified, the objects are merged, with the `options` properties taking precedence. The optional `callback` parameter will be added as a one-time listener for the `'response'` event. `http.request()` returns an instance of the `http.ClientRequest` class. The `ClientRequest` instance is a writable stream. If one needs to upload a file with a POST request, then write to the `ClientRequest` object. import http from 'node:http'; import { Buffer } from 'node:buffer'; const postData = JSON.stringify({ 'msg': 'Hello World!', }); const options = { hostname: 'www.google.com', port: 80, path: '/upload', method: 'POST', headers: { 'Content-Type': 'application/json', 'Content-Length': Buffer.byteLength(postData), }, }; const req = http.request(options, (res) => { console.log(`STATUS: ${res.statusCode}`); console.log(`HEADERS: ${JSON.stringify(res.headers)}`); res.setEncoding('utf8'); res.on('data', (chunk) => { console.log(`BODY: ${chunk}`); }); res.on('end', () => { console.log('No more data in response.'); }); }); req.on('error', (e) => { console.error(`problem with request: ${e.message}`); }); // Write data to request body req.write(postData); req.end(); In the example `req.end()` was called. With `http.request()` one must always call `req.end()` to signify the end of the request - even if there is no data being written to the request body. If any error is encountered during the request (be that with DNS resolution, TCP level errors, or actual HTTP parse errors) an `'error'` event is emitted on the returned request object. As with all `'error'` events, if no listeners are registered the error will be thrown. There are a few special headers that should be noted. * Sending a 'Connection: keep-alive' will notify Node.js that the connection to the server should be persisted until the next request. * Sending a 'Content-Length' header will disable the default chunked encoding. * Sending an 'Expect' header will immediately send the request headers. Usually, when sending 'Expect: 100-continue', both a timeout and a listener for the `'continue'` event should be set. See RFC 2616 Section 8.2.3 for more information. * Sending an Authorization header will override using the `auth` option to compute basic authentication. Example using a `URL` as `options`: const options = new URL('http://abc:[email protected]'); const req = http.request(options, (res) => { // ... }); In a successful request, the following events will be emitted in the following order: * `'socket'` * `'response'` * `'data'` any number of times, on the `res` object (`'data'` will not be emitted at all if the response body is empty, for instance, in most redirects) * `'end'` on the `res` object * `'close'` In the case of a connection error, the following events will be emitted: * `'socket'` * `'error'` * `'close'` In the case of a premature connection close before the response is received, the following events will be emitted in the following order: * `'socket'` * `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'` * `'close'` In the case of a premature connection close after the response is received, the following events will be emitted in the following order: * `'socket'` * `'response'` * `'data'` any number of times, on the `res` object * (connection closed here) * `'aborted'` on the `res` object * `'close'` * `'error'` on the `res` object with an error with message `'Error: aborted'` and code `'ECONNRESET'` * `'close'` on the `res` object If `req.destroy()` is called before a socket is assigned, the following events will be emitted in the following order: * (`req.destroy()` called here) * `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'`, or the error with which `req.destroy()` was called * `'close'` If `req.destroy()` is called before the connection succeeds, the following events will be emitted in the following order: * `'socket'` * (`req.destroy()` called here) * `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'`, or the error with which `req.destroy()` was called * `'close'` If `req.destroy()` is called after the response is received, the following events will be emitted in the following order: * `'socket'` * `'response'` * `'data'` any number of times, on the `res` object * (`req.destroy()` called here) * `'aborted'` on the `res` object * `'close'` * `'error'` on the `res` object with an error with message `'Error: aborted'` and code `'ECONNRESET'`, or the error with which `req.destroy()` was called * `'close'` on the `res` object If `req.abort()` is called before a socket is assigned, the following events will be emitted in the following order: * (`req.abort()` called here) * `'abort'` * `'close'` If `req.abort()` is called before the connection succeeds, the following events will be emitted in the following order: * `'socket'` * (`req.abort()` called here) * `'abort'` * `'error'` with an error with message `'Error: socket hang up'` and code `'ECONNRESET'` * `'close'` If `req.abort()` is called after the response is received, the following events will be emitted in the following order: * `'socket'` * `'response'` * `'data'` any number of times, on the `res` object * (`req.abort()` called here) * `'abort'` * `'aborted'` on the `res` object * `'error'` on the `res` object with an error with message `'Error: aborted'` and code `'ECONNRESET'`. * `'close'` * `'close'` on the `res` object Setting the `timeout` option or using the `setTimeout()` function will not abort the request or do anything besides add a `'timeout'` event. Passing an `AbortSignal` and then calling `abort()` on the corresponding `AbortController` will behave the same way as calling `.destroy()` on the request. Specifically, the `'error'` event will be emitted with an error with the message `'AbortError: The operation was aborted'`, the code `'ABORT_ERR'` and the `cause`, if one was provided. ### `http.validateHeaderName(name[, label])`# History VersionChanges v19.5.0, v18.14.0 The `label` parameter is added. v14.3.0 Added in: v14.3.0 * `name` * `label` Label for error message. Default: `'Header name'`. Performs the low-level validations on the provided `name` that are done when `res.setHeader(name, value)` is called. Passing illegal value as `name` will result in a `TypeError` being thrown, identified by `code: 'ERR_INVALID_HTTP_TOKEN'`. It is not necessary to use this method before passing headers to an HTTP request or response. The HTTP module will automatically validate such headers. Example: import { validateHeaderName } from 'node:http'; try { validateHeaderName(''); } catch (err) { console.error(err instanceof TypeError); // --> true console.error(err.code); // --> 'ERR_INVALID_HTTP_TOKEN' console.error(err.message); // --> 'Header name must be a valid HTTP token [""]' } ### `http.validateHeaderValue(name, value)`# Added in: v14.3.0 * `name` * `value` Performs the low-level validations on the provided `value` that are done when `res.setHeader(name, value)` is called. Passing illegal value as `value` will result in a `TypeError` being thrown. * Undefined value error is identified by `code: 'ERR_HTTP_INVALID_HEADER_VALUE'`. * Invalid value character error is identified by `code: 'ERR_INVALID_CHAR'`. It is not necessary to use this method before passing headers to an HTTP request or response. The HTTP module will automatically validate such headers. Examples: import { validateHeaderValue } from 'node:http'; try { validateHeaderValue('x-my-header', undefined); } catch (err) { console.error(err instanceof TypeError); // --> true console.error(err.code === 'ERR_HTTP_INVALID_HEADER_VALUE'); // --> true console.error(err.message); // --> 'Invalid value "undefined" for header "x-my-header"' } try { validateHeaderValue('x-my-header', 'oʊmɪɡə'); } catch (err) { console.error(err instanceof TypeError); // --> true console.error(err.code === 'ERR_INVALID_CHAR'); // --> true console.error(err.message); // --> 'Invalid character in header content ["x-my-header"]' } ### `http.setMaxIdleHTTPParsers(max)`# Added in: v18.8.0, v16.18.0 * `max` Default: `1000`. Set the maximum number of idle HTTP parsers. ### Class: `WebSocket`# Added in: v22.5.0 A browser-compatible implementation of . ### Built-in Proxy Support# Added in: v24.5.0 Stability: 1.1 \- Active development When Node.js creates the global agent, if the `NODE_USE_ENV_PROXY` environment variable is set to `1` or `--use-env-proxy` is enabled, the global agent will be constructed with `proxyEnv: process.env`, enabling proxy support based on the environment variables. Custom agents can also be created with proxy support by passing a `proxyEnv` option when constructing the agent. The value can be `process.env` if they just want to inherit the configuration from the environment variables, or an object with specific setting overriding the environment. The following properties of the `proxyEnv` are checked to configure proxy support. * `HTTP_PROXY` or `http_proxy`: Proxy server URL for HTTP requests. If both are set, `http_proxy` takes precedence. * `HTTPS_PROXY` or `https_proxy`: Proxy server URL for HTTPS requests. If both are set, `https_proxy` takes precedence. * `NO_PROXY` or `no_proxy`: Comma-separated list of hosts to bypass the proxy. If both are set, `no_proxy` takes precedence. If the request is made to a Unix domain socket, the proxy settings will be ignored. #### Proxy URL Format# Proxy URLs can use either HTTP or HTTPS protocols: * HTTP proxy: `http://proxy.example.com:8080` * HTTPS proxy: `https://proxy.example.com:8080` * Proxy with authentication: `http://username:[email protected]:8080` #### `NO_PROXY` Format# The `NO_PROXY` environment variable supports several formats: * `*` \- Bypass proxy for all hosts * `example.com` \- Exact host name match * `.example.com` \- Domain suffix match (matches `sub.example.com`) * `*.example.com` \- Wildcard domain match * `192.168.1.100` \- Exact IP address match * `192.168.1.1-192.168.1.100` \- IP address range * `example.com:8080` \- Hostname with specific port Multiple entries should be separated by commas. #### Example# To start a Node.js process with proxy support enabled for all requests sent through the default global agent, either use the `NODE_USE_ENV_PROXY` environment variable: NODE_USE_ENV_PROXY=1 HTTP_PROXY=http://proxy.example.com:8080 NO_PROXY=localhost,127.0.0.1 node client.js Or the `--use-env-proxy` flag. HTTP_PROXY=http://proxy.example.com:8080 NO_PROXY=localhost,127.0.0.1 node --use-env-proxy client.js To create a custom agent with built-in proxy support: Alternatively, the following also works: ## HTTP/2# History VersionChanges v15.0.0 Requests with the `host` header (with or without `:authority`) can now be sent/received. v15.3.0, v14.17.0 It is possible to abort a request with an AbortSignal. v10.10.0 HTTP/2 is now Stable. Previously, it had been Experimental. v8.4.0 Added in: v8.4.0 Stability: 2 \- Stable Source Code: lib/http2.js The `node:http2` module provides an implementation of the HTTP/2 protocol. It can be accessed using: const http2 = require('node:http2'); ### Determining if crypto support is unavailable# It is possible for Node.js to be built without including support for the `node:crypto` module. In such cases, attempting to `import` from `node:http2` or calling `require('node:http2')` will result in an error being thrown. When using CommonJS, the error thrown can be caught using try/catch: When using the lexical ESM `import` keyword, the error can only be caught if a handler for `process.on('uncaughtException')` is registered before any attempt to load the module is made (using, for instance, a preload module). When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the `import()` function instead of the lexical `import` keyword: let http2; try { http2 = await import('node:http2'); } catch (err) { console.error('http2 support is disabled!'); } ### Core API# The Core API provides a low-level interface designed specifically around support for HTTP/2 protocol features. It is specifically not designed for compatibility with the existing HTTP/1 module API. However, the Compatibility API is. The `http2` Core API is much more symmetric between client and server than the `http` API. For instance, most events, like `'error'`, `'connect'` and `'stream'`, can be emitted either by client-side code or server-side code. #### Server-side example# The following illustrates a simple HTTP/2 server using the Core API. Since there are no browsers known that support unencrypted HTTP/2, the use of `http2.createSecureServer()` is necessary when communicating with browser clients. import { createSecureServer } from 'node:http2'; import { readFileSync } from 'node:fs'; const server = createSecureServer({ key: readFileSync('localhost-privkey.pem'), cert: readFileSync('localhost-cert.pem'), }); server.on('error', (err) => console.error(err)); server.on('stream', (stream, headers) => { // stream is a Duplex stream.respond({ 'content-type': 'text/html; charset=utf-8', ':status': 200, }); stream.end('

Hello World

'); }); server.listen(8443); To generate the certificate and key for this example, run: openssl req -x509 -newkey rsa:2048 -nodes -sha256 -subj '/CN=localhost' \ -keyout localhost-privkey.pem -out localhost-cert.pem #### Client-side example# The following illustrates an HTTP/2 client: import { connect } from 'node:http2'; import { readFileSync } from 'node:fs'; const client = connect('https://localhost:8443', { ca: readFileSync('localhost-cert.pem'), }); client.on('error', (err) => console.error(err)); const req = client.request({ ':path': '/' }); req.on('response', (headers, flags) => { for (const name in headers) { console.log(`${name}: ${headers[name]}`); } }); req.setEncoding('utf8'); let data = ''; req.on('data', (chunk) => { data += chunk; }); req.on('end', () => { console.log(`\n${data}`); client.close(); }); req.end(); #### Class: `Http2Session`# Added in: v8.4.0 * Extends: Instances of the `http2.Http2Session` class represent an active communications session between an HTTP/2 client and server. Instances of this class are not intended to be constructed directly by user code. Each `Http2Session` instance will exhibit slightly different behaviors depending on whether it is operating as a server or a client. The `http2session.type` property can be used to determine the mode in which an `Http2Session` is operating. On the server side, user code should rarely have occasion to work with the `Http2Session` object directly, with most actions typically taken through interactions with either the `Http2Server` or `Http2Stream` objects. User code will not create `Http2Session` instances directly. Server-side `Http2Session` instances are created by the `Http2Server` instance when a new HTTP/2 connection is received. Client-side `Http2Session` instances are created using the `http2.connect()` method. ##### `Http2Session` and sockets# Every `Http2Session` instance is associated with exactly one `net.Socket` or `tls.TLSSocket` when it is created. When either the `Socket` or the `Http2Session` are destroyed, both will be destroyed. Because of the specific serialization and processing requirements imposed by the HTTP/2 protocol, it is not recommended for user code to read data from or write data to a `Socket` instance bound to a `Http2Session`. Doing so can put the HTTP/2 session into an indeterminate state causing the session and the socket to become unusable. Once a `Socket` has been bound to an `Http2Session`, user code should rely solely on the API of the `Http2Session`. ##### Event: `'close'`# Added in: v8.4.0 The `'close'` event is emitted once the `Http2Session` has been destroyed. Its listener does not expect any arguments. ##### Event: `'connect'`# Added in: v8.4.0 * `session` * `socket` The `'connect'` event is emitted once the `Http2Session` has been successfully connected to the remote peer and communication may begin. User code will typically not listen for this event directly. ##### Event: `'error'`# Added in: v8.4.0 * `error` The `'error'` event is emitted when an error occurs during the processing of an `Http2Session`. ##### Event: `'frameError'`# Added in: v8.4.0 * `type` The frame type. * `code` The error code. * `id` The stream id (or `0` if the frame isn't associated with a stream). The `'frameError'` event is emitted when an error occurs while attempting to send a frame on the session. If the frame that could not be sent is associated with a specific `Http2Stream`, an attempt to emit a `'frameError'` event on the `Http2Stream` is made. If the `'frameError'` event is associated with a stream, the stream will be closed and destroyed immediately following the `'frameError'` event. If the event is not associated with a stream, the `Http2Session` will be shut down immediately following the `'frameError'` event. ##### Event: `'goaway'`# Added in: v8.4.0 * `errorCode` The HTTP/2 error code specified in the `GOAWAY` frame. * `lastStreamID` The ID of the last stream the remote peer successfully processed (or `0` if no ID is specified). * `opaqueData` If additional opaque data was included in the `GOAWAY` frame, a `Buffer` instance will be passed containing that data. The `'goaway'` event is emitted when a `GOAWAY` frame is received. The `Http2Session` instance will be shut down automatically when the `'goaway'` event is emitted. ##### Event: `'localSettings'`# Added in: v8.4.0 * `settings` A copy of the `SETTINGS` frame received. The `'localSettings'` event is emitted when an acknowledgment `SETTINGS` frame has been received. When using `http2session.settings()` to submit new settings, the modified settings do not take effect until the `'localSettings'` event is emitted. session.settings({ enablePush: false }); session.on('localSettings', (settings) => { /* Use the new settings */ }); ##### Event: `'ping'`# Added in: v10.12.0 * `payload` The `PING` frame 8-byte payload The `'ping'` event is emitted whenever a `PING` frame is received from the connected peer. ##### Event: `'remoteSettings'`# Added in: v8.4.0 * `settings` A copy of the `SETTINGS` frame received. The `'remoteSettings'` event is emitted when a new `SETTINGS` frame is received from the connected peer. session.on('remoteSettings', (settings) => { /* Use the new settings */ }); ##### Event: `'stream'`# Added in: v8.4.0 * `stream` A reference to the stream * `headers` An object describing the headers * `flags` The associated numeric flags * `rawHeaders` An array containing the raw headers The `'stream'` event is emitted when a new `Http2Stream` is created. session.on('stream', (stream, headers, flags) => { const method = headers[':method']; const path = headers[':path']; // ... stream.respond({ ':status': 200, 'content-type': 'text/plain; charset=utf-8', }); stream.write('hello '); stream.end('world'); }); On the server side, user code will typically not listen for this event directly, and would instead register a handler for the `'stream'` event emitted by the `net.Server` or `tls.Server` instances returned by `http2.createServer()` and `http2.createSecureServer()`, respectively, as in the example below: import { createServer } from 'node:http2'; // Create an unencrypted HTTP/2 server const server = createServer(); server.on('stream', (stream, headers) => { stream.respond({ 'content-type': 'text/html; charset=utf-8', ':status': 200, }); stream.on('error', (error) => console.error(error)); stream.end('

Hello World

'); }); server.listen(8000); Even though HTTP/2 streams and network sockets are not in a 1:1 correspondence, a network error will destroy each individual stream and must be handled on the stream level, as shown above. ##### Event: `'timeout'`# Added in: v8.4.0 After the `http2session.setTimeout()` method is used to set the timeout period for this `Http2Session`, the `'timeout'` event is emitted if there is no activity on the `Http2Session` after the configured number of milliseconds. Its listener does not expect any arguments. session.setTimeout(2000); session.on('timeout', () => { /* .. */ }); ##### `http2session.alpnProtocol`# Added in: v9.4.0 * Type: | Value will be `undefined` if the `Http2Session` is not yet connected to a socket, `h2c` if the `Http2Session` is not connected to a `TLSSocket`, or will return the value of the connected `TLSSocket`'s own `alpnProtocol` property. ##### `http2session.close([callback])`# Added in: v9.4.0 * `callback` Gracefully closes the `Http2Session`, allowing any existing streams to complete on their own and preventing new `Http2Stream` instances from being created. Once closed, `http2session.destroy()` might be called if there are no open `Http2Stream` instances. If specified, the `callback` function is registered as a handler for the `'close'` event. ##### `http2session.closed`# Added in: v9.4.0 * Type: Will be `true` if this `Http2Session` instance has been closed, otherwise `false`. ##### `http2session.connecting`# Added in: v10.0.0 * Type: Will be `true` if this `Http2Session` instance is still connecting, will be set to `false` before emitting `connect` event and/or calling the `http2.connect` callback. ##### `http2session.destroy([error][, code])`# Added in: v8.4.0 * `error` An `Error` object if the `Http2Session` is being destroyed due to an error. * `code` The HTTP/2 error code to send in the final `GOAWAY` frame. If unspecified, and `error` is not undefined, the default is `INTERNAL_ERROR`, otherwise defaults to `NO_ERROR`. Immediately terminates the `Http2Session` and the associated `net.Socket` or `tls.TLSSocket`. Once destroyed, the `Http2Session` will emit the `'close'` event. If `error` is not undefined, an `'error'` event will be emitted immediately before the `'close'` event. If there are any remaining open `Http2Streams` associated with the `Http2Session`, those will also be destroyed. ##### `http2session.destroyed`# Added in: v8.4.0 * Type: Will be `true` if this `Http2Session` instance has been destroyed and must no longer be used, otherwise `false`. ##### `http2session.encrypted`# Added in: v9.4.0 * Type: | Value is `undefined` if the `Http2Session` session socket has not yet been connected, `true` if the `Http2Session` is connected with a `TLSSocket`, and `false` if the `Http2Session` is connected to any other kind of socket or stream. ##### `http2session.goaway([code[, lastStreamID[, opaqueData]]])`# Added in: v9.4.0 * `code` An HTTP/2 error code * `lastStreamID` The numeric ID of the last processed `Http2Stream` * `opaqueData` | | A `TypedArray` or `DataView` instance containing additional data to be carried within the `GOAWAY` frame. Transmits a `GOAWAY` frame to the connected peer without shutting down the `Http2Session`. ##### `http2session.localSettings`# Added in: v8.4.0 * Type: A prototype-less object describing the current local settings of this `Http2Session`. The local settings are local to this `Http2Session` instance. ##### `http2session.originSet`# Added in: v9.4.0 * Type: | If the `Http2Session` is connected to a `TLSSocket`, the `originSet` property will return an `Array` of origins for which the `Http2Session` may be considered authoritative. The `originSet` property is only available when using a secure TLS connection. ##### `http2session.pendingSettingsAck`# Added in: v8.4.0 * Type: Indicates whether the `Http2Session` is currently waiting for acknowledgment of a sent `SETTINGS` frame. Will be `true` after calling the `http2session.settings()` method. Will be `false` once all sent `SETTINGS` frames have been acknowledged. ##### `http2session.ping([payload, ]callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.9.3 Added in: v8.9.3 * `payload` | | Optional ping payload. * `callback` * Returns: Sends a `PING` frame to the connected HTTP/2 peer. A `callback` function must be provided. The method will return `true` if the `PING` was sent, `false` otherwise. The maximum number of outstanding (unacknowledged) pings is determined by the `maxOutstandingPings` configuration option. The default maximum is 10. If provided, the `payload` must be a `Buffer`, `TypedArray`, or `DataView` containing 8 bytes of data that will be transmitted with the `PING` and returned with the ping acknowledgment. The callback will be invoked with three arguments: an error argument that will be `null` if the `PING` was successfully acknowledged, a `duration` argument that reports the number of milliseconds elapsed since the ping was sent and the acknowledgment was received, and a `Buffer` containing the 8-byte `PING` payload. session.ping(Buffer.from('abcdefgh'), (err, duration, payload) => { if (!err) { console.log(`Ping acknowledged in ${duration} milliseconds`); console.log(`With payload '${payload.toString()}'`); } }); If the `payload` argument is not specified, the default payload will be the 64-bit timestamp (little endian) marking the start of the `PING` duration. ##### `http2session.ref()`# Added in: v9.4.0 Calls `ref()` on this `Http2Session` instance's underlying `net.Socket`. ##### `http2session.remoteSettings`# Added in: v8.4.0 * Type: A prototype-less object describing the current remote settings of this `Http2Session`. The remote settings are set by the connected HTTP/2 peer. ##### `http2session.setLocalWindowSize(windowSize)`# Added in: v15.3.0, v14.18.0 * `windowSize` Sets the local endpoint's window size. The `windowSize` is the total window size to set, not the delta. import { createServer } from 'node:http2'; const server = createServer(); const expectedWindowSize = 2 ** 20; server.on('session', (session) => { // Set local window size to be 2 ** 20 session.setLocalWindowSize(expectedWindowSize); }); For http2 clients the proper event is either `'connect'` or `'remoteSettings'`. ##### `http2session.setTimeout(msecs, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.4.0 Added in: v8.4.0 * `msecs` * `callback` Used to set a callback function that is called when there is no activity on the `Http2Session` after `msecs` milliseconds. The given `callback` is registered as a listener on the `'timeout'` event. ##### `http2session.socket`# Added in: v8.4.0 * Type: | Returns a `Proxy` object that acts as a `net.Socket` (or `tls.TLSSocket`) but limits available methods to ones safe to use with HTTP/2. `destroy`, `emit`, `end`, `pause`, `read`, `resume`, and `write` will throw an error with code `ERR_HTTP2_NO_SOCKET_MANIPULATION`. See `Http2Session` and Sockets for more information. `setTimeout` method will be called on this `Http2Session`. All other interactions will be routed directly to the socket. ##### `http2session.state`# Added in: v8.4.0 Provides miscellaneous information about the current state of the `Http2Session`. * Type: * `effectiveLocalWindowSize` The current local (receive) flow control window size for the `Http2Session`. * `effectiveRecvDataLength` The current number of bytes that have been received since the last flow control `WINDOW_UPDATE`. * `nextStreamID` The numeric identifier to be used the next time a new `Http2Stream` is created by this `Http2Session`. * `localWindowSize` The number of bytes that the remote peer can send without receiving a `WINDOW_UPDATE`. * `lastProcStreamID` The numeric id of the `Http2Stream` for which a `HEADERS` or `DATA` frame was most recently received. * `remoteWindowSize` The number of bytes that this `Http2Session` may send without receiving a `WINDOW_UPDATE`. * `outboundQueueSize` The number of frames currently within the outbound queue for this `Http2Session`. * `deflateDynamicTableSize` The current size in bytes of the outbound header compression state table. * `inflateDynamicTableSize` The current size in bytes of the inbound header compression state table. An object describing the current status of this `Http2Session`. ##### `http2session.settings([settings][, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.4.0 Added in: v8.4.0 * `settings` * `callback` Callback that is called once the session is connected or right away if the session is already connected. * `err` | * `settings` The updated `settings` object. * `duration` Updates the current local settings for this `Http2Session` and sends a new `SETTINGS` frame to the connected HTTP/2 peer. Once called, the `http2session.pendingSettingsAck` property will be `true` while the session is waiting for the remote peer to acknowledge the new settings. The new settings will not become effective until the `SETTINGS` acknowledgment is received and the `'localSettings'` event is emitted. It is possible to send multiple `SETTINGS` frames while acknowledgment is still pending. ##### `http2session.type`# Added in: v8.4.0 * Type: The `http2session.type` will be equal to `http2.constants.NGHTTP2_SESSION_SERVER` if this `Http2Session` instance is a server, and `http2.constants.NGHTTP2_SESSION_CLIENT` if the instance is a client. ##### `http2session.unref()`# Added in: v9.4.0 Calls `unref()` on this `Http2Session` instance's underlying `net.Socket`. #### Class: `ServerHttp2Session`# Added in: v8.4.0 * Extends: ##### `serverhttp2session.altsvc(alt, originOrStream)`# Added in: v9.4.0 * `alt` A description of the alternative service configuration as defined by RFC 7838. * `originOrStream` | | | Either a URL string specifying the origin (or an `Object` with an `origin` property) or the numeric identifier of an active `Http2Stream` as given by the `http2stream.id` property. Submits an `ALTSVC` frame (as defined by RFC 7838) to the connected client. import { createServer } from 'node:http2'; const server = createServer(); server.on('session', (session) => { // Set altsvc for origin https://example.org:80 session.altsvc('h2=":8000"', 'https://example.org:80'); }); server.on('stream', (stream) => { // Set altsvc for a specific stream stream.session.altsvc('h2=":8000"', stream.id); }); Sending an `ALTSVC` frame with a specific stream ID indicates that the alternate service is associated with the origin of the given `Http2Stream`. The `alt` and origin string must contain only ASCII bytes and are strictly interpreted as a sequence of ASCII bytes. The special value `'clear'` may be passed to clear any previously set alternative service for a given domain. When a string is passed for the `originOrStream` argument, it will be parsed as a URL and the origin will be derived. For instance, the origin for the HTTP URL `'https://example.org/foo/bar'` is the ASCII string `'https://example.org'`. An error will be thrown if either the given string cannot be parsed as a URL or if a valid origin cannot be derived. A `URL` object, or any object with an `origin` property, may be passed as `originOrStream`, in which case the value of the `origin` property will be used. The value of the `origin` property must be a properly serialized ASCII origin. ##### Specifying alternative services# The format of the `alt` parameter is strictly defined by RFC 7838 as an ASCII string containing a comma-delimited list of "alternative" protocols associated with a specific host and port. For example, the value `'h2="example.org:81"'` indicates that the HTTP/2 protocol is available on the host `'example.org'` on TCP/IP port 81. The host and port must be contained within the quote (`"`) characters. Multiple alternatives may be specified, for instance: `'h2="example.org:81", h2=":82"'`. The protocol identifier (`'h2'` in the examples) may be any valid ALPN Protocol ID. The syntax of these values is not validated by the Node.js implementation and are passed through as provided by the user or received from the peer. ##### `serverhttp2session.origin(...origins)`# Added in: v10.12.0 * `origins` | | One or more URL Strings passed as separate arguments. Submits an `ORIGIN` frame (as defined by RFC 8336) to the connected client to advertise the set of origins for which the server is capable of providing authoritative responses. import { createSecureServer } from 'node:http2'; const options = getSecureOptionsSomehow(); const server = createSecureServer(options); server.on('stream', (stream) => { stream.respond(); stream.end('ok'); }); server.on('session', (session) => { session.origin('https://example.com', 'https://example.org'); }); When a string is passed as an `origin`, it will be parsed as a URL and the origin will be derived. For instance, the origin for the HTTP URL `'https://example.org/foo/bar'` is the ASCII string `'https://example.org'`. An error will be thrown if either the given string cannot be parsed as a URL or if a valid origin cannot be derived. A `URL` object, or any object with an `origin` property, may be passed as an `origin`, in which case the value of the `origin` property will be used. The value of the `origin` property must be a properly serialized ASCII origin. Alternatively, the `origins` option may be used when creating a new HTTP/2 server using the `http2.createSecureServer()` method: import { createSecureServer } from 'node:http2'; const options = getSecureOptionsSomehow(); options.origins = ['https://example.com', 'https://example.org']; const server = createSecureServer(options); server.on('stream', (stream) => { stream.respond(); stream.end('ok'); }); #### Class: `ClientHttp2Session`# Added in: v8.4.0 * Extends: ##### Event: `'altsvc'`# Added in: v9.4.0 * `alt` * `origin` * `streamId` The `'altsvc'` event is emitted whenever an `ALTSVC` frame is received by the client. The event is emitted with the `ALTSVC` value, origin, and stream ID. If no `origin` is provided in the `ALTSVC` frame, `origin` will be an empty string. import { connect } from 'node:http2'; const client = connect('https://example.org'); client.on('altsvc', (alt, origin, streamId) => { console.log(alt); console.log(origin); console.log(streamId); }); ##### Event: `'origin'`# Added in: v10.12.0 * `origins` The `'origin'` event is emitted whenever an `ORIGIN` frame is received by the client. The event is emitted with an array of `origin` strings. The `http2session.originSet` will be updated to include the received origins. import { connect } from 'node:http2'; const client = connect('https://example.org'); client.on('origin', (origins) => { for (let n = 0; n < origins.length; n++) console.log(origins[n]); }); The `'origin'` event is only emitted when using a secure TLS connection. ##### `clienthttp2session.request(headers[, options])`# History VersionChanges v24.2.0 The `weight` option is now ignored, setting it will trigger a runtime warning. v24.2.0 Following the deprecation of priority signaling as of RFC 9113, `weight` option is deprecated. v24.0.0, v22.17.0 Allow passing headers in raw array format. v8.4.0 Added in: v8.4.0 * `headers` | * `options` * `endStream` `true` if the `Http2Stream` writable side should be closed initially, such as when sending a `GET` request that should not expect a payload body. * `exclusive` When `true` and `parent` identifies a parent Stream, the created stream is made the sole direct dependency of the parent, with all other existing dependents made a dependent of the newly created stream. Default: `false`. * `parent` Specifies the numeric identifier of a stream the newly created stream is dependent on. * `waitForTrailers` When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent. * `signal` An AbortSignal that may be used to abort an ongoing request. * Returns: For HTTP/2 Client `Http2Session` instances only, the `http2session.request()` creates and returns an `Http2Stream` instance that can be used to send an HTTP/2 request to the connected server. When a `ClientHttp2Session` is first created, the socket may not yet be connected. if `clienthttp2session.request()` is called during this time, the actual request will be deferred until the socket is ready to go. If the `session` is closed before the actual request be executed, an `ERR_HTTP2_GOAWAY_SESSION` is thrown. This method is only available if `http2session.type` is equal to `http2.constants.NGHTTP2_SESSION_CLIENT`. import { connect, constants } from 'node:http2'; const clientSession = connect('https://localhost:1234'); const { HTTP2_HEADER_PATH, HTTP2_HEADER_STATUS, } = constants; const req = clientSession.request({ [HTTP2_HEADER_PATH]: '/' }); req.on('response', (headers) => { console.log(headers[HTTP2_HEADER_STATUS]); req.on('data', (chunk) => { /* .. */ }); req.on('end', () => { /* .. */ }); }); When the `options.waitForTrailers` option is set, the `'wantTrailers'` event is emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be called to send trailing headers to the peer. When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code must call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`. When `options.signal` is set with an `AbortSignal` and then `abort` on the corresponding `AbortController` is called, the request will emit an `'error'` event with an `AbortError` error. The `:method` and `:path` pseudo-headers are not specified within `headers`, they respectively default to: * `:method` = `'GET'` * `:path` = `/` #### Class: `Http2Stream`# Added in: v8.4.0 * Extends: Each instance of the `Http2Stream` class represents a bidirectional HTTP/2 communications stream over an `Http2Session` instance. Any single `Http2Session` may have up to 231-1 `Http2Stream` instances over its lifetime. User code will not construct `Http2Stream` instances directly. Rather, these are created, managed, and provided to user code through the `Http2Session` instance. On the server, `Http2Stream` instances are created either in response to an incoming HTTP request (and handed off to user code via the `'stream'` event), or in response to a call to the `http2stream.pushStream()` method. On the client, `Http2Stream` instances are created and returned when either the `http2session.request()` method is called, or in response to an incoming `'push'` event. The `Http2Stream` class is a base for the `ServerHttp2Stream` and `ClientHttp2Stream` classes, each of which is used specifically by either the Server or Client side, respectively. All `Http2Stream` instances are `Duplex` streams. The `Writable` side of the `Duplex` is used to send data to the connected peer, while the `Readable` side is used to receive data sent by the connected peer. The default text character encoding for an `Http2Stream` is UTF-8. When using an `Http2Stream` to send text, use the `'content-type'` header to set the character encoding. stream.respond({ 'content-type': 'text/html; charset=utf-8', ':status': 200, }); ##### `Http2Stream` Lifecycle# ###### Creation# On the server side, instances of `ServerHttp2Stream` are created either when: * A new HTTP/2 `HEADERS` frame with a previously unused stream ID is received; * The `http2stream.pushStream()` method is called. On the client side, instances of `ClientHttp2Stream` are created when the `http2session.request()` method is called. On the client, the `Http2Stream` instance returned by `http2session.request()` may not be immediately ready for use if the parent `Http2Session` has not yet been fully established. In such cases, operations called on the `Http2Stream` will be buffered until the `'ready'` event is emitted. User code should rarely, if ever, need to handle the `'ready'` event directly. The ready status of an `Http2Stream` can be determined by checking the value of `http2stream.id`. If the value is `undefined`, the stream is not yet ready for use. ###### Destruction# All `Http2Stream` instances are destroyed either when: * An `RST_STREAM` frame for the stream is received by the connected peer, and (for client streams only) pending data has been read. * The `http2stream.close()` method is called, and (for client streams only) pending data has been read. * The `http2stream.destroy()` or `http2session.destroy()` methods are called. When an `Http2Stream` instance is destroyed, an attempt will be made to send an `RST_STREAM` frame to the connected peer. When the `Http2Stream` instance is destroyed, the `'close'` event will be emitted. Because `Http2Stream` is an instance of `stream.Duplex`, the `'end'` event will also be emitted if the stream data is currently flowing. The `'error'` event may also be emitted if `http2stream.destroy()` was called with an `Error` passed as the first argument. After the `Http2Stream` has been destroyed, the `http2stream.destroyed` property will be `true` and the `http2stream.rstCode` property will specify the `RST_STREAM` error code. The `Http2Stream` instance is no longer usable once destroyed. ##### Event: `'aborted'`# Added in: v8.4.0 The `'aborted'` event is emitted whenever a `Http2Stream` instance is abnormally aborted in mid-communication. Its listener does not expect any arguments. The `'aborted'` event will only be emitted if the `Http2Stream` writable side has not been ended. ##### Event: `'close'`# Added in: v8.4.0 The `'close'` event is emitted when the `Http2Stream` is destroyed. Once this event is emitted, the `Http2Stream` instance is no longer usable. The HTTP/2 error code used when closing the stream can be retrieved using the `http2stream.rstCode` property. If the code is any value other than `NGHTTP2_NO_ERROR` (`0`), an `'error'` event will have also been emitted. ##### Event: `'error'`# Added in: v8.4.0 * `error` The `'error'` event is emitted when an error occurs during the processing of an `Http2Stream`. ##### Event: `'frameError'`# Added in: v8.4.0 * `type` The frame type. * `code` The error code. * `id` The stream id (or `0` if the frame isn't associated with a stream). The `'frameError'` event is emitted when an error occurs while attempting to send a frame. When invoked, the handler function will receive an integer argument identifying the frame type, and an integer argument identifying the error code. The `Http2Stream` instance will be destroyed immediately after the `'frameError'` event is emitted. ##### Event: `'ready'`# Added in: v8.4.0 The `'ready'` event is emitted when the `Http2Stream` has been opened, has been assigned an `id`, and can be used. The listener does not expect any arguments. ##### Event: `'timeout'`# Added in: v8.4.0 The `'timeout'` event is emitted after no activity is received for this `Http2Stream` within the number of milliseconds set using `http2stream.setTimeout()`. Its listener does not expect any arguments. ##### Event: `'trailers'`# Added in: v8.4.0 * `headers` An object describing the headers * `flags` The associated numeric flags The `'trailers'` event is emitted when a block of headers associated with trailing header fields is received. The listener callback is passed the HTTP/2 Headers Object and flags associated with the headers. This event might not be emitted if `http2stream.end()` is called before trailers are received and the incoming data is not being read or listened for. stream.on('trailers', (headers, flags) => { console.log(headers); }); ##### Event: `'wantTrailers'`# Added in: v10.0.0 The `'wantTrailers'` event is emitted when the `Http2Stream` has queued the final `DATA` frame to be sent on a frame and the `Http2Stream` is ready to send trailing headers. When initiating a request or response, the `waitForTrailers` option must be set for this event to be emitted. ##### `http2stream.aborted`# Added in: v8.4.0 * Type: Set to `true` if the `Http2Stream` instance was aborted abnormally. When set, the `'aborted'` event will have been emitted. ##### `http2stream.bufferSize`# Added in: v11.2.0, v10.16.0 * Type: This property shows the number of characters currently buffered to be written. See `net.Socket.bufferSize` for details. ##### `http2stream.close(code[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.4.0 Added in: v8.4.0 * `code` Unsigned 32-bit integer identifying the error code. Default: `http2.constants.NGHTTP2_NO_ERROR` (`0x00`). * `callback` An optional function registered to listen for the `'close'` event. Closes the `Http2Stream` instance by sending an `RST_STREAM` frame to the connected HTTP/2 peer. ##### `http2stream.closed`# Added in: v9.4.0 * Type: Set to `true` if the `Http2Stream` instance has been closed. ##### `http2stream.destroyed`# Added in: v8.4.0 * Type: Set to `true` if the `Http2Stream` instance has been destroyed and is no longer usable. ##### `http2stream.endAfterHeaders`# Added in: v10.11.0 * Type: Set to `true` if the `END_STREAM` flag was set in the request or response HEADERS frame received, indicating that no additional data should be received and the readable side of the `Http2Stream` will be closed. ##### `http2stream.id`# Added in: v8.4.0 * Type: | The numeric stream identifier of this `Http2Stream` instance. Set to `undefined` if the stream identifier has not yet been assigned. ##### `http2stream.pending`# Added in: v9.4.0 * Type: Set to `true` if the `Http2Stream` instance has not yet been assigned a numeric stream identifier. ##### `http2stream.priority(options)`# History VersionChanges v24.2.0 This method no longer sets the priority of the stream. Using it now triggers a runtime warning. v24.2.0 Deprecated since: v24.2.0 v8.4.0 Added in: v8.4.0 Stability: 0 \- Deprecated: support for priority signaling has been deprecated in the RFC 9113 and is no longer supported in Node.js. Empty method, only there to maintain some backward compatibility. ##### `http2stream.rstCode`# Added in: v8.4.0 * Type: Set to the `RST_STREAM` error code reported when the `Http2Stream` is destroyed after either receiving an `RST_STREAM` frame from the connected peer, calling `http2stream.close()`, or `http2stream.destroy()`. Will be `undefined` if the `Http2Stream` has not been closed. ##### `http2stream.sentHeaders`# Added in: v9.5.0 * Type: An object containing the outbound headers sent for this `Http2Stream`. ##### `http2stream.sentInfoHeaders`# Added in: v9.5.0 * Type: An array of objects containing the outbound informational (additional) headers sent for this `Http2Stream`. ##### `http2stream.sentTrailers`# Added in: v9.5.0 * Type: An object containing the outbound trailers sent for this `HttpStream`. ##### `http2stream.session`# Added in: v8.4.0 * Type: A reference to the `Http2Session` instance that owns this `Http2Stream`. The value will be `undefined` after the `Http2Stream` instance is destroyed. ##### `http2stream.setTimeout(msecs, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.4.0 Added in: v8.4.0 * `msecs` * `callback` import { connect, constants } from 'node:http2'; const client = connect('http://example.org:8000'); const { NGHTTP2_CANCEL } = constants; const req = client.request({ ':path': '/' }); // Cancel the stream if there's no activity after 5 seconds req.setTimeout(5000, () => req.close(NGHTTP2_CANCEL)); ##### `http2stream.state`# History VersionChanges v24.2.0 The `state.weight` property is now always set to 16 and `sumDependencyWeight` is always set to 0. v24.2.0 Following the deprecation of priority signaling as of RFC 9113, `weight` and `sumDependencyWeight` options are deprecated. v8.4.0 Added in: v8.4.0 Provides miscellaneous information about the current state of the `Http2Stream`. * Type: * `localWindowSize` The number of bytes the connected peer may send for this `Http2Stream` without receiving a `WINDOW_UPDATE`. * `state` A flag indicating the low-level current state of the `Http2Stream` as determined by `nghttp2`. * `localClose` `1` if this `Http2Stream` has been closed locally. * `remoteClose` `1` if this `Http2Stream` has been closed remotely. * `sumDependencyWeight` Legacy property, always set to `0`. * `weight` Legacy property, always set to `16`. A current state of this `Http2Stream`. ##### `http2stream.sendTrailers(headers)`# Added in: v10.0.0 * `headers` Sends a trailing `HEADERS` frame to the connected HTTP/2 peer. This method will cause the `Http2Stream` to be immediately closed and must only be called after the `'wantTrailers'` event has been emitted. When sending a request or sending a response, the `options.waitForTrailers` option must be set in order to keep the `Http2Stream` open after the final `DATA` frame so that trailers can be sent. import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream) => { stream.respond(undefined, { waitForTrailers: true }); stream.on('wantTrailers', () => { stream.sendTrailers({ xyz: 'abc' }); }); stream.end('Hello World'); }); The HTTP/1 specification forbids trailers from containing HTTP/2 pseudo-header fields (e.g. `':method'`, `':path'`, etc). #### Class: `ClientHttp2Stream`# Added in: v8.4.0 * Extends The `ClientHttp2Stream` class is an extension of `Http2Stream` that is used exclusively on HTTP/2 Clients. `Http2Stream` instances on the client provide events such as `'response'` and `'push'` that are only relevant on the client. ##### Event: `'continue'`# Added in: v8.5.0 Emitted when the server sends a `100 Continue` status, usually because the request contained `Expect: 100-continue`. This is an instruction that the client should send the request body. ##### Event: `'headers'`# Added in: v8.4.0 * `headers` * `flags` * `rawHeaders` The `'headers'` event is emitted when an additional block of headers is received for a stream, such as when a block of `1xx` informational headers is received. The listener callback is passed the HTTP/2 Headers Object, flags associated with the headers, and the headers in raw format (see HTTP/2 Raw Headers). stream.on('headers', (headers, flags) => { console.log(headers); }); ##### Event: `'push'`# Added in: v8.4.0 * `headers` * `flags` The `'push'` event is emitted when response headers for a Server Push stream are received. The listener callback is passed the HTTP/2 Headers Object and flags associated with the headers. stream.on('push', (headers, flags) => { console.log(headers); }); ##### Event: `'response'`# Added in: v8.4.0 * `headers` * `flags` * `rawHeaders` The `'response'` event is emitted when a response `HEADERS` frame has been received for this stream from the connected HTTP/2 server. The listener is invoked with three arguments: an `Object` containing the received HTTP/2 Headers Object, flags associated with the headers, and the headers in raw format (see HTTP/2 Raw Headers). import { connect } from 'node:http2'; const client = connect('https://localhost'); const req = client.request({ ':path': '/' }); req.on('response', (headers, flags) => { console.log(headers[':status']); }); #### Class: `ServerHttp2Stream`# Added in: v8.4.0 * Extends: The `ServerHttp2Stream` class is an extension of `Http2Stream` that is used exclusively on HTTP/2 Servers. `Http2Stream` instances on the server provide additional methods such as `http2stream.pushStream()` and `http2stream.respond()` that are only relevant on the server. ##### `http2stream.additionalHeaders(headers)`# Added in: v8.4.0 * `headers` Sends an additional informational `HEADERS` frame to the connected HTTP/2 peer. ##### `http2stream.headersSent`# Added in: v8.4.0 * Type: True if headers were sent, false otherwise (read-only). ##### `http2stream.pushAllowed`# Added in: v8.4.0 * Type: Read-only property mapped to the `SETTINGS_ENABLE_PUSH` flag of the remote client's most recent `SETTINGS` frame. Will be `true` if the remote peer accepts push streams, `false` otherwise. Settings are the same for every `Http2Stream` in the same `Http2Session`. ##### `http2stream.pushStream(headers[, options], callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.4.0 Added in: v8.4.0 * `headers` * `options` * `exclusive` When `true` and `parent` identifies a parent Stream, the created stream is made the sole direct dependency of the parent, with all other existing dependents made a dependent of the newly created stream. Default: `false`. * `parent` Specifies the numeric identifier of a stream the newly created stream is dependent on. * `callback` Callback that is called once the push stream has been initiated. * `err` * `pushStream` The returned `pushStream` object. * `headers` Headers object the `pushStream` was initiated with. Initiates a push stream. The callback is invoked with the new `Http2Stream` instance created for the push stream passed as the second argument, or an `Error` passed as the first argument. import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream) => { stream.respond({ ':status': 200 }); stream.pushStream({ ':path': '/' }, (err, pushStream, headers) => { if (err) throw err; pushStream.respond({ ':status': 200 }); pushStream.end('some pushed data'); }); stream.end('some data'); }); Setting the weight of a push stream is not allowed in the `HEADERS` frame. Pass a `weight` value to `http2stream.priority` with the `silent` option set to `true` to enable server-side bandwidth balancing between concurrent streams. Calling `http2stream.pushStream()` from within a pushed stream is not permitted and will throw an error. ##### `http2stream.respond([headers[, options]])`# History VersionChanges v24.7.0 Allow passing headers in raw array format. v14.5.0, v12.19.0 Allow explicitly setting date headers. v8.4.0 Added in: v8.4.0 * `headers` | * `options` * `endStream` Set to `true` to indicate that the response will not include payload data. * `waitForTrailers` When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent. import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream) => { stream.respond({ ':status': 200 }); stream.end('some data'); }); Initiates a response. When the `options.waitForTrailers` option is set, the `'wantTrailers'` event will be emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be used to sent trailing header fields to the peer. When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code must call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`. import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream) => { stream.respond({ ':status': 200 }, { waitForTrailers: true }); stream.on('wantTrailers', () => { stream.sendTrailers({ ABC: 'some value to send' }); }); stream.end('some data'); }); ##### `http2stream.respondWithFD(fd[, headers[, options]])`# History VersionChanges v14.5.0, v12.19.0 Allow explicitly setting date headers. v12.12.0 The `fd` option may now be a `FileHandle`. v10.0.0 Any readable file descriptor, not necessarily for a regular file, is supported now. v8.4.0 Added in: v8.4.0 * `fd` | A readable file descriptor. * `headers` * `options` * `statCheck` * `waitForTrailers` When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent. * `offset` The offset position at which to begin reading. * `length` The amount of data from the fd to send. Initiates a response whose data is read from the given file descriptor. No validation is performed on the given file descriptor. If an error occurs while attempting to read data using the file descriptor, the `Http2Stream` will be closed using an `RST_STREAM` frame using the standard `INTERNAL_ERROR` code. When used, the `Http2Stream` object's `Duplex` interface will be closed automatically. import { createServer } from 'node:http2'; import { openSync, fstatSync, closeSync } from 'node:fs'; const server = createServer(); server.on('stream', (stream) => { const fd = openSync('/some/file', 'r'); const stat = fstatSync(fd); const headers = { 'content-length': stat.size, 'last-modified': stat.mtime.toUTCString(), 'content-type': 'text/plain; charset=utf-8', }; stream.respondWithFD(fd, headers); stream.on('close', () => closeSync(fd)); }); The optional `options.statCheck` function may be specified to give user code an opportunity to set additional content headers based on the `fs.Stat` details of the given fd. If the `statCheck` function is provided, the `http2stream.respondWithFD()` method will perform an `fs.fstat()` call to collect details on the provided file descriptor. The `offset` and `length` options may be used to limit the response to a specific range subset. This can be used, for instance, to support HTTP Range requests. The file descriptor or `FileHandle` is not closed when the stream is closed, so it will need to be closed manually once it is no longer needed. Using the same file descriptor concurrently for multiple streams is not supported and may result in data loss. Re-using a file descriptor after a stream has finished is supported. When the `options.waitForTrailers` option is set, the `'wantTrailers'` event will be emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be used to sent trailing header fields to the peer. When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code must call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`. import { createServer } from 'node:http2'; import { openSync, fstatSync, closeSync } from 'node:fs'; const server = createServer(); server.on('stream', (stream) => { const fd = openSync('/some/file', 'r'); const stat = fstatSync(fd); const headers = { 'content-length': stat.size, 'last-modified': stat.mtime.toUTCString(), 'content-type': 'text/plain; charset=utf-8', }; stream.respondWithFD(fd, headers, { waitForTrailers: true }); stream.on('wantTrailers', () => { stream.sendTrailers({ ABC: 'some value to send' }); }); stream.on('close', () => closeSync(fd)); }); ##### `http2stream.respondWithFile(path[, headers[, options]])`# History VersionChanges v14.5.0, v12.19.0 Allow explicitly setting date headers. v10.0.0 Any readable file, not necessarily a regular file, is supported now. v8.4.0 Added in: v8.4.0 * `path` | | * `headers` * `options` * `statCheck` * `onError` Callback function invoked in the case of an error before send. * `waitForTrailers` When `true`, the `Http2Stream` will emit the `'wantTrailers'` event after the final `DATA` frame has been sent. * `offset` The offset position at which to begin reading. * `length` The amount of data from the fd to send. Sends a regular file as the response. The `path` must specify a regular file or an `'error'` event will be emitted on the `Http2Stream` object. When used, the `Http2Stream` object's `Duplex` interface will be closed automatically. The optional `options.statCheck` function may be specified to give user code an opportunity to set additional content headers based on the `fs.Stat` details of the given file: If an error occurs while attempting to read the file data, the `Http2Stream` will be closed using an `RST_STREAM` frame using the standard `INTERNAL_ERROR` code. If the `onError` callback is defined, then it will be called. Otherwise the stream will be destroyed. Example using a file path: import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream) => { function statCheck(stat, headers) { headers['last-modified'] = stat.mtime.toUTCString(); } function onError(err) { // stream.respond() can throw if the stream has been destroyed by // the other side. try { if (err.code === 'ENOENT') { stream.respond({ ':status': 404 }); } else { stream.respond({ ':status': 500 }); } } catch (err) { // Perform actual error handling. console.error(err); } stream.end(); } stream.respondWithFile('/some/file', { 'content-type': 'text/plain; charset=utf-8' }, { statCheck, onError }); }); The `options.statCheck` function may also be used to cancel the send operation by returning `false`. For instance, a conditional request may check the stat results to determine if the file has been modified to return an appropriate `304` response: import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream) => { function statCheck(stat, headers) { // Check the stat here... stream.respond({ ':status': 304 }); return false; // Cancel the send operation } stream.respondWithFile('/some/file', { 'content-type': 'text/plain; charset=utf-8' }, { statCheck }); }); The `content-length` header field will be automatically set. The `offset` and `length` options may be used to limit the response to a specific range subset. This can be used, for instance, to support HTTP Range requests. The `options.onError` function may also be used to handle all the errors that could happen before the delivery of the file is initiated. The default behavior is to destroy the stream. When the `options.waitForTrailers` option is set, the `'wantTrailers'` event will be emitted immediately after queuing the last chunk of payload data to be sent. The `http2stream.sendTrailers()` method can then be used to sent trailing header fields to the peer. When `options.waitForTrailers` is set, the `Http2Stream` will not automatically close when the final `DATA` frame is transmitted. User code must call either `http2stream.sendTrailers()` or `http2stream.close()` to close the `Http2Stream`. import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream) => { stream.respondWithFile('/some/file', { 'content-type': 'text/plain; charset=utf-8' }, { waitForTrailers: true }); stream.on('wantTrailers', () => { stream.sendTrailers({ ABC: 'some value to send' }); }); }); #### Class: `Http2Server`# Added in: v8.4.0 * Extends: Instances of `Http2Server` are created using the `http2.createServer()` function. The `Http2Server` class is not exported directly by the `node:http2` module. ##### Event: `'checkContinue'`# Added in: v8.5.0 * `request` * `response` If a `'request'` listener is registered or `http2.createServer()` is supplied a callback function, the `'checkContinue'` event is emitted each time a request with an HTTP `Expect: 100-continue` is received. If this event is not listened for, the server will automatically respond with a status `100 Continue` as appropriate. Handling this event involves calling `response.writeContinue()` if the client should continue to send the request body, or generating an appropriate HTTP response (e.g. 400 Bad Request) if the client should not continue to send the request body. When this event is emitted and handled, the `'request'` event will not be emitted. ##### Event: `'connection'`# Added in: v8.4.0 * `socket` This event is emitted when a new TCP stream is established. `socket` is typically an object of type `net.Socket`. Usually users will not want to access this event. This event can also be explicitly emitted by users to inject connections into the HTTP server. In that case, any `Duplex` stream can be passed. ##### Event: `'request'`# Added in: v8.4.0 * `request` * `response` Emitted each time there is a request. There may be multiple requests per session. See the Compatibility API. ##### Event: `'session'`# Added in: v8.4.0 * `session` The `'session'` event is emitted when a new `Http2Session` is created by the `Http2Server`. ##### Event: `'sessionError'`# Added in: v8.4.0 * `error` * `session` The `'sessionError'` event is emitted when an `'error'` event is emitted by an `Http2Session` object associated with the `Http2Server`. ##### Event: `'stream'`# Added in: v8.4.0 * `stream` A reference to the stream * `headers` An object describing the headers * `flags` The associated numeric flags * `rawHeaders` An array containing the raw headers The `'stream'` event is emitted when a `'stream'` event has been emitted by an `Http2Session` associated with the server. See also `Http2Session`'s `'stream'` event. import { createServer, constants } from 'node:http2'; const { HTTP2_HEADER_METHOD, HTTP2_HEADER_PATH, HTTP2_HEADER_STATUS, HTTP2_HEADER_CONTENT_TYPE, } = constants; const server = createServer(); server.on('stream', (stream, headers, flags) => { const method = headers[HTTP2_HEADER_METHOD]; const path = headers[HTTP2_HEADER_PATH]; // ... stream.respond({ [HTTP2_HEADER_STATUS]: 200, [HTTP2_HEADER_CONTENT_TYPE]: 'text/plain; charset=utf-8', }); stream.write('hello '); stream.end('world'); }); ##### Event: `'timeout'`# History VersionChanges v13.0.0 The default timeout changed from 120s to 0 (no timeout). v8.4.0 Added in: v8.4.0 The `'timeout'` event is emitted when there is no activity on the Server for a given number of milliseconds set using `http2server.setTimeout()`. Default: 0 (no timeout) ##### `server.close([callback])`# Added in: v8.4.0 * `callback` Stops the server from establishing new sessions. This does not prevent new request streams from being created due to the persistent nature of HTTP/2 sessions. To gracefully shut down the server, call `http2session.close()` on all active sessions. If `callback` is provided, it is not invoked until all active sessions have been closed, although the server has already stopped allowing new sessions. See `net.Server.close()` for more details. ##### `server[Symbol.asyncDispose]()`# History VersionChanges v24.2.0 No longer experimental. v20.4.0 Added in: v20.4.0 Calls `server.close()` and returns a promise that fulfills when the server has closed. ##### `server.setTimeout([msecs][, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v13.0.0 The default timeout changed from 120s to 0 (no timeout). v8.4.0 Added in: v8.4.0 * `msecs` Default: 0 (no timeout) * `callback` * Returns: Used to set the timeout value for http2 server requests, and sets a callback function that is called when there is no activity on the `Http2Server` after `msecs` milliseconds. The given callback is registered as a listener on the `'timeout'` event. In case if `callback` is not a function, a new `ERR_INVALID_ARG_TYPE` error will be thrown. ##### `server.timeout`# History VersionChanges v13.0.0 The default timeout changed from 120s to 0 (no timeout). v8.4.0 Added in: v8.4.0 * Type: Timeout in milliseconds. Default: 0 (no timeout) The number of milliseconds of inactivity before a socket is presumed to have timed out. A value of `0` will disable the timeout behavior on incoming connections. The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections. ##### `server.updateSettings([settings])`# Added in: v15.1.0, v14.17.0 * `settings` Used to update the server with the provided settings. Throws `ERR_HTTP2_INVALID_SETTING_VALUE` for invalid `settings` values. Throws `ERR_INVALID_ARG_TYPE` for invalid `settings` argument. #### Class: `Http2SecureServer`# Added in: v8.4.0 * Extends: Instances of `Http2SecureServer` are created using the `http2.createSecureServer()` function. The `Http2SecureServer` class is not exported directly by the `node:http2` module. ##### Event: `'checkContinue'`# Added in: v8.5.0 * `request` * `response` If a `'request'` listener is registered or `http2.createSecureServer()` is supplied a callback function, the `'checkContinue'` event is emitted each time a request with an HTTP `Expect: 100-continue` is received. If this event is not listened for, the server will automatically respond with a status `100 Continue` as appropriate. Handling this event involves calling `response.writeContinue()` if the client should continue to send the request body, or generating an appropriate HTTP response (e.g. 400 Bad Request) if the client should not continue to send the request body. When this event is emitted and handled, the `'request'` event will not be emitted. ##### Event: `'connection'`# Added in: v8.4.0 * `socket` This event is emitted when a new TCP stream is established, before the TLS handshake begins. `socket` is typically an object of type `net.Socket`. Usually users will not want to access this event. This event can also be explicitly emitted by users to inject connections into the HTTP server. In that case, any `Duplex` stream can be passed. ##### Event: `'request'`# Added in: v8.4.0 * `request` * `response` Emitted each time there is a request. There may be multiple requests per session. See the Compatibility API. ##### Event: `'session'`# Added in: v8.4.0 * `session` The `'session'` event is emitted when a new `Http2Session` is created by the `Http2SecureServer`. ##### Event: `'sessionError'`# Added in: v8.4.0 * `error` * `session` The `'sessionError'` event is emitted when an `'error'` event is emitted by an `Http2Session` object associated with the `Http2SecureServer`. ##### Event: `'stream'`# Added in: v8.4.0 * `stream` A reference to the stream * `headers` An object describing the headers * `flags` The associated numeric flags * `rawHeaders` An array containing the raw headers The `'stream'` event is emitted when a `'stream'` event has been emitted by an `Http2Session` associated with the server. See also `Http2Session`'s `'stream'` event. import { createSecureServer, constants } from 'node:http2'; const { HTTP2_HEADER_METHOD, HTTP2_HEADER_PATH, HTTP2_HEADER_STATUS, HTTP2_HEADER_CONTENT_TYPE, } = constants; const options = getOptionsSomehow(); const server = createSecureServer(options); server.on('stream', (stream, headers, flags) => { const method = headers[HTTP2_HEADER_METHOD]; const path = headers[HTTP2_HEADER_PATH]; // ... stream.respond({ [HTTP2_HEADER_STATUS]: 200, [HTTP2_HEADER_CONTENT_TYPE]: 'text/plain; charset=utf-8', }); stream.write('hello '); stream.end('world'); }); ##### Event: `'timeout'`# Added in: v8.4.0 The `'timeout'` event is emitted when there is no activity on the Server for a given number of milliseconds set using `http2secureServer.setTimeout()`. Default: 2 minutes. ##### Event: `'unknownProtocol'`# History VersionChanges v19.0.0 This event will only be emitted if the client did not transmit an ALPN extension during the TLS handshake. v8.4.0 Added in: v8.4.0 * `socket` The `'unknownProtocol'` event is emitted when a connecting client fails to negotiate an allowed protocol (i.e. HTTP/2 or HTTP/1.1). The event handler receives the socket for handling. If no listener is registered for this event, the connection is terminated. A timeout may be specified using the `'unknownProtocolTimeout'` option passed to `http2.createSecureServer()`. In earlier versions of Node.js, this event would be emitted if `allowHTTP1` is `false` and, during the TLS handshake, the client either does not send an ALPN extension or sends an ALPN extension that does not include HTTP/2 (`h2`). Newer versions of Node.js only emit this event if `allowHTTP1` is `false` and the client does not send an ALPN extension. If the client sends an ALPN extension that does not include HTTP/2 (or HTTP/1.1 if `allowHTTP1` is `true`), the TLS handshake will fail and no secure connection will be established. See the Compatibility API. ##### `server.close([callback])`# Added in: v8.4.0 * `callback` Stops the server from establishing new sessions. This does not prevent new request streams from being created due to the persistent nature of HTTP/2 sessions. To gracefully shut down the server, call `http2session.close()` on all active sessions. If `callback` is provided, it is not invoked until all active sessions have been closed, although the server has already stopped allowing new sessions. See `tls.Server.close()` for more details. ##### `server.setTimeout([msecs][, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.4.0 Added in: v8.4.0 * `msecs` Default: `120000` (2 minutes) * `callback` * Returns: Used to set the timeout value for http2 secure server requests, and sets a callback function that is called when there is no activity on the `Http2SecureServer` after `msecs` milliseconds. The given callback is registered as a listener on the `'timeout'` event. In case if `callback` is not a function, a new `ERR_INVALID_ARG_TYPE` error will be thrown. ##### `server.timeout`# History VersionChanges v13.0.0 The default timeout changed from 120s to 0 (no timeout). v8.4.0 Added in: v8.4.0 * Type: Timeout in milliseconds. Default: 0 (no timeout) The number of milliseconds of inactivity before a socket is presumed to have timed out. A value of `0` will disable the timeout behavior on incoming connections. The socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections. ##### `server.updateSettings([settings])`# Added in: v15.1.0, v14.17.0 * `settings` Used to update the server with the provided settings. Throws `ERR_HTTP2_INVALID_SETTING_VALUE` for invalid `settings` values. Throws `ERR_INVALID_ARG_TYPE` for invalid `settings` argument. #### `http2.createServer([options][, onRequestHandler])`# History VersionChanges v23.0.0, v22.10.0 Added `streamResetBurst` and `streamResetRate`. v13.0.0 The `PADDING_STRATEGY_CALLBACK` has been made equivalent to providing `PADDING_STRATEGY_ALIGNED` and `selectPadding` has been removed. v13.3.0, v12.16.0 Added `maxSessionRejectedStreams` option with a default of 100. v13.3.0, v12.16.0 Added `maxSessionInvalidFrames` option with a default of 1000. v12.4.0 The `options` parameter now supports `net.createServer()` options. v15.10.0, v14.16.0, v12.21.0, v10.24.0 Added `unknownProtocolTimeout` option with a default of 10000. v14.4.0, v12.18.0, v10.21.0 Added `maxSettings` option with a default of 32. v9.6.0 Added the `Http1IncomingMessage` and `Http1ServerResponse` option. v8.9.3 Added the `maxOutstandingPings` option with a default limit of 10. v8.9.3 Added the `maxHeaderListPairs` option with a default limit of 128 header pairs. v8.4.0 Added in: v8.4.0 * `options` * `maxDeflateDynamicTableSize` Sets the maximum dynamic table size for deflating header fields. Default: `4Kib`. * `maxSettings` Sets the maximum number of settings entries per `SETTINGS` frame. The minimum value allowed is `1`. Default: `32`. * `maxSessionMemory` Sets the maximum memory that the `Http2Session` is permitted to use. The value is expressed in terms of number of megabytes, e.g. `1` equal 1 megabyte. The minimum value allowed is `1`. This is a credit based limit, existing `Http2Stream`s may cause this limit to be exceeded, but new `Http2Stream` instances will be rejected while this limit is exceeded. The current number of `Http2Stream` sessions, the current memory use of the header compression tables, current data queued to be sent, and unacknowledged `PING` and `SETTINGS` frames are all counted towards the current limit. Default: `10`. * `maxHeaderListPairs` Sets the maximum number of header entries. This is similar to `server.maxHeadersCount` or `request.maxHeadersCount` in the `node:http` module. The minimum value is `4`. Default: `128`. * `maxOutstandingPings` Sets the maximum number of outstanding, unacknowledged pings. Default: `10`. * `maxSendHeaderBlockLength` Sets the maximum allowed size for a serialized, compressed block of headers. Attempts to send headers that exceed this limit will result in a `'frameError'` event being emitted and the stream being closed and destroyed. While this sets the maximum allowed size to the entire block of headers, `nghttp2` (the internal http2 library) has a limit of `65536` for each decompressed key/value pair. * `paddingStrategy` The strategy used for determining the amount of padding to use for `HEADERS` and `DATA` frames. Default: `http2.constants.PADDING_STRATEGY_NONE`. Value may be one of: * `http2.constants.PADDING_STRATEGY_NONE`: No padding is applied. * `http2.constants.PADDING_STRATEGY_MAX`: The maximum amount of padding, determined by the internal implementation, is applied. * `http2.constants.PADDING_STRATEGY_ALIGNED`: Attempts to apply enough padding to ensure that the total frame length, including the 9-byte header, is a multiple of 8. For each frame, there is a maximum allowed number of padding bytes that is determined by current flow control state and settings. If this maximum is less than the calculated amount needed to ensure alignment, the maximum is used and the total frame length is not necessarily aligned at 8 bytes. * `peerMaxConcurrentStreams` Sets the maximum number of concurrent streams for the remote peer as if a `SETTINGS` frame had been received. Will be overridden if the remote peer sets its own value for `maxConcurrentStreams`. Default: `100`. * `maxSessionInvalidFrames` Sets the maximum number of invalid frames that will be tolerated before the session is closed. Default: `1000`. * `maxSessionRejectedStreams` Sets the maximum number of rejected upon creation streams that will be tolerated before the session is closed. Each rejection is associated with an `NGHTTP2_ENHANCE_YOUR_CALM` error that should tell the peer to not open any more streams, continuing to open streams is therefore regarded as a sign of a misbehaving peer. Default: `100`. * `settings` The initial settings to send to the remote peer upon connection. * `streamResetBurst` and `streamResetRate` Sets the rate limit for the incoming stream reset (RST_STREAM frame). Both settings must be set to have any effect, and default to 1000 and 33 respectively. * `remoteCustomSettings` The array of integer values determines the settings types, which are included in the `CustomSettings`-property of the received remoteSettings. Please see the `CustomSettings`-property of the `Http2Settings` object for more information, on the allowed setting types. * `Http1IncomingMessage` Specifies the `IncomingMessage` class to used for HTTP/1 fallback. Useful for extending the original `http.IncomingMessage`. Default: `http.IncomingMessage`. * `Http1ServerResponse` Specifies the `ServerResponse` class to used for HTTP/1 fallback. Useful for extending the original `http.ServerResponse`. Default: `http.ServerResponse`. * `Http2ServerRequest` Specifies the `Http2ServerRequest` class to use. Useful for extending the original `Http2ServerRequest`. Default: `Http2ServerRequest`. * `Http2ServerResponse` Specifies the `Http2ServerResponse` class to use. Useful for extending the original `Http2ServerResponse`. Default: `Http2ServerResponse`. * `unknownProtocolTimeout` Specifies a timeout in milliseconds that a server should wait when an `'unknownProtocol'` is emitted. If the socket has not been destroyed by that time the server will destroy it. Default: `10000`. * `strictFieldWhitespaceValidation` If `true`, it turns on strict leading and trailing whitespace validation for HTTP/2 header field names and values as per RFC-9113. Default: `true`. * `...options` Any `net.createServer()` option can be provided. * `onRequestHandler` See Compatibility API * Returns: Returns a `net.Server` instance that creates and manages `Http2Session` instances. Since there are no browsers known that support unencrypted HTTP/2, the use of `http2.createSecureServer()` is necessary when communicating with browser clients. import { createServer } from 'node:http2'; // Create an unencrypted HTTP/2 server. // Since there are no browsers known that support // unencrypted HTTP/2, the use of `createSecureServer()` // is necessary when communicating with browser clients. const server = createServer(); server.on('stream', (stream, headers) => { stream.respond({ 'content-type': 'text/html; charset=utf-8', ':status': 200, }); stream.end('

Hello World

'); }); server.listen(8000); #### `http2.createSecureServer(options[, onRequestHandler])`# History VersionChanges v13.0.0 The `PADDING_STRATEGY_CALLBACK` has been made equivalent to providing `PADDING_STRATEGY_ALIGNED` and `selectPadding` has been removed. v13.3.0, v12.16.0 Added `maxSessionRejectedStreams` option with a default of 100. v13.3.0, v12.16.0 Added `maxSessionInvalidFrames` option with a default of 1000. v15.10.0, v14.16.0, v12.21.0, v10.24.0 Added `unknownProtocolTimeout` option with a default of 10000. v14.4.0, v12.18.0, v10.21.0 Added `maxSettings` option with a default of 32. v10.12.0 Added the `origins` option to automatically send an `ORIGIN` frame on `Http2Session` startup. v8.9.3 Added the `maxOutstandingPings` option with a default limit of 10. v8.9.3 Added the `maxHeaderListPairs` option with a default limit of 128 header pairs. v8.4.0 Added in: v8.4.0 * `options` * `allowHTTP1` Incoming client connections that do not support HTTP/2 will be downgraded to HTTP/1.x when set to `true`. See the `'unknownProtocol'` event. See ALPN negotiation. Default: `false`. * `maxDeflateDynamicTableSize` Sets the maximum dynamic table size for deflating header fields. Default: `4Kib`. * `maxSettings` Sets the maximum number of settings entries per `SETTINGS` frame. The minimum value allowed is `1`. Default: `32`. * `maxSessionMemory` Sets the maximum memory that the `Http2Session` is permitted to use. The value is expressed in terms of number of megabytes, e.g. `1` equal 1 megabyte. The minimum value allowed is `1`. This is a credit based limit, existing `Http2Stream`s may cause this limit to be exceeded, but new `Http2Stream` instances will be rejected while this limit is exceeded. The current number of `Http2Stream` sessions, the current memory use of the header compression tables, current data queued to be sent, and unacknowledged `PING` and `SETTINGS` frames are all counted towards the current limit. Default: `10`. * `maxHeaderListPairs` Sets the maximum number of header entries. This is similar to `server.maxHeadersCount` or `request.maxHeadersCount` in the `node:http` module. The minimum value is `4`. Default: `128`. * `maxOutstandingPings` Sets the maximum number of outstanding, unacknowledged pings. Default: `10`. * `maxSendHeaderBlockLength` Sets the maximum allowed size for a serialized, compressed block of headers. Attempts to send headers that exceed this limit will result in a `'frameError'` event being emitted and the stream being closed and destroyed. * `paddingStrategy` Strategy used for determining the amount of padding to use for `HEADERS` and `DATA` frames. Default: `http2.constants.PADDING_STRATEGY_NONE`. Value may be one of: * `http2.constants.PADDING_STRATEGY_NONE`: No padding is applied. * `http2.constants.PADDING_STRATEGY_MAX`: The maximum amount of padding, determined by the internal implementation, is applied. * `http2.constants.PADDING_STRATEGY_ALIGNED`: Attempts to apply enough padding to ensure that the total frame length, including the 9-byte header, is a multiple of 8. For each frame, there is a maximum allowed number of padding bytes that is determined by current flow control state and settings. If this maximum is less than the calculated amount needed to ensure alignment, the maximum is used and the total frame length is not necessarily aligned at 8 bytes. * `peerMaxConcurrentStreams` Sets the maximum number of concurrent streams for the remote peer as if a `SETTINGS` frame had been received. Will be overridden if the remote peer sets its own value for `maxConcurrentStreams`. Default: `100`. * `maxSessionInvalidFrames` Sets the maximum number of invalid frames that will be tolerated before the session is closed. Default: `1000`. * `maxSessionRejectedStreams` Sets the maximum number of rejected upon creation streams that will be tolerated before the session is closed. Each rejection is associated with an `NGHTTP2_ENHANCE_YOUR_CALM` error that should tell the peer to not open any more streams, continuing to open streams is therefore regarded as a sign of a misbehaving peer. Default: `100`. * `settings` The initial settings to send to the remote peer upon connection. * `streamResetBurst` and `streamResetRate` Sets the rate limit for the incoming stream reset (RST_STREAM frame). Both settings must be set to have any effect, and default to 1000 and 33 respectively. * `remoteCustomSettings` The array of integer values determines the settings types, which are included in the `customSettings`-property of the received remoteSettings. Please see the `customSettings`-property of the `Http2Settings` object for more information, on the allowed setting types. * `...options` Any `tls.createServer()` options can be provided. For servers, the identity options (`pfx` or `key`/`cert`) are usually required. * `origins` An array of origin strings to send within an `ORIGIN` frame immediately following creation of a new server `Http2Session`. * `unknownProtocolTimeout` Specifies a timeout in milliseconds that a server should wait when an `'unknownProtocol'` event is emitted. If the socket has not been destroyed by that time the server will destroy it. Default: `10000`. * `strictFieldWhitespaceValidation` If `true`, it turns on strict leading and trailing whitespace validation for HTTP/2 header field names and values as per RFC-9113. Default: `true`. * `onRequestHandler` See Compatibility API * Returns: Returns a `tls.Server` instance that creates and manages `Http2Session` instances. import { createSecureServer } from 'node:http2'; import { readFileSync } from 'node:fs'; const options = { key: readFileSync('server-key.pem'), cert: readFileSync('server-cert.pem'), }; // Create a secure HTTP/2 server const server = createSecureServer(options); server.on('stream', (stream, headers) => { stream.respond({ 'content-type': 'text/html; charset=utf-8', ':status': 200, }); stream.end('

Hello World

'); }); server.listen(8443); #### `http2.connect(authority[, options][, listener])`# History VersionChanges v13.0.0 The `PADDING_STRATEGY_CALLBACK` has been made equivalent to providing `PADDING_STRATEGY_ALIGNED` and `selectPadding` has been removed. v15.10.0, v14.16.0, v12.21.0, v10.24.0 Added `unknownProtocolTimeout` option with a default of 10000. v14.4.0, v12.18.0, v10.21.0 Added `maxSettings` option with a default of 32. v8.9.3 Added the `maxOutstandingPings` option with a default limit of 10. v8.9.3 Added the `maxHeaderListPairs` option with a default limit of 128 header pairs. v8.4.0 Added in: v8.4.0 * `authority` | The remote HTTP/2 server to connect to. This must be in the form of a minimal, valid URL with the `http://` or `https://` prefix, host name, and IP port (if a non-default port is used). Userinfo (user ID and password), path, querystring, and fragment details in the URL will be ignored. * `options` * `maxDeflateDynamicTableSize` Sets the maximum dynamic table size for deflating header fields. Default: `4Kib`. * `maxSettings` Sets the maximum number of settings entries per `SETTINGS` frame. The minimum value allowed is `1`. Default: `32`. * `maxSessionMemory` Sets the maximum memory that the `Http2Session` is permitted to use. The value is expressed in terms of number of megabytes, e.g. `1` equal 1 megabyte. The minimum value allowed is `1`. This is a credit based limit, existing `Http2Stream`s may cause this limit to be exceeded, but new `Http2Stream` instances will be rejected while this limit is exceeded. The current number of `Http2Stream` sessions, the current memory use of the header compression tables, current data queued to be sent, and unacknowledged `PING` and `SETTINGS` frames are all counted towards the current limit. Default: `10`. * `maxHeaderListPairs` Sets the maximum number of header entries. This is similar to `server.maxHeadersCount` or `request.maxHeadersCount` in the `node:http` module. The minimum value is `1`. Default: `128`. * `maxOutstandingPings` Sets the maximum number of outstanding, unacknowledged pings. Default: `10`. * `maxReservedRemoteStreams` Sets the maximum number of reserved push streams the client will accept at any given time. Once the current number of currently reserved push streams exceeds reaches this limit, new push streams sent by the server will be automatically rejected. The minimum allowed value is 0. The maximum allowed value is 232-1. A negative value sets this option to the maximum allowed value. Default: `200`. * `maxSendHeaderBlockLength` Sets the maximum allowed size for a serialized, compressed block of headers. Attempts to send headers that exceed this limit will result in a `'frameError'` event being emitted and the stream being closed and destroyed. * `paddingStrategy` Strategy used for determining the amount of padding to use for `HEADERS` and `DATA` frames. Default: `http2.constants.PADDING_STRATEGY_NONE`. Value may be one of: * `http2.constants.PADDING_STRATEGY_NONE`: No padding is applied. * `http2.constants.PADDING_STRATEGY_MAX`: The maximum amount of padding, determined by the internal implementation, is applied. * `http2.constants.PADDING_STRATEGY_ALIGNED`: Attempts to apply enough padding to ensure that the total frame length, including the 9-byte header, is a multiple of 8. For each frame, there is a maximum allowed number of padding bytes that is determined by current flow control state and settings. If this maximum is less than the calculated amount needed to ensure alignment, the maximum is used and the total frame length is not necessarily aligned at 8 bytes. * `peerMaxConcurrentStreams` Sets the maximum number of concurrent streams for the remote peer as if a `SETTINGS` frame had been received. Will be overridden if the remote peer sets its own value for `maxConcurrentStreams`. Default: `100`. * `protocol` The protocol to connect with, if not set in the `authority`. Value may be either `'http:'` or `'https:'`. Default: `'https:'` * `settings` The initial settings to send to the remote peer upon connection. * `remoteCustomSettings` The array of integer values determines the settings types, which are included in the `CustomSettings`-property of the received remoteSettings. Please see the `CustomSettings`-property of the `Http2Settings` object for more information, on the allowed setting types. * `createConnection` An optional callback that receives the `URL` instance passed to `connect` and the `options` object, and returns any `Duplex` stream that is to be used as the connection for this session. * `...options` Any `net.connect()` or `tls.connect()` options can be provided. * `unknownProtocolTimeout` Specifies a timeout in milliseconds that a server should wait when an `'unknownProtocol'` event is emitted. If the socket has not been destroyed by that time the server will destroy it. Default: `10000`. * `strictFieldWhitespaceValidation` If `true`, it turns on strict leading and trailing whitespace validation for HTTP/2 header field names and values as per RFC-9113. Default: `true`. * `listener` Will be registered as a one-time listener of the `'connect'` event. * Returns: Returns a `ClientHttp2Session` instance. import { connect } from 'node:http2'; const client = connect('https://localhost:1234'); /* Use the client */ client.close(); #### `http2.constants`# Added in: v8.4.0 ##### Error codes for `RST_STREAM` and `GOAWAY`# ValueNameConstant `0x00`No Error`http2.constants.NGHTTP2_NO_ERROR` `0x01`Protocol Error`http2.constants.NGHTTP2_PROTOCOL_ERROR` `0x02`Internal Error`http2.constants.NGHTTP2_INTERNAL_ERROR` `0x03`Flow Control Error`http2.constants.NGHTTP2_FLOW_CONTROL_ERROR` `0x04`Settings Timeout`http2.constants.NGHTTP2_SETTINGS_TIMEOUT` `0x05`Stream Closed`http2.constants.NGHTTP2_STREAM_CLOSED` `0x06`Frame Size Error`http2.constants.NGHTTP2_FRAME_SIZE_ERROR` `0x07`Refused Stream`http2.constants.NGHTTP2_REFUSED_STREAM` `0x08`Cancel`http2.constants.NGHTTP2_CANCEL` `0x09`Compression Error`http2.constants.NGHTTP2_COMPRESSION_ERROR` `0x0a`Connect Error`http2.constants.NGHTTP2_CONNECT_ERROR` `0x0b`Enhance Your Calm`http2.constants.NGHTTP2_ENHANCE_YOUR_CALM` `0x0c`Inadequate Security`http2.constants.NGHTTP2_INADEQUATE_SECURITY` `0x0d`HTTP/1.1 Required`http2.constants.NGHTTP2_HTTP_1_1_REQUIRED` The `'timeout'` event is emitted when there is no activity on the Server for a given number of milliseconds set using `http2server.setTimeout()`. #### `http2.getDefaultSettings()`# Added in: v8.4.0 * Returns: Returns an object containing the default settings for an `Http2Session` instance. This method returns a new object instance every time it is called so instances returned may be safely modified for use. #### `http2.getPackedSettings([settings])`# Added in: v8.4.0 * `settings` * Returns: Returns a `Buffer` instance containing serialized representation of the given HTTP/2 settings as specified in the HTTP/2 specification. This is intended for use with the `HTTP2-Settings` header field. import { getPackedSettings } from 'node:http2'; const packed = getPackedSettings({ enablePush: false }); console.log(packed.toString('base64')); // Prints: AAIAAAAA #### `http2.getUnpackedSettings(buf)`# Added in: v8.4.0 * `buf` | The packed settings. * Returns: Returns a HTTP/2 Settings Object containing the deserialized settings from the given `Buffer` as generated by `http2.getPackedSettings()`. #### `http2.performServerHandshake(socket[, options])`# Added in: v21.7.0, v20.12.0 * `socket` * `options` Any `http2.createServer()` option can be provided. * Returns: Create an HTTP/2 server session from an existing socket. #### `http2.sensitiveHeaders`# Added in: v15.0.0, v14.18.0 * Type: This symbol can be set as a property on the HTTP/2 headers object with an array value in order to provide a list of headers considered sensitive. See Sensitive headers for more details. #### Headers object# Headers are represented as own-properties on JavaScript objects. The property keys will be serialized to lower-case. Property values should be strings (if they are not they will be coerced to strings) or an `Array` of strings (in order to send more than one value per header field). const headers = { ':status': '200', 'content-type': 'text-plain', 'ABC': ['has', 'more', 'than', 'one', 'value'], }; stream.respond(headers); Header objects passed to callback functions will have a `null` prototype. This means that normal JavaScript object methods such as `Object.prototype.toString()` and `Object.prototype.hasOwnProperty()` will not work. For incoming headers: * The `:status` header is converted to `number`. * Duplicates of `:status`, `:method`, `:authority`, `:scheme`, `:path`, `:protocol`, `age`, `authorization`, `access-control-allow-credentials`, `access-control-max-age`, `access-control-request-method`, `content-encoding`, `content-language`, `content-length`, `content-location`, `content-md5`, `content-range`, `content-type`, `date`, `dnt`, `etag`, `expires`, `from`, `host`, `if-match`, `if-modified-since`, `if-none-match`, `if-range`, `if-unmodified-since`, `last-modified`, `location`, `max-forwards`, `proxy-authorization`, `range`, `referer`,`retry-after`, `tk`, `upgrade-insecure-requests`, `user-agent` or `x-content-type-options` are discarded. * `set-cookie` is always an array. Duplicates are added to the array. * For duplicate `cookie` headers, the values are joined together with '; '. * For all other headers, the values are joined together with ', '. import { createServer } from 'node:http2'; const server = createServer(); server.on('stream', (stream, headers) => { console.log(headers[':path']); console.log(headers.ABC); }); ##### Raw headers# In some APIs, in addition to object format, headers can also be passed or accessed as a raw flat array, preserving details of ordering and duplicate keys to match the raw transmission format. In this format the keys and values are in the same list. It is not a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values. Duplicate headers are not merged and so each key-value pair will appear separately. This can be useful for cases such as proxies, where existing headers should be exactly forwarded as received, or as a performance optimization when the headers are already available in raw format. const rawHeaders = [ ':status', '404', 'content-type', 'text/plain', ]; stream.respond(rawHeaders); ##### Sensitive headers# HTTP2 headers can be marked as sensitive, which means that the HTTP/2 header compression algorithm will never index them. This can make sense for header values with low entropy and that may be considered valuable to an attacker, for example `Cookie` or `Authorization`. To achieve this, add the header name to the `[http2.sensitiveHeaders]` property as an array: const headers = { ':status': '200', 'content-type': 'text-plain', 'cookie': 'some-cookie', 'other-sensitive-header': 'very secret data', [http2.sensitiveHeaders]: ['cookie', 'other-sensitive-header'], }; stream.respond(headers); For some headers, such as `Authorization` and short `Cookie` headers, this flag is set automatically. This property is also set for received headers. It will contain the names of all headers marked as sensitive, including ones marked that way automatically. For raw headers, this should still be set as a property on the array, like `rawHeadersArray[http2.sensitiveHeaders] = ['cookie']`, not as a separate key and value pair within the array itself. #### Settings object# History VersionChanges v12.12.0 The `maxConcurrentStreams` setting is stricter. v8.9.3 The `maxHeaderListSize` setting is now strictly enforced. v8.4.0 Added in: v8.4.0 The `http2.getDefaultSettings()`, `http2.getPackedSettings()`, `http2.createServer()`, `http2.createSecureServer()`, `http2session.settings()`, `http2session.localSettings`, and `http2session.remoteSettings` APIs either return or receive as input an object that defines configuration settings for an `Http2Session` object. These objects are ordinary JavaScript objects containing the following properties. * `headerTableSize` Specifies the maximum number of bytes used for header compression. The minimum allowed value is 0. The maximum allowed value is 232-1. Default: `4096`. * `enablePush` Specifies `true` if HTTP/2 Push Streams are to be permitted on the `Http2Session` instances. Default: `true`. * `initialWindowSize` Specifies the sender's initial window size in bytes for stream-level flow control. The minimum allowed value is 0. The maximum allowed value is 232-1. Default: `65535`. * `maxFrameSize` Specifies the size in bytes of the largest frame payload. The minimum allowed value is 16,384. The maximum allowed value is 224-1. Default: `16384`. * `maxConcurrentStreams` Specifies the maximum number of concurrent streams permitted on an `Http2Session`. There is no default value which implies, at least theoretically, 232-1 streams may be open concurrently at any given time in an `Http2Session`. The minimum value is 0. The maximum allowed value is 232-1. Default: `4294967295`. * `maxHeaderListSize` Specifies the maximum size (uncompressed octets) of header list that will be accepted. The minimum allowed value is 0. The maximum allowed value is 232-1. Default: `65535`. * `maxHeaderSize` Alias for `maxHeaderListSize`. * `enableConnectProtocol` Specifies `true` if the "Extended Connect Protocol" defined by RFC 8441 is to be enabled. This setting is only meaningful if sent by the server. Once the `enableConnectProtocol` setting has been enabled for a given `Http2Session`, it cannot be disabled. Default: `false`. * `customSettings` Specifies additional settings, yet not implemented in node and the underlying libraries. The key of the object defines the numeric value of the settings type (as defined in the "HTTP/2 SETTINGS" registry established by [RFC 7540]) and the values the actual numeric value of the settings. The settings type has to be an integer in the range from 1 to 2^16-1. It should not be a settings type already handled by node, i.e. currently it should be greater than 6, although it is not an error. The values need to be unsigned integers in the range from 0 to 2^32-1. Currently, a maximum of up 10 custom settings is supported. It is only supported for sending SETTINGS, or for receiving settings values specified in the `remoteCustomSettings` options of the server or client object. Do not mix the `customSettings`-mechanism for a settings id with interfaces for the natively handled settings, in case a setting becomes natively supported in a future node version. All additional properties on the settings object are ignored. #### Error handling# There are several types of error conditions that may arise when using the `node:http2` module: Validation errors occur when an incorrect argument, option, or setting value is passed in. These will always be reported by a synchronous `throw`. State errors occur when an action is attempted at an incorrect time (for instance, attempting to send data on a stream after it has closed). These will be reported using either a synchronous `throw` or via an `'error'` event on the `Http2Stream`, `Http2Session` or HTTP/2 Server objects, depending on where and when the error occurs. Internal errors occur when an HTTP/2 session fails unexpectedly. These will be reported via an `'error'` event on the `Http2Session` or HTTP/2 Server objects. Protocol errors occur when various HTTP/2 protocol constraints are violated. These will be reported using either a synchronous `throw` or via an `'error'` event on the `Http2Stream`, `Http2Session` or HTTP/2 Server objects, depending on where and when the error occurs. #### Invalid character handling in header names and values# The HTTP/2 implementation applies stricter handling of invalid characters in HTTP header names and values than the HTTP/1 implementation. Header field names are case-insensitive and are transmitted over the wire strictly as lower-case strings. The API provided by Node.js allows header names to be set as mixed-case strings (e.g. `Content-Type`) but will convert those to lower-case (e.g. `content-type`) upon transmission. Header field-names must only contain one or more of the following ASCII characters: `a`-`z`, `A`-`Z`, `0`-`9`, `!`, `#`, `$`, `%`, `&`, `'`, `*`, `+`, `-`, `.`, `^`, `_`, ``` (backtick), `|`, and `~`. Using invalid characters within an HTTP header field name will cause the stream to be closed with a protocol error being reported. Header field values are handled with more leniency but should not contain new-line or carriage return characters and should be limited to US-ASCII characters, per the requirements of the HTTP specification. #### Push streams on the client# To receive pushed streams on the client, set a listener for the `'stream'` event on the `ClientHttp2Session`: import { connect } from 'node:http2'; const client = connect('http://localhost'); client.on('stream', (pushedStream, requestHeaders) => { pushedStream.on('push', (responseHeaders) => { // Process response headers }); pushedStream.on('data', (chunk) => { /* handle pushed data */ }); }); const req = client.request({ ':path': '/' }); #### Supporting the `CONNECT` method# The `CONNECT` method is used to allow an HTTP/2 server to be used as a proxy for TCP/IP connections. A simple TCP Server: import { createServer } from 'node:net'; const server = createServer((socket) => { let name = ''; socket.setEncoding('utf8'); socket.on('data', (chunk) => name += chunk); socket.on('end', () => socket.end(`hello ${name}`)); }); server.listen(8000); An HTTP/2 CONNECT proxy: import { createServer, constants } from 'node:http2'; const { NGHTTP2_REFUSED_STREAM, NGHTTP2_CONNECT_ERROR } = constants; import { connect } from 'node:net'; const proxy = createServer(); proxy.on('stream', (stream, headers) => { if (headers[':method'] !== 'CONNECT') { // Only accept CONNECT requests stream.close(NGHTTP2_REFUSED_STREAM); return; } const auth = new URL(`tcp://${headers[':authority']}`); // It's a very good idea to verify that hostname and port are // things this proxy should be connecting to. const socket = connect(auth.port, auth.hostname, () => { stream.respond(); socket.pipe(stream); stream.pipe(socket); }); socket.on('error', (error) => { stream.close(NGHTTP2_CONNECT_ERROR); }); }); proxy.listen(8001); An HTTP/2 CONNECT client: import { connect, constants } from 'node:http2'; const client = connect('http://localhost:8001'); // Must not specify the ':path' and ':scheme' headers // for CONNECT requests or an error will be thrown. const req = client.request({ ':method': 'CONNECT', ':authority': 'localhost:8000', }); req.on('response', (headers) => { console.log(headers[constants.HTTP2_HEADER_STATUS]); }); let data = ''; req.setEncoding('utf8'); req.on('data', (chunk) => data += chunk); req.on('end', () => { console.log(`The server says: ${data}`); client.close(); }); req.end('Jane'); #### The extended `CONNECT` protocol# RFC 8441 defines an "Extended CONNECT Protocol" extension to HTTP/2 that may be used to bootstrap the use of an `Http2Stream` using the `CONNECT` method as a tunnel for other communication protocols (such as WebSockets). The use of the Extended CONNECT Protocol is enabled by HTTP/2 servers by using the `enableConnectProtocol` setting: import { createServer } from 'node:http2'; const settings = { enableConnectProtocol: true }; const server = createServer({ settings }); Once the client receives the `SETTINGS` frame from the server indicating that the extended CONNECT may be used, it may send `CONNECT` requests that use the `':protocol'` HTTP/2 pseudo-header: import { connect } from 'node:http2'; const client = connect('http://localhost:8080'); client.on('remoteSettings', (settings) => { if (settings.enableConnectProtocol) { const req = client.request({ ':method': 'CONNECT', ':protocol': 'foo' }); // ... } }); ### Compatibility API# The Compatibility API has the goal of providing a similar developer experience of HTTP/1 when using HTTP/2, making it possible to develop applications that support both HTTP/1 and HTTP/2. This API targets only the public API of the HTTP/1. However many modules use internal methods or state, and those are not supported as it is a completely different implementation. The following example creates an HTTP/2 server using the compatibility API: import { createServer } from 'node:http2'; const server = createServer((req, res) => { res.setHeader('Content-Type', 'text/html'); res.setHeader('X-Foo', 'bar'); res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' }); res.end('ok'); }); In order to create a mixed HTTPS and HTTP/2 server, refer to the ALPN negotiation section. Upgrading from non-tls HTTP/1 servers is not supported. The HTTP/2 compatibility API is composed of `Http2ServerRequest` and `Http2ServerResponse`. They aim at API compatibility with HTTP/1, but they do not hide the differences between the protocols. As an example, the status message for HTTP codes is ignored. #### ALPN negotiation# ALPN negotiation allows supporting both HTTPS and HTTP/2 over the same socket. The `req` and `res` objects can be either HTTP/1 or HTTP/2, and an application must restrict itself to the public API of HTTP/1, and detect if it is possible to use the more advanced features of HTTP/2. The following example creates a server that supports both protocols: import { createSecureServer } from 'node:http2'; import { readFileSync } from 'node:fs'; const cert = readFileSync('./cert.pem'); const key = readFileSync('./key.pem'); const server = createSecureServer( { cert, key, allowHTTP1: true }, onRequest, ).listen(8000); function onRequest(req, res) { // Detects if it is a HTTPS request or HTTP/2 const { socket: { alpnProtocol } } = req.httpVersion === '2.0' ? req.stream.session : req; res.writeHead(200, { 'content-type': 'application/json' }); res.end(JSON.stringify({ alpnProtocol, httpVersion: req.httpVersion, })); } The `'request'` event works identically on both HTTPS and HTTP/2. #### Class: `http2.Http2ServerRequest`# Added in: v8.4.0 * Extends: A `Http2ServerRequest` object is created by `http2.Server` or `http2.SecureServer` and passed as the first argument to the `'request'` event. It may be used to access a request status, headers, and data. ##### Event: `'aborted'`# Added in: v8.4.0 The `'aborted'` event is emitted whenever a `Http2ServerRequest` instance is abnormally aborted in mid-communication. The `'aborted'` event will only be emitted if the `Http2ServerRequest` writable side has not been ended. ##### Event: `'close'`# Added in: v8.4.0 Indicates that the underlying `Http2Stream` was closed. Just like `'end'`, this event occurs only once per response. ##### `request.aborted`# Added in: v10.1.0 * Type: The `request.aborted` property will be `true` if the request has been aborted. ##### `request.authority`# Added in: v8.4.0 * Type: The request authority pseudo header field. Because HTTP/2 allows requests to set either `:authority` or `host`, this value is derived from `req.headers[':authority']` if present. Otherwise, it is derived from `req.headers['host']`. ##### `request.complete`# Added in: v12.10.0 * Type: The `request.complete` property will be `true` if the request has been completed, aborted, or destroyed. ##### `request.connection`# Added in: v8.4.0Deprecated since: v13.0.0 Stability: 0 \- Deprecated. Use `request.socket`. * Type: | See `request.socket`. ##### `request.destroy([error])`# Added in: v8.4.0 * `error` Calls `destroy()` on the `Http2Stream` that received the `Http2ServerRequest`. If `error` is provided, an `'error'` event is emitted and `error` is passed as an argument to any listeners on the event. It does nothing if the stream was already destroyed. ##### `request.headers`# Added in: v8.4.0 * Type: The request/response headers object. Key-value pairs of header names and values. Header names are lower-cased. // Prints something like: // // { 'user-agent': 'curl/7.22.0', // host: '127.0.0.1:8000', // accept: '*/*' } console.log(request.headers); See HTTP/2 Headers Object. In HTTP/2, the request path, host name, protocol, and method are represented as special headers prefixed with the `:` character (e.g. `':path'`). These special headers will be included in the `request.headers` object. Care must be taken not to inadvertently modify these special headers or errors may occur. For instance, removing all headers from the request will cause errors to occur: removeAllHeaders(request.headers); assert(request.url); // Fails because the :path header has been removed ##### `request.httpVersion`# Added in: v8.4.0 * Type: In case of server request, the HTTP version sent by the client. In the case of client response, the HTTP version of the connected-to server. Returns `'2.0'`. Also `message.httpVersionMajor` is the first integer and `message.httpVersionMinor` is the second. ##### `request.method`# Added in: v8.4.0 * Type: The request method as a string. Read-only. Examples: `'GET'`, `'DELETE'`. ##### `request.rawHeaders`# Added in: v8.4.0 * Type: The raw request/response headers list exactly as they were received. // Prints something like: // // [ 'user-agent', // 'this is invalid because there can be only one', // 'User-Agent', // 'curl/7.22.0', // 'Host', // '127.0.0.1:8000', // 'ACCEPT', // '*/*' ] console.log(request.rawHeaders); ##### `request.rawTrailers`# Added in: v8.4.0 * Type: The raw request/response trailer keys and values exactly as they were received. Only populated at the `'end'` event. ##### `request.scheme`# Added in: v8.4.0 * Type: The request scheme pseudo header field indicating the scheme portion of the target URL. ##### `request.setTimeout(msecs, callback)`# Added in: v8.4.0 * `msecs` * `callback` * Returns: Sets the `Http2Stream`'s timeout value to `msecs`. If a callback is provided, then it is added as a listener on the `'timeout'` event on the response object. If no `'timeout'` listener is added to the request, the response, or the server, then `Http2Stream`s are destroyed when they time out. If a handler is assigned to the request, the response, or the server's `'timeout'` events, timed out sockets must be handled explicitly. ##### `request.socket`# Added in: v8.4.0 * Type: | Returns a `Proxy` object that acts as a `net.Socket` (or `tls.TLSSocket`) but applies getters, setters, and methods based on HTTP/2 logic. `destroyed`, `readable`, and `writable` properties will be retrieved from and set on `request.stream`. `destroy`, `emit`, `end`, `on` and `once` methods will be called on `request.stream`. `setTimeout` method will be called on `request.stream.session`. `pause`, `read`, `resume`, and `write` will throw an error with code `ERR_HTTP2_NO_SOCKET_MANIPULATION`. See `Http2Session` and Sockets for more information. All other interactions will be routed directly to the socket. With TLS support, use `request.socket.getPeerCertificate()` to obtain the client's authentication details. ##### `request.stream`# Added in: v8.4.0 * Type: The `Http2Stream` object backing the request. ##### `request.trailers`# Added in: v8.4.0 * Type: The request/response trailers object. Only populated at the `'end'` event. ##### `request.url`# Added in: v8.4.0 * Type: Request URL string. This contains only the URL that is present in the actual HTTP request. If the request is: GET /status?name=ryan HTTP/1.1 Accept: text/plain Then `request.url` will be: '/status?name=ryan' To parse the url into its parts, `new URL()` can be used: $ node > new URL('/status?name=ryan', 'http://example.com') URL { href: 'http://example.com/status?name=ryan', origin: 'http://example.com', protocol: 'http:', username: '', password: '', host: 'example.com', hostname: 'example.com', port: '', pathname: '/status', search: '?name=ryan', searchParams: URLSearchParams { 'name' => 'ryan' }, hash: '' } #### Class: `http2.Http2ServerResponse`# Added in: v8.4.0 * Extends: This object is created internally by an HTTP server, not by the user. It is passed as the second parameter to the `'request'` event. ##### Event: `'close'`# Added in: v8.4.0 Indicates that the underlying `Http2Stream` was terminated before `response.end()` was called or able to flush. ##### Event: `'finish'`# Added in: v8.4.0 Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the HTTP/2 multiplexing for transmission over the network. It does not imply that the client has received anything yet. After this event, no more events will be emitted on the response object. ##### `response.addTrailers(headers)`# Added in: v8.4.0 * `headers` This method adds HTTP trailing headers (a header but at the end of the message) to the response. Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. ##### `response.appendHeader(name, value)`# Added in: v21.7.0, v20.12.0 * `name` * `value` | Append a single header value to the header object. If the value is an array, this is equivalent to calling this method multiple times. If there were no previous values for the header, this is equivalent to calling `response.setHeader()`. Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. // Returns headers including "set-cookie: a" and "set-cookie: b" const server = http2.createServer((req, res) => { res.setHeader('set-cookie', 'a'); res.appendHeader('set-cookie', 'b'); res.writeHead(200); res.end('ok'); }); ##### `response.connection`# Added in: v8.4.0Deprecated since: v13.0.0 Stability: 0 \- Deprecated. Use `response.socket`. * Type: | See `response.socket`. ##### `response.createPushResponse(headers, callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.4.0 Added in: v8.4.0 * `headers` An object describing the headers * `callback` Called once `http2stream.pushStream()` is finished, or either when the attempt to create the pushed `Http2Stream` has failed or has been rejected, or the state of `Http2ServerRequest` is closed prior to calling the `http2stream.pushStream()` method * `err` * `res` The newly-created `Http2ServerResponse` object Call `http2stream.pushStream()` with the given headers, and wrap the given `Http2Stream` on a newly created `Http2ServerResponse` as the callback parameter if successful. When `Http2ServerRequest` is closed, the callback is called with an error `ERR_HTTP2_INVALID_STREAM`. ##### `response.end([data[, encoding]][, callback])`# History VersionChanges v10.0.0 This method now returns a reference to `ServerResponse`. v8.4.0 Added in: v8.4.0 * `data` | | * `encoding` * `callback` * Returns: This method signals to the server that all of the response headers and body have been sent; that server should consider this message complete. The method, `response.end()`, MUST be called on each response. If `data` is specified, it is equivalent to calling `response.write(data, encoding)` followed by `response.end(callback)`. If `callback` is specified, it will be called when the response stream is finished. ##### `response.finished`# Added in: v8.4.0Deprecated since: v13.4.0, v12.16.0 Stability: 0 \- Deprecated. Use `response.writableEnded`. * Type: Boolean value that indicates whether the response has completed. Starts as `false`. After `response.end()` executes, the value will be `true`. ##### `response.getHeader(name)`# Added in: v8.4.0 * `name` * Returns: Reads out a header that has already been queued but not sent to the client. The name is case-insensitive. const contentType = response.getHeader('content-type'); ##### `response.getHeaderNames()`# Added in: v8.4.0 * Returns: Returns an array containing the unique names of the current outgoing headers. All header names are lowercase. response.setHeader('Foo', 'bar'); response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headerNames = response.getHeaderNames(); // headerNames === ['foo', 'set-cookie'] ##### `response.getHeaders()`# Added in: v8.4.0 * Returns: Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related http module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase. The object returned by the `response.getHeaders()` method does not prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and will not work. response.setHeader('Foo', 'bar'); response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headers = response.getHeaders(); // headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] } ##### `response.hasHeader(name)`# Added in: v8.4.0 * `name` * Returns: Returns `true` if the header identified by `name` is currently set in the outgoing headers. The header name matching is case-insensitive. const hasContentType = response.hasHeader('content-type'); ##### `response.headersSent`# Added in: v8.4.0 * Type: True if headers were sent, false otherwise (read-only). ##### `response.removeHeader(name)`# Added in: v8.4.0 * `name` Removes a header that has been queued for implicit sending. response.removeHeader('Content-Encoding'); ##### `response.req`# Added in: v15.7.0 * Type: A reference to the original HTTP2 `request` object. ##### `response.sendDate`# Added in: v8.4.0 * Type: When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true. This should only be disabled for testing; HTTP requires the Date header in responses. ##### `response.setHeader(name, value)`# Added in: v8.4.0 * `name` * `value` | Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here to send multiple headers with the same name. response.setHeader('Content-Type', 'text/html; charset=utf-8'); or response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']); Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. When headers have been set with `response.setHeader()`, they will be merged with any headers passed to `response.writeHead()`, with the headers passed to `response.writeHead()` given precedence. // Returns content-type = text/plain const server = http2.createServer((req, res) => { res.setHeader('Content-Type', 'text/html; charset=utf-8'); res.setHeader('X-Foo', 'bar'); res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' }); res.end('ok'); }); ##### `response.setTimeout(msecs[, callback])`# Added in: v8.4.0 * `msecs` * `callback` * Returns: Sets the `Http2Stream`'s timeout value to `msecs`. If a callback is provided, then it is added as a listener on the `'timeout'` event on the response object. If no `'timeout'` listener is added to the request, the response, or the server, then `Http2Stream`s are destroyed when they time out. If a handler is assigned to the request, the response, or the server's `'timeout'` events, timed out sockets must be handled explicitly. ##### `response.socket`# Added in: v8.4.0 * Type: | Returns a `Proxy` object that acts as a `net.Socket` (or `tls.TLSSocket`) but applies getters, setters, and methods based on HTTP/2 logic. `destroyed`, `readable`, and `writable` properties will be retrieved from and set on `response.stream`. `destroy`, `emit`, `end`, `on` and `once` methods will be called on `response.stream`. `setTimeout` method will be called on `response.stream.session`. `pause`, `read`, `resume`, and `write` will throw an error with code `ERR_HTTP2_NO_SOCKET_MANIPULATION`. See `Http2Session` and Sockets for more information. All other interactions will be routed directly to the socket. import { createServer } from 'node:http2'; const server = createServer((req, res) => { const ip = req.socket.remoteAddress; const port = req.socket.remotePort; res.end(`Your IP address is ${ip} and your source port is ${port}.`); }).listen(3000); ##### `response.statusCode`# Added in: v8.4.0 * Type: When using implicit headers (not calling `response.writeHead()` explicitly), this property controls the status code that will be sent to the client when the headers get flushed. response.statusCode = 404; After response header was sent to the client, this property indicates the status code which was sent out. ##### `response.statusMessage`# Added in: v8.4.0 * Type: Status message is not supported by HTTP/2 (RFC 7540 8.1.2.4). It returns an empty string. ##### `response.stream`# Added in: v8.4.0 * Type: The `Http2Stream` object backing the response. ##### `response.writableEnded`# Added in: v12.9.0 * Type: Is `true` after `response.end()` has been called. This property does not indicate whether the data has been flushed, for this use `writable.writableFinished` instead. ##### `response.write(chunk[, encoding][, callback])`# Added in: v8.4.0 * `chunk` | | * `encoding` * `callback` * Returns: If this method is called and `response.writeHead()` has not been called, it will switch to implicit header mode and flush the implicit headers. This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body. In the `node:http` module, the response body is omitted when the request is a HEAD request. Similarly, the `204` and `304` responses must not include a message body. `chunk` can be a string or a buffer. If `chunk` is a string, the second parameter specifies how to encode it into a byte stream. By default the `encoding` is `'utf8'`. `callback` will be called when this chunk of data is flushed. This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used. The first time `response.write()` is called, it will send the buffered header information and the first chunk of the body to the client. The second time `response.write()` is called, Node.js assumes data will be streamed, and sends the new data separately. That is, the response is buffered up to the first chunk of the body. Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. `'drain'` will be emitted when the buffer is free again. ##### `response.writeContinue()`# Added in: v8.4.0 Sends a status `100 Continue` to the client, indicating that the request body should be sent. See the `'checkContinue'` event on `Http2Server` and `Http2SecureServer`. ##### `response.writeEarlyHints(hints)`# Added in: v18.11.0 * `hints` Sends a status `103 Early Hints` to the client with a Link header, indicating that the user agent can preload/preconnect the linked resources. The `hints` is an object containing the values of headers to be sent with early hints message. Example const earlyHintsLink = '; rel=preload; as=style'; response.writeEarlyHints({ 'link': earlyHintsLink, }); const earlyHintsLinks = [ '; rel=preload; as=style', '; rel=preload; as=script', ]; response.writeEarlyHints({ 'link': earlyHintsLinks, }); ##### `response.writeHead(statusCode[, statusMessage][, headers])`# History VersionChanges v11.10.0, v10.17.0 Return `this` from `writeHead()` to allow chaining with `end()`. v8.4.0 Added in: v8.4.0 * `statusCode` * `statusMessage` * `headers` | * Returns: Sends a response header to the request. The status code is a 3-digit HTTP status code, like `404`. The last argument, `headers`, are the response headers. Returns a reference to the `Http2ServerResponse`, so that calls can be chained. For compatibility with HTTP/1, a human-readable `statusMessage` may be passed as the second argument. However, because the `statusMessage` has no meaning within HTTP/2, the argument will have no effect and a process warning will be emitted. const body = 'hello world'; response.writeHead(200, { 'Content-Length': Buffer.byteLength(body), 'Content-Type': 'text/plain; charset=utf-8', }); `Content-Length` is given in bytes not characters. The `Buffer.byteLength()` API may be used to determine the number of bytes in a given encoding. On outbound messages, Node.js does not check if Content-Length and the length of the body being transmitted are equal or not. However, when receiving messages, Node.js will automatically reject messages when the `Content-Length` does not match the actual payload size. This method may be called at most one time on a message before `response.end()` is called. If `response.write()` or `response.end()` are called before calling this, the implicit/mutable headers will be calculated and call this function. When headers have been set with `response.setHeader()`, they will be merged with any headers passed to `response.writeHead()`, with the headers passed to `response.writeHead()` given precedence. // Returns content-type = text/plain const server = http2.createServer((req, res) => { res.setHeader('Content-Type', 'text/html; charset=utf-8'); res.setHeader('X-Foo', 'bar'); res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' }); res.end('ok'); }); Attempting to set a header field name or value that contains invalid characters will result in a `TypeError` being thrown. ### Collecting HTTP/2 performance metrics# The Performance Observer API can be used to collect basic performance metrics for each `Http2Session` and `Http2Stream` instance. import { PerformanceObserver } from 'node:perf_hooks'; const obs = new PerformanceObserver((items) => { const entry = items.getEntries()[0]; console.log(entry.entryType); // prints 'http2' if (entry.name === 'Http2Session') { // Entry contains statistics about the Http2Session } else if (entry.name === 'Http2Stream') { // Entry contains statistics about the Http2Stream } }); obs.observe({ entryTypes: ['http2'] }); The `entryType` property of the `PerformanceEntry` will be equal to `'http2'`. The `name` property of the `PerformanceEntry` will be equal to either `'Http2Stream'` or `'Http2Session'`. If `name` is equal to `Http2Stream`, the `PerformanceEntry` will contain the following additional properties: * `bytesRead` The number of `DATA` frame bytes received for this `Http2Stream`. * `bytesWritten` The number of `DATA` frame bytes sent for this `Http2Stream`. * `id` The identifier of the associated `Http2Stream` * `timeToFirstByte` The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first `DATA` frame. * `timeToFirstByteSent` The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and sending of the first `DATA` frame. * `timeToFirstHeader` The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first header. If `name` is equal to `Http2Session`, the `PerformanceEntry` will contain the following additional properties: * `bytesRead` The number of bytes received for this `Http2Session`. * `bytesWritten` The number of bytes sent for this `Http2Session`. * `framesReceived` The number of HTTP/2 frames received by the `Http2Session`. * `framesSent` The number of HTTP/2 frames sent by the `Http2Session`. * `maxConcurrentStreams` The maximum number of streams concurrently open during the lifetime of the `Http2Session`. * `pingRTT` The number of milliseconds elapsed since the transmission of a `PING` frame and the reception of its acknowledgment. Only present if a `PING` frame has been sent on the `Http2Session`. * `streamAverageDuration` The average duration (in milliseconds) for all `Http2Stream` instances. * `streamCount` The number of `Http2Stream` instances processed by the `Http2Session`. * `type` Either `'server'` or `'client'` to identify the type of `Http2Session`. ### Note on `:authority` and `host`# HTTP/2 requires requests to have either the `:authority` pseudo-header or the `host` header. Prefer `:authority` when constructing an HTTP/2 request directly, and `host` when converting from HTTP/1 (in proxies, for instance). The compatibility API falls back to `host` if `:authority` is not present. See `request.authority` for more information. However, if you don't use the compatibility API (or use `req.headers` directly), you need to implement any fall-back behavior yourself. ## HTTPS# Stability: 2 \- Stable Source Code: lib/https.js HTTPS is the HTTP protocol over TLS/SSL. In Node.js this is implemented as a separate module. ### Determining if crypto support is unavailable# It is possible for Node.js to be built without including support for the `node:crypto` module. In such cases, attempting to `import` from `https` or calling `require('node:https')` will result in an error being thrown. When using CommonJS, the error thrown can be caught using try/catch: When using the lexical ESM `import` keyword, the error can only be caught if a handler for `process.on('uncaughtException')` is registered before any attempt to load the module is made (using, for instance, a preload module). When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the `import()` function instead of the lexical `import` keyword: let https; try { https = await import('node:https'); } catch (err) { console.error('https support is disabled!'); } ### Class: `https.Agent`# History VersionChanges v5.3.0 support `0` `maxCachedSessions` to disable TLS session caching. v2.5.0 parameter `maxCachedSessions` added to `options` for TLS sessions reuse. v0.4.5 Added in: v0.4.5 An `Agent` object for HTTPS similar to `http.Agent`. See `https.request()` for more information. #### `new Agent([options])`# History VersionChanges v24.5.0 Add support for `proxyEnv`. v24.5.0 Add support for `defaultPort` and `protocol`. v12.5.0 do not automatically set servername if the target host was specified using an IP address. * `options` Set of configurable options to set on the agent. Can have the same fields as for `http.Agent(options)`, and * `maxCachedSessions` maximum number of TLS cached sessions. Use `0` to disable TLS session caching. Default: `100`. * `servername` the value of Server Name Indication extension to be sent to the server. Use empty string `''` to disable sending the extension. Default: host name of the target server, unless the target server is specified using an IP address, in which case the default is `''` (no extension). See `Session Resumption` for information about TLS session reuse. ##### Event: `'keylog'`# Added in: v13.2.0, v12.16.0 * `line` Line of ASCII text, in NSS `SSLKEYLOGFILE` format. * `tlsSocket` The `tls.TLSSocket` instance on which it was generated. The `keylog` event is emitted when key material is generated or received by a connection managed by this agent (typically before handshake has completed, but not necessarily). This keying material can be stored for debugging, as it allows captured TLS traffic to be decrypted. It may be emitted multiple times for each socket. A typical use case is to append received lines to a common text file, which is later used by software (such as Wireshark) to decrypt the traffic: // ... https.globalAgent.on('keylog', (line, tlsSocket) => { fs.appendFileSync('/tmp/ssl-keys.log', line, { mode: 0o600 }); }); ### Class: `https.Server`# Added in: v0.3.4 * Extends: See `http.Server` for more information. #### `server.close([callback])`# Added in: v0.1.90 * `callback` * Returns: See `server.close()` in the `node:http` module. #### `server[Symbol.asyncDispose]()`# History VersionChanges v24.2.0 No longer experimental. v20.4.0 Added in: v20.4.0 Calls `server.close()` and returns a promise that fulfills when the server has closed. #### `server.closeAllConnections()`# Added in: v18.2.0 See `server.closeAllConnections()` in the `node:http` module. #### `server.closeIdleConnections()`# Added in: v18.2.0 See `server.closeIdleConnections()` in the `node:http` module. #### `server.headersTimeout`# Added in: v11.3.0 * Type: Default: `60000` See `server.headersTimeout` in the `node:http` module. #### `server.listen()`# Starts the HTTPS server listening for encrypted connections. This method is identical to `server.listen()` from `net.Server`. #### `server.maxHeadersCount`# * Type: Default: `2000` See `server.maxHeadersCount` in the `node:http` module. #### `server.requestTimeout`# History VersionChanges v18.0.0 The default request timeout changed from no timeout to 300s (5 minutes). v14.11.0 Added in: v14.11.0 * Type: Default: `300000` See `server.requestTimeout` in the `node:http` module. #### `server.setTimeout([msecs][, callback])`# Added in: v0.11.2 * `msecs` Default: `120000` (2 minutes) * `callback` * Returns: See `server.setTimeout()` in the `node:http` module. #### `server.timeout`# History VersionChanges v13.0.0 The default timeout changed from 120s to 0 (no timeout). v0.11.2 Added in: v0.11.2 * Type: Default: 0 (no timeout) See `server.timeout` in the `node:http` module. #### `server.keepAliveTimeout`# Added in: v8.0.0 * Type: Default: `5000` (5 seconds) See `server.keepAliveTimeout` in the `node:http` module. ### `https.createServer([options][, requestListener])`# Added in: v0.3.4 * `options` Accepts `options` from `tls.createServer()`, `tls.createSecureContext()` and `http.createServer()`. * `requestListener` A listener to be added to the `'request'` event. * Returns: // curl -k https://localhost:8000/ import { createServer } from 'node:https'; import { readFileSync } from 'node:fs'; const options = { key: readFileSync('private-key.pem'), cert: readFileSync('certificate.pem'), }; createServer(options, (req, res) => { res.writeHead(200); res.end('hello world\n'); }).listen(8000); Or import { createServer } from 'node:https'; import { readFileSync } from 'node:fs'; const options = { pfx: readFileSync('test_cert.pfx'), passphrase: 'sample', }; createServer(options, (req, res) => { res.writeHead(200); res.end('hello world\n'); }).listen(8000); To generate the certificate and key for this example, run: openssl req -x509 -newkey rsa:2048 -nodes -sha256 -subj '/CN=localhost' \ -keyout private-key.pem -out certificate.pem Then, to generate the `pfx` certificate for this example, run: openssl pkcs12 -certpbe AES-256-CBC -export -out test_cert.pfx \ -inkey private-key.pem -in certificate.pem -passout pass:sample ### `https.get(options[, callback])`# ### `https.get(url[, options][, callback])`# History VersionChanges v10.9.0 The `url` parameter can now be passed along with a separate `options` object. v7.5.0 The `options` parameter can be a WHATWG `URL` object. v0.3.6 Added in: v0.3.6 * `url` | * `options` | | Accepts the same `options` as `https.request()`, with the method set to GET by default. * `callback` * Returns: Like `http.get()` but for HTTPS. `options` can be an object, a string, or a `URL` object. If `options` is a string, it is automatically parsed with `new URL()`. If it is a `URL` object, it will be automatically converted to an ordinary `options` object. import { get } from 'node:https'; import process from 'node:process'; get('https://encrypted.google.com/', (res) => { console.log('statusCode:', res.statusCode); console.log('headers:', res.headers); res.on('data', (d) => { process.stdout.write(d); }); }).on('error', (e) => { console.error(e); }); ### `https.globalAgent`# History VersionChanges v19.0.0 The agent now uses HTTP Keep-Alive and a 5 second timeout by default. v0.5.9 Added in: v0.5.9 Global instance of `https.Agent` for all HTTPS client requests. Diverges from a default `https.Agent` configuration by having `keepAlive` enabled and a `timeout` of 5 seconds. ### `https.request(options[, callback])`# ### `https.request(url[, options][, callback])`# History VersionChanges v22.4.0, v20.16.0 The `clientCertEngine` option depends on custom engine support in OpenSSL which is deprecated in OpenSSL 3. v16.7.0, v14.18.0 When using a `URL` object parsed username and password will now be properly URI decoded. v14.1.0, v13.14.0 The `highWaterMark` option is accepted now. v10.9.0 The `url` parameter can now be passed along with a separate `options` object. v9.3.0 The `options` parameter can now include `clientCertEngine`. v7.5.0 The `options` parameter can be a WHATWG `URL` object. v0.3.6 Added in: v0.3.6 * `url` | * `options` | | Accepts all `options` from `http.request()`, with some differences in default values: * `protocol` Default: `'https:'` * `port` Default: `443` * `agent` Default: `https.globalAgent` * `callback` * Returns: Makes a request to a secure web server. The following additional `options` from `tls.connect()` are also accepted: `ca`, `cert`, `ciphers`, `clientCertEngine` (deprecated), `crl`, `dhparam`, `ecdhCurve`, `honorCipherOrder`, `key`, `passphrase`, `pfx`, `rejectUnauthorized`, `secureOptions`, `secureProtocol`, `servername`, `sessionIdContext`, `highWaterMark`. `options` can be an object, a string, or a `URL` object. If `options` is a string, it is automatically parsed with `new URL()`. If it is a `URL` object, it will be automatically converted to an ordinary `options` object. `https.request()` returns an instance of the `http.ClientRequest` class. The `ClientRequest` instance is a writable stream. If one needs to upload a file with a POST request, then write to the `ClientRequest` object. import { request } from 'node:https'; import process from 'node:process'; const options = { hostname: 'encrypted.google.com', port: 443, path: '/', method: 'GET', }; const req = request(options, (res) => { console.log('statusCode:', res.statusCode); console.log('headers:', res.headers); res.on('data', (d) => { process.stdout.write(d); }); }); req.on('error', (e) => { console.error(e); }); req.end(); Example using options from `tls.connect()`: const options = { hostname: 'encrypted.google.com', port: 443, path: '/', method: 'GET', key: fs.readFileSync('private-key.pem'), cert: fs.readFileSync('certificate.pem'), }; options.agent = new https.Agent(options); const req = https.request(options, (res) => { // ... }); Alternatively, opt out of connection pooling by not using an `Agent`. const options = { hostname: 'encrypted.google.com', port: 443, path: '/', method: 'GET', key: fs.readFileSync('private-key.pem'), cert: fs.readFileSync('certificate.pem'), agent: false, }; const req = https.request(options, (res) => { // ... }); Example using a `URL` as `options`: const options = new URL('https://abc:[email protected]'); const req = https.request(options, (res) => { // ... }); Example pinning on certificate fingerprint, or the public key (similar to `pin-sha256`): import { checkServerIdentity } from 'node:tls'; import { Agent, request } from 'node:https'; import { createHash } from 'node:crypto'; function sha256(s) { return createHash('sha256').update(s).digest('base64'); } const options = { hostname: 'github.com', port: 443, path: '/', method: 'GET', checkServerIdentity: function(host, cert) { // Make sure the certificate is issued to the host we are connected to const err = checkServerIdentity(host, cert); if (err) { return err; } // Pin the public key, similar to HPKP pin-sha256 pinning const pubkey256 = 'SIXvRyDmBJSgatgTQRGbInBaAK+hZOQ18UmrSwnDlK8='; if (sha256(cert.pubkey) !== pubkey256) { const msg = 'Certificate verification error: ' + `The public key of '${cert.subject.CN}' ` + 'does not match our pinned fingerprint'; return new Error(msg); } // Pin the exact certificate, rather than the pub key const cert256 = 'FD:6E:9B:0E:F3:98:BC:D9:04:C3:B2:EC:16:7A:7B:' + '0F:DA:72:01:C9:03:C5:3A:6A:6A:E5:D0:41:43:63:EF:65'; if (cert.fingerprint256 !== cert256) { const msg = 'Certificate verification error: ' + `The certificate of '${cert.subject.CN}' ` + 'does not match our pinned fingerprint'; return new Error(msg); } // This loop is informational only. // Print the certificate and public key fingerprints of all certs in the // chain. Its common to pin the public key of the issuer on the public // internet, while pinning the public key of the service in sensitive // environments. let lastprint256; do { console.log('Subject Common Name:', cert.subject.CN); console.log(' Certificate SHA256 fingerprint:', cert.fingerprint256); const hash = createHash('sha256'); console.log(' Public key ping-sha256:', sha256(cert.pubkey)); lastprint256 = cert.fingerprint256; cert = cert.issuerCertificate; } while (cert.fingerprint256 !== lastprint256); }, }; options.agent = new Agent(options); const req = request(options, (res) => { console.log('All OK. Server matched our pinned cert or public key'); console.log('statusCode:', res.statusCode); res.on('data', (d) => {}); }); req.on('error', (e) => { console.error(e.message); }); req.end(); Outputs for example: Subject Common Name: github.com Certificate SHA256 fingerprint: FD:6E:9B:0E:F3:98:BC:D9:04:C3:B2:EC:16:7A:7B:0F:DA:72:01:C9:03:C5:3A:6A:6A:E5:D0:41:43:63:EF:65 Public key ping-sha256: SIXvRyDmBJSgatgTQRGbInBaAK+hZOQ18UmrSwnDlK8= Subject Common Name: Sectigo ECC Domain Validation Secure Server CA Certificate SHA256 fingerprint: 61:E9:73:75:E9:F6:DA:98:2F:F5:C1:9E:2F:94:E6:6C:4E:35:B6:83:7C:E3:B9:14:D2:24:5C:7F:5F:65:82:5F Public key ping-sha256: Eep0p/AsSa9lFUH6KT2UY+9s1Z8v7voAPkQ4fGknZ2g= Subject Common Name: USERTrust ECC Certification Authority Certificate SHA256 fingerprint: A6:CF:64:DB:B4:C8:D5:FD:19:CE:48:89:60:68:DB:03:B5:33:A8:D1:33:6C:62:56:A8:7D:00:CB:B3:DE:F3:EA Public key ping-sha256: UJM2FOhG9aTNY0Pg4hgqjNzZ/lQBiMGRxPD5Y2/e0bw= Subject Common Name: AAA Certificate Services Certificate SHA256 fingerprint: D7:A7:A0:FB:5D:7E:27:31:D7:71:E9:48:4E:BC:DE:F7:1D:5F:0C:3E:0A:29:48:78:2B:C8:3E:E0:EA:69:9E:F4 Public key ping-sha256: vRU+17BDT2iGsXvOi76E7TQMcTLXAqj0+jGPdW7L1vM= All OK. Server matched our pinned cert or public key statusCode: 200 ## Inspector# Stability: 2 \- Stable Source Code: lib/inspector.js The `node:inspector` module provides an API for interacting with the V8 inspector. It can be accessed using: import * as inspector from 'node:inspector/promises'; or import * as inspector from 'node:inspector'; ### Promises API# Added in: v19.0.0 Stability: 1 \- Experimental #### Class: `inspector.Session`# * Extends: The `inspector.Session` is used for dispatching messages to the V8 inspector back-end and receiving message responses and notifications. ##### `new inspector.Session()`# Added in: v8.0.0 Create a new instance of the `inspector.Session` class. The inspector session needs to be connected through `session.connect()` before the messages can be dispatched to the inspector backend. When using `Session`, the object outputted by the console API will not be released, unless we performed manually `Runtime.DiscardConsoleEntries` command. ##### Event: `'inspectorNotification'`# Added in: v8.0.0 * Type: The notification message object Emitted when any notification from the V8 Inspector is received. session.on('inspectorNotification', (message) => console.log(message.method)); // Debugger.paused // Debugger.resumed > Caveat Breakpoints with same-thread session is not recommended, see support of breakpoints. It is also possible to subscribe only to notifications with specific method: ##### Event: ``# Added in: v8.0.0 * Type: The notification message object Emitted when an inspector notification is received that has its method field set to the `` value. The following snippet installs a listener on the `'Debugger.paused'` event, and prints the reason for program suspension whenever program execution is suspended (through breakpoints, for example): session.on('Debugger.paused', ({ params }) => { console.log(params.hitBreakpoints); }); // [ '/the/file/that/has/the/breakpoint.js:11:0' ] > Caveat Breakpoints with same-thread session is not recommended, see support of breakpoints. ##### `session.connect()`# Added in: v8.0.0 Connects a session to the inspector back-end. ##### `session.connectToMainThread()`# Added in: v12.11.0 Connects a session to the main thread inspector back-end. An exception will be thrown if this API was not called on a Worker thread. ##### `session.disconnect()`# Added in: v8.0.0 Immediately close the session. All pending message callbacks will be called with an error. `session.connect()` will need to be called to be able to send messages again. Reconnected session will lose all inspector state, such as enabled agents or configured breakpoints. ##### `session.post(method[, params])`# Added in: v19.0.0 * `method` * `params` * Returns: Posts a message to the inspector back-end. import { Session } from 'node:inspector/promises'; try { const session = new Session(); session.connect(); const result = await session.post('Runtime.evaluate', { expression: '2 + 2' }); console.log(result); } catch (error) { console.error(error); } // Output: { result: { type: 'number', value: 4, description: '4' } } The latest version of the V8 inspector protocol is published on the Chrome DevTools Protocol Viewer. Node.js inspector supports all the Chrome DevTools Protocol domains declared by V8. Chrome DevTools Protocol domain provides an interface for interacting with one of the runtime agents used to inspect the application state and listen to the run-time events. ##### Example usage# Apart from the debugger, various V8 Profilers are available through the DevTools protocol. ###### CPU profiler# Here's an example showing how to use the CPU Profiler: import { Session } from 'node:inspector/promises'; import fs from 'node:fs'; const session = new Session(); session.connect(); await session.post('Profiler.enable'); await session.post('Profiler.start'); // Invoke business logic under measurement here... // some time later... const { profile } = await session.post('Profiler.stop'); // Write profile to disk, upload, etc. fs.writeFileSync('./profile.cpuprofile', JSON.stringify(profile)); ###### Heap profiler# Here's an example showing how to use the Heap Profiler: import { Session } from 'node:inspector/promises'; import fs from 'node:fs'; const session = new Session(); const fd = fs.openSync('profile.heapsnapshot', 'w'); session.connect(); session.on('HeapProfiler.addHeapSnapshotChunk', (m) => { fs.writeSync(fd, m.params.chunk); }); const result = await session.post('HeapProfiler.takeHeapSnapshot', null); console.log('HeapProfiler.takeHeapSnapshot done:', result); session.disconnect(); fs.closeSync(fd); ### Callback API# #### Class: `inspector.Session`# * Extends: The `inspector.Session` is used for dispatching messages to the V8 inspector back-end and receiving message responses and notifications. ##### `new inspector.Session()`# Added in: v8.0.0 Create a new instance of the `inspector.Session` class. The inspector session needs to be connected through `session.connect()` before the messages can be dispatched to the inspector backend. When using `Session`, the object outputted by the console API will not be released, unless we performed manually `Runtime.DiscardConsoleEntries` command. ##### Event: `'inspectorNotification'`# Added in: v8.0.0 * Type: The notification message object Emitted when any notification from the V8 Inspector is received. session.on('inspectorNotification', (message) => console.log(message.method)); // Debugger.paused // Debugger.resumed > Caveat Breakpoints with same-thread session is not recommended, see support of breakpoints. It is also possible to subscribe only to notifications with specific method: ##### Event: ``;# Added in: v8.0.0 * Type: The notification message object Emitted when an inspector notification is received that has its method field set to the `` value. The following snippet installs a listener on the `'Debugger.paused'` event, and prints the reason for program suspension whenever program execution is suspended (through breakpoints, for example): session.on('Debugger.paused', ({ params }) => { console.log(params.hitBreakpoints); }); // [ '/the/file/that/has/the/breakpoint.js:11:0' ] > Caveat Breakpoints with same-thread session is not recommended, see support of breakpoints. ##### `session.connect()`# Added in: v8.0.0 Connects a session to the inspector back-end. ##### `session.connectToMainThread()`# Added in: v12.11.0 Connects a session to the main thread inspector back-end. An exception will be thrown if this API was not called on a Worker thread. ##### `session.disconnect()`# Added in: v8.0.0 Immediately close the session. All pending message callbacks will be called with an error. `session.connect()` will need to be called to be able to send messages again. Reconnected session will lose all inspector state, such as enabled agents or configured breakpoints. ##### `session.post(method[, params][, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.0.0 Added in: v8.0.0 * `method` * `params` * `callback` Posts a message to the inspector back-end. `callback` will be notified when a response is received. `callback` is a function that accepts two optional arguments: error and message-specific result. session.post('Runtime.evaluate', { expression: '2 + 2' }, (error, { result }) => console.log(result)); // Output: { type: 'number', value: 4, description: '4' } The latest version of the V8 inspector protocol is published on the Chrome DevTools Protocol Viewer. Node.js inspector supports all the Chrome DevTools Protocol domains declared by V8. Chrome DevTools Protocol domain provides an interface for interacting with one of the runtime agents used to inspect the application state and listen to the run-time events. You can not set `reportProgress` to `true` when sending a `HeapProfiler.takeHeapSnapshot` or `HeapProfiler.stopTrackingHeapObjects` command to V8. ##### Example usage# Apart from the debugger, various V8 Profilers are available through the DevTools protocol. ###### CPU profiler# Here's an example showing how to use the CPU Profiler: const inspector = require('node:inspector'); const fs = require('node:fs'); const session = new inspector.Session(); session.connect(); session.post('Profiler.enable', () => { session.post('Profiler.start', () => { // Invoke business logic under measurement here... // some time later... session.post('Profiler.stop', (err, { profile }) => { // Write profile to disk, upload, etc. if (!err) { fs.writeFileSync('./profile.cpuprofile', JSON.stringify(profile)); } }); }); }); ###### Heap profiler# Here's an example showing how to use the Heap Profiler: const inspector = require('node:inspector'); const fs = require('node:fs'); const session = new inspector.Session(); const fd = fs.openSync('profile.heapsnapshot', 'w'); session.connect(); session.on('HeapProfiler.addHeapSnapshotChunk', (m) => { fs.writeSync(fd, m.params.chunk); }); session.post('HeapProfiler.takeHeapSnapshot', null, (err, r) => { console.log('HeapProfiler.takeHeapSnapshot done:', err, r); session.disconnect(); fs.closeSync(fd); }); ### Common Objects# #### `inspector.close()`# History VersionChanges v18.10.0 The API is exposed in the worker threads. v9.0.0 Added in: v9.0.0 Attempts to close all remaining connections, blocking the event loop until all are closed. Once all connections are closed, deactivates the inspector. #### `inspector.console`# * Type: An object to send messages to the remote inspector console. require('node:inspector').console.log('a message'); The inspector console does not have API parity with Node.js console. #### `inspector.open([port[, host[, wait]]])`# History VersionChanges v20.6.0 inspector.open() now returns a `Disposable` object. * `port` Port to listen on for inspector connections. Optional. Default: what was specified on the CLI. * `host` Host to listen on for inspector connections. Optional. Default: what was specified on the CLI. * `wait` Block until a client has connected. Optional. Default: `false`. * Returns: A Disposable that calls `inspector.close()`. Activate inspector on host and port. Equivalent to `node --inspect=[[host:]port]`, but can be done programmatically after node has started. If wait is `true`, will block until a client has connected to the inspect port and flow control has been passed to the debugger client. See the security warning regarding the `host` parameter usage. #### `inspector.url()`# * Returns: | Return the URL of the active inspector, or `undefined` if there is none. $ node --inspect -p 'inspector.url()' Debugger listening on ws://127.0.0.1:9229/166e272e-7a30-4d09-97ce-f1c012b43c34 For help, see: https://nodejs.org/en/docs/inspector ws://127.0.0.1:9229/166e272e-7a30-4d09-97ce-f1c012b43c34 $ node --inspect=localhost:3000 -p 'inspector.url()' Debugger listening on ws://localhost:3000/51cf8d0e-3c36-4c59-8efd-54519839e56a For help, see: https://nodejs.org/en/docs/inspector ws://localhost:3000/51cf8d0e-3c36-4c59-8efd-54519839e56a $ node -p 'inspector.url()' undefined #### `inspector.waitForDebugger()`# Added in: v12.7.0 Blocks until a client (existing or connected later) has sent `Runtime.runIfWaitingForDebugger` command. An exception will be thrown if there is no active inspector. ### Integration with DevTools# Stability: 1.1 \- Active development The `node:inspector` module provides an API for integrating with devtools that support Chrome DevTools Protocol. DevTools frontends connected to a running Node.js instance can capture protocol events emitted from the instance and display them accordingly to facilitate debugging. The following methods broadcast a protocol event to all connected frontends. The `params` passed to the methods can be optional, depending on the protocol. // The `Network.requestWillBeSent` event will be fired. inspector.Network.requestWillBeSent({ requestId: 'request-id-1', timestamp: Date.now() / 1000, wallTime: Date.now(), request: { url: 'https://nodejs.org/en', method: 'GET', }, }); #### `inspector.Network.dataReceived([params])`# Added in: v24.2.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.dataReceived` event to connected frontends, or buffers the data if `Network.streamResourceContent` command was not invoked for the given request yet. Also enables `Network.getResponseBody` command to retrieve the response data. #### `inspector.Network.dataSent([params])`# Added in: v24.3.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Enables `Network.getRequestPostData` command to retrieve the request data. #### `inspector.Network.requestWillBeSent([params])`# Added in: v22.6.0, v20.18.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.requestWillBeSent` event to connected frontends. This event indicates that the application is about to send an HTTP request. #### `inspector.Network.responseReceived([params])`# Added in: v22.6.0, v20.18.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.responseReceived` event to connected frontends. This event indicates that HTTP response is available. #### `inspector.Network.loadingFinished([params])`# Added in: v22.6.0, v20.18.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.loadingFinished` event to connected frontends. This event indicates that HTTP request has finished loading. #### `inspector.Network.loadingFailed([params])`# Added in: v22.7.0, v20.18.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.loadingFailed` event to connected frontends. This event indicates that HTTP request has failed to load. #### `inspector.Network.webSocketCreated([params])`# Added in: v24.7.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.webSocketCreated` event to connected frontends. This event indicates that a WebSocket connection has been initiated. #### `inspector.Network.webSocketHandshakeResponseReceived([params])`# Added in: v24.7.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.webSocketHandshakeResponseReceived` event to connected frontends. This event indicates that the WebSocket handshake response has been received. #### `inspector.Network.webSocketClosed([params])`# Added in: v24.7.0 * `params` This feature is only available with the `--experimental-network-inspection` flag enabled. Broadcasts the `Network.webSocketClosed` event to connected frontends. This event indicates that a WebSocket connection has been closed. #### `inspector.NetworkResources.put`# Added in: v24.5.0 Stability: 1.1 \- Active Development This feature is only available with the `--experimental-inspector-network-resource` flag enabled. The inspector.NetworkResources.put method is used to provide a response for a loadNetworkResource request issued via the Chrome DevTools Protocol (CDP). This is typically triggered when a source map is specified by URL, and a DevTools frontend—such as Chrome—requests the resource to retrieve the source map. This method allows developers to predefine the resource content to be served in response to such CDP requests. const inspector = require('node:inspector'); // By preemptively calling put to register the resource, a source map can be resolved when // a loadNetworkResource request is made from the frontend. async function setNetworkResources() { const mapUrl = 'http://localhost:3000/dist/app.js.map'; const tsUrl = 'http://localhost:3000/src/app.ts'; const distAppJsMap = await fetch(mapUrl).then((res) => res.text()); const srcAppTs = await fetch(tsUrl).then((res) => res.text()); inspector.NetworkResources.put(mapUrl, distAppJsMap); inspector.NetworkResources.put(tsUrl, srcAppTs); }; setNetworkResources().then(() => { require('./dist/app'); }); For more details, see the official CDP documentation: Network.loadNetworkResource ### Support of breakpoints# The Chrome DevTools Protocol `Debugger` domain allows an `inspector.Session` to attach to a program and set breakpoints to step through the codes. However, setting breakpoints with a same-thread `inspector.Session`, which is connected by `session.connect()`, should be avoided as the program being attached and paused is exactly the debugger itself. Instead, try connect to the main thread by `session.connectToMainThread()` and set breakpoints in a worker thread, or connect with a Debugger program over WebSocket connection. ## Internationalization support# Node.js has many features that make it easier to write internationalized programs. Some of them are: * Locale-sensitive or Unicode-aware functions in the ECMAScript Language Specification: * `String.prototype.normalize()` * `String.prototype.toLowerCase()` * `String.prototype.toUpperCase()` * All functionality described in the ECMAScript Internationalization API Specification (aka ECMA-402): * `Intl` object * Locale-sensitive methods like `String.prototype.localeCompare()` and `Date.prototype.toLocaleString()` * The WHATWG URL parser's internationalized domain names (IDNs) support * `require('node:buffer').transcode()` * More accurate REPL line editing * `require('node:util').TextDecoder` * `RegExp` Unicode Property Escapes Node.js and the underlying V8 engine use International Components for Unicode (ICU) to implement these features in native C/C++ code. The full ICU data set is provided by Node.js by default. However, due to the size of the ICU data file, several options are provided for customizing the ICU data set either when building or running Node.js. ### Options for building Node.js# To control how ICU is used in Node.js, four `configure` options are available during compilation. Additional details on how to compile Node.js are documented in BUILDING.md. * `--with-intl=none`/`--without-intl` * `--with-intl=system-icu` * `--with-intl=small-icu` * `--with-intl=full-icu` (default) An overview of available Node.js and JavaScript features for each `configure` option: Feature`none``system-icu``small-icu``full-icu` `String.prototype.normalize()`none (function is no-op)fullfullfull `String.prototype.to*Case()`fullfullfullfull `Intl`none (object does not exist)partial/full (depends on OS)partial (English-only)full `String.prototype.localeCompare()`partial (not locale-aware)fullfullfull `String.prototype.toLocale*Case()`partial (not locale-aware)fullfullfull `Number.prototype.toLocaleString()`partial (not locale-aware)partial/full (depends on OS)partial (English-only)full `Date.prototype.toLocale*String()`partial (not locale-aware)partial/full (depends on OS)partial (English-only)full Legacy URL Parserpartial (no IDN support)fullfullfull WHATWG URL Parserpartial (no IDN support)fullfullfull `require('node:buffer').transcode()`none (function does not exist)fullfullfull REPLpartial (inaccurate line editing)fullfullfull `require('node:util').TextDecoder`partial (basic encodings support)partial/full (depends on OS)partial (Unicode-only)full `RegExp` Unicode Property Escapesnone (invalid `RegExp` error)fullfullfull The "(not locale-aware)" designation denotes that the function carries out its operation just like the non-`Locale` version of the function, if one exists. For example, under `none` mode, `Date.prototype.toLocaleString()`'s operation is identical to that of `Date.prototype.toString()`. #### Disable all internationalization features (`none`)# If this option is chosen, ICU is disabled and most internationalization features mentioned above will be unavailable in the resulting `node` binary. #### Build with a pre-installed ICU (`system-icu`)# Node.js can link against an ICU build already installed on the system. In fact, most Linux distributions already come with ICU installed, and this option would make it possible to reuse the same set of data used by other components in the OS. Functionalities that only require the ICU library itself, such as `String.prototype.normalize()` and the WHATWG URL parser, are fully supported under `system-icu`. Features that require ICU locale data in addition, such as `Intl.DateTimeFormat` may be fully or partially supported, depending on the completeness of the ICU data installed on the system. #### Embed a limited set of ICU data (`small-icu`)# This option makes the resulting binary link against the ICU library statically, and includes a subset of ICU data (typically only the English locale) within the `node` executable. Functionalities that only require the ICU library itself, such as `String.prototype.normalize()` and the WHATWG URL parser, are fully supported under `small-icu`. Features that require ICU locale data in addition, such as `Intl.DateTimeFormat`, generally only work with the English locale: const january = new Date(9e8); const english = new Intl.DateTimeFormat('en', { month: 'long' }); const spanish = new Intl.DateTimeFormat('es', { month: 'long' }); console.log(english.format(january)); // Prints "January" console.log(spanish.format(january)); // Prints either "M01" or "January" on small-icu, depending on the user’s default locale // Should print "enero" This mode provides a balance between features and binary size. ##### Providing ICU data at runtime# If the `small-icu` option is used, one can still provide additional locale data at runtime so that the JS methods would work for all ICU locales. Assuming the data file is stored at `/runtime/directory/with/dat/file`, it can be made available to ICU through either: * The `--with-icu-default-data-dir` configure option: ./configure --with-icu-default-data-dir=/runtime/directory/with/dat/file --with-intl=small-icu This only embeds the default data directory path into the binary. The actual data file is going to be loaded at runtime from this directory path. * The `NODE_ICU_DATA` environment variable: env NODE_ICU_DATA=/runtime/directory/with/dat/file node * The `--icu-data-dir` CLI parameter: node --icu-data-dir=/runtime/directory/with/dat/file When more than one of them is specified, the `--icu-data-dir` CLI parameter has the highest precedence, then the `NODE_ICU_DATA` environment variable, then the `--with-icu-default-data-dir` configure option. ICU is able to automatically find and load a variety of data formats, but the data must be appropriate for the ICU version, and the file correctly named. The most common name for the data file is `icudtX[bl].dat`, where `X` denotes the intended ICU version, and `b` or `l` indicates the system's endianness. Node.js would fail to load if the expected data file cannot be read from the specified directory. The name of the data file corresponding to the current Node.js version can be computed with: `icudt${process.versions.icu.split('.')[0]}${os.endianness()[0].toLowerCase()}.dat`; Check "ICU Data" article in the ICU User Guide for other supported formats and more details on ICU data in general. The full-icu npm module can greatly simplify ICU data installation by detecting the ICU version of the running `node` executable and downloading the appropriate data file. After installing the module through `npm i full-icu`, the data file will be available at `./node_modules/full-icu`. This path can be then passed either to `NODE_ICU_DATA` or `--icu-data-dir` as shown above to enable full `Intl` support. #### Embed the entire ICU (`full-icu`)# This option makes the resulting binary link against ICU statically and include a full set of ICU data. A binary created this way has no further external dependencies and supports all locales, but might be rather large. This is the default behavior if no `--with-intl` flag is passed. The official binaries are also built in this mode. ### Detecting internationalization support# To verify that ICU is enabled at all (`system-icu`, `small-icu`, or `full-icu`), simply checking the existence of `Intl` should suffice: const hasICU = typeof Intl === 'object'; Alternatively, checking for `process.versions.icu`, a property defined only when ICU is enabled, works too: const hasICU = typeof process.versions.icu === 'string'; To check for support for a non-English locale (i.e. `full-icu` or `system-icu`), `Intl.DateTimeFormat` can be a good distinguishing factor: const hasFullICU = (() => { try { const january = new Date(9e8); const spanish = new Intl.DateTimeFormat('es', { month: 'long' }); return spanish.format(january) === 'enero'; } catch (err) { return false; } })(); For more verbose tests for `Intl` support, the following resources may be found to be helpful: * btest402: Generally used to check whether Node.js with `Intl` support is built correctly. * Test262: ECMAScript's official conformance test suite includes a section dedicated to ECMA-402. ## Modules: CommonJS modules# Stability: 2 \- Stable CommonJS modules are the original way to package JavaScript code for Node.js. Node.js also supports the ECMAScript modules standard used by browsers and other JavaScript runtimes. In Node.js, each file is treated as a separate module. For example, consider a file named `foo.js`: const circle = require('./circle.js'); console.log(`The area of a circle of radius 4 is ${circle.area(4)}`); On the first line, `foo.js` loads the module `circle.js` that is in the same directory as `foo.js`. Here are the contents of `circle.js`: const { PI } = Math; exports.area = (r) => PI * r ** 2; exports.circumference = (r) => 2 * PI * r; The module `circle.js` has exported the functions `area()` and `circumference()`. Functions and objects are added to the root of a module by specifying additional properties on the special `exports` object. Variables local to the module will be private, because the module is wrapped in a function by Node.js (see module wrapper). In this example, the variable `PI` is private to `circle.js`. The `module.exports` property can be assigned a new value (such as a function or object). In the following code, `bar.js` makes use of the `square` module, which exports a Square class: const Square = require('./square.js'); const mySquare = new Square(2); console.log(`The area of mySquare is ${mySquare.area()}`); The `square` module is defined in `square.js`: // Assigning to exports will not modify module, must use module.exports module.exports = class Square { constructor(width) { this.width = width; } area() { return this.width ** 2; } }; The CommonJS module system is implemented in the `module` core module. ### Enabling# Node.js has two module systems: CommonJS modules and ECMAScript modules. By default, Node.js will treat the following as CommonJS modules: * Files with a `.cjs` extension; * Files with a `.js` extension when the nearest parent `package.json` file contains a top-level field `"type"` with a value of `"commonjs"`. * Files with a `.js` extension or without an extension, when the nearest parent `package.json` file doesn't contain a top-level field `"type"` or there is no `package.json` in any parent folder; unless the file contains syntax that errors unless it is evaluated as an ES module. Package authors should include the `"type"` field, even in packages where all sources are CommonJS. Being explicit about the `type` of the package will make things easier for build tools and loaders to determine how the files in the package should be interpreted. * Files with an extension that is not `.mjs`, `.cjs`, `.json`, `.node`, or `.js` (when the nearest parent `package.json` file contains a top-level field `"type"` with a value of `"module"`, those files will be recognized as CommonJS modules only if they are being included via `require()`, not when used as the command-line entry point of the program). See Determining module system for more details. Calling `require()` always use the CommonJS module loader. Calling `import()` always use the ECMAScript module loader. ### Accessing the main module# When a file is run directly from Node.js, `require.main` is set to its `module`. That means that it is possible to determine whether a file has been run directly by testing `require.main === module`. For a file `foo.js`, this will be `true` if run via `node foo.js`, but `false` if run by `require('./foo')`. When the entry point is not a CommonJS module, `require.main` is `undefined`, and the main module is out of reach. ### Package manager tips# The semantics of the Node.js `require()` function were designed to be general enough to support reasonable directory structures. Package manager programs such as `dpkg`, `rpm`, and `npm` will hopefully find it possible to build native packages from Node.js modules without modification. In the following, we give a suggested directory structure that could work: Let's say that we wanted to have the folder at `/usr/lib/node//` hold the contents of a specific version of a package. Packages can depend on one another. In order to install package `foo`, it may be necessary to install a specific version of package `bar`. The `bar` package may itself have dependencies, and in some cases, these may even collide or form cyclic dependencies. Because Node.js looks up the `realpath` of any modules it loads (that is, it resolves symlinks) and then looks for their dependencies in `node_modules` folders, this situation can be resolved with the following architecture: * `/usr/lib/node/foo/1.2.3/`: Contents of the `foo` package, version 1.2.3. * `/usr/lib/node/bar/4.3.2/`: Contents of the `bar` package that `foo` depends on. * `/usr/lib/node/foo/1.2.3/node_modules/bar`: Symbolic link to `/usr/lib/node/bar/4.3.2/`. * `/usr/lib/node/bar/4.3.2/node_modules/*`: Symbolic links to the packages that `bar` depends on. Thus, even if a cycle is encountered, or if there are dependency conflicts, every module will be able to get a version of its dependency that it can use. When the code in the `foo` package does `require('bar')`, it will get the version that is symlinked into `/usr/lib/node/foo/1.2.3/node_modules/bar`. Then, when the code in the `bar` package calls `require('quux')`, it'll get the version that is symlinked into `/usr/lib/node/bar/4.3.2/node_modules/quux`. Furthermore, to make the module lookup process even more optimal, rather than putting packages directly in `/usr/lib/node`, we could put them in `/usr/lib/node_modules//`. Then Node.js will not bother looking for missing dependencies in `/usr/node_modules` or `/node_modules`. In order to make modules available to the Node.js REPL, it might be useful to also add the `/usr/lib/node_modules` folder to the `$NODE_PATH` environment variable. Since the module lookups using `node_modules` folders are all relative, and based on the real path of the files making the calls to `require()`, the packages themselves can be anywhere. ### Loading ECMAScript modules using `require()`# History VersionChanges v23.0.0, v22.12.0 Support `'module.exports'` interop export in `require(esm)`. v23.5.0, v22.13.0, v20.19.0 This feature no longer emits an experimental warning by default, though the warning can still be emitted by --trace-require-module. v23.0.0, v22.12.0, v20.19.0 This feature is no longer behind the `--experimental-require-module` CLI flag. v22.0.0, v20.17.0 Added in: v22.0.0, v20.17.0 Stability: 1.2 \- Release candidate The `.mjs` extension is reserved for ECMAScript Modules. See Determining module system section for more info regarding which files are parsed as ECMAScript modules. `require()` only supports loading ECMAScript modules that meet the following requirements: * The module is fully synchronous (contains no top-level `await`); and * One of these conditions are met: 1. The file has a `.mjs` extension. 2. The file has a `.js` extension, and the closest `package.json` contains `"type": "module"` 3. The file has a `.js` extension, the closest `package.json` does not contain `"type": "commonjs"`, and the module contains ES module syntax. If the ES Module being loaded meets the requirements, `require()` can load it and return the module namespace object. In this case it is similar to dynamic `import()` but is run synchronously and returns the name space object directly. With the following ES Modules: // distance.mjs export function distance(a, b) { return Math.sqrt((b.x - a.x) ** 2 + (b.y - a.y) ** 2); } // point.mjs export default class Point { constructor(x, y) { this.x = x; this.y = y; } } A CommonJS module can load them with `require()`: For interoperability with existing tools that convert ES Modules into CommonJS, which could then load real ES Modules through `require()`, the returned namespace would contain a `__esModule: true` property if it has a `default` export so that consuming code generated by tools can recognize the default exports in real ES Modules. If the namespace already defines `__esModule`, this would not be added. This property is experimental and can change in the future. It should only be used by tools converting ES modules into CommonJS modules, following existing ecosystem conventions. Code authored directly in CommonJS should avoid depending on it. When an ES Module contains both named exports and a default export, the result returned by `require()` is the module namespace object, which places the default export in the `.default` property, similar to the results returned by `import()`. To customize what should be returned by `require(esm)` directly, the ES Module can export the desired value using the string name `"module.exports"`. // point.mjs export default class Point { constructor(x, y) { this.x = x; this.y = y; } } // `distance` is lost to CommonJS consumers of this module, unless it's // added to `Point` as a static property. export function distance(a, b) { return Math.sqrt((b.x - a.x) ** 2 + (b.y - a.y) ** 2); } export { Point as 'module.exports' } Notice in the example above, when the `module.exports` export name is used, named exports will be lost to CommonJS consumers. To allow CommonJS consumers to continue accessing named exports, the module can make sure that the default export is an object with the named exports attached to it as properties. For example with the example above, `distance` can be attached to the default export, the `Point` class, as a static method. export function distance(a, b) { return Math.sqrt((b.x - a.x) ** 2 + (b.y - a.y) ** 2); } export default class Point { constructor(x, y) { this.x = x; this.y = y; } static distance = distance; } export { Point as 'module.exports' } If the module being `require()`'d contains top-level `await`, or the module graph it `import`s contains top-level `await`, `ERR_REQUIRE_ASYNC_MODULE` will be thrown. In this case, users should load the asynchronous module using `import()`. If `--experimental-print-required-tla` is enabled, instead of throwing `ERR_REQUIRE_ASYNC_MODULE` before evaluation, Node.js will evaluate the module, try to locate the top-level awaits, and print their location to help users fix them. Support for loading ES modules using `require()` is currently experimental and can be disabled using `--no-experimental-require-module`. To print where this feature is used, use `--trace-require-module`. This feature can be detected by checking if `process.features.require_module` is `true`. ### All together# To get the exact filename that will be loaded when `require()` is called, use the `require.resolve()` function. Putting together all of the above, here is the high-level algorithm in pseudocode of what `require()` does: require(X) from module at path Y 1. If X is a core module, a. return the core module b. STOP 2. If X begins with '/' a. set Y to the file system root 3. If X is equal to '.', or X begins with './', '/' or '../' a. LOAD_AS_FILE(Y + X) b. LOAD_AS_DIRECTORY(Y + X) c. THROW "not found" 4. If X begins with '#' a. LOAD_PACKAGE_IMPORTS(X, dirname(Y)) 5. LOAD_PACKAGE_SELF(X, dirname(Y)) 6. LOAD_NODE_MODULES(X, dirname(Y)) 7. THROW "not found" MAYBE_DETECT_AND_LOAD(X) 1. If X parses as a CommonJS module, load X as a CommonJS module. STOP. 2. Else, if the source code of X can be parsed as ECMAScript module using DETECT_MODULE_SYNTAX defined in the ESM resolver, a. Load X as an ECMAScript module. STOP. 3. THROW the SyntaxError from attempting to parse X as CommonJS in 1. STOP. LOAD_AS_FILE(X) 1. If X is a file, load X as its file extension format. STOP 2. If X.js is a file, a. Find the closest package scope SCOPE to X. b. If no scope was found 1. MAYBE_DETECT_AND_LOAD(X.js) c. If the SCOPE/package.json contains "type" field, 1. If the "type" field is "module", load X.js as an ECMAScript module. STOP. 2. If the "type" field is "commonjs", load X.js as a CommonJS module. STOP. d. MAYBE_DETECT_AND_LOAD(X.js) 3. If X.json is a file, load X.json to a JavaScript Object. STOP 4. If X.node is a file, load X.node as binary addon. STOP LOAD_INDEX(X) 1. If X/index.js is a file a. Find the closest package scope SCOPE to X. b. If no scope was found, load X/index.js as a CommonJS module. STOP. c. If the SCOPE/package.json contains "type" field, 1. If the "type" field is "module", load X/index.js as an ECMAScript module. STOP. 2. Else, load X/index.js as a CommonJS module. STOP. 2. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP 3. If X/index.node is a file, load X/index.node as binary addon. STOP LOAD_AS_DIRECTORY(X) 1. If X/package.json is a file, a. Parse X/package.json, and look for "main" field. b. If "main" is a falsy value, GOTO 2. c. let M = X + (json main field) d. LOAD_AS_FILE(M) e. LOAD_INDEX(M) f. LOAD_INDEX(X) DEPRECATED g. THROW "not found" 2. LOAD_INDEX(X) LOAD_NODE_MODULES(X, START) 1. let DIRS = NODE_MODULES_PATHS(START) 2. for each DIR in DIRS: a. LOAD_PACKAGE_EXPORTS(X, DIR) b. LOAD_AS_FILE(DIR/X) c. LOAD_AS_DIRECTORY(DIR/X) NODE_MODULES_PATHS(START) 1. let PARTS = path split(START) 2. let I = count of PARTS - 1 3. let DIRS = [] 4. while I >= 0, a. if PARTS[I] = "node_modules", GOTO d. b. DIR = path join(PARTS[0 .. I] + "node_modules") c. DIRS = DIR + DIRS d. let I = I - 1 5. return DIRS + GLOBAL_FOLDERS LOAD_PACKAGE_IMPORTS(X, DIR) 1. Find the closest package scope SCOPE to DIR. 2. If no scope was found, return. 3. If the SCOPE/package.json "imports" is null or undefined, return. 4. If `--experimental-require-module` is enabled a. let CONDITIONS = ["node", "require", "module-sync"] b. Else, let CONDITIONS = ["node", "require"] 5. let MATCH = PACKAGE_IMPORTS_RESOLVE(X, pathToFileURL(SCOPE), CONDITIONS) defined in the ESM resolver. 6. RESOLVE_ESM_MATCH(MATCH). LOAD_PACKAGE_EXPORTS(X, DIR) 1. Try to interpret X as a combination of NAME and SUBPATH where the name may have a @scope/ prefix and the subpath begins with a slash (`/`). 2. If X does not match this pattern or DIR/NAME/package.json is not a file, return. 3. Parse DIR/NAME/package.json, and look for "exports" field. 4. If "exports" is null or undefined, return. 5. If `--experimental-require-module` is enabled a. let CONDITIONS = ["node", "require", "module-sync"] b. Else, let CONDITIONS = ["node", "require"] 6. let MATCH = PACKAGE_EXPORTS_RESOLVE(pathToFileURL(DIR/NAME), "." + SUBPATH, `package.json` "exports", CONDITIONS) defined in the ESM resolver. 7. RESOLVE_ESM_MATCH(MATCH) LOAD_PACKAGE_SELF(X, DIR) 1. Find the closest package scope SCOPE to DIR. 2. If no scope was found, return. 3. If the SCOPE/package.json "exports" is null or undefined, return. 4. If the SCOPE/package.json "name" is not the first segment of X, return. 5. let MATCH = PACKAGE_EXPORTS_RESOLVE(pathToFileURL(SCOPE), "." + X.slice("name".length), `package.json` "exports", ["node", "require"]) defined in the ESM resolver. 6. RESOLVE_ESM_MATCH(MATCH) RESOLVE_ESM_MATCH(MATCH) 1. let RESOLVED_PATH = fileURLToPath(MATCH) 2. If the file at RESOLVED_PATH exists, load RESOLVED_PATH as its extension format. STOP 3. THROW "not found" ### Caching# Modules are cached after the first time they are loaded. This means (among other things) that every call to `require('foo')` will get exactly the same object returned, if it would resolve to the same file. Provided `require.cache` is not modified, multiple calls to `require('foo')` will not cause the module code to be executed multiple times. This is an important feature. With it, "partially done" objects can be returned, thus allowing transitive dependencies to be loaded even when they would cause cycles. To have a module execute code multiple times, export a function, and call that function. #### Module caching caveats# Modules are cached based on their resolved filename. Since modules may resolve to a different filename based on the location of the calling module (loading from `node_modules` folders), it is not a guarantee that `require('foo')` will always return the exact same object, if it would resolve to different files. Additionally, on case-insensitive file systems or operating systems, different resolved filenames can point to the same file, but the cache will still treat them as different modules and will reload the file multiple times. For example, `require('./foo')` and `require('./FOO')` return two different objects, irrespective of whether or not `./foo` and `./FOO` are the same file. ### Built-in modules# History VersionChanges v16.0.0, v14.18.0 Added `node:` import support to `require(...)`. Node.js has several modules compiled into the binary. These modules are described in greater detail elsewhere in this documentation. The built-in modules are defined within the Node.js source and are located in the `lib/` folder. Built-in modules can be identified using the `node:` prefix, in which case it bypasses the `require` cache. For instance, `require('node:http')` will always return the built in HTTP module, even if there is `require.cache` entry by that name. Some built-in modules are always preferentially loaded if their identifier is passed to `require()`. For instance, `require('http')` will always return the built-in HTTP module, even if there is a file by that name. The list of all the built-in modules can be retrieved from `module.builtinModules`. The modules being all listed without the `node:` prefix, except those that mandate such prefix (as explained in the next section). #### Built-in modules with mandatory `node:` prefix# When being loaded by `require()`, some built-in modules must be requested with the `node:` prefix. This requirement exists to prevent newly introduced built-in modules from having a conflict with user land packages that already have taken the name. Currently the built-in modules that requires the `node:` prefix are: * `node:sea` * `node:sqlite` * `node:test` * `node:test/reporters` The list of these modules is exposed in `module.builtinModules`, including the prefix. ### Cycles# When there are circular `require()` calls, a module might not have finished executing when it is returned. Consider this situation: `a.js`: console.log('a starting'); exports.done = false; const b = require('./b.js'); console.log('in a, b.done = %j', b.done); exports.done = true; console.log('a done'); `b.js`: console.log('b starting'); exports.done = false; const a = require('./a.js'); console.log('in b, a.done = %j', a.done); exports.done = true; console.log('b done'); `main.js`: console.log('main starting'); const a = require('./a.js'); const b = require('./b.js'); console.log('in main, a.done = %j, b.done = %j', a.done, b.done); When `main.js` loads `a.js`, then `a.js` in turn loads `b.js`. At that point, `b.js` tries to load `a.js`. In order to prevent an infinite loop, an unfinished copy of the `a.js` exports object is returned to the `b.js` module. `b.js` then finishes loading, and its `exports` object is provided to the `a.js` module. By the time `main.js` has loaded both modules, they're both finished. The output of this program would thus be: $ node main.js main starting a starting b starting in b, a.done = false b done in a, b.done = true a done in main, a.done = true, b.done = true Careful planning is required to allow cyclic module dependencies to work correctly within an application. ### File modules# If the exact filename is not found, then Node.js will attempt to load the required filename with the added extensions: `.js`, `.json`, and finally `.node`. When loading a file that has a different extension (e.g. `.cjs`), its full name must be passed to `require()`, including its file extension (e.g. `require('./file.cjs')`). `.json` files are parsed as JSON text files, `.node` files are interpreted as compiled addon modules loaded with `process.dlopen()`. Files using any other extension (or no extension at all) are parsed as JavaScript text files. Refer to the Determining module system section to understand what parse goal will be used. A required module prefixed with `'/'` is an absolute path to the file. For example, `require('/home/marco/foo.js')` will load the file at `/home/marco/foo.js`. A required module prefixed with `'./'` is relative to the file calling `require()`. That is, `circle.js` must be in the same directory as `foo.js` for `require('./circle')` to find it. Without a leading `'/'`, `'./'`, or `'../'` to indicate a file, the module must either be a core module or is loaded from a `node_modules` folder. If the given path does not exist, `require()` will throw a `MODULE_NOT_FOUND` error. ### Folders as modules# Stability: 3 \- Legacy: Use subpath exports or subpath imports instead. There are three ways in which a folder may be passed to `require()` as an argument. The first is to create a `package.json` file in the root of the folder, which specifies a `main` module. An example `package.json` file might look like this: { "name" : "some-library", "main" : "./lib/some-library.js" } If this was in a folder at `./some-library`, then `require('./some-library')` would attempt to load `./some-library/lib/some-library.js`. If there is no `package.json` file present in the directory, or if the `"main"` entry is missing or cannot be resolved, then Node.js will attempt to load an `index.js` or `index.node` file out of that directory. For example, if there was no `package.json` file in the previous example, then `require('./some-library')` would attempt to load: * `./some-library/index.js` * `./some-library/index.node` If these attempts fail, then Node.js will report the entire module as missing with the default error: Error: Cannot find module 'some-library' In all three above cases, an `import('./some-library')` call would result in a `ERR_UNSUPPORTED_DIR_IMPORT` error. Using package subpath exports or subpath imports can provide the same containment organization benefits as folders as modules, and work for both `require` and `import`. ### Loading from `node_modules` folders# If the module identifier passed to `require()` is not a built-in module, and does not begin with `'/'`, `'../'`, or `'./'`, then Node.js starts at the directory of the current module, and adds `/node_modules`, and attempts to load the module from that location. Node.js will not append `node_modules` to a path already ending in `node_modules`. If it is not found there, then it moves to the parent directory, and so on, until the root of the file system is reached. For example, if the file at `'/home/ry/projects/foo.js'` called `require('bar.js')`, then Node.js would look in the following locations, in this order: * `/home/ry/projects/node_modules/bar.js` * `/home/ry/node_modules/bar.js` * `/home/node_modules/bar.js` * `/node_modules/bar.js` This allows programs to localize their dependencies, so that they do not clash. It is possible to require specific files or sub modules distributed with a module by including a path suffix after the module name. For instance `require('example-module/path/to/file')` would resolve `path/to/file` relative to where `example-module` is located. The suffixed path follows the same module resolution semantics. ### Loading from the global folders# If the `NODE_PATH` environment variable is set to a colon-delimited list of absolute paths, then Node.js will search those paths for modules if they are not found elsewhere. On Windows, `NODE_PATH` is delimited by semicolons (`;`) instead of colons. `NODE_PATH` was originally created to support loading modules from varying paths before the current module resolution algorithm was defined. `NODE_PATH` is still supported, but is less necessary now that the Node.js ecosystem has settled on a convention for locating dependent modules. Sometimes deployments that rely on `NODE_PATH` show surprising behavior when people are unaware that `NODE_PATH` must be set. Sometimes a module's dependencies change, causing a different version (or even a different module) to be loaded as the `NODE_PATH` is searched. Additionally, Node.js will search in the following list of GLOBAL_FOLDERS: * 1: `$HOME/.node_modules` * 2: `$HOME/.node_libraries` * 3: `$PREFIX/lib/node` Where `$HOME` is the user's home directory, and `$PREFIX` is the Node.js configured `node_prefix`. These are mostly for historic reasons. It is strongly encouraged to place dependencies in the local `node_modules` folder. These will be loaded faster, and more reliably. ### The module wrapper# Before a module's code is executed, Node.js will wrap it with a function wrapper that looks like the following: (function(exports, require, module, __filename, __dirname) { // Module code actually lives in here }); By doing this, Node.js achieves a few things: * It keeps top-level variables (defined with `var`, `const`, or `let`) scoped to the module rather than the global object. * It helps to provide some global-looking variables that are actually specific to the module, such as: * The `module` and `exports` objects that the implementor can use to export values from the module. * The convenience variables `__filename` and `__dirname`, containing the module's absolute filename and directory path. ### The module scope# #### `__dirname`# Added in: v0.1.27 * Type: The directory name of the current module. This is the same as the `path.dirname()` of the `__filename`. Example: running `node example.js` from `/Users/mjr` console.log(__dirname); // Prints: /Users/mjr console.log(path.dirname(__filename)); // Prints: /Users/mjr #### `__filename`# Added in: v0.0.1 * Type: The file name of the current module. This is the current module file's absolute path with symlinks resolved. For a main program this is not necessarily the same as the file name used in the command line. See `__dirname` for the directory name of the current module. Examples: Running `node example.js` from `/Users/mjr` console.log(__filename); // Prints: /Users/mjr/example.js console.log(__dirname); // Prints: /Users/mjr Given two modules: `a` and `b`, where `b` is a dependency of `a` and there is a directory structure of: * `/Users/mjr/app/a.js` * `/Users/mjr/app/node_modules/b/b.js` References to `__filename` within `b.js` will return `/Users/mjr/app/node_modules/b/b.js` while references to `__filename` within `a.js` will return `/Users/mjr/app/a.js`. #### `exports`# Added in: v0.1.12 * Type: A reference to the `module.exports` that is shorter to type. See the section about the exports shortcut for details on when to use `exports` and when to use `module.exports`. #### `module`# Added in: v0.1.16 * Type: A reference to the current module, see the section about the `module` object. In particular, `module.exports` is used for defining what a module exports and makes available through `require()`. #### `require(id)`# Added in: v0.1.13 * `id` module name or path * Returns: exported module content Used to import modules, `JSON`, and local files. Modules can be imported from `node_modules`. Local modules and JSON files can be imported using a relative path (e.g. `./`, `./foo`, `./bar/baz`, `../foo`) that will be resolved against the directory named by `__dirname` (if defined) or the current working directory. The relative paths of POSIX style are resolved in an OS independent fashion, meaning that the examples above will work on Windows in the same way they would on Unix systems. // Importing a local module with a path relative to the `__dirname` or current // working directory. (On Windows, this would resolve to .\path\myLocalModule.) const myLocalModule = require('./path/myLocalModule'); // Importing a JSON file: const jsonData = require('./path/filename.json'); // Importing a module from node_modules or Node.js built-in module: const crypto = require('node:crypto'); ##### `require.cache`# Added in: v0.3.0 * Type: Modules are cached in this object when they are required. By deleting a key value from this object, the next `require` will reload the module. This does not apply to native addons, for which reloading will result in an error. Adding or replacing entries is also possible. This cache is checked before built-in modules and if a name matching a built-in module is added to the cache, only `node:`-prefixed require calls are going to receive the built-in module. Use with care! const assert = require('node:assert'); const realFs = require('node:fs'); const fakeFs = {}; require.cache.fs = { exports: fakeFs }; assert.strictEqual(require('fs'), fakeFs); assert.strictEqual(require('node:fs'), realFs); ##### `require.extensions`# Added in: v0.3.0Deprecated since: v0.10.6 Stability: 0 \- Deprecated * Type: Instruct `require` on how to handle certain file extensions. Process files with the extension `.sjs` as `.js`: require.extensions['.sjs'] = require.extensions['.js']; Deprecated. In the past, this list has been used to load non-JavaScript modules into Node.js by compiling them on-demand. However, in practice, there are much better ways to do this, such as loading modules via some other Node.js program, or compiling them to JavaScript ahead of time. Avoid using `require.extensions`. Use could cause subtle bugs and resolving the extensions gets slower with each registered extension. ##### `require.main`# Added in: v0.1.17 * Type: | The `Module` object representing the entry script loaded when the Node.js process launched, or `undefined` if the entry point of the program is not a CommonJS module. See "Accessing the main module". In `entry.js` script: console.log(require.main); node entry.js Module { id: '.', path: '/absolute/path/to', exports: {}, filename: '/absolute/path/to/entry.js', loaded: false, children: [], paths: [ '/absolute/path/to/node_modules', '/absolute/path/node_modules', '/absolute/node_modules', '/node_modules' ] } ##### `require.resolve(request[, options])`# History VersionChanges v8.9.0 The `paths` option is now supported. v0.3.0 Added in: v0.3.0 * `request` The module path to resolve. * `options` * `paths` Paths to resolve module location from. If present, these paths are used instead of the default resolution paths, with the exception of GLOBAL_FOLDERS like `$HOME/.node_modules`, which are always included. Each of these paths is used as a starting point for the module resolution algorithm, meaning that the `node_modules` hierarchy is checked from this location. * Returns: Use the internal `require()` machinery to look up the location of a module, but rather than loading the module, just return the resolved filename. If the module can not be found, a `MODULE_NOT_FOUND` error is thrown. ###### `require.resolve.paths(request)`# Added in: v8.9.0 * `request` The module path whose lookup paths are being retrieved. * Returns: | Returns an array containing the paths searched during resolution of `request` or `null` if the `request` string references a core module, for example `http` or `fs`. ### The `module` object# Added in: v0.1.16 * Type: In each module, the `module` free variable is a reference to the object representing the current module. For convenience, `module.exports` is also accessible via the `exports` module-global. `module` is not actually a global but rather local to each module. #### `module.children`# Added in: v0.1.16 * Type: The module objects required for the first time by this one. #### `module.exports`# Added in: v0.1.16 * Type: The `module.exports` object is created by the `Module` system. Sometimes this is not acceptable; many want their module to be an instance of some class. To do this, assign the desired export object to `module.exports`. Assigning the desired object to `exports` will simply rebind the local `exports` variable, which is probably not what is desired. For example, suppose we were making a module called `a.js`: const EventEmitter = require('node:events'); module.exports = new EventEmitter(); // Do some work, and after some time emit // the 'ready' event from the module itself. setTimeout(() => { module.exports.emit('ready'); }, 1000); Then in another file we could do: const a = require('./a'); a.on('ready', () => { console.log('module "a" is ready'); }); Assignment to `module.exports` must be done immediately. It cannot be done in any callbacks. This does not work: `x.js`: setTimeout(() => { module.exports = { a: 'hello' }; }, 0); `y.js`: const x = require('./x'); console.log(x.a); ##### `exports` shortcut# Added in: v0.1.16 The `exports` variable is available within a module's file-level scope, and is assigned the value of `module.exports` before the module is evaluated. It allows a shortcut, so that `module.exports.f = ...` can be written more succinctly as `exports.f = ...`. However, be aware that like any variable, if a new value is assigned to `exports`, it is no longer bound to `module.exports`: module.exports.hello = true; // Exported from require of module exports = { hello: false }; // Not exported, only available in the module When the `module.exports` property is being completely replaced by a new object, it is common to also reassign `exports`: module.exports = exports = function Constructor() { // ... etc. }; To illustrate the behavior, imagine this hypothetical implementation of `require()`, which is quite similar to what is actually done by `require()`: function require(/* ... */) { const module = { exports: {} }; ((module, exports) => { // Module code here. In this example, define a function. function someFunc() {} exports = someFunc; // At this point, exports is no longer a shortcut to module.exports, and // this module will still export an empty default object. module.exports = someFunc; // At this point, the module will now export someFunc, instead of the // default object. })(module, module.exports); return module.exports; } #### `module.filename`# Added in: v0.1.16 * Type: The fully resolved filename of the module. #### `module.id`# Added in: v0.1.16 * Type: The identifier for the module. Typically this is the fully resolved filename. #### `module.isPreloading`# Added in: v15.4.0, v14.17.0 * Type: `true` if the module is running during the Node.js preload phase. #### `module.loaded`# Added in: v0.1.16 * Type: Whether or not the module is done loading, or is in the process of loading. #### `module.parent`# Added in: v0.1.16Deprecated since: v14.6.0, v12.19.0 Stability: 0 \- Deprecated: Please use `require.main` and `module.children` instead. * Type: | | The module that first required this one, or `null` if the current module is the entry point of the current process, or `undefined` if the module was loaded by something that is not a CommonJS module (E.G.: REPL or `import`). #### `module.path`# Added in: v11.14.0 * Type: The directory name of the module. This is usually the same as the `path.dirname()` of the `module.id`. #### `module.paths`# Added in: v0.4.0 * Type: The search paths for the module. #### `module.require(id)`# Added in: v0.5.1 * `id` * Returns: exported module content The `module.require()` method provides a way to load a module as if `require()` was called from the original module. In order to do this, it is necessary to get a reference to the `module` object. Since `require()` returns the `module.exports`, and the `module` is typically only available within a specific module's code, it must be explicitly exported in order to be used. ### The `Module` object# This section was moved to Modules: `module` core module. * `module.builtinModules` * `module.createRequire(filename)` * `module.syncBuiltinESMExports()` ### Source map v3 support# This section was moved to Modules: `module` core module. * `module.findSourceMap(path)` * Class: `module.SourceMap` * `new SourceMap(payload)` * `sourceMap.payload` * `sourceMap.findEntry(lineNumber, columnNumber)` ## Modules: ECMAScript modules# History VersionChanges v22.0.0 Drop support for import assertions. v23.1.0, v22.12.0, v20.18.3, v18.20.5 Import attributes are no longer experimental. v21.0.0, v20.10.0, v18.20.0 Add experimental support for import attributes. v20.0.0, v18.19.0 Module customization hooks are executed off the main thread. v18.6.0, v16.17.0 Add support for chaining module customization hooks. v17.1.0, v16.14.0 Add experimental support for import assertions. v17.0.0, v16.12.0 Consolidate customization hooks, removed `getFormat`, `getSource`, `transformSource`, and `getGlobalPreloadCode` hooks added `load` and `globalPreload` hooks allowed returning `format` from either `resolve` or `load` hooks. v14.8.0 Unflag Top-Level Await. v15.3.0, v14.17.0, v12.22.0 Stabilize modules implementation. v14.13.0, v12.20.0 Support for detection of CommonJS named exports. v14.0.0, v13.14.0, v12.20.0 Remove experimental modules warning. v13.2.0, v12.17.0 Loading ECMAScript modules no longer requires a command-line flag. v12.0.0 Add support for ES modules using `.js` file extension via `package.json` `"type"` field. v8.5.0 Added in: v8.5.0 Stability: 2 \- Stable ### Introduction# ECMAScript modules are the official standard format to package JavaScript code for reuse. Modules are defined using a variety of `import` and `export` statements. The following example of an ES module exports a function: // addTwo.mjs function addTwo(num) { return num + 2; } export { addTwo }; The following example of an ES module imports the function from `addTwo.mjs`: // app.mjs import { addTwo } from './addTwo.mjs'; // Prints: 6 console.log(addTwo(4)); Node.js fully supports ECMAScript modules as they are currently specified and provides interoperability between them and its original module format, CommonJS. ### Enabling# Node.js has two module systems: CommonJS modules and ECMAScript modules. Authors can tell Node.js to interpret JavaScript as an ES module via the `.mjs` file extension, the `package.json` `"type"` field with a value `"module"`, or the `--input-type` flag with a value of `"module"`. These are explicit markers of code being intended to run as an ES module. Inversely, authors can explicitly tell Node.js to interpret JavaScript as CommonJS via the `.cjs` file extension, the `package.json` `"type"` field with a value `"commonjs"`, or the `--input-type` flag with a value of `"commonjs"`. When code lacks explicit markers for either module system, Node.js will inspect the source code of a module to look for ES module syntax. If such syntax is found, Node.js will run the code as an ES module; otherwise it will run the module as CommonJS. See Determining module system for more details. ### Packages# This section was moved to Modules: Packages. ### `import` Specifiers# #### Terminology# The specifier of an `import` statement is the string after the `from` keyword, e.g. `'node:path'` in `import { sep } from 'node:path'`. Specifiers are also used in `export from` statements, and as the argument to an `import()` expression. There are three types of specifiers: * Relative specifiers like `'./startup.js'` or `'../config.mjs'`. They refer to a path relative to the location of the importing file. The file extension is always necessary for these. * Bare specifiers like `'some-package'` or `'some-package/shuffle'`. They can refer to the main entry point of a package by the package name, or a specific feature module within a package prefixed by the package name as per the examples respectively. Including the file extension is only necessary for packages without an `"exports"` field. * Absolute specifiers like `'file:///opt/nodejs/config.js'`. They refer directly and explicitly to a full path. Bare specifier resolutions are handled by the Node.js module resolution and loading algorithm. All other specifier resolutions are always only resolved with the standard relative URL resolution semantics. Like in CommonJS, module files within packages can be accessed by appending a path to the package name unless the package's `package.json` contains an `"exports"` field, in which case files within packages can only be accessed via the paths defined in `"exports"`. For details on these package resolution rules that apply to bare specifiers in the Node.js module resolution, see the packages documentation. #### Mandatory file extensions# A file extension must be provided when using the `import` keyword to resolve relative or absolute specifiers. Directory indexes (e.g. `'./startup/index.js'`) must also be fully specified. This behavior matches how `import` behaves in browser environments, assuming a typically configured server. #### URLs# ES modules are resolved and cached as URLs. This means that special characters must be percent-encoded, such as `#` with `%23` and `?` with `%3F`. `file:`, `node:`, and `data:` URL schemes are supported. A specifier like `'https://example.com/app.js'` is not supported natively in Node.js unless using a custom HTTPS loader. ##### `file:` URLs# Modules are loaded multiple times if the `import` specifier used to resolve them has a different query or fragment. import './foo.mjs?query=1'; // loads ./foo.mjs with query of "?query=1" import './foo.mjs?query=2'; // loads ./foo.mjs with query of "?query=2" The volume root may be referenced via `/`, `//`, or `file:///`. Given the differences between URL and path resolution (such as percent encoding details), it is recommended to use url.pathToFileURL when importing a path. ##### `data:` imports# Added in: v12.10.0 `data:` URLs are supported for importing with the following MIME types: * `text/javascript` for ES modules * `application/json` for JSON * `application/wasm` for Wasm import 'data:text/javascript,console.log("hello!");'; import _ from 'data:application/json,"world!"' with { type: 'json' }; `data:` URLs only resolve bare specifiers for builtin modules and absolute specifiers. Resolving relative specifiers does not work because `data:` is not a special scheme. For example, attempting to load `./foo` from `data:text/javascript,import "./foo";` fails to resolve because there is no concept of relative resolution for `data:` URLs. ##### `node:` imports# History VersionChanges v16.0.0, v14.18.0 Added `node:` import support to `require(...)`. v14.13.1, v12.20.0 Added in: v14.13.1, v12.20.0 `node:` URLs are supported as an alternative means to load Node.js builtin modules. This URL scheme allows for builtin modules to be referenced by valid absolute URL strings. import fs from 'node:fs/promises'; ### Import attributes# History VersionChanges v21.0.0, v20.10.0, v18.20.0 Switch from Import Assertions to Import Attributes. v17.1.0, v16.14.0 Added in: v17.1.0, v16.14.0 Import attributes are an inline syntax for module import statements to pass on more information alongside the module specifier. import fooData from './foo.json' with { type: 'json' }; const { default: barData } = await import('./bar.json', { with: { type: 'json' } }); Node.js only supports the `type` attribute, for which it supports the following values: Attribute `type`Needed for `'json'`JSON modules The `type: 'json'` attribute is mandatory when importing JSON modules. ### Built-in modules# Built-in modules provide named exports of their public API. A default export is also provided which is the value of the CommonJS exports. The default export can be used for, among other things, modifying the named exports. Named exports of built-in modules are updated only by calling `module.syncBuiltinESMExports()`. import EventEmitter from 'node:events'; const e = new EventEmitter(); import { readFile } from 'node:fs'; readFile('./foo.txt', (err, source) => { if (err) { console.error(err); } else { console.log(source); } }); import fs, { readFileSync } from 'node:fs'; import { syncBuiltinESMExports } from 'node:module'; import { Buffer } from 'node:buffer'; fs.readFileSync = () => Buffer.from('Hello, ESM'); syncBuiltinESMExports(); fs.readFileSync === readFileSync; ### `import()` expressions# Dynamic `import()` provides an asynchronous way to import modules. It is supported in both CommonJS and ES modules, and can be used to load both CommonJS and ES modules. ### `import.meta`# * Type: The `import.meta` meta property is an `Object` that contains the following properties. It is only supported in ES modules. #### `import.meta.dirname`# History VersionChanges v24.0.0 This property is no longer experimental. v21.2.0, v20.11.0 Added in: v21.2.0, v20.11.0 * Type: The directory name of the current module. This is the same as the `path.dirname()` of the `import.meta.filename`. > Caveat: only present on `file:` modules. #### `import.meta.filename`# History VersionChanges v24.0.0 This property is no longer experimental. v21.2.0, v20.11.0 Added in: v21.2.0, v20.11.0 * Type: The full absolute path and filename of the current module, with symlinks resolved. This is the same as the `url.fileURLToPath()` of the `import.meta.url`. > Caveat only local modules support this property. Modules not using the `file:` protocol will not provide it. #### `import.meta.url`# * Type: The absolute `file:` URL of the module. This is defined exactly the same as it is in browsers providing the URL of the current module file. This enables useful patterns such as relative file loading: import { readFileSync } from 'node:fs'; const buffer = readFileSync(new URL('./data.proto', import.meta.url)); #### `import.meta.main`# Added in: v24.2.0 Stability: 1.0 \- Early development * Type: `true` when the current module is the entry point of the current process; `false` otherwise. Equivalent to `require.main === module` in CommonJS. Analogous to Python's `__name__ == "__main__"`. export function foo() { return 'Hello, world'; } function main() { const message = foo(); console.log(message); } if (import.meta.main) main(); // `foo` can be imported from another module without possible side-effects from `main` #### `import.meta.resolve(specifier)`# History VersionChanges v20.6.0, v18.19.0 No longer behind `--experimental-import-meta-resolve` CLI flag, except for the non-standard `parentURL` parameter. v20.6.0, v18.19.0 This API no longer throws when targeting `file:` URLs that do not map to an existing file on the local FS. v20.0.0, v18.19.0 This API now returns a string synchronously instead of a Promise. v16.2.0, v14.18.0 Add support for WHATWG `URL` object to `parentURL` parameter. v13.9.0, v12.16.2 Added in: v13.9.0, v12.16.2 Stability: 1.2 \- Release candidate * `specifier` The module specifier to resolve relative to the current module. * Returns: The absolute URL string that the specifier would resolve to. `import.meta.resolve` is a module-relative resolution function scoped to each module, returning the URL string. const dependencyAsset = import.meta.resolve('component-lib/asset.css'); // file:///app/node_modules/component-lib/asset.css import.meta.resolve('./dep.js'); // file:///app/dep.js All features of the Node.js module resolution are supported. Dependency resolutions are subject to the permitted exports resolutions within the package. Caveats: * This can result in synchronous file-system operations, which can impact performance similarly to `require.resolve`. * This feature is not available within custom loaders (it would create a deadlock). Non-standard API: When using the `--experimental-import-meta-resolve` flag, that function accepts a second argument: * `parent` | An optional absolute parent module URL to resolve from. Default: `import.meta.url` ### Interoperability with CommonJS# #### `import` statements# An `import` statement can reference an ES module or a CommonJS module. `import` statements are permitted only in ES modules, but dynamic `import()` expressions are supported in CommonJS for loading ES modules. When importing CommonJS modules, the `module.exports` object is provided as the default export. Named exports may be available, provided by static analysis as a convenience for better ecosystem compatibility. #### `require`# The CommonJS module `require` currently only supports loading synchronous ES modules (that is, ES modules that do not use top-level `await`). See Loading ECMAScript modules using `require()` for details. #### CommonJS Namespaces# History VersionChanges v23.0.0 Added `'module.exports'` export marker to CJS namespaces. v14.13.0 Added in: v14.13.0 CommonJS modules consist of a `module.exports` object which can be of any type. To support this, when importing CommonJS from an ECMAScript module, a namespace wrapper for the CommonJS module is constructed, which always provides a `default` export key pointing to the CommonJS `module.exports` value. In addition, a heuristic static analysis is performed against the source text of the CommonJS module to get a best-effort static list of exports to provide on the namespace from values on `module.exports`. This is necessary since these namespaces must be constructed prior to the evaluation of the CJS module. These CommonJS namespace objects also provide the `default` export as a `'module.exports'` named export, in order to unambiguously indicate that their representation in CommonJS uses this value, and not the namespace value. This mirrors the semantics of the handling of the `'module.exports'` export name in `require(esm)` interop support. When importing a CommonJS module, it can be reliably imported using the ES module default import or its corresponding sugar syntax: import { default as cjs } from 'cjs'; // Identical to the above import cjsSugar from 'cjs'; console.log(cjs); console.log(cjs === cjsSugar); // Prints: // // true This Module Namespace Exotic Object can be directly observed either when using `import * as m from 'cjs'` or a dynamic import: import * as m from 'cjs'; console.log(m); console.log(m === await import('cjs')); // Prints: // [Module] { default: , 'module.exports': } // true For better compatibility with existing usage in the JS ecosystem, Node.js in addition attempts to determine the CommonJS named exports of every imported CommonJS module to provide them as separate ES module exports using a static analysis process. For example, consider a CommonJS module written: The preceding module supports named imports in ES modules: import { name } from './cjs.cjs'; console.log(name); // Prints: 'exported' import cjs from './cjs.cjs'; console.log(cjs); // Prints: { name: 'exported' } import * as m from './cjs.cjs'; console.log(m); // Prints: // [Module] { // default: { name: 'exported' }, // 'module.exports': { name: 'exported' }, // name: 'exported' // } As can be seen from the last example of the Module Namespace Exotic Object being logged, the `name` export is copied off of the `module.exports` object and set directly on the ES module namespace when the module is imported. Live binding updates or new exports added to `module.exports` are not detected for these named exports. The detection of named exports is based on common syntax patterns but does not always correctly detect named exports. In these cases, using the default import form described above can be a better option. Named exports detection covers many common export patterns, reexport patterns and build tool and transpiler outputs. See cjs-module-lexer for the exact semantics implemented. #### Differences between ES modules and CommonJS# ##### No `require`, `exports`, or `module.exports`# In most cases, the ES module `import` can be used to load CommonJS modules. If needed, a `require` function can be constructed within an ES module using `module.createRequire()`. ##### No `__filename` or `__dirname`# These CommonJS variables are not available in ES modules. `__filename` and `__dirname` use cases can be replicated via `import.meta.filename` and `import.meta.dirname`. ##### No Addon Loading# Addons are not currently supported with ES module imports. They can instead be loaded with `module.createRequire()` or `process.dlopen`. ##### No `require.main`# To replace `require.main === module`, there is the `import.meta.main` API. ##### No `require.resolve`# Relative resolution can be handled via `new URL('./local', import.meta.url)`. For a complete `require.resolve` replacement, there is the import.meta.resolve API. Alternatively `module.createRequire()` can be used. ##### No `NODE_PATH`# `NODE_PATH` is not part of resolving `import` specifiers. Please use symlinks if this behavior is desired. ##### No `require.extensions`# `require.extensions` is not used by `import`. Module customization hooks can provide a replacement. ##### No `require.cache`# `require.cache` is not used by `import` as the ES module loader has its own separate cache. ### JSON modules# History VersionChanges v23.1.0, v22.12.0, v20.18.3, v18.20.5 JSON modules are no longer experimental. JSON files can be referenced by `import`: import packageConfig from './package.json' with { type: 'json' }; The `with { type: 'json' }` syntax is mandatory; see Import Attributes. The imported JSON only exposes a `default` export. There is no support for named exports. A cache entry is created in the CommonJS cache to avoid duplication. The same object is returned in CommonJS if the JSON module has already been imported from the same path. ### Wasm modules# History VersionChanges v24.5.0 Wasm modules no longer require the `--experimental-wasm-modules` flag. Importing both WebAssembly module instances and WebAssembly source phase imports is supported. Both of these integrations are in line with the ES Module Integration Proposal for WebAssembly. #### Wasm Source Phase Imports# Stability: 1.2 \- Release candidate Added in: v24.0.0 The Source Phase Imports proposal allows the `import source` keyword combination to import a `WebAssembly.Module` object directly, instead of getting a module instance already instantiated with its dependencies. This is useful when needing custom instantiations for Wasm, while still resolving and loading it through the ES module integration. For example, to create multiple instances of a module, or to pass custom imports into a new instance of `library.wasm`: import source libraryModule from './library.wasm'; const instance1 = await WebAssembly.instantiate(libraryModule, importObject1); const instance2 = await WebAssembly.instantiate(libraryModule, importObject2); In addition to the static source phase, there is also a dynamic variant of the source phase via the `import.source` dynamic phase import syntax: const dynamicLibrary = await import.source('./library.wasm'); const instance = await WebAssembly.instantiate(dynamicLibrary, importObject); #### JavaScript String Builtins# Stability: 1.2 \- Release candidate Added in: v24.5.0 When importing WebAssembly modules, the WebAssembly JS String Builtins Proposal is automatically enabled through the ESM Integration. This allows WebAssembly modules to directly use efficient compile-time string builtins from the `wasm:js-string` namespace. For example, the following Wasm module exports a string `getLength` function using the `wasm:js-string` `length` builtin: (module ;; Compile-time import of the string length builtin. (import "wasm:js-string" "length" (func $string_length (param externref) (result i32))) ;; Define getLength, taking a JS value parameter assumed to be a string, ;; calling string length on it and returning the result. (func $getLength (param $str externref) (result i32) local.get $str call $string_length ) ;; Export the getLength function. (export "getLength" (func $get_length)) ) import { getLength } from './string-len.wasm'; getLength('foo'); // Returns 3. Wasm builtins are compile-time imports that are linked during module compilation rather than during instantiation. They do not behave like normal module graph imports and they cannot be inspected via `WebAssembly.Module.imports(mod)` or virtualized unless recompiling the module using the direct `WebAssembly.compile` API with string builtins disabled. Importing a module in the source phase before it has been instantiated will also use the compile-time builtins automatically: import source mod from './string-len.wasm'; const { exports: { getLength } } = await WebAssembly.instantiate(mod, {}); getLength('foo'); // Also returns 3. #### Wasm Instance Phase Imports# Stability: 1.1 \- Active development Instance imports allow any `.wasm` files to be imported as normal modules, supporting their module imports in turn. For example, an `index.js` containing: import * as M from './library.wasm'; console.log(M); executed under: node index.mjs would provide the exports interface for the instantiation of `library.wasm`. #### Reserved Wasm Namespaces# Added in: v24.5.0 When importing WebAssembly module instances, they cannot use import module names or import/export names that start with reserved prefixes: * `wasm-js:` \- reserved in all module import names, module names and export names. * `wasm:` \- reserved in module import names and export names (imported module names are allowed in order to support future builtin polyfills). Importing a module using the above reserved names will throw a `WebAssembly.LinkError`. ### Top-level `await`# Added in: v14.8.0 The `await` keyword may be used in the top level body of an ECMAScript module. Assuming an `a.mjs` with export const five = await Promise.resolve(5); And a `b.mjs` with import { five } from './a.mjs'; console.log(five); // Logs `5` node b.mjs # works If a top level `await` expression never resolves, the `node` process will exit with a `13` status code. import { spawn } from 'node:child_process'; import { execPath } from 'node:process'; spawn(execPath, [ '--input-type=module', '--eval', // Never-resolving Promise: 'await new Promise(() => {})', ]).once('exit', (code) => { console.log(code); // Logs `13` }); ### Loaders# The former Loaders documentation is now at Modules: Customization hooks. ### Resolution and loading algorithm# #### Features# The default resolver has the following properties: * FileURL-based resolution as is used by ES modules * Relative and absolute URL resolution * No default extensions * No folder mains * Bare specifier package resolution lookup through node_modules * Does not fail on unknown extensions or protocols * Can optionally provide a hint of the format to the loading phase The default loader has the following properties * Support for builtin module loading via `node:` URLs * Support for "inline" module loading via `data:` URLs * Support for `file:` module loading * Fails on any other URL protocol * Fails on unknown extensions for `file:` loading (supports only `.cjs`, `.js`, and `.mjs`) #### Resolution algorithm# The algorithm to load an ES module specifier is given through the ESM_RESOLVE method below. It returns the resolved URL for a module specifier relative to a parentURL. The resolution algorithm determines the full resolved URL for a module load, along with its suggested module format. The resolution algorithm does not determine whether the resolved URL protocol can be loaded, or whether the file extensions are permitted, instead these validations are applied by Node.js during the load phase (for example, if it was asked to load a URL that has a protocol that is not `file:`, `data:` or `node:`. The algorithm also tries to determine the format of the file based on the extension (see `ESM_FILE_FORMAT` algorithm below). If it does not recognize the file extension (eg if it is not `.mjs`, `.cjs`, or `.json`), then a format of `undefined` is returned, which will throw during the load phase. The algorithm to determine the module format of a resolved URL is provided by ESM_FILE_FORMAT, which returns the unique module format for any file. The "module" format is returned for an ECMAScript Module, while the "commonjs" format is used to indicate loading through the legacy CommonJS loader. Additional formats such as "addon" can be extended in future updates. In the following algorithms, all subroutine errors are propagated as errors of these top-level routines unless stated otherwise. defaultConditions is the conditional environment name array, `["node", "import"]`. The resolver can throw the following errors: * Invalid Module Specifier: Module specifier is an invalid URL, package name or package subpath specifier. * Invalid Package Configuration: package.json configuration is invalid or contains an invalid configuration. * Invalid Package Target: Package exports or imports define a target module for the package that is an invalid type or string target. * Package Path Not Exported: Package exports do not define or permit a target subpath in the package for the given module. * Package Import Not Defined: Package imports do not define the specifier. * Module Not Found: The package or module requested does not exist. * Unsupported Directory Import: The resolved path corresponds to a directory, which is not a supported target for module imports. #### Resolution Algorithm Specification# ESM_RESOLVE(specifier, parentURL) > 1. Let resolved be undefined. > 2. If specifier is a valid URL, then > 1. Set resolved to the result of parsing and reserializing specifier as a URL. > 3. Otherwise, if specifier starts with "/", "./", or "../", then > 1. Set resolved to the URL resolution of specifier relative to parentURL. > 4. Otherwise, if specifier starts with "#", then > 1. Set resolved to the result of PACKAGE_IMPORTS_RESOLVE(specifier, parentURL, defaultConditions). > 5. Otherwise, > 1. Note: specifier is now a bare specifier. > 2. Set resolved the result of PACKAGE_RESOLVE(specifier, parentURL). > 6. Let format be undefined. > 7. If resolved is a "file:" URL, then > 1. If resolved contains any percent encodings of "/" or "\" ("%2F" and "%5C" respectively), then > 1. Throw an Invalid Module Specifier error. > 2. If the file at resolved is a directory, then > 1. Throw an Unsupported Directory Import error. > 3. If the file at resolved does not exist, then > 1. Throw a Module Not Found error. > 4. Set resolved to the real path of resolved, maintaining the same URL querystring and fragment components. > 5. Set format to the result of ESM_FILE_FORMAT(resolved). > 8. Otherwise, > 1. Set format the module format of the content type associated with the URL resolved. > 9. Return format and resolved to the loading phase > PACKAGE_RESOLVE(packageSpecifier, parentURL) > 1. Let packageName be undefined. > 2. If packageSpecifier is an empty string, then > 1. Throw an Invalid Module Specifier error. > 3. If packageSpecifier is a Node.js builtin module name, then > 1. Return the string "node:" concatenated with packageSpecifier. > 4. If packageSpecifier does not start with "@", then > 1. Set packageName to the substring of packageSpecifier until the first "/" separator or the end of the string. > 5. Otherwise, > 1. If packageSpecifier does not contain a "/" separator, then > 1. Throw an Invalid Module Specifier error. > 2. Set packageName to the substring of packageSpecifier until the second "/" separator or the end of the string. > 6. If packageName starts with "." or contains "\" or "%", then > 1. Throw an Invalid Module Specifier error. > 7. Let packageSubpath be "." concatenated with the substring of packageSpecifier from the position at the length of packageName. > 8. Let selfUrl be the result of PACKAGE_SELF_RESOLVE(packageName, packageSubpath, parentURL). > 9. If selfUrl is not undefined, return selfUrl. > 10. While parentURL is not the file system root, > 1. Let packageURL be the URL resolution of "node_modules/" concatenated with packageName, relative to parentURL. > 2. Set parentURL to the parent folder URL of parentURL. > 3. If the folder at packageURL does not exist, then > 1. Continue the next loop iteration. > 4. Let pjson be the result of READ_PACKAGE_JSON(packageURL). > 5. If pjson is not null and pjson.exports is not null or undefined, then > 1. Return the result of PACKAGE_EXPORTS_RESOLVE(packageURL, packageSubpath, pjson.exports, defaultConditions). > 6. Otherwise, if packageSubpath is equal to ".", then > 1. If pjson.main is a string, then > 1. Return the URL resolution of main in packageURL. > 7. Otherwise, > 1. Return the URL resolution of packageSubpath in packageURL. > 11. Throw a Module Not Found error. > PACKAGE_SELF_RESOLVE(packageName, packageSubpath, parentURL) > 1. Let packageURL be the result of LOOKUP_PACKAGE_SCOPE(parentURL). > 2. If packageURL is null, then > 1. Return undefined. > 3. Let pjson be the result of READ_PACKAGE_JSON(packageURL). > 4. If pjson is null or if pjson.exports is null or undefined, then > 1. Return undefined. > 5. If pjson.name is equal to packageName, then > 1. Return the result of PACKAGE_EXPORTS_RESOLVE(packageURL, packageSubpath, pjson.exports, defaultConditions). > 6. Otherwise, return undefined. > PACKAGE_EXPORTS_RESOLVE(packageURL, subpath, exports, conditions) Note: This function is directly invoked by the CommonJS resolution algorithm. > 1. If exports is an Object with both a key starting with "." and a key not starting with ".", throw an Invalid Package Configuration error. > 2. If subpath is equal to ".", then > 1. Let mainExport be undefined. > 2. If exports is a String or Array, or an Object containing no keys starting with ".", then > 1. Set mainExport to exports. > 3. Otherwise if exports is an Object containing a "." property, then > 1. Set mainExport to exports["."]. > 4. If mainExport is not undefined, then > 1. Let resolved be the result of PACKAGE_TARGET_RESOLVE( packageURL, mainExport, null, false, conditions). > 2. If resolved is not null or undefined, return resolved. > 3. Otherwise, if exports is an Object and all keys of exports start with ".", then > 1. Assert: subpath begins with "./". > 2. Let resolved be the result of PACKAGE_IMPORTS_EXPORTS_RESOLVE( subpath, exports, packageURL, false, conditions). > 3. If resolved is not null or undefined, return resolved. > 4. Throw a Package Path Not Exported error. > PACKAGE_IMPORTS_RESOLVE(specifier, parentURL, conditions) Note: This function is directly invoked by the CommonJS resolution algorithm. > 1. Assert: specifier begins with "#". > 2. If specifier is exactly equal to "#" or starts with "#/", then > 1. Throw an Invalid Module Specifier error. > 3. Let packageURL be the result of LOOKUP_PACKAGE_SCOPE(parentURL). > 4. If packageURL is not null, then > 1. Let pjson be the result of READ_PACKAGE_JSON(packageURL). > 2. If pjson.imports is a non-null Object, then > 1. Let resolved be the result of PACKAGE_IMPORTS_EXPORTS_RESOLVE( specifier, pjson.imports, packageURL, true, conditions). > 2. If resolved is not null or undefined, return resolved. > 5. Throw a Package Import Not Defined error. > PACKAGE_IMPORTS_EXPORTS_RESOLVE(matchKey, matchObj, packageURL, isImports, conditions) > 1. If matchKey ends in "/", then > 1. Throw an Invalid Module Specifier error. > 2. If matchKey is a key of matchObj and does not contain "*", then > 1. Let target be the value of matchObj[matchKey]. > 2. Return the result of PACKAGE_TARGET_RESOLVE(packageURL, target, null, isImports, conditions). > 3. Let expansionKeys be the list of keys of matchObj containing only a single "*", sorted by the sorting function PATTERN_KEY_COMPARE which orders in descending order of specificity. > 4. For each key expansionKey in expansionKeys, do > 1. Let patternBase be the substring of expansionKey up to but excluding the first "*" character. > 2. If matchKey starts with but is not equal to patternBase, then > 1. Let patternTrailer be the substring of expansionKey from the index after the first "*" character. > 2. If patternTrailer has zero length, or if matchKey ends with patternTrailer and the length of matchKey is greater than or equal to the length of expansionKey, then > 1. Let target be the value of matchObj[expansionKey]. > 2. Let patternMatch be the substring of matchKey starting at the index of the length of patternBase up to the length of matchKey minus the length of patternTrailer. > 3. Return the result of PACKAGE_TARGET_RESOLVE(packageURL, target, patternMatch, isImports, conditions). > 5. Return null. > PATTERN_KEY_COMPARE(keyA, keyB) > 1. Assert: keyA contains only a single "*". > 2. Assert: keyB contains only a single "*". > 3. Let baseLengthA be the index of "*" in keyA. > 4. Let baseLengthB be the index of "*" in keyB. > 5. If baseLengthA is greater than baseLengthB, return -1. > 6. If baseLengthB is greater than baseLengthA, return 1. > 7. If the length of keyA is greater than the length of keyB, return -1. > 8. If the length of keyB is greater than the length of keyA, return 1. > 9. Return 0. > PACKAGE_TARGET_RESOLVE(packageURL, target, patternMatch, isImports, conditions) > 1. If target is a String, then > 1. If target does not start with "./", then > 1. If isImports is false, or if target starts with "../" or "/", or if target is a valid URL, then > 1. Throw an Invalid Package Target error. > 2. If patternMatch is a String, then > 1. Return PACKAGE_RESOLVE(target with every instance of "*" replaced by patternMatch, packageURL \+ "/"). > 3. Return PACKAGE_RESOLVE(target, packageURL \+ "/"). > 2. If target split on "/" or "\" contains any "", ".", "..", or "node_modules" segments after the first "." segment, case insensitive and including percent encoded variants, throw an Invalid Package Target error. > 3. Let resolvedTarget be the URL resolution of the concatenation of packageURL and target. > 4. Assert: packageURL is contained in resolvedTarget. > 5. If patternMatch is null, then > 1. Return resolvedTarget. > 6. If patternMatch split on "/" or "\" contains any "", ".", "..", or "node_modules" segments, case insensitive and including percent encoded variants, throw an Invalid Module Specifier error. > 7. Return the URL resolution of resolvedTarget with every instance of "*" replaced with patternMatch. > 2. Otherwise, if target is a non-null Object, then > 1. If target contains any index property keys, as defined in ECMA-262 6.1.7 Array Index, throw an Invalid Package Configuration error. > 2. For each property p of target, in object insertion order as, > 1. If p equals "default" or conditions contains an entry for p, then > 1. Let targetValue be the value of the p property in target. > 2. Let resolved be the result of PACKAGE_TARGET_RESOLVE( packageURL, targetValue, patternMatch, isImports, conditions). > 3. If resolved is equal to undefined, continue the loop. > 4. Return resolved. > 3. Return undefined. > 3. Otherwise, if target is an Array, then > 1. If _target.length is zero, return null. > 2. For each item targetValue in target, do > 1. Let resolved be the result of PACKAGE_TARGET_RESOLVE( packageURL, targetValue, patternMatch, isImports, conditions), continuing the loop on any Invalid Package Target error. > 2. If resolved is undefined, continue the loop. > 3. Return resolved. > 3. Return or throw the last fallback resolution null return or error. > 4. Otherwise, if target is null, return null. > 5. Otherwise throw an Invalid Package Target error. > ESM_FILE_FORMAT(url) > 1. Assert: url corresponds to an existing file. > 2. If url ends in ".mjs", then > 1. Return "module". > 3. If url ends in ".cjs", then > 1. Return "commonjs". > 4. If url ends in ".json", then > 1. Return "json". > 5. If url ends in ".wasm", then > 1. Return "wasm". > 6. If `--experimental-addon-modules` is enabled and url ends in ".node", then > 1. Return "addon". > 7. Let packageURL be the result of LOOKUP_PACKAGE_SCOPE(url). > 8. Let pjson be the result of READ_PACKAGE_JSON(packageURL). > 9. Let packageType be null. > 10. If pjson?.type is "module" or "commonjs", then > 1. Set packageType to pjson.type. > 11. If url ends in ".js", then > 1. If packageType is not null, then > 1. Return packageType. > 2. If the result of DETECT_MODULE_SYNTAX(source) is true, then > 1. Return "module". > 3. Return "commonjs". > 12. If url does not have any extension, then > 1. If packageType is "module" and the file at url contains the "application/wasm" content type header for a WebAssembly module, then > 1. Return "wasm". > 2. If packageType is not null, then > 1. Return packageType. > 3. If the result of DETECT_MODULE_SYNTAX(source) is true, then > 1. Return "module". > 4. Return "commonjs". > 13. Return undefined (will throw during load phase). > LOOKUP_PACKAGE_SCOPE(url) > 1. Let scopeURL be url. > 2. While scopeURL is not the file system root, > 1. Set scopeURL to the parent URL of scopeURL. > 2. If scopeURL ends in a "node_modules" path segment, return null. > 3. Let pjsonURL be the resolution of "package.json" within scopeURL. > 4. if the file at pjsonURL exists, then > 1. Return scopeURL. > 3. Return null. > READ_PACKAGE_JSON(packageURL) > 1. Let pjsonURL be the resolution of "package.json" within packageURL. > 2. If the file at pjsonURL does not exist, then > 1. Return null. > 3. If the file at packageURL does not parse as valid JSON, then > 1. Throw an Invalid Package Configuration error. > 4. Return the parsed JSON source of the file at pjsonURL. > DETECT_MODULE_SYNTAX(source) > 1. Parse source as an ECMAScript module. > 2. If the parse is successful, then > 1. If source contains top-level `await`, static `import` or `export` statements, or `import.meta`, return true. > 2. If source contains a top-level lexical declaration (`const`, `let`, or `class`) of any of the CommonJS wrapper variables (`require`, `exports`, `module`, `__filename`, or `__dirname`) then return true. > 3. Else return false. > #### Customizing ESM specifier resolution algorithm# Module customization hooks provide a mechanism for customizing the ESM specifier resolution algorithm. An example that provides CommonJS-style resolution for ESM specifiers is commonjs-extension-resolution-loader. ## Modules: `node:module` API# Added in: v0.3.7 ### The `Module` object# * Type: Provides general utility methods when interacting with instances of `Module`, the `module` variable often seen in CommonJS modules. Accessed via `import 'node:module'` or `require('node:module')`. #### `module.builtinModules`# History VersionChanges v23.5.0 The list now also contains prefix-only modules. v9.3.0, v8.10.0, v6.13.0 Added in: v9.3.0, v8.10.0, v6.13.0 * Type: A list of the names of all modules provided by Node.js. Can be used to verify if a module is maintained by a third party or not. `module` in this context isn't the same object that's provided by the module wrapper. To access it, require the `Module` module: // module.mjs // In an ECMAScript module import { builtinModules as builtin } from 'node:module'; #### `module.createRequire(filename)`# Added in: v12.2.0 * `filename` | Filename to be used to construct the require function. Must be a file URL object, file URL string, or absolute path string. * Returns: Require function import { createRequire } from 'node:module'; const require = createRequire(import.meta.url); // sibling-module.js is a CommonJS module. const siblingModule = require('./sibling-module'); #### `module.findPackageJSON(specifier[, base])`# Added in: v23.2.0, v22.14.0 Stability: 1.1 \- Active Development * `specifier` | The specifier for the module whose `package.json` to retrieve. When passing a bare specifier, the `package.json` at the root of the package is returned. When passing a relative specifier or an absolute specifier, the closest parent `package.json` is returned. * `base` | The absolute location (`file:` URL string or FS path) of the containing module. For CJS, use `__filename` (not `__dirname`!); for ESM, use `import.meta.url`. You do not need to pass it if `specifier` is an `absolute specifier`. * Returns: | A path if the `package.json` is found. When `specifier` is a package, the package's root `package.json`; when a relative or unresolved, the closest `package.json` to the `specifier`. > Caveat: Do not use this to try to determine module format. There are many things affecting that determination; the `type` field of package.json is the least definitive (ex file extension supersedes it, and a loader hook supersedes that). > Caveat: This currently leverages only the built-in default resolver; if `resolve` customization hooks are registered, they will not affect the resolution. This may change in the future. /path/to/project ├ packages/ ├ bar/ ├ bar.js └ package.json // name = '@foo/bar' └ qux/ ├ node_modules/ └ some-package/ └ package.json // name = 'some-package' ├ qux.js └ package.json // name = '@foo/qux' ├ main.js └ package.json // name = '@foo' // /path/to/project/packages/bar/bar.js import { findPackageJSON } from 'node:module'; findPackageJSON('..', import.meta.url); // '/path/to/project/package.json' // Same result when passing an absolute specifier instead: findPackageJSON(new URL('../', import.meta.url)); findPackageJSON(import.meta.resolve('../')); findPackageJSON('some-package', import.meta.url); // '/path/to/project/packages/bar/node_modules/some-package/package.json' // When passing an absolute specifier, you might get a different result if the // resolved module is inside a subfolder that has nested `package.json`. findPackageJSON(import.meta.resolve('some-package')); // '/path/to/project/packages/bar/node_modules/some-package/some-subfolder/package.json' findPackageJSON('@foo/qux', import.meta.url); // '/path/to/project/packages/qux/package.json' #### `module.isBuiltin(moduleName)`# Added in: v18.6.0, v16.17.0 * `moduleName` name of the module * Returns: returns true if the module is builtin else returns false import { isBuiltin } from 'node:module'; isBuiltin('node:fs'); // true isBuiltin('fs'); // true isBuiltin('wss'); // false #### `module.register(specifier[, parentURL][, options])`# History VersionChanges v23.6.1, v22.13.1, v20.18.2 Using this feature with the permission model enabled requires passing `--allow-worker`. v20.8.0, v18.19.0 Add support for WHATWG URL instances. v20.6.0, v18.19.0 Added in: v20.6.0, v18.19.0 Stability: 1.2 \- Release candidate * `specifier` | Customization hooks to be registered; this should be the same string that would be passed to `import()`, except that if it is relative, it is resolved relative to `parentURL`. * `parentURL` | If you want to resolve `specifier` relative to a base URL, such as `import.meta.url`, you can pass that URL here. Default: `'data:'` * `options` * `parentURL` | If you want to resolve `specifier` relative to a base URL, such as `import.meta.url`, you can pass that URL here. This property is ignored if the `parentURL` is supplied as the second argument. Default: `'data:'` * `data` Any arbitrary, cloneable JavaScript value to pass into the `initialize` hook. * `transferList` transferable objects to be passed into the `initialize` hook. Register a module that exports hooks that customize Node.js module resolution and loading behavior. See Customization hooks. This feature requires `--allow-worker` if used with the Permission Model. #### `module.registerHooks(options)`# Added in: v23.5.0, v22.15.0 Stability: 1.1 \- Active development * `options` * `load` | See load hook. Default: `undefined`. * `resolve` | See resolve hook. Default: `undefined`. Register hooks that customize Node.js module resolution and loading behavior. See Customization hooks. #### `module.stripTypeScriptTypes(code[, options])`# Added in: v23.2.0, v22.13.0 Stability: 1.2 \- Release candidate * `code` The code to strip type annotations from. * `options` * `mode` Default: `'strip'`. Possible values are: * `'strip'` Only strip type annotations without performing the transformation of TypeScript features. * `'transform'` Strip type annotations and transform TypeScript features to JavaScript. * `sourceMap` Default: `false`. Only when `mode` is `'transform'`, if `true`, a source map will be generated for the transformed code. * `sourceUrl` Specifies the source url used in the source map. * Returns: The code with type annotations stripped. `module.stripTypeScriptTypes()` removes type annotations from TypeScript code. It can be used to strip type annotations from TypeScript code before running it with `vm.runInContext()` or `vm.compileFunction()`. By default, it will throw an error if the code contains TypeScript features that require transformation such as `Enums`, see type-stripping for more information. When mode is `'transform'`, it also transforms TypeScript features to JavaScript, see transform TypeScript features for more information. When mode is `'strip'`, source maps are not generated, because locations are preserved. If `sourceMap` is provided, when mode is `'strip'`, an error will be thrown. WARNING: The output of this function should not be considered stable across Node.js versions, due to changes in the TypeScript parser. import { stripTypeScriptTypes } from 'node:module'; const code = 'const a: number = 1;'; const strippedCode = stripTypeScriptTypes(code); console.log(strippedCode); // Prints: const a = 1; If `sourceUrl` is provided, it will be used appended as a comment at the end of the output: import { stripTypeScriptTypes } from 'node:module'; const code = 'const a: number = 1;'; const strippedCode = stripTypeScriptTypes(code, { mode: 'strip', sourceUrl: 'source.ts' }); console.log(strippedCode); // Prints: const a = 1\n\n//# sourceURL=source.ts; When `mode` is `'transform'`, the code is transformed to JavaScript: import { stripTypeScriptTypes } from 'node:module'; const code = ` namespace MathUtil { export const add = (a: number, b: number) => a + b; }`; const strippedCode = stripTypeScriptTypes(code, { mode: 'transform', sourceMap: true }); console.log(strippedCode); // Prints: // var MathUtil; // (function(MathUtil) { // MathUtil.add = (a, b)=>a + b; // })(MathUtil || (MathUtil = {})); // # sourceMappingURL=data:application/json;base64, ... #### `module.syncBuiltinESMExports()`# Added in: v12.12.0 The `module.syncBuiltinESMExports()` method updates all the live bindings for builtin ES Modules to match the properties of the CommonJS exports. It does not add or remove exported names from the ES Modules. const fs = require('node:fs'); const assert = require('node:assert'); const { syncBuiltinESMExports } = require('node:module'); fs.readFile = newAPI; delete fs.readFileSync; function newAPI() { // ... } fs.newAPI = newAPI; syncBuiltinESMExports(); import('node:fs').then((esmFS) => { // It syncs the existing readFile property with the new value assert.strictEqual(esmFS.readFile, newAPI); // readFileSync has been deleted from the required fs assert.strictEqual('readFileSync' in fs, false); // syncBuiltinESMExports() does not remove readFileSync from esmFS assert.strictEqual('readFileSync' in esmFS, true); // syncBuiltinESMExports() does not add names assert.strictEqual(esmFS.newAPI, undefined); }); ### Module compile cache# History VersionChanges v22.8.0 add initial JavaScript APIs for runtime access. v22.1.0 Added in: v22.1.0 The module compile cache can be enabled either using the `module.enableCompileCache()` method or the `NODE_COMPILE_CACHE=dir` environment variable. After it is enabled, whenever Node.js compiles a CommonJS or a ECMAScript Module, it will use on-disk V8 code cache persisted in the specified directory to speed up the compilation. This may slow down the first load of a module graph, but subsequent loads of the same module graph may get a significant speedup if the contents of the modules do not change. To clean up the generated compile cache on disk, simply remove the cache directory. The cache directory will be recreated the next time the same directory is used for for compile cache storage. To avoid filling up the disk with stale cache, it is recommended to use a directory under the `os.tmpdir()`. If the compile cache is enabled by a call to `module.enableCompileCache()` without specifying the directory, Node.js will use the `NODE_COMPILE_CACHE=dir` environment variable if it's set, or defaults to `path.join(os.tmpdir(), 'node-compile-cache')` otherwise. To locate the compile cache directory used by a running Node.js instance, use `module.getCompileCacheDir()`. Currently when using the compile cache with V8 JavaScript code coverage, the coverage being collected by V8 may be less precise in functions that are deserialized from the code cache. It's recommended to turn this off when running tests to generate precise coverage. The enabled module compile cache can be disabled by the `NODE_DISABLE_COMPILE_CACHE=1` environment variable. This can be useful when the compile cache leads to unexpected or undesired behaviors (e.g. less precise test coverage). Compilation cache generated by one version of Node.js can not be reused by a different version of Node.js. Cache generated by different versions of Node.js will be stored separately if the same base directory is used to persist the cache, so they can co-exist. At the moment, when the compile cache is enabled and a module is loaded afresh, the code cache is generated from the compiled code immediately, but will only be written to disk when the Node.js instance is about to exit. This is subject to change. The `module.flushCompileCache()` method can be used to ensure the accumulated code cache is flushed to disk in case the application wants to spawn other Node.js instances and let them share the cache long before the parent exits. #### `module.constants.compileCacheStatus`# Added in: v22.8.0 Stability: 1.1 \- Active Development The following constants are returned as the `status` field in the object returned by `module.enableCompileCache()` to indicate the result of the attempt to enable the module compile cache. Constant Description `ENABLED` Node.js has enabled the compile cache successfully. The directory used to store the compile cache will be returned in the `directory` field in the returned object. `ALREADY_ENABLED` The compile cache has already been enabled before, either by a previous call to `module.enableCompileCache()`, or by the `NODE_COMPILE_CACHE=dir` environment variable. The directory used to store the compile cache will be returned in the `directory` field in the returned object. `FAILED` Node.js fails to enable the compile cache. This can be caused by the lack of permission to use the specified directory, or various kinds of file system errors. The detail of the failure will be returned in the `message` field in the returned object. `DISABLED` Node.js cannot enable the compile cache because the environment variable `NODE_DISABLE_COMPILE_CACHE=1` has been set. #### `module.enableCompileCache([cacheDir])`# Added in: v22.8.0 Stability: 1.1 \- Active Development * `cacheDir` | Optional path to specify the directory where the compile cache will be stored/retrieved. * Returns: * `status` One of the `module.constants.compileCacheStatus` * `message` | If Node.js cannot enable the compile cache, this contains the error message. Only set if `status` is `module.constants.compileCacheStatus.FAILED`. * `directory` | If the compile cache is enabled, this contains the directory where the compile cache is stored. Only set if `status` is `module.constants.compileCacheStatus.ENABLED` or `module.constants.compileCacheStatus.ALREADY_ENABLED`. Enable module compile cache in the current Node.js instance. If `cacheDir` is not specified, Node.js will either use the directory specified by the `NODE_COMPILE_CACHE=dir` environment variable if it's set, or use `path.join(os.tmpdir(), 'node-compile-cache')` otherwise. For general use cases, it's recommended to call `module.enableCompileCache()` without specifying the `cacheDir`, so that the directory can be overridden by the `NODE_COMPILE_CACHE` environment variable when necessary. Since compile cache is supposed to be a quiet optimization that is not required for the application to be functional, this method is designed to not throw any exception when the compile cache cannot be enabled. Instead, it will return an object containing an error message in the `message` field to aid debugging. If compile cache is enabled successfully, the `directory` field in the returned object contains the path to the directory where the compile cache is stored. The `status` field in the returned object would be one of the `module.constants.compileCacheStatus` values to indicate the result of the attempt to enable the module compile cache. This method only affects the current Node.js instance. To enable it in child worker threads, either call this method in child worker threads too, or set the `process.env.NODE_COMPILE_CACHE` value to compile cache directory so the behavior can be inherited into the child workers. The directory can be obtained either from the `directory` field returned by this method, or with `module.getCompileCacheDir()`. #### `module.flushCompileCache()`# Added in: v23.0.0, v22.10.0 Stability: 1.1 \- Active Development Flush the module compile cache accumulated from modules already loaded in the current Node.js instance to disk. This returns after all the flushing file system operations come to an end, no matter they succeed or not. If there are any errors, this will fail silently, since compile cache misses should not interfere with the actual operation of the application. #### `module.getCompileCacheDir()`# Added in: v22.8.0 Stability: 1.1 \- Active Development * Returns: | Path to the module compile cache directory if it is enabled, or `undefined` otherwise. ### Customization Hooks# History VersionChanges v23.5.0, v22.15.0 Add support for synchronous and in-thread hooks. v20.6.0, v18.19.0 Added `initialize` hook to replace `globalPreload`. v18.6.0, v16.17.0 Add support for chaining loaders. v16.12.0 Removed `getFormat`, `getSource`, `transformSource`, and `globalPreload`; added `load` hook and `getGlobalPreload` hook. v8.8.0 Added in: v8.8.0 Stability: 1.2 \- Release candidate (asynchronous version) Stability: 1.1 - Active development (synchronous version) There are two types of module customization hooks that are currently supported: 1. `module.register(specifier[, parentURL][, options])` which takes a module that exports asynchronous hook functions. The functions are run on a separate loader thread. 2. `module.registerHooks(options)` which takes synchronous hook functions that are run directly on the thread where the module is loaded. #### Enabling# Module resolution and loading can be customized by: 1. Registering a file which exports a set of asynchronous hook functions, using the `register` method from `node:module`, 2. Registering a set of synchronous hook functions using the `registerHooks` method from `node:module`. The hooks can be registered before the application code is run by using the `--import` or `--require` flag: node --import ./register-hooks.js ./my-app.js node --require ./register-hooks.js ./my-app.js // register-hooks.js // This file can only be require()-ed if it doesn't contain top-level await. // Use module.register() to register asynchronous hooks in a dedicated thread. import { register } from 'node:module'; register('./hooks.mjs', import.meta.url); // Use module.registerHooks() to register synchronous hooks in the main thread. import { registerHooks } from 'node:module'; registerHooks({ resolve(specifier, context, nextResolve) { /* implementation */ }, load(url, context, nextLoad) { /* implementation */ }, }); The file passed to `--import` or `--require` can also be an export from a dependency: node --import some-package/register ./my-app.js node --require some-package/register ./my-app.js Where `some-package` has an `"exports"` field defining the `/register` export to map to a file that calls `register()`, like the following `register-hooks.js` example. Using `--import` or `--require` ensures that the hooks are registered before any application files are imported, including the entry point of the application and for any worker threads by default as well. Alternatively, `register()` and `registerHooks()` can be called from the entry point, though dynamic `import()` must be used for any ESM code that should be run after the hooks are registered. import { register } from 'node:module'; register('http-to-https', import.meta.url); // Because this is a dynamic `import()`, the `http-to-https` hooks will run // to handle `./my-app.js` and any other files it imports or requires. await import('./my-app.js'); Customization hooks will run for any modules loaded later than the registration and the modules they reference via `import` and the built-in `require`. `require` function created by users using `module.createRequire()` can only be customized by the synchronous hooks. In this example, we are registering the `http-to-https` hooks, but they will only be available for subsequently imported modules — in this case, `my-app.js` and anything it references via `import` or built-in `require` in CommonJS dependencies. If the `import('./my-app.js')` had instead been a static `import './my-app.js'`, the app would have already been loaded before the `http-to-https` hooks were registered. This due to the ES modules specification, where static imports are evaluated from the leaves of the tree first, then back to the trunk. There can be static imports within `my-app.js`, which will not be evaluated until `my-app.js` is dynamically imported. If synchronous hooks are used, both `import`, `require` and user `require` created using `createRequire()` are supported. import { registerHooks, createRequire } from 'node:module'; registerHooks({ /* implementation of synchronous hooks */ }); const require = createRequire(import.meta.url); // The synchronous hooks affect import, require() and user require() function // created through createRequire(). await import('./my-app.js'); require('./my-app-2.js'); Finally, if all you want to do is register hooks before your app runs and you don't want to create a separate file for that purpose, you can pass a `data:` URL to `--import`: node --import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register("http-to-https", pathToFileURL("./"));' ./my-app.js #### Chaining# It's possible to call `register` more than once: // entrypoint.mjs import { register } from 'node:module'; register('./foo.mjs', import.meta.url); register('./bar.mjs', import.meta.url); await import('./my-app.mjs'); In this example, the registered hooks will form chains. These chains run last-in, first out (LIFO). If both `foo.mjs` and `bar.mjs` define a `resolve` hook, they will be called like so (note the right-to-left): node's default ← `./foo.mjs` ← `./bar.mjs` (starting with `./bar.mjs`, then `./foo.mjs`, then the Node.js default). The same applies to all the other hooks. The registered hooks also affect `register` itself. In this example, `bar.mjs` will be resolved and loaded via the hooks registered by `foo.mjs` (because `foo`'s hooks will have already been added to the chain). This allows for things like writing hooks in non-JavaScript languages, so long as earlier registered hooks transpile into JavaScript. The `register` method cannot be called from within the module that defines the hooks. Chaining of `registerHooks` work similarly. If synchronous and asynchronous hooks are mixed, the synchronous hooks are always run first before the asynchronous hooks start running, that is, in the last synchronous hook being run, its next hook includes invocation of the asynchronous hooks. // entrypoint.mjs import { registerHooks } from 'node:module'; const hook1 = { /* implementation of hooks */ }; const hook2 = { /* implementation of hooks */ }; // hook2 run before hook1. registerHooks(hook1); registerHooks(hook2); #### Communication with module customization hooks# Asynchronous hooks run on a dedicated thread, separate from the main thread that runs application code. This means mutating global variables won't affect the other thread(s), and message channels must be used to communicate between the threads. The `register` method can be used to pass data to an `initialize` hook. The data passed to the hook may include transferable objects like ports. import { register } from 'node:module'; import { MessageChannel } from 'node:worker_threads'; // This example demonstrates how a message channel can be used to // communicate with the hooks, by sending `port2` to the hooks. const { port1, port2 } = new MessageChannel(); port1.on('message', (msg) => { console.log(msg); }); port1.unref(); register('./my-hooks.mjs', { parentURL: import.meta.url, data: { number: 1, port: port2 }, transferList: [port2], }); Synchronous module hooks are run on the same thread where the application code is run. They can directly mutate the globals of the context accessed by the main thread. #### Hooks# ##### Asynchronous hooks accepted by `module.register()`# The `register` method can be used to register a module that exports a set of hooks. The hooks are functions that are called by Node.js to customize the module resolution and loading process. The exported functions must have specific names and signatures, and they must be exported as named exports. export async function initialize({ number, port }) { // Receives data from `register`. } export async function resolve(specifier, context, nextResolve) { // Take an `import` or `require` specifier and resolve it to a URL. } export async function load(url, context, nextLoad) { // Take a resolved URL and return the source code to be evaluated. } Asynchronous hooks are run in a separate thread, isolated from the main thread where application code runs. That means it is a different realm. The hooks thread may be terminated by the main thread at any time, so do not depend on asynchronous operations (like `console.log`) to complete. They are inherited into child workers by default. ##### Synchronous hooks accepted by `module.registerHooks()`# Added in: v23.5.0, v22.15.0 Stability: 1.1 \- Active development The `module.registerHooks()` method accepts synchronous hook functions. `initialize()` is not supported nor necessary, as the hook implementer can simply run the initialization code directly before the call to `module.registerHooks()`. function resolve(specifier, context, nextResolve) { // Take an `import` or `require` specifier and resolve it to a URL. } function load(url, context, nextLoad) { // Take a resolved URL and return the source code to be evaluated. } Synchronous hooks are run in the same thread and the same realm where the modules are loaded. Unlike the asynchronous hooks they are not inherited into child worker threads by default, though if the hooks are registered using a file preloaded by `--import` or `--require`, child worker threads can inherit the preloaded scripts via `process.execArgv` inheritance. See the documentation of `Worker` for detail. In synchronous hooks, users can expect `console.log()` to complete in the same way that they expect `console.log()` in module code to complete. ##### Conventions of hooks# Hooks are part of a chain, even if that chain consists of only one custom (user-provided) hook and the default hook, which is always present. Hook functions nest: each one must always return a plain object, and chaining happens as a result of each function calling `next()`, which is a reference to the subsequent loader's hook (in LIFO order). A hook that returns a value lacking a required property triggers an exception. A hook that returns without calling `next()` and without returning `shortCircuit: true` also triggers an exception. These errors are to help prevent unintentional breaks in the chain. Return `shortCircuit: true` from a hook to signal that the chain is intentionally ending at your hook. ##### `initialize()`# Added in: v20.6.0, v18.19.0 Stability: 1.2 \- Release candidate * `data` The data from `register(loader, import.meta.url, { data })`. The `initialize` hook is only accepted by `register`. `registerHooks()` does not support nor need it since initialization done for synchronous hooks can be run directly before the call to `registerHooks()`. The `initialize` hook provides a way to define a custom function that runs in the hooks thread when the hooks module is initialized. Initialization happens when the hooks module is registered via `register`. This hook can receive data from a `register` invocation, including ports and other transferable objects. The return value of `initialize` can be a , in which case it will be awaited before the main application thread execution resumes. Module customization code: // path-to-my-hooks.js export async function initialize({ number, port }) { port.postMessage(`increment: ${number + 1}`); } Caller code: import assert from 'node:assert'; import { register } from 'node:module'; import { MessageChannel } from 'node:worker_threads'; // This example showcases how a message channel can be used to communicate // between the main (application) thread and the hooks running on the hooks // thread, by sending `port2` to the `initialize` hook. const { port1, port2 } = new MessageChannel(); port1.on('message', (msg) => { assert.strictEqual(msg, 'increment: 2'); }); port1.unref(); register('./path-to-my-hooks.js', { parentURL: import.meta.url, data: { number: 1, port: port2 }, transferList: [port2], }); ##### `resolve(specifier, context, nextResolve)`# History VersionChanges v23.5.0, v22.15.0 Add support for synchronous and in-thread hooks. v21.0.0, v20.10.0, v18.19.0 The property `context.importAssertions` is replaced with `context.importAttributes`. Using the old name is still supported and will emit an experimental warning. v18.6.0, v16.17.0 Add support for chaining resolve hooks. Each hook must either call `nextResolve()` or include a `shortCircuit` property set to `true` in its return. v17.1.0, v16.14.0 Add support for import assertions. * `specifier` * `context` * `conditions` Export conditions of the relevant `package.json` * `importAttributes` An object whose key-value pairs represent the attributes for the module to import * `parentURL` | The module importing this one, or undefined if this is the Node.js entry point * `nextResolve` The subsequent `resolve` hook in the chain, or the Node.js default `resolve` hook after the last user-supplied `resolve` hook * `specifier` * `context` | When omitted, the defaults are provided. When provided, defaults are merged in with preference to the provided properties. * Returns: | The asynchronous version takes either an object containing the following properties, or a `Promise` that will resolve to such an object. The synchronous version only accepts an object returned synchronously. * `format` | | A hint to the `load` hook (it might be ignored). It can be a module format (such as `'commonjs'` or `'module'`) or an arbitrary value like `'css'` or `'yaml'`. * `importAttributes` | The import attributes to use when caching the module (optional; if excluded the input will be used) * `shortCircuit` | A signal that this hook intends to terminate the chain of `resolve` hooks. Default: `false` * `url` The absolute URL to which this input resolves > Warning In the case of the asynchronous version, despite support for returning promises and async functions, calls to `resolve` may still block the main thread which can impact performance. The `resolve` hook chain is responsible for telling Node.js where to find and how to cache a given `import` statement or expression, or `require` call. It can optionally return a format (such as `'module'`) as a hint to the `load` hook. If a format is specified, the `load` hook is ultimately responsible for providing the final `format` value (and it is free to ignore the hint provided by `resolve`); if `resolve` provides a `format`, a custom `load` hook is required even if only to pass the value to the Node.js default `load` hook. Import type attributes are part of the cache key for saving loaded modules into the internal module cache. The `resolve` hook is responsible for returning an `importAttributes` object if the module should be cached with different attributes than were present in the source code. The `conditions` property in `context` is an array of conditions that will be used to match package exports conditions for this resolution request. They can be used for looking up conditional mappings elsewhere or to modify the list when calling the default resolution logic. The current package exports conditions are always in the `context.conditions` array passed into the hook. To guarantee default Node.js module specifier resolution behavior when calling `defaultResolve`, the `context.conditions` array passed to it must include all elements of the `context.conditions` array originally passed into the `resolve` hook. // Asynchronous version accepted by module.register(). export async function resolve(specifier, context, nextResolve) { const { parentURL = null } = context; if (Math.random() > 0.5) { // Some condition. // For some or all specifiers, do some custom logic for resolving. // Always return an object of the form {url: }. return { shortCircuit: true, url: parentURL ? new URL(specifier, parentURL).href : new URL(specifier).href, }; } if (Math.random() < 0.5) { // Another condition. // When calling `defaultResolve`, the arguments can be modified. In this // case it's adding another value for matching conditional exports. return nextResolve(specifier, { ...context, conditions: [...context.conditions, 'another-condition'], }); } // Defer to the next hook in the chain, which would be the // Node.js default resolve if this is the last user-specified loader. return nextResolve(specifier); } // Synchronous version accepted by module.registerHooks(). function resolve(specifier, context, nextResolve) { // Similar to the asynchronous resolve() above, since that one does not have // any asynchronous logic. } ##### `load(url, context, nextLoad)`# History VersionChanges v23.5.0, v22.15.0 Add support for synchronous and in-thread version. v22.6.0 Add support for `source` with format `commonjs-typescript` and `module-typescript`. v20.6.0 Add support for `source` with format `commonjs`. v18.6.0, v16.17.0 Add support for chaining load hooks. Each hook must either call `nextLoad()` or include a `shortCircuit` property set to `true` in its return. * `url` The URL returned by the `resolve` chain * `context` * `conditions` Export conditions of the relevant `package.json` * `format` | | The format optionally supplied by the `resolve` hook chain. This can be any string value as an input; input values do not need to conform to the list of acceptable return values described below. * `importAttributes` * `nextLoad` The subsequent `load` hook in the chain, or the Node.js default `load` hook after the last user-supplied `load` hook * `url` * `context` | When omitted, defaults are provided. When provided, defaults are merged in with preference to the provided properties. In the default `nextLoad`, if the module pointed to by `url` does not have explicit module type information, `context.format` is mandatory. * Returns: | The asynchronous version takes either an object containing the following properties, or a `Promise` that will resolve to such an object. The synchronous version only accepts an object returned synchronously. * `format` * `shortCircuit` | A signal that this hook intends to terminate the chain of `load` hooks. Default: `false` * `source` | | The source for Node.js to evaluate The `load` hook provides a way to define a custom method of determining how a URL should be interpreted, retrieved, and parsed. It is also in charge of validating the import attributes. The final value of `format` must be one of the following: `format`DescriptionAcceptable types for `source` returned by `load` `'addon'`Load a Node.js addon `'builtin'`Load a Node.js builtin module `'commonjs-typescript'`Load a Node.js CommonJS module with TypeScript syntax | | | | `'commonjs'`Load a Node.js CommonJS module | | | | `'json'`Load a JSON file | | `'module-typescript'`Load an ES module with TypeScript syntax | | `'module'`Load an ES module | | `'wasm'`Load a WebAssembly module | The value of `source` is ignored for type `'builtin'` because currently it is not possible to replace the value of a Node.js builtin (core) module. ###### Caveat in the asynchronous `load` hook# When using the asynchronous `load` hook, omitting vs providing a `source` for `'commonjs'` has very different effects: * When a `source` is provided, all `require` calls from this module will be processed by the ESM loader with registered `resolve` and `load` hooks; all `require.resolve` calls from this module will be processed by the ESM loader with registered `resolve` hooks; only a subset of the CommonJS API will be available (e.g. no `require.extensions`, no `require.cache`, no `require.resolve.paths`) and monkey-patching on the CommonJS module loader will not apply. * If `source` is undefined or `null`, it will be handled by the CommonJS module loader and `require`/`require.resolve` calls will not go through the registered hooks. This behavior for nullish `source` is temporary — in the future, nullish `source` will not be supported. These caveats do not apply to the synchronous `load` hook, in which case the complete set of CommonJS APIs available to the customized CommonJS modules, and `require`/`require.resolve` always go through the registered hooks. The Node.js internal asynchronous `load` implementation, which is the value of `next` for the last hook in the `load` chain, returns `null` for `source` when `format` is `'commonjs'` for backward compatibility. Here is an example hook that would opt-in to using the non-default behavior: import { readFile } from 'node:fs/promises'; // Asynchronous version accepted by module.register(). This fix is not needed // for the synchronous version accepted by module.registerHooks(). export async function load(url, context, nextLoad) { const result = await nextLoad(url, context); if (result.format === 'commonjs') { result.source ??= await readFile(new URL(result.responseURL ?? url)); } return result; } This doesn't apply to the synchronous `load` hook either, in which case the `source` returned contains source code loaded by the next hook, regardless of module format. > Warning: The asynchronous `load` hook and namespaced exports from CommonJS modules are incompatible. Attempting to use them together will result in an empty object from the import. This may be addressed in the future. This does not apply to the synchronous `load` hook, in which case exports can be used as usual. > These types all correspond to classes defined in ECMAScript. * The specific object is a . * The specific object is a . If the source value of a text-based format (i.e., `'json'`, `'module'`) is not a string, it is converted to a string using `util.TextDecoder`. The `load` hook provides a way to define a custom method for retrieving the source code of a resolved URL. This would allow a loader to potentially avoid reading files from disk. It could also be used to map an unrecognized format to a supported one, for example `yaml` to `module`. // Asynchronous version accepted by module.register(). export async function load(url, context, nextLoad) { const { format } = context; if (Math.random() > 0.5) { // Some condition /* For some or all URLs, do some custom logic for retrieving the source. Always return an object of the form { format: , source: , }. */ return { format, shortCircuit: true, source: '...', }; } // Defer to the next hook in the chain. return nextLoad(url); } // Synchronous version accepted by module.registerHooks(). function load(url, context, nextLoad) { // Similar to the asynchronous load() above, since that one does not have // any asynchronous logic. } In a more advanced scenario, this can also be used to transform an unsupported source to a supported one (see Examples below). #### Examples# The various module customization hooks can be used together to accomplish wide-ranging customizations of the Node.js code loading and evaluation behaviors. ##### Import from HTTPS# The hook below registers hooks to enable rudimentary support for such specifiers. While this may seem like a significant improvement to Node.js core functionality, there are substantial downsides to actually using these hooks: performance is much slower than loading files from disk, there is no caching, and there is no security. // https-hooks.mjs import { get } from 'node:https'; export function load(url, context, nextLoad) { // For JavaScript to be loaded over the network, we need to fetch and // return it. if (url.startsWith('https://')) { return new Promise((resolve, reject) => { get(url, (res) => { let data = ''; res.setEncoding('utf8'); res.on('data', (chunk) => data += chunk); res.on('end', () => resolve({ // This example assumes all network-provided JavaScript is ES module // code. format: 'module', shortCircuit: true, source: data, })); }).on('error', (err) => reject(err)); }); } // Let Node.js handle all other URLs. return nextLoad(url); } // main.mjs import { VERSION } from 'https://coffeescript.org/browser-compiler-modern/coffeescript.js'; console.log(VERSION); With the preceding hooks module, running `node --import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register(pathToFileURL("./https-hooks.mjs"));' ./main.mjs` prints the current version of CoffeeScript per the module at the URL in `main.mjs`. ##### Transpilation# Sources that are in formats Node.js doesn't understand can be converted into JavaScript using the `load` hook. This is less performant than transpiling source files before running Node.js; transpiler hooks should only be used for development and testing purposes. ###### Asynchronous version# // coffeescript-hooks.mjs import { readFile } from 'node:fs/promises'; import { findPackageJSON } from 'node:module'; import coffeescript from 'coffeescript'; const extensionsRegex = /\.(coffee|litcoffee|coffee\.md)$/; export async function load(url, context, nextLoad) { if (extensionsRegex.test(url)) { // CoffeeScript files can be either CommonJS or ES modules. Use a custom format // to tell Node.js not to detect its module type. const { source: rawSource } = await nextLoad(url, { ...context, format: 'coffee' }); // This hook converts CoffeeScript source code into JavaScript source code // for all imported CoffeeScript files. const transformedSource = coffeescript.compile(rawSource.toString(), url); // To determine how Node.js would interpret the transpilation result, // search up the file system for the nearest parent package.json file // and read its "type" field. return { format: await getPackageType(url), shortCircuit: true, source: transformedSource, }; } // Let Node.js handle all other URLs. return nextLoad(url, context); } async function getPackageType(url) { // `url` is only a file path during the first iteration when passed the // resolved url from the load() hook // an actual file path from load() will contain a file extension as it's // required by the spec // this simple truthy check for whether `url` contains a file extension will // work for most projects but does not cover some edge-cases (such as // extensionless files or a url ending in a trailing space) const pJson = findPackageJSON(url); return readFile(pJson, 'utf8') .then(JSON.parse) .then((json) => json?.type) .catch(() => undefined); } ###### Synchronous version# // coffeescript-sync-hooks.mjs import { readFileSync } from 'node:fs'; import { registerHooks, findPackageJSON } from 'node:module'; import coffeescript from 'coffeescript'; const extensionsRegex = /\.(coffee|litcoffee|coffee\.md)$/; function load(url, context, nextLoad) { if (extensionsRegex.test(url)) { const { source: rawSource } = nextLoad(url, { ...context, format: 'coffee' }); const transformedSource = coffeescript.compile(rawSource.toString(), url); return { format: getPackageType(url), shortCircuit: true, source: transformedSource, }; } return nextLoad(url, context); } function getPackageType(url) { const pJson = findPackageJSON(url); if (!pJson) { return undefined; } try { const file = readFileSync(pJson, 'utf-8'); return JSON.parse(file)?.type; } catch { return undefined; } } registerHooks({ load }); ##### Running hooks# # main.coffee import { scream } from './scream.coffee' console.log scream 'hello, world' import { version } from 'node:process' console.log "Brought to you by Node.js version #{version}" # scream.coffee export scream = (str) -> str.toUpperCase() For the sake of running the example, add a `package.json` file containing the module type of the CoffeeScript files. { "type": "module" } This is only for running the example. In real world loaders, `getPackageType()` must be able to return an `format` known to Node.js even in the absence of an explicit type in a `package.json`, or otherwise the `nextLoad` call would throw `ERR_UNKNOWN_FILE_EXTENSION` (if undefined) or `ERR_UNKNOWN_MODULE_FORMAT` (if it's not a known format listed in the load hook documentation). With the preceding hooks modules, running `node --import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register(pathToFileURL("./coffeescript-hooks.mjs"));' ./main.coffee` or `node --import ./coffeescript-sync-hooks.mjs ./main.coffee` causes `main.coffee` to be turned into JavaScript after its source code is loaded from disk but before Node.js executes it; and so on for any `.coffee`, `.litcoffee` or `.coffee.md` files referenced via `import` statements of any loaded file. ##### Import maps# The previous two examples defined `load` hooks. This is an example of a `resolve` hook. This hooks module reads an `import-map.json` file that defines which specifiers to override to other URLs (this is a very simplistic implementation of a small subset of the "import maps" specification). ###### Asynchronous version# // import-map-hooks.js import fs from 'node:fs/promises'; const { imports } = JSON.parse(await fs.readFile('import-map.json')); export async function resolve(specifier, context, nextResolve) { if (Object.hasOwn(imports, specifier)) { return nextResolve(imports[specifier], context); } return nextResolve(specifier, context); } ###### Synchronous version# // import-map-sync-hooks.js import fs from 'node:fs/promises'; import module from 'node:module'; const { imports } = JSON.parse(fs.readFileSync('import-map.json', 'utf-8')); function resolve(specifier, context, nextResolve) { if (Object.hasOwn(imports, specifier)) { return nextResolve(imports[specifier], context); } return nextResolve(specifier, context); } module.registerHooks({ resolve }); ###### Using the hooks# With these files: // main.js import 'a-module'; // import-map.json { "imports": { "a-module": "./some-module.js" } } // some-module.js console.log('some module!'); Running `node --import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register(pathToFileURL("./import-map-hooks.js"));' main.js` or `node --import ./import-map-sync-hooks.js main.js` should print `some module!`. ### Source Map Support# Added in: v13.7.0, v12.17.0 Stability: 1 \- Experimental Node.js supports TC39 ECMA-426 Source Map format (it was called Source map revision 3 format). The APIs in this section are helpers for interacting with the source map cache. This cache is populated when source map parsing is enabled and source map include directives are found in a modules' footer. To enable source map parsing, Node.js must be run with the flag `--enable-source-maps`, or with code coverage enabled by setting `NODE_V8_COVERAGE=dir`, or be enabled programmatically via `module.setSourceMapsSupport()`. // module.mjs // In an ECMAScript module import { findSourceMap, SourceMap } from 'node:module'; #### `module.getSourceMapsSupport()`# Added in: v23.7.0, v22.14.0 * Returns: * `enabled` If the source maps support is enabled * `nodeModules` If the support is enabled for files in `node_modules`. * `generatedCode` If the support is enabled for generated code from `eval` or `new Function`. This method returns whether the Source Map v3 support for stack traces is enabled. #### `module.findSourceMap(path)`# Added in: v13.7.0, v12.17.0 * `path` * Returns: | Returns `module.SourceMap` if a source map is found, `undefined` otherwise. `path` is the resolved path for the file for which a corresponding source map should be fetched. #### `module.setSourceMapsSupport(enabled[, options])`# Added in: v23.7.0, v22.14.0 * `enabled` Enable the source map support. * `options` Optional * `nodeModules` If enabling the support for files in `node_modules`. Default: `false`. * `generatedCode` If enabling the support for generated code from `eval` or `new Function`. Default: `false`. This function enables or disables the Source Map v3 support for stack traces. It provides same features as launching Node.js process with commandline options `--enable-source-maps`, with additional options to alter the support for files in `node_modules` or generated codes. Only source maps in JavaScript files that are loaded after source maps has been enabled will be parsed and loaded. Preferably, use the commandline options `--enable-source-maps` to avoid losing track of source maps of modules loaded before this API call. #### Class: `module.SourceMap`# Added in: v13.7.0, v12.17.0 ##### `new SourceMap(payload[, { lineLengths }])`# History VersionChanges v20.5.0 Add support for `lineLengths`. * `payload` * `lineLengths` Creates a new `sourceMap` instance. `payload` is an object with keys matching the Source map format: * `file` * `version` * `sources` * `sourcesContent` * `names` * `mappings` * `sourceRoot` `lineLengths` is an optional array of the length of each line in the generated code. ##### `sourceMap.payload`# * Returns: Getter for the payload used to construct the `SourceMap` instance. ##### `sourceMap.findEntry(lineOffset, columnOffset)`# * `lineOffset` The zero-indexed line number offset in the generated source * `columnOffset` The zero-indexed column number offset in the generated source * Returns: Given a line offset and column offset in the generated source file, returns an object representing the SourceMap range in the original file if found, or an empty object if not. The object returned contains the following keys: * `generatedLine` The line offset of the start of the range in the generated source * `generatedColumn` The column offset of start of the range in the generated source * `originalSource` The file name of the original source, as reported in the SourceMap * `originalLine` The line offset of the start of the range in the original source * `originalColumn` The column offset of start of the range in the original source * `name` The returned value represents the raw range as it appears in the SourceMap, based on zero-indexed offsets, not 1-indexed line and column numbers as they appear in Error messages and CallSite objects. To get the corresponding 1-indexed line and column numbers from a lineNumber and columnNumber as they are reported by Error stacks and CallSite objects, use `sourceMap.findOrigin(lineNumber, columnNumber)` ##### `sourceMap.findOrigin(lineNumber, columnNumber)`# Added in: v20.4.0, v18.18.0 * `lineNumber` The 1-indexed line number of the call site in the generated source * `columnNumber` The 1-indexed column number of the call site in the generated source * Returns: Given a 1-indexed `lineNumber` and `columnNumber` from a call site in the generated source, find the corresponding call site location in the original source. If the `lineNumber` and `columnNumber` provided are not found in any source map, then an empty object is returned. Otherwise, the returned object contains the following keys: * `name` | The name of the range in the source map, if one was provided * `fileName` The file name of the original source, as reported in the SourceMap * `lineNumber` The 1-indexed lineNumber of the corresponding call site in the original source * `columnNumber` The 1-indexed columnNumber of the corresponding call site in the original source ## Modules: Packages# History VersionChanges v14.13.0, v12.20.0 Add support for `"exports"` patterns. v14.6.0, v12.19.0 Add package `"imports"` field. v13.7.0, v12.17.0 Unflag conditional exports. v13.7.0, v12.16.0 Remove the `--experimental-conditional-exports` option. In 12.16.0, conditional exports are still behind `--experimental-modules`. v13.6.0, v12.16.0 Unflag self-referencing a package using its name. v12.7.0 Introduce `"exports"` `package.json` field as a more powerful alternative to the classic `"main"` field. v12.0.0 Add support for ES modules using `.js` file extension via `package.json` `"type"` field. ### Introduction# A package is a folder tree described by a `package.json` file. The package consists of the folder containing the `package.json` file and all subfolders until the next folder containing another `package.json` file, or a folder named `node_modules`. This page provides guidance for package authors writing `package.json` files along with a reference for the `package.json` fields defined by Node.js. ### Determining module system# #### Introduction# Node.js will treat the following as ES modules when passed to `node` as the initial input, or when referenced by `import` statements or `import()` expressions: * Files with an `.mjs` extension. * Files with a `.js` extension when the nearest parent `package.json` file contains a top-level `"type"` field with a value of `"module"`. * Strings passed in as an argument to `--eval`, or piped to `node` via `STDIN`, with the flag `--input-type=module`. * Code containing syntax only successfully parsed as ES modules, such as `import` or `export` statements or `import.meta`, with no explicit marker of how it should be interpreted. Explicit markers are `.mjs` or `.cjs` extensions, `package.json` `"type"` fields with either `"module"` or `"commonjs"` values, or the `--input-type` flag. Dynamic `import()` expressions are supported in either CommonJS or ES modules and would not force a file to be treated as an ES module. See Syntax detection. Node.js will treat the following as CommonJS when passed to `node` as the initial input, or when referenced by `import` statements or `import()` expressions: * Files with a `.cjs` extension. * Files with a `.js` extension when the nearest parent `package.json` file contains a top-level field `"type"` with a value of `"commonjs"`. * Strings passed in as an argument to `--eval` or `--print`, or piped to `node` via `STDIN`, with the flag `--input-type=commonjs`. * Files with a `.js` extension with no parent `package.json` file or where the nearest parent `package.json` file lacks a `type` field, and where the code can evaluate successfully as CommonJS. In other words, Node.js tries to run such "ambiguous" files as CommonJS first, and will retry evaluating them as ES modules if the evaluation as CommonJS fails because the parser found ES module syntax. Writing ES module syntax in "ambiguous" files incurs a performance cost, and therefore it is encouraged that authors be explicit wherever possible. In particular, package authors should always include the `"type"` field in their `package.json` files, even in packages where all sources are CommonJS. Being explicit about the `type` of the package will future-proof the package in case the default type of Node.js ever changes, and it will also make things easier for build tools and loaders to determine how the files in the package should be interpreted. #### Syntax detection# History VersionChanges v22.7.0, v20.19.0 Syntax detection is enabled by default. v21.1.0, v20.10.0 Added in: v21.1.0, v20.10.0 Stability: 1.2 \- Release candidate Node.js will inspect the source code of ambiguous input to determine whether it contains ES module syntax; if such syntax is detected, the input will be treated as an ES module. Ambiguous input is defined as: * Files with a `.js` extension or no extension; and either no controlling `package.json` file or one that lacks a `type` field. * String input (`--eval` or `STDIN`) when `--input-type`is not specified. ES module syntax is defined as syntax that would throw when evaluated as CommonJS. This includes the following: * `import` statements (but not `import()` expressions, which are valid in CommonJS). * `export` statements. * `import.meta` references. * `await` at the top level of a module. * Lexical redeclarations of the CommonJS wrapper variables (`require`, `module`, `exports`, `__dirname`, `__filename`). #### Modules loaders# Node.js has two systems for resolving a specifier and loading modules. There is the CommonJS module loader: * It is fully synchronous. * It is responsible for handling `require()` calls. * It is monkey patchable. * It supports folders as modules. * When resolving a specifier, if no exact match is found, it will try to add extensions (`.js`, `.json`, and finally `.node`) and then attempt to resolve folders as modules. * It treats `.json` as JSON text files. * `.node` files are interpreted as compiled addon modules loaded with `process.dlopen()`. * It treats all files that lack `.json` or `.node` extensions as JavaScript text files. * It can only be used to load ECMAScript modules from CommonJS modules if the module graph is synchronous (that contains no top-level `await`). When used to load a JavaScript text file that is not an ECMAScript module, the file will be loaded as a CommonJS module. There is the ECMAScript module loader: * It is asynchronous, unless it's being used to load modules for `require()`. * It is responsible for handling `import` statements and `import()` expressions. * It is not monkey patchable, can be customized using loader hooks. * It does not support folders as modules, directory indexes (e.g. `'./startup/index.js'`) must be fully specified. * It does no extension searching. A file extension must be provided when the specifier is a relative or absolute file URL. * It can load JSON modules, but an import type attribute is required. * It accepts only `.js`, `.mjs`, and `.cjs` extensions for JavaScript text files. * It can be used to load JavaScript CommonJS modules. Such modules are passed through the `cjs-module-lexer` to try to identify named exports, which are available if they can be determined through static analysis. Imported CommonJS modules have their URLs converted to absolute paths and are then loaded via the CommonJS module loader. #### `package.json` and file extensions# Within a package, the `package.json` `"type"` field defines how Node.js should interpret `.js` files. If a `package.json` file does not have a `"type"` field, `.js` files are treated as CommonJS. A `package.json` `"type"` value of `"module"` tells Node.js to interpret `.js` files within that package as using ES module syntax. The `"type"` field applies not only to initial entry points (`node my-app.js`) but also to files referenced by `import` statements and `import()` expressions. // my-app.js, treated as an ES module because there is a package.json // file in the same folder with "type": "module". import './startup/init.js'; // Loaded as ES module since ./startup contains no package.json file, // and therefore inherits the "type" value from one level up. import 'commonjs-package'; // Loaded as CommonJS since ./node_modules/commonjs-package/package.json // lacks a "type" field or contains "type": "commonjs". import './node_modules/commonjs-package/index.js'; // Loaded as CommonJS since ./node_modules/commonjs-package/package.json // lacks a "type" field or contains "type": "commonjs". Files ending with `.mjs` are always loaded as ES modules regardless of the nearest parent `package.json`. Files ending with `.cjs` are always loaded as CommonJS regardless of the nearest parent `package.json`. import './legacy-file.cjs'; // Loaded as CommonJS since .cjs is always loaded as CommonJS. import 'commonjs-package/src/index.mjs'; // Loaded as ES module since .mjs is always loaded as ES module. The `.mjs` and `.cjs` extensions can be used to mix types within the same package: * Within a `"type": "module"` package, Node.js can be instructed to interpret a particular file as CommonJS by naming it with a `.cjs` extension (since both `.js` and `.mjs` files are treated as ES modules within a `"module"` package). * Within a `"type": "commonjs"` package, Node.js can be instructed to interpret a particular file as an ES module by naming it with an `.mjs` extension (since both `.js` and `.cjs` files are treated as CommonJS within a `"commonjs"` package). #### `--input-type` flag# Added in: v12.0.0 Strings passed in as an argument to `--eval` (or `-e`), or piped to `node` via `STDIN`, are treated as ES modules when the `--input-type=module` flag is set. node --input-type=module --eval "import { sep } from 'node:path'; console.log(sep);" echo "import { sep } from 'node:path'; console.log(sep);" | node --input-type=module For completeness there is also `--input-type=commonjs`, for explicitly running string input as CommonJS. This is the default behavior if `--input-type` is unspecified. ### Package entry points# In a package's `package.json` file, two fields can define entry points for a package: `"main"` and `"exports"`. Both fields apply to both ES module and CommonJS module entry points. The `"main"` field is supported in all versions of Node.js, but its capabilities are limited: it only defines the main entry point of the package. The `"exports"` provides a modern alternative to `"main"` allowing multiple entry points to be defined, conditional entry resolution support between environments, and preventing any other entry points besides those defined in `"exports"`. This encapsulation allows module authors to clearly define the public interface for their package. For new packages targeting the currently supported versions of Node.js, the `"exports"` field is recommended. For packages supporting Node.js 10 and below, the `"main"` field is required. If both `"exports"` and `"main"` are defined, the `"exports"` field takes precedence over `"main"` in supported versions of Node.js. Conditional exports can be used within `"exports"` to define different package entry points per environment, including whether the package is referenced via `require` or via `import`. For more information about supporting both CommonJS and ES modules in a single package please consult the dual CommonJS/ES module packages section. Existing packages introducing the `"exports"` field will prevent consumers of the package from using any entry points that are not defined, including the `package.json` (e.g. `require('your-package/package.json')`). This will likely be a breaking change. To make the introduction of `"exports"` non-breaking, ensure that every previously supported entry point is exported. It is best to explicitly specify entry points so that the package's public API is well-defined. For example, a project that previously exported `main`, `lib`, `feature`, and the `package.json` could use the following `package.exports`: { "name": "my-package", "exports": { ".": "./lib/index.js", "./lib": "./lib/index.js", "./lib/index": "./lib/index.js", "./lib/index.js": "./lib/index.js", "./feature": "./feature/index.js", "./feature/index": "./feature/index.js", "./feature/index.js": "./feature/index.js", "./package.json": "./package.json" } } Alternatively a project could choose to export entire folders both with and without extensioned subpaths using export patterns: { "name": "my-package", "exports": { ".": "./lib/index.js", "./lib": "./lib/index.js", "./lib/*": "./lib/*.js", "./lib/*.js": "./lib/*.js", "./feature": "./feature/index.js", "./feature/*": "./feature/*.js", "./feature/*.js": "./feature/*.js", "./package.json": "./package.json" } } With the above providing backwards-compatibility for any minor package versions, a future major change for the package can then properly restrict the exports to only the specific feature exports exposed: { "name": "my-package", "exports": { ".": "./lib/index.js", "./feature/*.js": "./feature/*.js", "./feature/internal/*": null } } #### Main entry point export# When writing a new package, it is recommended to use the `"exports"` field: { "exports": "./index.js" } When the `"exports"` field is defined, all subpaths of the package are encapsulated and no longer available to importers. For example, `require('pkg/subpath.js')` throws an `ERR_PACKAGE_PATH_NOT_EXPORTED` error. This encapsulation of exports provides more reliable guarantees about package interfaces for tools and when handling semver upgrades for a package. It is not a strong encapsulation since a direct require of any absolute subpath of the package such as `require('/path/to/node_modules/pkg/subpath.js')` will still load `subpath.js`. All currently supported versions of Node.js and modern build tools support the `"exports"` field. For projects using an older version of Node.js or a related build tool, compatibility can be achieved by including the `"main"` field alongside `"exports"` pointing to the same module: { "main": "./index.js", "exports": "./index.js" } #### Subpath exports# Added in: v12.7.0 When using the `"exports"` field, custom subpaths can be defined along with the main entry point by treating the main entry point as the `"."` subpath: { "exports": { ".": "./index.js", "./submodule.js": "./src/submodule.js" } } Now only the defined subpath in `"exports"` can be imported by a consumer: import submodule from 'es-module-package/submodule.js'; // Loads ./node_modules/es-module-package/src/submodule.js While other subpaths will error: import submodule from 'es-module-package/private-module.js'; // Throws ERR_PACKAGE_PATH_NOT_EXPORTED ##### Extensions in subpaths# Package authors should provide either extensioned (`import 'pkg/subpath.js'`) or extensionless (`import 'pkg/subpath'`) subpaths in their exports. This ensures that there is only one subpath for each exported module so that all dependents import the same consistent specifier, keeping the package contract clear for consumers and simplifying package subpath completions. Traditionally, packages tended to use the extensionless style, which has the benefits of readability and of masking the true path of the file within the package. With import maps now providing a standard for package resolution in browsers and other JavaScript runtimes, using the extensionless style can result in bloated import map definitions. Explicit file extensions can avoid this issue by enabling the import map to utilize a packages folder mapping to map multiple subpaths where possible instead of a separate map entry per package subpath export. This also mirrors the requirement of using the full specifier path in relative and absolute import specifiers. ##### Path Rules and Validation for Export Targets# When defining paths as targets in the `"exports"` field, Node.js enforces several rules to ensure security, predictability, and proper encapsulation. Understanding these rules is crucial for authors publishing packages. ###### Targets must be relative URLs# All target paths in the `"exports"` map (the values associated with export keys) must be relative URL strings starting with `./`. // package.json { "name": "my-package", "exports": { ".": "./dist/main.js", // Correct "./feature": "./lib/feature.js", // Correct // "./origin-relative": "/dist/main.js", // Incorrect: Must start with ./ // "./absolute": "file:///dev/null", // Incorrect: Must start with ./ // "./outside": "../common/util.js" // Incorrect: Must start with ./ } } Reasons for this behavior include: * Security: Prevents exporting arbitrary files from outside the package's own directory. * Encapsulation: Ensures all exported paths are resolved relative to the package root, making the package self-contained. ###### No path traversal or invalid segments# Export targets must not resolve to a location outside the package's root directory. Additionally, path segments like `.` (single dot), `..` (double dot), or `node_modules` (and their URL-encoded equivalents) are generally disallowed within the `target` string after the initial `./` and in any `subpath` part substituted into a target pattern. // package.json { "name": "my-package", "exports": { // ".": "./dist/../../elsewhere/file.js", // Invalid: path traversal // ".": "././dist/main.js", // Invalid: contains "." segment // ".": "./dist/../dist/main.js", // Invalid: contains ".." segment // "./utils/./helper.js": "./utils/helper.js" // Key has invalid segment } } #### Exports sugar# Added in: v12.11.0 If the `"."` export is the only export, the `"exports"` field provides sugar for this case being the direct `"exports"` field value. { "exports": { ".": "./index.js" } } can be written: { "exports": "./index.js" } #### Subpath imports# Added in: v14.6.0, v12.19.0 In addition to the `"exports"` field, there is a package `"imports"` field to create private mappings that only apply to import specifiers from within the package itself. Entries in the `"imports"` field must always start with `#` to ensure they are disambiguated from external package specifiers. For example, the imports field can be used to gain the benefits of conditional exports for internal modules: // package.json { "imports": { "#dep": { "node": "dep-node-native", "default": "./dep-polyfill.js" } }, "dependencies": { "dep-node-native": "^1.0.0" } } where `import '#dep'` does not get the resolution of the external package `dep-node-native` (including its exports in turn), and instead gets the local file `./dep-polyfill.js` relative to the package in other environments. Unlike the `"exports"` field, the `"imports"` field permits mapping to external packages. The resolution rules for the imports field are otherwise analogous to the exports field. #### Subpath patterns# History VersionChanges v16.10.0, v14.19.0 Support pattern trailers in "imports" field. v16.9.0, v14.19.0 Support pattern trailers. v14.13.0, v12.20.0 Added in: v14.13.0, v12.20.0 For packages with a small number of exports or imports, we recommend explicitly listing each exports subpath entry. But for packages that have large numbers of subpaths, this might cause `package.json` bloat and maintenance issues. For these use cases, subpath export patterns can be used instead: // ./node_modules/es-module-package/package.json { "exports": { "./features/*.js": "./src/features/*.js" }, "imports": { "#internal/*.js": "./src/internal/*.js" } } `*` maps expose nested subpaths as it is a string replacement syntax only. All instances of `*` on the right hand side will then be replaced with this value, including if it contains any `/` separators. import featureX from 'es-module-package/features/x.js'; // Loads ./node_modules/es-module-package/src/features/x.js import featureY from 'es-module-package/features/y/y.js'; // Loads ./node_modules/es-module-package/src/features/y/y.js import internalZ from '#internal/z.js'; // Loads ./node_modules/es-module-package/src/internal/z.js This is a direct static matching and replacement without any special handling for file extensions. Including the `"*.js"` on both sides of the mapping restricts the exposed package exports to only JS files. The property of exports being statically enumerable is maintained with exports patterns since the individual exports for a package can be determined by treating the right hand side target pattern as a `**` glob against the list of files within the package. Because `node_modules` paths are forbidden in exports targets, this expansion is dependent on only the files of the package itself. To exclude private subfolders from patterns, `null` targets can be used: // ./node_modules/es-module-package/package.json { "exports": { "./features/*.js": "./src/features/*.js", "./features/private-internal/*": null } } import featureInternal from 'es-module-package/features/private-internal/m.js'; // Throws: ERR_PACKAGE_PATH_NOT_EXPORTED import featureX from 'es-module-package/features/x.js'; // Loads ./node_modules/es-module-package/src/features/x.js #### Conditional exports# History VersionChanges v13.7.0, v12.16.0 Unflag conditional exports. v13.2.0, v12.16.0 Added in: v13.2.0, v12.16.0 Conditional exports provide a way to map to different paths depending on certain conditions. They are supported for both CommonJS and ES module imports. For example, a package that wants to provide different ES module exports for `require()` and `import` can be written: // package.json { "exports": { "import": "./index-module.js", "require": "./index-require.cjs" }, "type": "module" } Node.js implements the following conditions, listed in order from most specific to least specific as conditions should be defined: * `"node-addons"` \- similar to `"node"` and matches for any Node.js environment. This condition can be used to provide an entry point which uses native C++ addons as opposed to an entry point which is more universal and doesn't rely on native addons. This condition can be disabled via the `--no-addons` flag. * `"node"` \- matches for any Node.js environment. Can be a CommonJS or ES module file. In most cases explicitly calling out the Node.js platform is not necessary. * `"import"` \- matches when the package is loaded via `import` or `import()`, or via any top-level import or resolve operation by the ECMAScript module loader. Applies regardless of the module format of the target file. Always mutually exclusive with `"require"`. * `"require"` \- matches when the package is loaded via `require()`. The referenced file should be loadable with `require()` although the condition matches regardless of the module format of the target file. Expected formats include CommonJS, JSON, native addons, and ES modules. Always mutually exclusive with `"import"`. * `"module-sync"` \- matches no matter the package is loaded via `import`, `import()` or `require()`. The format is expected to be ES modules that does not contain top-level await in its module graph - if it does, `ERR_REQUIRE_ASYNC_MODULE` will be thrown when the module is `require()`-ed. * `"default"` \- the generic fallback that always matches. Can be a CommonJS or ES module file. This condition should always come last. Within the `"exports"` object, key order is significant. During condition matching, earlier entries have higher priority and take precedence over later entries. The general rule is that conditions should be from most specific to least specific in object order. Using the `"import"` and `"require"` conditions can lead to some hazards, which are further explained in the dual CommonJS/ES module packages section. The `"node-addons"` condition can be used to provide an entry point which uses native C++ addons. However, this condition can be disabled via the `--no-addons` flag. When using `"node-addons"`, it's recommended to treat `"default"` as an enhancement that provides a more universal entry point, e.g. using WebAssembly instead of a native addon. Conditional exports can also be extended to exports subpaths, for example: { "exports": { ".": "./index.js", "./feature.js": { "node": "./feature-node.js", "default": "./feature.js" } } } Defines a package where `require('pkg/feature.js')` and `import 'pkg/feature.js'` could provide different implementations between Node.js and other JS environments. When using environment branches, always include a `"default"` condition where possible. Providing a `"default"` condition ensures that any unknown JS environments are able to use this universal implementation, which helps avoid these JS environments from having to pretend to be existing environments in order to support packages with conditional exports. For this reason, using `"node"` and `"default"` condition branches is usually preferable to using `"node"` and `"browser"` condition branches. #### Nested conditions# In addition to direct mappings, Node.js also supports nested condition objects. For example, to define a package that only has dual mode entry points for use in Node.js but not the browser: { "exports": { "node": { "import": "./feature-node.mjs", "require": "./feature-node.cjs" }, "default": "./feature.mjs" } } Conditions continue to be matched in order as with flat conditions. If a nested condition does not have any mapping it will continue checking the remaining conditions of the parent condition. In this way nested conditions behave analogously to nested JavaScript `if` statements. #### Resolving user conditions# Added in: v14.9.0, v12.19.0 When running Node.js, custom user conditions can be added with the `--conditions` flag: node --conditions=development index.js which would then resolve the `"development"` condition in package imports and exports, while resolving the existing `"node"`, `"node-addons"`, `"default"`, `"import"`, and `"require"` conditions as appropriate. Any number of custom conditions can be set with repeat flags. Typical conditions should only contain alphanumerical characters, using ":", "-", or "=" as separators if necessary. Anything else may run into compability issues outside of node. In node, conditions have very few restrictions, but specifically these include: 1. They must contain at least one character. 2. They cannot start with "." since they may appear in places that also allow relative paths. 3. They cannot contain "," since they may be parsed as a comma-separated list by some CLI tools. 4. They cannot be integer property keys like "10" since that can have unexpected effects on property key ordering for JS objects. #### Community Conditions Definitions# Condition strings other than the `"import"`, `"require"`, `"node"`, `"module-sync"`, `"node-addons"` and `"default"` conditions implemented in Node.js core are ignored by default. Other platforms may implement other conditions and user conditions can be enabled in Node.js via the `--conditions` / `-C` flag. Since custom package conditions require clear definitions to ensure correct usage, a list of common known package conditions and their strict definitions is provided below to assist with ecosystem coordination. * `"types"` \- can be used by typing systems to resolve the typing file for the given export. This condition should always be included first. * `"browser"` \- any web browser environment. * `"development"` \- can be used to define a development-only environment entry point, for example to provide additional debugging context such as better error messages when running in a development mode. Must always be mutually exclusive with `"production"`. * `"production"` \- can be used to define a production environment entry point. Must always be mutually exclusive with `"development"`. For other runtimes, platform-specific condition key definitions are maintained by the WinterCG in the Runtime Keys proposal specification. New conditions definitions may be added to this list by creating a pull request to the Node.js documentation for this section. The requirements for listing a new condition definition here are that: * The definition should be clear and unambiguous for all implementers. * The use case for why the condition is needed should be clearly justified. * There should exist sufficient existing implementation usage. * The condition name should not conflict with another condition definition or condition in wide usage. * The listing of the condition definition should provide a coordination benefit to the ecosystem that wouldn't otherwise be possible. For example, this would not necessarily be the case for company-specific or application-specific conditions. * The condition should be such that a Node.js user would expect it to be in Node.js core documentation. The `"types"` condition is a good example: It doesn't really belong in the Runtime Keys proposal but is a good fit here in the Node.js docs. The above definitions may be moved to a dedicated conditions registry in due course. #### Self-referencing a package using its name# History VersionChanges v13.6.0, v12.16.0 Unflag self-referencing a package using its name. v13.1.0, v12.16.0 Added in: v13.1.0, v12.16.0 Within a package, the values defined in the package's `package.json` `"exports"` field can be referenced via the package's name. For example, assuming the `package.json` is: // package.json { "name": "a-package", "exports": { ".": "./index.mjs", "./foo.js": "./foo.js" } } Then any module in that package can reference an export in the package itself: // ./a-module.mjs import { something } from 'a-package'; // Imports "something" from ./index.mjs. Self-referencing is available only if `package.json` has `"exports"`, and will allow importing only what that `"exports"` (in the `package.json`) allows. So the code below, given the previous package, will generate a runtime error: // ./another-module.mjs // Imports "another" from ./m.mjs. Fails because // the "package.json" "exports" field // does not provide an export named "./m.mjs". import { another } from 'a-package/m.mjs'; Self-referencing is also available when using `require`, both in an ES module, and in a CommonJS one. For example, this code will also work: Finally, self-referencing also works with scoped packages. For example, this code will also work: // package.json { "name": "@my/package", "exports": "./index.js" } $ node other.js 42 ### Dual CommonJS/ES module packages# See the package examples repository for details. ### Node.js `package.json` field definitions# This section describes the fields used by the Node.js runtime. Other tools (such as npm) use additional fields which are ignored by Node.js and not documented here. The following fields in `package.json` files are used in Node.js: * `"name"` \- Relevant when using named imports within a package. Also used by package managers as the name of the package. * `"main"` \- The default module when loading the package, if exports is not specified, and in versions of Node.js prior to the introduction of exports. * `"type"` \- The package type determining whether to load `.js` files as CommonJS or ES modules. * `"exports"` \- Package exports and conditional exports. When present, limits which submodules can be loaded from within the package. * `"imports"` \- Package imports, for use by modules within the package itself. #### `"name"`# History VersionChanges v13.6.0, v12.16.0 Remove the `--experimental-resolve-self` option. v13.1.0, v12.16.0 Added in: v13.1.0, v12.16.0 * Type: { "name": "package-name" } The `"name"` field defines your package's name. Publishing to the npm registry requires a name that satisfies certain requirements. The `"name"` field can be used in addition to the `"exports"` field to self-reference a package using its name. #### `"main"`# Added in: v0.4.0 * Type: { "main": "./index.js" } The `"main"` field defines the entry point of a package when imported by name via a `node_modules` lookup. Its value is a path. When a package has an `"exports"` field, this will take precedence over the `"main"` field when importing the package by name. It also defines the script that is used when the package directory is loaded via `require()`. #### `"type"`# History VersionChanges v13.2.0, v12.17.0 Unflag `--experimental-modules`. v12.0.0 Added in: v12.0.0 * Type: The `"type"` field defines the module format that Node.js uses for all `.js` files that have that `package.json` file as their nearest parent. Files ending with `.js` are loaded as ES modules when the nearest parent `package.json` file contains a top-level field `"type"` with a value of `"module"`. The nearest parent `package.json` is defined as the first `package.json` found when searching in the current folder, that folder's parent, and so on up until a node_modules folder or the volume root is reached. // package.json { "type": "module" } # In same folder as preceding package.json node my-app.js # Runs as ES module If the nearest parent `package.json` lacks a `"type"` field, or contains `"type": "commonjs"`, `.js` files are treated as CommonJS. If the volume root is reached and no `package.json` is found, `.js` files are treated as CommonJS. `import` statements of `.js` files are treated as ES modules if the nearest parent `package.json` contains `"type": "module"`. // my-app.js, part of the same example as above import './startup.js'; // Loaded as ES module because of package.json Regardless of the value of the `"type"` field, `.mjs` files are always treated as ES modules and `.cjs` files are always treated as CommonJS. #### `"exports"`# History VersionChanges v14.13.0, v12.20.0 Add support for `"exports"` patterns. v13.7.0, v12.17.0 Unflag conditional exports. v13.7.0, v12.16.0 Implement logical conditional exports ordering. v13.7.0, v12.16.0 Remove the `--experimental-conditional-exports` option. In 12.16.0, conditional exports are still behind `--experimental-modules`. v13.2.0, v12.16.0 Implement conditional exports. v12.7.0 Added in: v12.7.0 * Type: | | { "exports": "./index.js" } The `"exports"` field allows defining the entry points of a package when imported by name loaded either via a `node_modules` lookup or a self-reference to its own name. It is supported in Node.js 12+ as an alternative to the `"main"` that can support defining subpath exports and conditional exports while encapsulating internal unexported modules. Conditional Exports can also be used within `"exports"` to define different package entry points per environment, including whether the package is referenced via `require` or via `import`. All paths defined in the `"exports"` must be relative file URLs starting with `./`. #### `"imports"`# Added in: v14.6.0, v12.19.0 * Type: // package.json { "imports": { "#dep": { "node": "dep-node-native", "default": "./dep-polyfill.js" } }, "dependencies": { "dep-node-native": "^1.0.0" } } Entries in the imports field must be strings starting with `#`. Package imports permit mapping to external packages. This field defines subpath imports for the current package. ## Modules: TypeScript# History VersionChanges v24.3.0 Type stripping no longer emits an experimental warning. v23.6.0 Type stripping is enabled by default. v22.7.0 Added `--experimental-transform-types` flag. Stability: 1.2 \- Release candidate ### Enabling# There are two ways to enable runtime TypeScript support in Node.js: 1. For full support of all of TypeScript's syntax and features, including using any version of TypeScript, use a third-party package. 2. For lightweight support, you can use the built-in support for type stripping. ### Full TypeScript support# To use TypeScript with full support for all TypeScript features, including `tsconfig.json`, you can use a third-party package. These instructions use `tsx` as an example but there are many other similar libraries available. 1. Install the package as a development dependency using whatever package manager you're using for your project. For example, with `npm`: npm install --save-dev tsx 2. Then you can run your TypeScript code via: npx tsx your-file.ts Or alternatively, you can run with `node` via: node --import=tsx your-file.ts ### Type stripping# Added in: v22.6.0 By default Node.js will execute TypeScript files that contains only erasable TypeScript syntax. Node.js will replace TypeScript syntax with whitespace, and no type checking is performed. To enable the transformation of non erasable TypeScript syntax, which requires JavaScript code generation, such as `enum` declarations, parameter properties use the flag `--experimental-transform-types`. To disable this feature, use the flag `--no-experimental-strip-types`. Node.js ignores `tsconfig.json` files and therefore features that depend on settings within `tsconfig.json`, such as paths or converting newer JavaScript syntax to older standards, are intentionally unsupported. To get full TypeScript support, see Full TypeScript support. The type stripping feature is designed to be lightweight. By intentionally not supporting syntaxes that require JavaScript code generation, and by replacing inline types with whitespace, Node.js can run TypeScript code without the need for source maps. Type stripping is compatible with most versions of TypeScript but we recommend version 5.8 or newer with the following `tsconfig.json` settings: { "compilerOptions": { "noEmit": true, // Optional - see note below "target": "esnext", "module": "nodenext", "rewriteRelativeImportExtensions": true, "erasableSyntaxOnly": true, "verbatimModuleSyntax": true } } Use the `noEmit` option if you intend to only execute `*.ts` files, for example a build script. You won't need this flag if you intend to distribute `*.js` files. #### Determining module system# Node.js supports both CommonJS and ES Modules syntax in TypeScript files. Node.js will not convert from one module system to another; if you want your code to run as an ES module, you must use `import` and `export` syntax, and if you want your code to run as CommonJS you must use `require` and `module.exports`. * `.ts` files will have their module system determined the same way as `.js` files. To use `import` and `export` syntax, add `"type": "module"` to the nearest parent `package.json`. * `.mts` files will always be run as ES modules, similar to `.mjs` files. * `.cts` files will always be run as CommonJS modules, similar to `.cjs` files. * `.tsx` files are unsupported. As in JavaScript files, file extensions are mandatory in `import` statements and `import()` expressions: `import './file.ts'`, not `import './file'`. Because of backward compatibility, file extensions are also mandatory in `require()` calls: `require('./file.ts')`, not `require('./file')`, similar to how the `.cjs` extension is mandatory in `require` calls in CommonJS files. The `tsconfig.json` option `allowImportingTsExtensions` will allow the TypeScript compiler `tsc` to type-check files with `import` specifiers that include the `.ts` extension. #### TypeScript features# Since Node.js is only removing inline types, any TypeScript features that involve replacing TypeScript syntax with new JavaScript syntax will error, unless the flag `--experimental-transform-types` is passed. The most prominent features that require transformation are: * `Enum` declarations * `namespace` with runtime code * legacy `module` with runtime code * parameter properties * import aliases `namespaces` and `module` that do not contain runtime code are supported. This example will work correctly: // This namespace is exporting a type namespace TypeOnly { export type A = string; } This will result in `ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX` error: // This namespace is exporting a value namespace A { export let x = 1 } Since Decorators are currently a TC39 Stage 3 proposal and will soon be supported by the JavaScript engine, they are not transformed and will result in a parser error. This is a temporary limitation and will be resolved in the future. In addition, Node.js does not read `tsconfig.json` files and does not support features that depend on settings within `tsconfig.json`, such as paths or converting newer JavaScript syntax into older standards. #### Importing types without `type` keyword# Due to the nature of type stripping, the `type` keyword is necessary to correctly strip type imports. Without the `type` keyword, Node.js will treat the import as a value import, which will result in a runtime error. The tsconfig option `verbatimModuleSyntax` can be used to match this behavior. This example will work correctly: import type { Type1, Type2 } from './module.ts'; import { fn, type FnParams } from './fn.ts'; This will result in a runtime error: import { Type1, Type2 } from './module.ts'; import { fn, FnParams } from './fn.ts'; #### Non-file forms of input# Type stripping can be enabled for `--eval` and STDIN. The module system will be determined by `--input-type`, as it is for JavaScript. TypeScript syntax is unsupported in the REPL, `--check`, and `inspect`. #### Source maps# Since inline types are replaced by whitespace, source maps are unnecessary for correct line numbers in stack traces; and Node.js does not generate them. When `--experimental-transform-types` is enabled, source-maps are enabled by default. #### Type stripping in dependencies# To discourage package authors from publishing packages written in TypeScript, Node.js refuses to handle TypeScript files inside folders under a `node_modules` path. #### Paths aliases# `tsconfig` "paths" won't be transformed and therefore produce an error. The closest feature available is subpath imports with the limitation that they need to start with `#`. ## Net# Stability: 2 \- Stable Source Code: lib/net.js The `node:net` module provides an asynchronous network API for creating stream-based TCP or IPC servers (`net.createServer()`) and clients (`net.createConnection()`). It can be accessed using: import net from 'node:net'; ### IPC support# History VersionChanges v20.8.0 Support binding to abstract Unix domain socket path like `\0abstract`. We can bind '\0' for Node.js `< v20.4.0`. The `node:net` module supports IPC with named pipes on Windows, and Unix domain sockets on other operating systems. #### Identifying paths for IPC connections# `net.connect()`, `net.createConnection()`, `server.listen()`, and `socket.connect()` take a `path` parameter to identify IPC endpoints. On Unix, the local domain is also known as the Unix domain. The path is a file system pathname. It will throw an error when the length of pathname is greater than the length of `sizeof(sockaddr_un.sun_path)`. Typical values are 107 bytes on Linux and 103 bytes on macOS. If a Node.js API abstraction creates the Unix domain socket, it will unlink the Unix domain socket as well. For example, `net.createServer()` may create a Unix domain socket and `server.close()` will unlink it. But if a user creates the Unix domain socket outside of these abstractions, the user will need to remove it. The same applies when a Node.js API creates a Unix domain socket but the program then crashes. In short, a Unix domain socket will be visible in the file system and will persist until unlinked. On Linux, You can use Unix abstract socket by adding `\0` to the beginning of the path, such as `\0abstract`. The path to the Unix abstract socket is not visible in the file system and it will disappear automatically when all open references to the socket are closed. On Windows, the local domain is implemented using a named pipe. The path must refer to an entry in `\\?\pipe\` or `\\.\pipe\`. Any characters are permitted, but the latter may do some processing of pipe names, such as resolving `..` sequences. Despite how it might look, the pipe namespace is flat. Pipes will not persist. They are removed when the last reference to them is closed. Unlike Unix domain sockets, Windows will close and remove the pipe when the owning process exits. JavaScript string escaping requires paths to be specified with extra backslash escaping such as: net.createServer().listen( path.join('\\\\?\\pipe', process.cwd(), 'myctl')); ### Class: `net.BlockList`# Added in: v15.0.0, v14.18.0 The `BlockList` object can be used with some network APIs to specify rules for disabling inbound or outbound access to specific IP addresses, IP ranges, or IP subnets. #### `blockList.addAddress(address[, type])`# Added in: v15.0.0, v14.18.0 * `address` | An IPv4 or IPv6 address. * `type` Either `'ipv4'` or `'ipv6'`. Default: `'ipv4'`. Adds a rule to block the given IP address. #### `blockList.addRange(start, end[, type])`# Added in: v15.0.0, v14.18.0 * `start` | The starting IPv4 or IPv6 address in the range. * `end` | The ending IPv4 or IPv6 address in the range. * `type` Either `'ipv4'` or `'ipv6'`. Default: `'ipv4'`. Adds a rule to block a range of IP addresses from `start` (inclusive) to `end` (inclusive). #### `blockList.addSubnet(net, prefix[, type])`# Added in: v15.0.0, v14.18.0 * `net` | The network IPv4 or IPv6 address. * `prefix` The number of CIDR prefix bits. For IPv4, this must be a value between `0` and `32`. For IPv6, this must be between `0` and `128`. * `type` Either `'ipv4'` or `'ipv6'`. Default: `'ipv4'`. Adds a rule to block a range of IP addresses specified as a subnet mask. #### `blockList.check(address[, type])`# Added in: v15.0.0, v14.18.0 * `address` | The IP address to check * `type` Either `'ipv4'` or `'ipv6'`. Default: `'ipv4'`. * Returns: Returns `true` if the given IP address matches any of the rules added to the `BlockList`. const blockList = new net.BlockList(); blockList.addAddress('123.123.123.123'); blockList.addRange('10.0.0.1', '10.0.0.10'); blockList.addSubnet('8592:757c:efae:4e45::', 64, 'ipv6'); console.log(blockList.check('123.123.123.123')); // Prints: true console.log(blockList.check('10.0.0.3')); // Prints: true console.log(blockList.check('222.111.111.222')); // Prints: false // IPv6 notation for IPv4 addresses works: console.log(blockList.check('::ffff:7b7b:7b7b', 'ipv6')); // Prints: true console.log(blockList.check('::ffff:123.123.123.123', 'ipv6')); // Prints: true #### `blockList.rules`# Added in: v15.0.0, v14.18.0 * Type: The list of rules added to the blocklist. #### `BlockList.isBlockList(value)`# Added in: v23.4.0, v22.13.0 * `value` Any JS value * Returns `true` if the `value` is a `net.BlockList`. #### `blockList.fromJSON(value)`# Stability: 1 \- Experimental const blockList = new net.BlockList(); const data = [ 'Subnet: IPv4 192.168.1.0/24', 'Address: IPv4 10.0.0.5', 'Range: IPv4 192.168.2.1-192.168.2.10', 'Range: IPv4 10.0.0.1-10.0.0.10', ]; blockList.fromJSON(data); blockList.fromJSON(JSON.stringify(data)); * `value` Blocklist.rules #### `blockList.toJSON()`# Stability: 1 \- Experimental * Returns Blocklist.rules ### Class: `net.SocketAddress`# Added in: v15.14.0, v14.18.0 #### `new net.SocketAddress([options])`# Added in: v15.14.0, v14.18.0 * `options` * `address` The network address as either an IPv4 or IPv6 string. Default: `'127.0.0.1'` if `family` is `'ipv4'`; `'::'` if `family` is `'ipv6'`. * `family` One of either `'ipv4'` or `'ipv6'`. Default: `'ipv4'`. * `flowlabel` An IPv6 flow-label used only if `family` is `'ipv6'`. * `port` An IP port. #### `socketaddress.address`# Added in: v15.14.0, v14.18.0 * Type: #### `socketaddress.family`# Added in: v15.14.0, v14.18.0 * Type: Either `'ipv4'` or `'ipv6'`. #### `socketaddress.flowlabel`# Added in: v15.14.0, v14.18.0 * Type: #### `socketaddress.port`# Added in: v15.14.0, v14.18.0 * Type: #### `SocketAddress.parse(input)`# Added in: v23.4.0, v22.13.0 * `input` An input string containing an IP address and optional port, e.g. `123.1.2.3:1234` or `[1::1]:1234`. * Returns: Returns a `SocketAddress` if parsing was successful. Otherwise returns `undefined`. ### Class: `net.Server`# Added in: v0.1.90 * Extends: This class is used to create a TCP or IPC server. #### `new net.Server([options][, connectionListener])`# * `options` See `net.createServer([options][, connectionListener])`. * `connectionListener` Automatically set as a listener for the `'connection'` event. * Returns: `net.Server` is an `EventEmitter` with the following events: #### Event: `'close'`# Added in: v0.5.0 Emitted when the server closes. If connections exist, this event is not emitted until all connections are ended. #### Event: `'connection'`# Added in: v0.1.90 * Type: The connection object Emitted when a new connection is made. `socket` is an instance of `net.Socket`. #### Event: `'error'`# Added in: v0.1.90 * Type: Emitted when an error occurs. Unlike `net.Socket`, the `'close'` event will not be emitted directly following this event unless `server.close()` is manually called. See the example in discussion of `server.listen()`. #### Event: `'listening'`# Added in: v0.1.90 Emitted when the server has been bound after calling `server.listen()`. #### Event: `'drop'`# Added in: v18.6.0, v16.17.0 When the number of connections reaches the threshold of `server.maxConnections`, the server will drop new connections and emit `'drop'` event instead. If it is a TCP server, the argument is as follows, otherwise the argument is `undefined`. * `data` The argument passed to event listener. * `localAddress` Local address. * `localPort` Local port. * `localFamily` Local family. * `remoteAddress` Remote address. * `remotePort` Remote port. * `remoteFamily` Remote IP family. `'IPv4'` or `'IPv6'`. #### `server.address()`# History VersionChanges v18.4.0 The `family` property now returns a string instead of a number. v18.0.0 The `family` property now returns a number instead of a string. v0.1.90 Added in: v0.1.90 * Returns: | | Returns the bound `address`, the address `family` name, and `port` of the server as reported by the operating system if listening on an IP socket (useful to find which port was assigned when getting an OS-assigned address): `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }`. For a server listening on a pipe or Unix domain socket, the name is returned as a string. const server = net.createServer((socket) => { socket.end('goodbye\n'); }).on('error', (err) => { // Handle errors here. throw err; }); // Grab an arbitrary unused port. server.listen(() => { console.log('opened server on', server.address()); }); `server.address()` returns `null` before the `'listening'` event has been emitted or after calling `server.close()`. #### `server.close([callback])`# Added in: v0.1.90 * `callback` Called when the server is closed. * Returns: Stops the server from accepting new connections and keeps existing connections. This function is asynchronous, the server is finally closed when all connections are ended and the server emits a `'close'` event. The optional `callback` will be called once the `'close'` event occurs. Unlike that event, it will be called with an `Error` as its only argument if the server was not open when it was closed. #### `server[Symbol.asyncDispose]()`# History VersionChanges v24.2.0 No longer experimental. v20.5.0, v18.18.0 Added in: v20.5.0, v18.18.0 Calls `server.close()` and returns a promise that fulfills when the server has closed. #### `server.getConnections(callback)`# Added in: v0.9.7 * `callback` * Returns: Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks. Callback should take two arguments `err` and `count`. #### `server.listen()`# Start a server listening for connections. A `net.Server` can be a TCP or an IPC server depending on what it listens to. Possible signatures: * `server.listen(handle[, backlog][, callback])` * `server.listen(options[, callback])` * `server.listen(path[, backlog][, callback])` for IPC servers * `server.listen([port[, host[, backlog]]][, callback])` for TCP servers This function is asynchronous. When the server starts listening, the `'listening'` event will be emitted. The last parameter `callback` will be added as a listener for the `'listening'` event. All `listen()` methods can take a `backlog` parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as `tcp_max_syn_backlog` and `somaxconn` on Linux. The default value of this parameter is 511 (not 512). All `net.Socket` are set to `SO_REUSEADDR` (see `socket(7)` for details). The `server.listen()` method can be called again if and only if there was an error during the first `server.listen()` call or `server.close()` has been called. Otherwise, an `ERR_SERVER_ALREADY_LISTEN` error will be thrown. One of the most common errors raised when listening is `EADDRINUSE`. This happens when another server is already listening on the requested `port`/`path`/`handle`. One way to handle this would be to retry after a certain amount of time: server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } }); ##### `server.listen(handle[, backlog][, callback])`# Added in: v0.5.10 * `handle` * `backlog` Common parameter of `server.listen()` functions * `callback` * Returns: Start a server listening for connections on a given `handle` that has already been bound to a port, a Unix domain socket, or a Windows named pipe. The `handle` object can be either a server, a socket (anything with an underlying `_handle` member), or an object with an `fd` member that is a valid file descriptor. Listening on a file descriptor is not supported on Windows. ##### `server.listen(options[, callback])`# History VersionChanges v23.1.0, v22.12.0 The `reusePort` option is supported. v15.6.0 AbortSignal support was added. v11.4.0 The `ipv6Only` option is supported. v0.11.14 Added in: v0.11.14 * `options` Required. Supports the following properties: * `backlog` Common parameter of `server.listen()` functions. * `exclusive` Default: `false` * `host` * `ipv6Only` For TCP servers, setting `ipv6Only` to `true` will disable dual-stack support, i.e., binding to host `::` won't make `0.0.0.0` be bound. Default: `false`. * `reusePort` For TCP servers, setting `reusePort` to `true` allows multiple sockets on the same host to bind to the same port. Incoming connections are distributed by the operating system to listening sockets. This option is available only on some platforms, such as Linux 3.9+, DragonFlyBSD 3.6+, FreeBSD 12.0+, Solaris 11.4, and AIX 7.2.5+. Default: `false`. * `path` Will be ignored if `port` is specified. See Identifying paths for IPC connections. * `port` * `readableAll` For IPC servers makes the pipe readable for all users. Default: `false`. * `signal` An AbortSignal that may be used to close a listening server. * `writableAll` For IPC servers makes the pipe writable for all users. Default: `false`. * `callback` functions. * Returns: If `port` is specified, it behaves the same as `server.listen([port[, host[, backlog]]][, callback])`. Otherwise, if `path` is specified, it behaves the same as `server.listen(path[, backlog][, callback])`. If none of them is specified, an error will be thrown. If `exclusive` is `false` (default), then cluster workers will use the same underlying handle, allowing connection handling duties to be shared. When `exclusive` is `true`, the handle is not shared, and attempted port sharing results in an error. An example which listens on an exclusive port is shown below. server.listen({ host: 'localhost', port: 80, exclusive: true, }); When `exclusive` is `true` and the underlying handle is shared, it is possible that several workers query a handle with different backlogs. In this case, the first `backlog` passed to the master process will be used. Starting an IPC server as root may cause the server path to be inaccessible for unprivileged users. Using `readableAll` and `writableAll` will make the server accessible for all users. If the `signal` option is enabled, calling `.abort()` on the corresponding `AbortController` is similar to calling `.close()` on the server: const controller = new AbortController(); server.listen({ host: 'localhost', port: 80, signal: controller.signal, }); // Later, when you want to close the server. controller.abort(); ##### `server.listen(path[, backlog][, callback])`# Added in: v0.1.90 * `path` Path the server should listen to. See Identifying paths for IPC connections. * `backlog` Common parameter of `server.listen()` functions. * `callback` . * Returns: Start an IPC server listening for connections on the given `path`. ##### `server.listen([port[, host[, backlog]]][, callback])`# Added in: v0.1.90 * `port` * `host` * `backlog` Common parameter of `server.listen()` functions. * `callback` . * Returns: Start a TCP server listening for connections on the given `port` and `host`. If `port` is omitted or is 0, the operating system will assign an arbitrary unused port, which can be retrieved by using `server.address().port` after the `'listening'` event has been emitted. If `host` is omitted, the server will accept connections on the unspecified IPv6 address (`::`) when IPv6 is available, or the unspecified IPv4 address (`0.0.0.0`) otherwise. In most operating systems, listening to the unspecified IPv6 address (`::`) may cause the `net.Server` to also listen on the unspecified IPv4 address (`0.0.0.0`). #### `server.listening`# Added in: v5.7.0 * Type: Indicates whether or not the server is listening for connections. #### `server.maxConnections`# History VersionChanges v21.0.0 Setting `maxConnections` to `0` drops all the incoming connections. Previously, it was interpreted as `Infinity`. v0.2.0 Added in: v0.2.0 * Type: When the number of connections reaches the `server.maxConnections` threshold: 1. If the process is not running in cluster mode, Node.js will close the connection. 2. If the process is running in cluster mode, Node.js will, by default, route the connection to another worker process. To close the connection instead, set [`server.dropMaxConnection`][] to `true`. It is not recommended to use this option once a socket has been sent to a child with `child_process.fork()`. #### `server.dropMaxConnection`# Added in: v23.1.0, v22.12.0 * Type: Set this property to `true` to begin closing connections once the number of connections reaches the [`server.maxConnections`][] threshold. This setting is only effective in cluster mode. #### `server.ref()`# Added in: v0.9.1 * Returns: Opposite of `unref()`, calling `ref()` on a previously `unref`ed server will not let the program exit if it's the only server left (the default behavior). If the server is `ref`ed calling `ref()` again will have no effect. #### `server.unref()`# Added in: v0.9.1 * Returns: Calling `unref()` on a server will allow the program to exit if this is the only active server in the event system. If the server is already `unref`ed calling `unref()` again will have no effect. ### Class: `net.Socket`# Added in: v0.3.4 * Extends: This class is an abstraction of a TCP socket or a streaming IPC endpoint (uses named pipes on Windows, and Unix domain sockets otherwise). It is also an `EventEmitter`. A `net.Socket` can be created by the user and used directly to interact with a server. For example, it is returned by `net.createConnection()`, so the user can use it to talk to the server. It can also be created by Node.js and passed to the user when a connection is received. For example, it is passed to the listeners of a `'connection'` event emitted on a `net.Server`, so the user can use it to interact with the client. #### `new net.Socket([options])`# History VersionChanges v15.14.0 AbortSignal support was added. v12.10.0 Added `onread` option. v0.3.4 Added in: v0.3.4 * `options` Available options are: * `allowHalfOpen` If set to `false`, then the socket will automatically end the writable side when the readable side ends. See `net.createServer()` and the `'end'` event for details. Default: `false`. * `fd` If specified, wrap around an existing socket with the given file descriptor, otherwise a new socket will be created. * `onread` If specified, incoming data is stored in a single `buffer` and passed to the supplied `callback` when data arrives on the socket. This will cause the streaming functionality to not provide any data. The socket will emit events like `'error'`, `'end'`, and `'close'` as usual. Methods like `pause()` and `resume()` will also behave as expected. * `buffer` | | Either a reusable chunk of memory to use for storing incoming data or a function that returns such. * `callback` This function is called for every chunk of incoming data. Two arguments are passed to it: the number of bytes written to `buffer` and a reference to `buffer`. Return `false` from this function to implicitly `pause()` the socket. This function will be executed in the global context. * `readable` Allow reads on the socket when an `fd` is passed, otherwise ignored. Default: `false`. * `signal` An Abort signal that may be used to destroy the socket. * `writable` Allow writes on the socket when an `fd` is passed, otherwise ignored. Default: `false`. * Returns: Creates a new socket object. The newly created socket can be either a TCP socket or a streaming IPC endpoint, depending on what it `connect()` to. #### Event: `'close'`# Added in: v0.1.90 * `hadError` `true` if the socket had a transmission error. Emitted once the socket is fully closed. The argument `hadError` is a boolean which says if the socket was closed due to a transmission error. #### Event: `'connect'`# Added in: v0.1.90 Emitted when a socket connection is successfully established. See `net.createConnection()`. #### Event: `'connectionAttempt'`# Added in: v21.6.0, v20.12.0 * `ip` The IP which the socket is attempting to connect to. * `port` The port which the socket is attempting to connect to. * `family` The family of the IP. It can be `6` for IPv6 or `4` for IPv4. Emitted when a new connection attempt is started. This may be emitted multiple times if the family autoselection algorithm is enabled in `socket.connect(options)`. #### Event: `'connectionAttemptFailed'`# Added in: v21.6.0, v20.12.0 * `ip` The IP which the socket attempted to connect to. * `port` The port which the socket attempted to connect to. * `family` The family of the IP. It can be `6` for IPv6 or `4` for IPv4. * `error` The error associated with the failure. Emitted when a connection attempt failed. This may be emitted multiple times if the family autoselection algorithm is enabled in `socket.connect(options)`. #### Event: `'connectionAttemptTimeout'`# Added in: v21.6.0, v20.12.0 * `ip` The IP which the socket attempted to connect to. * `port` The port which the socket attempted to connect to. * `family` The family of the IP. It can be `6` for IPv6 or `4` for IPv4. Emitted when a connection attempt timed out. This is only emitted (and may be emitted multiple times) if the family autoselection algorithm is enabled in `socket.connect(options)`. #### Event: `'data'`# Added in: v0.1.90 * Type: | Emitted when data is received. The argument `data` will be a `Buffer` or `String`. Encoding of data is set by `socket.setEncoding()`. The data will be lost if there is no listener when a `Socket` emits a `'data'` event. #### Event: `'drain'`# Added in: v0.1.90 Emitted when the write buffer becomes empty. Can be used to throttle uploads. See also: the return values of `socket.write()`. #### Event: `'end'`# Added in: v0.1.90 Emitted when the other end of the socket signals the end of transmission, thus ending the readable side of the socket. By default (`allowHalfOpen` is `false`) the socket will send an end of transmission packet back and destroy its file descriptor once it has written out its pending write queue. However, if `allowHalfOpen` is set to `true`, the socket will not automatically `end()` its writable side, allowing the user to write arbitrary amounts of data. The user must call `end()` explicitly to close the connection (i.e. sending a FIN packet back). #### Event: `'error'`# Added in: v0.1.90 * Type: Emitted when an error occurs. The `'close'` event will be called directly following this event. #### Event: `'lookup'`# History VersionChanges v5.10.0 The `host` parameter is supported now. v0.11.3 Added in: v0.11.3 Emitted after resolving the host name but before connecting. Not applicable to Unix sockets. * `err` | The error object. See `dns.lookup()`. * `address` The IP address. * `family` | The address type. See `dns.lookup()`. * `host` The host name. #### Event: `'ready'`# Added in: v9.11.0 Emitted when a socket is ready to be used. Triggered immediately after `'connect'`. #### Event: `'timeout'`# Added in: v0.1.90 Emitted if the socket times out from inactivity. This is only to notify that the socket has been idle. The user must manually close the connection. See also: `socket.setTimeout()`. #### `socket.address()`# History VersionChanges v18.4.0 The `family` property now returns a string instead of a number. v18.0.0 The `family` property now returns a number instead of a string. v0.1.90 Added in: v0.1.90 * Returns: Returns the bound `address`, the address `family` name and `port` of the socket as reported by the operating system: `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }` #### `socket.autoSelectFamilyAttemptedAddresses`# Added in: v19.4.0, v18.18.0 * Type: This property is only present if the family autoselection algorithm is enabled in `socket.connect(options)` and it is an array of the addresses that have been attempted. Each address is a string in the form of `$IP:$PORT`. If the connection was successful, then the last address is the one that the socket is currently connected to. #### `socket.bufferSize`# Added in: v0.3.8Deprecated since: v14.6.0 Stability: 0 \- Deprecated: Use `writable.writableLength` instead. * Type: This property shows the number of characters buffered for writing. The buffer may contain strings whose length after encoding is not yet known. So this number is only an approximation of the number of bytes in the buffer. `net.Socket` has the property that `socket.write()` always works. This is to help users get up and running quickly. The computer cannot always keep up with the amount of data that is written to a socket. The network connection simply might be too slow. Node.js will internally queue up the data written to a socket and send it out over the wire when it is possible. The consequence of this internal buffering is that memory may grow. Users who experience large or growing `bufferSize` should attempt to "throttle" the data flows in their program with `socket.pause()` and `socket.resume()`. #### `socket.bytesRead`# Added in: v0.5.3 * Type: The amount of received bytes. #### `socket.bytesWritten`# Added in: v0.5.3 * Type: The amount of bytes sent. #### `socket.connect()`# Initiate a connection on a given socket. Possible signatures: * `socket.connect(options[, connectListener])` * `socket.connect(path[, connectListener])` for IPC connections. * `socket.connect(port[, host][, connectListener])` for TCP connections. * Returns: The socket itself. This function is asynchronous. When the connection is established, the `'connect'` event will be emitted. If there is a problem connecting, instead of a `'connect'` event, an `'error'` event will be emitted with the error passed to the `'error'` listener. The last parameter `connectListener`, if supplied, will be added as a listener for the `'connect'` event once. This function should only be used for reconnecting a socket after `'close'` has been emitted or otherwise it may lead to undefined behavior. ##### `socket.connect(options[, connectListener])`# History VersionChanges v19.4.0 The default value for autoSelectFamily option can be changed at runtime using `setDefaultAutoSelectFamily` or via the command line option `--enable-network-family-autoselection`. v20.0.0, v18.18.0 The default value for the autoSelectFamily option is now true. The `--enable-network-family-autoselection` CLI flag has been renamed to `--network-family-autoselection`. The old name is now an alias but it is discouraged. v19.3.0, v18.13.0 Added the `autoSelectFamily` option. v17.7.0, v16.15.0 The `noDelay`, `keepAlive`, and `keepAliveInitialDelay` options are supported now. v6.0.0 The `hints` option defaults to `0` in all cases now. Previously, in the absence of the `family` option it would default to `dns.ADDRCONFIG | dns.V4MAPPED`. v5.11.0 The `hints` option is supported now. v0.1.90 Added in: v0.1.90 * `options` * `connectListener` Common parameter of `socket.connect()` methods. Will be added as a listener for the `'connect'` event once. * Returns: The socket itself. Initiate a connection on a given socket. Normally this method is not needed, the socket should be created and opened with `net.createConnection()`. Use this only when implementing a custom Socket. For TCP connections, available `options` are: * `autoSelectFamily` : If set to `true`, it enables a family autodetection algorithm that loosely implements section 5 of RFC 8305. The `all` option passed to lookup is set to `true` and the sockets attempts to connect to all obtained IPv6 and IPv4 addresses, in sequence, until a connection is established. The first returned AAAA address is tried first, then the first returned A address, then the second returned AAAA address and so on. Each connection attempt (but the last one) is given the amount of time specified by the `autoSelectFamilyAttemptTimeout` option before timing out and trying the next address. Ignored if the `family` option is not `0` or if `localAddress` is set. Connection errors are not emitted if at least one connection succeeds. If all connections attempts fails, a single `AggregateError` with all failed attempts is emitted. Default: `net.getDefaultAutoSelectFamily()`. * `autoSelectFamilyAttemptTimeout` : The amount of time in milliseconds to wait for a connection attempt to finish before trying the next address when using the `autoSelectFamily` option. If set to a positive integer less than `10`, then the value `10` will be used instead. Default: `net.getDefaultAutoSelectFamilyAttemptTimeout()`. * `family` : Version of IP stack. Must be `4`, `6`, or `0`. The value `0` indicates that both IPv4 and IPv6 addresses are allowed. Default: `0`. * `hints` Optional `dns.lookup()` hints. * `host` Host the socket should connect to. Default: `'localhost'`. * `keepAlive` If set to `true`, it enables keep-alive functionality on the socket immediately after the connection is established, similarly on what is done in `socket.setKeepAlive()`. Default: `false`. * `keepAliveInitialDelay` If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket. Default: `0`. * `localAddress` Local address the socket should connect from. * `localPort` Local port the socket should connect from. * `lookup` Custom lookup function. Default: `dns.lookup()`. * `noDelay` If set to `true`, it disables the use of Nagle's algorithm immediately after the socket is established. Default: `false`. * `port` Required. Port the socket should connect to. * `blockList` `blockList` can be used for disabling outbound access to specific IP addresses, IP ranges, or IP subnets. For IPC connections, available `options` are: * `path` Required. Path the client should connect to. See Identifying paths for IPC connections. If provided, the TCP-specific options above are ignored. ##### `socket.connect(path[, connectListener])`# * `path` Path the client should connect to. See Identifying paths for IPC connections. * `connectListener` Common parameter of `socket.connect()` methods. Will be added as a listener for the `'connect'` event once. * Returns: The socket itself. Initiate an IPC connection on the given socket. Alias to `socket.connect(options[, connectListener])` called with `{ path: path }` as `options`. ##### `socket.connect(port[, host][, connectListener])`# Added in: v0.1.90 * `port` Port the client should connect to. * `host` Host the client should connect to. * `connectListener` Common parameter of `socket.connect()` methods. Will be added as a listener for the `'connect'` event once. * Returns: The socket itself. Initiate a TCP connection on the given socket. Alias to `socket.connect(options[, connectListener])` called with `{port: port, host: host}` as `options`. #### `socket.connecting`# Added in: v6.1.0 * Type: If `true`, `socket.connect(options[, connectListener])` was called and has not yet finished. It will stay `true` until the socket becomes connected, then it is set to `false` and the `'connect'` event is emitted. Note that the `socket.connect(options[, connectListener])` callback is a listener for the `'connect'` event. #### `socket.destroy([error])`# Added in: v0.1.90 * `error` * Returns: Ensures that no more I/O activity happens on this socket. Destroys the stream and closes the connection. See `writable.destroy()` for further details. #### `socket.destroyed`# * Type: Indicates if the connection is destroyed or not. Once a connection is destroyed no further data can be transferred using it. See `writable.destroyed` for further details. #### `socket.destroySoon()`# Added in: v0.3.4 Destroys the socket after all data is written. If the `'finish'` event was already emitted the socket is destroyed immediately. If the socket is still writable it implicitly calls `socket.end()`. #### `socket.end([data[, encoding]][, callback])`# Added in: v0.1.90 * `data` | | * `encoding` Only used when data is `string`. Default: `'utf8'`. * `callback` Optional callback for when the socket is finished. * Returns: The socket itself. Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data. See `writable.end()` for further details. #### `socket.localAddress`# Added in: v0.9.6 * Type: The string representation of the local IP address the remote client is connecting on. For example, in a server listening on `'0.0.0.0'`, if a client connects on `'192.168.1.1'`, the value of `socket.localAddress` would be `'192.168.1.1'`. #### `socket.localPort`# Added in: v0.9.6 * Type: The numeric representation of the local port. For example, `80` or `21`. #### `socket.localFamily`# Added in: v18.8.0, v16.18.0 * Type: The string representation of the local IP family. `'IPv4'` or `'IPv6'`. #### `socket.pause()`# * Returns: The socket itself. Pauses the reading of data. That is, `'data'` events will not be emitted. Useful to throttle back an upload. #### `socket.pending`# Added in: v11.2.0, v10.16.0 * Type: This is `true` if the socket is not connected yet, either because `.connect()` has not yet been called or because it is still in the process of connecting (see `socket.connecting`). #### `socket.ref()`# Added in: v0.9.1 * Returns: The socket itself. Opposite of `unref()`, calling `ref()` on a previously `unref`ed socket will not let the program exit if it's the only socket left (the default behavior). If the socket is `ref`ed calling `ref` again will have no effect. #### `socket.remoteAddress`# Added in: v0.5.10 * Type: The string representation of the remote IP address. For example, `'74.125.127.100'` or `'2001:4860:a005::68'`. Value may be `undefined` if the socket is destroyed (for example, if the client disconnected). #### `socket.remoteFamily`# Added in: v0.11.14 * Type: The string representation of the remote IP family. `'IPv4'` or `'IPv6'`. Value may be `undefined` if the socket is destroyed (for example, if the client disconnected). #### `socket.remotePort`# Added in: v0.5.10 * Type: The numeric representation of the remote port. For example, `80` or `21`. Value may be `undefined` if the socket is destroyed (for example, if the client disconnected). #### `socket.resetAndDestroy()`# Added in: v18.3.0, v16.17.0 * Returns: Close the TCP connection by sending an RST packet and destroy the stream. If this TCP socket is in connecting status, it will send an RST packet and destroy this TCP socket once it is connected. Otherwise, it will call `socket.destroy` with an `ERR_SOCKET_CLOSED` Error. If this is not a TCP socket (for example, a pipe), calling this method will immediately throw an `ERR_INVALID_HANDLE_TYPE` Error. #### `socket.resume()`# * Returns: The socket itself. Resumes reading after a call to `socket.pause()`. #### `socket.setEncoding([encoding])`# Added in: v0.1.90 * `encoding` * Returns: The socket itself. Set the encoding for the socket as a Readable Stream. See `readable.setEncoding()` for more information. #### `socket.setKeepAlive([enable][, initialDelay])`# History VersionChanges v13.12.0, v12.17.0 New defaults for `TCP_KEEPCNT` and `TCP_KEEPINTVL` socket options were added. v0.1.92 Added in: v0.1.92 * `enable` Default: `false` * `initialDelay` Default: `0` * Returns: The socket itself. Enable/disable keep-alive functionality, and optionally set the initial delay before the first keepalive probe is sent on an idle socket. Set `initialDelay` (in milliseconds) to set the delay between the last data packet received and the first keepalive probe. Setting `0` for `initialDelay` will leave the value unchanged from the default (or previous) setting. Enabling the keep-alive functionality will set the following socket options: * `SO_KEEPALIVE=1` * `TCP_KEEPIDLE=initialDelay` * `TCP_KEEPCNT=10` * `TCP_KEEPINTVL=1` #### `socket.setNoDelay([noDelay])`# Added in: v0.1.90 * `noDelay` Default: `true` * Returns: The socket itself. Enable/disable the use of Nagle's algorithm. When a TCP connection is created, it will have Nagle's algorithm enabled. Nagle's algorithm delays data before it is sent via the network. It attempts to optimize throughput at the expense of latency. Passing `true` for `noDelay` or not passing an argument will disable Nagle's algorithm for the socket. Passing `false` for `noDelay` will enable Nagle's algorithm. #### `socket.setTimeout(timeout[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v0.1.90 Added in: v0.1.90 * `timeout` * `callback` * Returns: The socket itself. Sets the socket to timeout after `timeout` milliseconds of inactivity on the socket. By default `net.Socket` do not have a timeout. When an idle timeout is triggered the socket will receive a `'timeout'` event but the connection will not be severed. The user must manually call `socket.end()` or `socket.destroy()` to end the connection. socket.setTimeout(3000); socket.on('timeout', () => { console.log('socket timeout'); socket.end(); }); If `timeout` is 0, then the existing idle timeout is disabled. The optional `callback` parameter will be added as a one-time listener for the `'timeout'` event. #### `socket.timeout`# Added in: v10.7.0 * Type: | The socket timeout in milliseconds as set by `socket.setTimeout()`. It is `undefined` if a timeout has not been set. #### `socket.unref()`# Added in: v0.9.1 * Returns: The socket itself. Calling `unref()` on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already `unref`ed calling `unref()` again will have no effect. #### `socket.write(data[, encoding][, callback])`# Added in: v0.1.90 * `data` | | * `encoding` Only used when data is `string`. Default: `utf8`. * `callback` * Returns: Sends data on the socket. The second parameter specifies the encoding in the case of a string. It defaults to UTF8 encoding. Returns `true` if the entire data was flushed successfully to the kernel buffer. Returns `false` if all or part of the data was queued in user memory. `'drain'` will be emitted when the buffer is again free. The optional `callback` parameter will be executed when the data is finally written out, which may not be immediately. See `Writable` stream `write()` method for more information. #### `socket.readyState`# Added in: v0.5.0 * Type: This property represents the state of the connection as a string. * If the stream is connecting `socket.readyState` is `opening`. * If the stream is readable and writable, it is `open`. * If the stream is readable and not writable, it is `readOnly`. * If the stream is not readable and writable, it is `writeOnly`. ### `net.connect()`# Aliases to `net.createConnection()`. Possible signatures: * `net.connect(options[, connectListener])` * `net.connect(path[, connectListener])` for IPC connections. * `net.connect(port[, host][, connectListener])` for TCP connections. #### `net.connect(options[, connectListener])`# Added in: v0.7.0 * `options` * `connectListener` * Returns: Alias to `net.createConnection(options[, connectListener])`. #### `net.connect(path[, connectListener])`# Added in: v0.1.90 * `path` * `connectListener` * Returns: Alias to `net.createConnection(path[, connectListener])`. #### `net.connect(port[, host][, connectListener])`# Added in: v0.1.90 * `port` * `host` * `connectListener` * Returns: Alias to `net.createConnection(port[, host][, connectListener])`. ### `net.createConnection()`# A factory function, which creates a new `net.Socket`, immediately initiates connection with `socket.connect()`, then returns the `net.Socket` that starts the connection. When the connection is established, a `'connect'` event will be emitted on the returned socket. The last parameter `connectListener`, if supplied, will be added as a listener for the `'connect'` event once. Possible signatures: * `net.createConnection(options[, connectListener])` * `net.createConnection(path[, connectListener])` for IPC connections. * `net.createConnection(port[, host][, connectListener])` for TCP connections. The `net.connect()` function is an alias to this function. #### `net.createConnection(options[, connectListener])`# Added in: v0.1.90 * `options` Required. Will be passed to both the `new net.Socket([options])` call and the `socket.connect(options[, connectListener])` method. * `connectListener` Common parameter of the `net.createConnection()` functions. If supplied, will be added as a listener for the `'connect'` event on the returned socket once. * Returns: The newly created socket used to start the connection. For available options, see `new net.Socket([options])` and `socket.connect(options[, connectListener])`. Additional options: * `timeout` If set, will be used to call `socket.setTimeout(timeout)` after the socket is created, but before it starts the connection. Following is an example of a client of the echo server described in the `net.createServer()` section: import net from 'node:net'; const client = net.createConnection({ port: 8124 }, () => { // 'connect' listener. console.log('connected to server!'); client.write('world!\r\n'); }); client.on('data', (data) => { console.log(data.toString()); client.end(); }); client.on('end', () => { console.log('disconnected from server'); }); To connect on the socket `/tmp/echo.sock`: const client = net.createConnection({ path: '/tmp/echo.sock' }); Following is an example of a client using the `port` and `onread` option. In this case, the `onread` option will be only used to call `new net.Socket([options])` and the `port` option will be used to call `socket.connect(options[, connectListener])`. import net from 'node:net'; import { Buffer } from 'node:buffer'; net.createConnection({ port: 8124, onread: { // Reuses a 4KiB Buffer for every read from the socket. buffer: Buffer.alloc(4 * 1024), callback: function(nread, buf) { // Received data is available in `buf` from 0 to `nread`. console.log(buf.toString('utf8', 0, nread)); }, }, }); #### `net.createConnection(path[, connectListener])`# Added in: v0.1.90 * `path` Path the socket should connect to. Will be passed to `socket.connect(path[, connectListener])`. See Identifying paths for IPC connections. * `connectListener` Common parameter of the `net.createConnection()` functions, an "once" listener for the `'connect'` event on the initiating socket. Will be passed to `socket.connect(path[, connectListener])`. * Returns: The newly created socket used to start the connection. Initiates an IPC connection. This function creates a new `net.Socket` with all options set to default, immediately initiates connection with `socket.connect(path[, connectListener])`, then returns the `net.Socket` that starts the connection. #### `net.createConnection(port[, host][, connectListener])`# Added in: v0.1.90 * `port` Port the socket should connect to. Will be passed to `socket.connect(port[, host][, connectListener])`. * `host` Host the socket should connect to. Will be passed to `socket.connect(port[, host][, connectListener])`. Default: `'localhost'`. * `connectListener` Common parameter of the `net.createConnection()` functions, an "once" listener for the `'connect'` event on the initiating socket. Will be passed to `socket.connect(port[, host][, connectListener])`. * Returns: The newly created socket used to start the connection. Initiates a TCP connection. This function creates a new `net.Socket` with all options set to default, immediately initiates connection with `socket.connect(port[, host][, connectListener])`, then returns the `net.Socket` that starts the connection. ### `net.createServer([options][, connectionListener])`# History VersionChanges v20.1.0, v18.17.0 The `highWaterMark` option is supported now. v17.7.0, v16.15.0 The `noDelay`, `keepAlive`, and `keepAliveInitialDelay` options are supported now. v0.5.0 Added in: v0.5.0 * `options` * `allowHalfOpen` If set to `false`, then the socket will automatically end the writable side when the readable side ends. Default: `false`. * `highWaterMark` Optionally overrides all `net.Socket`s' `readableHighWaterMark` and `writableHighWaterMark`. Default: See `stream.getDefaultHighWaterMark()`. * `keepAlive` If set to `true`, it enables keep-alive functionality on the socket immediately after a new incoming connection is received, similarly on what is done in `socket.setKeepAlive()`. Default: `false`. * `keepAliveInitialDelay` If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket. Default: `0`. * `noDelay` If set to `true`, it disables the use of Nagle's algorithm immediately after a new incoming connection is received. Default: `false`. * `pauseOnConnect` Indicates whether the socket should be paused on incoming connections. Default: `false`. * `blockList` `blockList` can be used for disabling inbound access to specific IP addresses, IP ranges, or IP subnets. This does not work if the server is behind a reverse proxy, NAT, etc. because the address checked against the block list is the address of the proxy, or the one specified by the NAT. * `connectionListener` Automatically set as a listener for the `'connection'` event. * Returns: Creates a new TCP or IPC server. If `allowHalfOpen` is set to `true`, when the other end of the socket signals the end of transmission, the server will only send back the end of transmission when `socket.end()` is explicitly called. For example, in the context of TCP, when a FIN packed is received, a FIN packed is sent back only when `socket.end()` is explicitly called. Until then the connection is half-closed (non-readable but still writable). See `'end'` event and RFC 1122 (section 4.2.2.13) for more information. If `pauseOnConnect` is set to `true`, then the socket associated with each incoming connection will be paused, and no data will be read from its handle. This allows connections to be passed between processes without any data being read by the original process. To begin reading data from a paused socket, call `socket.resume()`. The server can be a TCP server or an IPC server, depending on what it `listen()` to. Here is an example of a TCP echo server which listens for connections on port 8124: import net from 'node:net'; const server = net.createServer((c) => { // 'connection' listener. console.log('client connected'); c.on('end', () => { console.log('client disconnected'); }); c.write('hello\r\n'); c.pipe(c); }); server.on('error', (err) => { throw err; }); server.listen(8124, () => { console.log('server bound'); }); Test this by using `telnet`: telnet localhost 8124 To listen on the socket `/tmp/echo.sock`: server.listen('/tmp/echo.sock', () => { console.log('server bound'); }); Use `nc` to connect to a Unix domain socket server: nc -U /tmp/echo.sock ### `net.getDefaultAutoSelectFamily()`# Added in: v19.4.0 Gets the current default value of the `autoSelectFamily` option of `socket.connect(options)`. The initial default value is `true`, unless the command line option `--no-network-family-autoselection` is provided. * Returns: The current default value of the `autoSelectFamily` option. ### `net.setDefaultAutoSelectFamily(value)`# Added in: v19.4.0 Sets the default value of the `autoSelectFamily` option of `socket.connect(options)`. * `value` The new default value. The initial default value is `true`, unless the command line option `--no-network-family-autoselection` is provided. ### `net.getDefaultAutoSelectFamilyAttemptTimeout()`# Added in: v19.8.0, v18.18.0 Gets the current default value of the `autoSelectFamilyAttemptTimeout` option of `socket.connect(options)`. The initial default value is `250` or the value specified via the command line option `--network-family-autoselection-attempt-timeout`. * Returns: The current default value of the `autoSelectFamilyAttemptTimeout` option. ### `net.setDefaultAutoSelectFamilyAttemptTimeout(value)`# Added in: v19.8.0, v18.18.0 Sets the default value of the `autoSelectFamilyAttemptTimeout` option of `socket.connect(options)`. * `value` The new default value, which must be a positive number. If the number is less than `10`, the value `10` is used instead. The initial default value is `250` or the value specified via the command line option `--network-family-autoselection-attempt-timeout`. ### `net.isIP(input)`# Added in: v0.3.0 * `input` * Returns: Returns `6` if `input` is an IPv6 address. Returns `4` if `input` is an IPv4 address in dot-decimal notation with no leading zeroes. Otherwise, returns `0`. net.isIP('::1'); // returns 6 net.isIP('127.0.0.1'); // returns 4 net.isIP('127.000.000.001'); // returns 0 net.isIP('127.0.0.1/24'); // returns 0 net.isIP('fhqwhgads'); // returns 0 ### `net.isIPv4(input)`# Added in: v0.3.0 * `input` * Returns: Returns `true` if `input` is an IPv4 address in dot-decimal notation with no leading zeroes. Otherwise, returns `false`. net.isIPv4('127.0.0.1'); // returns true net.isIPv4('127.000.000.001'); // returns false net.isIPv4('127.0.0.1/24'); // returns false net.isIPv4('fhqwhgads'); // returns false ### `net.isIPv6(input)`# Added in: v0.3.0 * `input` * Returns: Returns `true` if `input` is an IPv6 address. Otherwise, returns `false`. net.isIPv6('::1'); // returns true net.isIPv6('fhqwhgads'); // returns false ## OS# Stability: 2 \- Stable Source Code: lib/os.js The `node:os` module provides operating system-related utility methods and properties. It can be accessed using: import os from 'node:os'; ### `os.EOL`# Added in: v0.7.8 * Type: The operating system-specific end-of-line marker. * `\n` on POSIX * `\r\n` on Windows ### `os.availableParallelism()`# Added in: v19.4.0, v18.14.0 * Returns: Returns an estimate of the default amount of parallelism a program should use. Always returns a value greater than zero. This function is a small wrapper about libuv's `uv_available_parallelism()`. ### `os.arch()`# Added in: v0.5.0 * Returns: Returns the operating system CPU architecture for which the Node.js binary was compiled. Possible values are `'arm'`, `'arm64'`, `'ia32'`, `'loong64'`, `'mips'`, `'mipsel'`, `'ppc64'`, `'riscv64'`, `'s390x'`, and `'x64'`. The return value is equivalent to `process.arch`. ### `os.constants`# Added in: v6.3.0 * Type: Contains commonly used operating system-specific constants for error codes, process signals, and so on. The specific constants defined are described in OS constants. ### `os.cpus()`# Added in: v0.3.3 * Returns: Returns an array of objects containing information about each logical CPU core. The array will be empty if no CPU information is available, such as if the `/proc` file system is unavailable. The properties included on each object include: * `model` * `speed` (in MHz) * `times` * `user` The number of milliseconds the CPU has spent in user mode. * `nice` The number of milliseconds the CPU has spent in nice mode. * `sys` The number of milliseconds the CPU has spent in sys mode. * `idle` The number of milliseconds the CPU has spent in idle mode. * `irq` The number of milliseconds the CPU has spent in irq mode. [ { model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz', speed: 2926, times: { user: 252020, nice: 0, sys: 30340, idle: 1070356870, irq: 0, }, }, { model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz', speed: 2926, times: { user: 306960, nice: 0, sys: 26980, idle: 1071569080, irq: 0, }, }, { model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz', speed: 2926, times: { user: 248450, nice: 0, sys: 21750, idle: 1070919370, irq: 0, }, }, { model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz', speed: 2926, times: { user: 256880, nice: 0, sys: 19430, idle: 1070905480, irq: 20, }, }, ] `nice` values are POSIX-only. On Windows, the `nice` values of all processors are always 0. `os.cpus().length` should not be used to calculate the amount of parallelism available to an application. Use `os.availableParallelism()` for this purpose. ### `os.devNull`# Added in: v16.3.0, v14.18.0 * Type: The platform-specific file path of the null device. * `\\.\nul` on Windows * `/dev/null` on POSIX ### `os.endianness()`# Added in: v0.9.4 * Returns: Returns a string identifying the endianness of the CPU for which the Node.js binary was compiled. Possible values are `'BE'` for big endian and `'LE'` for little endian. ### `os.freemem()`# Added in: v0.3.3 * Returns: Returns the amount of free system memory in bytes as an integer. ### `os.getPriority([pid])`# Added in: v10.10.0 * `pid` The process ID to retrieve scheduling priority for. Default: `0`. * Returns: Returns the scheduling priority for the process specified by `pid`. If `pid` is not provided or is `0`, the priority of the current process is returned. ### `os.homedir()`# Added in: v2.3.0 * Returns: Returns the string path of the current user's home directory. On POSIX, it uses the `$HOME` environment variable if defined. Otherwise it uses the effective UID to look up the user's home directory. On Windows, it uses the `USERPROFILE` environment variable if defined. Otherwise it uses the path to the profile directory of the current user. ### `os.hostname()`# Added in: v0.3.3 * Returns: Returns the host name of the operating system as a string. ### `os.loadavg()`# Added in: v0.3.3 * Returns: Returns an array containing the 1, 5, and 15 minute load averages. The load average is a measure of system activity calculated by the operating system and expressed as a fractional number. The load average is a Unix-specific concept. On Windows, the return value is always `[0, 0, 0]`. ### `os.machine()`# Added in: v18.9.0, v16.18.0 * Returns: Returns the machine type as a string, such as `arm`, `arm64`, `aarch64`, `mips`, `mips64`, `ppc64`, `ppc64le`, `s390x`, `i386`, `i686`, `x86_64`. On POSIX systems, the machine type is determined by calling `uname(3)`. On Windows, `RtlGetVersion()` is used, and if it is not available, `GetVersionExW()` will be used. See https://en.wikipedia.org/wiki/Uname#Examples for more information. ### `os.networkInterfaces()`# History VersionChanges v18.4.0 The `family` property now returns a string instead of a number. v18.0.0 The `family` property now returns a number instead of a string. v0.6.0 Added in: v0.6.0 * Returns: Returns an object containing network interfaces that have been assigned a network address. Each key on the returned object identifies a network interface. The associated value is an array of objects that each describe an assigned network address. The properties available on the assigned network address object include: * `address` The assigned IPv4 or IPv6 address * `netmask` The IPv4 or IPv6 network mask * `family` Either `IPv4` or `IPv6` * `mac` The MAC address of the network interface * `internal` `true` if the network interface is a loopback or similar interface that is not remotely accessible; otherwise `false` * `scopeid` The numeric IPv6 scope ID (only specified when `family` is `IPv6`) * `cidr` The assigned IPv4 or IPv6 address with the routing prefix in CIDR notation. If the `netmask` is invalid, this property is set to `null`. { lo: [ { address: '127.0.0.1', netmask: '255.0.0.0', family: 'IPv4', mac: '00:00:00:00:00:00', internal: true, cidr: '127.0.0.1/8' }, { address: '::1', netmask: 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff', family: 'IPv6', mac: '00:00:00:00:00:00', scopeid: 0, internal: true, cidr: '::1/128' } ], eth0: [ { address: '192.168.1.108', netmask: '255.255.255.0', family: 'IPv4', mac: '01:02:03:0a:0b:0c', internal: false, cidr: '192.168.1.108/24' }, { address: 'fe80::a00:27ff:fe4e:66a1', netmask: 'ffff:ffff:ffff:ffff::', family: 'IPv6', mac: '01:02:03:0a:0b:0c', scopeid: 1, internal: false, cidr: 'fe80::a00:27ff:fe4e:66a1/64' } ] } ### `os.platform()`# Added in: v0.5.0 * Returns: Returns a string identifying the operating system platform for which the Node.js binary was compiled. The value is set at compile time. Possible values are `'aix'`, `'darwin'`, `'freebsd'`,`'linux'`, `'openbsd'`, `'sunos'`, and `'win32'`. The return value is equivalent to `process.platform`. The value `'android'` may also be returned if Node.js is built on the Android operating system. Android support is experimental. ### `os.release()`# Added in: v0.3.3 * Returns: Returns the operating system as a string. On POSIX systems, the operating system release is determined by calling `uname(3)`. On Windows, `GetVersionExW()` is used. See https://en.wikipedia.org/wiki/Uname#Examples for more information. ### `os.setPriority([pid, ]priority)`# Added in: v10.10.0 * `pid` The process ID to set scheduling priority for. Default: `0`. * `priority` The scheduling priority to assign to the process. Attempts to set the scheduling priority for the process specified by `pid`. If `pid` is not provided or is `0`, the process ID of the current process is used. The `priority` input must be an integer between `-20` (high priority) and `19` (low priority). Due to differences between Unix priority levels and Windows priority classes, `priority` is mapped to one of six priority constants in `os.constants.priority`. When retrieving a process priority level, this range mapping may cause the return value to be slightly different on Windows. To avoid confusion, set `priority` to one of the priority constants. On Windows, setting priority to `PRIORITY_HIGHEST` requires elevated user privileges. Otherwise the set priority will be silently reduced to `PRIORITY_HIGH`. ### `os.tmpdir()`# History VersionChanges v2.0.0 This function is now cross-platform consistent and no longer returns a path with a trailing slash on any platform. v0.9.9 Added in: v0.9.9 * Returns: Returns the operating system's default directory for temporary files as a string. On Windows, the result can be overridden by `TEMP` and `TMP` environment variables, and `TEMP` takes precedence over `TMP`. If neither is set, it defaults to `%SystemRoot%\temp` or `%windir%\temp`. On non-Windows platforms, `TMPDIR`, `TMP` and `TEMP` environment variables will be checked to override the result of this method, in the described order. If none of them is set, it defaults to `/tmp`. Some operating system distributions would either configure `TMPDIR` (non-Windows) or `TEMP` and `TMP` (Windows) by default without additional configurations by the system administrators. The result of `os.tmpdir()` typically reflects the system preference unless it's explicitly overridden by the users. ### `os.totalmem()`# Added in: v0.3.3 * Returns: Returns the total amount of system memory in bytes as an integer. ### `os.type()`# Added in: v0.3.3 * Returns: Returns the operating system name as returned by `uname(3)`. For example, it returns `'Linux'` on Linux, `'Darwin'` on macOS, and `'Windows_NT'` on Windows. See https://en.wikipedia.org/wiki/Uname#Examples for additional information about the output of running `uname(3)` on various operating systems. ### `os.uptime()`# History VersionChanges v10.0.0 The result of this function no longer contains a fraction component on Windows. v0.3.3 Added in: v0.3.3 * Returns: Returns the system uptime in number of seconds. ### `os.userInfo([options])`# Added in: v6.0.0 * `options` * `encoding` Character encoding used to interpret resulting strings. If `encoding` is set to `'buffer'`, the `username`, `shell`, and `homedir` values will be `Buffer` instances. Default: `'utf8'`. * Returns: Returns information about the currently effective user. On POSIX platforms, this is typically a subset of the password file. The returned object includes the `username`, `uid`, `gid`, `shell`, and `homedir`. On Windows, the `uid` and `gid` fields are `-1`, and `shell` is `null`. The value of `homedir` returned by `os.userInfo()` is provided by the operating system. This differs from the result of `os.homedir()`, which queries environment variables for the home directory before falling back to the operating system response. Throws a `SystemError` if a user has no `username` or `homedir`. ### `os.version()`# Added in: v13.11.0, v12.17.0 * Returns: Returns a string identifying the kernel version. On POSIX systems, the operating system release is determined by calling `uname(3)`. On Windows, `RtlGetVersion()` is used, and if it is not available, `GetVersionExW()` will be used. See https://en.wikipedia.org/wiki/Uname#Examples for more information. ### OS constants# The following constants are exported by `os.constants`. Not all constants will be available on every operating system. #### Signal constants# History VersionChanges v5.11.0 Added support for `SIGINFO`. The following signal constants are exported by `os.constants.signals`. Constant Description `SIGHUP` Sent to indicate when a controlling terminal is closed or a parent process exits. `SIGINT` Sent to indicate when a user wishes to interrupt a process (`Ctrl`+`C`). `SIGQUIT` Sent to indicate when a user wishes to terminate a process and perform a core dump. `SIGILL` Sent to a process to notify that it has attempted to perform an illegal, malformed, unknown, or privileged instruction. `SIGTRAP` Sent to a process when an exception has occurred. `SIGABRT` Sent to a process to request that it abort. `SIGIOT` Synonym for `SIGABRT` `SIGBUS` Sent to a process to notify that it has caused a bus error. `SIGFPE` Sent to a process to notify that it has performed an illegal arithmetic operation. `SIGKILL` Sent to a process to terminate it immediately. `SIGUSR1` `SIGUSR2` Sent to a process to identify user-defined conditions. `SIGSEGV` Sent to a process to notify of a segmentation fault. `SIGPIPE` Sent to a process when it has attempted to write to a disconnected pipe. `SIGALRM` Sent to a process when a system timer elapses. `SIGTERM` Sent to a process to request termination. `SIGCHLD` Sent to a process when a child process terminates. `SIGSTKFLT` Sent to a process to indicate a stack fault on a coprocessor. `SIGCONT` Sent to instruct the operating system to continue a paused process. `SIGSTOP` Sent to instruct the operating system to halt a process. `SIGTSTP` Sent to a process to request it to stop. `SIGBREAK` Sent to indicate when a user wishes to interrupt a process. `SIGTTIN` Sent to a process when it reads from the TTY while in the background. `SIGTTOU` Sent to a process when it writes to the TTY while in the background. `SIGURG` Sent to a process when a socket has urgent data to read. `SIGXCPU` Sent to a process when it has exceeded its limit on CPU usage. `SIGXFSZ` Sent to a process when it grows a file larger than the maximum allowed. `SIGVTALRM` Sent to a process when a virtual timer has elapsed. `SIGPROF` Sent to a process when a system timer has elapsed. `SIGWINCH` Sent to a process when the controlling terminal has changed its size. `SIGIO` Sent to a process when I/O is available. `SIGPOLL` Synonym for `SIGIO` `SIGLOST` Sent to a process when a file lock has been lost. `SIGPWR` Sent to a process to notify of a power failure. `SIGINFO` Synonym for `SIGPWR` `SIGSYS` Sent to a process to notify of a bad argument. `SIGUNUSED` Synonym for `SIGSYS` #### Error constants# The following error constants are exported by `os.constants.errno`. ##### POSIX error constants# Constant Description `E2BIG` Indicates that the list of arguments is longer than expected. `EACCES` Indicates that the operation did not have sufficient permissions. `EADDRINUSE` Indicates that the network address is already in use. `EADDRNOTAVAIL` Indicates that the network address is currently unavailable for use. `EAFNOSUPPORT` Indicates that the network address family is not supported. `EAGAIN` Indicates that there is no data available and to try the operation again later. `EALREADY` Indicates that the socket already has a pending connection in progress. `EBADF` Indicates that a file descriptor is not valid. `EBADMSG` Indicates an invalid data message. `EBUSY` Indicates that a device or resource is busy. `ECANCELED` Indicates that an operation was canceled. `ECHILD` Indicates that there are no child processes. `ECONNABORTED` Indicates that the network connection has been aborted. `ECONNREFUSED` Indicates that the network connection has been refused. `ECONNRESET` Indicates that the network connection has been reset. `EDEADLK` Indicates that a resource deadlock has been avoided. `EDESTADDRREQ` Indicates that a destination address is required. `EDOM` Indicates that an argument is out of the domain of the function. `EDQUOT` Indicates that the disk quota has been exceeded. `EEXIST` Indicates that the file already exists. `EFAULT` Indicates an invalid pointer address. `EFBIG` Indicates that the file is too large. `EHOSTUNREACH` Indicates that the host is unreachable. `EIDRM` Indicates that the identifier has been removed. `EILSEQ` Indicates an illegal byte sequence. `EINPROGRESS` Indicates that an operation is already in progress. `EINTR` Indicates that a function call was interrupted. `EINVAL` Indicates that an invalid argument was provided. `EIO` Indicates an otherwise unspecified I/O error. `EISCONN` Indicates that the socket is connected. `EISDIR` Indicates that the path is a directory. `ELOOP` Indicates too many levels of symbolic links in a path. `EMFILE` Indicates that there are too many open files. `EMLINK` Indicates that there are too many hard links to a file. `EMSGSIZE` Indicates that the provided message is too long. `EMULTIHOP` Indicates that a multihop was attempted. `ENAMETOOLONG` Indicates that the filename is too long. `ENETDOWN` Indicates that the network is down. `ENETRESET` Indicates that the connection has been aborted by the network. `ENETUNREACH` Indicates that the network is unreachable. `ENFILE` Indicates too many open files in the system. `ENOBUFS` Indicates that no buffer space is available. `ENODATA` Indicates that no message is available on the stream head read queue. `ENODEV` Indicates that there is no such device. `ENOENT` Indicates that there is no such file or directory. `ENOEXEC` Indicates an exec format error. `ENOLCK` Indicates that there are no locks available. `ENOLINK` Indications that a link has been severed. `ENOMEM` Indicates that there is not enough space. `ENOMSG` Indicates that there is no message of the desired type. `ENOPROTOOPT` Indicates that a given protocol is not available. `ENOSPC` Indicates that there is no space available on the device. `ENOSR` Indicates that there are no stream resources available. `ENOSTR` Indicates that a given resource is not a stream. `ENOSYS` Indicates that a function has not been implemented. `ENOTCONN` Indicates that the socket is not connected. `ENOTDIR` Indicates that the path is not a directory. `ENOTEMPTY` Indicates that the directory is not empty. `ENOTSOCK` Indicates that the given item is not a socket. `ENOTSUP` Indicates that a given operation is not supported. `ENOTTY` Indicates an inappropriate I/O control operation. `ENXIO` Indicates no such device or address. `EOPNOTSUPP` Indicates that an operation is not supported on the socket. Although `ENOTSUP` and `EOPNOTSUPP` have the same value on Linux, according to POSIX.1 these error values should be distinct.) `EOVERFLOW` Indicates that a value is too large to be stored in a given data type. `EPERM` Indicates that the operation is not permitted. `EPIPE` Indicates a broken pipe. `EPROTO` Indicates a protocol error. `EPROTONOSUPPORT` Indicates that a protocol is not supported. `EPROTOTYPE` Indicates the wrong type of protocol for a socket. `ERANGE` Indicates that the results are too large. `EROFS` Indicates that the file system is read only. `ESPIPE` Indicates an invalid seek operation. `ESRCH` Indicates that there is no such process. `ESTALE` Indicates that the file handle is stale. `ETIME` Indicates an expired timer. `ETIMEDOUT` Indicates that the connection timed out. `ETXTBSY` Indicates that a text file is busy. `EWOULDBLOCK` Indicates that the operation would block. `EXDEV` Indicates an improper link. ##### Windows-specific error constants# The following error codes are specific to the Windows operating system. Constant Description `WSAEINTR` Indicates an interrupted function call. `WSAEBADF` Indicates an invalid file handle. `WSAEACCES` Indicates insufficient permissions to complete the operation. `WSAEFAULT` Indicates an invalid pointer address. `WSAEINVAL` Indicates that an invalid argument was passed. `WSAEMFILE` Indicates that there are too many open files. `WSAEWOULDBLOCK` Indicates that a resource is temporarily unavailable. `WSAEINPROGRESS` Indicates that an operation is currently in progress. `WSAEALREADY` Indicates that an operation is already in progress. `WSAENOTSOCK` Indicates that the resource is not a socket. `WSAEDESTADDRREQ` Indicates that a destination address is required. `WSAEMSGSIZE` Indicates that the message size is too long. `WSAEPROTOTYPE` Indicates the wrong protocol type for the socket. `WSAENOPROTOOPT` Indicates a bad protocol option. `WSAEPROTONOSUPPORT` Indicates that the protocol is not supported. `WSAESOCKTNOSUPPORT` Indicates that the socket type is not supported. `WSAEOPNOTSUPP` Indicates that the operation is not supported. `WSAEPFNOSUPPORT` Indicates that the protocol family is not supported. `WSAEAFNOSUPPORT` Indicates that the address family is not supported. `WSAEADDRINUSE` Indicates that the network address is already in use. `WSAEADDRNOTAVAIL` Indicates that the network address is not available. `WSAENETDOWN` Indicates that the network is down. `WSAENETUNREACH` Indicates that the network is unreachable. `WSAENETRESET` Indicates that the network connection has been reset. `WSAECONNABORTED` Indicates that the connection has been aborted. `WSAECONNRESET` Indicates that the connection has been reset by the peer. `WSAENOBUFS` Indicates that there is no buffer space available. `WSAEISCONN` Indicates that the socket is already connected. `WSAENOTCONN` Indicates that the socket is not connected. `WSAESHUTDOWN` Indicates that data cannot be sent after the socket has been shutdown. `WSAETOOMANYREFS` Indicates that there are too many references. `WSAETIMEDOUT` Indicates that the connection has timed out. `WSAECONNREFUSED` Indicates that the connection has been refused. `WSAELOOP` Indicates that a name cannot be translated. `WSAENAMETOOLONG` Indicates that a name was too long. `WSAEHOSTDOWN` Indicates that a network host is down. `WSAEHOSTUNREACH` Indicates that there is no route to a network host. `WSAENOTEMPTY` Indicates that the directory is not empty. `WSAEPROCLIM` Indicates that there are too many processes. `WSAEUSERS` Indicates that the user quota has been exceeded. `WSAEDQUOT` Indicates that the disk quota has been exceeded. `WSAESTALE` Indicates a stale file handle reference. `WSAEREMOTE` Indicates that the item is remote. `WSASYSNOTREADY` Indicates that the network subsystem is not ready. `WSAVERNOTSUPPORTED` Indicates that the `winsock.dll` version is out of range. `WSANOTINITIALISED` Indicates that successful WSAStartup has not yet been performed. `WSAEDISCON` Indicates that a graceful shutdown is in progress. `WSAENOMORE` Indicates that there are no more results. `WSAECANCELLED` Indicates that an operation has been canceled. `WSAEINVALIDPROCTABLE` Indicates that the procedure call table is invalid. `WSAEINVALIDPROVIDER` Indicates an invalid service provider. `WSAEPROVIDERFAILEDINIT` Indicates that the service provider failed to initialized. `WSASYSCALLFAILURE` Indicates a system call failure. `WSASERVICE_NOT_FOUND` Indicates that a service was not found. `WSATYPE_NOT_FOUND` Indicates that a class type was not found. `WSA_E_NO_MORE` Indicates that there are no more results. `WSA_E_CANCELLED` Indicates that the call was canceled. `WSAEREFUSED` Indicates that a database query was refused. #### dlopen constants# If available on the operating system, the following constants are exported in `os.constants.dlopen`. See `dlopen(3)` for detailed information. Constant Description `RTLD_LAZY` Perform lazy binding. Node.js sets this flag by default. `RTLD_NOW` Resolve all undefined symbols in the library before dlopen(3) returns. `RTLD_GLOBAL` Symbols defined by the library will be made available for symbol resolution of subsequently loaded libraries. `RTLD_LOCAL` The converse of `RTLD_GLOBAL`. This is the default behavior if neither flag is specified. `RTLD_DEEPBIND` Make a self-contained library use its own symbols in preference to symbols from previously loaded libraries. #### Priority constants# Added in: v10.10.0 The following process scheduling constants are exported by `os.constants.priority`. Constant Description `PRIORITY_LOW` The lowest process scheduling priority. This corresponds to `IDLE_PRIORITY_CLASS` on Windows, and a nice value of `19` on all other platforms. `PRIORITY_BELOW_NORMAL` The process scheduling priority above `PRIORITY_LOW` and below `PRIORITY_NORMAL`. This corresponds to `BELOW_NORMAL_PRIORITY_CLASS` on Windows, and a nice value of `10` on all other platforms. `PRIORITY_NORMAL` The default process scheduling priority. This corresponds to `NORMAL_PRIORITY_CLASS` on Windows, and a nice value of `0` on all other platforms. `PRIORITY_ABOVE_NORMAL` The process scheduling priority above `PRIORITY_NORMAL` and below `PRIORITY_HIGH`. This corresponds to `ABOVE_NORMAL_PRIORITY_CLASS` on Windows, and a nice value of `-7` on all other platforms. `PRIORITY_HIGH` The process scheduling priority above `PRIORITY_ABOVE_NORMAL` and below `PRIORITY_HIGHEST`. This corresponds to `HIGH_PRIORITY_CLASS` on Windows, and a nice value of `-14` on all other platforms. `PRIORITY_HIGHEST` The highest process scheduling priority. This corresponds to `REALTIME_PRIORITY_CLASS` on Windows, and a nice value of `-20` on all other platforms. #### libuv constants# Constant Description `UV_UDP_REUSEADDR` ## Path# Stability: 2 \- Stable Source Code: lib/path.js The `node:path` module provides utilities for working with file and directory paths. It can be accessed using: import path from 'node:path'; ### Windows vs. POSIX# The default operation of the `node:path` module varies based on the operating system on which a Node.js application is running. Specifically, when running on a Windows operating system, the `node:path` module will assume that Windows-style paths are being used. So using `path.basename()` might yield different results on POSIX and Windows: On POSIX: path.basename('C:\\temp\\myfile.html'); // Returns: 'C:\\temp\\myfile.html' On Windows: path.basename('C:\\temp\\myfile.html'); // Returns: 'myfile.html' To achieve consistent results when working with Windows file paths on any operating system, use `path.win32`: On POSIX and Windows: path.win32.basename('C:\\temp\\myfile.html'); // Returns: 'myfile.html' To achieve consistent results when working with POSIX file paths on any operating system, use `path.posix`: On POSIX and Windows: path.posix.basename('/tmp/myfile.html'); // Returns: 'myfile.html' On Windows Node.js follows the concept of per-drive working directory. This behavior can be observed when using a drive path without a backslash. For example, `path.resolve('C:\\')` can potentially return a different result than `path.resolve('C:')`. For more information, see this MSDN page. ### `path.basename(path[, suffix])`# History VersionChanges v6.0.0 Passing a non-string as the `path` argument will throw now. v0.1.25 Added in: v0.1.25 * `path` * `suffix` An optional suffix to remove * Returns: The `path.basename()` method returns the last portion of a `path`, similar to the Unix `basename` command. Trailing directory separators are ignored. path.basename('/foo/bar/baz/asdf/quux.html'); // Returns: 'quux.html' path.basename('/foo/bar/baz/asdf/quux.html', '.html'); // Returns: 'quux' Although Windows usually treats file names, including file extensions, in a case-insensitive manner, this function does not. For example, `C:\\foo.html` and `C:\\foo.HTML` refer to the same file, but `basename` treats the extension as a case-sensitive string: path.win32.basename('C:\\foo.html', '.html'); // Returns: 'foo' path.win32.basename('C:\\foo.HTML', '.html'); // Returns: 'foo.HTML' A `TypeError` is thrown if `path` is not a string or if `suffix` is given and is not a string. ### `path.delimiter`# Added in: v0.9.3 * Type: Provides the platform-specific path delimiter: * `;` for Windows * `:` for POSIX For example, on POSIX: console.log(process.env.PATH); // Prints: '/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin' process.env.PATH.split(path.delimiter); // Returns: ['/usr/bin', '/bin', '/usr/sbin', '/sbin', '/usr/local/bin'] On Windows: console.log(process.env.PATH); // Prints: 'C:\Windows\system32;C:\Windows;C:\Program Files\node\' process.env.PATH.split(path.delimiter); // Returns ['C:\\Windows\\system32', 'C:\\Windows', 'C:\\Program Files\\node\\'] ### `path.dirname(path)`# History VersionChanges v6.0.0 Passing a non-string as the `path` argument will throw now. v0.1.16 Added in: v0.1.16 * `path` * Returns: The `path.dirname()` method returns the directory name of a `path`, similar to the Unix `dirname` command. Trailing directory separators are ignored, see `path.sep`. path.dirname('/foo/bar/baz/asdf/quux'); // Returns: '/foo/bar/baz/asdf' A `TypeError` is thrown if `path` is not a string. ### `path.extname(path)`# History VersionChanges v6.0.0 Passing a non-string as the `path` argument will throw now. v0.1.25 Added in: v0.1.25 * `path` * Returns: The `path.extname()` method returns the extension of the `path`, from the last occurrence of the `.` (period) character to end of string in the last portion of the `path`. If there is no `.` in the last portion of the `path`, or if there are no `.` characters other than the first character of the basename of `path` (see `path.basename()`) , an empty string is returned. path.extname('index.html'); // Returns: '.html' path.extname('index.coffee.md'); // Returns: '.md' path.extname('index.'); // Returns: '.' path.extname('index'); // Returns: '' path.extname('.index'); // Returns: '' path.extname('.index.md'); // Returns: '.md' A `TypeError` is thrown if `path` is not a string. ### `path.format(pathObject)`# History VersionChanges v19.0.0 The dot will be added if it is not specified in `ext`. v0.11.15 Added in: v0.11.15 * `pathObject` Any JavaScript object having the following properties: * `dir` * `root` * `base` * `name` * `ext` * Returns: The `path.format()` method returns a path string from an object. This is the opposite of `path.parse()`. When providing properties to the `pathObject` remember that there are combinations where one property has priority over another: * `pathObject.root` is ignored if `pathObject.dir` is provided * `pathObject.ext` and `pathObject.name` are ignored if `pathObject.base` exists For example, on POSIX: // If `dir`, `root` and `base` are provided, // `${dir}${path.sep}${base}` // will be returned. `root` is ignored. path.format({ root: '/ignored', dir: '/home/user/dir', base: 'file.txt', }); // Returns: '/home/user/dir/file.txt' // `root` will be used if `dir` is not specified. // If only `root` is provided or `dir` is equal to `root` then the // platform separator will not be included. `ext` will be ignored. path.format({ root: '/', base: 'file.txt', ext: 'ignored', }); // Returns: '/file.txt' // `name` + `ext` will be used if `base` is not specified. path.format({ root: '/', name: 'file', ext: '.txt', }); // Returns: '/file.txt' // The dot will be added if it is not specified in `ext`. path.format({ root: '/', name: 'file', ext: 'txt', }); // Returns: '/file.txt' On Windows: path.format({ dir: 'C:\\path\\dir', base: 'file.txt', }); // Returns: 'C:\\path\\dir\\file.txt' ### `path.matchesGlob(path, pattern)`# History VersionChanges v24.8.0 Marking the API stable. v22.5.0, v20.17.0 Added in: v22.5.0, v20.17.0 * `path` The path to glob-match against. * `pattern` The glob to check the path against. * Returns: Whether or not the `path` matched the `pattern`. The `path.matchesGlob()` method determines if `path` matches the `pattern`. For example: path.matchesGlob('/foo/bar', '/foo/*'); // true path.matchesGlob('/foo/bar*', 'foo/bird'); // false A `TypeError` is thrown if `path` or `pattern` are not strings. ### `path.isAbsolute(path)`# Added in: v0.11.2 * `path` * Returns: The `path.isAbsolute()` method determines if the literal `path` is absolute. Therefore, it’s not safe for mitigating path traversals. If the given `path` is a zero-length string, `false` will be returned. For example, on POSIX: path.isAbsolute('/foo/bar'); // true path.isAbsolute('/baz/..'); // true path.isAbsolute('/baz/../..'); // true path.isAbsolute('qux/'); // false path.isAbsolute('.'); // false On Windows: path.isAbsolute('//server'); // true path.isAbsolute('\\\\server'); // true path.isAbsolute('C:/foo/..'); // true path.isAbsolute('C:\\foo\\..'); // true path.isAbsolute('bar\\baz'); // false path.isAbsolute('bar/baz'); // false path.isAbsolute('.'); // false A `TypeError` is thrown if `path` is not a string. ### `path.join([...paths])`# Added in: v0.1.16 * `...paths` A sequence of path segments * Returns: The `path.join()` method joins all given `path` segments together using the platform-specific separator as a delimiter, then normalizes the resulting path. Zero-length `path` segments are ignored. If the joined path string is a zero-length string then `'.'` will be returned, representing the current working directory. path.join('/foo', 'bar', 'baz/asdf', 'quux', '..'); // Returns: '/foo/bar/baz/asdf' path.join('foo', {}, 'bar'); // Throws 'TypeError: Path must be a string. Received {}' A `TypeError` is thrown if any of the path segments is not a string. ### `path.normalize(path)`# Added in: v0.1.23 * `path` * Returns: The `path.normalize()` method normalizes the given `path`, resolving `'..'` and `'.'` segments. When multiple, sequential path segment separation characters are found (e.g. `/` on POSIX and either `\` or `/` on Windows), they are replaced by a single instance of the platform-specific path segment separator (`/` on POSIX and `\` on Windows). Trailing separators are preserved. If the `path` is a zero-length string, `'.'` is returned, representing the current working directory. On POSIX, the types of normalization applied by this function do not strictly adhere to the POSIX specification. For example, this function will replace two leading forward slashes with a single slash as if it was a regular absolute path, whereas a few POSIX systems assign special meaning to paths beginning with exactly two forward slashes. Similarly, other substitutions performed by this function, such as removing `..` segments, may change how the underlying system resolves the path. For example, on POSIX: path.normalize('/foo/bar//baz/asdf/quux/..'); // Returns: '/foo/bar/baz/asdf' On Windows: path.normalize('C:\\temp\\\\foo\\bar\\..\\'); // Returns: 'C:\\temp\\foo\\' Since Windows recognizes multiple path separators, both separators will be replaced by instances of the Windows preferred separator (`\`): path.win32.normalize('C:////temp\\\\/\\/\\/foo/bar'); // Returns: 'C:\\temp\\foo\\bar' A `TypeError` is thrown if `path` is not a string. ### `path.parse(path)`# Added in: v0.11.15 * `path` * Returns: The `path.parse()` method returns an object whose properties represent significant elements of the `path`. Trailing directory separators are ignored, see `path.sep`. The returned object will have the following properties: * `dir` * `root` * `base` * `name` * `ext` For example, on POSIX: path.parse('/home/user/dir/file.txt'); // Returns: // { root: '/', // dir: '/home/user/dir', // base: 'file.txt', // ext: '.txt', // name: 'file' } ┌─────────────────────┬────────────┐ │ dir │ base │ ├──────┬ ├──────┬─────┤ │ root │ │ name │ ext │ " / home/user/dir / file .txt " └──────┴──────────────┴──────┴─────┘ (All spaces in the "" line should be ignored. They are purely for formatting.) On Windows: path.parse('C:\\path\\dir\\file.txt'); // Returns: // { root: 'C:\\', // dir: 'C:\\path\\dir', // base: 'file.txt', // ext: '.txt', // name: 'file' } ┌─────────────────────┬────────────┐ │ dir │ base │ ├──────┬ ├──────┬─────┤ │ root │ │ name │ ext │ " C:\ path\dir \ file .txt " └──────┴──────────────┴──────┴─────┘ (All spaces in the "" line should be ignored. They are purely for formatting.) A `TypeError` is thrown if `path` is not a string. ### `path.posix`# History VersionChanges v15.3.0 Exposed as `require('path/posix')`. v0.11.15 Added in: v0.11.15 * Type: The `path.posix` property provides access to POSIX specific implementations of the `path` methods. The API is accessible via `require('node:path').posix` or `require('node:path/posix')`. ### `path.relative(from, to)`# History VersionChanges v6.8.0 On Windows, the leading slashes for UNC paths are now included in the return value. v0.5.0 Added in: v0.5.0 * `from` * `to` * Returns: The `path.relative()` method returns the relative path from `from` to `to` based on the current working directory. If `from` and `to` each resolve to the same path (after calling `path.resolve()` on each), a zero-length string is returned. If a zero-length string is passed as `from` or `to`, the current working directory will be used instead of the zero-length strings. For example, on POSIX: path.relative('/data/orandea/test/aaa', '/data/orandea/impl/bbb'); // Returns: '../../impl/bbb' On Windows: path.relative('C:\\orandea\\test\\aaa', 'C:\\orandea\\impl\\bbb'); // Returns: '..\\..\\impl\\bbb' A `TypeError` is thrown if either `from` or `to` is not a string. ### `path.resolve([...paths])`# Added in: v0.3.4 * `...paths` A sequence of paths or path segments * Returns: The `path.resolve()` method resolves a sequence of paths or path segments into an absolute path. The given sequence of paths is processed from right to left, with each subsequent `path` prepended until an absolute path is constructed. For instance, given the sequence of path segments: `/foo`, `/bar`, `baz`, calling `path.resolve('/foo', '/bar', 'baz')` would return `/bar/baz` because `'baz'` is not an absolute path but `'/bar' + '/' + 'baz'` is. If, after processing all given `path` segments, an absolute path has not yet been generated, the current working directory is used. The resulting path is normalized and trailing slashes are removed unless the path is resolved to the root directory. Zero-length `path` segments are ignored. If no `path` segments are passed, `path.resolve()` will return the absolute path of the current working directory. path.resolve('/foo/bar', './baz'); // Returns: '/foo/bar/baz' path.resolve('/foo/bar', '/tmp/file/'); // Returns: '/tmp/file' path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif'); // If the current working directory is /home/myself/node, // this returns '/home/myself/node/wwwroot/static_files/gif/image.gif' A `TypeError` is thrown if any of the arguments is not a string. ### `path.sep`# Added in: v0.7.9 * Type: Provides the platform-specific path segment separator: * `\` on Windows * `/` on POSIX For example, on POSIX: 'foo/bar/baz'.split(path.sep); // Returns: ['foo', 'bar', 'baz'] On Windows: 'foo\\bar\\baz'.split(path.sep); // Returns: ['foo', 'bar', 'baz'] On Windows, both the forward slash (`/`) and backward slash (`\`) are accepted as path segment separators; however, the `path` methods only add backward slashes (`\`). ### `path.toNamespacedPath(path)`# Added in: v9.0.0 * `path` * Returns: On Windows systems only, returns an equivalent namespace-prefixed path for the given `path`. If `path` is not a string, `path` will be returned without modifications. This method is meaningful only on Windows systems. On POSIX systems, the method is non-operational and always returns `path` without modifications. ### `path.win32`# History VersionChanges v15.3.0 Exposed as `require('path/win32')`. v0.11.15 Added in: v0.11.15 * Type: The `path.win32` property provides access to Windows-specific implementations of the `path` methods. The API is accessible via `require('node:path').win32` or `require('node:path/win32')`. ## Performance measurement APIs# Stability: 2 \- Stable Source Code: lib/perf_hooks.js This module provides an implementation of a subset of the W3C Web Performance APIs as well as additional APIs for Node.js-specific performance measurements. Node.js supports the following Web Performance APIs: * High Resolution Time * Performance Timeline * User Timing * Resource Timing import { performance, PerformanceObserver } from 'node:perf_hooks'; const obs = new PerformanceObserver((items) => { console.log(items.getEntries()[0].duration); performance.clearMarks(); }); obs.observe({ type: 'measure' }); performance.measure('Start to Now'); performance.mark('A'); doSomeLongRunningProcess(() => { performance.measure('A to Now', 'A'); performance.mark('B'); performance.measure('A to B', 'A', 'B'); }); ### `perf_hooks.performance`# Added in: v8.5.0 An object that can be used to collect performance metrics from the current Node.js instance. It is similar to `window.performance` in browsers. #### `performance.clearMarks([name])`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v8.5.0 Added in: v8.5.0 * `name` If `name` is not provided, removes all `PerformanceMark` objects from the Performance Timeline. If `name` is provided, removes only the named mark. #### `performance.clearMeasures([name])`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v16.7.0 Added in: v16.7.0 * `name` If `name` is not provided, removes all `PerformanceMeasure` objects from the Performance Timeline. If `name` is provided, removes only the named measure. #### `performance.clearResourceTimings([name])`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * `name` If `name` is not provided, removes all `PerformanceResourceTiming` objects from the Resource Timeline. If `name` is provided, removes only the named resource. #### `performance.eventLoopUtilization([utilization1[, utilization2]])`# Added in: v14.10.0, v12.19.0 * `utilization1` The result of a previous call to `eventLoopUtilization()`. * `utilization2` The result of a previous call to `eventLoopUtilization()` prior to `utilization1`. * Returns: * `idle` * `active` * `utilization` The `eventLoopUtilization()` method returns an object that contains the cumulative duration of time the event loop has been both idle and active as a high resolution milliseconds timer. The `utilization` value is the calculated Event Loop Utilization (ELU). If bootstrapping has not yet finished on the main thread the properties have the value of `0`. The ELU is immediately available on Worker threads since bootstrap happens within the event loop. Both `utilization1` and `utilization2` are optional parameters. If `utilization1` is passed, then the delta between the current call's `active` and `idle` times, as well as the corresponding `utilization` value are calculated and returned (similar to `process.hrtime()`). If `utilization1` and `utilization2` are both passed, then the delta is calculated between the two arguments. This is a convenience option because, unlike `process.hrtime()`, calculating the ELU is more complex than a single subtraction. ELU is similar to CPU utilization, except that it only measures event loop statistics and not CPU usage. It represents the percentage of time the event loop has spent outside the event loop's event provider (e.g. `epoll_wait`). No other CPU idle time is taken into consideration. The following is an example of how a mostly idle process will have a high ELU. import { eventLoopUtilization } from 'node:perf_hooks'; import { spawnSync } from 'node:child_process'; setImmediate(() => { const elu = eventLoopUtilization(); spawnSync('sleep', ['5']); console.log(eventLoopUtilization(elu).utilization); }); Although the CPU is mostly idle while running this script, the value of `utilization` is `1`. This is because the call to `child_process.spawnSync()` blocks the event loop from proceeding. Passing in a user-defined object instead of the result of a previous call to `eventLoopUtilization()` will lead to undefined behavior. The return values are not guaranteed to reflect any correct state of the event loop. #### `performance.getEntries()`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v16.7.0 Added in: v16.7.0 * Returns: Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime`. If you are only interested in performance entries of certain types or that have certain names, see `performance.getEntriesByType()` and `performance.getEntriesByName()`. #### `performance.getEntriesByName(name[, type])`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v16.7.0 Added in: v16.7.0 * `name` * `type` * Returns: Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.name` is equal to `name`, and optionally, whose `performanceEntry.entryType` is equal to `type`. #### `performance.getEntriesByType(type)`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v16.7.0 Added in: v16.7.0 * `type` * Returns: Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.entryType` is equal to `type`. #### `performance.mark(name[, options])`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. The name argument is no longer optional. v16.0.0 Updated to conform to the User Timing Level 3 specification. v8.5.0 Added in: v8.5.0 * `name` * `options` * `detail` Additional optional detail to include with the mark. * `startTime` An optional timestamp to be used as the mark time. Default: `performance.now()`. Creates a new `PerformanceMark` entry in the Performance Timeline. A `PerformanceMark` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'mark'`, and whose `performanceEntry.duration` is always `0`. Performance marks are used to mark specific significant moments in the Performance Timeline. The created `PerformanceMark` entry is put in the global Performance Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearMarks`. #### `performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode, bodyInfo, responseStatus[, deliveryType])`# History VersionChanges v22.2.0 Added bodyInfo, responseStatus, and deliveryType arguments. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * `timingInfo` Fetch Timing Info * `requestedUrl` The resource url * `initiatorType` The initiator name, e.g: 'fetch' * `global` * `cacheMode` The cache mode must be an empty string ('') or 'local' * `bodyInfo` Fetch Response Body Info * `responseStatus` The response's status code * `deliveryType` The delivery type. Default: `''`. This property is an extension by Node.js. It is not available in Web browsers. Creates a new `PerformanceResourceTiming` entry in the Resource Timeline. A `PerformanceResourceTiming` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'resource'`. Performance resources are used to mark moments in the Resource Timeline. The created `PerformanceMark` entry is put in the global Resource Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearResourceTimings`. #### `performance.measure(name[, startMarkOrOptions[, endMark]])`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v16.0.0 Updated to conform to the User Timing Level 3 specification. v13.13.0, v12.16.3 Make `startMark` and `endMark` parameters optional. v8.5.0 Added in: v8.5.0 * `name` * `startMarkOrOptions` | Optional. * `detail` Additional optional detail to include with the measure. * `duration` Duration between start and end times. * `end` | Timestamp to be used as the end time, or a string identifying a previously recorded mark. * `start` | Timestamp to be used as the start time, or a string identifying a previously recorded mark. * `endMark` Optional. Must be omitted if `startMarkOrOptions` is an . Creates a new `PerformanceMeasure` entry in the Performance Timeline. A `PerformanceMeasure` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'measure'`, and whose `performanceEntry.duration` measures the number of milliseconds elapsed since `startMark` and `endMark`. The `startMark` argument may identify any existing `PerformanceMark` in the Performance Timeline, or may identify any of the timestamp properties provided by the `PerformanceNodeTiming` class. If the named `startMark` does not exist, an error is thrown. The optional `endMark` argument must identify any existing `PerformanceMark` in the Performance Timeline or any of the timestamp properties provided by the `PerformanceNodeTiming` class. `endMark` will be `performance.now()` if no parameter is passed, otherwise if the named `endMark` does not exist, an error will be thrown. The created `PerformanceMeasure` entry is put in the global Performance Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearMeasures`. #### `performance.nodeTiming`# Added in: v8.5.0 * Type: This property is an extension by Node.js. It is not available in Web browsers. An instance of the `PerformanceNodeTiming` class that provides performance metrics for specific Node.js operational milestones. #### `performance.now()`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v8.5.0 Added in: v8.5.0 * Returns: Returns the current high resolution millisecond timestamp, where 0 represents the start of the current `node` process. #### `performance.setResourceTimingBufferSize(maxSize)`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v18.8.0 Added in: v18.8.0 Sets the global performance resource timing buffer size to the specified number of "resource" type performance entry objects. By default the max buffer size is set to 250. #### `performance.timeOrigin`# Added in: v8.5.0 * Type: The `timeOrigin` specifies the high resolution millisecond timestamp at which the current `node` process began, measured in Unix time. #### `performance.timerify(fn[, options])`# History VersionChanges v16.0.0 Added the histogram option. v16.0.0 Re-implemented to use pure-JavaScript and the ability to time async functions. v8.5.0 Added in: v8.5.0 * `fn` * `options` * `histogram` A histogram object created using `perf_hooks.createHistogram()` that will record runtime durations in nanoseconds. This property is an extension by Node.js. It is not available in Web browsers. Wraps a function within a new function that measures the running time of the wrapped function. A `PerformanceObserver` must be subscribed to the `'function'` event type in order for the timing details to be accessed. import { performance, PerformanceObserver } from 'node:perf_hooks'; function someFunction() { console.log('hello world'); } const wrapped = performance.timerify(someFunction); const obs = new PerformanceObserver((list) => { console.log(list.getEntries()[0].duration); performance.clearMarks(); performance.clearMeasures(); obs.disconnect(); }); obs.observe({ entryTypes: ['function'] }); // A performance timeline entry will be created wrapped(); If the wrapped function returns a promise, a finally handler will be attached to the promise and the duration will be reported once the finally handler is invoked. #### `performance.toJSON()`# History VersionChanges v19.0.0 This method must be called with the `performance` object as the receiver. v16.1.0 Added in: v16.1.0 An object which is JSON representation of the `performance` object. It is similar to `window.performance.toJSON` in browsers. ##### Event: `'resourcetimingbufferfull'`# Added in: v18.8.0 The `'resourcetimingbufferfull'` event is fired when the global performance resource timing buffer is full. Adjust resource timing buffer size with `performance.setResourceTimingBufferSize()` or clear the buffer with `performance.clearResourceTimings()` in the event listener to allow more entries to be added to the performance timeline buffer. ### Class: `PerformanceEntry`# Added in: v8.5.0 The constructor of this class is not exposed to users directly. #### `performanceEntry.duration`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceEntry` object as the receiver. v8.5.0 Added in: v8.5.0 * Type: The total number of milliseconds elapsed for this entry. This value will not be meaningful for all Performance Entry types. #### `performanceEntry.entryType`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceEntry` object as the receiver. v8.5.0 Added in: v8.5.0 * Type: The type of the performance entry. It may be one of: * `'dns'` (Node.js only) * `'function'` (Node.js only) * `'gc'` (Node.js only) * `'http2'` (Node.js only) * `'http'` (Node.js only) * `'mark'` (available on the Web) * `'measure'` (available on the Web) * `'net'` (Node.js only) * `'node'` (Node.js only) * `'resource'` (available on the Web) #### `performanceEntry.name`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceEntry` object as the receiver. v8.5.0 Added in: v8.5.0 * Type: The name of the performance entry. #### `performanceEntry.startTime`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceEntry` object as the receiver. v8.5.0 Added in: v8.5.0 * Type: The high resolution millisecond timestamp marking the starting time of the Performance Entry. ### Class: `PerformanceMark`# Added in: v18.2.0, v16.17.0 * Extends: Exposes marks created via the `Performance.mark()` method. #### `performanceMark.detail`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceMark` object as the receiver. v16.0.0 Added in: v16.0.0 * Type: Additional detail specified when creating with `Performance.mark()` method. ### Class: `PerformanceMeasure`# Added in: v18.2.0, v16.17.0 * Extends: Exposes measures created via the `Performance.measure()` method. The constructor of this class is not exposed to users directly. #### `performanceMeasure.detail`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceMeasure` object as the receiver. v16.0.0 Added in: v16.0.0 * Type: Additional detail specified when creating with `Performance.measure()` method. ### Class: `PerformanceNodeEntry`# Added in: v19.0.0 * Extends: This class is an extension by Node.js. It is not available in Web browsers. Provides detailed Node.js timing data. The constructor of this class is not exposed to users directly. #### `performanceNodeEntry.detail`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceNodeEntry` object as the receiver. v16.0.0 Added in: v16.0.0 * Type: Additional detail specific to the `entryType`. #### `performanceNodeEntry.flags`# History VersionChanges v16.0.0 Runtime deprecated. Now moved to the detail property when entryType is 'gc'. v13.9.0, v12.17.0 Added in: v13.9.0, v12.17.0 Stability: 0 \- Deprecated: Use `performanceNodeEntry.detail` instead. * Type: When `performanceEntry.entryType` is equal to `'gc'`, the `performance.flags` property contains additional information about garbage collection operation. The value may be one of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE` #### `performanceNodeEntry.kind`# History VersionChanges v16.0.0 Runtime deprecated. Now moved to the detail property when entryType is 'gc'. v8.5.0 Added in: v8.5.0 Stability: 0 \- Deprecated: Use `performanceNodeEntry.detail` instead. * Type: When `performanceEntry.entryType` is equal to `'gc'`, the `performance.kind` property identifies the type of garbage collection operation that occurred. The value may be one of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL` * `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB` #### Garbage Collection ('gc') Details# When `performanceEntry.type` is equal to `'gc'`, the `performanceNodeEntry.detail` property will be an with two properties: * `kind` One of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL` * `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB` * `flags` One of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE` #### HTTP ('http') Details# When `performanceEntry.type` is equal to `'http'`, the `performanceNodeEntry.detail` property will be an containing additional information. If `performanceEntry.name` is equal to `HttpClient`, the `detail` will contain the following properties: `req`, `res`. And the `req` property will be an containing `method`, `url`, `headers`, the `res` property will be an containing `statusCode`, `statusMessage`, `headers`. If `performanceEntry.name` is equal to `HttpRequest`, the `detail` will contain the following properties: `req`, `res`. And the `req` property will be an containing `method`, `url`, `headers`, the `res` property will be an containing `statusCode`, `statusMessage`, `headers`. This could add additional memory overhead and should only be used for diagnostic purposes, not left turned on in production by default. #### HTTP/2 ('http2') Details# When `performanceEntry.type` is equal to `'http2'`, the `performanceNodeEntry.detail` property will be an containing additional performance information. If `performanceEntry.name` is equal to `Http2Stream`, the `detail` will contain the following properties: * `bytesRead` The number of `DATA` frame bytes received for this `Http2Stream`. * `bytesWritten` The number of `DATA` frame bytes sent for this `Http2Stream`. * `id` The identifier of the associated `Http2Stream` * `timeToFirstByte` The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first `DATA` frame. * `timeToFirstByteSent` The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and sending of the first `DATA` frame. * `timeToFirstHeader` The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first header. If `performanceEntry.name` is equal to `Http2Session`, the `detail` will contain the following properties: * `bytesRead` The number of bytes received for this `Http2Session`. * `bytesWritten` The number of bytes sent for this `Http2Session`. * `framesReceived` The number of HTTP/2 frames received by the `Http2Session`. * `framesSent` The number of HTTP/2 frames sent by the `Http2Session`. * `maxConcurrentStreams` The maximum number of streams concurrently open during the lifetime of the `Http2Session`. * `pingRTT` The number of milliseconds elapsed since the transmission of a `PING` frame and the reception of its acknowledgment. Only present if a `PING` frame has been sent on the `Http2Session`. * `streamAverageDuration` The average duration (in milliseconds) for all `Http2Stream` instances. * `streamCount` The number of `Http2Stream` instances processed by the `Http2Session`. * `type` Either `'server'` or `'client'` to identify the type of `Http2Session`. #### Timerify ('function') Details# When `performanceEntry.type` is equal to `'function'`, the `performanceNodeEntry.detail` property will be an listing the input arguments to the timed function. #### Net ('net') Details# When `performanceEntry.type` is equal to `'net'`, the `performanceNodeEntry.detail` property will be an containing additional information. If `performanceEntry.name` is equal to `connect`, the `detail` will contain the following properties: `host`, `port`. #### DNS ('dns') Details# When `performanceEntry.type` is equal to `'dns'`, the `performanceNodeEntry.detail` property will be an containing additional information. If `performanceEntry.name` is equal to `lookup`, the `detail` will contain the following properties: `hostname`, `family`, `hints`, `verbatim`, `addresses`. If `performanceEntry.name` is equal to `lookupService`, the `detail` will contain the following properties: `host`, `port`, `hostname`, `service`. If `performanceEntry.name` is equal to `queryxxx` or `getHostByAddr`, the `detail` will contain the following properties: `host`, `ttl`, `result`. The value of `result` is same as the result of `queryxxx` or `getHostByAddr`. ### Class: `PerformanceNodeTiming`# Added in: v8.5.0 * Extends: This property is an extension by Node.js. It is not available in Web browsers. Provides timing details for Node.js itself. The constructor of this class is not exposed to users. #### `performanceNodeTiming.bootstrapComplete`# Added in: v8.5.0 * Type: The high resolution millisecond timestamp at which the Node.js process completed bootstrapping. If bootstrapping has not yet finished, the property has the value of -1. #### `performanceNodeTiming.environment`# Added in: v8.5.0 * Type: The high resolution millisecond timestamp at which the Node.js environment was initialized. #### `performanceNodeTiming.idleTime`# Added in: v14.10.0, v12.19.0 * Type: The high resolution millisecond timestamp of the amount of time the event loop has been idle within the event loop's event provider (e.g. `epoll_wait`). This does not take CPU usage into consideration. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of 0. #### `performanceNodeTiming.loopExit`# Added in: v8.5.0 * Type: The high resolution millisecond timestamp at which the Node.js event loop exited. If the event loop has not yet exited, the property has the value of -1. It can only have a value of not -1 in a handler of the `'exit'` event. #### `performanceNodeTiming.loopStart`# Added in: v8.5.0 * Type: The high resolution millisecond timestamp at which the Node.js event loop started. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of -1. #### `performanceNodeTiming.nodeStart`# Added in: v8.5.0 * Type: The high resolution millisecond timestamp at which the Node.js process was initialized. #### `performanceNodeTiming.uvMetricsInfo`# Added in: v22.8.0, v20.18.0 * Returns: * `loopCount` Number of event loop iterations. * `events` Number of events that have been processed by the event handler. * `eventsWaiting` Number of events that were waiting to be processed when the event provider was called. This is a wrapper to the `uv_metrics_info` function. It returns the current set of event loop metrics. It is recommended to use this property inside a function whose execution was scheduled using `setImmediate` to avoid collecting metrics before finishing all operations scheduled during the current loop iteration. import { performance } from 'node:perf_hooks'; setImmediate(() => { console.log(performance.nodeTiming.uvMetricsInfo); }); #### `performanceNodeTiming.v8Start`# Added in: v8.5.0 * Type: The high resolution millisecond timestamp at which the V8 platform was initialized. ### Class: `PerformanceResourceTiming`# Added in: v18.2.0, v16.17.0 * Extends: Provides detailed network timing data regarding the loading of an application's resources. The constructor of this class is not exposed to users directly. #### `performanceResourceTiming.workerStart`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp at immediately before dispatching the `fetch` request. If the resource is not intercepted by a worker the property will always return 0. #### `performanceResourceTiming.redirectStart`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp that represents the start time of the fetch which initiates the redirect. #### `performanceResourceTiming.redirectEnd`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp that will be created immediately after receiving the last byte of the response of the last redirect. #### `performanceResourceTiming.fetchStart`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp immediately before the Node.js starts to fetch the resource. #### `performanceResourceTiming.domainLookupStart`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp immediately before the Node.js starts the domain name lookup for the resource. #### `performanceResourceTiming.domainLookupEnd`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp representing the time immediately after the Node.js finished the domain name lookup for the resource. #### `performanceResourceTiming.connectStart`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp representing the time immediately before Node.js starts to establish the connection to the server to retrieve the resource. #### `performanceResourceTiming.connectEnd`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp representing the time immediately after Node.js finishes establishing the connection to the server to retrieve the resource. #### `performanceResourceTiming.secureConnectionStart`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp representing the time immediately before Node.js starts the handshake process to secure the current connection. #### `performanceResourceTiming.requestStart`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp representing the time immediately before Node.js receives the first byte of the response from the server. #### `performanceResourceTiming.responseEnd`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: The high resolution millisecond timestamp representing the time immediately after Node.js receives the last byte of the resource or immediately before the transport connection is closed, whichever comes first. #### `performanceResourceTiming.transferSize`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: A number representing the size (in octets) of the fetched resource. The size includes the response header fields plus the response payload body. #### `performanceResourceTiming.encodedBodySize`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: A number representing the size (in octets) received from the fetch (HTTP or cache), of the payload body, before removing any applied content-codings. #### `performanceResourceTiming.decodedBodySize`# History VersionChanges v19.0.0 This property getter must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 * Type: A number representing the size (in octets) received from the fetch (HTTP or cache), of the message body, after removing any applied content-codings. #### `performanceResourceTiming.toJSON()`# History VersionChanges v19.0.0 This method must be called with the `PerformanceResourceTiming` object as the receiver. v18.2.0, v16.17.0 Added in: v18.2.0, v16.17.0 Returns a `object` that is the JSON representation of the `PerformanceResourceTiming` object ### Class: `PerformanceObserver`# Added in: v8.5.0 #### `PerformanceObserver.supportedEntryTypes`# Added in: v16.0.0 * Type: Get supported types. #### `new PerformanceObserver(callback)`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v8.5.0 Added in: v8.5.0 * `callback` * `list` * `observer` `PerformanceObserver` objects provide notifications when new `PerformanceEntry` instances have been added to the Performance Timeline. import { performance, PerformanceObserver } from 'node:perf_hooks'; const obs = new PerformanceObserver((list, observer) => { console.log(list.getEntries()); performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ entryTypes: ['mark'], buffered: true }); performance.mark('test'); Because `PerformanceObserver` instances introduce their own additional performance overhead, instances should not be left subscribed to notifications indefinitely. Users should disconnect observers as soon as they are no longer needed. The `callback` is invoked when a `PerformanceObserver` is notified about new `PerformanceEntry` instances. The callback receives a `PerformanceObserverEntryList` instance and a reference to the `PerformanceObserver`. #### `performanceObserver.disconnect()`# Added in: v8.5.0 Disconnects the `PerformanceObserver` instance from all notifications. #### `performanceObserver.observe(options)`# History VersionChanges v16.7.0 Updated to conform to Performance Timeline Level 2. The buffered option has been added back. v16.0.0 Updated to conform to User Timing Level 3. The buffered option has been removed. v8.5.0 Added in: v8.5.0 * `options` * `type` A single type. Must not be given if `entryTypes` is already specified. * `entryTypes` An array of strings identifying the types of instances the observer is interested in. If not provided an error will be thrown. * `buffered` If true, the observer callback is called with a list global `PerformanceEntry` buffered entries. If false, only `PerformanceEntry`s created after the time point are sent to the observer callback. Default: `false`. Subscribes the instance to notifications of new instances identified either by `options.entryTypes` or `options.type`: import { performance, PerformanceObserver } from 'node:perf_hooks'; const obs = new PerformanceObserver((list, observer) => { // Called once asynchronously. `list` contains three items. }); obs.observe({ type: 'mark' }); for (let n = 0; n < 3; n++) performance.mark(`test${n}`); #### `performanceObserver.takeRecords()`# Added in: v16.0.0 * Returns: Current list of entries stored in the performance observer, emptying it out. ### Class: `PerformanceObserverEntryList`# Added in: v8.5.0 The `PerformanceObserverEntryList` class is used to provide access to the `PerformanceEntry` instances passed to a `PerformanceObserver`. The constructor of this class is not exposed to users. #### `performanceObserverEntryList.getEntries()`# Added in: v8.5.0 * Returns: Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime`. import { performance, PerformanceObserver } from 'node:perf_hooks'; const obs = new PerformanceObserver((perfObserverList, observer) => { console.log(perfObserverList.getEntries()); /** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 81.465639, * duration: 0, * detail: null * }, * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 81.860064, * duration: 0, * detail: null * } * ] */ performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ type: 'mark' }); performance.mark('test'); performance.mark('meow'); #### `performanceObserverEntryList.getEntriesByName(name[, type])`# Added in: v8.5.0 * `name` * `type` * Returns: Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.name` is equal to `name`, and optionally, whose `performanceEntry.entryType` is equal to `type`. import { performance, PerformanceObserver } from 'node:perf_hooks'; const obs = new PerformanceObserver((perfObserverList, observer) => { console.log(perfObserverList.getEntriesByName('meow')); /** * [ * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 98.545991, * duration: 0, * detail: null * } * ] */ console.log(perfObserverList.getEntriesByName('nope')); // [] console.log(perfObserverList.getEntriesByName('test', 'mark')); /** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 63.518931, * duration: 0, * detail: null * } * ] */ console.log(perfObserverList.getEntriesByName('test', 'measure')); // [] performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ entryTypes: ['mark', 'measure'] }); performance.mark('test'); performance.mark('meow'); #### `performanceObserverEntryList.getEntriesByType(type)`# Added in: v8.5.0 * `type` * Returns: Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.entryType` is equal to `type`. import { performance, PerformanceObserver } from 'node:perf_hooks'; const obs = new PerformanceObserver((perfObserverList, observer) => { console.log(perfObserverList.getEntriesByType('mark')); /** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 55.897834, * duration: 0, * detail: null * }, * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 56.350146, * duration: 0, * detail: null * } * ] */ performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ type: 'mark' }); performance.mark('test'); performance.mark('meow'); ### `perf_hooks.createHistogram([options])`# Added in: v15.9.0, v14.18.0 * `options` * `lowest` | The lowest discernible value. Must be an integer value greater than 0. Default: `1`. * `highest` | The highest recordable value. Must be an integer value that is equal to or greater than two times `lowest`. Default: `Number.MAX_SAFE_INTEGER`. * `figures` The number of accuracy digits. Must be a number between `1` and `5`. Default: `3`. * Returns: Returns a . ### `perf_hooks.monitorEventLoopDelay([options])`# Added in: v11.10.0 * `options` * `resolution` The sampling rate in milliseconds. Must be greater than zero. Default: `10`. * Returns: This property is an extension by Node.js. It is not available in Web browsers. Creates an `IntervalHistogram` object that samples and reports the event loop delay over time. The delays will be reported in nanoseconds. Using a timer to detect approximate event loop delay works because the execution of timers is tied specifically to the lifecycle of the libuv event loop. That is, a delay in the loop will cause a delay in the execution of the timer, and those delays are specifically what this API is intended to detect. import { monitorEventLoopDelay } from 'node:perf_hooks'; const h = monitorEventLoopDelay({ resolution: 20 }); h.enable(); // Do something. h.disable(); console.log(h.min); console.log(h.max); console.log(h.mean); console.log(h.stddev); console.log(h.percentiles); console.log(h.percentile(50)); console.log(h.percentile(99)); ### Class: `Histogram`# Added in: v11.10.0 #### `histogram.count`# Added in: v17.4.0, v16.14.0 * Type: The number of samples recorded by the histogram. #### `histogram.countBigInt`# Added in: v17.4.0, v16.14.0 * Type: The number of samples recorded by the histogram. #### `histogram.exceeds`# Added in: v11.10.0 * Type: The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold. #### `histogram.exceedsBigInt`# Added in: v17.4.0, v16.14.0 * Type: The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold. #### `histogram.max`# Added in: v11.10.0 * Type: The maximum recorded event loop delay. #### `histogram.maxBigInt`# Added in: v17.4.0, v16.14.0 * Type: The maximum recorded event loop delay. #### `histogram.mean`# Added in: v11.10.0 * Type: The mean of the recorded event loop delays. #### `histogram.min`# Added in: v11.10.0 * Type: The minimum recorded event loop delay. #### `histogram.minBigInt`# Added in: v17.4.0, v16.14.0 * Type: The minimum recorded event loop delay. #### `histogram.percentile(percentile)`# Added in: v11.10.0 * `percentile` A percentile value in the range (0, 100]. * Returns: Returns the value at the given percentile. #### `histogram.percentileBigInt(percentile)`# Added in: v17.4.0, v16.14.0 * `percentile` A percentile value in the range (0, 100]. * Returns: Returns the value at the given percentile. #### `histogram.percentiles`# Added in: v11.10.0 * Type: Returns a `Map` object detailing the accumulated percentile distribution. #### `histogram.percentilesBigInt`# Added in: v17.4.0, v16.14.0 * Type: Returns a `Map` object detailing the accumulated percentile distribution. #### `histogram.reset()`# Added in: v11.10.0 Resets the collected histogram data. #### `histogram.stddev`# Added in: v11.10.0 * Type: The standard deviation of the recorded event loop delays. ### Class: `IntervalHistogram extends Histogram`# A `Histogram` that is periodically updated on a given interval. #### `histogram.disable()`# Added in: v11.10.0 * Returns: Disables the update interval timer. Returns `true` if the timer was stopped, `false` if it was already stopped. #### `histogram.enable()`# Added in: v11.10.0 * Returns: Enables the update interval timer. Returns `true` if the timer was started, `false` if it was already started. #### `histogram[Symbol.dispose]()`# Added in: v24.2.0 Disables the update interval timer when the histogram is disposed. const { monitorEventLoopDelay } = require('node:perf_hooks'); { using hist = monitorEventLoopDelay({ resolution: 20 }); hist.enable(); // The histogram will be disabled when the block is exited. } #### Cloning an `IntervalHistogram`# instances can be cloned via . On the receiving end, the histogram is cloned as a plain object that does not implement the `enable()` and `disable()` methods. ### Class: `RecordableHistogram extends Histogram`# Added in: v15.9.0, v14.18.0 #### `histogram.add(other)`# Added in: v17.4.0, v16.14.0 * `other` Adds the values from `other` to this histogram. #### `histogram.record(val)`# Added in: v15.9.0, v14.18.0 * `val` | The amount to record in the histogram. #### `histogram.recordDelta()`# Added in: v15.9.0, v14.18.0 Calculates the amount of time (in nanoseconds) that has passed since the previous call to `recordDelta()` and records that amount in the histogram. ### Examples# #### Measuring the duration of async operations# The following example uses the Async Hooks and Performance APIs to measure the actual duration of a Timeout operation (including the amount of time it took to execute the callback). import { createHook } from 'node:async_hooks'; import { performance, PerformanceObserver } from 'node:perf_hooks'; const set = new Set(); const hook = createHook({ init(id, type) { if (type === 'Timeout') { performance.mark(`Timeout-${id}-Init`); set.add(id); } }, destroy(id) { if (set.has(id)) { set.delete(id); performance.mark(`Timeout-${id}-Destroy`); performance.measure(`Timeout-${id}`, `Timeout-${id}-Init`, `Timeout-${id}-Destroy`); } }, }); hook.enable(); const obs = new PerformanceObserver((list, observer) => { console.log(list.getEntries()[0]); performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ entryTypes: ['measure'], buffered: true }); setTimeout(() => {}, 1000); #### Measuring how long it takes to load dependencies# The following example measures the duration of `require()` operations to load dependencies: import { performance, PerformanceObserver } from 'node:perf_hooks'; // Activate the observer const obs = new PerformanceObserver((list) => { const entries = list.getEntries(); entries.forEach((entry) => { console.log(`import('${entry[0]}')`, entry.duration); }); performance.clearMarks(); performance.clearMeasures(); obs.disconnect(); }); obs.observe({ entryTypes: ['function'], buffered: true }); const timedImport = performance.timerify(async (module) => { return await import(module); }); await timedImport('some-module'); #### Measuring how long one HTTP round-trip takes# The following example is used to trace the time spent by HTTP client (`OutgoingMessage`) and HTTP request (`IncomingMessage`). For HTTP client, it means the time interval between starting the request and receiving the response, and for HTTP request, it means the time interval between receiving the request and sending the response: import { PerformanceObserver } from 'node:perf_hooks'; import { createServer, get } from 'node:http'; const obs = new PerformanceObserver((items) => { items.getEntries().forEach((item) => { console.log(item); }); }); obs.observe({ entryTypes: ['http'] }); const PORT = 8080; createServer((req, res) => { res.end('ok'); }).listen(PORT, () => { get(`http://127.0.0.1:${PORT}`); }); #### Measuring how long the `net.connect` (only for TCP) takes when the connection is successful# import { PerformanceObserver } from 'node:perf_hooks'; import { connect, createServer } from 'node:net'; const obs = new PerformanceObserver((items) => { items.getEntries().forEach((item) => { console.log(item); }); }); obs.observe({ entryTypes: ['net'] }); const PORT = 8080; createServer((socket) => { socket.destroy(); }).listen(PORT, () => { connect(PORT); }); #### Measuring how long the DNS takes when the request is successful# import { PerformanceObserver } from 'node:perf_hooks'; import { lookup, promises } from 'node:dns'; const obs = new PerformanceObserver((items) => { items.getEntries().forEach((item) => { console.log(item); }); }); obs.observe({ entryTypes: ['dns'] }); lookup('localhost', () => {}); promises.resolve('localhost'); ## Permissions# Permissions can be used to control what system resources the Node.js process has access to or what actions the process can take with those resources. * Process-based permissions control the Node.js process's access to resources. The resource can be entirely allowed or denied, or actions related to it can be controlled. For example, file system reads can be allowed while denying writes. This feature does not protect against malicious code. According to the Node.js Security Policy, Node.js trusts any code it is asked to run. The permission model implements a "seat belt" approach, which prevents trusted code from unintentionally changing files or using resources that access has not explicitly been granted to. It does not provide security guarantees in the presence of malicious code. Malicious code can bypass the permission model and execute arbitrary code without the restrictions imposed by the permission model. If you find a potential security vulnerability, please refer to our Security Policy. ### Process-based permissions# #### Permission Model# History VersionChanges v23.5.0, v22.13.0 This feature is no longer experimental. v20.0.0 Added in: v20.0.0 Stability: 2 \- Stable The Node.js Permission Model is a mechanism for restricting access to specific resources during execution. The API exists behind a flag `--permission` which when enabled, will restrict access to all available permissions. The available permissions are documented by the `--permission` flag. When starting Node.js with `--permission`, the ability to access the file system through the `fs` module, spawn processes, use `node:worker_threads`, use native addons, use WASI, and enable the runtime inspector will be restricted. $ node --permission index.js Error: Access to this API has been restricted at node:internal/main/run_main_module:23:47 { code: 'ERR_ACCESS_DENIED', permission: 'FileSystemRead', resource: '/home/user/index.js' } Allowing access to spawning a process and creating worker threads can be done using the `--allow-child-process` and `--allow-worker` respectively. To allow native addons when using permission model, use the `--allow-addons` flag. For WASI, use the `--allow-wasi` flag. ##### Runtime API# When enabling the Permission Model through the `--permission` flag a new property `permission` is added to the `process` object. This property contains one function: ###### `permission.has(scope[, reference])`# API call to check permissions at runtime (`permission.has()`) process.permission.has('fs.write'); // true process.permission.has('fs.write', '/home/rafaelgss/protected-folder'); // true process.permission.has('fs.read'); // true process.permission.has('fs.read', '/home/rafaelgss/protected-folder'); // false ##### File System Permissions# The Permission Model, by default, restricts access to the file system through the `node:fs` module. It does not guarantee that users will not be able to access the file system through other means, such as through the `node:sqlite` module. To allow access to the file system, use the `--allow-fs-read` and `--allow-fs-write` flags: $ node --permission --allow-fs-read=* --allow-fs-write=* index.js Hello world! By default the entrypoints of your application are included in the allowed file system read list. For example: $ node --permission index.js * `index.js` will be included in the allowed file system read list $ node -r /path/to/custom-require.js --permission index.js. * `/path/to/custom-require.js` will be included in the allowed file system read list. * `index.js` will be included in the allowed file system read list. The valid arguments for both flags are: * `*` \- To allow all `FileSystemRead` or `FileSystemWrite` operations, respectively. * Relative paths to the current working directory. * Absolute paths. Example: * `--allow-fs-read=*` \- It will allow all `FileSystemRead` operations. * `--allow-fs-write=*` \- It will allow all `FileSystemWrite` operations. * `--allow-fs-write=/tmp/` \- It will allow `FileSystemWrite` access to the `/tmp/` folder. * `--allow-fs-read=/tmp/ --allow-fs-read=/home/.gitignore` \- It allows `FileSystemRead` access to the `/tmp/` folder and the `/home/.gitignore` path. Wildcards are supported too: * `--allow-fs-read=/home/test*` will allow read access to everything that matches the wildcard. e.g: `/home/test/file1` or `/home/test2` After passing a wildcard character (`*`) all subsequent characters will be ignored. For example: `/home/*.js` will work similar to `/home/*`. When the permission model is initialized, it will automatically add a wildcard (*) if the specified directory exists. For example, if `/home/test/files` exists, it will be treated as `/home/test/files/*`. However, if the directory does not exist, the wildcard will not be added, and access will be limited to `/home/test/files`. If you want to allow access to a folder that does not exist yet, make sure to explicitly include the wildcard: `/my-path/folder-do-not-exist/*`. ##### Using the Permission Model with `npx`# If you're using `npx` to execute a Node.js script, you can enable the Permission Model by passing the `--node-options` flag. For example: npx --node-options="--permission" package-name This sets the `NODE_OPTIONS` environment variable for all Node.js processes spawned by `npx`, without affecting the `npx` process itself. FileSystemRead Error with `npx` The above command will likely throw a `FileSystemRead` invalid access error because Node.js requires file system read access to locate and execute the package. To avoid this: 1. Using a Globally Installed Package Grant read access to the global `node_modules` directory by running: npx --node-options="--permission --allow-fs-read=$(npm prefix -g)" package-name 2. Using the `npx` Cache If you are installing the package temporarily or relying on the `npx` cache, grant read access to the npm cache directory: npx --node-options="--permission --allow-fs-read=$(npm config get cache)" package-name Any arguments you would normally pass to `node` (e.g., `--allow-*` flags) can also be passed through the `--node-options` flag. This flexibility makes it easy to configure permissions as needed when using `npx`. ##### Permission Model constraints# There are constraints you need to know before using this system: * The model does not inherit to a worker thread. * When using the Permission Model the following features will be restricted: * Native modules * Child process * Worker Threads * Inspector protocol * File system access * WASI * The Permission Model is initialized after the Node.js environment is set up. However, certain flags such as `--env-file` or `--openssl-config` are designed to read files before environment initialization. As a result, such flags are not subject to the rules of the Permission Model. The same applies for V8 flags that can be set via runtime through `v8.setFlagsFromString`. * OpenSSL engines cannot be requested at runtime when the Permission Model is enabled, affecting the built-in crypto, https, and tls modules. * Run-Time Loadable Extensions cannot be loaded when the Permission Model is enabled, affecting the sqlite module. * Using existing file descriptors via the `node:fs` module bypasses the Permission Model. ##### Limitations and Known Issues# * Symbolic links will be followed even to locations outside of the set of paths that access has been granted to. Relative symbolic links may allow access to arbitrary files and directories. When starting applications with the permission model enabled, you must ensure that no paths to which access has been granted contain relative symbolic links. ## Process# Source Code: lib/process.js The `process` object provides information about, and control over, the current Node.js process. import process from 'node:process'; ### Process events# The `process` object is an instance of `EventEmitter`. #### Event: `'beforeExit'`# Added in: v0.11.12 The `'beforeExit'` event is emitted when Node.js empties its event loop and has no additional work to schedule. Normally, the Node.js process will exit when there is no work scheduled, but a listener registered on the `'beforeExit'` event can make asynchronous calls, and thereby cause the Node.js process to continue. The listener callback function is invoked with the value of `process.exitCode` passed as the only argument. The `'beforeExit'` event is not emitted for conditions causing explicit termination, such as calling `process.exit()` or uncaught exceptions. The `'beforeExit'` should not be used as an alternative to the `'exit'` event unless the intention is to schedule additional work. import process from 'node:process'; process.on('beforeExit', (code) => { console.log('Process beforeExit event with code: ', code); }); process.on('exit', (code) => { console.log('Process exit event with code: ', code); }); console.log('This message is displayed first.'); // Prints: // This message is displayed first. // Process beforeExit event with code: 0 // Process exit event with code: 0 #### Event: `'disconnect'`# Added in: v0.7.7 If the Node.js process is spawned with an IPC channel (see the Child Process and Cluster documentation), the `'disconnect'` event will be emitted when the IPC channel is closed. #### Event: `'exit'`# Added in: v0.1.7 * `code` The `'exit'` event is emitted when the Node.js process is about to exit as a result of either: * The `process.exit()` method being called explicitly; * The Node.js event loop no longer having any additional work to perform. There is no way to prevent the exiting of the event loop at this point, and once all `'exit'` listeners have finished running the Node.js process will terminate. The listener callback function is invoked with the exit code specified either by the `process.exitCode` property, or the `exitCode` argument passed to the `process.exit()` method. import process from 'node:process'; process.on('exit', (code) => { console.log(`About to exit with code: ${code}`); }); Listener functions must only perform synchronous operations. The Node.js process will exit immediately after calling the `'exit'` event listeners causing any additional work still queued in the event loop to be abandoned. In the following example, for instance, the timeout will never occur: import process from 'node:process'; process.on('exit', (code) => { setTimeout(() => { console.log('This will not run'); }, 0); }); #### Event: `'message'`# Added in: v0.5.10 * `message` | | | | a parsed JSON object or a serializable primitive value. * `sendHandle` | a `net.Server` or `net.Socket` object, or undefined. If the Node.js process is spawned with an IPC channel (see the Child Process and Cluster documentation), the `'message'` event is emitted whenever a message sent by a parent process using `childprocess.send()` is received by the child process. The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent. If the `serialization` option was set to `advanced` used when spawning the process, the `message` argument can contain data that JSON is not able to represent. See Advanced serialization for `child_process` for more details. #### Event: `'multipleResolves'`# Added in: v10.12.0Deprecated since: v17.6.0, v16.15.0 Stability: 0 \- Deprecated * `type` The resolution type. One of `'resolve'` or `'reject'`. * `promise` The promise that resolved or rejected more than once. * `value` The value with which the promise was either resolved or rejected after the original resolve. The `'multipleResolves'` event is emitted whenever a `Promise` has been either: * Resolved more than once. * Rejected more than once. * Rejected after resolve. * Resolved after reject. This is useful for tracking potential errors in an application while using the `Promise` constructor, as multiple resolutions are silently swallowed. However, the occurrence of this event does not necessarily indicate an error. For example, `Promise.race()` can trigger a `'multipleResolves'` event. Because of the unreliability of the event in cases like the `Promise.race()` example above it has been deprecated. import process from 'node:process'; process.on('multipleResolves', (type, promise, reason) => { console.error(type, promise, reason); setImmediate(() => process.exit(1)); }); async function main() { try { return await new Promise((resolve, reject) => { resolve('First call'); resolve('Swallowed resolve'); reject(new Error('Swallowed reject')); }); } catch { throw new Error('Failed'); } } main().then(console.log); // resolve: Promise { 'First call' } 'Swallowed resolve' // reject: Promise { 'First call' } Error: Swallowed reject // at Promise (*) // at new Promise () // at main (*) // First call #### Event: `'rejectionHandled'`# Added in: v1.4.1 * `promise` The late handled promise. The `'rejectionHandled'` event is emitted whenever a `Promise` has been rejected and an error handler was attached to it (using `promise.catch()`, for example) later than one turn of the Node.js event loop. The `Promise` object would have previously been emitted in an `'unhandledRejection'` event, but during the course of processing gained a rejection handler. There is no notion of a top level for a `Promise` chain at which rejections can always be handled. Being inherently asynchronous in nature, a `Promise` rejection can be handled at a future point in time, possibly much later than the event loop turn it takes for the `'unhandledRejection'` event to be emitted. Another way of stating this is that, unlike in synchronous code where there is an ever-growing list of unhandled exceptions, with Promises there can be a growing-and-shrinking list of unhandled rejections. In synchronous code, the `'uncaughtException'` event is emitted when the list of unhandled exceptions grows. In asynchronous code, the `'unhandledRejection'` event is emitted when the list of unhandled rejections grows, and the `'rejectionHandled'` event is emitted when the list of unhandled rejections shrinks. import process from 'node:process'; const unhandledRejections = new Map(); process.on('unhandledRejection', (reason, promise) => { unhandledRejections.set(promise, reason); }); process.on('rejectionHandled', (promise) => { unhandledRejections.delete(promise); }); In this example, the `unhandledRejections` `Map` will grow and shrink over time, reflecting rejections that start unhandled and then become handled. It is possible to record such errors in an error log, either periodically (which is likely best for long-running application) or upon process exit (which is likely most convenient for scripts). #### Event: `'workerMessage'`# Added in: v22.5.0, v20.19.0 * `value` A value transmitted using `postMessageToThread()`. * `source` The transmitting worker thread ID or `0` for the main thread. The `'workerMessage'` event is emitted for any incoming message send by the other party by using `postMessageToThread()`. #### Event: `'uncaughtException'`# History VersionChanges v12.0.0, v10.17.0 Added the `origin` argument. v0.1.18 Added in: v0.1.18 * `err` The uncaught exception. * `origin` Indicates if the exception originates from an unhandled rejection or from a synchronous error. Can either be `'uncaughtException'` or `'unhandledRejection'`. The latter is used when an exception happens in a `Promise` based async context (or if a `Promise` is rejected) and `--unhandled-rejections` flag set to `strict` or `throw` (which is the default) and the rejection is not handled, or when a rejection happens during the command line entry point's ES module static loading phase. The `'uncaughtException'` event is emitted when an uncaught JavaScript exception bubbles all the way back to the event loop. By default, Node.js handles such exceptions by printing the stack trace to `stderr` and exiting with code 1, overriding any previously set `process.exitCode`. Adding a handler for the `'uncaughtException'` event overrides this default behavior. Alternatively, change the `process.exitCode` in the `'uncaughtException'` handler which will result in the process exiting with the provided exit code. Otherwise, in the presence of such handler the process will exit with 0. import process from 'node:process'; import fs from 'node:fs'; process.on('uncaughtException', (err, origin) => { fs.writeSync( process.stderr.fd, `Caught exception: ${err}\n` + `Exception origin: ${origin}\n`, ); }); setTimeout(() => { console.log('This will still run.'); }, 500); // Intentionally cause an exception, but don't catch it. nonexistentFunc(); console.log('This will not run.'); It is possible to monitor `'uncaughtException'` events without overriding the default behavior to exit the process by installing a `'uncaughtExceptionMonitor'` listener. ##### Warning: Using `'uncaughtException'` correctly# `'uncaughtException'` is a crude mechanism for exception handling intended to be used only as a last resort. The event should not be used as an equivalent to `On Error Resume Next`. Unhandled exceptions inherently mean that an application is in an undefined state. Attempting to resume application code without properly recovering from the exception can cause additional unforeseen and unpredictable issues. Exceptions thrown from within the event handler will not be caught. Instead the process will exit with a non-zero exit code and the stack trace will be printed. This is to avoid infinite recursion. Attempting to resume normally after an uncaught exception can be similar to pulling out the power cord when upgrading a computer. Nine out of ten times, nothing happens. But the tenth time, the system becomes corrupted. The correct use of `'uncaughtException'` is to perform synchronous cleanup of allocated resources (e.g. file descriptors, handles, etc) before shutting down the process. It is not safe to resume normal operation after `'uncaughtException'`. To restart a crashed application in a more reliable way, whether `'uncaughtException'` is emitted or not, an external monitor should be employed in a separate process to detect application failures and recover or restart as needed. #### Event: `'uncaughtExceptionMonitor'`# Added in: v13.7.0, v12.17.0 * `err` The uncaught exception. * `origin` Indicates if the exception originates from an unhandled rejection or from synchronous errors. Can either be `'uncaughtException'` or `'unhandledRejection'`. The latter is used when an exception happens in a `Promise` based async context (or if a `Promise` is rejected) and `--unhandled-rejections` flag set to `strict` or `throw` (which is the default) and the rejection is not handled, or when a rejection happens during the command line entry point's ES module static loading phase. The `'uncaughtExceptionMonitor'` event is emitted before an `'uncaughtException'` event is emitted or a hook installed via `process.setUncaughtExceptionCaptureCallback()` is called. Installing an `'uncaughtExceptionMonitor'` listener does not change the behavior once an `'uncaughtException'` event is emitted. The process will still crash if no `'uncaughtException'` listener is installed. import process from 'node:process'; process.on('uncaughtExceptionMonitor', (err, origin) => { MyMonitoringTool.logSync(err, origin); }); // Intentionally cause an exception, but don't catch it. nonexistentFunc(); // Still crashes Node.js #### Event: `'unhandledRejection'`# History VersionChanges v7.0.0 Not handling `Promise` rejections is deprecated. v6.6.0 Unhandled `Promise` rejections will now emit a process warning. v1.4.1 Added in: v1.4.1 * `reason` | The object with which the promise was rejected (typically an `Error` object). * `promise` The rejected promise. The `'unhandledRejection'` event is emitted whenever a `Promise` is rejected and no error handler is attached to the promise within a turn of the event loop. When programming with Promises, exceptions are encapsulated as "rejected promises". Rejections can be caught and handled using `promise.catch()` and are propagated through a `Promise` chain. The `'unhandledRejection'` event is useful for detecting and keeping track of promises that were rejected whose rejections have not yet been handled. import process from 'node:process'; process.on('unhandledRejection', (reason, promise) => { console.log('Unhandled Rejection at:', promise, 'reason:', reason); // Application specific logging, throwing an error, or other logic here }); somePromise.then((res) => { return reportToUser(JSON.pasre(res)); // Note the typo (`pasre`) }); // No `.catch()` or `.then()` The following will also trigger the `'unhandledRejection'` event to be emitted: import process from 'node:process'; function SomeResource() { // Initially set the loaded status to a rejected promise this.loaded = Promise.reject(new Error('Resource not yet loaded!')); } const resource = new SomeResource(); // no .catch or .then on resource.loaded for at least a turn In this example case, it is possible to track the rejection as a developer error as would typically be the case for other `'unhandledRejection'` events. To address such failures, a non-operational `.catch(() => { })` handler may be attached to `resource.loaded`, which would prevent the `'unhandledRejection'` event from being emitted. If an `'unhandledRejection'` event is emitted but not handled it will be raised as an uncaught exception. This alongside other behaviors of `'unhandledRejection'` events can changed via the `--unhandled-rejections` flag. #### Event: `'warning'`# Added in: v6.0.0 * `warning` Key properties of the warning are: * `name` The name of the warning. Default: `'Warning'`. * `message` A system-provided description of the warning. * `stack` A stack trace to the location in the code where the warning was issued. The `'warning'` event is emitted whenever Node.js emits a process warning. A process warning is similar to an error in that it describes exceptional conditions that are being brought to the user's attention. However, warnings are not part of the normal Node.js and JavaScript error handling flow. Node.js can emit warnings whenever it detects bad coding practices that could lead to sub-optimal application performance, bugs, or security vulnerabilities. import process from 'node:process'; process.on('warning', (warning) => { console.warn(warning.name); // Print the warning name console.warn(warning.message); // Print the warning message console.warn(warning.stack); // Print the stack trace }); By default, Node.js will print process warnings to `stderr`. The `--no-warnings` command-line option can be used to suppress the default console output but the `'warning'` event will still be emitted by the `process` object. Currently, it is not possible to suppress specific warning types other than deprecation warnings. To suppress deprecation warnings, check out the `--no-deprecation` flag. The following example illustrates the warning that is printed to `stderr` when too many listeners have been added to an event: $ node > events.defaultMaxListeners = 1; > process.on('foo', () => {}); > process.on('foo', () => {}); > (node:38638) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 2 foo listeners added. Use emitter.setMaxListeners() to increase limit In contrast, the following example turns off the default warning output and adds a custom handler to the `'warning'` event: $ node --no-warnings > const p = process.on('warning', (warning) => console.warn('Do not do that!')); > events.defaultMaxListeners = 1; > process.on('foo', () => {}); > process.on('foo', () => {}); > Do not do that! The `--trace-warnings` command-line option can be used to have the default console output for warnings include the full stack trace of the warning. Launching Node.js using the `--throw-deprecation` command-line flag will cause custom deprecation warnings to be thrown as exceptions. Using the `--trace-deprecation` command-line flag will cause the custom deprecation to be printed to `stderr` along with the stack trace. Using the `--no-deprecation` command-line flag will suppress all reporting of the custom deprecation. The `*-deprecation` command-line flags only affect warnings that use the name `'DeprecationWarning'`. ##### Emitting custom warnings# See the `process.emitWarning()` method for issuing custom or application-specific warnings. ##### Node.js warning names# There are no strict guidelines for warning types (as identified by the `name` property) emitted by Node.js. New types of warnings can be added at any time. A few of the warning types that are most common include: * `'DeprecationWarning'` \- Indicates use of a deprecated Node.js API or feature. Such warnings must include a `'code'` property identifying the deprecation code. * `'ExperimentalWarning'` \- Indicates use of an experimental Node.js API or feature. Such features must be used with caution as they may change at any time and are not subject to the same strict semantic-versioning and long-term support policies as supported features. * `'MaxListenersExceededWarning'` \- Indicates that too many listeners for a given event have been registered on either an `EventEmitter` or `EventTarget`. This is often an indication of a memory leak. * `'TimeoutOverflowWarning'` \- Indicates that a numeric value that cannot fit within a 32-bit signed integer has been provided to either the `setTimeout()` or `setInterval()` functions. * `'TimeoutNegativeWarning'` \- Indicates that a negative number has provided to either the `setTimeout()` or `setInterval()` functions. * `'TimeoutNaNWarning'` \- Indicates that a value which is not a number has provided to either the `setTimeout()` or `setInterval()` functions. * `'UnsupportedWarning'` \- Indicates use of an unsupported option or feature that will be ignored rather than treated as an error. One example is use of the HTTP response status message when using the HTTP/2 compatibility API. #### Event: `'worker'`# Added in: v16.2.0, v14.18.0 * `worker` The that was created. The `'worker'` event is emitted after a new thread has been created. #### Signal events# Signal events will be emitted when the Node.js process receives a signal. Please refer to `signal(7)` for a listing of standard POSIX signal names such as `'SIGINT'`, `'SIGHUP'`, etc. Signals are not available on `Worker` threads. The signal handler will receive the signal's name (`'SIGINT'`, `'SIGTERM'`, etc.) as the first argument. The name of each event will be the uppercase common name for the signal (e.g. `'SIGINT'` for `SIGINT` signals). import process from 'node:process'; // Begin reading from stdin so the process does not exit. process.stdin.resume(); process.on('SIGINT', () => { console.log('Received SIGINT. Press Control-D to exit.'); }); // Using a single function to handle multiple signals function handle(signal) { console.log(`Received ${signal}`); } process.on('SIGINT', handle); process.on('SIGTERM', handle); * `'SIGUSR1'` is reserved by Node.js to start the debugger. It's possible to install a listener but doing so might interfere with the debugger. * `'SIGTERM'` and `'SIGINT'` have default handlers on non-Windows platforms that reset the terminal mode before exiting with code `128 + signal number`. If one of these signals has a listener installed, its default behavior will be removed (Node.js will no longer exit). * `'SIGPIPE'` is ignored by default. It can have a listener installed. * `'SIGHUP'` is generated on Windows when the console window is closed, and on other platforms under various similar conditions. See `signal(7)`. It can have a listener installed, however Node.js will be unconditionally terminated by Windows about 10 seconds later. On non-Windows platforms, the default behavior of `SIGHUP` is to terminate Node.js, but once a listener has been installed its default behavior will be removed. * `'SIGTERM'` is not supported on Windows, it can be listened on. * `'SIGINT'` from the terminal is supported on all platforms, and can usually be generated with `Ctrl`+`C` (though this may be configurable). It is not generated when terminal raw mode is enabled and `Ctrl`+`C` is used. * `'SIGBREAK'` is delivered on Windows when `Ctrl`+`Break` is pressed. On non-Windows platforms, it can be listened on, but there is no way to send or generate it. * `'SIGWINCH'` is delivered when the console has been resized. On Windows, this will only happen on write to the console when the cursor is being moved, or when a readable tty is used in raw mode. * `'SIGKILL'` cannot have a listener installed, it will unconditionally terminate Node.js on all platforms. * `'SIGSTOP'` cannot have a listener installed. * `'SIGBUS'`, `'SIGFPE'`, `'SIGSEGV'`, and `'SIGILL'`, when not raised artificially using `kill(2)`, inherently leave the process in a state from which it is not safe to call JS listeners. Doing so might cause the process to stop responding. * `0` can be sent to test for the existence of a process, it has no effect if the process exists, but will throw an error if the process does not exist. Windows does not support signals so has no equivalent to termination by signal, but Node.js offers some emulation with `process.kill()`, and `subprocess.kill()`: * Sending `SIGINT`, `SIGTERM`, and `SIGKILL` will cause the unconditional termination of the target process, and afterwards, subprocess will report that the process was terminated by signal. * Sending signal `0` can be used as a platform independent way to test for the existence of a process. ### `process.abort()`# Added in: v0.7.0 The `process.abort()` method causes the Node.js process to exit immediately and generate a core file. This feature is not available in `Worker` threads. ### `process.allowedNodeEnvironmentFlags`# Added in: v10.10.0 * Type: The `process.allowedNodeEnvironmentFlags` property is a special, read-only `Set` of flags allowable within the `NODE_OPTIONS` environment variable. `process.allowedNodeEnvironmentFlags` extends `Set`, but overrides `Set.prototype.has` to recognize several different possible flag representations. `process.allowedNodeEnvironmentFlags.has()` will return `true` in the following cases: * Flags may omit leading single (`-`) or double (`--`) dashes; e.g., `inspect-brk` for `--inspect-brk`, or `r` for `-r`. * Flags passed through to V8 (as listed in `--v8-options`) may replace one or more non-leading dashes for an underscore, or vice-versa; e.g., `--perf_basic_prof`, `--perf-basic-prof`, `--perf_basic-prof`, etc. * Flags may contain one or more equals (`=`) characters; all characters after and including the first equals will be ignored; e.g., `--stack-trace-limit=100`. * Flags must be allowable within `NODE_OPTIONS`. When iterating over `process.allowedNodeEnvironmentFlags`, flags will appear only once; each will begin with one or more dashes. Flags passed through to V8 will contain underscores instead of non-leading dashes: import { allowedNodeEnvironmentFlags } from 'node:process'; allowedNodeEnvironmentFlags.forEach((flag) => { // -r // --inspect-brk // --abort_on_uncaught_exception // ... }); The methods `add()`, `clear()`, and `delete()` of `process.allowedNodeEnvironmentFlags` do nothing, and will fail silently. If Node.js was compiled without `NODE_OPTIONS` support (shown in `process.config`), `process.allowedNodeEnvironmentFlags` will contain what would have been allowable. ### `process.arch`# Added in: v0.5.0 * Type: The operating system CPU architecture for which the Node.js binary was compiled. Possible values are: `'arm'`, `'arm64'`, `'ia32'`, `'loong64'`, `'mips'`, `'mipsel'`, `'ppc64'`, `'riscv64'`, `'s390'`, `'s390x'`, and `'x64'`. import { arch } from 'node:process'; console.log(`This processor architecture is ${arch}`); ### `process.argv`# Added in: v0.1.27 * Type: The `process.argv` property returns an array containing the command-line arguments passed when the Node.js process was launched. The first element will be `process.execPath`. See `process.argv0` if access to the original value of `argv[0]` is needed. The second element will be the path to the JavaScript file being executed. The remaining elements will be any additional command-line arguments. For example, assuming the following script for `process-args.js`: import { argv } from 'node:process'; // print process.argv argv.forEach((val, index) => { console.log(`${index}: ${val}`); }); Launching the Node.js process as: node process-args.js one two=three four Would generate the output: 0: /usr/local/bin/node 1: /Users/mjr/work/node/process-args.js 2: one 3: two=three 4: four ### `process.argv0`# Added in: v6.4.0 * Type: The `process.argv0` property stores a read-only copy of the original value of `argv[0]` passed when Node.js starts. $ bash -c 'exec -a customArgv0 ./node' > process.argv[0] '/Volumes/code/external/node/out/Release/node' > process.argv0 'customArgv0' ### `process.availableMemory()`# History VersionChanges v24.0.0 Change stability index for this feature from Experimental to Stable. v22.0.0, v20.13.0 Added in: v22.0.0, v20.13.0 * Type: Gets the amount of free memory that is still available to the process (in bytes). See `uv_get_available_memory` for more information. ### `process.channel`# History VersionChanges v14.0.0 The object no longer accidentally exposes native C++ bindings. v7.1.0 Added in: v7.1.0 * Type: If the Node.js process was spawned with an IPC channel (see the Child Process documentation), the `process.channel` property is a reference to the IPC channel. If no IPC channel exists, this property is `undefined`. #### `process.channel.ref()`# Added in: v7.1.0 This method makes the IPC channel keep the event loop of the process running if `.unref()` has been called before. Typically, this is managed through the number of `'disconnect'` and `'message'` listeners on the `process` object. However, this method can be used to explicitly request a specific behavior. #### `process.channel.unref()`# Added in: v7.1.0 This method makes the IPC channel not keep the event loop of the process running, and lets it finish even while the channel is open. Typically, this is managed through the number of `'disconnect'` and `'message'` listeners on the `process` object. However, this method can be used to explicitly request a specific behavior. ### `process.chdir(directory)`# Added in: v0.1.17 * `directory` The `process.chdir()` method changes the current working directory of the Node.js process or throws an exception if doing so fails (for instance, if the specified `directory` does not exist). import { chdir, cwd } from 'node:process'; console.log(`Starting directory: ${cwd()}`); try { chdir('/tmp'); console.log(`New directory: ${cwd()}`); } catch (err) { console.error(`chdir: ${err}`); } This feature is not available in `Worker` threads. ### `process.config`# History VersionChanges v19.0.0 The `process.config` object is now frozen. v16.0.0 Modifying process.config has been deprecated. v0.7.7 Added in: v0.7.7 * Type: The `process.config` property returns a frozen `Object` containing the JavaScript representation of the configure options used to compile the current Node.js executable. This is the same as the `config.gypi` file that was produced when running the `./configure` script. An example of the possible output looks like: { target_defaults: { cflags: [], default_configuration: 'Release', defines: [], include_dirs: [], libraries: [] }, variables: { host_arch: 'x64', napi_build_version: 5, node_install_npm: 'true', node_prefix: '', node_shared_cares: 'false', node_shared_http_parser: 'false', node_shared_libuv: 'false', node_shared_zlib: 'false', node_use_openssl: 'true', node_shared_openssl: 'false', target_arch: 'x64', v8_use_snapshot: 1 } } ### `process.connected`# Added in: v0.7.2 * Type: If the Node.js process is spawned with an IPC channel (see the Child Process and Cluster documentation), the `process.connected` property will return `true` so long as the IPC channel is connected and will return `false` after `process.disconnect()` is called. Once `process.connected` is `false`, it is no longer possible to send messages over the IPC channel using `process.send()`. ### `process.constrainedMemory()`# History VersionChanges v24.0.0 Change stability index for this feature from Experimental to Stable. v22.0.0, v20.13.0 Aligned return value with `uv_get_constrained_memory`. v19.6.0, v18.15.0 Added in: v19.6.0, v18.15.0 * Type: Gets the amount of memory available to the process (in bytes) based on limits imposed by the OS. If there is no such constraint, or the constraint is unknown, `0` is returned. See `uv_get_constrained_memory` for more information. ### `process.cpuUsage([previousValue])`# Added in: v6.1.0 * `previousValue` A previous return value from calling `process.cpuUsage()` * Returns: * `user` * `system` The `process.cpuUsage()` method returns the user and system CPU time usage of the current process, in an object with properties `user` and `system`, whose values are microsecond values (millionth of a second). These values measure time spent in user and system code respectively, and may end up being greater than actual elapsed time if multiple CPU cores are performing work for this process. The result of a previous call to `process.cpuUsage()` can be passed as the argument to the function, to get a diff reading. import { cpuUsage } from 'node:process'; const startUsage = cpuUsage(); // { user: 38579, system: 6986 } // spin the CPU for 500 milliseconds const now = Date.now(); while (Date.now() - now < 500); console.log(cpuUsage(startUsage)); // { user: 514883, system: 11226 } ### `process.cwd()`# Added in: v0.1.8 * Returns: The `process.cwd()` method returns the current working directory of the Node.js process. import { cwd } from 'node:process'; console.log(`Current directory: ${cwd()}`); ### `process.debugPort`# Added in: v0.7.2 * Type: The port used by the Node.js debugger when enabled. import process from 'node:process'; process.debugPort = 5858; ### `process.disconnect()`# Added in: v0.7.2 If the Node.js process is spawned with an IPC channel (see the Child Process and Cluster documentation), the `process.disconnect()` method will close the IPC channel to the parent process, allowing the child process to exit gracefully once there are no other connections keeping it alive. The effect of calling `process.disconnect()` is the same as calling `ChildProcess.disconnect()` from the parent process. If the Node.js process was not spawned with an IPC channel, `process.disconnect()` will be `undefined`. ### `process.dlopen(module, filename[, flags])`# History VersionChanges v9.0.0 Added support for the `flags` argument. v0.1.16 Added in: v0.1.16 * `module` * `filename` * `flags` Default: `os.constants.dlopen.RTLD_LAZY` The `process.dlopen()` method allows dynamically loading shared objects. It is primarily used by `require()` to load C++ Addons, and should not be used directly, except in special cases. In other words, `require()` should be preferred over `process.dlopen()` unless there are specific reasons such as custom dlopen flags or loading from ES modules. The `flags` argument is an integer that allows to specify dlopen behavior. See the `os.constants.dlopen` documentation for details. An important requirement when calling `process.dlopen()` is that the `module` instance must be passed. Functions exported by the C++ Addon are then accessible via `module.exports`. The example below shows how to load a C++ Addon, named `local.node`, that exports a `foo` function. All the symbols are loaded before the call returns, by passing the `RTLD_NOW` constant. In this example the constant is assumed to be available. import { dlopen } from 'node:process'; import { constants } from 'node:os'; import { fileURLToPath } from 'node:url'; const module = { exports: {} }; dlopen(module, fileURLToPath(new URL('local.node', import.meta.url)), constants.dlopen.RTLD_NOW); module.exports.foo(); ### `process.emitWarning(warning[, options])`# Added in: v8.0.0 * `warning` | The warning to emit. * `options` * `type` When `warning` is a `String`, `type` is the name to use for the type of warning being emitted. Default: `'Warning'`. * `code` A unique identifier for the warning instance being emitted. * `ctor` When `warning` is a `String`, `ctor` is an optional function used to limit the generated stack trace. Default: `process.emitWarning`. * `detail` Additional text to include with the error. The `process.emitWarning()` method can be used to emit custom or application specific process warnings. These can be listened for by adding a handler to the `'warning'` event. import { emitWarning } from 'node:process'; // Emit a warning with a code and additional detail. emitWarning('Something happened!', { code: 'MY_WARNING', detail: 'This is some additional information', }); // Emits: // (node:56338) [MY_WARNING] Warning: Something happened! // This is some additional information In this example, an `Error` object is generated internally by `process.emitWarning()` and passed through to the `'warning'` handler. import process from 'node:process'; process.on('warning', (warning) => { console.warn(warning.name); // 'Warning' console.warn(warning.message); // 'Something happened!' console.warn(warning.code); // 'MY_WARNING' console.warn(warning.stack); // Stack trace console.warn(warning.detail); // 'This is some additional information' }); If `warning` is passed as an `Error` object, the `options` argument is ignored. ### `process.emitWarning(warning[, type[, code]][, ctor])`# Added in: v6.0.0 * `warning` | The warning to emit. * `type` When `warning` is a `String`, `type` is the name to use for the type of warning being emitted. Default: `'Warning'`. * `code` A unique identifier for the warning instance being emitted. * `ctor` When `warning` is a `String`, `ctor` is an optional function used to limit the generated stack trace. Default: `process.emitWarning`. The `process.emitWarning()` method can be used to emit custom or application specific process warnings. These can be listened for by adding a handler to the `'warning'` event. import { emitWarning } from 'node:process'; // Emit a warning using a string. emitWarning('Something happened!'); // Emits: (node: 56338) Warning: Something happened! import { emitWarning } from 'node:process'; // Emit a warning using a string and a type. emitWarning('Something Happened!', 'CustomWarning'); // Emits: (node:56338) CustomWarning: Something Happened! import { emitWarning } from 'node:process'; emitWarning('Something happened!', 'CustomWarning', 'WARN001'); // Emits: (node:56338) [WARN001] CustomWarning: Something happened! In each of the previous examples, an `Error` object is generated internally by `process.emitWarning()` and passed through to the `'warning'` handler. import process from 'node:process'; process.on('warning', (warning) => { console.warn(warning.name); console.warn(warning.message); console.warn(warning.code); console.warn(warning.stack); }); If `warning` is passed as an `Error` object, it will be passed through to the `'warning'` event handler unmodified (and the optional `type`, `code` and `ctor` arguments will be ignored): import { emitWarning } from 'node:process'; // Emit a warning using an Error object. const myWarning = new Error('Something happened!'); // Use the Error name property to specify the type name myWarning.name = 'CustomWarning'; myWarning.code = 'WARN001'; emitWarning(myWarning); // Emits: (node:56338) [WARN001] CustomWarning: Something happened! A `TypeError` is thrown if `warning` is anything other than a string or `Error` object. While process warnings use `Error` objects, the process warning mechanism is not a replacement for normal error handling mechanisms. The following additional handling is implemented if the warning `type` is `'DeprecationWarning'`: * If the `--throw-deprecation` command-line flag is used, the deprecation warning is thrown as an exception rather than being emitted as an event. * If the `--no-deprecation` command-line flag is used, the deprecation warning is suppressed. * If the `--trace-deprecation` command-line flag is used, the deprecation warning is printed to `stderr` along with the full stack trace. #### Avoiding duplicate warnings# As a best practice, warnings should be emitted only once per process. To do so, place the `emitWarning()` behind a boolean. import { emitWarning } from 'node:process'; function emitMyWarning() { if (!emitMyWarning.warned) { emitMyWarning.warned = true; emitWarning('Only warn once!'); } } emitMyWarning(); // Emits: (node: 56339) Warning: Only warn once! emitMyWarning(); // Emits nothing ### `process.env`# History VersionChanges v11.14.0 Worker threads will now use a copy of the parent thread's `process.env` by default, configurable through the `env` option of the `Worker` constructor. v10.0.0 Implicit conversion of variable value to string is deprecated. v0.1.27 Added in: v0.1.27 * Type: The `process.env` property returns an object containing the user environment. See `environ(7)`. An example of this object looks like: { TERM: 'xterm-256color', SHELL: '/usr/local/bin/bash', USER: 'maciej', PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin', PWD: '/Users/maciej', EDITOR: 'vim', SHLVL: '1', HOME: '/Users/maciej', LOGNAME: 'maciej', _: '/usr/local/bin/node' } It is possible to modify this object, but such modifications will not be reflected outside the Node.js process, or (unless explicitly requested) to other `Worker` threads. In other words, the following example would not work: node -e 'process.env.foo = "bar"' && echo $foo While the following will: import { env } from 'node:process'; env.foo = 'bar'; console.log(env.foo); Assigning a property on `process.env` will implicitly convert the value to a string. This behavior is deprecated. Future versions of Node.js may throw an error when the value is not a string, number, or boolean. import { env } from 'node:process'; env.test = null; console.log(env.test); // => 'null' env.test = undefined; console.log(env.test); // => 'undefined' Use `delete` to delete a property from `process.env`. import { env } from 'node:process'; env.TEST = 1; delete env.TEST; console.log(env.TEST); // => undefined On Windows operating systems, environment variables are case-insensitive. import { env } from 'node:process'; env.TEST = 1; console.log(env.test); // => 1 Unless explicitly specified when creating a `Worker` instance, each `Worker` thread has its own copy of `process.env`, based on its parent thread's `process.env`, or whatever was specified as the `env` option to the `Worker` constructor. Changes to `process.env` will not be visible across `Worker` threads, and only the main thread can make changes that are visible to the operating system or to native add-ons. On Windows, a copy of `process.env` on a `Worker` instance operates in a case-sensitive manner unlike the main thread. ### `process.execArgv`# Added in: v0.7.7 * Type: The `process.execArgv` property returns the set of Node.js-specific command-line options passed when the Node.js process was launched. These options do not appear in the array returned by the `process.argv` property, and do not include the Node.js executable, the name of the script, or any options following the script name. These options are useful in order to spawn child processes with the same execution environment as the parent. node --icu-data-dir=./foo --require ./bar.js script.js --version Results in `process.execArgv`: ["--icu-data-dir=./foo", "--require", "./bar.js"] And `process.argv`: ['/usr/local/bin/node', 'script.js', '--version'] Refer to `Worker` constructor for the detailed behavior of worker threads with this property. ### `process.execPath`# Added in: v0.1.100 * Type: The `process.execPath` property returns the absolute pathname of the executable that started the Node.js process. Symbolic links, if any, are resolved. '/usr/local/bin/node' ### `process.execve(file[, args[, env]])`# Added in: v23.11.0, v22.15.0 Stability: 1 \- Experimental * `file` The name or path of the executable file to run. * `args` List of string arguments. No argument can contain a null-byte (`\u0000`). * `env` Environment key-value pairs. No key or value can contain a null-byte (`\u0000`). Default: `process.env`. Replaces the current process with a new process. This is achieved by using the `execve` POSIX function and therefore no memory or other resources from the current process are preserved, except for the standard input, standard output and standard error file descriptor. All other resources are discarded by the system when the processes are swapped, without triggering any exit or close events and without running any cleanup handler. This function will never return, unless an error occurred. This function is not available on Windows or IBM i. ### `process.exit([code])`# History VersionChanges v20.0.0 Only accepts a code of type number, or of type string if it represents an integer. v0.1.13 Added in: v0.1.13 * `code` | | | The exit code. For string type, only integer strings (e.g.,'1') are allowed. Default: `0`. The `process.exit()` method instructs Node.js to terminate the process synchronously with an exit status of `code`. If `code` is omitted, exit uses either the 'success' code `0` or the value of `process.exitCode` if it has been set. Node.js will not terminate until all the `'exit'` event listeners are called. To exit with a 'failure' code: import { exit } from 'node:process'; exit(1); The shell that executed Node.js should see the exit code as `1`. Calling `process.exit()` will force the process to exit as quickly as possible even if there are still asynchronous operations pending that have not yet completed fully, including I/O operations to `process.stdout` and `process.stderr`. In most situations, it is not actually necessary to call `process.exit()` explicitly. The Node.js process will exit on its own if there is no additional work pending in the event loop. The `process.exitCode` property can be set to tell the process which exit code to use when the process exits gracefully. For instance, the following example illustrates a misuse of the `process.exit()` method that could lead to data printed to stdout being truncated and lost: import { exit } from 'node:process'; // This is an example of what *not* to do: if (someConditionNotMet()) { printUsageToStdout(); exit(1); } The reason this is problematic is because writes to `process.stdout` in Node.js are sometimes asynchronous and may occur over multiple ticks of the Node.js event loop. Calling `process.exit()`, however, forces the process to exit before those additional writes to `stdout` can be performed. Rather than calling `process.exit()` directly, the code should set the `process.exitCode` and allow the process to exit naturally by avoiding scheduling any additional work for the event loop: import process from 'node:process'; // How to properly set the exit code while letting // the process exit gracefully. if (someConditionNotMet()) { printUsageToStdout(); process.exitCode = 1; } If it is necessary to terminate the Node.js process due to an error condition, throwing an uncaught error and allowing the process to terminate accordingly is safer than calling `process.exit()`. In `Worker` threads, this function stops the current thread rather than the current process. ### `process.exitCode`# History VersionChanges v20.0.0 Only accepts a code of type number, or of type string if it represents an integer. v0.11.8 Added in: v0.11.8 * Type: | | | The exit code. For string type, only integer strings (e.g.,'1') are allowed. Default: `undefined`. A number which will be the process exit code, when the process either exits gracefully, or is exited via `process.exit()` without specifying a code. The value of `process.exitCode` can be updated by either assigning a value to `process.exitCode` or by passing an argument to `process.exit()`: $ node -e 'process.exitCode = 9'; echo $? 9 $ node -e 'process.exit(42)'; echo $? 42 $ node -e 'process.exitCode = 9; process.exit(42)'; echo $? 42 The value can also be set implicitly by Node.js when unrecoverable errors occur (e.g. such as the encountering of an unsettled top-level await). However explicit manipulations of the exit code always take precedence over implicit ones: $ node --input-type=module -e 'await new Promise(() => {})'; echo $? 13 $ node --input-type=module -e 'process.exitCode = 9; await new Promise(() => {})'; echo $? 9 ### `process.features.cached_builtins`# Added in: v12.0.0 * Type: A boolean value that is `true` if the current Node.js build is caching builtin modules. ### `process.features.debug`# Added in: v0.5.5 * Type: A boolean value that is `true` if the current Node.js build is a debug build. ### `process.features.inspector`# Added in: v11.10.0 * Type: A boolean value that is `true` if the current Node.js build includes the inspector. ### `process.features.ipv6`# Added in: v0.5.3Deprecated since: v23.4.0, v22.13.0 Stability: 0 \- Deprecated. This property is always true, and any checks based on it are redundant. * Type: A boolean value that is `true` if the current Node.js build includes support for IPv6. Since all Node.js builds have IPv6 support, this value is always `true`. ### `process.features.require_module`# Added in: v23.0.0, v22.10.0, v20.19.0 * Type: A boolean value that is `true` if the current Node.js build supports loading ECMAScript modules using `require()`. ### `process.features.tls`# Added in: v0.5.3 * Type: A boolean value that is `true` if the current Node.js build includes support for TLS. ### `process.features.tls_alpn`# Added in: v4.8.0Deprecated since: v23.4.0, v22.13.0 Stability: 0 \- Deprecated. Use `process.features.tls` instead. * Type: A boolean value that is `true` if the current Node.js build includes support for ALPN in TLS. In Node.js 11.0.0 and later versions, the OpenSSL dependencies feature unconditional ALPN support. This value is therefore identical to that of `process.features.tls`. ### `process.features.tls_ocsp`# Added in: v0.11.13Deprecated since: v23.4.0, v22.13.0 Stability: 0 \- Deprecated. Use `process.features.tls` instead. * Type: A boolean value that is `true` if the current Node.js build includes support for OCSP in TLS. In Node.js 11.0.0 and later versions, the OpenSSL dependencies feature unconditional OCSP support. This value is therefore identical to that of `process.features.tls`. ### `process.features.tls_sni`# Added in: v0.5.3Deprecated since: v23.4.0, v22.13.0 Stability: 0 \- Deprecated. Use `process.features.tls` instead. * Type: A boolean value that is `true` if the current Node.js build includes support for SNI in TLS. In Node.js 11.0.0 and later versions, the OpenSSL dependencies feature unconditional SNI support. This value is therefore identical to that of `process.features.tls`. ### `process.features.typescript`# Added in: v23.0.0, v22.10.0 Stability: 1.2 \- Release candidate * Type: | A value that is `"strip"` by default, `"transform"` if Node.js is run with `--experimental-transform-types`, and `false` if Node.js is run with `--no-experimental-strip-types`. ### `process.features.uv`# Added in: v0.5.3Deprecated since: v23.4.0, v22.13.0 Stability: 0 \- Deprecated. This property is always true, and any checks based on it are redundant. * Type: A boolean value that is `true` if the current Node.js build includes support for libuv. Since it's not possible to build Node.js without libuv, this value is always `true`. ### `process.finalization.register(ref, callback)`# Added in: v22.5.0 Stability: 1.1 \- Active Development * `ref` | The reference to the resource that is being tracked. * `callback` The callback function to be called when the resource is finalized. * `ref` | The reference to the resource that is being tracked. * `event` The event that triggered the finalization. Defaults to 'exit'. This function registers a callback to be called when the process emits the `exit` event if the `ref` object was not garbage collected. If the object `ref` was garbage collected before the `exit` event is emitted, the callback will be removed from the finalization registry, and it will not be called on process exit. Inside the callback you can release the resources allocated by the `ref` object. Be aware that all limitations applied to the `beforeExit` event are also applied to the `callback` function, this means that there is a possibility that the callback will not be called under special circumstances. The idea of ​​this function is to help you free up resources when the starts process exiting, but also let the object be garbage collected if it is no longer being used. Eg: you can register an object that contains a buffer, you want to make sure that buffer is released when the process exit, but if the object is garbage collected before the process exit, we no longer need to release the buffer, so in this case we just remove the callback from the finalization registry. import { finalization } from 'node:process'; // Please make sure that the function passed to finalization.register() // does not create a closure around unnecessary objects. function onFinalize(obj, event) { // You can do whatever you want with the object obj.dispose(); } function setup() { // This object can be safely garbage collected, // and the resulting shutdown function will not be called. // There are no leaks. const myDisposableObject = { dispose() { // Free your resources synchronously }, }; finalization.register(myDisposableObject, onFinalize); } setup(); The code above relies on the following assumptions: * arrow functions are avoided * regular functions are recommended to be within the global context (root) Regular functions could reference the context where the `obj` lives, making the `obj` not garbage collectible. Arrow functions will hold the previous context. Consider, for example: class Test { constructor() { finalization.register(this, (ref) => ref.dispose()); // Even something like this is highly discouraged // finalization.register(this, () => this.dispose()); } dispose() {} } It is very unlikely (not impossible) that this object will be garbage collected, but if it is not, `dispose` will be called when `process.exit` is called. Be careful and avoid relying on this feature for the disposal of critical resources, as it is not guaranteed that the callback will be called under all circumstances. ### `process.finalization.registerBeforeExit(ref, callback)`# Added in: v22.5.0 Stability: 1.1 \- Active Development * `ref` | The reference to the resource that is being tracked. * `callback` The callback function to be called when the resource is finalized. * `ref` | The reference to the resource that is being tracked. * `event` The event that triggered the finalization. Defaults to 'beforeExit'. This function behaves exactly like the `register`, except that the callback will be called when the process emits the `beforeExit` event if `ref` object was not garbage collected. Be aware that all limitations applied to the `beforeExit` event are also applied to the `callback` function, this means that there is a possibility that the callback will not be called under special circumstances. ### `process.finalization.unregister(ref)`# Added in: v22.5.0 Stability: 1.1 \- Active Development * `ref` | The reference to the resource that was registered previously. This function remove the register of the object from the finalization registry, so the callback will not be called anymore. import { finalization } from 'node:process'; // Please make sure that the function passed to finalization.register() // does not create a closure around unnecessary objects. function onFinalize(obj, event) { // You can do whatever you want with the object obj.dispose(); } function setup() { // This object can be safely garbage collected, // and the resulting shutdown function will not be called. // There are no leaks. const myDisposableObject = { dispose() { // Free your resources synchronously }, }; // Please make sure that the function passed to finalization.register() // does not create a closure around unnecessary objects. function onFinalize(obj, event) { // You can do whatever you want with the object obj.dispose(); } finalization.register(myDisposableObject, onFinalize); // Do something myDisposableObject.dispose(); finalization.unregister(myDisposableObject); } setup(); ### `process.getActiveResourcesInfo()`# History VersionChanges v24.0.0 Change stability index for this feature from Experimental to Stable. v17.3.0, v16.14.0 Added in: v17.3.0, v16.14.0 * Returns: The `process.getActiveResourcesInfo()` method returns an array of strings containing the types of the active resources that are currently keeping the event loop alive. import { getActiveResourcesInfo } from 'node:process'; import { setTimeout } from 'node:timers'; console.log('Before:', getActiveResourcesInfo()); setTimeout(() => {}, 1000); console.log('After:', getActiveResourcesInfo()); // Prints: // Before: [ 'CloseReq', 'TTYWrap', 'TTYWrap', 'TTYWrap' ] // After: [ 'CloseReq', 'TTYWrap', 'TTYWrap', 'TTYWrap', 'Timeout' ] ### `process.getBuiltinModule(id)`# Added in: v22.3.0, v20.16.0 * `id` ID of the built-in module being requested. * Returns: | `process.getBuiltinModule(id)` provides a way to load built-in modules in a globally available function. ES Modules that need to support other environments can use it to conditionally load a Node.js built-in when it is run in Node.js, without having to deal with the resolution error that can be thrown by `import` in a non-Node.js environment or having to use dynamic `import()` which either turns the module into an asynchronous module, or turns a synchronous API into an asynchronous one. if (globalThis.process?.getBuiltinModule) { // Run in Node.js, use the Node.js fs module. const fs = globalThis.process.getBuiltinModule('fs'); // If `require()` is needed to load user-modules, use createRequire() const module = globalThis.process.getBuiltinModule('module'); const require = module.createRequire(import.meta.url); const foo = require('foo'); } If `id` specifies a built-in module available in the current Node.js process, `process.getBuiltinModule(id)` method returns the corresponding built-in module. If `id` does not correspond to any built-in module, `undefined` is returned. `process.getBuiltinModule(id)` accepts built-in module IDs that are recognized by `module.isBuiltin(id)`. Some built-in modules must be loaded with the `node:` prefix, see built-in modules with mandatory `node:` prefix. The references returned by `process.getBuiltinModule(id)` always point to the built-in module corresponding to `id` even if users modify `require.cache` so that `require(id)` returns something else. ### `process.getegid()`# Added in: v2.0.0 The `process.getegid()` method returns the numerical effective group identity of the Node.js process. (See `getegid(2)`.) import process from 'node:process'; if (process.getegid) { console.log(`Current gid: ${process.getegid()}`); } This function is only available on POSIX platforms (i.e. not Windows or Android). ### `process.geteuid()`# Added in: v2.0.0 * Returns: The `process.geteuid()` method returns the numerical effective user identity of the process. (See `geteuid(2)`.) import process from 'node:process'; if (process.geteuid) { console.log(`Current uid: ${process.geteuid()}`); } This function is only available on POSIX platforms (i.e. not Windows or Android). ### `process.getgid()`# Added in: v0.1.31 * Returns: The `process.getgid()` method returns the numerical group identity of the process. (See `getgid(2)`.) import process from 'node:process'; if (process.getgid) { console.log(`Current gid: ${process.getgid()}`); } This function is only available on POSIX platforms (i.e. not Windows or Android). ### `process.getgroups()`# Added in: v0.9.4 * Returns: The `process.getgroups()` method returns an array with the supplementary group IDs. POSIX leaves it unspecified if the effective group ID is included but Node.js ensures it always is. import process from 'node:process'; if (process.getgroups) { console.log(process.getgroups()); // [ 16, 21, 297 ] } This function is only available on POSIX platforms (i.e. not Windows or Android). ### `process.getuid()`# Added in: v0.1.28 * Returns: The `process.getuid()` method returns the numeric user identity of the process. (See `getuid(2)`.) import process from 'node:process'; if (process.getuid) { console.log(`Current uid: ${process.getuid()}`); } This function not available on Windows. ### `process.hasUncaughtExceptionCaptureCallback()`# Added in: v9.3.0 * Returns: Indicates whether a callback has been set using `process.setUncaughtExceptionCaptureCallback()`. ### `process.hrtime([time])`# Added in: v0.7.6 Stability: 3 \- Legacy. Use `process.hrtime.bigint()` instead. * `time` The result of a previous call to `process.hrtime()` * Returns: This is the legacy version of `process.hrtime.bigint()` before `bigint` was introduced in JavaScript. The `process.hrtime()` method returns the current high-resolution real time in a `[seconds, nanoseconds]` tuple `Array`, where `nanoseconds` is the remaining part of the real time that can't be represented in second precision. `time` is an optional parameter that must be the result of a previous `process.hrtime()` call to diff with the current time. If the parameter passed in is not a tuple `Array`, a `TypeError` will be thrown. Passing in a user-defined array instead of the result of a previous call to `process.hrtime()` will lead to undefined behavior. These times are relative to an arbitrary time in the past, and not related to the time of day and therefore not subject to clock drift. The primary use is for measuring performance between intervals: import { hrtime } from 'node:process'; const NS_PER_SEC = 1e9; const time = hrtime(); // [ 1800216, 25 ] setTimeout(() => { const diff = hrtime(time); // [ 1, 552 ] console.log(`Benchmark took ${diff[0] * NS_PER_SEC + diff[1]} nanoseconds`); // Benchmark took 1000000552 nanoseconds }, 1000); ### `process.hrtime.bigint()`# Added in: v10.7.0 * Returns: The `bigint` version of the `process.hrtime()` method returning the current high-resolution real time in nanoseconds as a `bigint`. Unlike `process.hrtime()`, it does not support an additional `time` argument since the difference can just be computed directly by subtraction of the two `bigint`s. import { hrtime } from 'node:process'; const start = hrtime.bigint(); // 191051479007711n setTimeout(() => { const end = hrtime.bigint(); // 191052633396993n console.log(`Benchmark took ${end - start} nanoseconds`); // Benchmark took 1154389282 nanoseconds }, 1000); ### `process.initgroups(user, extraGroup)`# Added in: v0.9.4 * `user` | The user name or numeric identifier. * `extraGroup` | A group name or numeric identifier. The `process.initgroups()` method reads the `/etc/group` file and initializes the group access list, using all groups of which the user is a member. This is a privileged operation that requires that the Node.js process either have `root` access or the `CAP_SETGID` capability. Use care when dropping privileges: import { getgroups, initgroups, setgid } from 'node:process'; console.log(getgroups()); // [ 0 ] initgroups('nodeuser', 1000); // switch user console.log(getgroups()); // [ 27, 30, 46, 1000, 0 ] setgid(1000); // drop root gid console.log(getgroups()); // [ 27, 30, 46, 1000 ] This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in `Worker` threads. ### `process.kill(pid[, signal])`# Added in: v0.0.6 * `pid` A process ID * `signal` | The signal to send, either as a string or number. Default: `'SIGTERM'`. The `process.kill()` method sends the `signal` to the process identified by `pid`. Signal names are strings such as `'SIGINT'` or `'SIGHUP'`. See Signal Events and `kill(2)` for more information. This method will throw an error if the target `pid` does not exist. As a special case, a signal of `0` can be used to test for the existence of a process. Windows platforms will throw an error if the `pid` is used to kill a process group. Even though the name of this function is `process.kill()`, it is really just a signal sender, like the `kill` system call. The signal sent may do something other than kill the target process. import process, { kill } from 'node:process'; process.on('SIGHUP', () => { console.log('Got SIGHUP signal.'); }); setTimeout(() => { console.log('Exiting.'); process.exit(0); }, 100); kill(process.pid, 'SIGHUP'); When `SIGUSR1` is received by a Node.js process, Node.js will start the debugger. See Signal Events. ### `process.loadEnvFile(path)`# Added in: v21.7.0, v20.12.0 Stability: 1.1 \- Active development * `path` | | | . Default: `'./.env'` Loads the `.env` file into `process.env`. Usage of `NODE_OPTIONS` in the `.env` file will not have any effect on Node.js. import { loadEnvFile } from 'node:process'; loadEnvFile(); ### `process.mainModule`# Added in: v0.1.17Deprecated since: v14.0.0 Stability: 0 \- Deprecated: Use `require.main` instead. * Type: The `process.mainModule` property provides an alternative way of retrieving `require.main`. The difference is that if the main module changes at runtime, `require.main` may still refer to the original main module in modules that were required before the change occurred. Generally, it's safe to assume that the two refer to the same module. As with `require.main`, `process.mainModule` will be `undefined` if there is no entry script. ### `process.memoryUsage()`# History VersionChanges v13.9.0, v12.17.0 Added `arrayBuffers` to the returned object. v7.2.0 Added `external` to the returned object. v0.1.16 Added in: v0.1.16 * Returns: * `rss` * `heapTotal` * `heapUsed` * `external` * `arrayBuffers` Returns an object describing the memory usage of the Node.js process measured in bytes. import { memoryUsage } from 'node:process'; console.log(memoryUsage()); // Prints: // { // rss: 4935680, // heapTotal: 1826816, // heapUsed: 650472, // external: 49879, // arrayBuffers: 9386 // } * `heapTotal` and `heapUsed` refer to V8's memory usage. * `external` refers to the memory usage of C++ objects bound to JavaScript objects managed by V8. * `rss`, Resident Set Size, is the amount of space occupied in the main memory device (that is a subset of the total allocated memory) for the process, including all C++ and JavaScript objects and code. * `arrayBuffers` refers to memory allocated for `ArrayBuffer`s and `SharedArrayBuffer`s, including all Node.js `Buffer`s. This is also included in the `external` value. When Node.js is used as an embedded library, this value may be `0` because allocations for `ArrayBuffer`s may not be tracked in that case. When using `Worker` threads, `rss` will be a value that is valid for the entire process, while the other fields will only refer to the current thread. The `process.memoryUsage()` method iterates over each page to gather information about memory usage which might be slow depending on the program memory allocations. #### A note on process memoryUsage# On Linux or other systems where glibc is commonly used, an application may have sustained `rss` growth despite stable `heapTotal` due to fragmentation caused by the glibc `malloc` implementation. See nodejs/node#21973 on how to switch to an alternative `malloc` implementation to address the performance issue. ### `process.memoryUsage.rss()`# Added in: v15.6.0, v14.18.0 * Returns: The `process.memoryUsage.rss()` method returns an integer representing the Resident Set Size (RSS) in bytes. The Resident Set Size, is the amount of space occupied in the main memory device (that is a subset of the total allocated memory) for the process, including all C++ and JavaScript objects and code. This is the same value as the `rss` property provided by `process.memoryUsage()` but `process.memoryUsage.rss()` is faster. import { memoryUsage } from 'node:process'; console.log(memoryUsage.rss()); // 35655680 ### `process.nextTick(callback[, ...args])`# History VersionChanges v22.7.0, v20.18.0 Changed stability to Legacy. v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v1.8.1 Additional arguments after `callback` are now supported. v0.1.26 Added in: v0.1.26 Stability: 3 \- Legacy: Use `queueMicrotask()` instead. * `callback` * `...args` Additional arguments to pass when invoking the `callback` `process.nextTick()` adds `callback` to the "next tick queue". This queue is fully drained after the current operation on the JavaScript stack runs to completion and before the event loop is allowed to continue. It's possible to create an infinite loop if one were to recursively call `process.nextTick()`. See the Event Loop guide for more background. import { nextTick } from 'node:process'; console.log('start'); nextTick(() => { console.log('nextTick callback'); }); console.log('scheduled'); // Output: // start // scheduled // nextTick callback This is important when developing APIs in order to give users the opportunity to assign event handlers after an object has been constructed but before any I/O has occurred: import { nextTick } from 'node:process'; function MyThing(options) { this.setupOptions(options); nextTick(() => { this.startDoingStuff(); }); } const thing = new MyThing(); thing.getReadyForStuff(); // thing.startDoingStuff() gets called now, not before. It is very important for APIs to be either 100% synchronous or 100% asynchronous. Consider this example: // WARNING! DO NOT USE! BAD UNSAFE HAZARD! function maybeSync(arg, cb) { if (arg) { cb(); return; } fs.stat('file', cb); } This API is hazardous because in the following case: const maybeTrue = Math.random() > 0.5; maybeSync(maybeTrue, () => { foo(); }); bar(); It is not clear whether `foo()` or `bar()` will be called first. The following approach is much better: import { nextTick } from 'node:process'; function definitelyAsync(arg, cb) { if (arg) { nextTick(cb); return; } fs.stat('file', cb); } #### When to use `queueMicrotask()` vs. `process.nextTick()`# The `queueMicrotask()` API is an alternative to `process.nextTick()` that instead of using the "next tick queue" defers execution of a function using the same microtask queue used to execute the then, catch, and finally handlers of resolved promises. Within Node.js, every time the "next tick queue" is drained, the microtask queue is drained immediately after. So in CJS modules `process.nextTick()` callbacks are always run before `queueMicrotask()` ones. However since ESM modules are processed already as part of the microtask queue, there `queueMicrotask()` callbacks are always executed before `process.nextTick()` ones since Node.js is already in the process of draining the microtask queue. import { nextTick } from 'node:process'; Promise.resolve().then(() => console.log('resolve')); queueMicrotask(() => console.log('microtask')); nextTick(() => console.log('nextTick')); // Output: // resolve // microtask // nextTick For most userland use cases, the `queueMicrotask()` API provides a portable and reliable mechanism for deferring execution that works across multiple JavaScript platform environments and should be favored over `process.nextTick()`. In simple scenarios, `queueMicrotask()` can be a drop-in replacement for `process.nextTick()`. console.log('start'); queueMicrotask(() => { console.log('microtask callback'); }); console.log('scheduled'); // Output: // start // scheduled // microtask callback One note-worthy difference between the two APIs is that `process.nextTick()` allows specifying additional values that will be passed as arguments to the deferred function when it is called. Achieving the same result with `queueMicrotask()` requires using either a closure or a bound function: function deferred(a, b) { console.log('microtask', a + b); } console.log('start'); queueMicrotask(deferred.bind(undefined, 1, 2)); console.log('scheduled'); // Output: // start // scheduled // microtask 3 There are minor differences in the way errors raised from within the next tick queue and microtask queue are handled. Errors thrown within a queued microtask callback should be handled within the queued callback when possible. If they are not, the `process.on('uncaughtException')` event handler can be used to capture and handle the errors. When in doubt, unless the specific capabilities of `process.nextTick()` are needed, use `queueMicrotask()`. ### `process.noDeprecation`# Added in: v0.8.0 * Type: The `process.noDeprecation` property indicates whether the `--no-deprecation` flag is set on the current Node.js process. See the documentation for the `'warning'` event and the `emitWarning()` method for more information about this flag's behavior. ### `process.permission`# Added in: v20.0.0 * Type: This API is available through the `--permission` flag. `process.permission` is an object whose methods are used to manage permissions for the current process. Additional documentation is available in the Permission Model. #### `process.permission.has(scope[, reference])`# Added in: v20.0.0 * `scope` * `reference` * Returns: Verifies that the process is able to access the given scope and reference. If no reference is provided, a global scope is assumed, for instance, `process.permission.has('fs.read')` will check if the process has ALL file system read permissions. The reference has a meaning based on the provided scope. For example, the reference when the scope is File System means files and folders. The available scopes are: * `fs` \- All File System * `fs.read` \- File System read operations * `fs.write` \- File System write operations * `child` \- Child process spawning operations * `worker` \- Worker thread spawning operation // Check if the process has permission to read the README file process.permission.has('fs.read', './README.md'); // Check if the process has read permission operations process.permission.has('fs.read'); ### `process.pid`# Added in: v0.1.15 * Type: The `process.pid` property returns the PID of the process. import { pid } from 'node:process'; console.log(`This process is pid ${pid}`); ### `process.platform`# Added in: v0.1.16 * Type: The `process.platform` property returns a string identifying the operating system platform for which the Node.js binary was compiled. Currently possible values are: * `'aix'` * `'darwin'` * `'freebsd'` * `'linux'` * `'openbsd'` * `'sunos'` * `'win32'` import { platform } from 'node:process'; console.log(`This platform is ${platform}`); The value `'android'` may also be returned if the Node.js is built on the Android operating system. However, Android support in Node.js is experimental. ### `process.ppid`# Added in: v9.2.0, v8.10.0, v6.13.0 * Type: The `process.ppid` property returns the PID of the parent of the current process. import { ppid } from 'node:process'; console.log(`The parent process is pid ${ppid}`); ### `process.ref(maybeRefable)`# Added in: v23.6.0, v22.14.0 Stability: 1 \- Experimental * `maybeRefable` An object that may be "refable". An object is "refable" if it implements the Node.js "Refable protocol". Specifically, this means that the object implements the `Symbol.for('nodejs.ref')` and `Symbol.for('nodejs.unref')` methods. "Ref'd" objects will keep the Node.js event loop alive, while "unref'd" objects will not. Historically, this was implemented by using `ref()` and `unref()` methods directly on the objects. This pattern, however, is being deprecated in favor of the "Refable protocol" in order to better support Web Platform API types whose APIs cannot be modified to add `ref()` and `unref()` methods but still need to support that behavior. ### `process.release`# History VersionChanges v4.2.0 The `lts` property is now supported. v3.0.0 Added in: v3.0.0 * Type: The `process.release` property returns an `Object` containing metadata related to the current release, including URLs for the source tarball and headers-only tarball. `process.release` contains the following properties: * `name` A value that will always be `'node'`. * `sourceUrl` an absolute URL pointing to a `.tar.gz` file containing the source code of the current release. * `headersUrl` an absolute URL pointing to a `.tar.gz` file containing only the source header files for the current release. This file is significantly smaller than the full source file and can be used for compiling Node.js native add-ons. * `libUrl` | an absolute URL pointing to a `node.lib` file matching the architecture and version of the current release. This file is used for compiling Node.js native add-ons. This property is only present on Windows builds of Node.js and will be missing on all other platforms. * `lts` | a string label identifying the LTS label for this release. This property only exists for LTS releases and is `undefined` for all other release types, including Current releases. Valid values include the LTS Release code names (including those that are no longer supported). * `'Fermium'` for the 14.x LTS line beginning with 14.15.0. * `'Gallium'` for the 16.x LTS line beginning with 16.13.0. * `'Hydrogen'` for the 18.x LTS line beginning with 18.12.0. For other LTS Release code names, see Node.js Changelog Archive { name: 'node', lts: 'Hydrogen', sourceUrl: 'https://nodejs.org/download/release/v18.12.0/node-v18.12.0.tar.gz', headersUrl: 'https://nodejs.org/download/release/v18.12.0/node-v18.12.0-headers.tar.gz', libUrl: 'https://nodejs.org/download/release/v18.12.0/win-x64/node.lib' } In custom builds from non-release versions of the source tree, only the `name` property may be present. The additional properties should not be relied upon to exist. ### `process.report`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.8.0 Added in: v11.8.0 * Type: `process.report` is an object whose methods are used to generate diagnostic reports for the current process. Additional documentation is available in the report documentation. #### `process.report.compact`# Added in: v13.12.0, v12.17.0 * Type: Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption. import { report } from 'node:process'; console.log(`Reports are compact? ${report.compact}`); #### `process.report.directory`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.12.0 Added in: v11.12.0 * Type: Directory where the report is written. The default value is the empty string, indicating that reports are written to the current working directory of the Node.js process. import { report } from 'node:process'; console.log(`Report directory is ${report.directory}`); #### `process.report.filename`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.12.0 Added in: v11.12.0 * Type: Filename where the report is written. If set to the empty string, the output filename will be comprised of a timestamp, PID, and sequence number. The default value is the empty string. If the value of `process.report.filename` is set to `'stdout'` or `'stderr'`, the report is written to the stdout or stderr of the process respectively. import { report } from 'node:process'; console.log(`Report filename is ${report.filename}`); #### `process.report.getReport([err])`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.8.0 Added in: v11.8.0 * `err` A custom error used for reporting the JavaScript stack. * Returns: Returns a JavaScript Object representation of a diagnostic report for the running process. The report's JavaScript stack trace is taken from `err`, if present. import { report } from 'node:process'; import util from 'node:util'; const data = report.getReport(); console.log(data.header.nodejsVersion); // Similar to process.report.writeReport() import fs from 'node:fs'; fs.writeFileSync('my-report.log', util.inspect(data), 'utf8'); Additional documentation is available in the report documentation. #### `process.report.reportOnFatalError`# History VersionChanges v15.0.0, v14.17.0 This API is no longer experimental. v11.12.0 Added in: v11.12.0 * Type: If `true`, a diagnostic report is generated on fatal errors, such as out of memory errors or failed C++ assertions. import { report } from 'node:process'; console.log(`Report on fatal error: ${report.reportOnFatalError}`); #### `process.report.reportOnSignal`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.12.0 Added in: v11.12.0 * Type: If `true`, a diagnostic report is generated when the process receives the signal specified by `process.report.signal`. import { report } from 'node:process'; console.log(`Report on signal: ${report.reportOnSignal}`); #### `process.report.reportOnUncaughtException`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.12.0 Added in: v11.12.0 * Type: If `true`, a diagnostic report is generated on uncaught exception. import { report } from 'node:process'; console.log(`Report on exception: ${report.reportOnUncaughtException}`); #### `process.report.excludeEnv`# Added in: v23.3.0, v22.13.0 * Type: If `true`, a diagnostic report is generated without the environment variables. #### `process.report.signal`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.12.0 Added in: v11.12.0 * Type: The signal used to trigger the creation of a diagnostic report. Defaults to `'SIGUSR2'`. import { report } from 'node:process'; console.log(`Report signal: ${report.signal}`); #### `process.report.writeReport([filename][, err])`# History VersionChanges v13.12.0, v12.17.0 This API is no longer experimental. v11.8.0 Added in: v11.8.0 * `filename` Name of the file where the report is written. This should be a relative path, that will be appended to the directory specified in `process.report.directory`, or the current working directory of the Node.js process, if unspecified. * `err` A custom error used for reporting the JavaScript stack. * Returns: Returns the filename of the generated report. Writes a diagnostic report to a file. If `filename` is not provided, the default filename includes the date, time, PID, and a sequence number. The report's JavaScript stack trace is taken from `err`, if present. If the value of `filename` is set to `'stdout'` or `'stderr'`, the report is written to the stdout or stderr of the process respectively. import { report } from 'node:process'; report.writeReport(); Additional documentation is available in the report documentation. ### `process.resourceUsage()`# Added in: v12.6.0 * Returns: the resource usage for the current process. All of these values come from the `uv_getrusage` call which returns a `uv_rusage_t` struct. * `userCPUTime` maps to `ru_utime` computed in microseconds. It is the same value as `process.cpuUsage().user`. * `systemCPUTime` maps to `ru_stime` computed in microseconds. It is the same value as `process.cpuUsage().system`. * `maxRSS` maps to `ru_maxrss` which is the maximum resident set size used in kibibytes (1024 bytes). * `sharedMemorySize` maps to `ru_ixrss` but is not supported by any platform. * `unsharedDataSize` maps to `ru_idrss` but is not supported by any platform. * `unsharedStackSize` maps to `ru_isrss` but is not supported by any platform. * `minorPageFault` maps to `ru_minflt` which is the number of minor page faults for the process, see this article for more details. * `majorPageFault` maps to `ru_majflt` which is the number of major page faults for the process, see this article for more details. This field is not supported on Windows. * `swappedOut` maps to `ru_nswap` but is not supported by any platform. * `fsRead` maps to `ru_inblock` which is the number of times the file system had to perform input. * `fsWrite` maps to `ru_oublock` which is the number of times the file system had to perform output. * `ipcSent` maps to `ru_msgsnd` but is not supported by any platform. * `ipcReceived` maps to `ru_msgrcv` but is not supported by any platform. * `signalsCount` maps to `ru_nsignals` but is not supported by any platform. * `voluntaryContextSwitches` maps to `ru_nvcsw` which is the number of times a CPU context switch resulted due to a process voluntarily giving up the processor before its time slice was completed (usually to await availability of a resource). This field is not supported on Windows. * `involuntaryContextSwitches` maps to `ru_nivcsw` which is the number of times a CPU context switch resulted due to a higher priority process becoming runnable or because the current process exceeded its time slice. This field is not supported on Windows. import { resourceUsage } from 'node:process'; console.log(resourceUsage()); /* Will output: { userCPUTime: 82872, systemCPUTime: 4143, maxRSS: 33164, sharedMemorySize: 0, unsharedDataSize: 0, unsharedStackSize: 0, minorPageFault: 2469, majorPageFault: 0, swappedOut: 0, fsRead: 0, fsWrite: 8, ipcSent: 0, ipcReceived: 0, signalsCount: 0, voluntaryContextSwitches: 79, involuntaryContextSwitches: 1 } */ ### `process.send(message[, sendHandle[, options]][, callback])`# Added in: v0.5.9 * `message` * `sendHandle` | * `options` used to parameterize the sending of certain types of handles.`options` supports the following properties: * `keepOpen` A value that can be used when passing instances of `net.Socket`. When `true`, the socket is kept open in the sending process. Default: `false`. * `callback` * Returns: If Node.js is spawned with an IPC channel, the `process.send()` method can be used to send messages to the parent process. Messages will be received as a `'message'` event on the parent's `ChildProcess` object. If Node.js was not spawned with an IPC channel, `process.send` will be `undefined`. The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent. ### `process.setegid(id)`# Added in: v2.0.0 * `id` | A group name or ID The `process.setegid()` method sets the effective group identity of the process. (See `setegid(2)`.) The `id` can be passed as either a numeric ID or a group name string. If a group name is specified, this method blocks while resolving the associated a numeric ID. import process from 'node:process'; if (process.getegid && process.setegid) { console.log(`Current gid: ${process.getegid()}`); try { process.setegid(501); console.log(`New gid: ${process.getegid()}`); } catch (err) { console.error(`Failed to set gid: ${err}`); } } This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in `Worker` threads. ### `process.seteuid(id)`# Added in: v2.0.0 * `id` | A user name or ID The `process.seteuid()` method sets the effective user identity of the process. (See `seteuid(2)`.) The `id` can be passed as either a numeric ID or a username string. If a username is specified, the method blocks while resolving the associated numeric ID. import process from 'node:process'; if (process.geteuid && process.seteuid) { console.log(`Current uid: ${process.geteuid()}`); try { process.seteuid(501); console.log(`New uid: ${process.geteuid()}`); } catch (err) { console.error(`Failed to set uid: ${err}`); } } This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in `Worker` threads. ### `process.setgid(id)`# Added in: v0.1.31 * `id` | The group name or ID The `process.setgid()` method sets the group identity of the process. (See `setgid(2)`.) The `id` can be passed as either a numeric ID or a group name string. If a group name is specified, this method blocks while resolving the associated numeric ID. import process from 'node:process'; if (process.getgid && process.setgid) { console.log(`Current gid: ${process.getgid()}`); try { process.setgid(501); console.log(`New gid: ${process.getgid()}`); } catch (err) { console.error(`Failed to set gid: ${err}`); } } This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in `Worker` threads. ### `process.setgroups(groups)`# Added in: v0.9.4 * `groups` The `process.setgroups()` method sets the supplementary group IDs for the Node.js process. This is a privileged operation that requires the Node.js process to have `root` or the `CAP_SETGID` capability. The `groups` array can contain numeric group IDs, group names, or both. import process from 'node:process'; if (process.getgroups && process.setgroups) { try { process.setgroups([501]); console.log(process.getgroups()); // new groups } catch (err) { console.error(`Failed to set groups: ${err}`); } } This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in `Worker` threads. ### `process.setuid(id)`# Added in: v0.1.28 * `id` | The `process.setuid(id)` method sets the user identity of the process. (See `setuid(2)`.) The `id` can be passed as either a numeric ID or a username string. If a username is specified, the method blocks while resolving the associated numeric ID. import process from 'node:process'; if (process.getuid && process.setuid) { console.log(`Current uid: ${process.getuid()}`); try { process.setuid(501); console.log(`New uid: ${process.getuid()}`); } catch (err) { console.error(`Failed to set uid: ${err}`); } } This function is only available on POSIX platforms (i.e. not Windows or Android). This feature is not available in `Worker` threads. ### `process.setSourceMapsEnabled(val)`# Added in: v16.6.0, v14.18.0 Stability: 1 \- Experimental: Use `module.setSourceMapsSupport()` instead. * `val` This function enables or disables the Source Map support for stack traces. It provides same features as launching Node.js process with commandline options `--enable-source-maps`. Only source maps in JavaScript files that are loaded after source maps has been enabled will be parsed and loaded. This implies calling `module.setSourceMapsSupport()` with an option `{ nodeModules: true, generatedCode: true }`. ### `process.setUncaughtExceptionCaptureCallback(fn)`# Added in: v9.3.0 * `fn` | The `process.setUncaughtExceptionCaptureCallback()` function sets a function that will be invoked when an uncaught exception occurs, which will receive the exception value itself as its first argument. If such a function is set, the `'uncaughtException'` event will not be emitted. If `--abort-on-uncaught-exception` was passed from the command line or set through `v8.setFlagsFromString()`, the process will not abort. Actions configured to take place on exceptions such as report generations will be affected too To unset the capture function, `process.setUncaughtExceptionCaptureCallback(null)` may be used. Calling this method with a non-`null` argument while another capture function is set will throw an error. Using this function is mutually exclusive with using the deprecated `domain` built-in module. ### `process.sourceMapsEnabled`# Added in: v20.7.0, v18.19.0 Stability: 1 \- Experimental: Use `module.getSourceMapsSupport()` instead. * Type: The `process.sourceMapsEnabled` property returns whether the Source Map support for stack traces is enabled. ### `process.stderr`# * Type: The `process.stderr` property returns a stream connected to `stderr` (fd `2`). It is a `net.Socket` (which is a Duplex stream) unless fd `2` refers to a file, in which case it is a Writable stream. `process.stderr` differs from other Node.js streams in important ways. See note on process I/O for more information. #### `process.stderr.fd`# * Type: This property refers to the value of underlying file descriptor of `process.stderr`. The value is fixed at `2`. In `Worker` threads, this field does not exist. ### `process.stdin`# * Type: The `process.stdin` property returns a stream connected to `stdin` (fd `0`). It is a `net.Socket` (which is a Duplex stream) unless fd `0` refers to a file, in which case it is a Readable stream. For details of how to read from `stdin` see `readable.read()`. As a Duplex stream, `process.stdin` can also be used in "old" mode that is compatible with scripts written for Node.js prior to v0.10. For more information see Stream compatibility. In "old" streams mode the `stdin` stream is paused by default, so one must call `process.stdin.resume()` to read from it. Note also that calling `process.stdin.resume()` itself would switch stream to "old" mode. #### `process.stdin.fd`# * Type: This property refers to the value of underlying file descriptor of `process.stdin`. The value is fixed at `0`. In `Worker` threads, this field does not exist. ### `process.stdout`# * Type: The `process.stdout` property returns a stream connected to `stdout` (fd `1`). It is a `net.Socket` (which is a Duplex stream) unless fd `1` refers to a file, in which case it is a Writable stream. For example, to copy `process.stdin` to `process.stdout`: import { stdin, stdout } from 'node:process'; stdin.pipe(stdout); `process.stdout` differs from other Node.js streams in important ways. See note on process I/O for more information. #### `process.stdout.fd`# * Type: This property refers to the value of underlying file descriptor of `process.stdout`. The value is fixed at `1`. In `Worker` threads, this field does not exist. #### A note on process I/O# `process.stdout` and `process.stderr` differ from other Node.js streams in important ways: 1. They are used internally by `console.log()` and `console.error()`, respectively. 2. Writes may be synchronous depending on what the stream is connected to and whether the system is Windows or POSIX: * Files: synchronous on Windows and POSIX * TTYs (Terminals): asynchronous on Windows, synchronous on POSIX * Pipes (and sockets): synchronous on Windows, asynchronous on POSIX These behaviors are partly for historical reasons, as changing them would create backward incompatibility, but they are also expected by some users. Synchronous writes avoid problems such as output written with `console.log()` or `console.error()` being unexpectedly interleaved, or not written at all if `process.exit()` is called before an asynchronous write completes. See `process.exit()` for more information. Warning: Synchronous writes block the event loop until the write has completed. This can be near instantaneous in the case of output to a file, but under high system load, pipes that are not being read at the receiving end, or with slow terminals or file systems, it's possible for the event loop to be blocked often enough and long enough to have severe negative performance impacts. This may not be a problem when writing to an interactive terminal session, but consider this particularly careful when doing production logging to the process output streams. To check if a stream is connected to a TTY context, check the `isTTY` property. For instance: $ node -p "Boolean(process.stdin.isTTY)" true $ echo "foo" | node -p "Boolean(process.stdin.isTTY)" false $ node -p "Boolean(process.stdout.isTTY)" true $ node -p "Boolean(process.stdout.isTTY)" | cat false See the TTY documentation for more information. ### `process.throwDeprecation`# Added in: v0.9.12 * Type: The initial value of `process.throwDeprecation` indicates whether the `--throw-deprecation` flag is set on the current Node.js process. `process.throwDeprecation` is mutable, so whether or not deprecation warnings result in errors may be altered at runtime. See the documentation for the `'warning'` event and the `emitWarning()` method for more information. $ node --throw-deprecation -p "process.throwDeprecation" true $ node -p "process.throwDeprecation" undefined $ node > process.emitWarning('test', 'DeprecationWarning'); undefined > (node:26598) DeprecationWarning: test > process.throwDeprecation = true; true > process.emitWarning('test', 'DeprecationWarning'); Thrown: [DeprecationWarning: test] { name: 'DeprecationWarning' } ### `process.threadCpuUsage([previousValue])`# Added in: v23.9.0 * `previousValue` A previous return value from calling `process.threadCpuUsage()` * Returns: * `user` * `system` The `process.threadCpuUsage()` method returns the user and system CPU time usage of the current worker thread, in an object with properties `user` and `system`, whose values are microsecond values (millionth of a second). The result of a previous call to `process.threadCpuUsage()` can be passed as the argument to the function, to get a diff reading. ### `process.title`# Added in: v0.1.104 * Type: The `process.title` property returns the current process title (i.e. returns the current value of `ps`). Assigning a new value to `process.title` modifies the current value of `ps`. When a new value is assigned, different platforms will impose different maximum length restrictions on the title. Usually such restrictions are quite limited. For instance, on Linux and macOS, `process.title` is limited to the size of the binary name plus the length of the command-line arguments because setting the `process.title` overwrites the `argv` memory of the process. Node.js v0.8 allowed for longer process title strings by also overwriting the `environ` memory but that was potentially insecure and confusing in some (rather obscure) cases. Assigning a value to `process.title` might not result in an accurate label within process manager applications such as macOS Activity Monitor or Windows Services Manager. ### `process.traceDeprecation`# Added in: v0.8.0 * Type: The `process.traceDeprecation` property indicates whether the `--trace-deprecation` flag is set on the current Node.js process. See the documentation for the `'warning'` event and the `emitWarning()` method for more information about this flag's behavior. ### `process.umask()`# History VersionChanges v14.0.0, v12.19.0 Calling `process.umask()` with no arguments is deprecated. v0.1.19 Added in: v0.1.19 Stability: 0 \- Deprecated. Calling `process.umask()` with no argument causes the process-wide umask to be written twice. This introduces a race condition between threads, and is a potential security vulnerability. There is no safe, cross-platform alternative API. `process.umask()` returns the Node.js process's file mode creation mask. Child processes inherit the mask from the parent process. ### `process.umask(mask)`# Added in: v0.1.19 * `mask` | `process.umask(mask)` sets the Node.js process's file mode creation mask. Child processes inherit the mask from the parent process. Returns the previous mask. import { umask } from 'node:process'; const newmask = 0o022; const oldmask = umask(newmask); console.log( `Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`, ); In `Worker` threads, `process.umask(mask)` will throw an exception. ### `process.unref(maybeRefable)`# Added in: v23.6.0, v22.14.0 Stability: 1 \- Experimental * `maybeUnfefable` An object that may be "unref'd". An object is "unrefable" if it implements the Node.js "Refable protocol". Specifically, this means that the object implements the `Symbol.for('nodejs.ref')` and `Symbol.for('nodejs.unref')` methods. "Ref'd" objects will keep the Node.js event loop alive, while "unref'd" objects will not. Historically, this was implemented by using `ref()` and `unref()` methods directly on the objects. This pattern, however, is being deprecated in favor of the "Refable protocol" in order to better support Web Platform API types whose APIs cannot be modified to add `ref()` and `unref()` methods but still need to support that behavior. ### `process.uptime()`# Added in: v0.5.0 * Returns: The `process.uptime()` method returns the number of seconds the current Node.js process has been running. The return value includes fractions of a second. Use `Math.floor()` to get whole seconds. ### `process.version`# Added in: v0.1.3 * Type: The `process.version` property contains the Node.js version string. import { version } from 'node:process'; console.log(`Version: ${version}`); // Version: v14.8.0 To get the version string without the prepended v, use `process.versions.node`. ### `process.versions`# History VersionChanges v9.0.0 The `v8` property now includes a Node.js specific suffix. v4.2.0 The `icu` property is now supported. v0.2.0 Added in: v0.2.0 * Type: The `process.versions` property returns an object listing the version strings of Node.js and its dependencies. `process.versions.modules` indicates the current ABI version, which is increased whenever a C++ API changes. Node.js will refuse to load modules that were compiled against a different module ABI version. import { versions } from 'node:process'; console.log(versions); Will generate an object similar to: { node: '23.0.0', acorn: '8.11.3', ada: '2.7.8', ares: '1.28.1', base64: '0.5.2', brotli: '1.1.0', cjs_module_lexer: '1.2.2', cldr: '45.0', icu: '75.1', llhttp: '9.2.1', modules: '127', napi: '9', nghttp2: '1.61.0', nghttp3: '0.7.0', ngtcp2: '1.3.0', openssl: '3.0.13+quic', simdjson: '3.8.0', simdutf: '5.2.4', sqlite: '3.46.0', tz: '2024a', undici: '6.13.0', unicode: '15.1', uv: '1.48.0', uvwasi: '0.0.20', v8: '12.4.254.14-node.11', zlib: '1.3.0.1-motley-7d77fb7' } ### Exit codes# Node.js will normally exit with a `0` status code when no more async operations are pending. The following status codes are used in other cases: * `1` Uncaught Fatal Exception: There was an uncaught exception, and it was not handled by a domain or an `'uncaughtException'` event handler. * `2`: Unused (reserved by Bash for builtin misuse) * `3` Internal JavaScript Parse Error: The JavaScript source code internal in the Node.js bootstrapping process caused a parse error. This is extremely rare, and generally can only happen during development of Node.js itself. * `4` Internal JavaScript Evaluation Failure: The JavaScript source code internal in the Node.js bootstrapping process failed to return a function value when evaluated. This is extremely rare, and generally can only happen during development of Node.js itself. * `5` Fatal Error: There was a fatal unrecoverable error in V8. Typically a message will be printed to stderr with the prefix `FATAL ERROR`. * `6` Non-function Internal Exception Handler: There was an uncaught exception, but the internal fatal exception handler function was somehow set to a non-function, and could not be called. * `7` Internal Exception Handler Run-Time Failure: There was an uncaught exception, and the internal fatal exception handler function itself threw an error while attempting to handle it. This can happen, for example, if an `'uncaughtException'` or `domain.on('error')` handler throws an error. * `8`: Unused. In previous versions of Node.js, exit code 8 sometimes indicated an uncaught exception. * `9` Invalid Argument: Either an unknown option was specified, or an option requiring a value was provided without a value. * `10` Internal JavaScript Run-Time Failure: The JavaScript source code internal in the Node.js bootstrapping process threw an error when the bootstrapping function was called. This is extremely rare, and generally can only happen during development of Node.js itself. * `12` Invalid Debug Argument: The `--inspect` and/or `--inspect-brk` options were set, but the port number chosen was invalid or unavailable. * `13` Unsettled Top-Level Await: `await` was used outside of a function in the top-level code, but the passed `Promise` never settled. * `14` Snapshot Failure: Node.js was started to build a V8 startup snapshot and it failed because certain requirements of the state of the application were not met. * `>128` Signal Exits: If Node.js receives a fatal signal such as `SIGKILL` or `SIGHUP`, then its exit code will be `128` plus the value of the signal code. This is a standard POSIX practice, since exit codes are defined to be 7-bit integers, and signal exits set the high-order bit, and then contain the value of the signal code. For example, signal `SIGABRT` has value `6`, so the expected exit code will be `128` \+ `6`, or `134`. ## Punycode# Deprecated since: v7.0.0 Stability: 0 \- Deprecated Source Code: lib/punycode.js The version of the punycode module bundled in Node.js is being deprecated. In a future major version of Node.js this module will be removed. Users currently depending on the `punycode` module should switch to using the userland-provided Punycode.js module instead. For punycode-based URL encoding, see `url.domainToASCII` or, more generally, the WHATWG URL API. The `punycode` module is a bundled version of the Punycode.js module. It can be accessed using: const punycode = require('node:punycode'); Punycode is a character encoding scheme defined by RFC 3492 that is primarily intended for use in Internationalized Domain Names. Because host names in URLs are limited to ASCII characters only, Domain Names that contain non-ASCII characters must be converted into ASCII using the Punycode scheme. For instance, the Japanese character that translates into the English word, `'example'` is `'例'`. The Internationalized Domain Name, `'例.com'` (equivalent to `'example.com'`) is represented by Punycode as the ASCII string `'xn--fsq.com'`. The `punycode` module provides a simple implementation of the Punycode standard. The `punycode` module is a third-party dependency used by Node.js and made available to developers as a convenience. Fixes or other modifications to the module must be directed to the Punycode.js project. ### `punycode.decode(string)`# Added in: v0.5.1 * `string` The `punycode.decode()` method converts a Punycode string of ASCII-only characters to the equivalent string of Unicode codepoints. punycode.decode('maana-pta'); // 'mañana' punycode.decode('--dqo34k'); // '☃-⌘' ### `punycode.encode(string)`# Added in: v0.5.1 * `string` The `punycode.encode()` method converts a string of Unicode codepoints to a Punycode string of ASCII-only characters. punycode.encode('mañana'); // 'maana-pta' punycode.encode('☃-⌘'); // '--dqo34k' ### `punycode.toASCII(domain)`# Added in: v0.6.1 * `domain` The `punycode.toASCII()` method converts a Unicode string representing an Internationalized Domain Name to Punycode. Only the non-ASCII parts of the domain name will be converted. Calling `punycode.toASCII()` on a string that already only contains ASCII characters will have no effect. // encode domain names punycode.toASCII('mañana.com'); // 'xn--maana-pta.com' punycode.toASCII('☃-⌘.com'); // 'xn----dqo34k.com' punycode.toASCII('example.com'); // 'example.com' ### `punycode.toUnicode(domain)`# Added in: v0.6.1 * `domain` The `punycode.toUnicode()` method converts a string representing a domain name containing Punycode encoded characters into Unicode. Only the Punycode encoded parts of the domain name are be converted. // decode domain names punycode.toUnicode('xn--maana-pta.com'); // 'mañana.com' punycode.toUnicode('xn----dqo34k.com'); // '☃-⌘.com' punycode.toUnicode('example.com'); // 'example.com' ### `punycode.ucs2`# Added in: v0.7.0 #### `punycode.ucs2.decode(string)`# Added in: v0.7.0 * `string` The `punycode.ucs2.decode()` method returns an array containing the numeric codepoint values of each Unicode symbol in the string. punycode.ucs2.decode('abc'); // [0x61, 0x62, 0x63] // surrogate pair for U+1D306 tetragram for centre: punycode.ucs2.decode('\uD834\uDF06'); // [0x1D306] #### `punycode.ucs2.encode(codePoints)`# Added in: v0.7.0 * `codePoints` The `punycode.ucs2.encode()` method returns a string based on an array of numeric code point values. punycode.ucs2.encode([0x61, 0x62, 0x63]); // 'abc' punycode.ucs2.encode([0x1D306]); // '\uD834\uDF06' ### `punycode.version`# Added in: v0.6.1 * Type: Returns a string identifying the current Punycode.js version number. ## Query string# Stability: 2 \- Stable Source Code: lib/querystring.js The `node:querystring` module provides utilities for parsing and formatting URL query strings. It can be accessed using: const querystring = require('node:querystring'); `querystring` is more performant than but is not a standardized API. Use when performance is not critical or when compatibility with browser code is desirable. ### `querystring.decode()`# Added in: v0.1.99 The `querystring.decode()` function is an alias for `querystring.parse()`. ### `querystring.encode()`# Added in: v0.1.99 The `querystring.encode()` function is an alias for `querystring.stringify()`. ### `querystring.escape(str)`# Added in: v0.1.25 * `str` The `querystring.escape()` method performs URL percent-encoding on the given `str` in a manner that is optimized for the specific requirements of URL query strings. The `querystring.escape()` method is used by `querystring.stringify()` and is generally not expected to be used directly. It is exported primarily to allow application code to provide a replacement percent-encoding implementation if necessary by assigning `querystring.escape` to an alternative function. ### `querystring.parse(str[, sep[, eq[, options]]])`# History VersionChanges v8.0.0 Multiple empty entries are now parsed correctly (e.g. `&=&=`). v6.0.0 The returned object no longer inherits from `Object.prototype`. v6.0.0, v4.2.4 The `eq` parameter may now have a length of more than `1`. v0.1.25 Added in: v0.1.25 * `str` The URL query string to parse * `sep` The substring used to delimit key and value pairs in the query string. Default: `'&'`. * `eq` . The substring used to delimit keys and values in the query string. Default: `'='`. * `options` * `decodeURIComponent` The function to use when decoding percent-encoded characters in the query string. Default: `querystring.unescape()`. * `maxKeys` Specifies the maximum number of keys to parse. Specify `0` to remove key counting limitations. Default: `1000`. The `querystring.parse()` method parses a URL query string (`str`) into a collection of key and value pairs. For example, the query string `'foo=bar&abc=xyz&abc=123'` is parsed into: { "foo": "bar", "abc": ["xyz", "123"] } The object returned by the `querystring.parse()` method does not prototypically inherit from the JavaScript `Object`. This means that typical `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others are not defined and will not work. By default, percent-encoded characters within the query string will be assumed to use UTF-8 encoding. If an alternative character encoding is used, then an alternative `decodeURIComponent` option will need to be specified: // Assuming gbkDecodeURIComponent function already exists... querystring.parse('w=%D6%D0%CE%C4&foo=bar', null, null, { decodeURIComponent: gbkDecodeURIComponent }); ### `querystring.stringify(obj[, sep[, eq[, options]]])`# Added in: v0.1.25 * `obj` The object to serialize into a URL query string * `sep` The substring used to delimit key and value pairs in the query string. Default: `'&'`. * `eq` . The substring used to delimit keys and values in the query string. Default: `'='`. * `options` * `encodeURIComponent` The function to use when converting URL-unsafe characters to percent-encoding in the query string. Default: `querystring.escape()`. The `querystring.stringify()` method produces a URL query string from a given `obj` by iterating through the object's "own properties". It serializes the following types of values passed in `obj`: | | | | | | | The numeric values must be finite. Any other input values will be coerced to empty strings. querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' }); // Returns 'foo=bar&baz=qux&baz=quux&corge=' querystring.stringify({ foo: 'bar', baz: 'qux' }, ';', ':'); // Returns 'foo:bar;baz:qux' By default, characters requiring percent-encoding within the query string will be encoded as UTF-8. If an alternative encoding is required, then an alternative `encodeURIComponent` option will need to be specified: // Assuming gbkEncodeURIComponent function already exists, querystring.stringify({ w: '中文', foo: 'bar' }, null, null, { encodeURIComponent: gbkEncodeURIComponent }); ### `querystring.unescape(str)`# Added in: v0.1.25 * `str` The `querystring.unescape()` method performs decoding of URL percent-encoded characters on the given `str`. The `querystring.unescape()` method is used by `querystring.parse()` and is generally not expected to be used directly. It is exported primarily to allow application code to provide a replacement decoding implementation if necessary by assigning `querystring.unescape` to an alternative function. By default, the `querystring.unescape()` method will attempt to use the JavaScript built-in `decodeURIComponent()` method to decode. If that fails, a safer equivalent that does not throw on malformed URLs will be used. ## Readline# Stability: 2 \- Stable Source Code: lib/readline.js The `node:readline` module provides an interface for reading data from a Readable stream (such as `process.stdin`) one line at a time. To use the promise-based APIs: import * as readline from 'node:readline/promises'; To use the callback and sync APIs: import * as readline from 'node:readline'; The following simple example illustrates the basic use of the `node:readline` module. import * as readline from 'node:readline/promises'; import { stdin as input, stdout as output } from 'node:process'; const rl = readline.createInterface({ input, output }); const answer = await rl.question('What do you think of Node.js? '); console.log(`Thank you for your valuable feedback: ${answer}`); rl.close(); Once this code is invoked, the Node.js application will not terminate until the `readline.Interface` is closed because the interface waits for data to be received on the `input` stream. ### Class: `InterfaceConstructor`# Added in: v0.1.104 * Extends: Instances of the `InterfaceConstructor` class are constructed using the `readlinePromises.createInterface()` or `readline.createInterface()` method. Every instance is associated with a single `input` Readable stream and a single `output` Writable stream. The `output` stream is used to print prompts for user input that arrives on, and is read from, the `input` stream. #### Event: `'close'`# Added in: v0.1.98 The `'close'` event is emitted when one of the following occur: * The `rl.close()` method is called and the `InterfaceConstructor` instance has relinquished control over the `input` and `output` streams; * The `input` stream receives its `'end'` event; * The `input` stream receives `Ctrl`+`D` to signal end-of-transmission (EOT); * The `input` stream receives `Ctrl`+`C` to signal `SIGINT` and there is no `'SIGINT'` event listener registered on the `InterfaceConstructor` instance. The listener function is called without passing any arguments. The `InterfaceConstructor` instance is finished once the `'close'` event is emitted. #### Event: `'line'`# Added in: v0.1.98 The `'line'` event is emitted whenever the `input` stream receives an end-of-line input (`\n`, `\r`, or `\r\n`). This usually occurs when the user presses `Enter` or `Return`. The `'line'` event is also emitted if new data has been read from a stream and that stream ends without a final end-of-line marker. The listener function is called with a string containing the single line of received input. rl.on('line', (input) => { console.log(`Received: ${input}`); }); #### Event: `'history'`# Added in: v15.8.0, v14.18.0 The `'history'` event is emitted whenever the history array has changed. The listener function is called with an array containing the history array. It will reflect all changes, added lines and removed lines due to `historySize` and `removeHistoryDuplicates`. The primary purpose is to allow a listener to persist the history. It is also possible for the listener to change the history object. This could be useful to prevent certain lines to be added to the history, like a password. rl.on('history', (history) => { console.log(`Received: ${history}`); }); #### Event: `'pause'`# Added in: v0.7.5 The `'pause'` event is emitted when one of the following occur: * The `input` stream is paused. * The `input` stream is not paused and receives the `'SIGCONT'` event. (See events `'SIGTSTP'` and `'SIGCONT'`.) The listener function is called without passing any arguments. rl.on('pause', () => { console.log('Readline paused.'); }); #### Event: `'resume'`# Added in: v0.7.5 The `'resume'` event is emitted whenever the `input` stream is resumed. The listener function is called without passing any arguments. rl.on('resume', () => { console.log('Readline resumed.'); }); #### Event: `'SIGCONT'`# Added in: v0.7.5 The `'SIGCONT'` event is emitted when a Node.js process previously moved into the background using `Ctrl`+`Z` (i.e. `SIGTSTP`) is then brought back to the foreground using `fg(1p)`. If the `input` stream was paused before the `SIGTSTP` request, this event will not be emitted. The listener function is invoked without passing any arguments. rl.on('SIGCONT', () => { // `prompt` will automatically resume the stream rl.prompt(); }); The `'SIGCONT'` event is not supported on Windows. #### Event: `'SIGINT'`# Added in: v0.3.0 The `'SIGINT'` event is emitted whenever the `input` stream receives a `Ctrl+C` input, known typically as `SIGINT`. If there are no `'SIGINT'` event listeners registered when the `input` stream receives a `SIGINT`, the `'pause'` event will be emitted. The listener function is invoked without passing any arguments. rl.on('SIGINT', () => { rl.question('Are you sure you want to exit? ', (answer) => { if (answer.match(/^y(es)?$/i)) rl.pause(); }); }); #### Event: `'SIGTSTP'`# Added in: v0.7.5 The `'SIGTSTP'` event is emitted when the `input` stream receives a `Ctrl`+`Z` input, typically known as `SIGTSTP`. If there are no `'SIGTSTP'` event listeners registered when the `input` stream receives a `SIGTSTP`, the Node.js process will be sent to the background. When the program is resumed using `fg(1p)`, the `'pause'` and `'SIGCONT'` events will be emitted. These can be used to resume the `input` stream. The `'pause'` and `'SIGCONT'` events will not be emitted if the `input` was paused before the process was sent to the background. The listener function is invoked without passing any arguments. rl.on('SIGTSTP', () => { // This will override SIGTSTP and prevent the program from going to the // background. console.log('Caught SIGTSTP.'); }); The `'SIGTSTP'` event is not supported on Windows. #### `rl.close()`# Added in: v0.1.98 The `rl.close()` method closes the `InterfaceConstructor` instance and relinquishes control over the `input` and `output` streams. When called, the `'close'` event will be emitted. Calling `rl.close()` does not immediately stop other events (including `'line'`) from being emitted by the `InterfaceConstructor` instance. #### `rl[Symbol.dispose]()`# Added in: v23.10.0, v22.15.0 Alias for `rl.close()`. #### `rl.pause()`# Added in: v0.3.4 The `rl.pause()` method pauses the `input` stream, allowing it to be resumed later if necessary. Calling `rl.pause()` does not immediately pause other events (including `'line'`) from being emitted by the `InterfaceConstructor` instance. #### `rl.prompt([preserveCursor])`# Added in: v0.1.98 * `preserveCursor` If `true`, prevents the cursor placement from being reset to `0`. The `rl.prompt()` method writes the `InterfaceConstructor` instances configured `prompt` to a new line in `output` in order to provide a user with a new location at which to provide input. When called, `rl.prompt()` will resume the `input` stream if it has been paused. If the `InterfaceConstructor` was created with `output` set to `null` or `undefined` the prompt is not written. #### `rl.resume()`# Added in: v0.3.4 The `rl.resume()` method resumes the `input` stream if it has been paused. #### `rl.setPrompt(prompt)`# Added in: v0.1.98 * `prompt` The `rl.setPrompt()` method sets the prompt that will be written to `output` whenever `rl.prompt()` is called. #### `rl.getPrompt()`# Added in: v15.3.0, v14.17.0 * Returns: the current prompt string The `rl.getPrompt()` method returns the current prompt used by `rl.prompt()`. #### `rl.write(data[, key])`# Added in: v0.1.98 * `data` * `key` * `ctrl` `true` to indicate the `Ctrl` key. * `meta` `true` to indicate the `Meta` key. * `shift` `true` to indicate the `Shift` key. * `name` The name of the a key. The `rl.write()` method will write either `data` or a key sequence identified by `key` to the `output`. The `key` argument is supported only if `output` is a TTY text terminal. See TTY keybindings for a list of key combinations. If `key` is specified, `data` is ignored. When called, `rl.write()` will resume the `input` stream if it has been paused. If the `InterfaceConstructor` was created with `output` set to `null` or `undefined` the `data` and `key` are not written. rl.write('Delete this!'); // Simulate Ctrl+U to delete the line written previously rl.write(null, { ctrl: true, name: 'u' }); The `rl.write()` method will write the data to the `readline` `Interface`'s `input` as if it were provided by the user. #### `rl[Symbol.asyncIterator]()`# History VersionChanges v11.14.0, v10.17.0 Symbol.asyncIterator support is no longer experimental. v11.4.0, v10.16.0 Added in: v11.4.0, v10.16.0 * Returns: Create an `AsyncIterator` object that iterates through each line in the input stream as a string. This method allows asynchronous iteration of `InterfaceConstructor` objects through `for await...of` loops. Errors in the input stream are not forwarded. If the loop is terminated with `break`, `throw`, or `return`, `rl.close()` will be called. In other words, iterating over a `InterfaceConstructor` will always consume the input stream fully. Performance is not on par with the traditional `'line'` event API. Use `'line'` instead for performance-sensitive applications. async function processLineByLine() { const rl = readline.createInterface({ // ... }); for await (const line of rl) { // Each line in the readline input will be successively available here as // `line`. } } `readline.createInterface()` will start to consume the input stream once invoked. Having asynchronous operations between interface creation and asynchronous iteration may result in missed lines. #### `rl.line`# History VersionChanges v15.8.0, v14.18.0 Value will always be a string, never undefined. v0.1.98 Added in: v0.1.98 * Type: The current input data being processed by node. This can be used when collecting input from a TTY stream to retrieve the current value that has been processed thus far, prior to the `line` event being emitted. Once the `line` event has been emitted, this property will be an empty string. Be aware that modifying the value during the instance runtime may have unintended consequences if `rl.cursor` is not also controlled. If not using a TTY stream for input, use the `'line'` event. One possible use case would be as follows: const values = ['lorem ipsum', 'dolor sit amet']; const rl = readline.createInterface(process.stdin); const showResults = debounce(() => { console.log( '\n', values.filter((val) => val.startsWith(rl.line)).join(' '), ); }, 300); process.stdin.on('keypress', (c, k) => { showResults(); }); #### `rl.cursor`# Added in: v0.1.98 * Type: | The cursor position relative to `rl.line`. This will track where the current cursor lands in the input string, when reading input from a TTY stream. The position of cursor determines the portion of the input string that will be modified as input is processed, as well as the column where the terminal caret will be rendered. #### `rl.getCursorPos()`# Added in: v13.5.0, v12.16.0 * Returns: * `rows` the row of the prompt the cursor currently lands on * `cols` the screen column the cursor currently lands on Returns the real position of the cursor in relation to the input prompt + string. Long input (wrapping) strings, as well as multiple line prompts are included in the calculations. ### Promises API# History VersionChanges v24.0.0 Marking the API stable. v17.0.0 Added in: v17.0.0 #### Class: `readlinePromises.Interface`# Added in: v17.0.0 * Extends: Instances of the `readlinePromises.Interface` class are constructed using the `readlinePromises.createInterface()` method. Every instance is associated with a single `input` Readable stream and a single `output` Writable stream. The `output` stream is used to print prompts for user input that arrives on, and is read from, the `input` stream. ##### `rl.question(query[, options])`# Added in: v17.0.0 * `query` A statement or query to write to `output`, prepended to the prompt. * `options` * `signal` Optionally allows the `question()` to be canceled using an `AbortSignal`. * Returns: A promise that is fulfilled with the user's input in response to the `query`. The `rl.question()` method displays the `query` by writing it to the `output`, waits for user input to be provided on `input`, then invokes the `callback` function passing the provided input as the first argument. When called, `rl.question()` will resume the `input` stream if it has been paused. If the `readlinePromises.Interface` was created with `output` set to `null` or `undefined` the `query` is not written. If the question is called after `rl.close()`, it returns a rejected promise. Example usage: const answer = await rl.question('What is your favorite food? '); console.log(`Oh, so your favorite food is ${answer}`); Using an `AbortSignal` to cancel a question. const signal = AbortSignal.timeout(10_000); signal.addEventListener('abort', () => { console.log('The food question timed out'); }, { once: true }); const answer = await rl.question('What is your favorite food? ', { signal }); console.log(`Oh, so your favorite food is ${answer}`); #### Class: `readlinePromises.Readline`# Added in: v17.0.0 ##### `new readlinePromises.Readline(stream[, options])`# Added in: v17.0.0 * `stream` A TTY stream. * `options` * `autoCommit` If `true`, no need to call `rl.commit()`. ##### `rl.clearLine(dir)`# Added in: v17.0.0 * `dir` * `-1`: to the left from cursor * `1`: to the right from cursor * `0`: the entire line * Returns: this The `rl.clearLine()` method adds to the internal list of pending action an action that clears current line of the associated `stream` in a specified direction identified by `dir`. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor. ##### `rl.clearScreenDown()`# Added in: v17.0.0 * Returns: this The `rl.clearScreenDown()` method adds to the internal list of pending action an action that clears the associated stream from the current position of the cursor down. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor. ##### `rl.commit()`# Added in: v17.0.0 * Returns: The `rl.commit()` method sends all the pending actions to the associated `stream` and clears the internal list of pending actions. ##### `rl.cursorTo(x[, y])`# Added in: v17.0.0 * `x` * `y` * Returns: this The `rl.cursorTo()` method adds to the internal list of pending action an action that moves cursor to the specified position in the associated `stream`. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor. ##### `rl.moveCursor(dx, dy)`# Added in: v17.0.0 * `dx` * `dy` * Returns: this The `rl.moveCursor()` method adds to the internal list of pending action an action that moves the cursor relative to its current position in the associated `stream`. Call `rl.commit()` to see the effect of this method, unless `autoCommit: true` was passed to the constructor. ##### `rl.rollback()`# Added in: v17.0.0 * Returns: this The `rl.rollback` methods clears the internal list of pending actions without sending it to the associated `stream`. #### `readlinePromises.createInterface(options)`# Added in: v17.0.0 * `options` * `input` The Readable stream to listen to. This option is required. * `output` The Writable stream to write readline data to. * `completer` An optional function used for Tab autocompletion. * `terminal` `true` if the `input` and `output` streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Default: checking `isTTY` on the `output` stream upon instantiation. * `history` Initial list of history lines. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. Default: `[]`. * `historySize` Maximum number of history lines retained. To disable the history set this value to `0`. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. Default: `30`. * `removeHistoryDuplicates` If `true`, when a new input line added to the history list duplicates an older one, this removes the older line from the list. Default: `false`. * `prompt` The prompt string to use. Default: `'> '`. * `crlfDelay` If the delay between `\r` and `\n` exceeds `crlfDelay` milliseconds, both `\r` and `\n` will be treated as separate end-of-line input. `crlfDelay` will be coerced to a number no less than `100`. It can be set to `Infinity`, in which case `\r` followed by `\n` will always be considered a single newline (which may be reasonable for reading files with `\r\n` line delimiter). Default: `100`. * `escapeCodeTimeout` The duration `readlinePromises` will wait for a character (when reading an ambiguous key sequence in milliseconds one that can both form a complete key sequence using the input read so far and can take additional input to complete a longer key sequence). Default: `500`. * `tabSize` The number of spaces a tab is equal to (minimum 1). Default: `8`. * `signal` Allows closing the interface using an AbortSignal. * Returns: The `readlinePromises.createInterface()` method creates a new `readlinePromises.Interface` instance. import { createInterface } from 'node:readline/promises'; import { stdin, stdout } from 'node:process'; const rl = createInterface({ input: stdin, output: stdout, }); Once the `readlinePromises.Interface` instance is created, the most common case is to listen for the `'line'` event: rl.on('line', (line) => { console.log(`Received: ${line}`); }); If `terminal` is `true` for this instance then the `output` stream will get the best compatibility if it defines an `output.columns` property and emits a `'resize'` event on the `output` if or when the columns ever change (`process.stdout` does this automatically when it is a TTY). ##### Use of the `completer` function# The `completer` function takes the current line entered by the user as an argument, and returns an `Array` with 2 entries: * An `Array` with matching entries for the completion. * The substring that was used for the matching. For instance: `[[substr1, substr2, ...], originalsubstring]`. function completer(line) { const completions = '.help .error .exit .quit .q'.split(' '); const hits = completions.filter((c) => c.startsWith(line)); // Show all completions if none found return [hits.length ? hits : completions, line]; } The `completer` function can also return a , or be asynchronous: async function completer(linePartial) { await someAsyncWork(); return [['123'], linePartial]; } ### Callback API# Added in: v0.1.104 #### Class: `readline.Interface`# History VersionChanges v17.0.0 The class `readline.Interface` now inherits from `Interface`. v0.1.104 Added in: v0.1.104 * Extends: Instances of the `readline.Interface` class are constructed using the `readline.createInterface()` method. Every instance is associated with a single `input` Readable stream and a single `output` Writable stream. The `output` stream is used to print prompts for user input that arrives on, and is read from, the `input` stream. ##### `rl.question(query[, options], callback)`# Added in: v0.3.3 * `query` A statement or query to write to `output`, prepended to the prompt. * `options` * `signal` Optionally allows the `question()` to be canceled using an `AbortController`. * `callback` A callback function that is invoked with the user's input in response to the `query`. The `rl.question()` method displays the `query` by writing it to the `output`, waits for user input to be provided on `input`, then invokes the `callback` function passing the provided input as the first argument. When called, `rl.question()` will resume the `input` stream if it has been paused. If the `readline.Interface` was created with `output` set to `null` or `undefined` the `query` is not written. The `callback` function passed to `rl.question()` does not follow the typical pattern of accepting an `Error` object or `null` as the first argument. The `callback` is called with the provided answer as the only argument. An error will be thrown if calling `rl.question()` after `rl.close()`. Example usage: rl.question('What is your favorite food? ', (answer) => { console.log(`Oh, so your favorite food is ${answer}`); }); Using an `AbortController` to cancel a question. const ac = new AbortController(); const signal = ac.signal; rl.question('What is your favorite food? ', { signal }, (answer) => { console.log(`Oh, so your favorite food is ${answer}`); }); signal.addEventListener('abort', () => { console.log('The food question timed out'); }, { once: true }); setTimeout(() => ac.abort(), 10000); #### `readline.clearLine(stream, dir[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v12.7.0 The stream's write() callback and return value are exposed. v0.7.7 Added in: v0.7.7 * `stream` * `dir` * `-1`: to the left from cursor * `1`: to the right from cursor * `0`: the entire line * `callback` Invoked once the operation completes. * Returns: `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`. The `readline.clearLine()` method clears current line of given TTY stream in a specified direction identified by `dir`. #### `readline.clearScreenDown(stream[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v12.7.0 The stream's write() callback and return value are exposed. v0.7.7 Added in: v0.7.7 * `stream` * `callback` Invoked once the operation completes. * Returns: `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`. The `readline.clearScreenDown()` method clears the given TTY stream from the current position of the cursor down. #### `readline.createInterface(options)`# History VersionChanges v15.14.0, v14.18.0 The `signal` option is supported now. v15.8.0, v14.18.0 The `history` option is supported now. v13.9.0 The `tabSize` option is supported now. v8.3.0, v6.11.4 Remove max limit of `crlfDelay` option. v6.6.0 The `crlfDelay` option is supported now. v6.3.0 The `prompt` option is supported now. v6.0.0 The `historySize` option can be `0` now. v0.1.98 Added in: v0.1.98 * `options` * `input` The Readable stream to listen to. This option is required. * `output` The Writable stream to write readline data to. * `completer` An optional function used for Tab autocompletion. * `terminal` `true` if the `input` and `output` streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Default: checking `isTTY` on the `output` stream upon instantiation. * `history` Initial list of history lines. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. Default: `[]`. * `historySize` Maximum number of history lines retained. To disable the history set this value to `0`. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. Default: `30`. * `removeHistoryDuplicates` If `true`, when a new input line added to the history list duplicates an older one, this removes the older line from the list. Default: `false`. * `prompt` The prompt string to use. Default: `'> '`. * `crlfDelay` If the delay between `\r` and `\n` exceeds `crlfDelay` milliseconds, both `\r` and `\n` will be treated as separate end-of-line input. `crlfDelay` will be coerced to a number no less than `100`. It can be set to `Infinity`, in which case `\r` followed by `\n` will always be considered a single newline (which may be reasonable for reading files with `\r\n` line delimiter). Default: `100`. * `escapeCodeTimeout` The duration `readline` will wait for a character (when reading an ambiguous key sequence in milliseconds one that can both form a complete key sequence using the input read so far and can take additional input to complete a longer key sequence). Default: `500`. * `tabSize` The number of spaces a tab is equal to (minimum 1). Default: `8`. * `signal` Allows closing the interface using an AbortSignal. Aborting the signal will internally call `close` on the interface. * Returns: The `readline.createInterface()` method creates a new `readline.Interface` instance. import { createInterface } from 'node:readline'; import { stdin, stdout } from 'node:process'; const rl = createInterface({ input: stdin, output: stdout, }); Once the `readline.Interface` instance is created, the most common case is to listen for the `'line'` event: rl.on('line', (line) => { console.log(`Received: ${line}`); }); If `terminal` is `true` for this instance then the `output` stream will get the best compatibility if it defines an `output.columns` property and emits a `'resize'` event on the `output` if or when the columns ever change (`process.stdout` does this automatically when it is a TTY). When creating a `readline.Interface` using `stdin` as input, the program will not terminate until it receives an EOF character. To exit without waiting for user input, call `process.stdin.unref()`. ##### Use of the `completer` function# The `completer` function takes the current line entered by the user as an argument, and returns an `Array` with 2 entries: * An `Array` with matching entries for the completion. * The substring that was used for the matching. For instance: `[[substr1, substr2, ...], originalsubstring]`. function completer(line) { const completions = '.help .error .exit .quit .q'.split(' '); const hits = completions.filter((c) => c.startsWith(line)); // Show all completions if none found return [hits.length ? hits : completions, line]; } The `completer` function can be called asynchronously if it accepts two arguments: function completer(linePartial, callback) { callback(null, [['123'], linePartial]); } #### `readline.cursorTo(stream, x[, y][, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v12.7.0 The stream's write() callback and return value are exposed. v0.7.7 Added in: v0.7.7 * `stream` * `x` * `y` * `callback` Invoked once the operation completes. * Returns: `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`. The `readline.cursorTo()` method moves cursor to the specified position in a given TTY `stream`. #### `readline.moveCursor(stream, dx, dy[, callback])`# History VersionChanges v18.0.0 Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. v12.7.0 The stream's write() callback and return value are exposed. v0.7.7 Added in: v0.7.7 * `stream` * `dx` * `dy` * `callback` Invoked once the operation completes. * Returns: `false` if `stream` wishes for the calling code to wait for the `'drain'` event to be emitted before continuing to write additional data; otherwise `true`. The `readline.moveCursor()` method moves the cursor relative to its current position in a given TTY `stream`. ### `readline.emitKeypressEvents(stream[, interface])`# Added in: v0.7.7 * `stream` * `interface` The `readline.emitKeypressEvents()` method causes the given Readable stream to begin emitting `'keypress'` events corresponding to received input. Optionally, `interface` specifies a `readline.Interface` instance for which autocompletion is disabled when copy-pasted input is detected. If the `stream` is a TTY, then it must be in raw mode. This is automatically called by any readline instance on its `input` if the `input` is a terminal. Closing the `readline` instance does not stop the `input` from emitting `'keypress'` events. readline.emitKeypressEvents(process.stdin); if (process.stdin.isTTY) process.stdin.setRawMode(true); ### Example: Tiny CLI# The following example illustrates the use of `readline.Interface` class to implement a small command-line interface: import { createInterface } from 'node:readline'; import { exit, stdin, stdout } from 'node:process'; const rl = createInterface({ input: stdin, output: stdout, prompt: 'OHAI> ', }); rl.prompt(); rl.on('line', (line) => { switch (line.trim()) { case 'hello': console.log('world!'); break; default: console.log(`Say what? I might have heard '${line.trim()}'`); break; } rl.prompt(); }).on('close', () => { console.log('Have a great day!'); exit(0); }); ### Example: Read file stream line-by-Line# A common use case for `readline` is to consume an input file one line at a time. The easiest way to do so is leveraging the `fs.ReadStream` API as well as a `for await...of` loop: import { createReadStream } from 'node:fs'; import { createInterface } from 'node:readline'; async function processLineByLine() { const fileStream = createReadStream('input.txt'); const rl = createInterface({ input: fileStream, crlfDelay: Infinity, }); // Note: we use the crlfDelay option to recognize all instances of CR LF // ('\r\n') in input.txt as a single line break. for await (const line of rl) { // Each line in input.txt will be successively available here as `line`. console.log(`Line from file: ${line}`); } } processLineByLine(); Alternatively, one could use the `'line'` event: import { createReadStream } from 'node:fs'; import { createInterface } from 'node:readline'; const rl = createInterface({ input: createReadStream('sample.txt'), crlfDelay: Infinity, }); rl.on('line', (line) => { console.log(`Line from file: ${line}`); }); Currently, `for await...of` loop can be a bit slower. If `async` / `await` flow and speed are both essential, a mixed approach can be applied: import { once } from 'node:events'; import { createReadStream } from 'node:fs'; import { createInterface } from 'node:readline'; (async function processLineByLine() { try { const rl = createInterface({ input: createReadStream('big-file.txt'), crlfDelay: Infinity, }); rl.on('line', (line) => { // Process the line. }); await once(rl, 'close'); console.log('File processed.'); } catch (err) { console.error(err); } })(); ### TTY keybindings# Keybindings Description Notes `Ctrl`+`Shift`+`Backspace` Delete line left Doesn't work on Linux, Mac and Windows `Ctrl`+`Shift`+`Delete` Delete line right Doesn't work on Mac `Ctrl`+`C` Emit `SIGINT` or close the readline instance `Ctrl`+`H` Delete left `Ctrl`+`D` Delete right or close the readline instance in case the current line is empty / EOF Doesn't work on Windows `Ctrl`+`U` Delete from the current position to the line start `Ctrl`+`K` Delete from the current position to the end of line `Ctrl`+`Y` Yank (Recall) the previously deleted text Only works with text deleted by `Ctrl`+`U` or `Ctrl`+`K` `Meta`+`Y` Cycle among previously deleted texts Only available when the last keystroke is `Ctrl`+`Y` or `Meta`+`Y` `Ctrl`+`A` Go to start of line `Ctrl`+`E` Go to end of line `Ctrl`+`B` Back one character `Ctrl`+`F` Forward one character `Ctrl`+`L` Clear screen `Ctrl`+`N` Next history item `Ctrl`+`P` Previous history item `Ctrl`+`-` Undo previous change Any keystroke that emits key code `0x1F` will do this action. In many terminals, for example `xterm`, this is bound to `Ctrl`+`-`. `Ctrl`+`6` Redo previous change Many terminals don't have a default redo keystroke. We choose key code `0x1E` to perform redo. In `xterm`, it is bound to `Ctrl`+`6` by default. `Ctrl`+`Z` Moves running process into background. Type `fg` and press `Enter` to return. Doesn't work on Windows `Ctrl`+`W` or `Ctrl` +`Backspace` Delete backward to a word boundary `Ctrl`+`Backspace` Doesn't work on Linux, Mac and Windows `Ctrl`+`Delete` Delete forward to a word boundary Doesn't work on Mac `Ctrl`+`Left arrow` or `Meta`+`B` Word left `Ctrl`+`Left arrow` Doesn't work on Mac `Ctrl`+`Right arrow` or `Meta`+`F` Word right `Ctrl`+`Right arrow` Doesn't work on Mac `Meta`+`D` or `Meta` +`Delete` Delete word right `Meta`+`Delete` Doesn't work on windows `Meta`+`Backspace` Delete word left Doesn't work on Mac ## REPL# Stability: 2 \- Stable Source Code: lib/repl.js The `node:repl` module provides a Read-Eval-Print-Loop (REPL) implementation that is available both as a standalone program or includible in other applications. It can be accessed using: import repl from 'node:repl'; ### Design and features# The `node:repl` module exports the `repl.REPLServer` class. While running, instances of `repl.REPLServer` will accept individual lines of user input, evaluate those according to a user-defined evaluation function, then output the result. Input and output may be from `stdin` and `stdout`, respectively, or may be connected to any Node.js stream. Instances of `repl.REPLServer` support automatic completion of inputs, completion preview, simplistic Emacs-style line editing, multi-line inputs, ZSH-like reverse-i-search, ZSH-like substring-based history search, ANSI-styled output, saving and restoring current REPL session state, error recovery, and customizable evaluation functions. Terminals that do not support ANSI styles and Emacs-style line editing automatically fall back to a limited feature set. #### Commands and special keys# The following special commands are supported by all REPL instances: * `.break`: When in the process of inputting a multi-line expression, enter the `.break` command (or press `Ctrl`+`C`) to abort further input or processing of that expression. * `.clear`: Resets the REPL `context` to an empty object and clears any multi-line expression being input. * `.exit`: Close the I/O stream, causing the REPL to exit. * `.help`: Show this list of special commands. * `.save`: Save the current REPL session to a file: `> .save ./file/to/save.js` * `.load`: Load a file into the current REPL session. `> .load ./file/to/load.js` * `.editor`: Enter editor mode (`Ctrl`+`D` to finish, `Ctrl`+`C` to cancel). > .editor // Entering editor mode (^D to finish, ^C to cancel) function welcome(name) { return `Hello ${name}!`; } welcome('Node.js User'); // ^D 'Hello Node.js User!' > The following key combinations in the REPL have these special effects: * `Ctrl`+`C`: When pressed once, has the same effect as the `.break` command. When pressed twice on a blank line, has the same effect as the `.exit` command. * `Ctrl`+`D`: Has the same effect as the `.exit` command. * `Tab`: When pressed on a blank line, displays global and local (scope) variables. When pressed while entering other input, displays relevant autocompletion options. For key bindings related to the reverse-i-search, see `reverse-i-search`. For all other key bindings, see TTY keybindings. #### Default evaluation# By default, all instances of `repl.REPLServer` use an evaluation function that evaluates JavaScript expressions and provides access to Node.js built-in modules. This default behavior can be overridden by passing in an alternative evaluation function when the `repl.REPLServer` instance is created. ##### JavaScript expressions# The default evaluator supports direct evaluation of JavaScript expressions: > 1 + 1 2 > const m = 2 undefined > m + 1 3 Unless otherwise scoped within blocks or functions, variables declared either implicitly or using the `const`, `let`, or `var` keywords are declared at the global scope. ##### Global and local scope# The default evaluator provides access to any variables that exist in the global scope. It is possible to expose a variable to the REPL explicitly by assigning it to the `context` object associated with each `REPLServer`: import repl from 'node:repl'; const msg = 'message'; repl.start('> ').context.m = msg; Properties in the `context` object appear as local within the REPL: $ node repl_test.js > m 'message' Context properties are not read-only by default. To specify read-only globals, context properties must be defined using `Object.defineProperty()`: import repl from 'node:repl'; const msg = 'message'; const r = repl.start('> '); Object.defineProperty(r.context, 'm', { configurable: false, enumerable: true, value: msg, }); ##### Accessing core Node.js modules# The default evaluator will automatically load Node.js core modules into the REPL environment when used. For instance, unless otherwise declared as a global or scoped variable, the input `fs` will be evaluated on-demand as `global.fs = require('node:fs')`. > fs.createReadStream('./some/file'); ##### Global uncaught exceptions# History VersionChanges v12.3.0 The `'uncaughtException'` event is from now on triggered if the repl is used as standalone program. The REPL uses the `domain` module to catch all uncaught exceptions for that REPL session. This use of the `domain` module in the REPL has these side effects: * Uncaught exceptions only emit the `'uncaughtException'` event in the standalone REPL. Adding a listener for this event in a REPL within another Node.js program results in `ERR_INVALID_REPL_INPUT`. const r = repl.start(); r.write('process.on("uncaughtException", () => console.log("Foobar"));\n'); // Output stream includes: // TypeError [ERR_INVALID_REPL_INPUT]: Listeners for `uncaughtException` // cannot be used in the REPL r.close(); * Trying to use `process.setUncaughtExceptionCaptureCallback()` throws an `ERR_DOMAIN_CANNOT_SET_UNCAUGHT_EXCEPTION_CAPTURE` error. ##### Assignment of the `_` (underscore) variable# History VersionChanges v9.8.0 Added `_error` support. The default evaluator will, by default, assign the result of the most recently evaluated expression to the special variable `_` (underscore). Explicitly setting `_` to a value will disable this behavior. > [ 'a', 'b', 'c' ] [ 'a', 'b', 'c' ] > _.length 3 > _ += 1 Expression assignment to _ now disabled. 4 > 1 + 1 2 > _ 4 Similarly, `_error` will refer to the last seen error, if there was any. Explicitly setting `_error` to a value will disable this behavior. > throw new Error('foo'); Uncaught Error: foo > _error.message 'foo' ##### `await` keyword# Support for the `await` keyword is enabled at the top level. > await Promise.resolve(123) 123 > await Promise.reject(new Error('REPL await')) Uncaught Error: REPL await at REPL2:1:54 > const timeout = util.promisify(setTimeout); undefined > const old = Date.now(); await timeout(1000); console.log(Date.now() - old); 1002 undefined One known limitation of using the `await` keyword in the REPL is that it will invalidate the lexical scoping of the `const` keywords. For example: > const m = await Promise.resolve(123) undefined > m 123 > m = await Promise.resolve(234) 234 // redeclaring the constant does error > const m = await Promise.resolve(345) Uncaught SyntaxError: Identifier 'm' has already been declared `--no-experimental-repl-await` shall disable top-level await in REPL. #### Reverse-i-search# Added in: v13.6.0, v12.17.0 The REPL supports bi-directional reverse-i-search similar to ZSH. It is triggered with `Ctrl`+`R` to search backward and `Ctrl`+`S` to search forwards. Duplicated history entries will be skipped. Entries are accepted as soon as any key is pressed that doesn't correspond with the reverse search. Cancelling is possible by pressing `Esc` or `Ctrl`+`C`. Changing the direction immediately searches for the next entry in the expected direction from the current position on. #### Custom evaluation functions# When a new `repl.REPLServer` is created, a custom evaluation function may be provided. This can be used, for instance, to implement fully customized REPL applications. An evaluation function accepts the following four arguments: * `code` The code to be executed (e.g. `1 + 1`). * `context` The context in which the code is executed. This can either be the JavaScript `global` context or a context specific to the REPL instance, depending on the `useGlobal` option. * `replResourceName` An identifier for the REPL resource associated with the current code evaluation. This can be useful for debugging purposes. * `callback` A function to invoke once the code evaluation is complete. The callback takes two parameters: * An error object to provide if an error occurred during evaluation, or `null`/`undefined` if no error occurred. * The result of the code evaluation (this is not relevant if an error is provided). The following illustrates an example of a REPL that squares a given number, an error is instead printed if the provided input is not actually a number: import repl from 'node:repl'; function byThePowerOfTwo(number) { return number * number; } function myEval(code, context, replResourceName, callback) { if (isNaN(code)) { callback(new Error(`${code.trim()} is not a number`)); } else { callback(null, byThePowerOfTwo(code)); } } repl.start({ prompt: 'Enter a number: ', eval: myEval }); ##### Recoverable errors# At the REPL prompt, pressing `Enter` sends the current line of input to the `eval` function. In order to support multi-line input, the `eval` function can return an instance of `repl.Recoverable` to the provided callback function: function myEval(cmd, context, filename, callback) { let result; try { result = vm.runInThisContext(cmd); } catch (e) { if (isRecoverableError(e)) { return callback(new repl.Recoverable(e)); } } callback(null, result); } function isRecoverableError(error) { if (error.name === 'SyntaxError') { return /^(Unexpected end of input|Unexpected token)/.test(error.message); } return false; } #### Customizing REPL output# By default, `repl.REPLServer` instances format output using the `util.inspect()` method before writing the output to the provided `Writable` stream (`process.stdout` by default). The `showProxy` inspection option is set to true by default and the `colors` option is set to true depending on the REPL's `useColors` option. The `useColors` boolean option can be specified at construction to instruct the default writer to use ANSI style codes to colorize the output from the `util.inspect()` method. If the REPL is run as standalone program, it is also possible to change the REPL's inspection defaults from inside the REPL by using the `inspect.replDefaults` property which mirrors the `defaultOptions` from `util.inspect()`. > util.inspect.replDefaults.compact = false; false > [1] [ 1 ] > To fully customize the output of a `repl.REPLServer` instance pass in a new function for the `writer` option on construction. The following example, for instance, simply converts any input text to upper case: import repl from 'node:repl'; const r = repl.start({ prompt: '> ', eval: myEval, writer: myWriter }); function myEval(cmd, context, filename, callback) { callback(null, cmd); } function myWriter(output) { return output.toUpperCase(); } ### Class: `REPLServer`# Added in: v0.1.91 * `options` | See `repl.start()` * Extends: Instances of `repl.REPLServer` are created using the `repl.start()` method or directly using the JavaScript `new` keyword. import repl from 'node:repl'; const options = { useColors: true }; const firstInstance = repl.start(options); const secondInstance = new repl.REPLServer(options); #### Event: `'exit'`# Added in: v0.7.7 The `'exit'` event is emitted when the REPL is exited either by receiving the `.exit` command as input, the user pressing `Ctrl`+`C` twice to signal `SIGINT`, or by pressing `Ctrl`+`D` to signal `'end'` on the input stream. The listener callback is invoked without any arguments. replServer.on('exit', () => { console.log('Received "exit" event from repl!'); process.exit(); }); #### Event: `'reset'`# Added in: v0.11.0 The `'reset'` event is emitted when the REPL's context is reset. This occurs whenever the `.clear` command is received as input unless the REPL is using the default evaluator and the `repl.REPLServer` instance was created with the `useGlobal` option set to `true`. The listener callback will be called with a reference to the `context` object as the only argument. This can be used primarily to re-initialize REPL context to some pre-defined state: import repl from 'node:repl'; function initializeContext(context) { context.m = 'test'; } const r = repl.start({ prompt: '> ' }); initializeContext(r.context); r.on('reset', initializeContext); When this code is executed, the global `'m'` variable can be modified but then reset to its initial value using the `.clear` command: $ ./node example.js > m 'test' > m = 1 1 > m 1 > .clear Clearing context... > m 'test' > #### `replServer.defineCommand(keyword, cmd)`# Added in: v0.3.0 * `keyword` The command keyword (without a leading `.` character). * `cmd` | The function to invoke when the command is processed. The `replServer.defineCommand()` method is used to add new `.`-prefixed commands to the REPL instance. Such commands are invoked by typing a `.` followed by the `keyword`. The `cmd` is either a `Function` or an `Object` with the following properties: * `help` Help text to be displayed when `.help` is entered (Optional). * `action` The function to execute, optionally accepting a single string argument. The following example shows two new commands added to the REPL instance: import repl from 'node:repl'; const replServer = repl.start({ prompt: '> ' }); replServer.defineCommand('sayhello', { help: 'Say hello', action(name) { this.clearBufferedCommand(); console.log(`Hello, ${name}!`); this.displayPrompt(); }, }); replServer.defineCommand('saybye', function saybye() { console.log('Goodbye!'); this.close(); }); The new commands can then be used from within the REPL instance: > .sayhello Node.js User Hello, Node.js User! > .saybye Goodbye! #### `replServer.displayPrompt([preserveCursor])`# Added in: v0.1.91 * `preserveCursor` The `replServer.displayPrompt()` method readies the REPL instance for input from the user, printing the configured `prompt` to a new line in the `output` and resuming the `input` to accept new input. When multi-line input is being entered, a pipe `'|'` is printed rather than the 'prompt'. When `preserveCursor` is `true`, the cursor placement will not be reset to `0`. The `replServer.displayPrompt` method is primarily intended to be called from within the action function for commands registered using the `replServer.defineCommand()` method. #### `replServer.clearBufferedCommand()`# Added in: v9.0.0 The `replServer.clearBufferedCommand()` method clears any command that has been buffered but not yet executed. This method is primarily intended to be called from within the action function for commands registered using the `replServer.defineCommand()` method. #### `replServer.setupHistory(historyConfig, callback)`# History VersionChanges v24.2.0 Updated the `historyConfig` parameter to accept an object with `filePath`, `size`, `removeHistoryDuplicates` and `onHistoryFileLoaded` properties. v11.10.0 Added in: v11.10.0 * `historyConfig` | the path to the history file If it is a string, it is the path to the history file. If it is an object, it can have the following properties: * `filePath` the path to the history file * `size` Maximum number of history lines retained. To disable the history set this value to `0`. This option makes sense only if `terminal` is set to `true` by the user or by an internal `output` check, otherwise the history caching mechanism is not initialized at all. Default: `30`. * `removeHistoryDuplicates` If `true`, when a new input line added to the history list duplicates an older one, this removes the older line from the list. Default: `false`. * `onHistoryFileLoaded` called when history writes are ready or upon error * `err` * `repl` * `callback` called when history writes are ready or upon error (Optional if provided as `onHistoryFileLoaded` in `historyConfig`) * `err` * `repl` Initializes a history log file for the REPL instance. When executing the Node.js binary and using the command-line REPL, a history file is initialized by default. However, this is not the case when creating a REPL programmatically. Use this method to initialize a history log file when working with REPL instances programmatically. ### `repl.builtinModules`# Added in: v14.5.0Deprecated since: v24.0.0 Stability: 0 \- Deprecated. Use `module.builtinModules` instead. * Type: A list of the names of some Node.js modules, e.g., `'http'`. ### `repl.start([options])`# History VersionChanges v24.1.0 Added the possibility to add/edit/remove multilines while adding a multiline command. v24.0.0 The multi-line indicator is now "|" instead of "...". Added support for multi-line history. It is now possible to "fix" multi-line commands with syntax errors by visiting the history and editing the command. When visiting the multiline history from an old node version, the multiline structure is not preserved. v13.4.0, v12.17.0 The `preview` option is now available. v12.0.0 The `terminal` option now follows the default description in all cases and `useColors` checks `hasColors()` if available. v10.0.0 The `REPL_MAGIC_MODE` `replMode` was removed. v6.3.0 The `breakEvalOnSigint` option is supported now. v5.8.0 The `options` parameter is optional now. v0.1.91 Added in: v0.1.91 * `options` | * `prompt` The input prompt to display. Default: `'> '` (with a trailing space). * `input` The `Readable` stream from which REPL input will be read. Default: `process.stdin`. * `output` The `Writable` stream to which REPL output will be written. Default: `process.stdout`. * `terminal` If `true`, specifies that the `output` should be treated as a TTY terminal. Default: checking the value of the `isTTY` property on the `output` stream upon instantiation. * `eval` The function to be used when evaluating each given line of input. Default: an async wrapper for the JavaScript `eval()` function. An `eval` function can error with `repl.Recoverable` to indicate the input was incomplete and prompt for additional lines. See the custom evaluation functions section for more details. * `useColors` If `true`, specifies that the default `writer` function should include ANSI color styling to REPL output. If a custom `writer` function is provided then this has no effect. Default: checking color support on the `output` stream if the REPL instance's `terminal` value is `true`. * `useGlobal` If `true`, specifies that the default evaluation function will use the JavaScript `global` as the context as opposed to creating a new separate context for the REPL instance. The node CLI REPL sets this value to `true`. Default: `false`. * `ignoreUndefined` If `true`, specifies that the default writer will not output the return value of a command if it evaluates to `undefined`. Default: `false`. * `writer` The function to invoke to format the output of each command before writing to `output`. Default: `util.inspect()`. * `completer` An optional function used for custom Tab auto completion. See `readline.InterfaceCompleter` for an example. * `replMode` A flag that specifies whether the default evaluator executes all JavaScript commands in strict mode or default (sloppy) mode. Acceptable values are: * `repl.REPL_MODE_SLOPPY` to evaluate expressions in sloppy mode. * `repl.REPL_MODE_STRICT` to evaluate expressions in strict mode. This is equivalent to prefacing every repl statement with `'use strict'`. * `breakEvalOnSigint` Stop evaluating the current piece of code when `SIGINT` is received, such as when `Ctrl`+`C` is pressed. This cannot be used together with a custom `eval` function. Default: `false`. * `preview` Defines if the repl prints autocomplete and output previews or not. Default: `true` with the default eval function and `false` in case a custom eval function is used. If `terminal` is falsy, then there are no previews and the value of `preview` has no effect. * Returns: The `repl.start()` method creates and starts a `repl.REPLServer` instance. If `options` is a string, then it specifies the input prompt: import repl from 'node:repl'; // a Unix style prompt repl.start('$ '); ### The Node.js REPL# Node.js itself uses the `node:repl` module to provide its own interactive interface for executing JavaScript. This can be used by executing the Node.js binary without passing any arguments (or by passing the `-i` argument): $ node > const a = [1, 2, 3]; undefined > a [ 1, 2, 3 ] > a.forEach((v) => { ... console.log(v); ... }); 1 2 3 #### Environment variable options# Various behaviors of the Node.js REPL can be customized using the following environment variables: * `NODE_REPL_HISTORY`: When a valid path is given, persistent REPL history will be saved to the specified file rather than `.node_repl_history` in the user's home directory. Setting this value to `''` (an empty string) will disable persistent REPL history. Whitespace will be trimmed from the value. On Windows platforms environment variables with empty values are invalid so set this variable to one or more spaces to disable persistent REPL history. * `NODE_REPL_HISTORY_SIZE`: Controls how many lines of history will be persisted if history is available. Must be a positive number. Default: `1000`. * `NODE_REPL_MODE`: May be either `'sloppy'` or `'strict'`. Default: `'sloppy'`, which will allow non-strict mode code to be run. #### Persistent history# By default, the Node.js REPL will persist history between `node` REPL sessions by saving inputs to a `.node_repl_history` file located in the user's home directory. This can be disabled by setting the environment variable `NODE_REPL_HISTORY=''`. #### Using the Node.js REPL with advanced line-editors# For advanced line-editors, start Node.js with the environment variable `NODE_NO_READLINE=1`. This will start the main and debugger REPL in canonical terminal settings, which will allow use with `rlwrap`. For example, the following can be added to a `.bashrc` file: alias node="env NODE_NO_READLINE=1 rlwrap node" #### Starting multiple REPL instances in the same process# It is possible to create and run multiple REPL instances against a single running instance of Node.js that share a single `global` object (by setting the `useGlobal` option to `true`) but have separate I/O interfaces. The following example, for instance, provides separate REPLs on `stdin`, a Unix socket, and a TCP socket, all sharing the same `global` object: import net from 'node:net'; import repl from 'node:repl'; import process from 'node:process'; import fs from 'node:fs'; let connections = 0; repl.start({ prompt: 'Node.js via stdin> ', useGlobal: true, input: process.stdin, output: process.stdout, }); const unixSocketPath = '/tmp/node-repl-sock'; // If the socket file already exists let's remove it fs.rmSync(unixSocketPath, { force: true }); net.createServer((socket) => { connections += 1; repl.start({ prompt: 'Node.js via Unix socket> ', useGlobal: true, input: socket, output: socket, }).on('exit', () => { socket.end(); }); }).listen(unixSocketPath); net.createServer((socket) => { connections += 1; repl.start({ prompt: 'Node.js via TCP socket> ', useGlobal: true, input: socket, output: socket, }).on('exit', () => { socket.end(); }); }).listen(5001); Running this application from the command line will start a REPL on stdin. Other REPL clients may connect through the Unix socket or TCP socket. `telnet`, for instance, is useful for connecting to TCP sockets, while `socat` can be used to connect to both Unix and TCP sockets. By starting a REPL from a Unix socket-based server instead of stdin, it is possible to connect to a long-running Node.js process without restarting it. #### Examples# ##### Full-featured "terminal" REPL over `net.Server` and `net.Socket`# This is an example on how to run a "full-featured" (terminal) REPL using `net.Server` and `net.Socket` The following script starts an HTTP server on port `1337` that allows clients to establish socket connections to its REPL instance. // repl-server.js import repl from 'node:repl'; import net from 'node:net'; net .createServer((socket) => { const r = repl.start({ prompt: `socket ${socket.remoteAddress}:${socket.remotePort}> `, input: socket, output: socket, terminal: true, useGlobal: false, }); r.on('exit', () => { socket.end(); }); r.context.socket = socket; }) .listen(1337); While the following implements a client that can create a socket connection with the above defined server over port `1337`. // repl-client.js import net from 'node:net'; import process from 'node:process'; const sock = net.connect(1337); process.stdin.pipe(sock); sock.pipe(process.stdout); sock.on('connect', () => { process.stdin.resume(); process.stdin.setRawMode(true); }); sock.on('close', () => { process.stdin.setRawMode(false); process.stdin.pause(); sock.removeListener('close', done); }); process.stdin.on('end', () => { sock.destroy(); console.log(); }); process.stdin.on('data', (b) => { if (b.length === 1 && b[0] === 4) { process.stdin.emit('end'); } }); To run the example open two different terminals on your machine, start the server with `node repl-server.js` in one terminal and `node repl-client.js` on the other. Original code from https://gist.github.com/TooTallNate/2209310. ##### REPL over `curl`# This is an example on how to run a REPL instance over `curl()` The following script starts an HTTP server on port `8000` that can accept a connection established via `curl()`. import http from 'node:http'; import repl from 'node:repl'; const server = http.createServer((req, res) => { res.setHeader('content-type', 'multipart/octet-stream'); repl.start({ prompt: 'curl repl> ', input: req, output: res, terminal: false, useColors: true, useGlobal: false, }); }); server.listen(8000); When the above script is running you can then use `curl()` to connect to the server and connect to its REPL instance by running `curl --no-progress-meter -sSNT. localhost:8000`. Warning This example is intended purely for educational purposes to demonstrate how Node.js REPLs can be started using different I/O streams. It should not be used in production environments or any context where security is a concern without additional protective measures. If you need to implement REPLs in a real-world application, consider alternative approaches that mitigate these risks, such as using secure input mechanisms and avoiding open network interfaces. Original code from https://gist.github.com/TooTallNate/2053342. ## Diagnostic report# Stability: 2 \- Stable History VersionChanges v23.3.0, v22.13.0 Added `--report-exclude-env` option for excluding environment variables from report generation. v22.0.0, v20.13.0 Added `--report-exclude-network` option for excluding networking operations that can slow down report generation in some cases. Delivers a JSON-formatted diagnostic summary, written to a file. The report is intended for development, test, and production use, to capture and preserve information for problem determination. It includes JavaScript and native stack traces, heap statistics, platform information, resource usage etc. With the report option enabled, diagnostic reports can be triggered on unhandled exceptions, fatal errors and user signals, in addition to triggering programmatically through API calls. A complete example report that was generated on an uncaught exception is provided below for reference. { "header": { "reportVersion": 5, "event": "exception", "trigger": "Exception", "filename": "report.20181221.005011.8974.0.001.json", "dumpEventTime": "2018-12-21T00:50:11Z", "dumpEventTimeStamp": "1545371411331", "processId": 8974, "cwd": "/home/nodeuser/project/node", "commandLine": [ "/home/nodeuser/project/node/out/Release/node", "--report-uncaught-exception", "/home/nodeuser/project/node/test/report/test-exception.js", "child" ], "nodejsVersion": "v12.0.0-pre", "glibcVersionRuntime": "2.17", "glibcVersionCompiler": "2.17", "wordSize": "64 bit", "arch": "x64", "platform": "linux", "componentVersions": { "node": "12.0.0-pre", "v8": "7.1.302.28-node.5", "uv": "1.24.1", "zlib": "1.2.11", "ares": "1.15.0", "modules": "68", "nghttp2": "1.34.0", "napi": "3", "llhttp": "1.0.1", "openssl": "1.1.0j" }, "release": { "name": "node" }, "osName": "Linux", "osRelease": "3.10.0-862.el7.x86_64", "osVersion": "#1 SMP Wed Mar 21 18:14:51 EDT 2018", "osMachine": "x86_64", "cpus": [ { "model": "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz", "speed": 2700, "user": 88902660, "nice": 0, "sys": 50902570, "idle": 241732220, "irq": 0 }, { "model": "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz", "speed": 2700, "user": 88902660, "nice": 0, "sys": 50902570, "idle": 241732220, "irq": 0 } ], "networkInterfaces": [ { "name": "en0", "internal": false, "mac": "13:10:de:ad:be:ef", "address": "10.0.0.37", "netmask": "255.255.255.0", "family": "IPv4" } ], "host": "test_machine" }, "javascriptStack": { "message": "Error: *** test-exception.js: throwing uncaught Error", "stack": [ "at myException (/home/nodeuser/project/node/test/report/test-exception.js:9:11)", "at Object. (/home/nodeuser/project/node/test/report/test-exception.js:12:3)", "at Module._compile (internal/modules/cjs/loader.js:718:30)", "at Object.Module._extensions..js (internal/modules/cjs/loader.js:729:10)", "at Module.load (internal/modules/cjs/loader.js:617:32)", "at tryModuleLoad (internal/modules/cjs/loader.js:560:12)", "at Function.Module._load (internal/modules/cjs/loader.js:552:3)", "at Function.Module.runMain (internal/modules/cjs/loader.js:771:12)", "at executeUserCode (internal/bootstrap/node.js:332:15)" ] }, "nativeStack": [ { "pc": "0x000055b57f07a9ef", "symbol": "report::GetNodeReport(v8::Isolate*, node::Environment*, char const*, char const*, v8::Local, std::ostream&) [./node]" }, { "pc": "0x000055b57f07cf03", "symbol": "report::GetReport(v8::FunctionCallbackInfo const&) [./node]" }, { "pc": "0x000055b57f1bccfd", "symbol": " [./node]" }, { "pc": "0x000055b57f1be048", "symbol": "v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*) [./node]" }, { "pc": "0x000055b57feeda0e", "symbol": " [./node]" } ], "javascriptHeap": { "totalMemory": 5660672, "executableMemory": 524288, "totalCommittedMemory": 5488640, "availableMemory": 4341379928, "totalGlobalHandlesMemory": 8192, "usedGlobalHandlesMemory": 3136, "usedMemory": 4816432, "memoryLimit": 4345298944, "mallocedMemory": 254128, "externalMemory": 315644, "peakMallocedMemory": 98752, "nativeContextCount": 1, "detachedContextCount": 0, "doesZapGarbage": 0, "heapSpaces": { "read_only_space": { "memorySize": 524288, "committedMemory": 39208, "capacity": 515584, "used": 30504, "available": 485080 }, "new_space": { "memorySize": 2097152, "committedMemory": 2019312, "capacity": 1031168, "used": 985496, "available": 45672 }, "old_space": { "memorySize": 2273280, "committedMemory": 1769008, "capacity": 1974640, "used": 1725488, "available": 249152 }, "code_space": { "memorySize": 696320, "committedMemory": 184896, "capacity": 152128, "used": 152128, "available": 0 }, "map_space": { "memorySize": 536576, "committedMemory": 344928, "capacity": 327520, "used": 327520, "available": 0 }, "large_object_space": { "memorySize": 0, "committedMemory": 0, "capacity": 1520590336, "used": 0, "available": 1520590336 }, "new_large_object_space": { "memorySize": 0, "committedMemory": 0, "capacity": 0, "used": 0, "available": 0 } } }, "resourceUsage": { "rss": "35766272", "free_memory": "1598337024", "total_memory": "17179869184", "available_memory": "1598337024", "maxRss": "36624662528", "constrained_memory": "36624662528", "userCpuSeconds": 0.040072, "kernelCpuSeconds": 0.016029, "cpuConsumptionPercent": 5.6101, "userCpuConsumptionPercent": 4.0072, "kernelCpuConsumptionPercent": 1.6029, "pageFaults": { "IORequired": 0, "IONotRequired": 4610 }, "fsActivity": { "reads": 0, "writes": 0 } }, "uvthreadResourceUsage": { "userCpuSeconds": 0.039843, "kernelCpuSeconds": 0.015937, "cpuConsumptionPercent": 5.578, "userCpuConsumptionPercent": 3.9843, "kernelCpuConsumptionPercent": 1.5937, "fsActivity": { "reads": 0, "writes": 0 } }, "libuv": [ { "type": "async", "is_active": true, "is_referenced": false, "address": "0x0000000102910900", "details": "" }, { "type": "timer", "is_active": false, "is_referenced": false, "address": "0x00007fff5fbfeab0", "repeat": 0, "firesInMsFromNow": 94403548320796, "expired": true }, { "type": "check", "is_active": true, "is_referenced": false, "address": "0x00007fff5fbfeb48" }, { "type": "idle", "is_active": false, "is_referenced": true, "address": "0x00007fff5fbfebc0" }, { "type": "prepare", "is_active": false, "is_referenced": false, "address": "0x00007fff5fbfec38" }, { "type": "check", "is_active": false, "is_referenced": false, "address": "0x00007fff5fbfecb0" }, { "type": "async", "is_active": true, "is_referenced": false, "address": "0x000000010188f2e0" }, { "type": "tty", "is_active": false, "is_referenced": true, "address": "0x000055b581db0e18", "width": 204, "height": 55, "fd": 17, "writeQueueSize": 0, "readable": true, "writable": true }, { "type": "signal", "is_active": true, "is_referenced": false, "address": "0x000055b581d80010", "signum": 28, "signal": "SIGWINCH" }, { "type": "tty", "is_active": true, "is_referenced": true, "address": "0x000055b581df59f8", "width": 204, "height": 55, "fd": 19, "writeQueueSize": 0, "readable": true, "writable": true }, { "type": "loop", "is_active": true, "address": "0x000055fc7b2cb180", "loopIdleTimeSeconds": 22644.8 }, { "type": "tcp", "is_active": true, "is_referenced": true, "address": "0x000055e70fcb85d8", "localEndpoint": { "host": "localhost", "ip4": "127.0.0.1", "port": 48986 }, "remoteEndpoint": { "host": "localhost", "ip4": "127.0.0.1", "port": 38573 }, "sendBufferSize": 2626560, "recvBufferSize": 131072, "fd": 24, "writeQueueSize": 0, "readable": true, "writable": true } ], "workers": [], "environmentVariables": { "REMOTEHOST": "REMOVED", "MANPATH": "/opt/rh/devtoolset-3/root/usr/share/man:", "XDG_SESSION_ID": "66126", "HOSTNAME": "test_machine", "HOST": "test_machine", "TERM": "xterm-256color", "SHELL": "/bin/csh", "SSH_CLIENT": "REMOVED", "PERL5LIB": "/opt/rh/devtoolset-3/root//usr/lib64/perl5/vendor_perl:/opt/rh/devtoolset-3/root/usr/lib/perl5:/opt/rh/devtoolset-3/root//usr/share/perl5/vendor_perl", "OLDPWD": "/home/nodeuser/project/node/src", "JAVACONFDIRS": "/opt/rh/devtoolset-3/root/etc/java:/etc/java", "SSH_TTY": "/dev/pts/0", "PCP_DIR": "/opt/rh/devtoolset-3/root", "GROUP": "normaluser", "USER": "nodeuser", "LD_LIBRARY_PATH": "/opt/rh/devtoolset-3/root/usr/lib64:/opt/rh/devtoolset-3/root/usr/lib", "HOSTTYPE": "x86_64-linux", "XDG_CONFIG_DIRS": "/opt/rh/devtoolset-3/root/etc/xdg:/etc/xdg", "MAIL": "/var/spool/mail/nodeuser", "PATH": "/home/nodeuser/project/node:/opt/rh/devtoolset-3/root/usr/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin", "PWD": "/home/nodeuser/project/node", "LANG": "en_US.UTF-8", "PS1": "\\u@\\h : \\[\\e[31m\\]\\w\\[\\e[m\\] > ", "SHLVL": "2", "HOME": "/home/nodeuser", "OSTYPE": "linux", "VENDOR": "unknown", "PYTHONPATH": "/opt/rh/devtoolset-3/root/usr/lib64/python2.7/site-packages:/opt/rh/devtoolset-3/root/usr/lib/python2.7/site-packages", "MACHTYPE": "x86_64", "LOGNAME": "nodeuser", "XDG_DATA_DIRS": "/opt/rh/devtoolset-3/root/usr/share:/usr/local/share:/usr/share", "LESSOPEN": "||/usr/bin/lesspipe.sh %s", "INFOPATH": "/opt/rh/devtoolset-3/root/usr/share/info", "XDG_RUNTIME_DIR": "/run/user/50141", "_": "./node" }, "userLimits": { "core_file_size_blocks": { "soft": "", "hard": "unlimited" }, "data_seg_size_bytes": { "soft": "unlimited", "hard": "unlimited" }, "file_size_blocks": { "soft": "unlimited", "hard": "unlimited" }, "max_locked_memory_bytes": { "soft": "unlimited", "hard": 65536 }, "max_memory_size_bytes": { "soft": "unlimited", "hard": "unlimited" }, "open_files": { "soft": "unlimited", "hard": 4096 }, "stack_size_bytes": { "soft": "unlimited", "hard": "unlimited" }, "cpu_time_seconds": { "soft": "unlimited", "hard": "unlimited" }, "max_user_processes": { "soft": "unlimited", "hard": 4127290 }, "virtual_memory_bytes": { "soft": "unlimited", "hard": "unlimited" } }, "sharedObjects": [ "/lib64/libdl.so.2", "/lib64/librt.so.1", "/lib64/libstdc++.so.6", "/lib64/libm.so.6", "/lib64/libgcc_s.so.1", "/lib64/libpthread.so.0", "/lib64/libc.so.6", "/lib64/ld-linux-x86-64.so.2" ] } ### Usage# node --report-uncaught-exception --report-on-signal \ --report-on-fatalerror app.js * `--report-uncaught-exception` Enables report to be generated on un-caught exceptions. Useful when inspecting JavaScript stack in conjunction with native stack and other runtime environment data. * `--report-on-signal` Enables report to be generated upon receiving the specified (or predefined) signal to the running Node.js process. (See below on how to modify the signal that triggers the report.) Default signal is `SIGUSR2`. Useful when a report needs to be triggered from another program. Application monitors may leverage this feature to collect report at regular intervals and plot rich set of internal runtime data to their views. Signal based report generation is not supported in Windows. Under normal circumstances, there is no need to modify the report triggering signal. However, if `SIGUSR2` is already used for other purposes, then this flag helps to change the signal for report generation and preserve the original meaning of `SIGUSR2` for the said purposes. * `--report-on-fatalerror` Enables the report to be triggered on fatal errors (internal errors within the Node.js runtime, such as out of memory) that leads to termination of the application. Useful to inspect various diagnostic data elements such as heap, stack, event loop state, resource consumption etc. to reason about the fatal error. * `--report-compact` Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption. * `--report-directory` Location at which the report will be generated. * `--report-filename` Name of the file to which the report will be written. * `--report-signal` Sets or resets the signal for report generation (not supported on Windows). Default signal is `SIGUSR2`. * `--report-exclude-network` Exclude `header.networkInterfaces` and disable the reverse DNS queries in `libuv.*.(remote|local)Endpoint.host` from the diagnostic report. By default this is not set and the network interfaces are included. * `--report-exclude-env` Exclude `environmentVariables` from the diagnostic report. By default this is not set and the environment variables are included. A report can also be triggered via an API call from a JavaScript application: process.report.writeReport(); This function takes an optional additional argument `filename`, which is the name of a file into which the report is written. process.report.writeReport('./foo.json'); This function takes an optional additional argument `err` which is an `Error` object that will be used as the context for the JavaScript stack printed in the report. When using report to handle errors in a callback or an exception handler, this allows the report to include the location of the original error as well as where it was handled. try { process.chdir('/non-existent-path'); } catch (err) { process.report.writeReport(err); } // Any other code If both filename and error object are passed to `writeReport()` the error object must be the second parameter. try { process.chdir('/non-existent-path'); } catch (err) { process.report.writeReport(filename, err); } // Any other code The content of the diagnostic report can be returned as a JavaScript Object via an API call from a JavaScript application: const report = process.report.getReport(); console.log(typeof report === 'object'); // true // Similar to process.report.writeReport() output console.log(JSON.stringify(report, null, 2)); This function takes an optional additional argument `err`, which is an `Error` object that will be used as the context for the JavaScript stack printed in the report. const report = process.report.getReport(new Error('custom error')); console.log(typeof report === 'object'); // true The API versions are useful when inspecting the runtime state from within the application, in expectation of self-adjusting the resource consumption, load balancing, monitoring etc. The content of the report consists of a header section containing the event type, date, time, PID, and Node.js version, sections containing JavaScript and native stack traces, a section containing V8 heap information, a section containing `libuv` handle information, and an OS platform information section showing CPU and memory usage and system limits. An example report can be triggered using the Node.js REPL: $ node > process.report.writeReport(); Writing Node.js report to file: report.20181126.091102.8480.0.001.json Node.js report completed > When a report is written, start and end messages are issued to stderr and the filename of the report is returned to the caller. The default filename includes the date, time, PID, and a sequence number. The sequence number helps in associating the report dump with the runtime state if generated multiple times for the same Node.js process. ### Report Version# Diagnostic report has an associated single-digit version number (`report.header.reportVersion`), uniquely representing the report format. The version number is bumped when new key is added or removed, or the data type of a value is changed. Report version definitions are consistent across LTS releases. #### Version history# ##### Version 5# History VersionChanges v23.5.0, v22.13.0 Fix typos in the memory limit units. Replace the keys `data_seg_size_kbytes`, `max_memory_size_kbytes`, and `virtual_memory_kbytes` with `data_seg_size_bytes`, `max_memory_size_bytes`, and `virtual_memory_bytes` respectively in the `userLimits` section, as these values are given in bytes. { "userLimits": { // Skip some keys ... "data_seg_size_bytes": { // replacing data_seg_size_kbytes "soft": "unlimited", "hard": "unlimited" }, // ... "max_memory_size_bytes": { // replacing max_memory_size_kbytes "soft": "unlimited", "hard": "unlimited" }, // ... "virtual_memory_bytes": { // replacing virtual_memory_kbytes "soft": "unlimited", "hard": "unlimited" } } } ##### Version 4# History VersionChanges v23.3.0, v22.13.0 Added `--report-exclude-env` option for excluding environment variables from report generation. New fields `ipv4` and `ipv6` are added to `tcp` and `udp` libuv handles endpoints. Examples: { "libuv": [ { "type": "tcp", "is_active": true, "is_referenced": true, "address": "0x000055e70fcb85d8", "localEndpoint": { "host": "localhost", "ip4": "127.0.0.1", // new key "port": 48986 }, "remoteEndpoint": { "host": "localhost", "ip4": "127.0.0.1", // new key "port": 38573 }, "sendBufferSize": 2626560, "recvBufferSize": 131072, "fd": 24, "writeQueueSize": 0, "readable": true, "writable": true }, { "type": "tcp", "is_active": true, "is_referenced": true, "address": "0x000055e70fcd68c8", "localEndpoint": { "host": "ip6-localhost", "ip6": "::1", // new key "port": 52266 }, "remoteEndpoint": { "host": "ip6-localhost", "ip6": "::1", // new key "port": 38573 }, "sendBufferSize": 2626560, "recvBufferSize": 131072, "fd": 25, "writeQueueSize": 0, "readable": false, "writable": false } ] } ##### Version 3# History VersionChanges v19.1.0, v18.13.0 Add more memory info. The following memory usage keys are added to the `resourceUsage` section. { "resourceUsage": { "rss": "35766272", "free_memory": "1598337024", "total_memory": "17179869184", "available_memory": "1598337024", "constrained_memory": "36624662528" } } ##### Version 2# History VersionChanges v13.9.0, v12.16.2 Workers are now included in the report. Added `Worker` support. Refer to Interaction with workers section for more details. ##### Version 1# This is the first version of the diagnostic report. ### Configuration# Additional runtime configuration of report generation is available via the following properties of `process.report`: `reportOnFatalError` triggers diagnostic reporting on fatal errors when `true`. Defaults to `false`. `reportOnSignal` triggers diagnostic reporting on signal when `true`. This is not supported on Windows. Defaults to `false`. `reportOnUncaughtException` triggers diagnostic reporting on uncaught exception when `true`. Defaults to `false`. `signal` specifies the POSIX signal identifier that will be used to intercept external triggers for report generation. Defaults to `'SIGUSR2'`. `filename` specifies the name of the output file in the file system. Special meaning is attached to `stdout` and `stderr`. Usage of these will result in report being written to the associated standard streams. In cases where standard streams are used, the value in `directory` is ignored. URLs are not supported. Defaults to a composite filename that contains timestamp, PID, and sequence number. `directory` specifies the file system directory where the report will be written. URLs are not supported. Defaults to the current working directory of the Node.js process. `excludeNetwork` excludes `header.networkInterfaces` from the diagnostic report. // Trigger report only on uncaught exceptions. process.report.reportOnFatalError = false; process.report.reportOnSignal = false; process.report.reportOnUncaughtException = true; // Trigger report for both internal errors as well as external signal. process.report.reportOnFatalError = true; process.report.reportOnSignal = true; process.report.reportOnUncaughtException = false; // Change the default signal to 'SIGQUIT' and enable it. process.report.reportOnFatalError = false; process.report.reportOnUncaughtException = false; process.report.reportOnSignal = true; process.report.signal = 'SIGQUIT'; // Disable network interfaces reporting process.report.excludeNetwork = true; Configuration on module initialization is also available via environment variables: NODE_OPTIONS="--report-uncaught-exception \ --report-on-fatalerror --report-on-signal \ --report-signal=SIGUSR2 --report-filename=./report.json \ --report-directory=/home/nodeuser" Specific API documentation can be found under `process API documentation` section. ### Interaction with workers# History VersionChanges v13.9.0, v12.16.2 Workers are now included in the report. `Worker` threads can create reports in the same way that the main thread does. Reports will include information on any Workers that are children of the current thread as part of the `workers` section, with each Worker generating a report in the standard report format. The thread which is generating the report will wait for the reports from Worker threads to finish. However, the latency for this will usually be low, as both running JavaScript and the event loop are interrupted to generate the report. ## Single executable applications# History VersionChanges v20.6.0 Added support for "useSnapshot". v20.6.0 Added support for "useCodeCache". v19.7.0, v18.16.0 Added in: v19.7.0, v18.16.0 Stability: 1.1 \- Active development Source Code: src/node_sea.cc This feature allows the distribution of a Node.js application conveniently to a system that does not have Node.js installed. Node.js supports the creation of single executable applications by allowing the injection of a blob prepared by Node.js, which can contain a bundled script, into the `node` binary. During start up, the program checks if anything has been injected. If the blob is found, it executes the script in the blob. Otherwise Node.js operates as it normally does. The single executable application feature currently only supports running a single embedded script using the CommonJS module system. Users can create a single executable application from their bundled script with the `node` binary itself and any tool which can inject resources into the binary. Here are the steps for creating a single executable application using one such tool, postject: 1. Create a JavaScript file: echo 'console.log(`Hello, ${process.argv[2]}!`);' > hello.js 2. Create a configuration file building a blob that can be injected into the single executable application (see Generating single executable preparation blobs for details): echo '{ "main": "hello.js", "output": "sea-prep.blob" }' > sea-config.json 3. Generate the blob to be injected: node --experimental-sea-config sea-config.json 4. Create a copy of the `node` executable and name it according to your needs: * On systems other than Windows: cp $(command -v node) hello * On Windows: node -e "require('fs').copyFileSync(process.execPath, 'hello.exe')" The `.exe` extension is necessary. 5. Remove the signature of the binary (macOS and Windows only): * On macOS: codesign --remove-signature hello * On Windows (optional): signtool can be used from the installed Windows SDK. If this step is skipped, ignore any signature-related warning from postject. signtool remove /s hello.exe 6. Inject the blob into the copied binary by running `postject` with the following options: * `hello` / `hello.exe` \- The name of the copy of the `node` executable created in step 4. * `NODE_SEA_BLOB` \- The name of the resource / note / section in the binary where the contents of the blob will be stored. * `sea-prep.blob` \- The name of the blob created in step 1. * `--sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2` \- The fuse used by the Node.js project to detect if a file has been injected. * `--macho-segment-name NODE_SEA` (only needed on macOS) - The name of the segment in the binary where the contents of the blob will be stored. To summarize, here is the required command for each platform: * On Linux: npx postject hello NODE_SEA_BLOB sea-prep.blob \ --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2 * On Windows - PowerShell: npx postject hello.exe NODE_SEA_BLOB sea-prep.blob ` --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2 * On Windows - Command Prompt: npx postject hello.exe NODE_SEA_BLOB sea-prep.blob ^ --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2 * On macOS: npx postject hello NODE_SEA_BLOB sea-prep.blob \ --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2 \ --macho-segment-name NODE_SEA 7. Sign the binary (macOS and Windows only): * On macOS: codesign --sign - hello * On Windows (optional): A certificate needs to be present for this to work. However, the unsigned binary would still be runnable. signtool sign /fd SHA256 hello.exe 8. Run the binary: * On systems other than Windows $ ./hello world Hello, world! * On Windows $ .\hello.exe world Hello, world! ### Generating single executable preparation blobs# Single executable preparation blobs that are injected into the application can be generated using the `--experimental-sea-config` flag of the Node.js binary that will be used to build the single executable. It takes a path to a configuration file in JSON format. If the path passed to it isn't absolute, Node.js will use the path relative to the current working directory. The configuration currently reads the following top-level fields: { "main": "/path/to/bundled/script.js", "output": "/path/to/write/the/generated/blob.blob", "disableExperimentalSEAWarning": true, // Default: false "useSnapshot": false, // Default: false "useCodeCache": true, // Default: false "execArgv": ["--no-warnings", "--max-old-space-size=4096"], // Optional "execArgvExtension": "env", // Default: "env", options: "none", "env", "cli" "assets": { // Optional "a.dat": "/path/to/a.dat", "b.txt": "/path/to/b.txt" } } If the paths are not absolute, Node.js will use the path relative to the current working directory. The version of the Node.js binary used to produce the blob must be the same as the one to which the blob will be injected. Note: When generating cross-platform SEAs (e.g., generating a SEA for `linux-x64` on `darwin-arm64`), `useCodeCache` and `useSnapshot` must be set to false to avoid generating incompatible executables. Since code cache and snapshots can only be loaded on the same platform where they are compiled, the generated executable might crash on startup when trying to load code cache or snapshots built on a different platform. #### Assets# Users can include assets by adding a key-path dictionary to the configuration as the `assets` field. At build time, Node.js would read the assets from the specified paths and bundle them into the preparation blob. In the generated executable, users can retrieve the assets using the `sea.getAsset()` and `sea.getAssetAsBlob()` APIs. { "main": "/path/to/bundled/script.js", "output": "/path/to/write/the/generated/blob.blob", "assets": { "a.jpg": "/path/to/a.jpg", "b.txt": "/path/to/b.txt" } } The single-executable application can access the assets as follows: See documentation of the `sea.getAsset()`, `sea.getAssetAsBlob()`, `sea.getRawAsset()` and `sea.getAssetKeys()` APIs for more information. #### Startup snapshot support# The `useSnapshot` field can be used to enable startup snapshot support. In this case the `main` script would not be when the final executable is launched. Instead, it would be run when the single executable application preparation blob is generated on the building machine. The generated preparation blob would then include a snapshot capturing the states initialized by the `main` script. The final executable with the preparation blob injected would deserialize the snapshot at run time. When `useSnapshot` is true, the main script must invoke the `v8.startupSnapshot.setDeserializeMainFunction()` API to configure code that needs to be run when the final executable is launched by the users. The typical pattern for an application to use snapshot in a single executable application is: 1. At build time, on the building machine, the main script is run to initialize the heap to a state that's ready to take user input. The script should also configure a main function with `v8.startupSnapshot.setDeserializeMainFunction()`. This function will be compiled and serialized into the snapshot, but not invoked at build time. 2. At run time, the main function will be run on top of the deserialized heap on the user machine to process user input and generate output. The general constraints of the startup snapshot scripts also apply to the main script when it's used to build snapshot for the single executable application, and the main script can use the `v8.startupSnapshot` API to adapt to these constraints. See documentation about startup snapshot support in Node.js. #### V8 code cache support# When `useCodeCache` is set to `true` in the configuration, during the generation of the single executable preparation blob, Node.js will compile the `main` script to generate the V8 code cache. The generated code cache would be part of the preparation blob and get injected into the final executable. When the single executable application is launched, instead of compiling the `main` script from scratch, Node.js would use the code cache to speed up the compilation, then execute the script, which would improve the startup performance. Note: `import()` does not work when `useCodeCache` is `true`. #### Execution arguments# The `execArgv` field can be used to specify Node.js-specific arguments that will be automatically applied when the single executable application starts. This allows application developers to configure Node.js runtime options without requiring end users to be aware of these flags. For example, the following configuration: { "main": "/path/to/bundled/script.js", "output": "/path/to/write/the/generated/blob.blob", "execArgv": ["--no-warnings", "--max-old-space-size=2048"] } will instruct the SEA to be launched with the `--no-warnings` and `--max-old-space-size=2048` flags. In the scripts embedded in the executable, these flags can be accessed using the `process.execArgv` property: // If the executable is launched with `sea user-arg1 user-arg2` console.log(process.execArgv); // Prints: ['--no-warnings', '--max-old-space-size=2048'] console.log(process.argv); // Prints ['/path/to/sea', 'path/to/sea', 'user-arg1', 'user-arg2'] The user-provided arguments are in the `process.argv` array starting from index 2, similar to what would happen if the application is started with: node --no-warnings --max-old-space-size=2048 /path/to/bundled/script.js user-arg1 user-arg2 #### Execution argument extension# The `execArgvExtension` field controls how additional execution arguments can be provided beyond those specified in the `execArgv` field. It accepts one of three string values: * `"none"`: No extension is allowed. Only the arguments specified in `execArgv` will be used, and the `NODE_OPTIONS` environment variable will be ignored. * `"env"`: (Default) The `NODE_OPTIONS` environment variable can extend the execution arguments. This is the default behavior to maintain backward compatibility. * `"cli"`: The executable can be launched with `--node-options="--flag1 --flag2"`, and those flags will be parsed as execution arguments for Node.js instead of being passed to the user script. This allows using arguments that are not supported by the `NODE_OPTIONS` environment variable. For example, with `"execArgvExtension": "cli"`: { "main": "/path/to/bundled/script.js", "output": "/path/to/write/the/generated/blob.blob", "execArgv": ["--no-warnings"], "execArgvExtension": "cli" } The executable can be launched as: ./my-sea --node-options="--trace-exit" user-arg1 user-arg2 This would be equivalent to running: node --no-warnings --trace-exit /path/to/bundled/script.js user-arg1 user-arg2 ### In the injected main script# #### Single-executable application API# The `node:sea` builtin allows interaction with the single-executable application from the JavaScript main script embedded into the executable. ##### `sea.isSea()`# Added in: v21.7.0, v20.12.0 * Returns: Whether this script is running inside a single-executable application. #### `sea.getAsset(key[, encoding])`# Added in: v21.7.0, v20.12.0 This method can be used to retrieve the assets configured to be bundled into the single-executable application at build time. An error is thrown when no matching asset can be found. * `key` the key for the asset in the dictionary specified by the `assets` field in the single-executable application configuration. * `encoding` If specified, the asset will be decoded as a string. Any encoding supported by the `TextDecoder` is accepted. If unspecified, an `ArrayBuffer` containing a copy of the asset would be returned instead. * Returns: | #### `sea.getAssetAsBlob(key[, options])`# Added in: v21.7.0, v20.12.0 Similar to `sea.getAsset()`, but returns the result in a . An error is thrown when no matching asset can be found. * `key` the key for the asset in the dictionary specified by the `assets` field in the single-executable application configuration. * `options` * `type` An optional mime type for the blob. * Returns: #### `sea.getRawAsset(key)`# Added in: v21.7.0, v20.12.0 This method can be used to retrieve the assets configured to be bundled into the single-executable application at build time. An error is thrown when no matching asset can be found. Unlike `sea.getAsset()` or `sea.getAssetAsBlob()`, this method does not return a copy. Instead, it returns the raw asset bundled inside the executable. For now, users should avoid writing to the returned array buffer. If the injected section is not marked as writable or not aligned properly, writes to the returned array buffer is likely to result in a crash. * `key` the key for the asset in the dictionary specified by the `assets` field in the single-executable application configuration. * Returns: #### `sea.getAssetKeys()`# Added in: v24.8.0 * Returns An array containing all the keys of the assets embedded in the executable. If no assets are embedded, returns an empty array. This method can be used to retrieve an array of all the keys of assets embedded into the single-executable application. An error is thrown when not running inside a single-executable application. #### `require(id)` in the injected main script is not file based# `require()` in the injected main script is not the same as the `require()` available to modules that are not injected. It also does not have any of the properties that non-injected `require()` has except `require.main`. It can only be used to load built-in modules. Attempting to load a module that can only be found in the file system will throw an error. Instead of relying on a file based `require()`, users can bundle their application into a standalone JavaScript file to inject into the executable. This also ensures a more deterministic dependency graph. However, if a file based `require()` is still needed, that can also be achieved: const { createRequire } = require('node:module'); require = createRequire(__filename); #### `__filename` and `module.filename` in the injected main script# The values of `__filename` and `module.filename` in the injected main script are equal to `process.execPath`. #### `__dirname` in the injected main script# The value of `__dirname` in the injected main script is equal to the directory name of `process.execPath`. ### Notes# #### Single executable application creation process# A tool aiming to create a single executable Node.js application must inject the contents of the blob prepared with `--experimental-sea-config"` into: * a resource named `NODE_SEA_BLOB` if the `node` binary is a PE file * a section named `NODE_SEA_BLOB` in the `NODE_SEA` segment if the `node` binary is a Mach-O file * a note named `NODE_SEA_BLOB` if the `node` binary is an ELF file Search the binary for the `NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2:0` fuse string and flip the last character to `1` to indicate that a resource has been injected. #### Platform support# Single-executable support is tested regularly on CI only on the following platforms: * Windows * macOS * Linux (all distributions supported by Node.js except Alpine and all architectures supported by Node.js except s390x) This is due to a lack of better tools to generate single-executables that can be used to test this feature on other platforms. Suggestions for other resource injection tools/workflows are welcomed. Please start a discussion at https://github.com/nodejs/single-executable/discussions to help us document them. ## SQLite# Added in: v22.5.0 Stability: 1.1 \- Active development. Source Code: lib/sqlite.js The `node:sqlite` module facilitates working with SQLite databases. To access it: import sqlite from 'node:sqlite'; This module is only available under the `node:` scheme. The following example shows the basic usage of the `node:sqlite` module to open an in-memory database, write data to the database, and then read the data back. import { DatabaseSync } from 'node:sqlite'; const database = new DatabaseSync(':memory:'); // Execute SQL statements from strings. database.exec(` CREATE TABLE data( key INTEGER PRIMARY KEY, value TEXT ) STRICT `); // Create a prepared statement to insert data into the database. const insert = database.prepare('INSERT INTO data (key, value) VALUES (?, ?)'); // Execute the prepared statement with bound values. insert.run(1, 'hello'); insert.run(2, 'world'); // Create a prepared statement to read data from the database. const query = database.prepare('SELECT * FROM data ORDER BY key'); // Execute the prepared statement and log the result set. console.log(query.all()); // Prints: [ { key: 1, value: 'hello' }, { key: 2, value: 'world' } ] ### Class: `DatabaseSync`# History VersionChanges v24.0.0 Add `timeout` option. v23.10.0, v22.15.0 The `path` argument now supports Buffer and URL objects. v22.5.0 Added in: v22.5.0 This class represents a single connection to a SQLite database. All APIs exposed by this class execute synchronously. #### `new DatabaseSync(path[, options])`# History VersionChanges v24.4.0 Add new SQLite database options. v22.5.0 Added in: v22.5.0 * `path` | | The path of the database. A SQLite database can be stored in a file or completely in memory. To use a file-backed database, the path should be a file path. To use an in-memory database, the path should be the special name `':memory:'`. * `options` Configuration options for the database connection. The following options are supported: * `open` If `true`, the database is opened by the constructor. When this value is `false`, the database must be opened via the `open()` method. Default: `true`. * `readOnly` If `true`, the database is opened in read-only mode. If the database does not exist, opening it will fail. Default: `false`. * `enableForeignKeyConstraints` If `true`, foreign key constraints are enabled. This is recommended but can be disabled for compatibility with legacy database schemas. The enforcement of foreign key constraints can be enabled and disabled after opening the database using `PRAGMA foreign_keys`. Default: `true`. * `enableDoubleQuotedStringLiterals` If `true`, SQLite will accept double-quoted string literals. This is not recommended but can be enabled for compatibility with legacy database schemas. Default: `false`. * `allowExtension` If `true`, the `loadExtension` SQL function and the `loadExtension()` method are enabled. You can call `enableLoadExtension(false)` later to disable this feature. Default: `false`. * `timeout` The busy timeout in milliseconds. This is the maximum amount of time that SQLite will wait for a database lock to be released before returning an error. Default: `0`. * `readBigInts` If `true`, integer fields are read as JavaScript `BigInt` values. If `false`, integer fields are read as JavaScript numbers. Default: `false`. * `returnArrays` If `true`, query results are returned as arrays instead of objects. Default: `false`. * `allowBareNamedParameters` If `true`, allows binding named parameters without the prefix character (e.g., `foo` instead of `:foo`). Default: `true`. * `allowUnknownNamedParameters` If `true`, unknown named parameters are ignored when binding. If `false`, an exception is thrown for unknown named parameters. Default: `false`. Constructs a new `DatabaseSync` instance. #### `database.aggregate(name, options)`# Added in: v24.0.0 Registers a new aggregate function with the SQLite database. This method is a wrapper around `sqlite3_create_window_function()`. * `name` The name of the SQLite function to create. * `options` Function configuration settings. * `deterministic` If `true`, the `SQLITE_DETERMINISTIC` flag is set on the created function. Default: `false`. * `directOnly` If `true`, the `SQLITE_DIRECTONLY` flag is set on the created function. Default: `false`. * `useBigIntArguments` If `true`, integer arguments to `options.step` and `options.inverse` are converted to `BigInt`s. If `false`, integer arguments are passed as JavaScript numbers. Default: `false`. * `varargs` If `true`, `options.step` and `options.inverse` may be invoked with any number of arguments (between zero and `SQLITE_MAX_FUNCTION_ARG`). If `false`, `inverse` and `step` must be invoked with exactly `length` arguments. Default: `false`. * `start` | | | | | The identity value for the aggregation function. This value is used when the aggregation function is initialized. When a is passed the identity will be its return value. * `step` The function to call for each row in the aggregation. The function receives the current state and the row value. The return value of this function should be the new state. * `result` The function to call to get the result of the aggregation. The function receives the final state and should return the result of the aggregation. * `inverse` When this function is provided, the `aggregate` method will work as a window function. The function receives the current state and the dropped row value. The return value of this function should be the new state. When used as a window function, the `result` function will be called multiple times. import { DatabaseSync } from 'node:sqlite'; const db = new DatabaseSync(':memory:'); db.exec(` CREATE TABLE t3(x, y); INSERT INTO t3 VALUES ('a', 4), ('b', 5), ('c', 3), ('d', 8), ('e', 1); `); db.aggregate('sumint', { start: 0, step: (acc, value) => acc + value, }); db.prepare('SELECT sumint(y) as total FROM t3').get(); // { total: 21 } #### `database.close()`# Added in: v22.5.0 Closes the database connection. An exception is thrown if the database is not open. This method is a wrapper around `sqlite3_close_v2()`. #### `database.loadExtension(path)`# Added in: v23.5.0, v22.13.0 * `path` The path to the shared library to load. Loads a shared library into the database connection. This method is a wrapper around `sqlite3_load_extension()`. It is required to enable the `allowExtension` option when constructing the `DatabaseSync` instance. #### `database.enableLoadExtension(allow)`# Added in: v23.5.0, v22.13.0 * `allow` Whether to allow loading extensions. Enables or disables the `loadExtension` SQL function, and the `loadExtension()` method. When `allowExtension` is `false` when constructing, you cannot enable loading extensions for security reasons. #### `database.location([dbName])`# Added in: v24.0.0 * `dbName` Name of the database. This can be `'main'` (the default primary database) or any other database that has been added with `ATTACH DATABASE` Default: `'main'`. * Returns: | The location of the database file. When using an in-memory database, this method returns null. This method is a wrapper around `sqlite3_db_filename()` #### `database.exec(sql)`# Added in: v22.5.0 * `sql` A SQL string to execute. This method allows one or more SQL statements to be executed without returning any results. This method is useful when executing SQL statements read from a file. This method is a wrapper around `sqlite3_exec()`. #### `database.function(name[, options], function)`# Added in: v23.5.0, v22.13.0 * `name` The name of the SQLite function to create. * `options` Optional configuration settings for the function. The following properties are supported: * `deterministic` If `true`, the `SQLITE_DETERMINISTIC` flag is set on the created function. Default: `false`. * `directOnly` If `true`, the `SQLITE_DIRECTONLY` flag is set on the created function. Default: `false`. * `useBigIntArguments` If `true`, integer arguments to `function` are converted to `BigInt`s. If `false`, integer arguments are passed as JavaScript numbers. Default: `false`. * `varargs` If `true`, `function` may be invoked with any number of arguments (between zero and `SQLITE_MAX_FUNCTION_ARG`). If `false`, `function` must be invoked with exactly `function.length` arguments. Default: `false`. * `function` The JavaScript function to call when the SQLite function is invoked. The return value of this function should be a valid SQLite data type: see Type conversion between JavaScript and SQLite. The result defaults to `NULL` if the return value is `undefined`. This method is used to create SQLite user-defined functions. This method is a wrapper around `sqlite3_create_function_v2()`. #### `database.isOpen`# Added in: v23.11.0, v22.15.0 * Type: Whether the database is currently open or not. #### `database.isTransaction`# Added in: v24.0.0 * Type: Whether the database is currently within a transaction. This method is a wrapper around `sqlite3_get_autocommit()`. #### `database.open()`# Added in: v22.5.0 Opens the database specified in the `path` argument of the `DatabaseSync` constructor. This method should only be used when the database is not opened via the constructor. An exception is thrown if the database is already open. #### `database.prepare(sql)`# Added in: v22.5.0 * `sql` A SQL string to compile to a prepared statement. * Returns: The prepared statement. Compiles a SQL statement into a prepared statement. This method is a wrapper around `sqlite3_prepare_v2()`. #### `database.createSQLTagStore([maxSize])`# Added in: v24.9.0 * `maxSize` The maximum number of prepared statements to cache. Default: `1000`. * Returns: A new SQL tag store for caching prepared statements. Creates a new `SQLTagStore`, which is an LRU (Least Recently Used) cache for storing prepared statements. This allows for the efficient reuse of prepared statements by tagging them with a unique identifier. When a tagged SQL literal is executed, the `SQLTagStore` checks if a prepared statement for that specific SQL string already exists in the cache. If it does, the cached statement is used. If not, a new prepared statement is created, executed, and then stored in the cache for future use. This mechanism helps to avoid the overhead of repeatedly parsing and preparing the same SQL statements. import { DatabaseSync } from 'node:sqlite'; const db = new DatabaseSync(':memory:'); const sql = db.createSQLTagStore(); db.exec('CREATE TABLE users (id INT, name TEXT)'); // Using the 'run' method to insert data. // The tagged literal is used to identify the prepared statement. sql.run`INSERT INTO users VALUES (1, 'Alice')`; sql.run`INSERT INTO users VALUES (2, 'Bob')`; // Using the 'get' method to retrieve a single row. const id = 1; const user = sql.get`SELECT * FROM users WHERE id = ${id}`; console.log(user); // { id: 1, name: 'Alice' } // Using the 'all' method to retrieve all rows. const allUsers = sql.all`SELECT * FROM users ORDER BY id`; console.log(allUsers); // [ // { id: 1, name: 'Alice' }, // { id: 2, name: 'Bob' } // ] #### `database.createSession([options])`# Added in: v23.3.0, v22.12.0 * `options` The configuration options for the session. * `table` A specific table to track changes for. By default, changes to all tables are tracked. * `db` Name of the database to track. This is useful when multiple databases have been added using `ATTACH DATABASE`. Default: `'main'`. * Returns: A session handle. Creates and attaches a session to the database. This method is a wrapper around `sqlite3session_create()` and `sqlite3session_attach()`. #### `database.applyChangeset(changeset[, options])`# Added in: v23.3.0, v22.12.0 * `changeset` A binary changeset or patchset. * `options` The configuration options for how the changes will be applied. * `filter` Skip changes that, when targeted table name is supplied to this function, return a truthy value. By default, all changes are attempted. * `onConflict` A function that determines how to handle conflicts. The function receives one argument, which can be one of the following values: * `SQLITE_CHANGESET_DATA`: A `DELETE` or `UPDATE` change does not contain the expected "before" values. * `SQLITE_CHANGESET_NOTFOUND`: A row matching the primary key of the `DELETE` or `UPDATE` change does not exist. * `SQLITE_CHANGESET_CONFLICT`: An `INSERT` change results in a duplicate primary key. * `SQLITE_CHANGESET_FOREIGN_KEY`: Applying a change would result in a foreign key violation. * `SQLITE_CHANGESET_CONSTRAINT`: Applying a change results in a `UNIQUE`, `CHECK`, or `NOT NULL` constraint violation. The function should return one of the following values: * `SQLITE_CHANGESET_OMIT`: Omit conflicting changes. * `SQLITE_CHANGESET_REPLACE`: Replace existing values with conflicting changes (only valid with `SQLITE_CHANGESET_DATA` or `SQLITE_CHANGESET_CONFLICT` conflicts). * `SQLITE_CHANGESET_ABORT`: Abort on conflict and roll back the database. When an error is thrown in the conflict handler or when any other value is returned from the handler, applying the changeset is aborted and the database is rolled back. Default: A function that returns `SQLITE_CHANGESET_ABORT`. * Returns: Whether the changeset was applied successfully without being aborted. An exception is thrown if the database is not open. This method is a wrapper around `sqlite3changeset_apply()`. const sourceDb = new DatabaseSync(':memory:'); const targetDb = new DatabaseSync(':memory:'); sourceDb.exec('CREATE TABLE data(key INTEGER PRIMARY KEY, value TEXT)'); targetDb.exec('CREATE TABLE data(key INTEGER PRIMARY KEY, value TEXT)'); const session = sourceDb.createSession(); const insert = sourceDb.prepare('INSERT INTO data (key, value) VALUES (?, ?)'); insert.run(1, 'hello'); insert.run(2, 'world'); const changeset = session.changeset(); targetDb.applyChangeset(changeset); // Now that the changeset has been applied, targetDb contains the same data as sourceDb. #### `database[Symbol.dispose]()`# History VersionChanges v24.2.0 No longer experimental. v23.11.0, v22.15.0 Added in: v23.11.0, v22.15.0 Closes the database connection. If the database connection is already closed then this is a no-op. ### Class: `Session`# Added in: v23.3.0, v22.12.0 #### `session.changeset()`# Added in: v23.3.0, v22.12.0 * Returns: Binary changeset that can be applied to other databases. Retrieves a changeset containing all changes since the changeset was created. Can be called multiple times. An exception is thrown if the database or the session is not open. This method is a wrapper around `sqlite3session_changeset()`. #### `session.patchset()`# Added in: v23.3.0, v22.12.0 * Returns: Binary patchset that can be applied to other databases. Similar to the method above, but generates a more compact patchset. See Changesets and Patchsets in the documentation of SQLite. An exception is thrown if the database or the session is not open. This method is a wrapper around `sqlite3session_patchset()`. #### `session.close()`.# Closes the session. An exception is thrown if the database or the session is not open. This method is a wrapper around `sqlite3session_delete()`. ### Class: `StatementSync`# Added in: v22.5.0 This class represents a single prepared statement. This class cannot be instantiated via its constructor. Instead, instances are created via the `database.prepare()` method. All APIs exposed by this class execute synchronously. A prepared statement is an efficient binary representation of the SQL used to create it. Prepared statements are parameterizable, and can be invoked multiple times with different bound values. Parameters also offer protection against SQL injection attacks. For these reasons, prepared statements are preferred over hand-crafted SQL strings when handling user input. ### Class: `SQLTagStore`# Added in: v24.9.0 This class represents a single LRU (Least Recently Used) cache for storing prepared statements. Instances of this class are created via the database.createSQLTagStore() method, not by using a constructor. The store caches prepared statements based on the provided SQL query string. When the same query is seen again, the store retrieves the cached statement and safely applies the new values through parameter binding, thereby preventing attacks like SQL injection. The cache has a maxSize that defaults to 1000 statements, but a custom size can be provided (e.g., database.createSQLTagStore(100)). All APIs exposed by this class execute synchronously. #### `sqlTagStore.all(sqlTemplate[, ...values])`# Added in: v24.9.0 * `sqlTemplate`