Node.js

- About this documentation
- Usage and example

- Assertion testing
- Asynchronous context tracking
- Async hooks
- Buffer
- C++ addons
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- Child processes
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- DNS
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- HTTP
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- Modules: CommonJS modules
- Modules: ECMAScript modules
- Modules: `module` API
- Modules: Packages
- Net
- OS
- Path
- Performance hooks
- Policies
- Process
- Punycode
- Query strings
- Readline
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- Timers
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- Trace events
- TTY
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- URL
- Utilities
- V8
- VM
- WASI
- Web Crypto API
- Web Streams API
- Worker threads
- Zlib

- Code repository and issue tracker

Table of contents

- Global objects
  - Class: `AbortController`
    - `abortController.abort()`
    - `abortController.signal`
    - Class: `AbortSignal`
      - Static method: `AbortSignal.abort()`
      - Event: `'abort'`
      - `abortSignal.aborted`
      - `abortSignal.onabort`
  - Class: `Buffer`
  - `__dirname`
  - `__filename`
  - `atob(data)`
  - `btoa(data)`
  - `clearImmediate(immediateObject)`
  - `clearInterval(intervalObject)`
  - `clearTimeout(timeoutObject)`
  - `console`
  - `Event`
  - `EventTarget`
  - `exports`
  - `global`
  - `MessageChannel`
  - `MessageEvent`
  - `MessagePort`
  - `module`
  - `performance`
  - `process`
  - `queueMicrotask(callback)`
  - `require()`
  - `setImmediate(callback[, ...args])`
  - `setInterval(callback, delay[, ...args])`
  - `setTimeout(callback, delay[, ...args])`
  - `TextDecoder`
  - `TextEncoder`
  - `URL`
  - `URLSearchParams`
  - `WebAssembly`

## Global objects#

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 modules, see the module system documentation:

- `__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

Version | Changes
--- | ---
v15.4.0 | No longer experimental.
v15.0.0 | Added in: v15.0.0

A utility class used to signal cancelation in selected `Promise`-based APIs. The API is based on the Web API `AbortController`.

    const ac = new AbortController();

    ac.signal.addEventListener('abort', () => console.log('Aborted!'),
                               { once: true });

    ac.abort();

    console.log(ac.signal.aborted);  // Prints True

#### `abortController.abort()`#

Added in: v15.0.0

Triggers the abort signal, causing the `abortController.signal` to emit the `'abort'` event.

#### `abortController.signal`#

Added in: v15.0.0

- Type: <AbortSignal>

#### Class: `AbortSignal`#

Added in: v15.0.0

- Extends: <EventTarget>

The `AbortSignal` is used to notify observers when the `abortController.abort()` method is called.

##### Static method: `AbortSignal.abort()`#

Added in: v15.12.0

- Returns: <AbortSignal>

Returns a new already aborted `AbortSignal`.

##### Event: `'abort'`#

Added in: v15.0.0

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

- Type: <boolean> True after the `AbortController` has been aborted.

##### `abortSignal.onabort`#

Added in: v15.0.0

- Type: <Function>

An optional callback function that may be set by user code to be notified when the `abortController.abort()` function has been called.

### Class: `Buffer`#

Added in: v0.1.103

- <Function>

Used to handle binary data. See the buffer section.

### `__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()`.

### `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.

### `console`#

Added in: v0.1.100

- <Object>

Used to print to stdout and stderr. See the `console` section.

### `Event`#

History

Version | Changes
--- | ---
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.

### `EventTarget`#

History

Version | Changes
--- | ---
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`.

### `global`#

Added in: v0.1.27

- <Object> The global namespace object.

In browsers, the top-level scope is the global scope. This means that within the browser `var something` will define a new global variable. 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.

### `MessageChannel`#

Added in: v15.0.0

The `MessageChannel` class. See `MessageChannel` for more details.

### `MessageEvent`#

Added in: v15.0.0

The `MessageEvent` class. See `MessageEvent` for more details.

### `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`.

### `performance`#

The `perf_hooks.performance` object.

### `process`#

Added in: v0.1.7

- <Object>

The process object. See the `process` object section.

### `queueMicrotask(callback)`#

Added in: v11.0.0

- `callback` <Function> 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);
    };

### `require()`#

This variable may appear to be global but is not. See `require()`.

### `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.

### `TextDecoder`#

Added in: v11.0.0

The WHATWG `TextDecoder` class. See the `TextDecoder` section.

### `TextEncoder`#

Added in: v11.0.0

The WHATWG `TextEncoder` class. See the `TextEncoder` section.

### `URL`#

Added in: v10.0.0

The WHATWG `URL` class. See the `URL` section.

### `URLSearchParams`#

Added in: v10.0.0

The WHATWG `URLSearchParams` class. See the `URLSearchParams` section.

### `WebAssembly`#

Added in: v8.0.0

- <Object>

The object that acts as the namespace for all W3C WebAssembly related functionality. See the Mozilla Developer Network for usage and compatibility.