globals.md

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 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

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([reason])

• reason {any} 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

• Type: {AbortSignal}

Class: AbortSignal

• Extends: {EventTarget}

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

Static method: AbortSignal.abort([reason])

• reason: {any}
• Returns: {AbortSignal}

Returns a new already aborted AbortSignal.

Static method: AbortSignal.timeout(delay)

• delay {number} 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)

• signals {AbortSignal[]} The AbortSignals 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'

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

• Type: {boolean} True after the AbortController has been aborted.

abortSignal.onabort

• Type: {Function}

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

abortSignal.reason

• Type: {any}

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()

If abortSignal.aborted is true, throws abortSignal.reason.

Class: Blob

See {Blob}.

Class: Buffer

• {Function}

Used to handle binary data. See the buffer section.

Class: ByteLengthQueuingStrategy

Stability: 1 - Experimental.

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)

Stability: 3 - Legacy. Use Buffer.from(data, 'base64') instead.

Global alias for buffer.atob().

BroadcastChannel

See {BroadcastChannel}.

btoa(data)

Stability: 3 - Legacy. Use buf.toString('base64') instead.

Global alias for buffer.btoa().

clearImmediate(immediateObject)

clearImmediate is described in the timers section.

clearInterval(intervalObject)

clearInterval is described in the timers section.

clearTimeout(timeoutObject)

clearTimeout is described in the timers section.

CloseEvent

The CloseEvent class. See CloseEvent for more details.

A browser-compatible implementation of CloseEvent. Disable this API with the --no-experimental-websocket CLI flag.

Class: CompressionStream

Stability: 1 - Experimental.

A browser-compatible implementation of CompressionStream.

console

• {Object}

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

Class: CountQueuingStrategy

Stability: 1 - Experimental.

A browser-compatible implementation of CountQueuingStrategy.

Crypto

Stability: 2 - Stable.

A browser-compatible implementation of {Crypto}. This global is available only if the Node.js binary was compiled with including support for the node:crypto module.

crypto

Stability: 2 - Stable.

A browser-compatible implementation of the Web Crypto API.

CryptoKey

Stability: 2 - Stable.

A browser-compatible implementation of {CryptoKey}. This global is available only if the Node.js binary was compiled with including support for the node:crypto module.

CustomEvent

Stability: 2 - Stable

A browser-compatible implementation of the CustomEvent Web API.

Class: DecompressionStream

Stability: 1 - Experimental.

A browser-compatible implementation of DecompressionStream.

Event

A browser-compatible implementation of the Event class. See EventTarget and Event API for more details.

EventSource

Stability: 1 - Experimental. Enable this API with the --experimental-eventsource CLI flag.

A browser-compatible implementation of the EventSource class.

EventTarget

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

Stability: 2 - Stable

A browser-compatible implementation of the fetch() function.

Class: File

See {File}.

Class FormData

Stability: 2 - Stable

A browser-compatible implementation of {FormData}.

global

Stability: 3 - Legacy. Use globalThis instead.

• {Object} 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

Stability: 2 - Stable

A browser-compatible implementation of {Headers}.

localStorage

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.

MessageChannel

The MessageChannel class. See MessageChannel for more details.

MessageEvent

The MessageEvent class. See MessageEvent for more details.

MessagePort

The MessagePort class. See MessagePort for more details.

module

This variable may appear to be global but is not. See module.

Navigator

Stability: 1.1 - Active development. Disable this API with the --no-experimental-global-navigator CLI flag.

A partial implementation of the Navigator API.

navigator

Stability: 1.1 - Active development. Disable this API with the --no-experimental-global-navigator CLI flag.

A partial implementation of window.navigator.

navigator.hardwareConcurrency

• {number}

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

• {string}

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

• {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

• {string}

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

• {string}

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"

PerformanceEntry

The PerformanceEntry class. See PerformanceEntry for more details.

PerformanceMark

The PerformanceMark class. See PerformanceMark for more details.

PerformanceMeasure

The PerformanceMeasure class. See PerformanceMeasure for more details.

PerformanceObserver

The PerformanceObserver class. See PerformanceObserver for more details.

PerformanceObserverEntryList

The PerformanceObserverEntryList class. See PerformanceObserverEntryList for more details.

PerformanceResourceTiming

The PerformanceResourceTiming class. See PerformanceResourceTiming for more details.

performance

The perf_hooks.performance object.

process

• {Object}

The process object. See the process object section.

queueMicrotask(callback)

• 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);
};

Class: ReadableByteStreamController

Stability: 1 - Experimental.

A browser-compatible implementation of ReadableByteStreamController.

Class: ReadableStream

Stability: 1 - Experimental.

A browser-compatible implementation of ReadableStream.

Class: ReadableStreamBYOBReader

Stability: 1 - Experimental.

A browser-compatible implementation of ReadableStreamBYOBReader.

Class: ReadableStreamBYOBRequest

Stability: 1 - Experimental.

A browser-compatible implementation of ReadableStreamBYOBRequest.

Class: ReadableStreamDefaultController

Stability: 1 - Experimental.

A browser-compatible implementation of ReadableStreamDefaultController.

Class: ReadableStreamDefaultReader

Stability: 1 - Experimental.

A browser-compatible implementation of ReadableStreamDefaultReader.

require()

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

Response

Stability: 2 - Stable

A browser-compatible implementation of {Response}.

Request

Stability: 2 - Stable

A browser-compatible implementation of {Request}.

sessionStorage

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])

setImmediate is described in the timers section.

setInterval(callback, delay[, ...args])

setInterval is described in the timers section.

setTimeout(callback, delay[, ...args])

setTimeout is described in the timers section.

Class: Storage

Stability: 1.0 - Early development.

A browser-compatible implementation of Storage. Enable this API with the --experimental-webstorage CLI flag.

structuredClone(value[, options])

The WHATWG structuredClone method.

SubtleCrypto

Stability: 2 - Stable.

A browser-compatible implementation of {SubtleCrypto}. This global is available only if the Node.js binary was compiled with including support for the node:crypto module.

DOMException

The WHATWG DOMException class. See DOMException for more details.

TextDecoder

The WHATWG TextDecoder class. See the TextDecoder section.

Class: TextDecoderStream

Stability: 1 - Experimental.

A browser-compatible implementation of TextDecoderStream.

TextEncoder

The WHATWG TextEncoder class. See the TextEncoder section.

Class: TextEncoderStream

Stability: 1 - Experimental.

A browser-compatible implementation of TextEncoderStream.

Class: TransformStream

Stability: 1 - Experimental.

A browser-compatible implementation of TransformStream.

Class: TransformStreamDefaultController

Stability: 1 - Experimental.

A browser-compatible implementation of TransformStreamDefaultController.

URL

The WHATWG URL class. See the URL section.

URLSearchParams

The WHATWG URLSearchParams class. See the URLSearchParams section.

WebAssembly

• {Object}

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

WebSocket

Stability: 2 - Stable.

A browser-compatible implementation of WebSocket. Disable this API with the --no-experimental-websocket CLI flag.

Class: WritableStream

Stability: 1 - Experimental.

A browser-compatible implementation of WritableStream.

Class: WritableStreamDefaultController

Stability: 1 - Experimental.

A browser-compatible implementation of WritableStreamDefaultController.

Class: WritableStreamDefaultWriter

Stability: 1 - Experimental.

A browser-compatible implementation of WritableStreamDefaultWriter.