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Class: WrapManager ​

Defined in: packages/net/src/wrapManager.ts:18

Extended EventEmitter that also emits all events to '*' listeners

Extends ​

Constructors ​

Constructor ​

new WrapManager(options): WrapManager

Defined in: packages/net/src/wrapManager.ts:23

Parameters ​

options ​

WrapManagerOptions

Returns ​

WrapManager

Overrides ​

Emitter.constructor

Properties ​

_recipientIndex ​

_recipientIndex: Map<string, WrapReference>

Defined in: packages/net/src/wrapManager.ts:21

_rumorIndex ​

_rumorIndex: Map<string, WrapReference>

Defined in: packages/net/src/wrapManager.ts:20

_wrapIndex ​

_wrapIndex: Map<string, WrapItem>

Defined in: packages/net/src/wrapManager.ts:19

options ​

readonly options: WrapManagerOptions

Defined in: packages/net/src/wrapManager.ts:23

captureRejections ​

static captureRejections: boolean

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:459

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.

Since ​

v13.4.0, v12.16.0

Inherited from ​

Emitter.captureRejections

captureRejectionSymbol ​

readonly static captureRejectionSymbol: typeof captureRejectionSymbol

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:452

Value: Symbol.for('nodejs.rejection')

See how to write a custom rejection handler.

Since ​

v13.4.0, v12.16.0

Inherited from ​

Emitter.captureRejectionSymbol

defaultMaxListeners ​

static defaultMaxListeners: number

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:498

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 allEventEmitter 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:

js
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'.

Since ​

v0.11.2

Inherited from ​

Emitter.defaultMaxListeners

errorMonitor ​

readonly static errorMonitor: typeof errorMonitor

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:445

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.

Since ​

v13.6.0, v12.17.0

Inherited from ​

Emitter.errorMonitor

Methods ​

_add() ​

_add(wrapItem): void

Defined in: packages/net/src/wrapManager.ts:99

Parameters ​

wrapItem ​

WrapItem

Returns ​

void

_addReference() ​

_addReference(index, key, wrapId): void

Defined in: packages/net/src/wrapManager.ts:105

Parameters ​

index ​

Map<string, WrapReference>

key ​

string

wrapId ​

string

Returns ​

void

_remove() ​

_remove(wrapItem): void

Defined in: packages/net/src/wrapManager.ts:115

Parameters ​

wrapItem ​

WrapItem

Returns ​

void

_removeReference() ​

_removeReference(index, key, wrapId): void

Defined in: packages/net/src/wrapManager.ts:121

Parameters ​

index ​

Map<string, WrapReference>

key ​

string

wrapId ​

string

Returns ​

void

[captureRejectionSymbol]()? ​

optional [captureRejectionSymbol]<K>(error, event, ...args): void

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:136

Type Parameters ​

K ​

K

Parameters ​

error ​

Error

event ​

string | symbol

args ​

...AnyRest

Returns ​

void

Inherited from ​

Emitter.[captureRejectionSymbol]

add() ​

add(__namedParameters): void

Defined in: packages/net/src/wrapManager.ts:61

Parameters ​

__namedParameters ​
recipient ​

string

rumor ​

HashedEvent

wrap ​

SignedEvent

Returns ​

void

addListener() ​

addListener<K>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:597

Alias for emitter.on(eventName, listener).

Type Parameters ​

K ​

K

Parameters ​

eventName ​

string | symbol

listener ​

(...args) => void

Returns ​

this

Since ​

v0.1.26

Inherited from ​

Emitter.addListener

clear() ​

clear(): void

Defined in: packages/net/src/wrapManager.ts:44

Returns ​

void

dump() ​

dump(): WrapItem[]

Defined in: packages/net/src/wrapManager.ts:29

Returns ​

WrapItem[]

emit() ​

emit(type, ...args): boolean

Defined in: packages/lib/src/Emitter.ts:13

Emits an event to listeners and to '*' listeners

Parameters ​

type ​

string

Event type/name

args ​

...any[]

Arguments to pass to listeners

Returns ​

boolean

True if event had listeners

Inherited from ​

Emitter.emit

eventNames() ​

eventNames(): (string | symbol)[]

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:922

Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.

js
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) ]

Returns ​

(string | symbol)[]

Since ​

v6.0.0

Inherited from ​

Emitter.eventNames

getMaxListeners() ​

getMaxListeners(): number

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:774

Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to EventEmitter.defaultMaxListeners.

Returns ​

number

Since ​

v1.0.0

Inherited from ​

Emitter.getMaxListeners

getRumor() ​

getRumor(wrapId): undefined | TrustedEvent

Defined in: packages/net/src/wrapManager.ts:34

Parameters ​

wrapId ​

string

Returns ​

undefined | TrustedEvent

getWraps() ​

getWraps(rumorId): WrapItem[]

Defined in: packages/net/src/wrapManager.ts:31

Parameters ​

rumorId ​

string

Returns ​

WrapItem[]

listenerCount() ​

listenerCount<K>(eventName, listener?): number

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:868

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.

Type Parameters ​

K ​

K

Parameters ​

eventName ​

The name of the event being listened for

string | symbol

listener? ​

Function

The event handler function

Returns ​

number

Since ​

v3.2.0

Inherited from ​

Emitter.listenerCount

listeners() ​

listeners<K>(eventName): Function[]

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:787

Returns a copy of the array of listeners for the event named eventName.

js
server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]

Type Parameters ​

K ​

K

Parameters ​

eventName ​

string | symbol

Returns ​

Function[]

Since ​

v0.1.26

Inherited from ​

Emitter.listeners

load() ​

load(wrapItems): void

Defined in: packages/net/src/wrapManager.ts:51

Parameters ​

wrapItems ​

WrapItem[]

Returns ​

void

off() ​

off<K>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:747

Alias for emitter.removeListener().

Type Parameters ​

K ​

K

Parameters ​

eventName ​

string | symbol

listener ​

(...args) => void

Returns ​

this

Since ​

v10.0.0

Inherited from ​

Emitter.off

on() ​

on<K>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:629

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.

js
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.

js
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

Type Parameters ​

K ​

K

Parameters ​

eventName ​

The name of the event.

string | symbol

listener ​

(...args) => void

The callback function

Returns ​

this

Since ​

v0.1.101

Inherited from ​

Emitter.on

once() ​

once<K>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:659

Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.

js
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.

js
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

Type Parameters ​

K ​

K

Parameters ​

eventName ​

The name of the event.

string | symbol

listener ​

(...args) => void

The callback function

Returns ​

this

Since ​

v0.3.0

Inherited from ​

Emitter.once

prependListener() ​

prependListener<K>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:886

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.

js
server.prependListener('connection', (stream) => {
  console.log('someone connected!');
});

Returns a reference to the EventEmitter, so that calls can be chained.

Type Parameters ​

K ​

K

Parameters ​

eventName ​

The name of the event.

string | symbol

listener ​

(...args) => void

The callback function

Returns ​

this

Since ​

v6.0.0

Inherited from ​

Emitter.prependListener

prependOnceListener() ​

prependOnceListener<K>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:902

Adds a one-timelistener 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.

js
server.prependOnceListener('connection', (stream) => {
  console.log('Ah, we have our first user!');
});

Returns a reference to the EventEmitter, so that calls can be chained.

Type Parameters ​

K ​

K

Parameters ​

eventName ​

The name of the event.

string | symbol

listener ​

(...args) => void

The callback function

Returns ​

this

Since ​

v6.0.0

Inherited from ​

Emitter.prependOnceListener

rawListeners() ​

rawListeners<K>(eventName): Function[]

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:818

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

js
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');

Type Parameters ​

K ​

K

Parameters ​

eventName ​

string | symbol

Returns ​

Function[]

Since ​

v9.4.0

Inherited from ​

Emitter.rawListeners

remove() ​

remove(id): void

Defined in: packages/net/src/wrapManager.ts:81

Parameters ​

id ​

string

Returns ​

void

removeAllListeners() ​

removeAllListeners(eventName?): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:758

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.

Parameters ​

eventName? ​

string | symbol

Returns ​

this

Since ​

v0.1.26

Inherited from ​

Emitter.removeAllListeners

removeByRumorId() ​

removeByRumorId(rumorId): void

Defined in: packages/net/src/wrapManager.ts:91

Parameters ​

rumorId ​

string

Returns ​

void

removeListener() ​

removeListener<K>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:742

Removes the specified listener from the listener array for the event named eventName.

js
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 fromemit() in progress. Subsequent events behave as expected.

js
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 indices 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:

js
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.

Type Parameters ​

K ​

K

Parameters ​

eventName ​

string | symbol

listener ​

(...args) => void

Returns ​

this

Since ​

v0.1.26

Inherited from ​

Emitter.removeListener

setMaxListeners() ​

setMaxListeners(n): this

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:768

By default EventEmitters 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.

Parameters ​

n ​

number

Returns ​

this

Since ​

v0.3.5

Inherited from ​

Emitter.setMaxListeners

addAbortListener() ​

static addAbortListener(signal, resource): Disposable

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:437

Experimental

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 AbortSignals 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.

js
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]();
  }
}

Parameters ​

signal ​

AbortSignal

resource ​

(event) => void

Returns ​

Disposable

Disposable that removes the abort listener.

Since ​

v20.5.0

Inherited from ​

Emitter.addAbortListener

getEventListeners() ​

static getEventListeners(emitter, name): Function[]

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:358

Returns a copy of the array of listeners for the event named eventName.

For EventEmitters this behaves exactly the same as calling .listeners on the emitter.

For EventTargets this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.

js
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] ]
}

Parameters ​

emitter ​

EventEmitter<DefaultEventMap> | EventTarget

name ​

string | symbol

Returns ​

Function[]

Since ​

v15.2.0, v14.17.0

Inherited from ​

Emitter.getEventListeners

getMaxListeners() ​

static getMaxListeners(emitter): number

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:387

Returns the currently set max amount of listeners.

For EventEmitters this behaves exactly the same as calling .getMaxListeners on the emitter.

For EventTargets 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.

js
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
}

Parameters ​

emitter ​

EventEmitter<DefaultEventMap> | EventTarget

Returns ​

number

Since ​

v19.9.0

Inherited from ​

Emitter.getMaxListeners

listenerCount() ​

static listenerCount(emitter, eventName): number

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:330

A class method that returns the number of listeners for the given eventName registered on the given emitter.

js
import { EventEmitter, listenerCount } from 'node:events';

const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2

Parameters ​

emitter ​

EventEmitter

The emitter to query

eventName ​

The event name

string | symbol

Returns ​

number

Since ​

v0.9.12

Deprecated ​

Since v3.2.0 - Use listenerCount instead.

Inherited from ​

Emitter.listenerCount

on() ​

Call Signature ​

static on(emitter, eventName, options?): AsyncIterator<any[]>

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:303

js
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 AbortSignal can be used to cancel waiting on events:

js
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());

Use the close option to specify an array of event names that will end the iteration:

js
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);
  ee.emit('close');
});

for await (const event of on(ee, 'foo', { close: ['close'] })) {
  console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'
Parameters ​
emitter ​

EventEmitter

eventName ​

string | symbol

options? ​

StaticEventEmitterIteratorOptions

Returns ​

AsyncIterator<any[]>

An AsyncIterator that iterates eventName events emitted by the emitter

Since ​

v13.6.0, v12.16.0

Inherited from ​

Emitter.on

Call Signature ​

static on(emitter, eventName, options?): AsyncIterator<any[]>

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:308

js
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 AbortSignal can be used to cancel waiting on events:

js
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());

Use the close option to specify an array of event names that will end the iteration:

js
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);
  ee.emit('close');
});

for await (const event of on(ee, 'foo', { close: ['close'] })) {
  console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'
Parameters ​
emitter ​

EventTarget

eventName ​

string

options? ​

StaticEventEmitterIteratorOptions

Returns ​

AsyncIterator<any[]>

An AsyncIterator that iterates eventName events emitted by the emitter

Since ​

v13.6.0, v12.16.0

Inherited from ​

Emitter.on

once() ​

Call Signature ​

static once(emitter, eventName, options?): Promise<any[]>

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:217

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.

js
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:

js
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 AbortSignal can be used to cancel waiting for the event:

js
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(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
Parameters ​
emitter ​

EventEmitter

eventName ​

string | symbol

options? ​

StaticEventEmitterOptions

Returns ​

Promise<any[]>

Since ​

v11.13.0, v10.16.0

Inherited from ​

Emitter.once

Call Signature ​

static once(emitter, eventName, options?): Promise<any[]>

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:222

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.

js
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:

js
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 AbortSignal can be used to cancel waiting for the event:

js
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(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
Parameters ​
emitter ​

EventTarget

eventName ​

string

options? ​

StaticEventEmitterOptions

Returns ​

Promise<any[]>

Since ​

v11.13.0, v10.16.0

Inherited from ​

Emitter.once

setMaxListeners() ​

static setMaxListeners(n?, ...eventTargets?): void

Defined in: node_modules/.pnpm/@types+node@22.13.17/node_modules/@types/node/events.d.ts:402

js
import { setMaxListeners, EventEmitter } from 'node:events';

const target = new EventTarget();
const emitter = new EventEmitter();

setMaxListeners(5, target, emitter);

Parameters ​

n? ​

number

A non-negative number. The maximum number of listeners per EventTarget event.

eventTargets? ​

...(EventEmitter<DefaultEventMap> | EventTarget)[]

Zero or more {EventTarget} or {EventEmitter} instances. If none are specified, n is set as the default max for all newly created {EventTarget} and {EventEmitter} objects.

Returns ​

void

Since ​

v15.4.0

Inherited from ​

Emitter.setMaxListeners