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AsyncEventEmitter

Extends

  • EventEmitter

Type Parameters

• T extends EventMap

Constructors

new AsyncEventEmitter()

new AsyncEventEmitter<T>(options?): AsyncEventEmitter<T>

Parameters

• options?: EventEmitterOptions

Returns

AsyncEventEmitter<T>

Inherited from

EventEmitter.constructor

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:149

Properties

captureRejectionSymbol

readonly static captureRejectionSymbol: typeof captureRejectionSymbol

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

See how to write a custom rejection handler.

Since

v13.4.0, v12.16.0

Inherited from

EventEmitter.captureRejectionSymbol

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:468

captureRejections

static captureRejections: boolean

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.

Since

v13.4.0, v12.16.0

Inherited from

EventEmitter.captureRejections

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:475

defaultMaxListeners

static defaultMaxListeners: number

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:

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

EventEmitter.defaultMaxListeners

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:514

errorMonitor

readonly static errorMonitor: typeof errorMonitor

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

EventEmitter.errorMonitor

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:461

Methods

[captureRejectionSymbol]()?

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

Type Parameters

• K

Parameters

• error: Error

• event: string | symbol

• …args: AnyRest

Returns

void

Inherited from

EventEmitter.[captureRejectionSymbol]

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:151

[captureRejectionSymbol]()?

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

Type Parameters

• K

Parameters

• error: Error

• event: string | symbol

• …args: AnyRest

Returns

void

Inherited from

EventEmitter.[captureRejectionSymbol]

Defined in

node_modules/.pnpm/@types+node@22.1.0/node_modules/@types/node/events.d.ts:592

[captureRejectionSymbol]()?

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

Type Parameters

• K

Parameters

• error: Error

• event: string | symbol

• …args: AnyRest

Returns

void

Inherited from

EventEmitter.[captureRejectionSymbol]

Defined in

node_modules/.pnpm/@types+node@20.12.14/node_modules/@types/node/events.d.ts:545

addListener()

addListener<E>(event, listener): this

Alias for emitter.on(eventName, listener).

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• listener: T[E]

Returns

this

Overrides

EventEmitter.addListener

Since

v0.1.26

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:23

after()

after<E>(event, target, listener): this

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• target: T[E]

• listener: T[E]

Returns

this

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:20

before()

before<E>(event, target, listener): this

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• target: T[E]

• listener: T[E]

Returns

this

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:19

emit()

emit<E>(event, …args): boolean

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

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• …args: Parameters<T[E]>

Returns

boolean

Overrides

EventEmitter.emit

Since

v0.1.26

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:16

eventNames()

eventNames(): keyof T & string[]

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

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

keyof T & string[]

Overrides

EventEmitter.eventNames

Since

v6.0.0

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:28

first()

first<E>(event, listener): this

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• listener: T[E]

Returns

this

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:18

getMaxListeners()

getMaxListeners(): number

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

Returns

number

Overrides

EventEmitter.getMaxListeners

Since

v1.0.0

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:31

listenerCount()

listenerCount(event): number

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.

Parameters

• event: keyof T & string

Returns

number

Overrides

EventEmitter.listenerCount

Since

v3.2.0

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:30

listeners()

listeners<E>(event): T[E][]

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] ]

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

Returns

T[E][]

Overrides

EventEmitter.listeners

Since

v0.1.26

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:29

off()

off(eventName, listener)

off<K>(eventName, listener): this

Alias for emitter.removeListener().

Type Parameters

• K

Parameters

• eventName: string | symbol

• listener

Returns

this

Inherited from

EventEmitter.off

Since

v10.0.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:763

off(eventName, listener)

off<K>(eventName, listener): this

Alias for emitter.removeListener().

Type Parameters

• K

Parameters

• eventName: string | symbol

• listener

Returns

this

Inherited from

EventEmitter.off

Since

v10.0.0

Defined in

node_modules/.pnpm/@types+node@22.1.0/node_modules/@types/node/events.d.ts:747

off(eventName, listener)

off<K>(eventName, listener): this

Alias for emitter.removeListener().

Type Parameters

• K

Parameters

• eventName: string | symbol

• listener

Returns

this

Inherited from

EventEmitter.off

Since

v10.0.0

Defined in

node_modules/.pnpm/@types+node@20.12.14/node_modules/@types/node/events.d.ts:700

on()

on<E>(event, listener): this

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

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• listener: T[E]

The callback function

Returns

this

Overrides

EventEmitter.on

Since

v0.1.101

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:22

once()

once<E>(event, listener): this

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

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• listener: T[E]

The callback function

Returns

this

Overrides

EventEmitter.once

Since

v0.3.0

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:17

prependListener()

prependListener<E>(event, listener): this

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.

Type Parameters

• E extends string | number | symbol

Parameters

• event: E & string

• listener: T[E]

The callback function

Returns

this

Overrides

EventEmitter.prependListener

Since

v6.0.0

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:24

prependOnceListener()

prependOnceListener<E>(event, listener): this

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.

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

• E extends string | number | symbol

Parameters

• event: E & string

• listener: T[E]

The callback function

Returns

this

Overrides

EventEmitter.prependOnceListener

Since

v6.0.0

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:25

rawListeners()

rawListeners(eventName)

rawListeners<K>(eventName): Function[]

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');
Type Parameters

• K

Parameters

• eventName: string | symbol

Returns

Function[]

Inherited from

EventEmitter.rawListeners

Since

v9.4.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:834

rawListeners(eventName)

rawListeners<K>(eventName): Function[]

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');
Type Parameters

• K

Parameters

• eventName: string | symbol

Returns

Function[]

Inherited from

EventEmitter.rawListeners

Since

v9.4.0

Defined in

node_modules/.pnpm/@types+node@22.1.0/node_modules/@types/node/events.d.ts:818

rawListeners(eventName)

rawListeners<K>(eventName): Function[]

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');
Type Parameters

• K

Parameters

• eventName: string | symbol

Returns

Function[]

Inherited from

EventEmitter.rawListeners

Since

v9.4.0

Defined in

node_modules/.pnpm/@types+node@20.12.14/node_modules/@types/node/events.d.ts:771

removeAllListeners()

removeAllListeners(event?): this

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

• event?: keyof T & string

Returns

this

Overrides

EventEmitter.removeAllListeners

Since

v0.1.26

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:26

removeListener()

removeListener<E>(event, listener): this

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 fromemit() 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 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:

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

• E extends string | number | symbol

Parameters

• event: E & string

• listener: T[E]

Returns

this

Overrides

EventEmitter.removeListener

Since

v0.1.26

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:27

setMaxListeners()

setMaxListeners(maxListeners): this

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

• maxListeners: number

Returns

this

Overrides

EventEmitter.setMaxListeners

Since

v0.3.5

Defined in

node_modules/.pnpm/@ethereumjs+util@9.0.3/node_modules/@ethereumjs/util/dist/esm/asyncEventEmitter.d.ts:32

addAbortListener()

static addAbortListener(signal, resource): Disposable

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.

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

Returns

Disposable

Disposable that removes the abort listener.

Inherited from

EventEmitter.addAbortListener

Since

v20.5.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:453

getEventListeners()

static getEventListeners(emitter, name): Function[]

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.

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[]

Inherited from

EventEmitter.getEventListeners

Since

v15.2.0, v14.17.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:374

getMaxListeners()

static getMaxListeners(emitter): number

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.

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

Inherited from

EventEmitter.getMaxListeners

Since

v19.9.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:403

listenerCount()

static listenerCount(emitter, eventName): number

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

Parameters

• emitter: EventEmitter<DefaultEventMap>

The emitter to query

• eventName: string | symbol

The event name

Returns

number

Inherited from

EventEmitter.listenerCount

Since

v0.9.12

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:346

on()

on(emitter, eventName, options)

static on(emitter, eventName, options?): AsyncIterableIterator<any>

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:

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:

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<DefaultEventMap>

• eventName: string | symbol

The name of the event being listened for

• options?: StaticEventEmitterOptions

Returns

AsyncIterableIterator<any>

An AsyncIterator that iterates eventName events emitted by the emitter

Inherited from

EventEmitter.on

Since

v13.6.0, v12.16.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:319

on(emitter, eventName, options)

static on(emitter, eventName, options?): AsyncIterableIterator<any>

Parameters

• emitter: EventTarget

• eventName: string

• options?: StaticEventEmitterIteratorOptions

Returns

AsyncIterableIterator<any>

Inherited from

EventEmitter.on

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:324

once()

once(emitter, eventName, options)

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

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

• emitter: EventEmitter<DefaultEventMap>

• eventName: string | symbol

• options?: Pick<StaticEventEmitterOptions, "signal">

Returns

Promise<any[]>

Inherited from

EventEmitter.once

Since

v11.13.0, v10.16.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:232

once(emitter, eventName, options)

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

Parameters

• emitter: EventTarget

• eventName: string

• options?: StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited from

EventEmitter.once

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:237

setMaxListeners()

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

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)[]

Returns

void

Inherited from

EventEmitter.setMaxListeners

Since

v15.4.0

Defined in

node_modules/.pnpm/@types+node@20.14.8/node_modules/@types/node/events.d.ts:418