Beacon

Defined in: src/models/beacon.ts:53

Typed Event Emitter class which can act as a Base Model for all our model and communication events. This makes it much easier for us to distinguish between events, as we now need to properly type this, so that our events are not stringly-based and prone to silly typos.

Type parameters:

Events - List of all events emitted by this TypedEventEmitter. Normally an enum type.
Arguments - A ListenerMap type providing mappings from event names to listener types.
SuperclassArguments - TODO: not really sure. Alternative listener mappings, I think? But only honoured for .emit?

Extends

TypedEventEmitter<Exclude<BeaconEvent, New>, BeaconEventHandlerMap>

Constructors

Constructor

new Beacon(rootEvent): Beacon

Defined in: src/models/beacon.ts:62

Parameters

rootEvent

DigitalWorldEvent

Returns

Beacon

Overrides

TypedEventEmitter.constructor

Properties

roomId

readonly roomId: string

Defined in: src/models/beacon.ts:54

captureRejections

static captureRejections: boolean

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:425

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.

Since

v13.4.0, v12.16.0

Inherited from

TypedEventEmitter.captureRejections

captureRejectionSymbol

readonly static captureRejectionSymbol: typeof captureRejectionSymbol

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:418

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

See how to write a custom rejection handler.

Since

v13.4.0, v12.16.0

Inherited from

TypedEventEmitter.captureRejectionSymbol

defaultMaxListeners

static defaultMaxListeners: number

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:464

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

TypedEventEmitter.defaultMaxListeners

errorMonitor

readonly static errorMonitor: typeof errorMonitor

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:411

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

TypedEventEmitter.errorMonitor

Accessors

beaconInfo

Get Signature

get beaconInfo(): BeaconInfoState

Defined in: src/models/beacon.ts:88

Returns

BeaconInfoState

beaconInfoEventType

Get Signature

get beaconInfoEventType(): string

Defined in: src/models/beacon.ts:84

Returns

string

beaconInfoId

Get Signature

get beaconInfoId(): string

Defined in: src/models/beacon.ts:76

Returns

string

beaconInfoOwner

Get Signature

get beaconInfoOwner(): string

Defined in: src/models/beacon.ts:80

Returns

string

identifier

Get Signature

get identifier(): string

Defined in: src/models/beacon.ts:72

Returns

string

isLive

Get Signature

get isLive(): boolean

Defined in: src/models/beacon.ts:68

Returns

boolean

latestLocationEvent

Get Signature

get latestLocationEvent(): DigitalWorldEvent | undefined

Defined in: src/models/beacon.ts:96

Returns

DigitalWorldEvent | undefined

latestLocationState

Get Signature

get latestLocationState(): BeaconLocationState | undefined

Defined in: src/models/beacon.ts:92

Returns

BeaconLocationState | undefined

Methods

[captureRejectionSymbol]()?

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

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:103

Type Parameters

K

K

Parameters

error

Error

event

string | symbol

args

…AnyRest

Returns

void

Inherited from

TypedEventEmitter.[captureRejectionSymbol]

addListener()

addListener<T>(event, listener): this

Defined in: src/models/typed-event-emitter.ts:70

Alias for on.

Type Parameters

T

T extends EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

listener

Listener<Update | LivenessChange | Destroy | LocationUpdate, BeaconEventHandlerMap, T>

Returns

this

Inherited from

TypedEventEmitter.addListener

addLocations()

addLocations(beaconLocationEvents): void

Defined in: src/models/beacon.ts:155

Process Beacon locations Emits BeaconEvent.LocationUpdate

Parameters

beaconLocationEvents

DigitalWorldEvent[]

Returns

void

destroy()

destroy(): void

Defined in: src/models/beacon.ts:115

Returns

void

emit()

Call Signature

emit<T>(event, …args): boolean

Defined in: src/models/typed-event-emitter.ts:86

Synchronously calls each of the listeners registered for the event named event, in the order they were registered, passing the supplied arguments to each.

Type Parameters

T

T extends Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event to emit

args

…Parameters<BeaconEventHandlerMap[T]>

Arguments to pass to the listener

Returns

boolean

true if the event had listeners, false otherwise.

Inherited from

TypedEventEmitter.emit

Call Signature

emit<T>(event, …args): boolean

Defined in: src/models/typed-event-emitter.ts:87

Synchronously calls each of the listeners registered for the event named event, in the order they were registered, passing the supplied arguments to each.

Type Parameters

T

T extends Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event to emit

args

…Parameters<BeaconEventHandlerMap[T]>

Arguments to pass to the listener

Returns

boolean

true if the event had listeners, false otherwise.

Inherited from

TypedEventEmitter.emit

emitPromised()

Call Signature

emitPromised<T>(event, …args): Promise<boolean>

Defined in: src/models/typed-event-emitter.ts:98

Similar to emit but calls all listeners within a Promise.all and returns the promise chain

Type Parameters

T

T extends Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event to emit

args

…Parameters<BeaconEventHandlerMap[T]>

Arguments to pass to the listener

Returns

Promise<boolean>

true if the event had listeners, false otherwise.

Inherited from

TypedEventEmitter.emitPromised

Call Signature

emitPromised<T>(event, …args): Promise<boolean>

Defined in: src/models/typed-event-emitter.ts:102

Similar to emit but calls all listeners within a Promise.all and returns the promise chain

Type Parameters

T

T extends Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event to emit

args

…Parameters<BeaconEventHandlerMap[T]>

Arguments to pass to the listener

Returns

Promise<boolean>

true if the event had listeners, false otherwise.

Inherited from

TypedEventEmitter.emitPromised

eventNames()

eventNames(): (string | symbol)[]

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:967

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

(string | symbol)[]

Since

v6.0.0

Inherited from

TypedEventEmitter.eventNames

getMaxListeners()

getMaxListeners(): number

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:819

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

TypedEventEmitter.getMaxListeners

listenerCount()

listenerCount(event): number

Defined in: src/models/typed-event-emitter.ts:115

Returns the number of listeners listening to the event named event.

Parameters

event

EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

The name of the event being listened for

Returns

number

Inherited from

TypedEventEmitter.listenerCount

listeners()

listeners(event): Function[]

Defined in: src/models/typed-event-emitter.ts:122

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

Parameters

event

EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Returns

Function[]

Inherited from

TypedEventEmitter.listeners

monitorLiveness()

monitorLiveness(): void

Defined in: src/models/beacon.ts:128

Monitor liveness of a beacon Emits BeaconEvent.LivenessChange when beacon expires

Returns

void

off()

off<T>(event, listener): this

Defined in: src/models/typed-event-emitter.ts:129

Alias for removeListener

Type Parameters

T

T extends EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

listener

Listener<Update | LivenessChange | Destroy | LocationUpdate, BeaconEventHandlerMap, T>

Returns

this

Inherited from

TypedEventEmitter.off

on()

on<T>(event, listener): this

Defined in: src/models/typed-event-emitter.ts:150

Adds the listener function to the end of the listeners array for the event named event.

No checks are made to see if the listener has already been added. Multiple calls passing the same combination of event and listener will result in the listener being added, and called, multiple times.

By default, event listeners are invoked in the order they are added. The prependListener method can be used as an alternative to add the event listener to the beginning of the listeners array.

Type Parameters

T

T extends EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event.

listener

Listener<Update | LivenessChange | Destroy | LocationUpdate, BeaconEventHandlerMap, T>

The callback function

Returns

this

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

Inherited from

TypedEventEmitter.on

once()

once<T>(event, listener): this

Defined in: src/models/typed-event-emitter.ts:169

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

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 prependOnceListener method can be used as an alternative to add the event listener to the beginning of the listeners array.

Type Parameters

T

T extends EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event.

listener

Listener<Update | LivenessChange | Destroy | LocationUpdate, BeaconEventHandlerMap, T>

The callback function

Returns

this

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

Inherited from

TypedEventEmitter.once

prependListener()

prependListener<T>(event, listener): this

Defined in: src/models/typed-event-emitter.ts:186

Adds the listener function to the beginning of the listeners array for the event named event.

Type Parameters

T

T extends EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event.

listener

Listener<Update | LivenessChange | Destroy | LocationUpdate, BeaconEventHandlerMap, T>

The callback function

Returns

this

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

Inherited from

TypedEventEmitter.prependListener

prependOnceListener()

prependOnceListener<T>(event, listener): this

Defined in: src/models/typed-event-emitter.ts:202

Adds a one-timelistener function for the event named event to the beginning of the listeners array. The next time event is triggered, this listener is removed, and then invoked.

Type Parameters

T

T extends EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

The name of the event.

listener

Listener<Update | LivenessChange | Destroy | LocationUpdate, BeaconEventHandlerMap, T>

The callback function

Returns

this

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

Inherited from

TypedEventEmitter.prependOnceListener

rawListeners()

rawListeners(event): Function[]

Defined in: src/models/typed-event-emitter.ts:243

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

Parameters

event

EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Returns

Function[]

Inherited from

TypedEventEmitter.rawListeners

removeAllListeners()

removeAllListeners(event?): this

Defined in: src/models/typed-event-emitter.ts:219

Removes all listeners, or those of the specified event.

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).

Parameters

event?

EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

The name of the event. If undefined, all listeners everywhere are removed.

Returns

this

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

Inherited from

TypedEventEmitter.removeAllListeners

removeListener()

removeListener<T>(event, listener): this

Defined in: src/models/typed-event-emitter.ts:232

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

Type Parameters

T

T extends EventEmitterEvents | Update | LivenessChange | Destroy | LocationUpdate

Parameters

event

T

listener

Listener<Update | LivenessChange | Destroy | LocationUpdate, BeaconEventHandlerMap, T>

Returns

this

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

Inherited from

TypedEventEmitter.removeListener

setMaxListeners()

setMaxListeners(n): this

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:813

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

TypedEventEmitter.setMaxListeners

update()

update(beaconInfoEvent): void

Defined in: src/models/beacon.ts:100

Parameters

beaconInfoEvent

DigitalWorldEvent

Returns

void

addAbortListener()

static addAbortListener(signal, resource): Disposable

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:403

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

(event) => void

Returns

Disposable

Disposable that removes the abort listener.

Since

v20.5.0

Inherited from

TypedEventEmitter.addAbortListener

getEventListeners()

static getEventListeners(emitter, name): Function[]

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:325

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[]

Since

v15.2.0, v14.17.0

Inherited from

TypedEventEmitter.getEventListeners

getMaxListeners()

static getMaxListeners(emitter): number

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:354

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

Since

v19.9.0

Inherited from

TypedEventEmitter.getMaxListeners

listenerCount()

static listenerCount(emitter, eventName): number

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:297

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

The emitter to query

eventName

string | symbol

The event name

Returns

number

Since

v0.9.12

Inherited from

TypedEventEmitter.listenerCount

on()

Call Signature

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

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:270

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

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

TypedEventEmitter.on

Call Signature

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

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:275

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

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

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

TypedEventEmitter.on

once()

Call Signature

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

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:184

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

eventName

string | symbol

options?

StaticEventEmitterOptions

Returns

Promise<any[]>

Since

v11.13.0, v10.16.0

Inherited from

TypedEventEmitter.once

Call Signature

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

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:189

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);
}

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

EventTarget

eventName

string

options?

StaticEventEmitterOptions

Returns

Promise<any[]>

Since

v11.13.0, v10.16.0

Inherited from

TypedEventEmitter.once

setMaxListeners()

static setMaxListeners(n?, …eventTargets): void

Defined in: node_modules/.pnpm/@types+node@22.20.0/node_modules/@types/node/events.d.ts:369

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

TypedEventEmitter.setMaxListeners