EventTimelineSet

Defined in: src/models/event-timeline-set.ts:130

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<EmittedEvents, EventTimelineSetHandlerMap>

Constructors

Constructor

new EventTimelineSet(room, opts?, client?, thread?, threadListType?): EventTimelineSet

Defined in: src/models/event-timeline-set.ts:169

Construct a set of EventTimeline objects, typically on behalf of a given room. A room may have multiple EventTimelineSets for different levels of filtering. The global notification list is also an EventTimelineSet, but lacks a room.

This is an ordered sequence of timelines, which may or may not be continuous. Each timeline lists a series of events, as well as tracking the room state at the start and the end of the timeline (if appropriate). It also tracks forward and backward pagination tokens, as well as containing links to the next timeline in the sequence.

There is one special timeline - the 'live' timeline, which represents the timeline to which events are being added in real-time as they are received from the /sync API. Note that you should not retain references to this timeline - even if it is the current timeline right now, it may not remain so if the server gives us a timeline gap in /sync.

In order that we can find events from their ids later, we also maintain a map from event_id to timeline and index.

Parameters

room

Room | undefined

Room for this timelineSet. May be null for non-room cases, such as the notification timeline.

opts?

IOpts = {}

Options inherited from Room.

client?

DigitalWorldClient

the Digital World client which owns this EventTimelineSet, can be omitted if room is specified.

thread?

Thread

the thread to which this timeline set relates.

threadListType?

ThreadFilterType | null

the type of thread list represented, if any (e.g., All threads or My threads)

Returns

EventTimelineSet

Overrides

TypedEventEmitter.constructor

Properties

relations

readonly relations: RelationsContainer

Defined in: src/models/event-timeline-set.ts:131

room

readonly room: Room | undefined

Defined in: src/models/event-timeline-set.ts:170

Room for this timelineSet. May be null for non-room cases, such as the notification timeline.

thread?

readonly optional thread?: Thread

Defined in: src/models/event-timeline-set.ts:173

the thread to which this timeline set relates.

threadListType

readonly threadListType: ThreadFilterType | null = null

Defined in: src/models/event-timeline-set.ts:174

the type of thread list represented, if any (e.g., All threads or My threads)

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

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]

addEventsToTimeline()

addEventsToTimeline(events, toStartOfTimeline, addToState, timeline, paginationToken?): void

Defined in: src/models/event-timeline-set.ts:395

Add events to a timeline

Will fire "Room.timeline" for each event added.

Parameters

events

DigitalWorldEvent[]

A list of events to add.

toStartOfTimeline

boolean

True to add these events to the start (oldest) instead of the end (newest) of the timeline. If true, the oldest event will be the last element of ‘events’.

addToState

boolean

timeline

EventTimeline

timeline to add events to.

paginationToken?

string | null

token for the next batch of events

Returns

void

Remarks

Fires RoomEvent.Timeline

addEventToTimeline()

addEventToTimeline(event, timeline, options): void

Defined in: src/models/event-timeline-set.ts:656

Add event to the given timeline, and emit Room.timeline. Assumes we have already checked we don’t know about this event.

Will fire “Room.timeline” for each event added.

Parameters

event

DigitalWorldEvent

the event to add

timeline

EventTimeline

the timeline onto which to add it

options

IAddEventToTimelineOptions

addEventToTimeline options

Returns

void

Remarks

Fires RoomEvent.Timeline

addListener()

addListener<T>(event, listener): this

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

Alias for on.

Type Parameters

T

T extends EventEmitterEvents | EmittedEvents

Parameters

event

T

listener

Listener<EmittedEvents, EventTimelineSetHandlerMap, T>

Returns

this

Inherited from

TypedEventEmitter.addListener

addLiveEvent()

addLiveEvent(event, options): void

Defined in: src/models/event-timeline-set.ts:599

Add an event to the end of this live timeline.

Parameters

event

DigitalWorldEvent

Event to be added

options

IAddLiveEventOptions

addLiveEvent options

Returns

void

addTimeline()

addTimeline(): EventTimeline

Defined in: src/models/event-timeline-set.ts:361

Add a new timeline to this timeline list

Returns

EventTimeline

newly-created timeline

canContain()

canContain(event): boolean

Defined in: src/models/event-timeline-set.ts:938

Determine whether a given event can sanely be added to this event timeline set, for timeline sets relating to a thread, only return true for events in the same thread timeline, for timeline sets not relating to a thread only return true for events which should be shown in the main room timeline. Requires the room property to have been set at EventTimelineSet construction time.

Parameters

event

DigitalWorldEvent

the event to check whether it belongs to this timeline set.

Returns

boolean

whether the event belongs to this timeline set.

Throws

Error if room was not set when constructing this timeline set.

compareEventOrdering()

compareEventOrdering(eventId1, eventId2): number | null

Defined in: src/models/event-timeline-set.ts:858

Determine where two events appear in the timeline relative to one another

Parameters

eventId1

string

The id of the first event

eventId2

string

The id of the second event

Returns

number | null

-1 if eventId1 precedes eventId2, and +1 eventId1 succeeds eventId2. 0 if they are the same event; null if we can’t tell (either because we don’t know about one of the events, or because they are in separate timelines which don’t join up).

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 EmittedEvents

Parameters

event

T

The name of the event to emit

args

…Parameters<EventTimelineSetHandlerMap[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 EmittedEvents

Parameters

event

T

The name of the event to emit

args

…Parameters<EventTimelineSetHandlerMap[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 EmittedEvents

Parameters

event

T

The name of the event to emit

args

…Parameters<EventTimelineSetHandlerMap[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 EmittedEvents

Parameters

event

T

The name of the event to emit

args

…Parameters<EventTimelineSetHandlerMap[T]>

Arguments to pass to the listener

Returns

Promise<boolean>

true if the event had listeners, false otherwise.

Inherited from

TypedEventEmitter.emitPromised

eventIdToTimeline()

eventIdToTimeline(eventId): EventTimeline | undefined

Defined in: src/models/event-timeline-set.ts:255

Return the timeline (if any) this event is in.

Parameters

eventId

string

the eventId being sought

Returns

EventTimeline | undefined

timeline

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

findEventById()

findEventById(eventId): DigitalWorldEvent | undefined

Defined in: src/models/event-timeline-set.ts:346

Get an event which is stored in our timelines

Parameters

eventId

string

event ID to look for

Returns

DigitalWorldEvent | undefined

the given event, or undefined if unknown

getFilter()

getFilter(): Filter | undefined

Defined in: src/models/event-timeline-set.ts:203

Get the filter object this timeline set is filtered on, if any

Returns

Filter | undefined

the optional filter for this timelineSet

getLiveTimeline()

getLiveTimeline(): EventTimeline

Defined in: src/models/event-timeline-set.ts:237

Get the live timeline for this room.

Returns

EventTimeline

live timeline

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

getPendingEvents()

getPendingEvents(): DigitalWorldEvent[]

Defined in: src/models/event-timeline-set.ts:225

Get the list of pending sent events for this timelineSet’s room, filtered by the timelineSet’s filter if appropriate.

Returns

DigitalWorldEvent[]

A list of the sent events waiting for remote echo.

Throws

If opts.pendingEventOrdering was not ‘detached’

getTimelineForEvent()

getTimelineForEvent(eventId?): EventTimeline | null

Defined in: src/models/event-timeline-set.ts:332

Get the timeline which contains the given event, if any

Parameters

eventId?

string

event ID to look for

Returns

EventTimeline | null

timeline containing the given event, or null if unknown

getTimelines()

getTimelines(): EventTimeline[]

Defined in: src/models/event-timeline-set.ts:195

Get all the timelines in this set

Returns

EventTimeline[]

the timelines in this set

handleRemoteEcho()

handleRemoteEcho(localEvent, oldEventId, newEventId): void

Defined in: src/models/event-timeline-set.ts:808

Replaces event with ID oldEventId with one with newEventId, if oldEventId is recognised. Otherwise, add to the live timeline. Used to handle remote echos.

Parameters

localEvent

DigitalWorldEvent

the new event to be added to the timeline

oldEventId

string

the ID of the original event

newEventId

string

the ID of the replacement event

Returns

void

Remarks

Fires RoomEvent.Timeline

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 | EmittedEvents

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 | EmittedEvents

Returns

Function[]

Inherited from

TypedEventEmitter.listeners

off()

off<T>(event, listener): this

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

Alias for removeListener

Type Parameters

T

T extends EventEmitterEvents | EmittedEvents

Parameters

event

T

listener

Listener<EmittedEvents, EventTimelineSetHandlerMap, 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 | EmittedEvents

Parameters

event

T

The name of the event.

listener

Listener<EmittedEvents, EventTimelineSetHandlerMap, 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 | EmittedEvents

Parameters

event

T

The name of the event.

listener

Listener<EmittedEvents, EventTimelineSetHandlerMap, 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 | EmittedEvents

Parameters

event

T

The name of the event.

listener

Listener<EmittedEvents, EventTimelineSetHandlerMap, 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 | EmittedEvents

Parameters

event

T

The name of the event.

listener

Listener<EmittedEvents, EventTimelineSetHandlerMap, 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 | EmittedEvents

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 | EmittedEvents

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

removeEvent()

removeEvent(eventId): DigitalWorldEvent | null

Defined in: src/models/event-timeline-set.ts:830

Removes a single event from this room.

Parameters

eventId

string

The id of the event to remove

Returns

DigitalWorldEvent | null

the removed event, or null if the event was not found in this room.

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 | EmittedEvents

Parameters

event

T

listener

Listener<EmittedEvents, EventTimelineSetHandlerMap, T>

Returns

this

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

Inherited from

TypedEventEmitter.removeListener

replaceEventId()

replaceEventId(oldEventId, newEventId): void

Defined in: src/models/event-timeline-set.ts:265

Track a new event as if it were in the same timeline as an old event, replacing it.

Parameters

oldEventId

string

event ID of the original event

newEventId

string

event ID of the replacement event

Returns

void

resetLiveTimeline()

resetLiveTimeline(backPaginationToken?, forwardPaginationToken?): void

Defined in: src/models/event-timeline-set.ts:285

Reset the live timeline, and start a new one.

This is used when /sync returns a 'limited' timeline.

Parameters

backPaginationToken?

string

token for back-paginating the new timeline

forwardPaginationToken?

string

token for forward-paginating the old live timeline, if absent or null, all timelines are reset.

Returns

void

Remarks

Fires RoomEvent.TimelineReset

setFilter()

setFilter(filter?): void

Defined in: src/models/event-timeline-set.ts:212

Set the filter object this timeline set is filtered on (passed to the server when paginating via /messages).

Parameters

filter?

Filter

the filter for this timelineSet

Returns

void

setLiveTimeline()

setLiveTimeline(timeline): void

Defined in: src/models/event-timeline-set.ts:246

Set the live timeline for this room.

Parameters

timeline

EventTimeline

Returns

void

live timeline

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

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