Pročitaj na engleskom

Deli putem

LiveMediaSessionCoordinator class

  • Reference
Package:
@microsoft/live-share-media

The LiveMediaSessionCoordinator tracks the playback & position state of all other clients being synchronized with. It is responsible for keeping the local media player in sync with the group.

Extends

EventEmitter

Properties

canPlayPause

Controls whether or not the local client is allowed to instruct the group to play or pause.
canSeek

Controls whether or not the local client is allowed to seek the group to a new playback position.
canSendPositionUpdates

Controls whether or not the local client is allowed to send position updates to the group.
canSetPlaybackRate

Controls whether or not the local client is allowed to change the playback rate.
canSetTrack

Controls whether or not the local client is allowed to change tracks.
canSetTrackData

Controls whether or not the local client is allowed to change the tracks custom data object.
isSuspended

Returns true if the local client is in a suspended state.
maxPlaybackDrift

Max amount of playback drift allowed in seconds.
positionUpdateInterval

Frequency with which position updates are broadcast to the rest of the group in seconds.

Inherited Properties

captureRejections

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.
captureRejectionSymbol

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

See how to write a custom rejection handler.
defaultMaxListeners

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:

JavaScript 
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'.
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.

Methods

beginSuspension(CoordinationWaitPoint)

Begins a new local suspension.
pause()

Instructs the group to pause the current track.
play()

Instructs the group to play the current track.
seekTo(number)

Instructs the group to seek to a new position within the current track.
setPlaybackRate(number)
setTrack(null | ExtendedMediaMetadata, CoordinationWaitPoint[])

Instructs the group to load a new track.
setTrackData(null | object)

Updates the track data object for the current track.

Inherited Methods

addAbortListener(AbortSignal, (event: Event) => void)

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.

JavaScript 
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]();
  }
}
addListener<K>(string | symbol, (args: any[]) => void)

Alias for emitter.on(eventName, listener).
emit<K>(string | symbol, AnyRest)

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.

JavaScript 
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
eventNames()

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

JavaScript 
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) ]
getEventListeners(EventEmitter<DefaultEventMap> | EventTarget, string | symbol)

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.

JavaScript 
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] ]
}
getMaxListeners()

Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to <xref:EventEmitter.defaultMaxListeners>.
getMaxListeners(EventEmitter<DefaultEventMap> | EventTarget)

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.

JavaScript 
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
}
listenerCount(EventEmitter<DefaultEventMap>, string | symbol)

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

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

const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2
listenerCount<K>(string | symbol, Function)

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.
listeners<K>(string | symbol)

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

JavaScript 
server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
off<K>(string | symbol, (args: any[]) => void)

Alias for emitter.removeListener().
on(EventEmitter<DefaultEventMap>, string | symbol, StaticEventEmitterIteratorOptions)
JavaScript 
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:

JavaScript 
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:

JavaScript 
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'
on(EventTarget, string, StaticEventEmitterIteratorOptions)
on<K>(string | symbol, (args: any[]) => void)

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.

JavaScript 
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.

JavaScript 
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
once(EventEmitter<DefaultEventMap>, string | symbol, StaticEventEmitterOptions)

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.

JavaScript 
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:

JavaScript 
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:

JavaScript 
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!
once(EventTarget, string, StaticEventEmitterOptions)
once<K>(string | symbol, (args: any[]) => void)

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

JavaScript 
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.

JavaScript 
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
prependListener<K>(string | symbol, (args: any[]) => void)

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.

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

Returns a reference to the EventEmitter, so that calls can be chained.
prependOnceListener<K>(string | symbol, (args: any[]) => void)

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.

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

Returns a reference to the EventEmitter, so that calls can be chained.
rawListeners<K>(string | symbol)

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

JavaScript 
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');
removeAllListeners(string | symbol)

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.
removeListener<K>(string | symbol, (args: any[]) => void)

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

JavaScript 
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.

JavaScript 
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:

JavaScript 
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.
setMaxListeners(number)

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.
setMaxListeners(number, (EventEmitter<DefaultEventMap> | EventTarget)[])
JavaScript 
import { setMaxListeners, EventEmitter } from 'node:events';

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

setMaxListeners(5, target, emitter);
[captureRejectionSymbol]<K>(Error, string | symbol, AnyRest)

Property Details

canPlayPause

Controls whether or not the local client is allowed to instruct the group to play or pause.

TypeScript 
canPlayPause: boolean

Property Value

boolean

Remarks

This flag largely meant to influence decisions made by the coordinator and can be used by the UI to determine what controls should be shown to the user. It does not provide any security in itself.

If your app is running in a semi-trusted environment where only some clients are allowed to play/pause media, you should use "role based verification" to enforce those policies.

canSeek

Controls whether or not the local client is allowed to seek the group to a new playback position.

TypeScript 
canSeek: boolean

Property Value

boolean

Remarks

This flag largely meant to influence decisions made by the coordinator and can be used by the UI to determine what controls should be shown to the user. It does not provide any security in itself.

If your app is running in a semi-trusted environment where only some clients are allowed to change the playback position, you should use "role based verification" to enforce those policies.

canSendPositionUpdates

Controls whether or not the local client is allowed to send position updates to the group.

TypeScript 
canSendPositionUpdates: boolean

Property Value

boolean

Remarks

This flag largely meant to limit the number of signals sent to the group for performance reasons. It does not provide any security in itself.

canSetPlaybackRate

Controls whether or not the local client is allowed to change the playback rate.

TypeScript 
canSetPlaybackRate: boolean

Property Value

boolean

Remarks

This flag largely meant to influence decisions made by the coordinator and can be used by the UI to determine what controls should be shown to the user. It does not provide any security in itself.

If your app is running in a semi-trusted environment where only some clients are allowed to change the tracks data object, you should use "role based verification" to enforce those policies.

canSetTrack

Controls whether or not the local client is allowed to change tracks.

TypeScript 
canSetTrack: boolean

Property Value

boolean

Remarks

This flag largely meant to influence decisions made by the coordinator and can be used by the UI to determine what controls should be shown to the user. It does not provide any security in itself.

If your app is running in a semi-trusted environment where only some clients are allowed to change tracks, you should use "role based verification" to enforce those policies.

canSetTrackData

Controls whether or not the local client is allowed to change the tracks custom data object.

TypeScript 
canSetTrackData: boolean

Property Value

boolean

Remarks

This flag largely meant to influence decisions made by the coordinator and can be used by the UI to determine what controls should be shown to the user. It does not provide any security in itself.

If your app is running in a semi-trusted environment where only some clients are allowed to change the tracks data object, you should use "role based verification" to enforce those policies.

isSuspended

Returns true if the local client is in a suspended state.

TypeScript 
boolean isSuspended

Property Value

boolean

maxPlaybackDrift

Max amount of playback drift allowed in seconds.

TypeScript 
number maxPlaybackDrift

Property Value

number

positionUpdateInterval

Frequency with which position updates are broadcast to the rest of the group in seconds.

TypeScript 
number positionUpdateInterval

Property Value

number

Inherited Property Details

captureRejections

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.

TypeScript 
static captureRejections: boolean

Property Value

boolean

Inherited From EventEmitter.captureRejections

captureRejectionSymbol

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

See how to write a custom rejection handler.

TypeScript 
static captureRejectionSymbol: typeof captureRejectionSymbol

Property Value

typeof captureRejectionSymbol

Inherited From EventEmitter.captureRejectionSymbol

defaultMaxListeners

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:

JavaScript 
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'.

TypeScript 
static defaultMaxListeners: number

Property Value

number

Inherited From EventEmitter.defaultMaxListeners

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.

TypeScript 
static errorMonitor: typeof errorMonitor

Property Value

typeof errorMonitor

Inherited From EventEmitter.errorMonitor

Method Details

beginSuspension(CoordinationWaitPoint)

Begins a new local suspension.

TypeScript 
function beginSuspension(waitPoint?: CoordinationWaitPoint): MediaSessionCoordinatorSuspension

Parameters

waitPoint
CoordinationWaitPoint

Optional. Dynamic wait point to broadcast to all of the clients.

Returns

MediaSessionCoordinatorSuspension

The suspension object. Call end() on the returned suspension to end the suspension.

Remarks

Suspension temporarily suspend the clients local synchronization with the group. This can be useful for displaying ads to users or temporarily disconnecting from the session while the user seeks the video using a timeline scrubber.

Multiple simultaneous suspensions are allowed and when the last suspension ends the local client will be immediately re-synchronized with the group.

A "Dynamic Wait Point" can be specified when beginSuspension() is called and the wait point will be broadcast to all other clients in the group. Those clients will then automatically enter a suspension state once they reach the positions specified by the wait point. Clients that are passed the wait point will immediately suspend.

Any wait point based suspension (dynamic or static) will result in all clients remaining in a suspension state until the list client ends their suspension. This behavior can be conditionally bypassed by settings the wait points maxClients value.

Throws an exception if the session/coordinator hasn't been initialized.

pause()

Instructs the group to pause the current track.

TypeScript 
function pause(): Promise<void>

Returns

Promise<void>

a void promise that resolves once complete, throws if user does not have proper roles

Remarks

Throws an exception if the session/coordinator hasn't been initialized, no track has been loaded, or canPlayPause is false.

play()

Instructs the group to play the current track.

TypeScript 
function play(): Promise<void>

Returns

Promise<void>

a void promise that resolves once complete, throws if user does not have proper roles

Remarks

Throws an exception if the session/coordinator hasn't been initialized, no track has been loaded, or canPlayPause is false.

seekTo(number)

Instructs the group to seek to a new position within the current track.

TypeScript 
function seekTo(time: number): Promise<void>

Parameters

time

number

Playback position in seconds to seek to.

Returns

Promise<void>

a void promise that resolves once complete, throws if user does not have proper roles

Remarks

Throws an exception if the session/coordinator hasn't been initialized, no track has been loaded, or canSeek is false.

setPlaybackRate(number)

TypeScript 
function setPlaybackRate(playbackRate: number): Promise<void>

Parameters

playbackRate

number

Returns

Promise<void>

setTrack(null | ExtendedMediaMetadata, CoordinationWaitPoint[])

Instructs the group to load a new track.

TypeScript 
function setTrack(metadata: null | ExtendedMediaMetadata, waitPoints?: CoordinationWaitPoint[]): Promise<void>

Parameters

metadata

null | ExtendedMediaMetadata

The track to load or null to indicate that the end of the track is reached.

waitPoints

CoordinationWaitPoint[]

Optional. List of static wait points to configure for the track. Dynamic wait points can be added via the beginSuspension() call.

Returns

Promise<void>

a void promise that resolves once complete, throws if user does not have proper roles

Remarks

Throws an exception if the session/coordinator hasn't been initialized or canSetTrack is false.

setTrackData(null | object)

Updates the track data object for the current track.

TypeScript 
function setTrackData(data: null | object): Promise<void>

Parameters

data

null | object

New data object to sync with the group. This value will be synchronized using a last writer wins strategy.

Returns

Promise<void>

a void promise that resolves once complete, throws if user does not have proper roles

Remarks

The track data object can be used by applications to synchronize things like pitch, roll, and yaw of a 360 video. This data object will be reset to null anytime the track changes.

Throws an exception if the session/coordinator hasn't been initialized or canSetTrackData is false.

Inherited Method Details

addAbortListener(AbortSignal, (event: Event) => void)

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.

JavaScript 
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]();
  }
}
TypeScript 
static function addAbortListener(signal: AbortSignal, resource: (event: Event) => void): Disposable

Parameters

signal

AbortSignal

resource

(event: Event) => void

Returns

Disposable

Disposable that removes the abort listener.

Inherited From EventEmitter.addAbortListener

addListener<K>(string | symbol, (args: any[]) => void)

Alias for emitter.on(eventName, listener).

TypeScript 
function addListener<K>(eventName: string | symbol, listener: (args: any[]) => void): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

listener

(args: any[]) => void

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.addListener

emit<K>(string | symbol, AnyRest)

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.

JavaScript 
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
TypeScript 
function emit<K>(eventName: string | symbol, args: AnyRest): boolean

Parameters

eventName

string | symbol

args

AnyRest

Returns

boolean

Inherited From EventEmitter.emit

eventNames()

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

JavaScript 
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) ]
TypeScript 
function eventNames(): (string | symbol)[]

Returns

(string | symbol)[]

Inherited From EventEmitter.eventNames

getEventListeners(EventEmitter<DefaultEventMap> | EventTarget, string | symbol)

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.

JavaScript 
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] ]
}
TypeScript 
static function getEventListeners(emitter: EventEmitter<DefaultEventMap> | EventTarget, name: string | symbol): Function[]

Parameters

emitter

EventEmitter<DefaultEventMap> | EventTarget

name

string | symbol

Returns

Function[]

Inherited From EventEmitter.getEventListeners

getMaxListeners()

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

TypeScript 
function getMaxListeners(): number

Returns

number

Inherited From EventEmitter.getMaxListeners

getMaxListeners(EventEmitter<DefaultEventMap> | EventTarget)

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.

JavaScript 
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
}
TypeScript 
static function getMaxListeners(emitter: EventEmitter<DefaultEventMap> | EventTarget): number

Parameters

emitter

EventEmitter<DefaultEventMap> | EventTarget

Returns

number

Inherited From EventEmitter.getMaxListeners

listenerCount(EventEmitter<DefaultEventMap>, string | symbol)

Warning

This API is now deprecated.

Since v3.2.0 - Use listenerCount instead.

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

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

const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2
TypeScript 
static function listenerCount(emitter: EventEmitter<DefaultEventMap>, eventName: string | symbol): number

Parameters

emitter

EventEmitter<DefaultEventMap>

The emitter to query

eventName

string | symbol

The event name

Returns

number

Inherited From EventEmitter.listenerCount

listenerCount<K>(string | symbol, Function)

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.

TypeScript 
function listenerCount<K>(eventName: string | symbol, listener?: Function): number

Parameters

eventName

string | symbol

The name of the event being listened for

listener

Function

The event handler function

Returns

number

Inherited From EventEmitter.listenerCount

listeners<K>(string | symbol)

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

JavaScript 
server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
TypeScript 
function listeners<K>(eventName: string | symbol): Function[]

Parameters

eventName

string | symbol

Returns

Function[]

Inherited From EventEmitter.listeners

off<K>(string | symbol, (args: any[]) => void)

Alias for emitter.removeListener().

TypeScript 
function off<K>(eventName: string | symbol, listener: (args: any[]) => void): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

listener

(args: any[]) => void

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.off

on(EventEmitter<DefaultEventMap>, string | symbol, StaticEventEmitterIteratorOptions)

JavaScript 
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:

JavaScript 
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:

JavaScript 
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'
TypeScript 
static function on(emitter: EventEmitter<DefaultEventMap>, eventName: string | symbol, options?: StaticEventEmitterIteratorOptions): AsyncIterator<any[], any, any>

Parameters

emitter

EventEmitter<DefaultEventMap>

eventName

string | symbol

options

StaticEventEmitterIteratorOptions

Returns

AsyncIterator<any[], any, any>

An AsyncIterator that iterates eventName events emitted by the emitter

Inherited From EventEmitter.on

on(EventTarget, string, StaticEventEmitterIteratorOptions)

TypeScript 
static function on(emitter: EventTarget, eventName: string, options?: StaticEventEmitterIteratorOptions): AsyncIterator<any[], any, any>

Parameters

emitter

EventTarget

eventName

string

options

StaticEventEmitterIteratorOptions

Returns

AsyncIterator<any[], any, any>

Inherited From EventEmitter.on

on<K>(string | symbol, (args: any[]) => void)

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.

JavaScript 
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.

JavaScript 
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
TypeScript 
function on<K>(eventName: string | symbol, listener: (args: any[]) => void): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

The name of the event.

listener

(args: any[]) => void

The callback function

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.on

once(EventEmitter<DefaultEventMap>, string | symbol, StaticEventEmitterOptions)

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.

JavaScript 
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:

JavaScript 
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:

JavaScript 
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!
TypeScript 
static function once(emitter: EventEmitter<DefaultEventMap>, eventName: string | symbol, options?: StaticEventEmitterOptions): Promise<any[]>

Parameters

emitter

EventEmitter<DefaultEventMap>

eventName

string | symbol

options

StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited From EventEmitter.once

once(EventTarget, string, StaticEventEmitterOptions)

TypeScript 
static function once(emitter: EventTarget, eventName: string, options?: StaticEventEmitterOptions): Promise<any[]>

Parameters

emitter

EventTarget

eventName

string

options

StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited From EventEmitter.once

once<K>(string | symbol, (args: any[]) => void)

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

JavaScript 
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.

JavaScript 
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
TypeScript 
function once<K>(eventName: string | symbol, listener: (args: any[]) => void): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

The name of the event.

listener

(args: any[]) => void

The callback function

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.once

prependListener<K>(string | symbol, (args: any[]) => void)

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.

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

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

TypeScript 
function prependListener<K>(eventName: string | symbol, listener: (args: any[]) => void): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

The name of the event.

listener

(args: any[]) => void

The callback function

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.prependListener

prependOnceListener<K>(string | symbol, (args: any[]) => void)

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.

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

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

TypeScript 
function prependOnceListener<K>(eventName: string | symbol, listener: (args: any[]) => void): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

The name of the event.

listener

(args: any[]) => void

The callback function

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.prependOnceListener

rawListeners<K>(string | symbol)

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

JavaScript 
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');
TypeScript 
function rawListeners<K>(eventName: string | symbol): Function[]

Parameters

eventName

string | symbol

Returns

Function[]

Inherited From EventEmitter.rawListeners

removeAllListeners(string | symbol)

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.

TypeScript 
function removeAllListeners(eventName?: string | symbol): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.removeAllListeners

removeListener<K>(string | symbol, (args: any[]) => void)

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

JavaScript 
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.

JavaScript 
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:

JavaScript 
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.

TypeScript 
function removeListener<K>(eventName: string | symbol, listener: (args: any[]) => void): LiveMediaSessionCoordinator

Parameters

eventName

string | symbol

listener

(args: any[]) => void

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.removeListener

setMaxListeners(number)

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.

TypeScript 
function setMaxListeners(n: number): LiveMediaSessionCoordinator

Parameters

n

number

Returns

LiveMediaSessionCoordinator

Inherited From EventEmitter.setMaxListeners

setMaxListeners(number, (EventEmitter<DefaultEventMap> | EventTarget)[])

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

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

setMaxListeners(5, target, emitter);
TypeScript 
static function setMaxListeners(n?: number, eventTargets: (EventEmitter<DefaultEventMap> | EventTarget)[])

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.

Inherited From EventEmitter.setMaxListeners

[captureRejectionSymbol]<K>(Error, string | symbol, AnyRest)

TypeScript 
function [captureRejectionSymbol]<K>(error: Error, event: string | symbol, args: AnyRest)

Parameters

error

Error

event

string | symbol

args

AnyRest

Inherited From EventEmitter.__@captureRejectionSymbol@122