LiveEvent class

Package:
@microsoft/live-share

Live fluid object that broadcasts an event to other clients and a set of static event related helpers.

remarks

Applications should call on('received', (evt, local) => {}) to listen for local events sent and remote events received. Events aren't guaranteed to be delivered so you should limit their use to sending events you're ok with potentially being missed. Reactions are a good use case for LiveEvents. Use something like the LiveState class when syncing state.

Extends

LiveDataObject<{ Events: ILiveEventEvents<TEvent> }>

Constructors

LiveEvent<TEvent>(IDataObjectProps<{ Events: ILiveEventEvents<TEvent> }>)

Properties

disposed
factory

The objects fluid type factory.
handle

Handle to a data store
id
IFluidHandle
IFluidLoadable
IFluidRouter
initializeState

The initialization status of the data object.
isInitialized

Flag that indicates whether initialization has succeeded or not.
TypeName

The objects fluid type/name.

Inherited Properties

addListener

Alias for emitter.on(eventName, listener).
off

Alias for emitter.removeListener().
on

Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

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

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

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

import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
//   b
//   a
once

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

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

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

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

import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
//   b
//   a
prependListener

Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

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

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

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

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

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

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

const callback = (stream) => {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.

Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them from emit() in progress. Subsequent events behave as expected.

import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();

const callbackA = () => {
  console.log('A');
  myEmitter.removeListener('event', callbackB);
};

const callbackB = () => {
  console.log('B');
};

myEmitter.on('event', callbackA);

myEmitter.on('event', callbackB);

// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
//   A
//   B

// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
//   A

Because listeners are managed using an internal array, calling this will change the position indexes of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.

When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:

import { EventEmitter } from 'node:events';
const ee = new EventEmitter();

function pong() {
  console.log('pong');
}

ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);

ee.emit('ping');
ee.emit('ping');

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

Methods

initialize(UserMeetingRole[])

Initialize the object to begin sending/receiving events through this DDS.
isNewer(IClientTimestamp | undefined, IClientTimestamp, number)

Returns true if a received event is newer then the current event.
send(TEvent)

Broadcasts an event to all other clients.

Inherited Methods

dispose()

Called when the host container closes and disposes itself
emit<E>(string | symbol, any[])

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

Returns true if the event had listeners, false otherwise.

import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();

// First listener
myEmitter.on('event', function firstListener() {
  console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
  console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
  const parameters = args.join(', ');
  console.log(`event with parameters ${parameters} in third listener`);
});

console.log(myEmitter.listeners('event'));

myEmitter.emit('event', 1, 2, 3, 4, 5);

// Prints:
// [
//   [Function: firstListener],
//   [Function: secondListener],
//   [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
eventNames()

Returns an array listing the events for which the emitter has registered listeners.

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) ]
finishInitialization(boolean)

Call this API to ensure PureDataObject is fully initialized. Initialization happens on demand, only on as-needed bases. In most cases you should allow factory/object to decide when to finish initialization. But if you are supplying your own implementation of DataStoreRuntime factory and overriding some methods and need a fully initialized object, then you can call this API to ensure object is fully initialized.
getClientInfo(string)

Get the client info for a given clientId
getDataObject(IFluidDataStoreRuntime)
getFluidObjectFromDirectory<T>(string, IDirectory, (id: string, directory: IDirectory) => IFluidHandle<FluidObject & IFluidLoadable> | undefined)

Retrieve Fluid object using the handle get
getMaxListeners()

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

Initializes internal objects and calls initialization overrides. Caller is responsible for ensuring this is only invoked once.
listenerCount<E>(string | symbol, (args: any[]) => void)

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<E>(string | symbol)

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

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

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

import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
removeAllListeners<E>(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.
request(IRequest)

{@inheritDoc PureDataObject.request}
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.
[captureRejectionSymbol](Error, string | symbol, any[])

The Symbol.for('nodejs.rejection') method is called in case a promise rejection happens when emitting an event and captureRejections is enabled on the emitter. It is possible to use events.captureRejectionSymbol in place of Symbol.for('nodejs.rejection').

import { EventEmitter, captureRejectionSymbol } from 'node:events';

class MyClass extends EventEmitter {
  constructor() {
    super({ captureRejections: true });
  }

  [captureRejectionSymbol](err, event, ...args) {
    console.log('rejection happened for', event, 'with', err, ...args);
    this.destroy(err);
  }

  destroy(err) {
    // Tear the resource down here.
  }
}

Constructor Details

LiveEvent<TEvent>(IDataObjectProps<{ Events: ILiveEventEvents<TEvent> }>) 

new LiveEvent(props: IDataObjectProps<{ Events: ILiveEventEvents<TEvent> }>)

Parameters

props

IDataObjectProps<{ Events: ILiveEventEvents<TEvent> }>

Property Details

disposed 

boolean disposed

Property Value

boolean

factory

The objects fluid type factory.

static factory: DataObjectFactory<LiveEvent<any>, DataObjectTypes>

Property Value

DataObjectFactory<LiveEvent<any>, DataObjectTypes>

handle

Handle to a data store

IFluidHandle<this> handle

Property Value

IFluidHandle<this>

id 

string id

Property Value

string

IFluidHandle 

IFluidHandle<this> IFluidHandle

Property Value

IFluidHandle<this>

IFluidLoadable 

this IFluidLoadable

Property Value

this

IFluidRouter 

this IFluidRouter

Property Value

this

initializeState

The initialization status of the data object.

LiveDataObjectInitializeState initializeState

Property Value

LiveDataObjectInitializeState

isInitialized

Flag that indicates whether initialization has succeeded or not.

boolean isInitialized

Property Value

boolean

TypeName

The objects fluid type/name.

static TypeName: "@microsoft/live-share:LiveEvent" = "@microsoft/live-share:LiveEvent"

Property Value

"@microsoft/live-share:LiveEvent"

Inherited Property Details

addListener

Alias for emitter.on(eventName, listener).

addListener: TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Property Value

TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Inherited From LiveDataObject.addListener

off

Alias for emitter.removeListener().

off: TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Property Value

TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Inherited From LiveDataObject.off

on

Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

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

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

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

import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
//   b
//   a

on: TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Property Value

TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Inherited From LiveDataObject.on

once

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

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

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

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

import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
//   b
//   a

once: TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Property Value

TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Inherited From LiveDataObject.once

prependListener

Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

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

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

prependListener: TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Property Value

TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Inherited From LiveDataObject.prependListener

prependOnceListener

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

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

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

prependOnceListener: TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Property Value

TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Inherited From LiveDataObject.prependOnceListener

removeListener

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

const callback = (stream) => {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.

Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them from emit() in progress. Subsequent events behave as expected.

import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();

const callbackA = () => {
  console.log('A');
  myEmitter.removeListener('event', callbackB);
};

const callbackB = () => {
  console.log('B');
};

myEmitter.on('event', callbackA);

myEmitter.on('event', callbackB);

// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
//   A
//   B

// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
//   A

Because listeners are managed using an internal array, calling this will change the position indexes of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.

When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:

import { EventEmitter } from 'node:events';
const ee = new EventEmitter();

function pong() {
  console.log('pong');
}

ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);

ee.emit('ping');
ee.emit('ping');

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

removeListener: TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Property Value

TypedEventTransform<LiveEvent<TEvent>, ILiveEventEvents<TEvent> & IEvent>

Inherited From LiveDataObject.removeListener

Method Details

initialize(UserMeetingRole[])

Initialize the object to begin sending/receiving events through this DDS.

function initialize(allowedRoles?: UserMeetingRole[]): Promise<void>

Parameters

allowedRoles

UserMeetingRole[]

Optional. List of roles allowed to send events.

Returns

Promise<void>

a void promise that resolves once complete.

Remarks

You should register received event listeners before calling this function to ensure no incoming events are missed. received events will not be emitted until after this function is called.

isNewer(IClientTimestamp | undefined, IClientTimestamp, number)

Returns true if a received event is newer then the current event.

static function isNewer(current: IClientTimestamp | undefined, received: IClientTimestamp, debouncePeriod?: number): boolean

Parameters

current

IClientTimestamp | undefined

Current event to compare received event against.

received
IClientTimestamp

Received event.

debouncePeriod

number

Optional. Time in milliseconds to ignore any new events for. Defaults to 0 ms.

Returns

boolean

True if the received event is newer then the current event and should replace the current one.

Remarks

Used when building new Live objects to process state change events. The isNewer() method implements an algorithm that deals with conflicting events that have the same timestamp and older events that should have debounced the current event.

  • When the received event has the same timestamp as the current event, each events clientId will be used as a tie breaker. The clientId containing the lower sort order wins any ties.
  • Older events are generally ignored unless a debounce period is specified. An older event that should have debounced the current event will be considered newer.

The algorithm employed by isNewer() helps ensure that all clients will eventually reach a consistent state with one other.

send(TEvent)

Broadcasts an event to all other clients.

function send(evt: TEvent): Promise<ILiveEvent<TEvent>>

Parameters

evt

TEvent

Event to send. If omitted, an event will still be sent but it won't include any custom event data.

Returns

Promise<ILiveEvent<TEvent>>

A promise with the full event object that was sent, including the timestamp of when the event was sent and the clientId if known. The clientId will be undefined if the client is disconnected at time of delivery.

Remarks

The event will be queued for delivery if the client isn't currently connected.

Inherited Method Details

dispose()

Called when the host container closes and disposes itself

function dispose()

Inherited From LiveDataObject.dispose

emit<E>(string | symbol, any[])

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

Returns true if the event had listeners, false otherwise.

import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();

// First listener
myEmitter.on('event', function firstListener() {
  console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
  console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
  const parameters = args.join(', ');
  console.log(`event with parameters ${parameters} in third listener`);
});

console.log(myEmitter.listeners('event'));

myEmitter.emit('event', 1, 2, 3, 4, 5);

// Prints:
// [
//   [Function: firstListener],
//   [Function: secondListener],
//   [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener

function emit<E>(eventName: string | symbol, args: any[]): boolean

Parameters

eventName

string | symbol

args

any[]

Returns

boolean

Inherited From LiveDataObject.emit

eventNames()

Returns an array listing the events for which the emitter has registered listeners.

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) ]

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

Returns

(string | symbol)[]

Inherited From LiveDataObject.eventNames

finishInitialization(boolean)

Call this API to ensure PureDataObject is fully initialized. Initialization happens on demand, only on as-needed bases. In most cases you should allow factory/object to decide when to finish initialization. But if you are supplying your own implementation of DataStoreRuntime factory and overriding some methods and need a fully initialized object, then you can call this API to ensure object is fully initialized.

function finishInitialization(existing: boolean): Promise<void>

Parameters

existing

boolean

Returns

Promise<void>

Inherited From LiveDataObject.finishInitialization

getClientInfo(string)

Get the client info for a given clientId

function getClientInfo(clientId: string): Promise<IClientInfo | undefined>

Parameters

clientId

string

Fluid clientId we are requesting user info for

Returns

Promise<IClientInfo | undefined>

IClientInfo object if the user is known, otherwise it will return undefined

Inherited From LiveDataObject.getClientInfo

getDataObject(IFluidDataStoreRuntime) 

static function getDataObject(runtime: IFluidDataStoreRuntime): Promise<PureDataObject<DataObjectTypes>>

Parameters

runtime

IFluidDataStoreRuntime

Returns

Promise<PureDataObject<DataObjectTypes>>

Inherited From LiveDataObject.getDataObject

getFluidObjectFromDirectory<T>(string, IDirectory, (id: string, directory: IDirectory) => IFluidHandle<FluidObject & IFluidLoadable> | undefined)

Retrieve Fluid object using the handle get

function getFluidObjectFromDirectory<T>(key: string, directory: IDirectory, getObjectFromDirectory?: (id: string, directory: IDirectory) => IFluidHandle<FluidObject & IFluidLoadable> | undefined): Promise<T | undefined>

Parameters

key

string

key that object (handle/id) is stored with in the directory

directory

IDirectory

directory containing the object

getObjectFromDirectory

(id: string, directory: IDirectory) => IFluidHandle<FluidObject & IFluidLoadable> | undefined

optional callback for fetching object from the directory, allows users to define custom types/getters for object retrieval

Returns

Promise<T | undefined>

Inherited From LiveDataObject.getFluidObjectFromDirectory

getMaxListeners()

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

function getMaxListeners(): number

Returns

number

Inherited From LiveDataObject.getMaxListeners

initializeInternal(boolean)

Initializes internal objects and calls initialization overrides. Caller is responsible for ensuring this is only invoked once.

function initializeInternal(existing: boolean): Promise<void>

Parameters

existing

boolean

Returns

Promise<void>

Inherited From LiveDataObject.initializeInternal

listenerCount<E>(string | symbol, (args: any[]) => void)

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.

function listenerCount<E>(eventName: string | symbol, listener?: (args: any[]) => void): number

Parameters

eventName

string | symbol

The name of the event being listened for

listener

(args: any[]) => void

The event handler function

Returns

number

Inherited From LiveDataObject.listenerCount

listeners<E>(string | symbol)

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

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

function listeners<E>(eventName: string | symbol): (args: any[]) => void[]

Parameters

eventName

string | symbol

Returns

(args: any[]) => void[]

Inherited From LiveDataObject.listeners

rawListeners<E>(string | symbol)

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

import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');

function rawListeners<E>(eventName: string | symbol): (args: any[]) => void[]

Parameters

eventName

string | symbol

Returns

(args: any[]) => void[]

Inherited From LiveDataObject.rawListeners

removeAllListeners<E>(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.

function removeAllListeners<E>(eventName?: string | symbol): this

Parameters

eventName

string | symbol

Returns

this

Inherited From LiveDataObject.removeAllListeners

request(IRequest)

{@inheritDoc PureDataObject.request}

function request(request: IRequest): Promise<IResponse>

Parameters

request

IRequest

Returns

Promise<IResponse>

Inherited From LiveDataObject.request

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.

function setMaxListeners(n: number): this

Parameters

n

number

Returns

this

Inherited From LiveDataObject.setMaxListeners

[captureRejectionSymbol](Error, string | symbol, any[])

The Symbol.for('nodejs.rejection') method is called in case a promise rejection happens when emitting an event and captureRejections is enabled on the emitter. It is possible to use events.captureRejectionSymbol in place of Symbol.for('nodejs.rejection').

import { EventEmitter, captureRejectionSymbol } from 'node:events';

class MyClass extends EventEmitter {
  constructor() {
    super({ captureRejections: true });
  }

  [captureRejectionSymbol](err, event, ...args) {
    console.log('rejection happened for', event, 'with', err, ...args);
    this.destroy(err);
  }

  destroy(err) {
    // Tear the resource down here.
  }
}

function [captureRejectionSymbol](error: Error, event: string | symbol, args: any[])

Parameters

error

Error

event

string | symbol

args

any[]

Inherited From LiveDataObject.[captureRejectionSymbol]