docs/Script API/interfaces/Backend_Script_API._internal_.EventEmitter.html
interface EventEmitter<T extends EventMap<T> = DefaultEventMap> {
"[captureRejectionSymbol]"<K>(
error: Error,
event: Key<K, T>,
...args: Args<K, T>,
): void;
addListener<K>(eventName: Key<K, T>, listener: Listener<K, T>): this;
emit<K>(eventName: Key<K, T>, ...args: Args<K, T>): boolean;
eventNames(): ((string | symbol) & Key2<unknown, T>)[];
getMaxListeners(): number;
listenerCount<K>(
eventName: Key<K, T>,
listener?: Listener<K, T, Function>,
): number;
listeners<K>(eventName: Key<K, T>): Listener<K, T, Function>[];
off<K>(eventName: Key<K, T>, listener: Listener<K, T>): this;
on<K>(eventName: Key<K, T>, listener: Listener<K, T>): this;
once<K>(eventName: Key<K, T>, listener: Listener<K, T>): this;
prependListener<K>(eventName: Key<K, T>, listener: Listener<K, T>): this;
prependOnceListener<K>(
eventName: Key<K, T>,
listener: Listener<K, T>,
): this;
rawListeners<K>(eventName: Key<K, T>): Listener<K, T, Function>[];
removeAllListeners(eventName?: Key<unknown, T>): this;
removeListener<K>(eventName: Key<K, T>, listener: Listener<K, T>): this;
setMaxListeners(n: number): this;
}
[captureRejectionSymbol]?addListeneremiteventNamesgetMaxListenerslistenerCountlistenersoffononceprependListenerprependOnceListenerrawListenersremoveAllListenersremoveListenersetMaxListeners
Optional[captureRejectionSymbol]"[captureRejectionSymbol]"<K>(
error: Error,
event: Key<K, T>,
...args: Args<K, T>,
): void
addListener<K>(eventName: Key<K, T>, listener: Listener<K, T>): this
Alias for emitter.on(eventName, listener).
v0.1.26
emit<K>(eventName: Key<K, T>, ...args: Args<K, T>): boolean
Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.
Returns true if the event had listeners, false otherwise.
import { EventEmitter } from 'node:events';const myEmitter = new EventEmitter();// First listenermyEmitter.on('event', function firstListener() { console.log('Helloooo! first listener');});// Second listenermyEmitter.on('event', function secondListener(arg1, arg2) { console.log(`event with parameters ${arg1}, ${arg2} in second listener`);});// Third listenermyEmitter.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 listenerCopy
v0.1.26
eventNames(): ((string | symbol) & Key2<unknown, T>)[]
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)]Copy
v6.0.0
getMaxListeners(): number
Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to EventEmitter.defaultMaxListeners.
v1.0.0
listenerCount<K>(
eventName: Key<K, T>,
listener?: Listener<K, T, Function>,
): number
Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.
The name of the event being listened for
The event handler function
v3.2.0
listeners<K>(eventName: Key<K, T>): Listener<K, T, Function>[]
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] ]Copy
v0.1.26
off<K>(eventName: Key<K, T>, listener: Listener<K, T>): this
Alias for emitter.removeListener().
v10.0.0
on<K>(eventName: Key<K, T>, listener: Listener<K, T>): this
Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.on('connection', (stream) => { console.log('someone connected!');});Copy
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// aCopy
The name of the event.
The callback function
v0.1.101
once<K>(eventName: Key<K, T>, listener: Listener<K, T>): this
Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => { console.log('Ah, we have our first user!');});Copy
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// aCopy
The name of the event.
The callback function
v0.3.0
prependListener<K>(eventName: Key<K, T>, listener: Listener<K, T>): this
Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.prependListener('connection', (stream) => { console.log('someone connected!');});Copy
Returns a reference to the EventEmitter, so that calls can be chained.
The name of the event.
The callback function
v6.0.0
prependOnceListener<K>(eventName: Key<K, T>, listener: Listener<K, T>): this
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!');});Copy
Returns a reference to the EventEmitter, so that calls can be chained.
The name of the event.
The callback function
v6.0.0
rawListeners<K>(eventName: Key<K, T>): Listener<K, T, Function>[]
Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).
import { EventEmitter } from 'node:events';const emitter = new EventEmitter();emitter.once('log', () => console.log('log once'));// Returns a new Array with a function `onceWrapper` which has a property// `listener` which contains the original listener bound aboveconst listeners = emitter.rawListeners('log');const logFnWrapper = listeners[0];// Logs "log once" to the console and does not unbind the `once` eventlogFnWrapper.listener();// Logs "log once" to the console and removes the listenerlogFnWrapper();emitter.on('log', () => console.log('log persistently'));// Will return a new Array with a single function bound by `.on()` aboveconst newListeners = emitter.rawListeners('log');// Logs "log persistently" twicenewListeners0;emitter.emit('log');Copy
v9.4.0
removeAllListeners(eventName?: Key<unknown, T>): this
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
v0.1.26
removeListener<K>(eventName: Key<K, T>, listener: Listener<K, T>): this
Removes the specified listener from the listener array for the event named eventName.
const callback = (stream) => { console.log('someone connected!');};server.on('connection', callback);// ...server.removeListener('connection', callback);Copy
removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them fromemit() in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events';class MyEmitter extends EventEmitter {}const myEmitter = new MyEmitter();const callbackA = () => { console.log('A'); myEmitter.removeListener('event', callbackB);};const callbackB = () => { console.log('B');};myEmitter.on('event', callbackA);myEmitter.on('event', callbackB);// callbackA removes listener callbackB but it will still be called.// Internal listener array at time of emit [callbackA, callbackB]myEmitter.emit('event');// Prints:// A// B// callbackB is now removed.// Internal listener array [callbackA]myEmitter.emit('event');// Prints:// ACopy
Because listeners are managed using an internal array, calling this will change the position indices of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.
When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:
import { EventEmitter } from 'node:events';const ee = new EventEmitter();function pong() { console.log('pong');}ee.on('ping', pong);ee.once('ping', pong);ee.removeListener('ping', pong);ee.emit('ping');ee.emit('ping');Copy
Returns a reference to the EventEmitter, so that calls can be chained.
v0.1.26
setMaxListeners(n: number): this
By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter, so that calls can be chained.
v0.3.5
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Methods [captureRejectionSymbol]addListeneremiteventNamesgetMaxListenerslistenerCountlistenersoffononceprependListenerprependOnceListenerrawListenersremoveAllListenersremoveListenersetMaxListeners