Hierarchy

Implemented by

Properties

writable: boolean

Methods

  • Parameters

    • error: Error
    • event: string
    • Rest ...args: any[]

    Returns void

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

    Parameters

    • eventName: string | symbol
    • listener: ((...args) => void)
        • (...args): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns WritableStream

    Since

    v0.1.26

  • Synchronously calls each of the listeners registered for the event namedeventName, 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

    Parameters

    • eventName: string | symbol
    • Rest ...args: any[]

    Returns boolean

    Since

    v0.1.26

  • Parameters

    • Optional cb: (() => void)
        • (): void
        • Returns void

    Returns WritableStream

  • Parameters

    • data: string | Uint8Array
    • Optional cb: (() => void)
        • (): void
        • Returns void

    Returns WritableStream

  • Parameters

    • str: string
    • Optional encoding: BufferEncoding
    • Optional cb: (() => void)
        • (): void
        • Returns void

    Returns WritableStream

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

    import { EventEmitter } from 'node:events';

    const myEE = new EventEmitter();
    myEE.on('foo', () => {});
    myEE.on('bar', () => {});

    const sym = Symbol('symbol');
    myEE.on(sym, () => {});

    console.log(myEE.eventNames());
    // Prints: [ 'foo', 'bar', Symbol(symbol) ]

    Returns (string | symbol)[]

    Since

    v6.0.0

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

    Returns number

    Since

    v1.0.0

  • 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.

    Parameters

    • eventName: string | symbol

      The name of the event being listened for

    • Optional listener: Function

      The event handler function

    Returns number

    Since

    v3.2.0

  • 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] ]

    Parameters

    • eventName: string | symbol

    Returns Function[]

    Since

    v0.1.26

  • Alias for emitter.removeListener().

    Parameters

    • eventName: string | symbol
    • listener: ((...args) => void)
        • (...args): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns WritableStream

    Since

    v10.0.0

  • 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 eventNameand 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. Theemitter.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

    Parameters

    • eventName: string | symbol

      The name of the event.

    • listener: ((...args) => void)

      The callback function

        • (...args): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns WritableStream

    Since

    v0.1.101

  • Adds a one-timelistener 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. Theemitter.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

    Parameters

    • eventName: string | symbol

      The name of the event.

    • listener: ((...args) => void)

      The callback function

        • (...args): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns WritableStream

    Since

    v0.3.0

  • 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 eventNameand 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.

    Parameters

    • eventName: string | symbol

      The name of the event.

    • listener: ((...args) => void)

      The callback function

        • (...args): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns WritableStream

    Since

    v6.0.0

  • 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.

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

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

    Parameters

    • eventName: string | symbol

      The name of the event.

    • listener: ((...args) => void)

      The callback function

        • (...args): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns WritableStream

    Since

    v6.0.0

  • 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');

    Parameters

    • eventName: string | symbol

    Returns Function[]

    Since

    v9.4.0

  • 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.

    Parameters

    • Optional event: string | symbol

    Returns WritableStream

    Since

    v0.1.26

  • Removes the specified listener from the listener array for the event namedeventName.

    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 anyremoveListener() 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:
    // 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:

    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.

    Parameters

    • eventName: string | symbol
    • listener: ((...args) => void)
        • (...args): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns WritableStream

    Since

    v0.1.26

  • 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 toInfinity (or 0) to indicate an unlimited number of listeners.

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

    Parameters

    • n: number

    Returns WritableStream

    Since

    v0.3.5

  • Parameters

    • buffer: string | Uint8Array
    • Optional cb: ((err?) => void)
        • (err?): void
        • Parameters

          • Optional err: null | Error

          Returns void

    Returns boolean

  • Parameters

    • str: string
    • Optional encoding: BufferEncoding
    • Optional cb: ((err?) => void)
        • (err?): void
        • Parameters

          • Optional err: null | Error

          Returns void

    Returns boolean

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