Instances of the readline.Interface class are constructed using thereadline.createInterface() method. Every instance is associated with a single input Readable stream and a single output Writable stream. The output stream is used to print prompts for user input that arrives on, and is read from, the input stream.

Since

v0.1.104

Hierarchy

Constructors

Properties

cursor: number

The cursor position relative to rl.line.

This will track where the current cursor lands in the input string, when reading input from a TTY stream. The position of cursor determines the portion of the input string that will be modified as input is processed, as well as the column where the terminal caret will be rendered.

Since

v0.1.98

line: string

The current input data being processed by node.

This can be used when collecting input from a TTY stream to retrieve the current value that has been processed thus far, prior to the line event being emitted. Once the line event has been emitted, this property will be an empty string.

Be aware that modifying the value during the instance runtime may have unintended consequences if rl.cursor is not also controlled.

If not using a TTY stream for input, use the 'line' event.

One possible use case would be as follows:

const values = ['lorem ipsum', 'dolor sit amet'];
const rl = readline.createInterface(process.stdin);
const showResults = debounce(() => {
console.log(
'\n',
values.filter((val) => val.startsWith(rl.line)).join(' ')
);
}, 300);
process.stdin.on('keypress', (c, k) => {
showResults();
});

Since

v0.1.98

terminal: boolean
captureRejectionSymbol: typeof captureRejectionSymbol
captureRejections: boolean

TODO: These should be described using static getter/setter pairs:

defaultMaxListeners: number
errorMonitor: typeof 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

  • events.EventEmitter

    1. close
    2. line
    3. pause
    4. resume
    5. SIGCONT
    6. SIGINT
    7. SIGTSTP
    8. history

    Parameters

    • event: string
    • listener: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns Interface

  • Parameters

    • event: "close"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "line"
    • listener: ((input: string) => void)
        • (input: string): void
        • Parameters

          • input: string

          Returns void

    Returns Interface

  • Parameters

    • event: "pause"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "resume"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGCONT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGINT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGTSTP"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "history"
    • listener: ((history: string[]) => void)
        • (history: string[]): void
        • Parameters

          • history: string[]

          Returns void

    Returns Interface

  • The rl.close() method closes the readline.Interface instance and relinquishes control over the input and output streams. When called, the 'close' event will be emitted.

    Calling rl.close() does not immediately stop other events (including 'line') from being emitted by the readline.Interface instance.

    Since

    v0.1.98

    Returns void

  • 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.

    const EventEmitter = require('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

    Since

    v0.1.26

    Parameters

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

    Returns boolean

  • Parameters

    • event: "close"

    Returns boolean

  • Parameters

    • event: "line"
    • input: string

    Returns boolean

  • Parameters

    • event: "pause"

    Returns boolean

  • Parameters

    • event: "resume"

    Returns boolean

  • Parameters

    • event: "SIGCONT"

    Returns boolean

  • Parameters

    • event: "SIGINT"

    Returns boolean

  • Parameters

    • event: "SIGTSTP"

    Returns boolean

  • Parameters

    • event: "history"
    • history: string[]

    Returns boolean

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

    const EventEmitter = require('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) ]

    Since

    v6.0.0

    Returns (string | symbol)[]

  • Returns the real position of the cursor in relation to the input prompt + string. Long input (wrapping) strings, as well as multiple line prompts are included in the calculations.

    Since

    v13.5.0, v12.16.0

    Returns CursorPos

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

    Since

    v1.0.0

    Returns number

  • The rl.getPrompt() method returns the current prompt used by rl.prompt().

    Since

    v15.3.0

    Returns

    the current prompt string

    Returns string

  • Returns the number of listeners listening to the event named eventName.

    Since

    v3.2.0

    Parameters

    • eventName: string | symbol

      The name of the event being listened for

    Returns number

  • 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] ]

    Since

    v0.1.26

    Parameters

    • eventName: string | symbol

    Returns Function[]

  • Alias for emitter.removeListener().

    Since

    v10.0.0

    Parameters

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

          • Rest ...args: any[]

          Returns void

    Returns Interface

  • 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.

    const myEE = new EventEmitter();
    myEE.on('foo', () => console.log('a'));
    myEE.prependListener('foo', () => console.log('b'));
    myEE.emit('foo');
    // Prints:
    // b
    // a

    Since

    v0.1.101

    Parameters

    • event: string

      The name of the event.

    • listener: ((...args: any[]) => void)

      The callback function

        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns Interface

  • Parameters

    • event: "close"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "line"
    • listener: ((input: string) => void)
        • (input: string): void
        • Parameters

          • input: string

          Returns void

    Returns Interface

  • Parameters

    • event: "pause"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "resume"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGCONT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGINT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGTSTP"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "history"
    • listener: ((history: string[]) => void)
        • (history: string[]): void
        • Parameters

          • history: string[]

          Returns void

    Returns Interface

  • 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.

    const myEE = new EventEmitter();
    myEE.once('foo', () => console.log('a'));
    myEE.prependOnceListener('foo', () => console.log('b'));
    myEE.emit('foo');
    // Prints:
    // b
    // a

    Since

    v0.3.0

    Parameters

    • event: string

      The name of the event.

    • listener: ((...args: any[]) => void)

      The callback function

        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns Interface

  • Parameters

    • event: "close"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "line"
    • listener: ((input: string) => void)
        • (input: string): void
        • Parameters

          • input: string

          Returns void

    Returns Interface

  • Parameters

    • event: "pause"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "resume"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGCONT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGINT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGTSTP"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "history"
    • listener: ((history: string[]) => void)
        • (history: string[]): void
        • Parameters

          • history: string[]

          Returns void

    Returns Interface

  • The rl.pause() method pauses the input stream, allowing it to be resumed later if necessary.

    Calling rl.pause() does not immediately pause other events (including'line') from being emitted by the readline.Interface instance.

    Since

    v0.3.4

    Returns Interface

  • 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.

    Since

    v6.0.0

    Parameters

    • event: string

      The name of the event.

    • listener: ((...args: any[]) => void)

      The callback function

        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns Interface

  • Parameters

    • event: "close"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "line"
    • listener: ((input: string) => void)
        • (input: string): void
        • Parameters

          • input: string

          Returns void

    Returns Interface

  • Parameters

    • event: "pause"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "resume"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGCONT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGINT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGTSTP"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "history"
    • listener: ((history: string[]) => void)
        • (history: string[]): void
        • Parameters

          • history: string[]

          Returns void

    Returns Interface

  • 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.

    Since

    v6.0.0

    Parameters

    • event: string

      The name of the event.

    • listener: ((...args: any[]) => void)

      The callback function

        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns Interface

  • Parameters

    • event: "close"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "line"
    • listener: ((input: string) => void)
        • (input: string): void
        • Parameters

          • input: string

          Returns void

    Returns Interface

  • Parameters

    • event: "pause"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "resume"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGCONT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGINT"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "SIGTSTP"
    • listener: (() => void)
        • (): void
        • Returns void

    Returns Interface

  • Parameters

    • event: "history"
    • listener: ((history: string[]) => void)
        • (history: string[]): void
        • Parameters

          • history: string[]

          Returns void

    Returns Interface

  • The rl.prompt() method writes the readline.Interface instances configuredprompt to a new line in output in order to provide a user with a new location at which to provide input.

    When called, rl.prompt() will resume the input stream if it has been paused.

    If the readline.Interface was created with output set to null orundefined the prompt is not written.

    Since

    v0.1.98

    Parameters

    • Optional preserveCursor: boolean

      If true, prevents the cursor placement from being reset to 0.

    Returns void

  • The rl.question() method displays the query by writing it to the output, waits for user input to be provided on input, then invokes the callbackfunction passing the provided input as the first argument.

    When called, rl.question() will resume the input stream if it has been paused.

    If the readline.Interface was created with output set to null orundefined the query is not written.

    The callback function passed to rl.question() does not follow the typical pattern of accepting an Error object or null as the first argument. The callback is called with the provided answer as the only argument.

    Example usage:

    rl.question('What is your favorite food? ', (answer) => {
    console.log(`Oh, so your favorite food is ${answer}`);
    });

    Using an AbortController to cancel a question.

    const ac = new AbortController();
    const signal = ac.signal;

    rl.question('What is your favorite food? ', { signal }, (answer) => {
    console.log(`Oh, so your favorite food is ${answer}`);
    });

    signal.addEventListener('abort', () => {
    console.log('The food question timed out');
    }, { once: true });

    setTimeout(() => ac.abort(), 10000);

    If this method is invoked as it's util.promisify()ed version, it returns a Promise that fulfills with the answer. If the question is canceled using an AbortController it will reject with an AbortError.

    const util = require('util');
    const question = util.promisify(rl.question).bind(rl);

    async function questionExample() {
    try {
    const answer = await question('What is you favorite food? ');
    console.log(`Oh, so your favorite food is ${answer}`);
    } catch (err) {
    console.error('Question rejected', err);
    }
    }
    questionExample();

    Since

    v0.3.3

    Parameters

    • query: string

      A statement or query to write to output, prepended to the prompt.

    • callback: ((answer: string) => void)

      A callback function that is invoked with the user's input in response to the query.

        • (answer: string): void
        • Parameters

          • answer: string

          Returns void

    Returns void

  • Parameters

    • query: string
    • options: Abortable
    • callback: ((answer: string) => void)
        • (answer: string): void
        • Parameters

          • answer: string

          Returns void

    Returns void

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

    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');

    Since

    v9.4.0

    Parameters

    • eventName: string | symbol

    Returns Function[]

  • 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.

    Since

    v0.1.26

    Parameters

    • Optional event: string | symbol

    Returns Interface

  • 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.

    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:

    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.

    Since

    v0.1.26

    Parameters

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

          • Rest ...args: any[]

          Returns void

    Returns Interface

  • The rl.resume() method resumes the input stream if it has been paused.

    Since

    v0.3.4

    Returns Interface

  • 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.

    Since

    v0.3.5

    Parameters

    • n: number

    Returns Interface

  • The rl.setPrompt() method sets the prompt that will be written to outputwhenever rl.prompt() is called.

    Since

    v0.1.98

    Parameters

    • prompt: string

    Returns void

  • The rl.write() method will write either data or a key sequence identified by key to the output. The key argument is supported only if output is a TTY text terminal. See TTY keybindings for a list of key combinations.

    If key is specified, data is ignored.

    When called, rl.write() will resume the input stream if it has been paused.

    If the readline.Interface was created with output set to null orundefined the data and key are not written.

    rl.write('Delete this!');
    // Simulate Ctrl+U to delete the line written previously
    rl.write(null, { ctrl: true, name: 'u' });

    The rl.write() method will write the data to the readline Interface'sinputas if it were provided by the user.

    Since

    v0.1.98

    Parameters

    Returns void

  • Parameters

    • data: undefined | null | string | Buffer
    • key: Key

    Returns void

  • 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.

    const { getEventListeners, EventEmitter } = require('events');

    {
    const ee = new EventEmitter();
    const listener = () => console.log('Events are fun');
    ee.on('foo', listener);
    getEventListeners(ee, 'foo'); // [listener]
    }
    {
    const et = new EventTarget();
    const listener = () => console.log('Events are fun');
    et.addEventListener('foo', listener);
    getEventListeners(et, 'foo'); // [listener]
    }

    Since

    v15.2.0, v14.17.0

    Parameters

    Returns Function[]

  • A class method that returns the number of listeners for the given eventNameregistered on the given emitter.

    const { EventEmitter, listenerCount } = require('events');
    const myEmitter = new EventEmitter();
    myEmitter.on('event', () => {});
    myEmitter.on('event', () => {});
    console.log(listenerCount(myEmitter, 'event'));
    // Prints: 2

    Since

    v0.9.12

    Deprecated

    Since v3.2.0 - Use listenerCount instead.

    Parameters

    • emitter: EventEmitter

      The emitter to query

    • eventName: string | symbol

      The event name

    Returns number

  • const { on, EventEmitter } = require('events');

    (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')) {
    // 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:

    const { on, EventEmitter } = require('events');
    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());

    Since

    v13.6.0, v12.16.0

    Returns

    that iterates eventName events emitted by the emitter

    Parameters

    Returns AsyncIterableIterator<any>

  • 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.

    const { once, EventEmitter } = require('events');

    async function run() {
    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.log('error happened', err);
    }
    }

    run();

    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:

    const { EventEmitter, once } = require('events');

    const ee = new EventEmitter();

    once(ee, 'error')
    .then(([err]) => console.log('ok', err.message))
    .catch((err) => console.log('error', err.message));

    ee.emit('error', new Error('boom'));

    // Prints: ok boom

    An AbortSignal can be used to cancel waiting for the event:

    const { EventEmitter, once } = require('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!

    Since

    v11.13.0, v10.16.0

    Parameters

    Returns Promise<any[]>

  • Parameters

    Returns Promise<any[]>

  • const {
    setMaxListeners,
    EventEmitter
    } = require('events');

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

    setMaxListeners(5, target, emitter);

    Since

    v15.4.0

    Parameters

    • Optional n: number

      A non-negative number. The maximum number of listeners per EventTarget event.

    • Rest ...eventTargets: (EventEmitter | _DOMEventTarget)[]

    Returns void