namespace

events.default

  • class EventEmitterAsyncResource

    Integrates EventEmitter with AsyncResource for EventEmitters that require manual async tracking. Specifically, all events emitted by instances of events.EventEmitterAsyncResource will run within its async context.

    import { EventEmitterAsyncResource, EventEmitter } from 'node:events';
import { notStrictEqual, strictEqual } from 'node:assert';
import { executionAsyncId, triggerAsyncId } from 'node:async_hooks';

// Async tracking tooling will identify this as 'Q'.
const ee1 = new EventEmitterAsyncResource({ name: 'Q' });

// 'foo' listeners will run in the EventEmitters async context.
ee1.on('foo', () => {
  strictEqual(executionAsyncId(), ee1.asyncId);
  strictEqual(triggerAsyncId(), ee1.triggerAsyncId);
});

const ee2 = new EventEmitter();

// 'foo' listeners on ordinary EventEmitters that do not track async
// context, however, run in the same async context as the emit().
ee2.on('foo', () => {
  notStrictEqual(executionAsyncId(), ee2.asyncId);
  notStrictEqual(triggerAsyncId(), ee2.triggerAsyncId);
});

Promise.resolve().then(() => {
  ee1.emit('foo');
  ee2.emit('foo');
});

    The EventEmitterAsyncResource class has the same methods and takes the same options as EventEmitter and AsyncResource themselves.

    • readonly asyncId: number

      The unique asyncId assigned to the resource.

    • readonly asyncResource: EventEmitterReferencingAsyncResource

      The returned AsyncResource object has an additional eventEmitter property that provides a reference to this EventEmitterAsyncResource.

    • readonly triggerAsyncId: number

      The same triggerAsyncId that is passed to the AsyncResource constructor.

    • error: Error,
      event: string | symbol,
      ...args: any[]
      ): void;

      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.
  }
}
    • addListener<E extends string | symbol>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Alias for emitter.on(eventName, listener).

    • emit<E extends string | symbol>(
      eventName: string | symbol,
      ...args: any[]
      ): 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 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
    • emitDestroy(): void;

      Call all destroy hooks. This should only ever be called once. An error will be thrown if it is called more than once. This must be manually called. If the resource is left to be collected by the GC then the destroy hooks will never be called.

    • eventNames(): string | symbol[];

      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) ]
    • getMaxListeners(): number;

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

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

      @param eventName

      The name of the event being listened for

      @param listener

      The event handler function

    • listeners<E extends string | symbol>(
      eventName: string | symbol
      ): (...args: any[]) => void[];

      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] ]
    • off<E extends string | symbol>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Alias for emitter.removeListener().

    • on<E extends string | symbol>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

      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
      @param eventName

      The name of the event.

      @param listener

      The callback function

    • once<E extends string | symbol>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

      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
      @param eventName

      The name of the event.

      @param listener

      The callback function

    • prependListener<E extends string | symbol>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

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

      @param eventName

      The name of the event.

      @param listener

      The callback function

    • prependOnceListener<E extends string | symbol>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

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

      @param eventName

      The name of the event.

      @param listener

      The callback function

    • rawListeners<E extends string | symbol>(
      eventName: string | symbol
      ): (...args: any[]) => void[];

      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 extends string | symbol>(
      eventName?: string | symbol
      ): 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.

    • removeListener<E extends string | symbol>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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);

      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.

    • 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.

  • interface EventEmitterAsyncResourceOptions

    • name?: string

      The type of async event.

    • requireManualDestroy?: boolean

      Disables automatic emitDestroy when the object is garbage collected. This usually does not need to be set (even if emitDestroy is called manually), unless the resource's asyncId is retrieved and the sensitive API's emitDestroy is called with it.

    • triggerAsyncId?: number

      The ID of the execution context that created this async event.

  • interface EventEmitterEventMap

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

  • interface EventEmitterReferencingAsyncResource

    The class AsyncResource is designed to be extended by the embedder's async resources. Using this, users can easily trigger the lifetime events of their own resources.

    The init hook will trigger when an AsyncResource is instantiated.

    The following is an overview of the AsyncResource API.

    import { AsyncResource, executionAsyncId } from 'node:async_hooks';

// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(
  type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false },
);

// Run a function in the execution context of the resource. This will
// * establish the context of the resource
// * trigger the AsyncHooks before callbacks
// * call the provided function `fn` with the supplied arguments
// * trigger the AsyncHooks after callbacks
// * restore the original execution context
asyncResource.runInAsyncScope(fn, thisArg, ...args);

// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();

// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();

// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
    • asyncId(): number;
      @returns

      The unique asyncId assigned to the resource.

    • bind<Func extends (...args: any[]) => any>(
      fn: Func
      ): Func;

      Binds the given function to execute to this AsyncResource's scope.

      @param fn

      The function to bind to the current AsyncResource.

    • emitDestroy(): this;

      Call all destroy hooks. This should only ever be called once. An error will be thrown if it is called more than once. This must be manually called. If the resource is left to be collected by the GC then the destroy hooks will never be called.

      @returns

      A reference to asyncResource.

    • runInAsyncScope<This, Result>(
      fn: (this: This, ...args: any[]) => Result,
      thisArg?: This,
      ...args: any[]
      ): Result;

      Call the provided function with the provided arguments in the execution context of the async resource. This will establish the context, trigger the AsyncHooks before callbacks, call the function, trigger the AsyncHooks after callbacks, and then restore the original execution context.

      @param fn

      The function to call in the execution context of this async resource.

      @param thisArg

      The receiver to be used for the function call.

      @param args

      Optional arguments to pass to the function.

    • triggerAsyncId(): number;
      @returns

      The same triggerAsyncId that is passed to the AsyncResource constructor.

  • interface InternalEventEmitter<T extends EventMap<T>>

    This is the interface from which event-emitting Node.js APIs inherit in the types package. It is not intended for consumer use.

    It provides event-mapped definitions similar to EventEmitter, except that its signatures are deliberately permissive: they provide type hinting, but not rigid type-checking, for compatibility reasons.

    Classes that inherit directly from EventEmitter in JavaScript can inherit directly from this interface in the type definitions. Classes that are more than one inheritance level away from EventEmitter (eg. net.Socket > stream.Duplex > EventEmitter) must instead copy these method definitions into the derived class. Search "#region InternalEventEmitter" for examples.

    • error: Error,
      event: string | symbol,
      ...args: any[]
      ): void;

      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.
  }
}
    • addListener<E extends string | number | symbol>(
      eventName: E,
      listener: (...args: T[E]) => void
      ): this;

      Alias for emitter.on(eventName, listener).

      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Alias for emitter.on(eventName, listener).

    • emit<E extends string | number | symbol>(
      eventName: E,
      ...args: T[E]
      ): 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 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
      eventName: string | symbol,
      ...args: any[]
      ): 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 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(): string | symbol[];

      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) ]
    • getMaxListeners(): number;

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

    • listenerCount<E extends string | number | symbol>(
      eventName: E,
      listener?: (...args: T[E]) => void
      ): 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.

      @param eventName

      The name of the event being listened for

      @param listener

      The event handler function

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

      @param eventName

      The name of the event being listened for

      @param listener

      The event handler function

    • listeners<E extends string | number | symbol>(
      eventName: E
      ): (...args: T[E]) => void[];

      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] ]
      eventName: string | symbol
      ): (...args: any[]) => void[];

      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] ]
    • off<E extends string | number | symbol>(
      eventName: E,
      listener: (...args: T[E]) => void
      ): this;

      Alias for emitter.removeListener().

      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Alias for emitter.removeListener().

    • on<E extends string | number | symbol>(
      eventName: E,
      listener: (...args: T[E]) => void
      ): 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!');
});

      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
      @param eventName

      The name of the event.

      @param listener

      The callback function

      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

      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
      @param eventName

      The name of the event.

      @param listener

      The callback function

    • once<E extends string | number | symbol>(
      eventName: E,
      listener: (...args: T[E]) => void
      ): 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!');
});

      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
      @param eventName

      The name of the event.

      @param listener

      The callback function

      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

      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
      @param eventName

      The name of the event.

      @param listener

      The callback function

    • prependListener<E extends string | number | symbol>(
      eventName: E,
      listener: (...args: T[E]) => void
      ): 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!');
});

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

      @param eventName

      The name of the event.

      @param listener

      The callback function

      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

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

      @param eventName

      The name of the event.

      @param listener

      The callback function

    • prependOnceListener<E extends string | number | symbol>(
      eventName: E,
      listener: (...args: T[E]) => void
      ): 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!');
});

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

      @param eventName

      The name of the event.

      @param listener

      The callback function

      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): 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!');
});

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

      @param eventName

      The name of the event.

      @param listener

      The callback function

    • rawListeners<E extends string | number | symbol>(
      eventName: E
      ): (...args: T[E]) => void[];

      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');
      eventName: string | symbol
      ): (...args: any[]) => void[];

      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 extends string | number | symbol>(
      eventName?: E
      ): 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.

      eventName?: string | symbol
      ): 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.

    • removeListener<E extends string | number | symbol>(
      eventName: E,
      listener: (...args: T[E]) => void
      ): 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);

      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.

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

      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.

    • 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.

  • interface NodeEventTarget

    The NodeEventTarget is a Node.js-specific extension to EventTarget that emulates a subset of the EventEmitter API.

    • type: string,
      callback: null | EventListenerOrEventListenerObject,
      options?: boolean | AddEventListenerOptions
      ): void;

      Appends an event listener for events whose type attribute value is type. The callback argument sets the callback that will be invoked when the event is dispatched.

      The options argument sets listener-specific options. For compatibility this can be a boolean, in which case the method behaves exactly as if the value was specified as options's capture.

      When set to true, options's capture prevents callback from being invoked when the event's eventPhase attribute value is BUBBLING_PHASE. When false (or not present), callback will not be invoked when event's eventPhase attribute value is CAPTURING_PHASE. Either way, callback will be invoked if event's eventPhase attribute value is AT_TARGET.

      When set to true, options's passive indicates that the callback will not cancel the event by invoking preventDefault(). This is used to enable performance optimizations described in § 2.8 Observing event listeners.

      When set to true, options's once indicates that the callback will only be invoked once after which the event listener will be removed.

      If an AbortSignal is passed for options's signal, then the event listener will be removed when signal is aborted.

      The event listener is appended to target's event listener list and is not appended if it has the same type, callback, and capture.

      MDN Reference

      type: string,
      listener: EventListener | EventListenerObject,
      options?: boolean | AddEventListenerOptions
      ): void;

      Adds a new handler for the type event. Any given listener is added only once per type and per capture option value.

      If the once option is true, the listener is removed after the next time a type event is dispatched.

      The capture option is not used by Node.js in any functional way other than tracking registered event listeners per the EventTarget specification. Specifically, the capture option is used as part of the key when registering a listener. Any individual listener may be added once with capture = false, and once with capture = true.

    • type: string,
      listener: (arg: any) => void
      ): this;

      Node.js-specific extension to the EventTarget class that emulates the equivalent EventEmitter API. The only difference between addListener() and addEventListener() is that addListener() will return a reference to the EventTarget.

    • event: Event
      ): boolean;

      Dispatches a synthetic event event to target and returns true if either event's cancelable attribute value is false or its preventDefault() method was not invoked, and false otherwise.

    • type: string,
      arg: any
      ): boolean;

      Node.js-specific extension to the EventTarget class that dispatches the arg to the list of handlers for type.

      @returns

      true if event listeners registered for the type exist, otherwise false.

    • eventNames(): string[];

      Node.js-specific extension to the EventTarget class that returns an array of event type names for which event listeners are registered.

    • getMaxListeners(): number;

      Node.js-specific extension to the EventTarget class that returns the number of max event listeners.

    • type: string
      ): number;

      Node.js-specific extension to the EventTarget class that returns the number of event listeners registered for the type.

    • type: string,
      listener: (arg: any) => void,
      options?: EventListenerOptions
      ): this;

      Node.js-specific alias for eventTarget.removeEventListener().

    • type: string,
      listener: (arg: any) => void
      ): this;

      Node.js-specific alias for eventTarget.addEventListener().

    • type: string,
      listener: (arg: any) => void
      ): this;

      Node.js-specific extension to the EventTarget class that adds a once listener for the given event type. This is equivalent to calling on with the once option set to true.

    • type?: string
      ): this;

      Node.js-specific extension to the EventTarget class. If type is specified, removes all registered listeners for type, otherwise removes all registered listeners.

    • type: string,
      callback: null | EventListenerOrEventListenerObject,
      options?: boolean | EventListenerOptions
      ): void;

      Removes the event listener in target's event listener list with the same type, callback, and options.

      MDN Reference

      type: string,
      listener: EventListener | EventListenerObject,
      options?: boolean | EventListenerOptions
      ): void;

      Removes the event listener in target's event listener list with the same type, callback, and options.

    • type: string,
      listener: (arg: any) => void,
      options?: EventListenerOptions
      ): this;

      Node.js-specific extension to the EventTarget class that removes the listener for the given type. The only difference between removeListener() and removeEventListener() is that removeListener() will return a reference to the EventTarget.

    • n: number
      ): void;

      Node.js-specific extension to the EventTarget class that sets the number of max event listeners as n.

  • interface OnOptions

    • close?: readonly string[]

      Names of events that will end the iteration.

    • highWaterMark?: number

      The high watermark. The emitter is paused every time the size of events being buffered is higher than it. Supported only on emitters implementing pause() and resume() methods.

    • lowWaterMark?: number

      The low watermark. The emitter is resumed every time the size of events being buffered is lower than it. Supported only on emitters implementing pause() and resume() methods.

  • type InternalEventTargetEventProperties<T> = { [K in keyof T & string]: (ev: T[K]) => void | null }
  • const captureRejections: boolean

    Change the default captureRejections option on all new EventEmitter objects.

  • const captureRejectionSymbol: unique symbol
  • const defaultMaxListeners: number

    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 all EventEmitter 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:

    defaultMaxListeners has no effect on AbortSignal instances. While it is still possible to use emitter.setMaxListeners(n) to set a warning limit for individual AbortSignal instances, per default AbortSignal instances will not warn.

    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'.

  • const errorMonitor: unique symbol

    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.

  • signal: AbortSignal,
    resource: (event: Event) => void
    ): Disposable;

    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.

    import { addAbortListener } from 'node:events';

function example(signal) {
  signal.addEventListener('abort', (e) => e.stopImmediatePropagation());
  // addAbortListener() returns a disposable, so the `using` keyword ensures
  // the abort listener is automatically removed when this scope exits.
  using _ = addAbortListener(signal, (e) => {
    // Do something when signal is aborted.
  });
}
    @returns

    Disposable that removes the abort listener.

  • emitter: EventEmitter,
    name: string | symbol
    ): (...args: any[]) => 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.

    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] ]
}
    emitter: EventTarget,
    name: string
    ): (...args: any[]) => 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.

    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] ]
}
  • function getMaxListeners(
    emitter: EventEmitter<any> | EventTarget
    ): number;

    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.

    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
}
  • function listenerCount(
    emitter: EventEmitter,
    eventName: string | symbol
    ): number;

    Returns the number of registered listeners for the event named eventName.

    For EventEmitters this behaves exactly the same as calling .listenerCount on the emitter.

    For EventTargets this is the only way to obtain the listener count. This can be useful for debugging and diagnostic purposes.

    function listenerCount(
    emitter: EventTarget,
    eventName: string
    ): number;

    Returns the number of registered listeners for the event named eventName.

    For EventEmitters this behaves exactly the same as calling .listenerCount on the emitter.

    For EventTargets this is the only way to obtain the listener count. This can be useful for debugging and diagnostic purposes.

  • function on(
    emitter: EventEmitter,
    eventName: string | symbol,
    options?: OnOptions
    ): AsyncIterator<any[]>;
    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:

    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());
    @returns

    AsyncIterator that iterates eventName events emitted by the emitter

    function on(
    emitter: EventTarget,
    eventName: string,
    options?: OnOptions
    ): AsyncIterator<any[]>;
    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:

    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());
    @returns

    AsyncIterator that iterates eventName events emitted by the emitter

  • function once(
    emitter: EventEmitter,
    eventName: string | symbol,
    options?: OnceOptions
    ): Promise<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][WHATWG-EventTarget] interface, which has no special 'error' event semantics and does not listen to the 'error' event.

    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:

    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:

    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(); // Prints: Waiting for the event was canceled!
    function once(
    emitter: EventTarget,
    eventName: string,
    options?: OnceOptions
    ): Promise<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][WHATWG-EventTarget] interface, which has no special 'error' event semantics and does not listen to the 'error' event.

    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:

    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:

    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(); // Prints: Waiting for the event was canceled!
  • function setMaxListeners(
    n: number,
    ...eventTargets: readonly EventEmitter<any> | EventTarget[]
    ): void;
    import { setMaxListeners, EventEmitter } from 'node:events';

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

setMaxListeners(5, target, emitter);
    @param n

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

    @param eventTargets

    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. objects.