Bun

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.

    • static captureRejections: boolean

      Value: boolean

      Change the default captureRejections option on all new EventEmitter objects.

    • readonly static captureRejectionSymbol: typeof captureRejectionSymbol

      Value: Symbol.for('nodejs.rejection')

      See how to write a custom rejection handler.

    • static 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 allEventEmitter 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:

      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'.

    • readonly static 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.

    • error: Error,
      event: string | symbol,
      ...args: AnyRest
      ): void;
    • eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Alias for emitter.on(eventName, listener).

    • emit<K>(
      eventName: string | symbol,
      ...args: AnyRest
      ): 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. 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) ]
      
    • getMaxListeners(): number;

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

    • eventName: string | symbol,
      listener?: Function
      ): number;

      Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.

      @param eventName

      The name of the event being listened for

      @param listener

      The event handler function

    • eventName: string | symbol
      ): Function[];

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

      server.on('connection', (stream) => {
        console.log('someone connected!');
      });
      console.log(util.inspect(server.listeners('connection')));
      // Prints: [ [Function] ]
      
    • off<K>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Alias for emitter.removeListener().

    • on<K>(
      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<K>(
      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

    • 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

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

      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.

      @param eventName

      The name of the event.

      @param listener

      The callback function

    • eventName: string | symbol
      ): Function[];

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

      import { EventEmitter } from 'node:events';
      const emitter = new EventEmitter();
      emitter.once('log', () => console.log('log once'));
      
      // Returns a new Array with a function `onceWrapper` which has a property
      // `listener` which contains the original listener bound 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
      ): 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,
      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 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.

    • 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.

    • 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) {
        let disposable;
        try {
          signal.addEventListener('abort', (e) => e.stopImmediatePropagation());
          disposable = addAbortListener(signal, (e) => {
            // Do something when signal is aborted.
          });
        } finally {
          disposable?.[Symbol.dispose]();
        }
      }
      
      @returns

      Disposable that removes the abort listener.

    • emitter: EventEmitter<DefaultEventMap> | EventTarget,
      name: string | symbol
      ): Function[];

      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: EventEmitter<DefaultEventMap> | 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
      }
      
    • static on(
      emitter: EventEmitter,
      eventName: string | symbol,
      options?: StaticEventEmitterIteratorOptions
      ): 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());
      

      Use the close option to specify an array of event names that will end the iteration:

      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);
        ee.emit('close');
      });
      
      for await (const event of on(ee, 'foo', { close: ['close'] })) {
        console.log(event); // prints ['bar'] [42]
      }
      // the loop will exit after 'close' is emitted
      console.log('done'); // prints 'done'
      
      @returns

      An AsyncIterator that iterates eventName events emitted by the emitter

      static on(
      emitter: EventTarget,
      eventName: string,
      options?: StaticEventEmitterIteratorOptions
      ): 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());
      

      Use the close option to specify an array of event names that will end the iteration:

      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);
        ee.emit('close');
      });
      
      for await (const event of on(ee, 'foo', { close: ['close'] })) {
        console.log(event); // prints ['bar'] [42]
      }
      // the loop will exit after 'close' is emitted
      console.log('done'); // prints 'done'
      
      @returns

      An AsyncIterator that iterates eventName events emitted by the emitter

    • static once(
      emitter: EventEmitter,
      eventName: string | symbol,
      options?: StaticEventEmitterOptions
      ): 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 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(); // Abort waiting for the event
      ee.emit('foo'); // Prints: Waiting for the event was canceled!
      
      static once(
      emitter: EventTarget,
      eventName: string,
      options?: StaticEventEmitterOptions
      ): 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 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(); // Abort waiting for the event
      ee.emit('foo'); // Prints: Waiting for the event was canceled!
      
    • n?: number,
      ...eventTargets: EventEmitter<DefaultEventMap> | 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.

  • interface Abortable

    • signal?: AbortSignal

      When provided the corresponding AbortController can be used to cancel an asynchronous action.

  • interface EventEmitterAsyncResourceOptions

    • captureRejections?: boolean

      Enables automatic capturing of promise rejection.

    • name?: string

      The type of async event, this is required when instantiating EventEmitterAsyncResource directly rather than as a child class.

    • 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 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.