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.
Since
v17.4.0, v16.14.0
Properties
Functions
Alias for emitter.on(eventName, listener).
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 an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.
Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to {@link defaultMaxListeners}.
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.
Returns a copy of the array of listeners for the event named eventName.
Alias for emitter.removeListener().
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.
Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.
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.
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.
Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).
Removes all listeners, or those of the specified eventName.
Removes the specified listener from the listener array for the event named eventName.
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.