Sets or gets the default captureRejection value for all emitters.
+
+
+
Static defaultMaxListeners
@@ -219,32 +260,62 @@
Static defaultMaxListe
+
+
+
Static errorMonitor
+
errorMonitor:keyof 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.
+
+
Methods
-
+
addListener
-
-
addListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this
Synchronously calls each of the listeners registered for the event namedeventName, in the order they were registered, passing the supplied arguments
+ to each.
+
+
Returns true if the event had listeners, false otherwise.
+
const EventEmitter = require('events');
+const myEmitter = new EventEmitter();
+
+// First listener
+myEmitter.on('event', functionfirstListener() {
+ console.log('Helloooo! first listener');
+});
+// Second listener
+myEmitter.on('event', functionsecondListener(arg1, arg2) {
+ console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
+});
+// Third listener
+myEmitter.on('event', functionthirdListener(...args) {
+ const parameters = args.join(', ');
+ console.log(`event with parameters ${parameters} in third listener`);
+});
+
+console.log(myEmitter.listeners('event'));
+
+myEmitter.emit('event', 1, 2, 3, 4, 5);
+
+// Prints:
+// [
+// [Function: firstListener],
+// [Function: secondListener],
+// [Function: thirdListener]
+// ]
+// Helloooo! first listener
+// event with parameters 1, 2 in second listener
+// event with parameters 1, 2, 3, 4, 5 in third listener
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Rest...args: any[]
@@ -352,40 +464,70 @@
Returns boolean
-
+
eventNames
-
+
eventNames(): Array<string | symbol>
+
+
+
Returns an array listing the events for which the emitter has registered
+ listeners. The values in the array are strings or Symbols.
prependListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependListener(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v6.0.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -779,28 +1024,48 @@
Returns this
-
+
prependOnceListener
-
-
prependOnceListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependOnceListener(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.
Returns a copy of the array of listeners for the event named eventName,
+ including any wrappers (such as those created by .once()).
+
+
const emitter = new EventEmitter();
+emitter.once('log', () => console.log('log once'));
+
+// Returns a new Array with a function `onceWrapper` which has a property
+// `listener` which contains the original listener bound above
+const listeners = emitter.rawListeners('log');
+const logFnWrapper = listeners[0];
+
+// Logs "log once" to the console and does not unbind the `once` event
+logFnWrapper.listener();
+
+// Logs "log once" to the console and removes the listener
+logFnWrapper();
+
+emitter.on('log', () => console.log('log persistently'));
+// Will return a new Array with a single function bound by `.on()` above
+const newListeners = emitter.rawListeners('log');
+
+// Logs "log persistently" twice
+newListeners[0]();
+emitter.emit('log');
+
+
since
+
v9.4.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Returns Function[]
-
+
removeAllListeners
-
+
removeAllListeners(event?: 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.
+
+
since
+
v0.1.26
+
+
+
Parameters
@@ -909,25 +1218,95 @@
Returns this
-
+
removeListener
-
-
removeListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Removes the specified listener from the listener array for the event namedeventName.
removeListener() will remove, at most, one instance of a listener from the
+ listener array. If any single listener has been added multiple times to the
+ listener array for the specified eventName, then removeListener() must be
+ called multiple times to remove each instance.
+
Once an event is emitted, all listeners attached to it at the
+ time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and_before_ the last listener finishes execution will
+ not remove them fromemit() in progress. Subsequent events behave as expected.
+
const myEmitter = new MyEmitter();
+
+const callbackA = () => {
+ console.log('A');
+ myEmitter.removeListener('event', callbackB);
+};
+
+const callbackB = () => {
+ console.log('B');
+};
+
+myEmitter.on('event', callbackA);
+
+myEmitter.on('event', callbackB);
+
+// callbackA removes listener callbackB but it will still be called.
+// Internal listener array at time of emit [callbackA, callbackB]
+myEmitter.emit('event');
+// Prints:
+// A
+// B
+
+// callbackB is now removed.
+// Internal listener array [callbackA]
+myEmitter.emit('event');
+// Prints:
+// A
+
Because listeners are managed using an internal array, calling this will
+ change the position indices of any listener registered after the listener
+ being removed. This will not impact the order in which listeners are called,
+ but it means that any copies of the listener array as returned by
+ the emitter.listeners() method will need to be recreated.
+
When a single function has been added as a handler multiple times for a single
+ event (as in the example below), removeListener() will remove the most
+ recently added instance. In the example the once('ping')listener is removed:
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
listener: (...args: any[]) => void
@@ -965,7 +1344,7 @@
removeRemoteService
Parameters
@@ -994,7 +1373,7 @@
requery
Parameters
@@ -1007,21 +1386,34 @@
Returns Promise
-
+
setMaxListeners
-
+
setMaxListeners(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 toInfinity (or 0) to indicate an unlimited number of listeners.
+
+
Returns a reference to the EventEmitter, so that calls can be chained.
```js
+ const { on, EventEmitter } = require('events');
+
+
(async () => {
+ const ee = new EventEmitter();
+
// Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
for await (const event of on(ee, 'foo')) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+ })();
+
+Returns an `AsyncIterator` that iterates `eventName` events. It will throw
+if the `EventEmitter` emits `'error'`. It removes all listeners when
+exiting the loop. The `value` returned by each iteration is an array
+composed of the emitted event arguments.
+
+An `AbortSignal` can be used to cancel waiting on events:
+
+```js
+const { on, EventEmitter } = require('events');
+const ac = new AbortController();
+
+(async () => {
+ const ee = new EventEmitter();
+
+ // Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
+ forawait (const event of on(ee, 'foo', { signal: ac.signal })) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+})();
+
+process.nextTick(() => ac.abort());
+
+
since
+
v13.6.0, v12.16.0
+
+
+
+
Parameters
+
+
+
emitter: EventEmitter
+
+
+
eventName: string
+
+
The name of the event being listened for
+
+
+
+
Optional options: StaticEventEmitterOptions
+
+
+
Returns AsyncIterableIterator<any>
+
that iterates eventName events emitted by the emitter
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 platformEventTarget interface, which has no special'error' event
+ semantics and does not listen to the 'error' event.
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
+ 'error' event itself, then it is treated as any other kind of event without
+ special handling:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+
+once(ee, 'error')
+ .then(([err]) =>console.log('ok', err.message))
+ .catch((err) =>console.log('error', err.message));
+
+ee.emit('error', newError('boom'));
+
+// Prints: ok boom
+
An AbortSignal can be used to cancel waiting for the event:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+const ac = new AbortController();
+
+asyncfunctionfoo(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!
Defined in node_modules/@types/node/events.d.ts:279
+
+
+
Static errorMonitor
+
errorMonitor:keyof 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.
+
+
Methods
-
+
addListener
-
-
addListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this
Synchronously calls each of the listeners registered for the event namedeventName, in the order they were registered, passing the supplied arguments
+ to each.
+
+
Returns true if the event had listeners, false otherwise.
+
const EventEmitter = require('events');
+const myEmitter = new EventEmitter();
+
+// First listener
+myEmitter.on('event', functionfirstListener() {
+ console.log('Helloooo! first listener');
+});
+// Second listener
+myEmitter.on('event', functionsecondListener(arg1, arg2) {
+ console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
+});
+// Third listener
+myEmitter.on('event', functionthirdListener(...args) {
+ const parameters = args.join(', ');
+ console.log(`event with parameters ${parameters} in third listener`);
+});
+
+console.log(myEmitter.listeners('event'));
+
+myEmitter.emit('event', 1, 2, 3, 4, 5);
+
+// Prints:
+// [
+// [Function: firstListener],
+// [Function: secondListener],
+// [Function: thirdListener]
+// ]
+// Helloooo! first listener
+// event with parameters 1, 2 in second listener
+// event with parameters 1, 2, 3, 4, 5 in third listener
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Rest...args: any[]
@@ -308,10 +423,10 @@
Returns boolean
-
+
eventNames
-
+
eventNames(): Array<string | symbol>
@@ -319,11 +434,31 @@
eventNames
+
+
+
Returns an array listing the events for which the emitter has registered
+ listeners. The values in the array are strings or Symbols.
prependListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependListener(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v6.0.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -862,28 +1110,48 @@
Returns this
-
+
prependOnceListener
-
-
prependOnceListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependOnceListener(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.
Returns a copy of the array of listeners for the event named eventName,
+ including any wrappers (such as those created by .once()).
+
+
const emitter = new EventEmitter();
+emitter.once('log', () => console.log('log once'));
+
+// Returns a new Array with a function `onceWrapper` which has a property
+// `listener` which contains the original listener bound above
+const listeners = emitter.rawListeners('log');
+const logFnWrapper = listeners[0];
+
+// Logs "log once" to the console and does not unbind the `once` event
+logFnWrapper.listener();
+
+// Logs "log once" to the console and removes the listener
+logFnWrapper();
+
+emitter.on('log', () => console.log('log persistently'));
+// Will return a new Array with a single function bound by `.on()` above
+const newListeners = emitter.rawListeners('log');
+
+// Logs "log persistently" twice
+newListeners[0]();
+emitter.emit('log');
+
+
since
+
v9.4.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Returns Function[]
-
+
removeAllListeners
-
+
removeAllListeners(event?: string | symbol): this
@@ -969,11 +1268,24 @@
removeAllListeners
+
+
+
Removes all listeners, or those of the specified eventName.
+
+
It is bad practice to remove listeners added elsewhere in the code,
+ particularly when the EventEmitter instance was created by some other
+ component or module (e.g. sockets or file streams).
+
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
@@ -984,25 +1296,95 @@
Returns this
-
+
removeListener
-
-
removeListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Removes the specified listener from the listener array for the event namedeventName.
removeListener() will remove, at most, one instance of a listener from the
+ listener array. If any single listener has been added multiple times to the
+ listener array for the specified eventName, then removeListener() must be
+ called multiple times to remove each instance.
+
Once an event is emitted, all listeners attached to it at the
+ time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and_before_ the last listener finishes execution will
+ not remove them fromemit() in progress. Subsequent events behave as expected.
+
const myEmitter = new MyEmitter();
+
+const callbackA = () => {
+ console.log('A');
+ myEmitter.removeListener('event', callbackB);
+};
+
+const callbackB = () => {
+ console.log('B');
+};
+
+myEmitter.on('event', callbackA);
+
+myEmitter.on('event', callbackB);
+
+// callbackA removes listener callbackB but it will still be called.
+// Internal listener array at time of emit [callbackA, callbackB]
+myEmitter.emit('event');
+// Prints:
+// A
+// B
+
+// callbackB is now removed.
+// Internal listener array [callbackA]
+myEmitter.emit('event');
+// Prints:
+// A
+
Because listeners are managed using an internal array, calling this will
+ change the position indices of any listener registered after the listener
+ being removed. This will not impact the order in which listeners are called,
+ but it means that any copies of the listener array as returned by
+ the emitter.listeners() method will need to be recreated.
+
When a single function has been added as a handler multiple times for a single
+ event (as in the example below), removeListener() will remove the most
+ recently added instance. In the example the once('ping')listener is removed:
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
listener: (...args: any[]) => void
@@ -1041,7 +1423,7 @@
respond
Parameters
@@ -1054,10 +1436,10 @@
Returns Promise
-
+
setMaxListeners
-
+
setMaxListeners(n: number): this
@@ -1065,11 +1447,24 @@
setMaxListeners
+
+
+
By default EventEmitters will print a warning if more than 10 listeners are
+ added for a particular event. This is a useful default that helps finding
+ memory leaks. The emitter.setMaxListeners() method allows the limit to be
+ modified for this specific EventEmitter instance. The value can be set toInfinity (or 0) to indicate an unlimited number of listeners.
+
+
Returns a reference to the EventEmitter, so that calls can be chained.
```js
+ const { on, EventEmitter } = require('events');
+
+
(async () => {
+ const ee = new EventEmitter();
+
// Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
for await (const event of on(ee, 'foo')) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+ })();
+
+Returns an `AsyncIterator` that iterates `eventName` events. It will throw
+if the `EventEmitter` emits `'error'`. It removes all listeners when
+exiting the loop. The `value` returned by each iteration is an array
+composed of the emitted event arguments.
+
+An `AbortSignal` can be used to cancel waiting on events:
+
+```js
+const { on, EventEmitter } = require('events');
+const ac = new AbortController();
+
+(async () => {
+ const ee = new EventEmitter();
+
+ // Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
+ forawait (const event of on(ee, 'foo', { signal: ac.signal })) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+})();
+
+process.nextTick(() => ac.abort());
+
+
since
+
v13.6.0, v12.16.0
+
+
+
+
Parameters
+
+
+
emitter: EventEmitter
+
+
+
eventName: string
+
+
The name of the event being listened for
+
+
+
+
Optional options: StaticEventEmitterOptions
+
+
+
Returns AsyncIterableIterator<any>
+
that iterates eventName events emitted by the emitter
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 platformEventTarget interface, which has no special'error' event
+ semantics and does not listen to the 'error' event.
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
+ 'error' event itself, then it is treated as any other kind of event without
+ special handling:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+
+once(ee, 'error')
+ .then(([err]) =>console.log('ok', err.message))
+ .catch((err) =>console.log('error', err.message));
+
+ee.emit('error', newError('boom'));
+
+// Prints: ok boom
+
An AbortSignal can be used to cancel waiting for the event:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+const ac = new AbortController();
+
+asyncfunctionfoo(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!
Defined in node_modules/@types/node/events.d.ts:279
+
+
+
Static errorMonitor
+
errorMonitor:keyof 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.
+
+
Methods
-
+
addListener
-
-
addListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this
Synchronously calls each of the listeners registered for the event namedeventName, in the order they were registered, passing the supplied arguments
+ to each.
+
+
Returns true if the event had listeners, false otherwise.
+
const EventEmitter = require('events');
+const myEmitter = new EventEmitter();
+
+// First listener
+myEmitter.on('event', functionfirstListener() {
+ console.log('Helloooo! first listener');
+});
+// Second listener
+myEmitter.on('event', functionsecondListener(arg1, arg2) {
+ console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
+});
+// Third listener
+myEmitter.on('event', functionthirdListener(...args) {
+ const parameters = args.join(', ');
+ console.log(`event with parameters ${parameters} in third listener`);
+});
+
+console.log(myEmitter.listeners('event'));
+
+myEmitter.emit('event', 1, 2, 3, 4, 5);
+
+// Prints:
+// [
+// [Function: firstListener],
+// [Function: secondListener],
+// [Function: thirdListener]
+// ]
+// Helloooo! first listener
+// event with parameters 1, 2 in second listener
+// event with parameters 1, 2, 3, 4, 5 in third listener
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Rest...args: any[]
@@ -297,10 +412,10 @@
Returns boolean
-
+
eventNames
-
+
eventNames(): Array<string | symbol>
@@ -308,11 +423,31 @@
eventNames
+
+
+
Returns an array listing the events for which the emitter has registered
+ listeners. The values in the array are strings or Symbols.
prependListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependListener(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v6.0.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -629,28 +877,48 @@
Returns this
-
+
prependOnceListener
-
-
prependOnceListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependOnceListener(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.
Returns a copy of the array of listeners for the event named eventName,
+ including any wrappers (such as those created by .once()).
+
+
const emitter = new EventEmitter();
+emitter.once('log', () => console.log('log once'));
+
+// Returns a new Array with a function `onceWrapper` which has a property
+// `listener` which contains the original listener bound above
+const listeners = emitter.rawListeners('log');
+const logFnWrapper = listeners[0];
+
+// Logs "log once" to the console and does not unbind the `once` event
+logFnWrapper.listener();
+
+// Logs "log once" to the console and removes the listener
+logFnWrapper();
+
+emitter.on('log', () => console.log('log persistently'));
+// Will return a new Array with a single function bound by `.on()` above
+const newListeners = emitter.rawListeners('log');
+
+// Logs "log persistently" twice
+newListeners[0]();
+emitter.emit('log');
+
+
since
+
v9.4.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Returns Function[]
-
+
removeAllListeners
-
+
removeAllListeners(event?: string | symbol): this
@@ -736,11 +1035,24 @@
removeAllListeners
+
+
+
Removes all listeners, or those of the specified eventName.
+
+
It is bad practice to remove listeners added elsewhere in the code,
+ particularly when the EventEmitter instance was created by some other
+ component or module (e.g. sockets or file streams).
+
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
@@ -751,25 +1063,95 @@
Returns this
-
+
removeListener
-
-
removeListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Removes the specified listener from the listener array for the event namedeventName.
removeListener() will remove, at most, one instance of a listener from the
+ listener array. If any single listener has been added multiple times to the
+ listener array for the specified eventName, then removeListener() must be
+ called multiple times to remove each instance.
+
Once an event is emitted, all listeners attached to it at the
+ time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and_before_ the last listener finishes execution will
+ not remove them fromemit() in progress. Subsequent events behave as expected.
+
const myEmitter = new MyEmitter();
+
+const callbackA = () => {
+ console.log('A');
+ myEmitter.removeListener('event', callbackB);
+};
+
+const callbackB = () => {
+ console.log('B');
+};
+
+myEmitter.on('event', callbackA);
+
+myEmitter.on('event', callbackB);
+
+// callbackA removes listener callbackB but it will still be called.
+// Internal listener array at time of emit [callbackA, callbackB]
+myEmitter.emit('event');
+// Prints:
+// A
+// B
+
+// callbackB is now removed.
+// Internal listener array [callbackA]
+myEmitter.emit('event');
+// Prints:
+// A
+
Because listeners are managed using an internal array, calling this will
+ change the position indices of any listener registered after the listener
+ being removed. This will not impact the order in which listeners are called,
+ but it means that any copies of the listener array as returned by
+ the emitter.listeners() method will need to be recreated.
+
When a single function has been added as a handler multiple times for a single
+ event (as in the example below), removeListener() will remove the most
+ recently added instance. In the example the once('ping')listener is removed:
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
listener: (...args: any[]) => void
@@ -808,7 +1190,7 @@
respond
Parameters
@@ -821,10 +1203,10 @@
Returns Promise
-
+
setMaxListeners
-
+
setMaxListeners(n: number): this
@@ -832,11 +1214,24 @@
setMaxListeners
+
+
+
By default EventEmitters will print a warning if more than 10 listeners are
+ added for a particular event. This is a useful default that helps finding
+ memory leaks. The emitter.setMaxListeners() method allows the limit to be
+ modified for this specific EventEmitter instance. The value can be set toInfinity (or 0) to indicate an unlimited number of listeners.
+
+
Returns a reference to the EventEmitter, so that calls can be chained.
```js
+ const { on, EventEmitter } = require('events');
+
+
(async () => {
+ const ee = new EventEmitter();
+
// Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
for await (const event of on(ee, 'foo')) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+ })();
+
+Returns an `AsyncIterator` that iterates `eventName` events. It will throw
+if the `EventEmitter` emits `'error'`. It removes all listeners when
+exiting the loop. The `value` returned by each iteration is an array
+composed of the emitted event arguments.
+
+An `AbortSignal` can be used to cancel waiting on events:
+
+```js
+const { on, EventEmitter } = require('events');
+const ac = new AbortController();
+
+(async () => {
+ const ee = new EventEmitter();
+
+ // Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
+ forawait (const event of on(ee, 'foo', { signal: ac.signal })) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+})();
+
+process.nextTick(() => ac.abort());
+
+
since
+
v13.6.0, v12.16.0
+
+
+
+
Parameters
+
+
+
emitter: EventEmitter
+
+
+
eventName: string
+
+
The name of the event being listened for
+
+
+
+
Optional options: StaticEventEmitterOptions
+
+
+
Returns AsyncIterableIterator<any>
+
that iterates eventName events emitted by the emitter
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 platformEventTarget interface, which has no special'error' event
+ semantics and does not listen to the 'error' event.
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
+ 'error' event itself, then it is treated as any other kind of event without
+ special handling:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+
+once(ee, 'error')
+ .then(([err]) =>console.log('ok', err.message))
+ .catch((err) =>console.log('error', err.message));
+
+ee.emit('error', newError('boom'));
+
+// Prints: ok boom
+
An AbortSignal can be used to cancel waiting for the event:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+const ac = new AbortController();
+
+asyncfunctionfoo(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!
Sets or gets the default captureRejection value for all emitters.
+
+
+
Static defaultMaxListeners
@@ -213,32 +254,62 @@
Static defaultMaxListe
+
+
+
Static errorMonitor
+
errorMonitor:keyof 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.
+
+
Methods
-
+
addListener
-
-
addListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this
Synchronously calls each of the listeners registered for the event namedeventName, in the order they were registered, passing the supplied arguments
+ to each.
+
+
Returns true if the event had listeners, false otherwise.
+
const EventEmitter = require('events');
+const myEmitter = new EventEmitter();
+
+// First listener
+myEmitter.on('event', functionfirstListener() {
+ console.log('Helloooo! first listener');
+});
+// Second listener
+myEmitter.on('event', functionsecondListener(arg1, arg2) {
+ console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
+});
+// Third listener
+myEmitter.on('event', functionthirdListener(...args) {
+ const parameters = args.join(', ');
+ console.log(`event with parameters ${parameters} in third listener`);
+});
+
+console.log(myEmitter.listeners('event'));
+
+myEmitter.emit('event', 1, 2, 3, 4, 5);
+
+// Prints:
+// [
+// [Function: firstListener],
+// [Function: secondListener],
+// [Function: thirdListener]
+// ]
+// Helloooo! first listener
+// event with parameters 1, 2 in second listener
+// event with parameters 1, 2, 3, 4, 5 in third listener
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Rest...args: any[]
@@ -360,94 +472,205 @@
Returns boolean
-
+
eventNames
-
+
eventNames(): Array<string | symbol>
+
+
+
Returns an array listing the events for which the emitter has registered
+ listeners. The values in the array are strings or Symbols.
prependListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependListener(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v6.0.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -732,28 +977,48 @@
Returns this
-
+
prependOnceListener
-
-
prependOnceListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependOnceListener(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.
Returns a copy of the array of listeners for the event named eventName,
+ including any wrappers (such as those created by .once()).
+
+
const emitter = new EventEmitter();
+emitter.once('log', () => console.log('log once'));
+
+// Returns a new Array with a function `onceWrapper` which has a property
+// `listener` which contains the original listener bound above
+const listeners = emitter.rawListeners('log');
+const logFnWrapper = listeners[0];
+
+// Logs "log once" to the console and does not unbind the `once` event
+logFnWrapper.listener();
+
+// Logs "log once" to the console and removes the listener
+logFnWrapper();
+
+emitter.on('log', () => console.log('log persistently'));
+// Will return a new Array with a single function bound by `.on()` above
+const newListeners = emitter.rawListeners('log');
+
+// Logs "log persistently" twice
+newListeners[0]();
+emitter.emit('log');
+
+
since
+
v9.4.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Returns Function[]
-
+
removeAllListeners
-
+
removeAllListeners(event?: 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.
+
+
since
+
v0.1.26
+
+
+
Parameters
@@ -851,25 +1160,95 @@
Returns this
-
+
removeListener
-
-
removeListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Removes the specified listener from the listener array for the event namedeventName.
removeListener() will remove, at most, one instance of a listener from the
+ listener array. If any single listener has been added multiple times to the
+ listener array for the specified eventName, then removeListener() must be
+ called multiple times to remove each instance.
+
Once an event is emitted, all listeners attached to it at the
+ time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and_before_ the last listener finishes execution will
+ not remove them fromemit() in progress. Subsequent events behave as expected.
+
const myEmitter = new MyEmitter();
+
+const callbackA = () => {
+ console.log('A');
+ myEmitter.removeListener('event', callbackB);
+};
+
+const callbackB = () => {
+ console.log('B');
+};
+
+myEmitter.on('event', callbackA);
+
+myEmitter.on('event', callbackB);
+
+// callbackA removes listener callbackB but it will still be called.
+// Internal listener array at time of emit [callbackA, callbackB]
+myEmitter.emit('event');
+// Prints:
+// A
+// B
+
+// callbackB is now removed.
+// Internal listener array [callbackA]
+myEmitter.emit('event');
+// Prints:
+// A
+
Because listeners are managed using an internal array, calling this will
+ change the position indices of any listener registered after the listener
+ being removed. This will not impact the order in which listeners are called,
+ but it means that any copies of the listener array as returned by
+ the emitter.listeners() method will need to be recreated.
+
When a single function has been added as a handler multiple times for a single
+ event (as in the example below), removeListener() will remove the most
+ recently added instance. In the example the once('ping')listener is removed:
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
listener: (...args: any[]) => void
@@ -907,7 +1286,7 @@
removeService
Parameters
@@ -920,21 +1299,34 @@
Returns void
-
+
setMaxListeners
-
+
setMaxListeners(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 toInfinity (or 0) to indicate an unlimited number of listeners.
+
+
Returns a reference to the EventEmitter, so that calls can be chained.
```js
+ const { on, EventEmitter } = require('events');
+
+
(async () => {
+ const ee = new EventEmitter();
+
// Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
for await (const event of on(ee, 'foo')) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+ })();
+
+Returns an `AsyncIterator` that iterates `eventName` events. It will throw
+if the `EventEmitter` emits `'error'`. It removes all listeners when
+exiting the loop. The `value` returned by each iteration is an array
+composed of the emitted event arguments.
+
+An `AbortSignal` can be used to cancel waiting on events:
+
+```js
+const { on, EventEmitter } = require('events');
+const ac = new AbortController();
+
+(async () => {
+ const ee = new EventEmitter();
+
+ // Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
+ forawait (const event of on(ee, 'foo', { signal: ac.signal })) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+})();
+
+process.nextTick(() => ac.abort());
+
+
since
+
v13.6.0, v12.16.0
+
+
+
+
Parameters
+
+
+
emitter: EventEmitter
+
+
+
eventName: string
+
+
The name of the event being listened for
+
+
+
+
Optional options: StaticEventEmitterOptions
+
+
+
Returns AsyncIterableIterator<any>
+
that iterates eventName events emitted by the emitter
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 platformEventTarget interface, which has no special'error' event
+ semantics and does not listen to the 'error' event.
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
+ 'error' event itself, then it is treated as any other kind of event without
+ special handling:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+
+once(ee, 'error')
+ .then(([err]) =>console.log('ok', err.message))
+ .catch((err) =>console.log('error', err.message));
+
+ee.emit('error', newError('boom'));
+
+// Prints: ok boom
+
An AbortSignal can be used to cancel waiting for the event:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+const ac = new AbortController();
+
+asyncfunctionfoo(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!
Sets or gets the default captureRejection value for all emitters.
+
+
+
Static defaultMaxListeners
@@ -317,32 +358,62 @@
Static defaultMaxListe
+
+
+
Static errorMonitor
+
errorMonitor:keyof 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.
+
+
Methods
-
+
addListener
-
-
addListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this
Synchronously calls each of the listeners registered for the event namedeventName, in the order they were registered, passing the supplied arguments
+ to each.
+
+
Returns true if the event had listeners, false otherwise.
+
const EventEmitter = require('events');
+const myEmitter = new EventEmitter();
+
+// First listener
+myEmitter.on('event', functionfirstListener() {
+ console.log('Helloooo! first listener');
+});
+// Second listener
+myEmitter.on('event', functionsecondListener(arg1, arg2) {
+ console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
+});
+// Third listener
+myEmitter.on('event', functionthirdListener(...args) {
+ const parameters = args.join(', ');
+ console.log(`event with parameters ${parameters} in third listener`);
+});
+
+console.log(myEmitter.listeners('event'));
+
+myEmitter.emit('event', 1, 2, 3, 4, 5);
+
+// Prints:
+// [
+// [Function: firstListener],
+// [Function: secondListener],
+// [Function: thirdListener]
+// ]
+// Helloooo! first listener
+// event with parameters 1, 2 in second listener
+// event with parameters 1, 2, 3, 4, 5 in third listener
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Rest...args: any[]
@@ -441,21 +553,41 @@
Returns boolean
-
+
eventNames
-
+
eventNames(): Array<string | symbol>
+
+
+
Returns an array listing the events for which the emitter has registered
+ listeners. The values in the array are strings or Symbols.
off(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
+
+
+
+
Alias for emitter.removeListener().
+
+
+
since
+
v10.0.0
+
+
+
+
Parameters
+
+
+
eventName: string | symbol
+
+
+
listener: (...args: any[]) => void
+
+
+
+
(...args: any[]): void
+
+
+
+
Parameters
+
+
+
Rest...args: any[]
+
+
+
Returns void
+
+
+
+
+
+
+
Returns this
+
+
+
on
@@ -591,7 +814,7 @@
on
Parameters
@@ -630,7 +853,7 @@
once
Parameters
@@ -658,28 +881,50 @@
Returns this
-
+
prependListener
-
-
prependListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependListener(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v6.0.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -704,28 +949,48 @@
Returns this
-
+
prependOnceListener
-
-
prependOnceListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependOnceListener(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.
Returns a copy of the array of listeners for the event named eventName,
+ including any wrappers (such as those created by .once()).
+
+
const emitter = new EventEmitter();
+emitter.once('log', () => console.log('log once'));
+
+// Returns a new Array with a function `onceWrapper` which has a property
+// `listener` which contains the original listener bound above
+const listeners = emitter.rawListeners('log');
+const logFnWrapper = listeners[0];
+
+// Logs "log once" to the console and does not unbind the `once` event
+logFnWrapper.listener();
+
+// Logs "log once" to the console and removes the listener
+logFnWrapper();
+
+emitter.on('log', () => console.log('log persistently'));
+// Will return a new Array with a single function bound by `.on()` above
+const newListeners = emitter.rawListeners('log');
+
+// Logs "log persistently" twice
+newListeners[0]();
+emitter.emit('log');
+
+
since
+
v9.4.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Returns Function[]
-
+
removeAllListeners
-
+
removeAllListeners(event?: 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.
+
+
since
+
v0.1.26
+
+
+
Parameters
@@ -800,25 +1109,95 @@
Returns this
-
+
removeListener
-
-
removeListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Removes the specified listener from the listener array for the event namedeventName.
removeListener() will remove, at most, one instance of a listener from the
+ listener array. If any single listener has been added multiple times to the
+ listener array for the specified eventName, then removeListener() must be
+ called multiple times to remove each instance.
+
Once an event is emitted, all listeners attached to it at the
+ time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and_before_ the last listener finishes execution will
+ not remove them fromemit() in progress. Subsequent events behave as expected.
+
const myEmitter = new MyEmitter();
+
+const callbackA = () => {
+ console.log('A');
+ myEmitter.removeListener('event', callbackB);
+};
+
+const callbackB = () => {
+ console.log('B');
+};
+
+myEmitter.on('event', callbackA);
+
+myEmitter.on('event', callbackB);
+
+// callbackA removes listener callbackB but it will still be called.
+// Internal listener array at time of emit [callbackA, callbackB]
+myEmitter.emit('event');
+// Prints:
+// A
+// B
+
+// callbackB is now removed.
+// Internal listener array [callbackA]
+myEmitter.emit('event');
+// Prints:
+// A
+
Because listeners are managed using an internal array, calling this will
+ change the position indices of any listener registered after the listener
+ being removed. This will not impact the order in which listeners are called,
+ but it means that any copies of the listener array as returned by
+ the emitter.listeners() method will need to be recreated.
+
When a single function has been added as a handler multiple times for a single
+ event (as in the example below), removeListener() will remove the most
+ recently added instance. In the example the once('ping')listener is removed:
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
listener: (...args: any[]) => void
@@ -856,28 +1235,41 @@
sendGoodbye
Returns Promise<void>
-
+
setMaxListeners
-
+
setMaxListeners(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 toInfinity (or 0) to indicate an unlimited number of listeners.
+
+
Returns a reference to the EventEmitter, so that calls can be chained.
```js
+ const { on, EventEmitter } = require('events');
+
+
(async () => {
+ const ee = new EventEmitter();
+
// Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
for await (const event of on(ee, 'foo')) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+ })();
+
+Returns an `AsyncIterator` that iterates `eventName` events. It will throw
+if the `EventEmitter` emits `'error'`. It removes all listeners when
+exiting the loop. The `value` returned by each iteration is an array
+composed of the emitted event arguments.
+
+An `AbortSignal` can be used to cancel waiting on events:
+
+```js
+const { on, EventEmitter } = require('events');
+const ac = new AbortController();
+
+(async () => {
+ const ee = new EventEmitter();
+
+ // Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
+ forawait (const event of on(ee, 'foo', { signal: ac.signal })) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+})();
+
+process.nextTick(() => ac.abort());
+
+
since
+
v13.6.0, v12.16.0
+
+
+
+
Parameters
+
+
+
emitter: EventEmitter
+
+
+
eventName: string
+
+
The name of the event being listened for
+
+
+
+
Optional options: StaticEventEmitterOptions
+
+
+
Returns AsyncIterableIterator<any>
+
that iterates eventName events emitted by the emitter
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 platformEventTarget interface, which has no special'error' event
+ semantics and does not listen to the 'error' event.
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
+ 'error' event itself, then it is treated as any other kind of event without
+ special handling:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+
+once(ee, 'error')
+ .then(([err]) =>console.log('ok', err.message))
+ .catch((err) =>console.log('error', err.message));
+
+ee.emit('error', newError('boom'));
+
+// Prints: ok boom
+
An AbortSignal can be used to cancel waiting for the event:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+const ac = new AbortController();
+
+asyncfunctionfoo(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!
Sets or gets the default captureRejection value for all emitters.
+
+
@@ -169,32 +242,62 @@
Static defaultMaxListe
+
+
+
Static errorMonitor
+
errorMonitor:keyof 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.
+
+
Methods
-
+
addListener
-
-
addListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this
Synchronously calls each of the listeners registered for the event namedeventName, in the order they were registered, passing the supplied arguments
+ to each.
+
+
Returns true if the event had listeners, false otherwise.
+
const EventEmitter = require('events');
+const myEmitter = new EventEmitter();
+
+// First listener
+myEmitter.on('event', functionfirstListener() {
+ console.log('Helloooo! first listener');
+});
+// Second listener
+myEmitter.on('event', functionsecondListener(arg1, arg2) {
+ console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
+});
+// Third listener
+myEmitter.on('event', functionthirdListener(...args) {
+ const parameters = args.join(', ');
+ console.log(`event with parameters ${parameters} in third listener`);
+});
+
+console.log(myEmitter.listeners('event'));
+
+myEmitter.emit('event', 1, 2, 3, 4, 5);
+
+// Prints:
+// [
+// [Function: firstListener],
+// [Function: secondListener],
+// [Function: thirdListener]
+// ]
+// Helloooo! first listener
+// event with parameters 1, 2 in second listener
+// event with parameters 1, 2, 3, 4, 5 in third listener
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Rest...args: any[]
@@ -267,40 +411,70 @@
Returns boolean
-
+
eventNames
-
+
eventNames(): Array<string | symbol>
+
+
+
Returns an array listing the events for which the emitter has registered
+ listeners. The values in the array are strings or Symbols.
prependListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependListener(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v6.0.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -700,28 +977,48 @@
Returns this
-
+
prependOnceListener
-
-
prependOnceListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependOnceListener(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.
Returns a copy of the array of listeners for the event named eventName,
+ including any wrappers (such as those created by .once()).
+
+
const emitter = new EventEmitter();
+emitter.once('log', () => console.log('log once'));
+
+// Returns a new Array with a function `onceWrapper` which has a property
+// `listener` which contains the original listener bound above
+const listeners = emitter.rawListeners('log');
+const logFnWrapper = listeners[0];
+
+// Logs "log once" to the console and does not unbind the `once` event
+logFnWrapper.listener();
+
+// Logs "log once" to the console and removes the listener
+logFnWrapper();
+
+emitter.on('log', () => console.log('log persistently'));
+// Will return a new Array with a single function bound by `.on()` above
+const newListeners = emitter.rawListeners('log');
+
+// Logs "log persistently" twice
+newListeners[0]();
+emitter.emit('log');
+
+
since
+
v9.4.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Returns Function[]
-
+
removeAllListeners
-
+
removeAllListeners(event?: 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.
+
+
since
+
v0.1.26
+
+
+
Parameters
@@ -796,25 +1137,95 @@
Returns this
-
+
removeListener
-
-
removeListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Removes the specified listener from the listener array for the event namedeventName.
removeListener() will remove, at most, one instance of a listener from the
+ listener array. If any single listener has been added multiple times to the
+ listener array for the specified eventName, then removeListener() must be
+ called multiple times to remove each instance.
+
Once an event is emitted, all listeners attached to it at the
+ time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and_before_ the last listener finishes execution will
+ not remove them fromemit() in progress. Subsequent events behave as expected.
+
const myEmitter = new MyEmitter();
+
+const callbackA = () => {
+ console.log('A');
+ myEmitter.removeListener('event', callbackB);
+};
+
+const callbackB = () => {
+ console.log('B');
+};
+
+myEmitter.on('event', callbackA);
+
+myEmitter.on('event', callbackB);
+
+// callbackA removes listener callbackB but it will still be called.
+// Internal listener array at time of emit [callbackA, callbackB]
+myEmitter.emit('event');
+// Prints:
+// A
+// B
+
+// callbackB is now removed.
+// Internal listener array [callbackA]
+myEmitter.emit('event');
+// Prints:
+// A
+
Because listeners are managed using an internal array, calling this will
+ change the position indices of any listener registered after the listener
+ being removed. This will not impact the order in which listeners are called,
+ but it means that any copies of the listener array as returned by
+ the emitter.listeners() method will need to be recreated.
+
When a single function has been added as a handler multiple times for a single
+ event (as in the example below), removeListener() will remove the most
+ recently added instance. In the example the once('ping')listener is removed:
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
listener: (...args: any[]) => void
@@ -842,21 +1253,34 @@
Returns this
-
+
setMaxListeners
-
+
setMaxListeners(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 toInfinity (or 0) to indicate an unlimited number of listeners.
+
+
Returns a reference to the EventEmitter, so that calls can be chained.
```js
+ const { on, EventEmitter } = require('events');
+
+
(async () => {
+ const ee = new EventEmitter();
+
// Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
for await (const event of on(ee, 'foo')) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+ })();
+
+Returns an `AsyncIterator` that iterates `eventName` events. It will throw
+if the `EventEmitter` emits `'error'`. It removes all listeners when
+exiting the loop. The `value` returned by each iteration is an array
+composed of the emitted event arguments.
+
+An `AbortSignal` can be used to cancel waiting on events:
+
+```js
+const { on, EventEmitter } = require('events');
+const ac = new AbortController();
+
+(async () => {
+ const ee = new EventEmitter();
+
+ // Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
+ forawait (const event of on(ee, 'foo', { signal: ac.signal })) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+})();
+
+process.nextTick(() => ac.abort());
+
+
since
+
v13.6.0, v12.16.0
+
+
+
+
Parameters
+
+
+
emitter: EventEmitter
+
+
+
eventName: string
+
+
The name of the event being listened for
+
+
+
+
Optional options: StaticEventEmitterOptions
+
+
+
Returns AsyncIterableIterator<any>
+
that iterates eventName events emitted by the emitter
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 platformEventTarget interface, which has no special'error' event
+ semantics and does not listen to the 'error' event.
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
+ 'error' event itself, then it is treated as any other kind of event without
+ special handling:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+
+once(ee, 'error')
+ .then(([err]) =>console.log('ok', err.message))
+ .catch((err) =>console.log('error', err.message));
+
+ee.emit('error', newError('boom'));
+
+// Prints: ok boom
+
An AbortSignal can be used to cancel waiting for the event:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+const ac = new AbortController();
+
+asyncfunctionfoo(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!
Sets or gets the default captureRejection value for all emitters.
+
+
+
Static defaultMaxListeners
@@ -132,32 +205,62 @@
Static defaultMaxListe
+
+
+
+
Static errorMonitor
+
errorMonitor:keyof 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.
+
Methods
-
+
addListener
-
-
addListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this
Synchronously calls each of the listeners registered for the event namedeventName, in the order they were registered, passing the supplied arguments
+ to each.
+
+
Returns true if the event had listeners, false otherwise.
+
const EventEmitter = require('events');
+const myEmitter = new EventEmitter();
+
+// First listener
+myEmitter.on('event', functionfirstListener() {
+ console.log('Helloooo! first listener');
+});
+// Second listener
+myEmitter.on('event', functionsecondListener(arg1, arg2) {
+ console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
+});
+// Third listener
+myEmitter.on('event', functionthirdListener(...args) {
+ const parameters = args.join(', ');
+ console.log(`event with parameters ${parameters} in third listener`);
+});
+
+console.log(myEmitter.listeners('event'));
+
+myEmitter.emit('event', 1, 2, 3, 4, 5);
+
+// Prints:
+// [
+// [Function: firstListener],
+// [Function: secondListener],
+// [Function: thirdListener]
+// ]
+// Helloooo! first listener
+// event with parameters 1, 2 in second listener
+// event with parameters 1, 2, 3, 4, 5 in third listener
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Rest...args: any[]
@@ -230,21 +374,41 @@
Returns boolean
-
+
eventNames
-
+
eventNames(): Array<string | symbol>
+
+
+
Returns an array listing the events for which the emitter has registered
+ listeners. The values in the array are strings or Symbols.
off(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
+
+
+
+
Alias for emitter.removeListener().
+
+
+
since
+
v10.0.0
+
+
+
+
Parameters
+
+
+
eventName: string | symbol
+
+
+
listener: (...args: any[]) => void
+
+
+
+
(...args: any[]): void
+
+
+
+
Parameters
+
+
+
Rest...args: any[]
+
+
+
Returns void
+
+
+
+
+
+
+
Returns this
+
+
+
+
on
-
-
on(event: string | symbol, listener: (...args: any[]) => void): this
+
+
on(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
By default, event listeners are invoked in the order they are added. Theemitter.prependListener() method can be used as an alternative to add the
+ event listener to the beginning of the listeners array.
+
const myEE = new EventEmitter();
+myEE.on('foo', () => console.log('a'));
+myEE.prependListener('foo', () => console.log('b'));
+myEE.emit('foo');
+// Prints:
+// b
+// a
+
+
since
+
v0.1.101
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -381,28 +667,57 @@
Returns this
-
+
once
-
-
once(event: string | symbol, listener: (...args: any[]) => void): this
+
+
once(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Adds a one-timelistener function for the event named eventName. The
+ next time eventName is triggered, this listener is removed and then invoked.
+
+
server.once('connection', (stream) => {
+ console.log('Ah, we have our first user!');
+});
+
Returns a reference to the EventEmitter, so that calls can be chained.
+
By default, event listeners are invoked in the order they are added. Theemitter.prependOnceListener() method can be used as an alternative to add the
+ event listener to the beginning of the listeners array.
+
const myEE = new EventEmitter();
+myEE.once('foo', () => console.log('a'));
+myEE.prependOnceListener('foo', () => console.log('b'));
+myEE.emit('foo');
+// Prints:
+// b
+// a
+
+
since
+
v0.3.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -427,28 +742,50 @@
Returns this
-
+
prependListener
-
-
prependListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependListener(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 eventNameand listener will result in the listener being added, and called, multiple
+ times.
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v6.0.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
+
+
The name of the event.
+
listener: (...args: any[]) => void
+
+
The callback function
+
@@ -473,28 +810,48 @@
Returns this
-
+
prependOnceListener
-
-
prependOnceListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
prependOnceListener(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.
Returns a copy of the array of listeners for the event named eventName,
+ including any wrappers (such as those created by .once()).
+
+
const emitter = new EventEmitter();
+emitter.once('log', () => console.log('log once'));
+
+// Returns a new Array with a function `onceWrapper` which has a property
+// `listener` which contains the original listener bound above
+const listeners = emitter.rawListeners('log');
+const logFnWrapper = listeners[0];
+
+// Logs "log once" to the console and does not unbind the `once` event
+logFnWrapper.listener();
+
+// Logs "log once" to the console and removes the listener
+logFnWrapper();
+
+emitter.on('log', () => console.log('log persistently'));
+// Will return a new Array with a single function bound by `.on()` above
+const newListeners = emitter.rawListeners('log');
+
+// Logs "log persistently" twice
+newListeners[0]();
+emitter.emit('log');
+
+
since
+
v9.4.0
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
Returns Function[]
-
+
removeAllListeners
-
+
removeAllListeners(event?: 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.
+
+
since
+
v0.1.26
+
+
+
Parameters
@@ -592,25 +993,95 @@
Returns this
-
+
removeListener
-
-
removeListener(event: string | symbol, listener: (...args: any[]) => void): this
+
+
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this
+
+
+
Removes the specified listener from the listener array for the event namedeventName.
removeListener() will remove, at most, one instance of a listener from the
+ listener array. If any single listener has been added multiple times to the
+ listener array for the specified eventName, then removeListener() must be
+ called multiple times to remove each instance.
+
Once an event is emitted, all listeners attached to it at the
+ time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and_before_ the last listener finishes execution will
+ not remove them fromemit() in progress. Subsequent events behave as expected.
+
const myEmitter = new MyEmitter();
+
+const callbackA = () => {
+ console.log('A');
+ myEmitter.removeListener('event', callbackB);
+};
+
+const callbackB = () => {
+ console.log('B');
+};
+
+myEmitter.on('event', callbackA);
+
+myEmitter.on('event', callbackB);
+
+// callbackA removes listener callbackB but it will still be called.
+// Internal listener array at time of emit [callbackA, callbackB]
+myEmitter.emit('event');
+// Prints:
+// A
+// B
+
+// callbackB is now removed.
+// Internal listener array [callbackA]
+myEmitter.emit('event');
+// Prints:
+// A
+
Because listeners are managed using an internal array, calling this will
+ change the position indices of any listener registered after the listener
+ being removed. This will not impact the order in which listeners are called,
+ but it means that any copies of the listener array as returned by
+ the emitter.listeners() method will need to be recreated.
+
When a single function has been added as a handler multiple times for a single
+ event (as in the example below), removeListener() will remove the most
+ recently added instance. In the example the once('ping')listener is removed:
Returns a reference to the EventEmitter, so that calls can be chained.
+
+
since
+
v0.1.26
+
+
+
Parameters
-
event: string | symbol
+
eventName: string | symbol
listener: (...args: any[]) => void
@@ -648,7 +1119,7 @@
respond
Parameters
@@ -661,21 +1132,34 @@
Returns Promise
-
+
setMaxListeners
-
+
setMaxListeners(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 toInfinity (or 0) to indicate an unlimited number of listeners.
+
+
Returns a reference to the EventEmitter, so that calls can be chained.
```js
+ const { on, EventEmitter } = require('events');
+
+
(async () => {
+ const ee = new EventEmitter();
+
// Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
for await (const event of on(ee, 'foo')) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+ })();
+
+Returns an `AsyncIterator` that iterates `eventName` events. It will throw
+if the `EventEmitter` emits `'error'`. It removes all listeners when
+exiting the loop. The `value` returned by each iteration is an array
+composed of the emitted event arguments.
+
+An `AbortSignal` can be used to cancel waiting on events:
+
+```js
+const { on, EventEmitter } = require('events');
+const ac = new AbortController();
+
+(async () => {
+ const ee = new EventEmitter();
+
+ // Emit later on
+ process.nextTick(() => {
+ ee.emit('foo', 'bar');
+ ee.emit('foo', 42);
+ });
+
+ forawait (const event of on(ee, 'foo', { signal: ac.signal })) {
+ // The execution of this inner block is synchronous and it
+ // processes one event at a time (even with await). Do not use
+ // if concurrent execution is required.
+ console.log(event); // prints ['bar'] [42]
+ }
+ // Unreachable here
+})();
+
+process.nextTick(() => ac.abort());
+
+
since
+
v13.6.0, v12.16.0
+
+
+
+
Parameters
+
+
+
emitter: EventEmitter
+
+
+
eventName: string
+
+
The name of the event being listened for
+
+
+
+
Optional options: StaticEventEmitterOptions
+
+
+
Returns AsyncIterableIterator<any>
+
that iterates eventName events emitted by the emitter
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 platformEventTarget interface, which has no special'error' event
+ semantics and does not listen to the 'error' event.
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
+ 'error' event itself, then it is treated as any other kind of event without
+ special handling:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+
+once(ee, 'error')
+ .then(([err]) =>console.log('ok', err.message))
+ .catch((err) =>console.log('error', err.message));
+
+ee.emit('error', newError('boom'));
+
+// Prints: ok boom
+
An AbortSignal can be used to cancel waiting for the event:
+
const { EventEmitter, once } = require('events');
+
+const ee = new EventEmitter();
+const ac = new AbortController();
+
+asyncfunctionfoo(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!
Sets or gets the default captureRejection value for all emitters.
+