Welshman Docs / @welshman/net / Relays
Class: Relays ​
Defined in: packages/net/src/target/Relays.ts:6
Extended EventEmitter that also emits all events to '*' listeners
Extends ​
Constructors ​
new Relays() ​
new Relays(
connections):Relays
Defined in: packages/net/src/target/Relays.ts:7
Parameters ​
connections ​
Returns ​
Overrides ​
Properties ​
connections ​
readonlyconnections:Connection[]
Defined in: packages/net/src/target/Relays.ts:7
captureRejections ​
staticcaptureRejections:boolean
Defined in: node_modules/@types/node/events.d.ts:459
Value: boolean
Change the default captureRejections option on all new EventEmitter objects.
Since ​
v13.4.0, v12.16.0
Inherited from ​
captureRejectionSymbol ​
readonlystaticcaptureRejectionSymbol: typeofcaptureRejectionSymbol
Defined in: node_modules/@types/node/events.d.ts:452
Value: Symbol.for('nodejs.rejection')
See how to write a custom rejection handler.
Since ​
v13.4.0, v12.16.0
Inherited from ​
Emitter.captureRejectionSymbol
defaultMaxListeners ​
staticdefaultMaxListeners:number
Defined in: node_modules/@types/node/events.d.ts:498
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'.
Since ​
v0.11.2
Inherited from ​
errorMonitor ​
readonlystaticerrorMonitor: typeoferrorMonitor
Defined in: node_modules/@types/node/events.d.ts:445
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.
Since ​
v13.6.0, v12.17.0
Inherited from ​
Methods ​
[captureRejectionSymbol]()? ​
optional[captureRejectionSymbol]<K>(error,event, ...args):void
Defined in: node_modules/@types/node/events.d.ts:136
Type Parameters ​
• K
Parameters ​
error ​
Error
event ​
string | symbol
args ​
...AnyRest
Returns ​
void
Inherited from ​
Emitter.[captureRejectionSymbol]
addListener() ​
addListener<
K>(eventName,listener):this
Defined in: node_modules/@types/node/events.d.ts:597
Alias for emitter.on(eventName, listener).
Type Parameters ​
• K
Parameters ​
eventName ​
string | symbol
listener ​
(...args) => void
Returns ​
this
Since ​
v0.1.26
Inherited from ​
cleanup() ​
cleanup():
void
Defined in: packages/net/src/target/Relays.ts:23
Returns ​
void
emit() ​
emit(
type, ...args):boolean
Defined in: packages/lib/build/src/Emitter.d.ts:12
Emits an event to listeners and to '*' listeners
Parameters ​
type ​
string
Event type/name
args ​
...any[]
Arguments to pass to listeners
Returns ​
boolean
True if event had listeners
Inherited from ​
eventNames() ​
eventNames(): (
string|symbol)[]
Defined in: node_modules/@types/node/events.d.ts:922
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) ]Returns ​
(string | symbol)[]
Since ​
v6.0.0
Inherited from ​
getMaxListeners() ​
getMaxListeners():
number
Defined in: node_modules/@types/node/events.d.ts:774
Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to EventEmitter.defaultMaxListeners.
Returns ​
number
Since ​
v1.0.0
Inherited from ​
listenerCount() ​
listenerCount<
K>(eventName,listener?):number
Defined in: node_modules/@types/node/events.d.ts:868
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.
Type Parameters ​
• K
Parameters ​
eventName ​
The name of the event being listened for
string | symbol
listener? ​
Function
The event handler function
Returns ​
number
Since ​
v3.2.0
Inherited from ​
listeners() ​
listeners<
K>(eventName):Function[]
Defined in: node_modules/@types/node/events.d.ts:787
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] ]Type Parameters ​
• K
Parameters ​
eventName ​
string | symbol
Returns ​
Function[]
Since ​
v0.1.26
Inherited from ​
off() ​
off<
K>(eventName,listener):this
Defined in: node_modules/@types/node/events.d.ts:747
Alias for emitter.removeListener().
Type Parameters ​
• K
Parameters ​
eventName ​
string | symbol
listener ​
(...args) => void
Returns ​
this
Since ​
v10.0.0
Inherited from ​
on() ​
on<
K>(eventName,listener):this
Defined in: node_modules/@types/node/events.d.ts:629
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
// aType Parameters ​
• K
Parameters ​
eventName ​
The name of the event.
string | symbol
listener ​
(...args) => void
The callback function
Returns ​
this
Since ​
v0.1.101
Inherited from ​
once() ​
once<
K>(eventName,listener):this
Defined in: node_modules/@types/node/events.d.ts:659
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
// aType Parameters ​
• K
Parameters ​
eventName ​
The name of the event.
string | symbol
listener ​
(...args) => void
The callback function
Returns ​
this
Since ​
v0.3.0
Inherited from ​
onMessage() ​
onMessage(
connection,__namedParameters):void
Defined in: packages/net/src/target/Relays.ts:19
Parameters ​
connection ​
__namedParameters ​
Returns ​
void
prependListener() ​
prependListener<
K>(eventName,listener):this
Defined in: node_modules/@types/node/events.d.ts:886
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.
Type Parameters ​
• K
Parameters ​
eventName ​
The name of the event.
string | symbol
listener ​
(...args) => void
The callback function
Returns ​
this
Since ​
v6.0.0
Inherited from ​
prependOnceListener() ​
prependOnceListener<
K>(eventName,listener):this
Defined in: node_modules/@types/node/events.d.ts:902
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.
Type Parameters ​
• K
Parameters ​
eventName ​
The name of the event.
string | symbol
listener ​
(...args) => void
The callback function
Returns ​
this
Since ​
v6.0.0
Inherited from ​
rawListeners() ​
rawListeners<
K>(eventName):Function[]
Defined in: node_modules/@types/node/events.d.ts:818
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');Type Parameters ​
• K
Parameters ​
eventName ​
string | symbol
Returns ​
Function[]
Since ​
v9.4.0
Inherited from ​
removeAllListeners() ​
removeAllListeners(
eventName?):this
Defined in: node_modules/@types/node/events.d.ts:758
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.
Parameters ​
eventName? ​
string | symbol
Returns ​
this
Since ​
v0.1.26
Inherited from ​
removeListener() ​
removeListener<
K>(eventName,listener):this
Defined in: node_modules/@types/node/events.d.ts:742
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:
// ABecause 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.
Type Parameters ​
• K
Parameters ​
eventName ​
string | symbol
listener ​
(...args) => void
Returns ​
this
Since ​
v0.1.26
Inherited from ​
send() ​
send(...
payload):Promise<void>
Defined in: packages/net/src/target/Relays.ts:15
Parameters ​
payload ​
...Message
Returns ​
Promise<void>
setMaxListeners() ​
setMaxListeners(
n):this
Defined in: node_modules/@types/node/events.d.ts:768
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.
Parameters ​
n ​
number
Returns ​
this
Since ​
v0.3.5
Inherited from ​
addAbortListener() ​
staticaddAbortListener(signal,resource):Disposable
Defined in: node_modules/@types/node/events.d.ts:437
Experimental
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]();
}
}Parameters ​
signal ​
AbortSignal
resource ​
(event) => void
Returns ​
Disposable
Disposable that removes the abort listener.
Since ​
v20.5.0
Inherited from ​
getEventListeners() ​
staticgetEventListeners(emitter,name):Function[]
Defined in: node_modules/@types/node/events.d.ts:358
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] ]
}Parameters ​
emitter ​
EventTarget | EventEmitter<DefaultEventMap>
name ​
string | symbol
Returns ​
Function[]
Since ​
v15.2.0, v14.17.0
Inherited from ​
getMaxListeners() ​
staticgetMaxListeners(emitter):number
Defined in: node_modules/@types/node/events.d.ts:387
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
}Parameters ​
emitter ​
EventTarget | EventEmitter<DefaultEventMap>
Returns ​
number
Since ​
v19.9.0
Inherited from ​
listenerCount() ​
staticlistenerCount(emitter,eventName):number
Defined in: node_modules/@types/node/events.d.ts:330
A class method that returns the number of listeners for the given eventName registered on the given emitter.
import { EventEmitter, listenerCount } from 'node:events';
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2Parameters ​
emitter ​
EventEmitter
The emitter to query
eventName ​
The event name
string | symbol
Returns ​
number
Since ​
v0.9.12
Deprecated ​
Since v3.2.0 - Use listenerCount instead.
Inherited from ​
on() ​
Call Signature ​
staticon(emitter,eventName,options?):AsyncIterator<any[]>
Defined in: node_modules/@types/node/events.d.ts:303
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 hereReturns 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'Parameters ​
emitter ​
EventEmitter
eventName ​
string | symbol
options? ​
StaticEventEmitterIteratorOptions
Returns ​
AsyncIterator<any[]>
An AsyncIterator that iterates eventName events emitted by the emitter
Since ​
v13.6.0, v12.16.0
Inherited from ​
Call Signature ​
staticon(emitter,eventName,options?):AsyncIterator<any[]>
Defined in: node_modules/@types/node/events.d.ts:308
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 hereReturns 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'Parameters ​
emitter ​
EventTarget
eventName ​
string
options? ​
StaticEventEmitterIteratorOptions
Returns ​
AsyncIterator<any[]>
An AsyncIterator that iterates eventName events emitted by the emitter
Since ​
v13.6.0, v12.16.0
Inherited from ​
once() ​
Call Signature ​
staticonce(emitter,eventName,options?):Promise<any[]>
Defined in: node_modules/@types/node/events.d.ts:217
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 boomAn 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!Parameters ​
emitter ​
EventEmitter
eventName ​
string | symbol
options? ​
StaticEventEmitterOptions
Returns ​
Promise<any[]>
Since ​
v11.13.0, v10.16.0
Inherited from ​
Call Signature ​
staticonce(emitter,eventName,options?):Promise<any[]>
Defined in: node_modules/@types/node/events.d.ts:222
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 boomAn 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!Parameters ​
emitter ​
EventTarget
eventName ​
string
options? ​
StaticEventEmitterOptions
Returns ​
Promise<any[]>
Since ​
v11.13.0, v10.16.0
Inherited from ​
setMaxListeners() ​
staticsetMaxListeners(n?, ...eventTargets?):void
Defined in: node_modules/@types/node/events.d.ts:402
import { setMaxListeners, EventEmitter } from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);Parameters ​
n? ​
number
A non-negative number. The maximum number of listeners per EventTarget event.
eventTargets? ​
...(EventTarget | EventEmitter<DefaultEventMap>)[]
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.
Returns ​
void
Since ​
v15.4.0