Optional options: EventEmitterOptionsOptional Readonly commandReadonly getOptional batchOptional comment?: anyOptional maxStatic Readonly captureStatic captureStatic defaultStatic Readonly errorThis 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.
Optional [captureRest ...args: Parameters<AbstractCursorEvents[EventKey]>Rest Iterates over all the documents for this cursor using the iterator, callback pattern.
If the iterator returns false, iteration will stop.
The iteration callback.
Map all documents using the provided function If there is a transform set on the cursor, that will be called first and the result passed to this function's transform.
The mapping transformation method.
Note Cursors use null internally to indicate that there are no more documents in the cursor. Providing a mapping
function that maps values to null will result in the cursor closing itself before it has finished iterating
all documents. This will not result in a memory leak, just surprising behavior. For example:
const cursor = collection.find({});
cursor.map(() => null);
const documents = await cursor.toArray();
// documents is always [], regardless of how many documents are in the collection.
Other falsey values are allowed:
const cursor = collection.find({});
cursor.map(() => '');
const documents = await cursor.toArray();
// documents is now an array of empty strings
Note for Typescript Users: adding a transform changes the return type of the iteration of this cursor, it does not return a new instance of a cursor. This means when calling map, you should always assign the result to a new variable in order to get a correctly typed cursor variable. Take note of the following example:
const cursor: FindCursor<Document> = coll.find();
const mappedCursor: FindCursor<number> = cursor.map(doc => Object.keys(doc).length);
const keyCounts: number[] = await mappedCursor.toArray(); // cursor.toArray() still returns Document[]
Optional event: string | symbol | EventKeyOptional Controls the getMore.batchSize field
Controls the getMore.comment field
any BSON value
Controls the getMore.maxTimeMS field. Only valid when cursor is tailable await
the number of milliseconds to wait for new data
Optional options: CursorStreamOptionsOptional Returns an array of documents. The caller is responsible for making sure that there is enough memory to store the results. Note that the array only contains partial results when this cursor had been previously accessed. In that case, cursor.rewind() can be used to reset the cursor.
Set the ReadPreference for the cursor.
The new read preference for the cursor.
Static getReturns 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);
getEventListeners(ee, 'foo'); // [listener]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
getEventListeners(et, 'foo'); // [listener]
}
v15.2.0
Static listenerA class method that returns the number of listeners for the given eventNameregistered 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: 2
The emitter to query
The event name
v0.9.12
Since v3.2.0 - Use listenerCount instead.
Static onimport { on, EventEmitter } from 'node: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:
import { on, EventEmitter } from 'node:events';
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());
The name of the event being listened for
Optional options: StaticEventEmitterOptionsOptional that iterates eventName events emitted by the emitter
v13.6.0, v12.16.0
Static onceCreates 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';
async function run() {
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.log('error happened', err);
}
}
run();
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.log('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
An AbortSignal can be used to cancel waiting for the event:
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
Optional options: StaticEventEmitterOptionsOptional v11.13.0, v10.16.0
Optional options: StaticEventEmitterOptionsOptional Static setimport {
setMaxListeners,
EventEmitter
} from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
Optional n: numberA non-negative number. The maximum number of listeners per EventTarget event.
Optional Rest ...eventTargets: (EventEmitter<DefaultEventMap> | DOMEventTarget)[]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.
Rest v15.4.0
Static Readonly CLOSEGenerated using TypeDoc
Sets or gets the default captureRejection value for all emitters.