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.
Add a cursor flag to the cursor
The flag to set, must be one of following ['tailable', 'oplogReplay', 'noCursorTimeout', 'awaitData', 'partial' -.
The flag boolean value.
Add a query modifier to the cursor query
The query modifier (must start with $, such as $orderby etc)
The modifier value.
Allows disk use for blocking sort operations exceeding 100MB memory. (MongoDB 3.2 or higher)
Set the batch size for the cursor.
The number of documents to return per batch. See find command documentation.
Returns current buffered documents length
Returns a new uninitialized copy of this cursor, with options matching those that have been set on the current instance
Set the collation options for the cursor.
The cursor collation options (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
Add a comment to the cursor query allowing for tracking the comment in the log.
The comment attached to this query.
Get the count of documents for this cursor
Execute the explain for the cursor
Set the cursor query
Iterates over all the documents for this cursor using the iterator, callback pattern.
The iteration callback.
Set the cursor hint
If specified, then the query system will only consider plans using the hinted index.
Set the limit for the cursor.
The limit for the cursor query.
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.
Set the cursor max
Specify a $max value to specify the exclusive upper bound for a specific index in order to constrain the results of find(). The $max specifies the upper bound for all keys of a specific index in order.
Set a maxAwaitTimeMS on a tailing cursor query to allow to customize the timeout value for the option awaitData (Only supported on MongoDB 3.2 or higher, ignored otherwise)
Number of milliseconds to wait before aborting the tailed query.
Set a maxTimeMS on the cursor query, allowing for hard timeout limits on queries (Only supported on MongoDB 2.6 or higher)
Number of milliseconds to wait before aborting the query.
Set the cursor min
Specify a $min value to specify the inclusive lower bound for a specific index in order to constrain the results of find(). The $min specifies the lower bound for all keys of a specific index in order.
Add a project stage to the aggregation pipeline
Returns current buffered documents
Set the cursor returnKey. If set to true, modifies the cursor to only return the index field or fields for the results of the query, rather than documents. If set to true and the query does not use an index to perform the read operation, the returned documents will not contain any fields.
the returnKey value.
Rewind this cursor to its uninitialized state. Any options that are present on the cursor will remain in effect. Iterating this cursor will cause new queries to be sent to the server, even if the resultant data has already been retrieved by this cursor.
Modifies the output of a query by adding a field $recordId to matching documents. $recordId is the internal key which uniquely identifies a document in a collection.
The $showDiskLoc option has now been deprecated and replaced with the showRecordId field. $showDiskLoc will still be accepted for OP_QUERY stye find.
Set the skip for the cursor.
The skip for the cursor query.
Sets the sort order of the cursor query.
The key or keys set for the sort.
The direction of the sorting (1 or -1).
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.
Try to get the next available document from the cursor or null
if an empty batch is returned
Set the ReadPreference for the cursor.
Set the ReadPreference for the cursor.
The new read preference for the cursor.
Returns a copy of the array of listeners for the event named eventName
.
For EventEmitter
s this behaves exactly the same as calling .listeners
on
the emitter.
For EventTarget
s this is the only way to get the event listeners for the
event target. This is useful for debugging and diagnostic purposes.
const { getEventListeners, EventEmitter } = require('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]
}
A class method that returns the number of listeners for the given eventName
registered on the given emitter
.
const { EventEmitter, listenerCount } = require('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
```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);
});
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
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 platform EventTarget interface, which has no special'error'
event
semantics and does not listen to the 'error'
event.
const { once, EventEmitter } = require('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:
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', new Error('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();
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!
By default EventEmitter
s 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 EventEmitter.setMaxListeners()
method allows the default limit to be
modified (if eventTargets is empty) or modify the limit specified in every EventTarget
| EventEmitter
passed as arguments.
The value can be set toInfinity
(or 0
) to indicate an unlimited number of listeners.
EventEmitter.setMaxListeners(20);
// Equivalent to
EventEmitter.defaultMaxListeners = 20;
const eventTarget = new EventTarget();
// Only way to increase limit for `EventTarget` instances
// as these doesn't expose its own `setMaxListeners` method
EventEmitter.setMaxListeners(20, eventTarget);
Generated using TypeDoc
Sets or gets the default captureRejection value for all emitters.