Private
Readonly
#auth
Private
#private_Private
#public_Private
Readonly
#signPrivate
Readonly
#symbol
Private
Readonly
#ws_Static
Readonly
captureValue: Symbol.for('nodejs.rejection')
See how to write a custom rejection handler
.
v13.4.0, v12.16.0
Static
captureValue: boolean
Change the default captureRejections
option on all
new EventEmitter
objects.
v13.4.0, v12.16.0
Static
default
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 allEventEmitter
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
singleEventEmitter
, 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'
.
v0.11.2
Static
Readonly
error
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.
v13.6.0, v12.17.0
Private WebSocket
Public WebSocket
Private
#connectWS
Private
#getPrivate
#ping
Private
#send
Private
#sendPrivate
#unsubscribeOptional
[captureAuthenticate to the private websocket.
Returns an array listing the events for which the emitter
has registered listeners. The values in the array are
strings or Symbol
s.
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) ]
v6.0.0
Returns the current max listener value for the
EventEmitter
which is either set by
emitter.setMaxListeners(n)
or defaults to
defaultMaxListeners.
v1.0.0
Get the list of current private subscriptions.
Get the list of current public subscriptions.
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.
The name of the event being listened for
Optional
listener:
Function
The event handler function
v3.2.0
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] ]
v0.1.26
Alias for emitter.removeListener()
.
Rest
...args:
any[]
v10.0.0
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');
v9.4.0
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.
Optional
event:
string | symbol
v0.1.26
Removes the specified listener
from the
listener array for the event namedeventName
.
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
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.
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:
// 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:
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.
Rest
...args:
any[]
v0.1.26
Send a message to the WebSocket server
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
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.
v0.3.5
Subscribe to the balances
channel.
Subscribe to the book
channel.
Subscribe to the channel
(candles).
Subscribe to the book_lv2
channel.
Subscribe to the orders
channel.
Subscribe to the ticker
channel.
Subscribe to the trades
channel.
Unsubscribe from the balances
channel.
Unsubscribe from the book
channel.
Unsubscribe from the channel
(candles).
Unsubscribe from the book_lv2
channel.
Unsubscribe from the orders
channel.
Unsubscribe from all public channels.
Unsubscribe from all public channels.
Unsubscribe from the ticker
channel.
Unsubscribe from the trades
channel.
Static
Private
#disconnectWS
Static
addExperimental
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 AbortSignal
s 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]();
}
}
Disposable that removes the abort
listener.
v20.5.0
Static
get
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.
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] ]
}
v15.2.0, v14.17.0
Static
getReturns the currently set max amount of listeners.
For EventEmitter
s this behaves exactly the same
as calling .getMaxListeners
on the emitter.
For EventTarget
s 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
}
v19.9.0
Static
listener
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: 2
The emitter to query
The event name
v0.9.12
Since v3.2.0 - Use listenerCount
instead.
Static
on
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 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';
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());
The name of the event being listened for
Optional
options:
StaticEventEmitterOptions
that iterates eventName
events emitted by the
emitter
v13.6.0, v12.16.0
Static
once
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 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:
StaticEventEmitterOptions
v11.13.0, v10.16.0
Optional
options:
StaticEventEmitterOptions
Static
setimport { setMaxListeners, EventEmitter } from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
Optional
n:
number
A non-negative number. The maximum number of listeners
per EventTarget
event.
Rest
...eventTargets:
(EventEmitter | _DOMEventTarget)[]
v15.4.0
Create WebSocketClient.