This class is used to create a TCP or IPC
server.
class
net.Server
class Server
- maxConnections: number
Set this property to reject connections when the server's connection count gets high.
It is not recommended to use this option once a socket has been sent to a child with
child_process.fork()
. - static captureRejections: boolean
Value: boolean
Change the default
captureRejections
option on all newEventEmitter
objects. - readonly static captureRejectionSymbol: typeof captureRejectionSymbol
Value:
Symbol.for('nodejs.rejection')
See how to write a custom
rejection handler
. - static defaultMaxListeners: number
By default, a maximum of
10
listeners can be registered for any single event. This limit can be changed for individualEventEmitter
instances using theemitter.setMaxListeners(n)
method. To change the default for allEventEmitter
instances, theevents.defaultMaxListeners
property can be used. If this value is not a positive number, aRangeError
is thrown.Take caution when setting the
events.defaultMaxListeners
because the change affects allEventEmitter
instances, including those created before the change is made. However, callingemitter.setMaxListeners(n)
still has precedence overevents.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
, theemitter.getMaxListeners()
andemitter.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 additionalemitter
,type
, andcount
properties, referring to the event emitter instance, the event's name and the number of attached listeners, respectively. Itsname
property is set to'MaxListenersExceededWarning'
. - readonly static errorMonitor: typeof errorMonitor
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. Calls () and returns a promise that fulfills when the server has closed.
- event: string,listener: (...args: any[]) => void): this;
events.EventEmitter
- close
- connection
- error
- listening
- drop
event: 'close',listener: () => void): this;events.EventEmitter
- close
- connection
- error
- listening
- drop
event: 'connection',): this;events.EventEmitter
- close
- connection
- error
- listening
- drop
event: 'error',): this;events.EventEmitter
- close
- connection
- error
- listening
- drop
event: 'listening',listener: () => void): this;events.EventEmitter
- close
- connection
- error
- listening
- drop
event: 'drop',): this;events.EventEmitter
- close
- connection
- error
- listening
- drop
Returns the bound
address
, the addressfamily
name, andport
of the server as reported by the operating system if listening on an IP socket (useful to find which port was assigned when getting an OS-assigned address):{ port: 12346, family: 'IPv4', address: '127.0.0.1' }
.For a server listening on a pipe or Unix domain socket, the name is returned as a string.
const server = net.createServer((socket) => { socket.end('goodbye\n'); }).on('error', (err) => { // Handle errors here. throw err; }); // Grab an arbitrary unused port. server.listen(() => { console.log('opened server on', server.address()); });
server.address()
returnsnull
before the'listening'
event has been emitted or after callingserver.close()
.- ): this;
Stops the server from accepting new connections and keeps existing connections. This function is asynchronous, the server is finally closed when all connections are ended and the server emits a
'close'
event. The optionalcallback
will be called once the'close'
event occurs. Unlike that event, it will be called with anError
as its only argument if the server was not open when it was closed.@param callbackCalled when the server is closed.
- emit(event: string | symbol,...args: any[]): boolean;
Synchronously calls each of the listeners registered for the event named
eventName
, in the order they were registered, passing the supplied arguments to each.Returns
true
if the event had listeners,false
otherwise.import { EventEmitter } from 'node:events'; const myEmitter = new EventEmitter(); // First listener myEmitter.on('event', function firstListener() { console.log('Helloooo! first listener'); }); // Second listener myEmitter.on('event', function secondListener(arg1, arg2) { console.log(`event with parameters ${arg1}, ${arg2} in second listener`); }); // Third listener myEmitter.on('event', function thirdListener(...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
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) ]
- ): void;
Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks.
Callback should take two arguments
err
andcount
. Returns the current max listener value for the
EventEmitter
which is either set byemitter.setMaxListeners(n)
or defaults to EventEmitter.defaultMaxListeners.- port?: number,hostname?: string,backlog?: number,listeningListener?: () => void): this;
Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
port?: number,hostname?: string,listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
port?: number,backlog?: number,listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
port?: number,listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
path: string,backlog?: number,listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
path: string,listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
handle: any,backlog?: number,listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
handle: any,listeningListener?: () => void): this;Start a server listening for connections. A
net.Server
can be a TCP or anIPC
server depending on what it listens to.Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback])
forIPC
serversserver.listen([port[, host[, backlog]]][, callback])
for TCP servers
This function is asynchronous. When the server starts listening, the
'listening'
event will be emitted. The last parametercallback
will be added as a listener for the'listening'
event.All
listen()
methods can take abacklog
parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such astcp_max_syn_backlog
andsomaxconn
on Linux. The default value of this parameter is 511 (not 512).All Socket are set to
SO_REUSEADDR
(seesocket(7)
for details).The
server.listen()
method can be called again if and only if there was an error during the firstserver.listen()
call orserver.close()
has been called. Otherwise, anERR_SERVER_ALREADY_LISTEN
error will be thrown.One of the most common errors raised when listening is
EADDRINUSE
. This happens when another server is already listening on the requestedport
/path
/handle
. One way to handle this would be to retry after a certain amount of time:server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
- eventName: string | symbol,listener?: Function): number;
Returns the number of listeners listening for the event named
eventName
. Iflistener
is provided, it will return how many times the listener is found in the list of the listeners of the event.@param eventNameThe name of the event being listened for
@param listenerThe event handler function
- eventName: string | symbol): Function[];
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] ]
- eventName: string | symbol,listener: (...args: any[]) => void): this;
Alias for
emitter.removeListener()
. - on(event: string,listener: (...args: any[]) => void): this;
Adds the
listener
function to the end of the listeners array for the event namedeventName
. No checks are made to see if thelistener
has already been added. Multiple calls passing the same combination ofeventName
andlistener
will result in thelistener
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 // a
@param listenerThe callback function
- once(event: string,listener: (...args: any[]) => void): this;
Adds a one-time
listener
function for the event namedeventName
. The next timeeventName
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 // a
@param listenerThe callback function
- event: string,listener: (...args: any[]) => void): this;
Adds the
listener
function to the beginning of the listeners array for the event namedeventName
. No checks are made to see if thelistener
has already been added. Multiple calls passing the same combination ofeventName
andlistener
will result in thelistener
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.@param listenerThe callback function
- event: string,listener: (...args: any[]) => void): this;
Adds a one-time
listener
function for the event namedeventName
to the beginning of the listeners array. The next timeeventName
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.@param listenerThe callback function
- eventName: string | symbol): Function[];
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');
Opposite of
unref()
, callingref()
on a previouslyunref
ed server will not let the program exit if it's the only server left (the default behavior). If the server isref
ed callingref()
again will have no effect.- eventName?: 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. - eventName: string | symbol,listener: (...args: any[]) => void): this;
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 specifiedeventName
, thenremoveListener()
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()
orremoveAllListeners()
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 theonce('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. - n: number): this;
By default
EventEmitter
s will print a warning if more than10
listeners are added for a particular event. This is a useful default that helps finding memory leaks. Theemitter.setMaxListeners()
method allows the limit to be modified for this specificEventEmitter
instance. The value can be set toInfinity
(or0
) to indicate an unlimited number of listeners.Returns a reference to the
EventEmitter
, so that calls can be chained. Calling
unref()
on a server will allow the program to exit if this is the only active server in the event system. If the server is alreadyunref
ed callingunref()
again will have no effect.- ): Disposable;
Listens once to the
abort
event on the providedsignal
.Listening to the
abort
event on abort signals is unsafe and may lead to resource leaks since another third party with the signal can calle.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 thatstopImmediatePropagation
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](); } }
@returnsDisposable that removes the
abort
listener. - name: string | symbol): Function[];
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] ] }
- ): number;
Returns 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 }
- emitter: EventEmitter,eventName: string | symbol,options?: StaticEventEmitterIteratorOptions): AsyncIterator<any[]>;
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 iterateseventName
events. It will throw if theEventEmitter
emits'error'
. It removes all listeners when exiting the loop. Thevalue
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'
@returnsAn
AsyncIterator
that iterateseventName
events emitted by theemitter
eventName: string,options?: StaticEventEmitterIteratorOptions): AsyncIterator<any[]>;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 iterateseventName
events. It will throw if theEventEmitter
emits'error'
. It removes all listeners when exiting the loop. Thevalue
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'
@returnsAn
AsyncIterator
that iterateseventName
events emitted by theemitter
- emitter: EventEmitter,eventName: string | symbol,options?: StaticEventEmitterOptions): Promise<any[]>;
Creates a
Promise
that is fulfilled when theEventEmitter
emits the given event or that is rejected if theEventEmitter
emits'error'
while waiting. ThePromise
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 whenevents.once()
is used to wait for another event. Ifevents.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!
eventName: string,options?: StaticEventEmitterOptions): Promise<any[]>;Creates a
Promise
that is fulfilled when theEventEmitter
emits the given event or that is rejected if theEventEmitter
emits'error'
while waiting. ThePromise
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 whenevents.once()
is used to wait for another event. Ifevents.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!
- n?: number,): void;
import { setMaxListeners, EventEmitter } from 'node:events'; const target = new EventTarget(); const emitter = new EventEmitter(); setMaxListeners(5, target, emitter);
@param nA non-negative number. The maximum number of listeners per
EventTarget
event.@param eventTargetsZero 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.