Class: Namespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData>

A Namespace is a communication channel that allows you to split the logic of your application over a single shared connection.

Each namespace has its own:

• event handlers

io.of("/orders").on("connection", (socket) => {
  socket.on("order:list", () => {});
  socket.on("order:create", () => {});
});

io.of("/users").on("connection", (socket) => {
  socket.on("user:list", () => {});
});

• rooms

const orderNamespace = io.of("/orders");

orderNamespace.on("connection", (socket) => {
  socket.join("room1");
  orderNamespace.to("room1").emit("hello");
});

const userNamespace = io.of("/users");

userNamespace.on("connection", (socket) => {
  socket.join("room1"); // distinct from the room in the "orders" namespace
  userNamespace.to("room1").emit("holà");
});

• middlewares

const orderNamespace = io.of("/orders");

orderNamespace.use((socket, next) => {
  // ensure the socket has access to the "orders" namespace
});

const userNamespace = io.of("/users");

userNamespace.use((socket, next) => {
  // ensure the socket has access to the "users" namespace
});

Extends

• StrictEventEmitter<ServerSideEvents, RemoveAcknowledgements<EmitEvents>, NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>>

Type Parameters

Type Parameter	Default type
ListenEvents extends EventsMap	DefaultEventsMap
EmitEvents extends EventsMap	ListenEvents
ServerSideEvents extends EventsMap	DefaultEventsMap
SocketData	any

Constructors

Constructor

new Namespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData>(server: Server<ListenEvents, EmitEvents, ServerSideEvents, SocketData>, name: string): Namespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData>;

Namespace constructor.

Parameters

Parameter	Type	Description
server	Server<ListenEvents, EmitEvents, ServerSideEvents, SocketData>	instance
name	string

Returns

Namespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData>

Overrides

StrictEventEmitter<ServerSideEvents, RemoveAcknowledgements<EmitEvents>, NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>>.constructor

Properties

Property	Modifier	Type	Description	Inherited from
adapter	public	Adapter	-	-
name	readonly	string	-	-
sockets	readonly	Map<string, RTUSocket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>>	A map of currently connected sockets.	-
captureRejections	static	boolean	Value: boolean Change the default captureRejections option on all new EventEmitter objects. Since v13.4.0, v12.16.0	StrictEventEmitter.captureRejections
captureRejectionSymbol	readonly	typeof captureRejectionSymbol	Value: Symbol.for('nodejs.rejection') See how to write a custom rejection handler. Since v13.4.0, v12.16.0	StrictEventEmitter.captureRejectionSymbol
defaultMaxListeners	static	number	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	StrictEventEmitter.defaultMaxListeners
errorMonitor	readonly	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. Since v13.6.0, v12.17.0	StrictEventEmitter.errorMonitor

Accessors

local

Get Signature

get local(): BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>;

Sets a modifier for a subsequent event emission that the event data will only be broadcast to the current node.

Example

const myNamespace = io.of("/my-namespace");

// the “foo” event will be broadcast to all connected clients on this node
myNamespace.local.emit("foo", "bar");

Returns

BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>

a new BroadcastOperator instance for chaining

---

volatile

Get Signature

get volatile(): BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>;

Sets a modifier for a subsequent event emission that the event data may be lost if the client is not ready to receive messages (because of network slowness or other issues, or because they’re connected through long polling and is in the middle of a request-response cycle).

Example

const myNamespace = io.of("/my-namespace");

myNamespace.volatile.emit("hello"); // the clients may or may not receive it

Returns

BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>

self

Methods

[captureRejectionSymbol]()?

optional [captureRejectionSymbol]<K>(
   error: Error,
   event: string | symbol, ...
   args: AnyRest): void;

Type Parameters

Type Parameter
K

Parameters

Parameter	Type
error	Error
event	string | symbol
...args	AnyRest

Returns

void

Inherited from

StrictEventEmitter.[captureRejectionSymbol]

---

addListener()

addListener<K>(eventName: string | symbol, listener: (...args: any[]) => void): this;

Alias for emitter.on(eventName, listener).

Type Parameters

Type Parameter
K

Parameters

Parameter	Type
eventName	string | symbol
listener	(...args: any[]) => void

Returns

this

Since

v0.1.26

Inherited from

StrictEventEmitter.addListener;

---

allSockets()

allSockets(): Promise<Set<string>>;

Gets a list of clients.

Returns

Promise<Set<string>>

Deprecated

this method will be removed in the next major release, please use Namespace#serverSideEmit or Namespace#fetchSockets instead.

---

compress()

compress(compress: boolean): BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>;

Sets the compress flag.

Parameters

Parameter	Type	Description
compress	boolean	if true, compresses the sending data

Returns

BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>

self

Example

const myNamespace = io.of("/my-namespace");

myNamespace.compress(false).emit("hello");

---

disconnectSockets()

disconnectSockets(close?: boolean): void;

Makes the matching socket instances disconnect.

Note: this method also works within a cluster of multiple Socket.IO servers, with a compatible Adapter.

Parameters

Parameter	Type	Description
close?	boolean	whether to close the underlying connection

Returns

void

Example

const myNamespace = io.of("/my-namespace");

// make all socket instances disconnect (the connections might be kept alive for other namespaces)
myNamespace.disconnectSockets();

// make all socket instances in the "room1" room disconnect and close the underlying connections
myNamespace.in("room1").disconnectSockets(true);

---

emit()

emit<Ev>(ev: Ev, ...args: EventParams<EmitEvents, Ev>): boolean;

Emits to all connected clients.

Type Parameters

Type Parameter
Ev extends string | symbol

Parameters

Parameter	Type
ev	Ev
...args	EventParams<EmitEvents, Ev>

Returns

boolean

Always true

Example

const myNamespace = io.of("/my-namespace");

myNamespace.emit("hello", "world");

// all serializable datastructures are supported (no need to call JSON.stringify)
myNamespace.emit("hello", 1, "2", { 3: ["4"], 5: Uint8Array.from([6]) });

// with an acknowledgement from the clients
myNamespace.timeout(1000).emit("some-event", (err, responses) => {
  if (err) {
    // some clients did not acknowledge the event in the given delay
  } else {
    console.log(responses); // one response per client
  }
});

Overrides

StrictEventEmitter.emit;

---

eventNames()

eventNames(): (string | symbol)[];

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

StrictEventEmitter.eventNames;

---

except()

except(room: string | string[]): BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>;

Excludes a room when emitting.

Parameters

Parameter	Type	Description
room	string | string[]	a room, or an array of rooms

Returns

BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>

a new BroadcastOperator instance for chaining

Example

const myNamespace = io.of("/my-namespace");

// the "foo" event will be broadcast to all connected clients, except the ones that are in the "room-101" room
myNamespace.except("room-101").emit("foo", "bar");

// with an array of rooms
myNamespace.except(["room-101", "room-102"]).emit("foo", "bar");

// with multiple chained calls
myNamespace.except("room-101").except("room-102").emit("foo", "bar");

---

fetchSockets()

fetchSockets(): Promise<RemoteSocket<EmitEvents, SocketData>[]>;

Returns the matching socket instances.

Note: this method also works within a cluster of multiple Socket.IO servers, with a compatible Adapter.

Returns

Promise<RemoteSocket<EmitEvents, SocketData>[]>

Example

const myNamespace = io.of("/my-namespace");

// return all Socket instances
const sockets = await myNamespace.fetchSockets();

// return all Socket instances in the "room1" room
const sockets = await myNamespace.in("room1").fetchSockets();

for (const socket of sockets) {
  console.log(socket.id);
  console.log(socket.handshake);
  console.log(socket.rooms);
  console.log(socket.data);

  socket.emit("hello");
  socket.join("room1");
  socket.leave("room2");
  socket.disconnect();
}

---

getMaxListeners()

getMaxListeners(): number;

Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to defaultMaxListeners.

Returns

number

Since

v1.0.0

Inherited from

StrictEventEmitter.getMaxListeners;

---

in()

in(room: string | string[]): BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>;

Targets a room when emitting. Similar to to(), but might feel clearer in some cases:

Parameters

Parameter	Type	Description
room	string | string[]	a room, or an array of rooms

Returns

BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>

a new BroadcastOperator instance for chaining

Example

const myNamespace = io.of("/my-namespace");

// disconnect all clients in the "room-101" room
myNamespace.in("room-101").disconnectSockets();

---

listenerCount()

listenerCount<K>(eventName: string | symbol, listener?: Function): number;

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

Type Parameter
K

Parameters

Parameter	Type	Description
eventName	string | symbol	The name of the event being listened for
listener?	Function	The event handler function

Returns

number

Since

v3.2.0

Inherited from

StrictEventEmitter.listenerCount;

---

listeners()

listeners<Ev>(event: Ev): FallbackToUntypedListener<Ev extends "connect" | "connection" ? NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>[Ev<Ev>] : Ev extends EventNames<ServerSideEvents> ? ServerSideEvents[Ev<Ev>] : never>[];

Returns the listeners listening to an event.

Type Parameters

Type Parameter
Ev extends string | symbol

Parameters

Parameter	Type	Description
event	Ev	Event name

Returns

FallbackToUntypedListener<Ev extends "connect" | "connection" ? NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>[Ev<Ev>] : Ev extends EventNames<ServerSideEvents> ? ServerSideEvents[Ev<Ev>] : never>[]

Array of listeners subscribed to event

Inherited from

StrictEventEmitter.listeners;

---

off()

off<K>(eventName: string | symbol, listener: (...args: any[]) => void): this;

Alias for emitter.removeListener().

Type Parameters

Type Parameter
K

Parameters

Parameter	Type
eventName	string | symbol
listener	(...args: any[]) => void

Returns

this

Since

v10.0.0

Inherited from

StrictEventEmitter.off;

---

on()

on<Ev>(ev: Ev, listener: FallbackToUntypedListener<Ev extends "connect" | "connection" ? NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>[Ev<Ev>] : Ev extends EventNames<ServerSideEvents> ? ServerSideEvents[Ev<Ev>] : never>): this;

Adds the listener function as an event listener for ev.

Type Parameters

Type Parameter
Ev extends string | symbol

Parameters

Parameter	Type	Description
ev	Ev	Name of the event
listener	FallbackToUntypedListener<Ev extends "connect" | "connection" ? NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>[Ev<Ev>] : Ev extends EventNames<ServerSideEvents> ? ServerSideEvents[Ev<Ev>] : never>	Callback function

Returns

this

Inherited from

StrictEventEmitter.on;

---

once()

once<Ev>(ev: Ev, listener: FallbackToUntypedListener<Ev extends "connect" | "connection" ? NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>[Ev<Ev>] : Ev extends EventNames<ServerSideEvents> ? ServerSideEvents[Ev<Ev>] : never>): this;

Adds a one-time listener function as an event listener for ev.

Type Parameters

Type Parameter
Ev extends string | symbol

Parameters

Parameter	Type	Description
ev	Ev	Name of the event
listener	FallbackToUntypedListener<Ev extends "connect" | "connection" ? NamespaceReservedEventsMap<ListenEvents, EmitEvents, ServerSideEvents, SocketData>[Ev<Ev>] : Ev extends EventNames<ServerSideEvents> ? ServerSideEvents[Ev<Ev>] : never>	Callback function

Returns

this

Inherited from

StrictEventEmitter.once;

---

prependListener()

prependListener<K>(eventName: string | symbol, listener: (...args: any[]) => void): this;

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

Type Parameter
K

Parameters

Parameter	Type	Description
eventName	string | symbol	The name of the event.
listener	(...args: any[]) => void	The callback function

Returns

this

Since

v6.0.0

Inherited from

StrictEventEmitter.prependListener;

---

prependOnceListener()

prependOnceListener<K>(eventName: string | symbol, listener: (...args: any[]) => void): this;

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

Type Parameter
K

Parameters

Parameter	Type	Description
eventName	string | symbol	The name of the event.
listener	(...args: any[]) => void	The callback function

Returns

this

Since

v6.0.0

Inherited from

StrictEventEmitter.prependOnceListener;

---

rawListeners()

rawListeners<K>(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");

Type Parameters

Type Parameter
K

Parameters

Parameter	Type
eventName	string | symbol

Returns

Function[]

Since

v9.4.0

Inherited from

StrictEventEmitter.rawListeners;

---

removeAllListeners()

removeAllListeners(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.

Parameters

Parameter	Type
eventName?	string | symbol

Returns

this

Since

v0.1.26

Inherited from

StrictEventEmitter.removeAllListeners;

---

removeListener()

removeListener<K>(eventName: string | symbol, listener: (...args: any[]) => void): this;

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:
//   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.

Type Parameters

Type Parameter
K

Parameters

Parameter	Type
eventName	string | symbol
listener	(...args: any[]) => void

Returns

this

Since

v0.1.26

Inherited from

StrictEventEmitter.removeListener;

---

send()

send(...args: Parameters<EmitEvents["message"]>): this;

Sends a message event to all clients.

This method mimics the WebSocket.send() method.

Parameters

Parameter	Type
...args	Parameters<EmitEvents["message"]>

Returns

this

self

See

https://developer.mozilla.org/en-US/docs/Web/API/WebSocket/send

Example

const myNamespace = io.of("/my-namespace");

myNamespace.send("hello");

// this is equivalent to
myNamespace.emit("message", "hello");

---

serverSideEmit()

serverSideEmit<Ev>(ev: Ev, ...args: EventParams<DecorateAcknowledgementsWithTimeoutAndMultipleResponses<ServerSideEvents>, Ev>): boolean;

Sends a message to the other Socket.IO servers of the cluster.

Type Parameters

Type Parameter
Ev extends string | symbol

Parameters

Parameter	Type	Description
ev	Ev	the event name
...args	EventParams<DecorateAcknowledgementsWithTimeoutAndMultipleResponses<ServerSideEvents>, Ev>	an array of arguments, which may include an acknowledgement callback at the end

Returns

boolean

Example

const myNamespace = io.of("/my-namespace");

myNamespace.serverSideEmit("hello", "world");

myNamespace.on("hello", (arg1) => {
  console.log(arg1); // prints "world"
});

// acknowledgements (without binary content) are supported too:
myNamespace.serverSideEmit("ping", (err, responses) => {
  if (err) {
    // some servers did not acknowledge the event in the given delay
  } else {
    console.log(responses); // one response per server (except the current one)
  }
});

myNamespace.on("ping", (cb) => {
  cb("pong");
});

---

serverSideEmitWithAck()

serverSideEmitWithAck<Ev>(ev: Ev, ...args: AllButLast<EventParams<ServerSideEvents, Ev>>): Promise<FirstNonErrorArg<Last<EventParams<ServerSideEvents, Ev>>>[]>;

Sends a message and expect an acknowledgement from the other Socket.IO servers of the cluster.

Type Parameters

Type Parameter
Ev extends string | symbol

Parameters

Parameter	Type	Description
ev	Ev	the event name
...args	AllButLast<EventParams<ServerSideEvents, Ev>>	an array of arguments

Returns

Promise<FirstNonErrorArg<Last<EventParams<ServerSideEvents, Ev>>>[]>

a Promise that will be fulfilled when all servers have acknowledged the event

Example

const myNamespace = io.of("/my-namespace");

try {
  const responses = await myNamespace.serverSideEmitWithAck("ping");
  console.log(responses); // one response per server (except the current one)
} catch (e) {
  // some servers did not acknowledge the event in the given delay
}

---

setMaxListeners()

setMaxListeners(n: number): this;

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

Parameter	Type
n	number

Returns

this

Since

v0.3.5

Inherited from

StrictEventEmitter.setMaxListeners;

---

socketsJoin()

socketsJoin(room: string | string[]): void;

Makes the matching socket instances join the specified rooms.

Note: this method also works within a cluster of multiple Socket.IO servers, with a compatible Adapter.

Parameters

Parameter	Type	Description
room	string | string[]	a room, or an array of rooms

Returns

void

Example

const myNamespace = io.of("/my-namespace");

// make all socket instances join the "room1" room
myNamespace.socketsJoin("room1");

// make all socket instances in the "room1" room join the "room2" and "room3" rooms
myNamespace.in("room1").socketsJoin(["room2", "room3"]);

---

socketsLeave()

socketsLeave(room: string | string[]): void;

Makes the matching socket instances leave the specified rooms.

Note: this method also works within a cluster of multiple Socket.IO servers, with a compatible Adapter.

Parameters

Parameter	Type	Description
room	string | string[]	a room, or an array of rooms

Returns

void

Example

const myNamespace = io.of("/my-namespace");

// make all socket instances leave the "room1" room
myNamespace.socketsLeave("room1");

// make all socket instances in the "room1" room leave the "room2" and "room3" rooms
myNamespace.in("room1").socketsLeave(["room2", "room3"]);

---

timeout()

timeout(timeout: number): BroadcastOperator<DecorateAcknowledgements<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>>, SocketData>;

Adds a timeout in milliseconds for the next operation.

Parameters

Parameter	Type	Description
timeout	number

Returns

BroadcastOperator<DecorateAcknowledgements<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>>, SocketData>

Example

const myNamespace = io.of("/my-namespace");

myNamespace.timeout(1000).emit("some-event", (err, responses) => {
  if (err) {
    // some clients did not acknowledge the event in the given delay
  } else {
    console.log(responses); // one response per client
  }
});

---

to()

to(room: string | string[]): BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>;

Targets a room when emitting.

Parameters

Parameter	Type	Description
room	string | string[]	a room, or an array of rooms

Returns

BroadcastOperator<DecorateAcknowledgementsWithMultipleResponses<EmitEvents>, SocketData>

a new BroadcastOperator instance for chaining

Example

const myNamespace = io.of("/my-namespace");

// the “foo” event will be broadcast to all connected clients in the “room-101” room
myNamespace.to("room-101").emit("foo", "bar");

// with an array of rooms (a client will be notified at most once)
myNamespace.to(["room-101", "room-102"]).emit("foo", "bar");

// with multiple chained calls
myNamespace.to("room-101").to("room-102").emit("foo", "bar");

---

use()

use(fn: (socket: RTUSocket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>, next: (err?: ExtendedError) => void) => void): this;

Registers a middleware, which is a function that gets executed for every incoming Socket.

Parameters

Parameter	Type	Description
fn	(socket: RTUSocket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>, next: (err?: ExtendedError) => void) => void	the middleware function

Returns

this

Example

const myNamespace = io.of("/my-namespace");

myNamespace.use((socket, next) => {
  // ...
  next();
});

---

write()

write(...args: Parameters<EmitEvents["message"]>): this;

Sends a message event to all clients. Sends a message event. Alias of send.

Parameters

Parameter	Type
...args	Parameters<EmitEvents["message"]>

Returns

this

self

---

addAbortListener()

static addAbortListener(signal: AbortSignal, resource: (event: Event) => void): Disposable;

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

Parameter	Type
signal	AbortSignal
resource	(event: Event) => void

Returns

Disposable

Disposable that removes the abort listener.

Since

v20.5.0

Inherited from

StrictEventEmitter.addAbortListener;

---

getEventListeners()

static getEventListeners(emitter: EventEmitter<DefaultEventMap> | EventTarget, name: string | symbol): Function[];

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

Parameter	Type
emitter	EventEmitter<DefaultEventMap> | EventTarget
name	string | symbol

Returns

Function[]

Since

v15.2.0, v14.17.0

Inherited from

StrictEventEmitter.getEventListeners;

---

getMaxListeners()

static getMaxListeners(emitter: EventEmitter<DefaultEventMap> | EventTarget): number;

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

Parameter	Type
emitter	EventEmitter<DefaultEventMap> | EventTarget

Returns

number

Since

v19.9.0

Inherited from

StrictEventEmitter.getMaxListeners;

---

listenerCount()

static listenerCount(emitter: EventEmitter, eventName: string | symbol): number;

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

Parameters

Parameter	Type	Description
emitter	EventEmitter	The emitter to query
eventName	string | symbol	The event name

Returns

number

Since

v0.9.12

Deprecated

Since v3.2.0 - Use listenerCount instead.

Inherited from

StrictEventEmitter.listenerCount;

---

on()

Call Signature

static on(
   emitter: EventEmitter,
   eventName: string | symbol,
options?: StaticEventEmitterIteratorOptions): AsyncIterableIterator<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 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

Parameter	Type
emitter	EventEmitter
eventName	string | symbol
options?	StaticEventEmitterIteratorOptions

Returns

AsyncIterableIterator<any[]>

An AsyncIterator that iterates eventName events emitted by the emitter

Since

v13.6.0, v12.16.0

Inherited from

StrictEventEmitter.on;

Call Signature

static on(
   emitter: EventTarget,
   eventName: string,
options?: StaticEventEmitterIteratorOptions): AsyncIterableIterator<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 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

Parameter	Type
emitter	EventTarget
eventName	string
options?	StaticEventEmitterIteratorOptions

Returns

AsyncIterableIterator<any[]>

An AsyncIterator that iterates eventName events emitted by the emitter

Since

v13.6.0, v12.16.0

Inherited from

StrictEventEmitter.on;

---

once()

Call Signature

static once(
   emitter: EventEmitter,
   eventName: string | symbol,
options?: StaticEventEmitterOptions): Promise<any[]>;

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!

Parameters

Parameter	Type
emitter	EventEmitter
eventName	string | symbol
options?	StaticEventEmitterOptions

Returns

Promise<any[]>

Since

v11.13.0, v10.16.0

Inherited from

StrictEventEmitter.once;

Call Signature

static once(
   emitter: EventTarget,
   eventName: string,
options?: StaticEventEmitterOptions): Promise<any[]>;

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!

Parameters

Parameter	Type
emitter	EventTarget
eventName	string
options?	StaticEventEmitterOptions

Returns

Promise<any[]>

Since

v11.13.0, v10.16.0

Inherited from

StrictEventEmitter.once;

---

setMaxListeners()

static setMaxListeners(n?: number, ...eventTargets?: (EventEmitter<DefaultEventMap> | EventTarget)[]): void;

import { setMaxListeners, EventEmitter } from "node:events";

const target = new EventTarget();
const emitter = new EventEmitter();

setMaxListeners(5, target, emitter);

Parameters

Parameter	Type	Description
n?	number	A non-negative number. The maximum number of listeners per EventTarget event.
...eventTargets?	(EventEmitter<DefaultEventMap> | EventTarget)[]	-

Returns

void

Since

v15.4.0

Inherited from

StrictEventEmitter.setMaxListeners;