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Socket

This class is an abstraction of a TCP socket or a streaming IPC endpoint (uses named pipes on Windows, and Unix domain sockets otherwise). It is also an EventEmitter.

A net.Socket can be created by the user and used directly to interact with a server. For example, it is returned by createConnection, so the user can use it to talk to the server.

It can also be created by Node.js and passed to the user when a connection is received. For example, it is passed to the listeners of a 'connection' event emitted on a Server, so the user can use it to interact with the client.

Since​

v0.3.4

Properties​

allowHalfOpenbooleanRequired
If false then the stream will automatically end the writable side when the readable side ends. Set initially by the allowHalfOpen constructor option, which defaults to true. This can be changed manually to change the half-open behavior of an existingDuplex stream instance, but must be changed before the 'end' event is emitted.
autoSelectFamilyAttemptedAddressesstring[]Required
This property is only present if the family autoselection algorithm is enabled in socket.connect(options) and it is an array of the addresses that have been attempted. Each address is a string in the form of $IP:$PORT. If the connection was successful, then the last address is the one that the socket is currently connected to.
bufferSizenumberRequired
This property shows the number of characters buffered for writing. The buffer may contain strings whose length after encoding is not yet known. So this number is only an approximation of the number of bytes in the buffer. net.Socket has the property that socket.write() always works. This is to help users get up and running quickly. The computer cannot always keep up with the amount of data that is written to a socket. The network connection simply might be too slow. Node.js will internally queue up the data written to a socket and send it out over the wire when it is possible. The consequence of this internal buffering is that memory may grow. Users who experience large or growing bufferSize should attempt to "throttle" the data flows in their program with socket.pause() and socket.resume().
bytesReadnumberRequired
The amount of received bytes.
bytesWrittennumberRequired
The amount of bytes sent.
closedbooleanRequired
Is true after 'close' has been emitted.
connectingbooleanRequired
If true,socket.connect(options[, connectListener]) was called and has not yet finished. It will stay true until the socket becomes connected, then it is set to false and the 'connect' event is emitted. Note that the socket.connect(options[, connectListener]) callback is a listener for the 'connect' event.
destroyedbooleanRequired
See writable.destroyed for further details.
errorednull | ErrorRequired
Returns error if the stream has been destroyed with an error.
localAddressstring
The string representation of the local IP address the remote client is connecting on. For example, in a server listening on '0.0.0.0', if a client connects on '192.168.1.1', the value of socket.localAddress would be'192.168.1.1'.
localFamilystring
The string representation of the local IP family. 'IPv4' or 'IPv6'.
localPortnumber
The numeric representation of the local port. For example, 80 or 21.
pendingbooleanRequired
This is true if the socket is not connected yet, either because .connect()has not yet been called or because it is still in the process of connecting (see socket.connecting).
readablebooleanRequired
Is true if it is safe to call readable.read(), which means the stream has not been destroyed or emitted 'error' or 'end'.
readableAbortedbooleanRequired
Returns whether the stream was destroyed or errored before emitting 'end'.
readableDidReadbooleanRequired
Returns whether 'data' has been emitted.
readableEncodingnull | BufferEncodingRequired
Getter for the property encoding of a given Readable stream. The encodingproperty can be set using the readable.setEncoding() method.
readableEndedbooleanRequired
Becomes true when 'end' event is emitted.
readableFlowingnull | booleanRequired
This property reflects the current state of a Readable stream as described in the Three states section.
readableHighWaterMarknumberRequired
Returns the value of highWaterMark passed when creating this Readable.
readableLengthnumberRequired
This property contains the number of bytes (or objects) in the queue ready to be read. The value provides introspection data regarding the status of the highWaterMark.
readableObjectModebooleanRequired
Getter for the property objectMode of a given Readable stream.
readyStateSocketReadyStateRequired
This property represents the state of the connection as a string. * If the stream is connecting socket.readyState is opening. * If the stream is readable and writable, it is open. * If the stream is readable and not writable, it is readOnly. * If the stream is not readable and writable, it is writeOnly.
remoteAddressstring
The string representation of the remote IP address. For example,'74.125.127.100' or '2001:4860:a005::68'. Value may be undefined if the socket is destroyed (for example, if the client disconnected).
remoteFamilystring
The string representation of the remote IP family. 'IPv4' or 'IPv6'. Value may be undefined if the socket is destroyed (for example, if the client disconnected).
remotePortnumber
The numeric representation of the remote port. For example, 80 or 21. Value may be undefined if the socket is destroyed (for example, if the client disconnected).
timeoutnumber
The socket timeout in milliseconds as set by socket.setTimeout(). It is undefined if a timeout has not been set.
writablebooleanRequired
Is true if it is safe to call writable.write(), which means the stream has not been destroyed, errored, or ended.
writableCorkednumberRequired
Number of times writable.uncork() needs to be called in order to fully uncork the stream.
writableEndedbooleanRequired
Is true after writable.end() has been called. This property does not indicate whether the data has been flushed, for this use writable.writableFinished instead.
writableFinishedbooleanRequired
Is set to true immediately before the 'finish' event is emitted.
writableHighWaterMarknumberRequired
Return the value of highWaterMark passed when creating this Writable.
writableLengthnumberRequired
This property contains the number of bytes (or objects) in the queue ready to be written. The value provides introspection data regarding the status of the highWaterMark.
writableNeedDrainbooleanRequired
Is true if the stream's buffer has been full and stream will emit 'drain'.
writableObjectModebooleanRequired
Getter for the property objectMode of a given Writable stream.
captureRejectionSymboltypeof captureRejectionSymbolRequired
Value: Symbol.for('nodejs.rejection') See how to write a custom rejection handler.
captureRejectionsbooleanRequired
Value: boolean Change the default captureRejections option on all new EventEmitter objects.
defaultMaxListenersnumberRequired
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 _all_EventEmitter instances, the events.defaultMaxListenersproperty can be used. If this value is not a positive number, a RangeErroris 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 singleEventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners()methods can be used to temporarily avoid this warning: js 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'.
errorMonitortypeof errorMonitorRequired
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.

Methods​

[asyncDispose]​

Calls readable.destroy() with an AbortError and returns a promise that fulfills when the stream is finished.

Returns​

PromisePromise<void>Required

Since​

v20.4.0

[asyncIterator]​

Returns​

AsyncIterableIteratorAsyncIterableIterator<any>Required

[captureRejectionSymbol]​

Parameters​

errorErrorRequired
eventstringRequired
argsany[]Required

Returns​

voidvoid

_construct​

Parameters​

callback(error?: null | Error) => voidRequired

Returns​

voidvoid

_destroy​

Parameters​

errornull | ErrorRequired
callback(error: null | Error) => voidRequired

Returns​

voidvoid

_final​

Parameters​

callback(error?: null | Error) => voidRequired

Returns​

voidvoid

_read​

Parameters​

sizenumberRequired

Returns​

voidvoid

_write​

Parameters​

chunkanyRequired
encodingBufferEncodingRequired
callback(error?: null | Error) => voidRequired

Returns​

voidvoid

_writev​

Parameters​

chunks{ chunk: any ; encoding: [BufferEncoding](/references/js-client/internal/types/internal.BufferEncoding) }[]Required
callback(error?: null | Error) => voidRequired

Returns​

voidvoid

addListener​

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

events.EventEmitter

  1. close
  2. connect
  3. data
  4. drain
  5. end
  6. error
  7. lookup
  8. ready
  9. timeout

Parameters​

eventstringRequired
listener(...args: any[]) => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"close"Required
listener(hadError: boolean) => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"connect"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"data"Required
listener(data: Buffer) => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"drain"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"end"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"error"Required
listener(err: Error) => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"lookup"Required
listener(err: Error, address: string, family: string | number, host: string) => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"ready"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**addListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"timeout"Required
listener() => voidRequired

Returns​

SocketSocketRequired

address​

Returns the bound address, the address family name and port of the socket as reported by the operating system:{ port: 12346, family: 'IPv4', address: '127.0.0.1' }

Returns​

&#123;&#125; \| AddressInfo{} | AddressInfo

Since​

v0.1.90

asIndexedPairs​

This method returns a new stream with chunks of the underlying stream paired with a counter in the form [index, chunk]. The first index value is 0 and it increases by 1 for each chunk produced.

Parameters​

optionsPick<ArrayOptions, "signal">

Returns​

ReadableReadableRequired
a stream of indexed pairs.

Since​

v17.5.0

compose​

Parameters​

streamComposeFnParam | T | Iterable<T> | AsyncIterable<T>Required
optionsobject
options.signalAbortSignalRequired

Returns​

connect​

**connect**(options, connectionListener?): [Socket](/references/js-client/internal/classes/internal.Socket)

Initiate a connection on a given socket.

Possible signatures:

  • socket.connect(options[, connectListener])
  • socket.connect(path[, connectListener]) for IPC connections.
  • socket.connect(port[, host][, connectListener]) for TCP connections.
  • Returns: net.Socket The socket itself.

This function is asynchronous. When the connection is established, the 'connect' event will be emitted. If there is a problem connecting, instead of a 'connect' event, an 'error' event will be emitted with the error passed to the 'error' listener. The last parameter connectListener, if supplied, will be added as a listener for the 'connect' event once.

This function should only be used for reconnecting a socket after'close' has been emitted or otherwise it may lead to undefined behavior.

Parameters​

optionsSocketConnectOptsRequired
connectionListener() => void

Returns​

SocketSocketRequired

**connect**(port, host, connectionListener?): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

portnumberRequired
hoststringRequired
connectionListener() => void

Returns​

SocketSocketRequired

**connect**(port, connectionListener?): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

portnumberRequired
connectionListener() => void

Returns​

SocketSocketRequired

**connect**(path, connectionListener?): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

pathstringRequired
connectionListener() => void

Returns​

SocketSocketRequired

cork​

The writable.cork() method forces all written data to be buffered in memory. The buffered data will be flushed when either the uncork or end methods are called.

The primary intent of writable.cork() is to accommodate a situation in which several small chunks are written to the stream in rapid succession. Instead of immediately forwarding them to the underlying destination, writable.cork()buffers all the chunks until writable.uncork() is called, which will pass them all to writable._writev(), if present. This prevents a head-of-line blocking situation where data is being buffered while waiting for the first small chunk to be processed. However, use of writable.cork() without implementingwritable._writev() may have an adverse effect on throughput.

See also: writable.uncork(), writable._writev().

Returns​

voidvoid

Since​

v0.11.2

destroy​

Destroy the stream. Optionally emit an 'error' event, and emit a 'close'event (unless emitClose is set to false). After this call, the readable stream will release any internal resources and subsequent calls to push()will be ignored.

Once destroy() has been called any further calls will be a no-op and no further errors except from _destroy() may be emitted as 'error'.

Implementors should not override this method, but instead implement readable._destroy().

Parameters​

errorError
Error which will be passed as payload in 'error' event

Returns​

SocketSocketRequired

Since​

v8.0.0

destroySoon​

Destroys the socket after all data is written. If the finish event was already emitted the socket is destroyed immediately. If the socket is still writable it implicitly calls socket.end().

Returns​

voidvoid

Since​

v0.3.4

drop​

This method returns a new stream with the first limit chunks dropped from the start.

Parameters​

limitnumberRequired
the number of chunks to drop from the readable.
optionsPick<ArrayOptions, "signal">

Returns​

ReadableReadableRequired
a stream with limit chunks dropped from the start.

Since​

v17.5.0

emit​

**emit**(event, ...args): boolean

Synchronously calls each of the listeners registered for the event namedeventName, 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

Parameters​

eventstring | symbolRequired
argsany[]Required

Returns​

booleanboolean

Since​

v0.1.26

**emit**(event, hadError): boolean

Parameters​

event"close"Required
hadErrorbooleanRequired

Returns​

booleanboolean

**emit**(event): boolean

Parameters​

event"connect"Required

Returns​

booleanboolean

**emit**(event, data): boolean

Parameters​

event"data"Required
dataBufferRequired

Returns​

booleanboolean

**emit**(event): boolean

Parameters​

event"drain"Required

Returns​

booleanboolean

**emit**(event): boolean

Parameters​

event"end"Required

Returns​

booleanboolean

**emit**(event, err): boolean

Parameters​

event"error"Required
errErrorRequired

Returns​

booleanboolean

**emit**(event, err, address, family, host): boolean

Parameters​

event"lookup"Required
errErrorRequired
addressstringRequired
familystring | numberRequired
hoststringRequired

Returns​

booleanboolean

**emit**(event): boolean

Parameters​

event"ready"Required

Returns​

booleanboolean

**emit**(event): boolean

Parameters​

event"timeout"Required

Returns​

booleanboolean

end​

**end**(callback?): [Socket](/references/js-client/internal/classes/internal.Socket)

Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.

See writable.end() for further details.

Parameters​

callback() => void
Optional callback for when the socket is finished.

Returns​

SocketSocketRequired
The socket itself.

Since​

v0.1.90

**end**(buffer, callback?): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

bufferstring | Uint8ArrayRequired
callback() => void

Returns​

SocketSocketRequired

**end**(str, encoding?, callback?): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

strstring | Uint8ArrayRequired
encodingBufferEncoding
callback() => void

Returns​

SocketSocketRequired

eventNames​

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)[](string | symbol)[]Required

Since​

v6.0.0

every​

This method is similar to Array.prototype.every and calls fn on each chunk in the stream to check if all awaited return values are truthy value for fn. Once an fn call on a chunk awaited return value is falsy, the stream is destroyed and the promise is fulfilled with false. If all of the fn calls on the chunks return a truthy value, the promise is fulfilled with true.

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => boolean | Promise<boolean>Required
a function to call on each chunk of the stream. Async or not.
optionsArrayOptions

Returns​

PromisePromise<boolean>Required
a promise evaluating to true if fn returned a truthy value for every one of the chunks.

Since​

v17.5.0

filter​

This method allows filtering the stream. For each chunk in the stream the fn function will be called and if it returns a truthy value, the chunk will be passed to the result stream. If the fn function returns a promise - that promise will be awaited.

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => boolean | Promise<boolean>Required
a function to filter chunks from the stream. Async or not.
optionsArrayOptions

Returns​

ReadableReadableRequired
a stream filtered with the predicate fn.

Since​

v17.4.0, v16.14.0

find​

**find**<TypeParameter T>(fn, options?): Promise&#60;undefined \| T&#62;

This method is similar to Array.prototype.find and calls fn on each chunk in the stream to find a chunk with a truthy value for fn. Once an fn call's awaited return value is truthy, the stream is destroyed and the promise is fulfilled with value for which fn returned a truthy value. If all of the fn calls on the chunks return a falsy value, the promise is fulfilled with undefined.

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => data is TRequired
a function to call on each chunk of the stream. Async or not.
optionsArrayOptions

Returns​

PromisePromise<undefined | T>Required
a promise evaluating to the first chunk for which fn evaluated with a truthy value, or undefined if no element was found.

Since​

v17.5.0

**find**(fn, options?): Promise&#60;any&#62;

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => boolean | Promise<boolean>Required
optionsArrayOptions

Returns​

PromisePromise<any>Required

flatMap​

This method returns a new stream by applying the given callback to each chunk of the stream and then flattening the result.

It is possible to return a stream or another iterable or async iterable from fn and the result streams will be merged (flattened) into the returned stream.

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => anyRequired
a function to map over every chunk in the stream. May be async. May be a stream or generator.
optionsArrayOptions

Returns​

ReadableReadableRequired
a stream flat-mapped with the function fn.

Since​

v17.5.0

forEach​

This method allows iterating a stream. For each chunk in the stream the fn function will be called. If the fn function returns a promise - that promise will be awaited.

This method is different from for await...of loops in that it can optionally process chunks concurrently. In addition, a forEach iteration can only be stopped by having passed a signal option and aborting the related AbortController while for await...of can be stopped with break or return. In either case the stream will be destroyed.

This method is different from listening to the 'data' event in that it uses the readable event in the underlying machinary and can limit the number of concurrent fn calls.

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => void | Promise<void>Required
a function to call on each chunk of the stream. Async or not.
optionsArrayOptions

Returns​

PromisePromise<void>Required
a promise for when the stream has finished.

Since​

v17.5.0

getMaxListeners​

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

Returns​

numbernumber

Since​

v1.0.0

isPaused​

The readable.isPaused() method returns the current operating state of theReadable. This is used primarily by the mechanism that underlies thereadable.pipe() method. In most typical cases, there will be no reason to use this method directly.

const readable = new stream.Readable();

readable.isPaused(); // === false
readable.pause();
readable.isPaused(); // === true
readable.resume();
readable.isPaused(); // === false

Returns​

booleanboolean

Since​

v0.11.14

iterator​

The iterator created by this method gives users the option to cancel the destruction of the stream if the for await...of loop is exited by return, break, or throw, or if the iterator should destroy the stream if the stream emitted an error during iteration.

Parameters​

optionsobject
options.destroyOnReturnboolean
When set to false, calling return on the async iterator, or exiting a for await...of iteration using a break, return, or throw will not destroy the stream. Default: true.

Returns​

AsyncIterableIteratorAsyncIterableIterator<any>Required

Since​

v16.3.0

listenerCount​

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.

Parameters​

eventNamestring | symbolRequired
The name of the event being listened for
listenerFunction
The event handler function

Returns​

numbernumber

Since​

v3.2.0

listeners​

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] ]

Parameters​

eventNamestring | symbolRequired

Returns​

Function[]Function[]Required

Since​

v0.1.26

map​

This method allows mapping over the stream. The fn function will be called for every chunk in the stream. If the fn function returns a promise - that promise will be awaited before being passed to the result stream.

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => anyRequired
a function to map over every chunk in the stream. Async or not.
optionsArrayOptions

Returns​

ReadableReadableRequired
a stream mapped with the function fn.

Since​

v17.4.0, v16.14.0

off​

Alias for emitter.removeListener().

Parameters​

eventNamestring | symbolRequired
listener(...args: any[]) => voidRequired

Returns​

SocketSocketRequired

Since​

v10.0.0

on​

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Adds the listener function to the end 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 eventNameand listener will result in the listener 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. Theemitter.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

Parameters​

eventstringRequired
The name of the event.
listener(...args: any[]) => voidRequired
The callback function

Returns​

SocketSocketRequired

Since​

v0.1.101

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"close"Required
listener(hadError: boolean) => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"connect"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"data"Required
listener(data: Buffer) => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"drain"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"end"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"error"Required
listener(err: Error) => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"lookup"Required
listener(err: Error, address: string, family: string | number, host: string) => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"ready"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**on**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"timeout"Required
listener() => voidRequired

Returns​

SocketSocketRequired

once​

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Adds a one-timelistener function for the event named eventName. The next time eventName 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. Theemitter.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

Parameters​

eventstringRequired
The name of the event.
listener(...args: any[]) => voidRequired
The callback function

Returns​

SocketSocketRequired

Since​

v0.3.0

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"close"Required
listener(hadError: boolean) => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"connect"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"data"Required
listener(data: Buffer) => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"drain"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"end"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"error"Required
listener(err: Error) => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"lookup"Required
listener(err: Error, address: string, family: string | number, host: string) => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"ready"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**once**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"timeout"Required
listener() => voidRequired

Returns​

SocketSocketRequired

pause​

Pauses the reading of data. That is, 'data' events will not be emitted. Useful to throttle back an upload.

Returns​

SocketSocketRequired
The socket itself.

pipe​

Parameters​

destinationTRequired
optionsobject
options.endboolean

Returns​

prependListener​

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

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 eventNameand 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.

Parameters​

eventstringRequired
The name of the event.
listener(...args: any[]) => voidRequired
The callback function

Returns​

SocketSocketRequired

Since​

v6.0.0

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"close"Required
listener(hadError: boolean) => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"connect"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"data"Required
listener(data: Buffer) => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"drain"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"end"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"error"Required
listener(err: Error) => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"lookup"Required
listener(err: Error, address: string, family: string | number, host: string) => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"ready"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"timeout"Required
listener() => voidRequired

Returns​

SocketSocketRequired

prependOnceListener​

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

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.

Parameters​

eventstringRequired
The name of the event.
listener(...args: any[]) => voidRequired
The callback function

Returns​

SocketSocketRequired

Since​

v6.0.0

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"close"Required
listener(hadError: boolean) => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"connect"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"data"Required
listener(data: Buffer) => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"drain"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"end"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"error"Required
listener(err: Error) => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"lookup"Required
listener(err: Error, address: string, family: string | number, host: string) => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"ready"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**prependOnceListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"timeout"Required
listener() => voidRequired

Returns​

SocketSocketRequired

push​

Parameters​

chunkanyRequired
encodingBufferEncoding

Returns​

booleanboolean

rawListeners​

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');

Parameters​

eventNamestring | symbolRequired

Returns​

Function[]Function[]Required

Since​

v9.4.0

read​

The readable.read() method reads data out of the internal buffer and returns it. If no data is available to be read, null is returned. By default, the data is returned as a Buffer object unless an encoding has been specified using the readable.setEncoding() method or the stream is operating in object mode.

The optional size argument specifies a specific number of bytes to read. Ifsize bytes are not available to be read, null will be returned _unless_the stream has ended, in which case all of the data remaining in the internal buffer will be returned.

If the size argument is not specified, all of the data contained in the internal buffer will be returned.

The size argument must be less than or equal to 1 GiB.

The readable.read() method should only be called on Readable streams operating in paused mode. In flowing mode, readable.read() is called automatically until the internal buffer is fully drained.

const readable = getReadableStreamSomehow();

// 'readable' may be triggered multiple times as data is buffered in
readable.on('readable', () => {
  let chunk;
  console.log('Stream is readable (new data received in buffer)');
  // Use a loop to make sure we read all currently available data
  while (null !== (chunk = readable.read())) {
    console.log(`Read ${chunk.length} bytes of data...`);
  }
});

// 'end' will be triggered once when there is no more data available
readable.on('end', () => {
  console.log('Reached end of stream.');
});

Each call to readable.read() returns a chunk of data, or null. The chunks are not concatenated. A while loop is necessary to consume all data currently in the buffer. When reading a large file .read() may return null, having consumed all buffered content so far, but there is still more data to come not yet buffered. In this case a new 'readable' event will be emitted when there is more data in the buffer. Finally the 'end' event will be emitted when there is no more data to come.

Therefore to read a file's whole contents from a readable, it is necessary to collect chunks across multiple 'readable' events:

const chunks = [];

readable.on('readable', () => {
  let chunk;
  while (null !== (chunk = readable.read())) {
    chunks.push(chunk);
  }
});

readable.on('end', () => {
  const content = chunks.join('');
});

A Readable stream in object mode will always return a single item from a call to readable.read(size), regardless of the value of thesize argument.

If the readable.read() method returns a chunk of data, a 'data' event will also be emitted.

Calling read after the 'end' event has been emitted will return null. No runtime error will be raised.

Parameters​

sizenumber
Optional argument to specify how much data to read.

Returns​

anyany

Since​

v0.9.4

reduce​

**reduce**<TypeParameter T>(fn, initial?, options?): Promise&#60;T&#62;

This method calls fn on each chunk of the stream in order, passing it the result from the calculation on the previous element. It returns a promise for the final value of the reduction.

If no initial value is supplied the first chunk of the stream is used as the initial value. If the stream is empty, the promise is rejected with a TypeError with the ERR_INVALID_ARGS code property.

The reducer function iterates the stream element-by-element which means that there is no concurrency parameter or parallelism. To perform a reduce concurrently, you can extract the async function to readable.map method.

Parameters​

fn(previous: any, data: any, options?: Pick<ArrayOptions, "signal">) => TRequired
a reducer function to call over every chunk in the stream. Async or not.
initialundefined
the initial value to use in the reduction.
optionsPick<ArrayOptions, "signal">

Returns​

PromisePromise<T>Required
a promise for the final value of the reduction.

Since​

v17.5.0

**reduce**<TypeParameter T>(fn, initial, options?): Promise&#60;T&#62;

Parameters​

fn(previous: T, data: any, options?: Pick<ArrayOptions, "signal">) => TRequired
initialTRequired
optionsPick<ArrayOptions, "signal">

Returns​

PromisePromise<T>Required

ref​

Opposite of unref(), calling ref() on a previously unrefed socket will _not_ let the program exit if it's the only socket left (the default behavior). If the socket is refed calling ref again will have no effect.

Returns​

SocketSocketRequired
The socket itself.

Since​

v0.9.1

removeAllListeners​

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​

eventstring | symbol

Returns​

SocketSocketRequired

Since​

v0.1.26

removeListener​

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

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.

Parameters​

event"close"Required
listener() => voidRequired

Returns​

SocketSocketRequired

Since​

v0.1.26

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"data"Required
listener(chunk: any) => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"drain"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"end"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"error"Required
listener(err: Error) => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"finish"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"pause"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"pipe"Required
listener(src: Readable) => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"readable"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"resume"Required
listener() => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

event"unpipe"Required
listener(src: Readable) => voidRequired

Returns​

SocketSocketRequired

**removeListener**(event, listener): [Socket](/references/js-client/internal/classes/internal.Socket)

Parameters​

eventstring | symbolRequired
listener(...args: any[]) => voidRequired

Returns​

SocketSocketRequired

resetAndDestroy​

Close the TCP connection by sending an RST packet and destroy the stream. If this TCP socket is in connecting status, it will send an RST packet and destroy this TCP socket once it is connected. Otherwise, it will call socket.destroy with an ERR_SOCKET_CLOSED Error. If this is not a TCP socket (for example, a pipe), calling this method will immediately throw an ERR_INVALID_HANDLE_TYPE Error.

Returns​

SocketSocketRequired

Since​

v18.3.0, v16.17.0

resume​

Resumes reading after a call to socket.pause().

Returns​

SocketSocketRequired
The socket itself.

setDefaultEncoding​

The writable.setDefaultEncoding() method sets the default encoding for a Writable stream.

Parameters​

encodingBufferEncodingRequired
The new default encoding

Returns​

SocketSocketRequired

Since​

v0.11.15

setEncoding​

Set the encoding for the socket as a Readable Stream. See readable.setEncoding() for more information.

Parameters​

Returns​

SocketSocketRequired
The socket itself.

Since​

v0.1.90

setKeepAlive​

Enable/disable keep-alive functionality, and optionally set the initial delay before the first keepalive probe is sent on an idle socket.

Set initialDelay (in milliseconds) to set the delay between the last data packet received and the first keepalive probe. Setting 0 forinitialDelay will leave the value unchanged from the default (or previous) setting.

Enabling the keep-alive functionality will set the following socket options:

  • SO_KEEPALIVE=1
  • TCP_KEEPIDLE=initialDelay
  • TCP_KEEPCNT=10
  • TCP_KEEPINTVL=1

Parameters​

enableboolean
initialDelaynumber

Returns​

SocketSocketRequired
The socket itself.

Since​

v0.1.92

setMaxListeners​

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 toInfinity (or 0) to indicate an unlimited number of listeners.

Returns a reference to the EventEmitter, so that calls can be chained.

Parameters​

nnumberRequired

Returns​

SocketSocketRequired

Since​

v0.3.5

setNoDelay​

Enable/disable the use of Nagle's algorithm.

When a TCP connection is created, it will have Nagle's algorithm enabled.

Nagle's algorithm delays data before it is sent via the network. It attempts to optimize throughput at the expense of latency.

Passing true for noDelay or not passing an argument will disable Nagle's algorithm for the socket. Passing false for noDelay will enable Nagle's algorithm.

Parameters​

noDelayboolean

Returns​

SocketSocketRequired
The socket itself.

Since​

v0.1.90

setTimeout​

Sets the socket to timeout after timeout milliseconds of inactivity on the socket. By default net.Socket do not have a timeout.

When an idle timeout is triggered the socket will receive a 'timeout' event but the connection will not be severed. The user must manually call socket.end() or socket.destroy() to end the connection.

socket.setTimeout(3000);
socket.on('timeout', () => {
  console.log('socket timeout');
  socket.end();
});

If timeout is 0, then the existing idle timeout is disabled.

The optional callback parameter will be added as a one-time listener for the 'timeout' event.

Parameters​

timeoutnumberRequired
callback() => void

Returns​

SocketSocketRequired
The socket itself.

Since​

v0.1.90

some​

This method is similar to Array.prototype.some and calls fn on each chunk in the stream until the awaited return value is true (or any truthy value). Once an fn call on a chunk awaited return value is truthy, the stream is destroyed and the promise is fulfilled with true. If none of the fn calls on the chunks return a truthy value, the promise is fulfilled with false.

Parameters​

fn(data: any, options?: Pick<ArrayOptions, "signal">) => boolean | Promise<boolean>Required
a function to call on each chunk of the stream. Async or not.
optionsArrayOptions

Returns​

PromisePromise<boolean>Required
a promise evaluating to true if fn returned a truthy value for at least one of the chunks.

Since​

v17.5.0

take​

This method returns a new stream with the first limit chunks.

Parameters​

limitnumberRequired
the number of chunks to take from the readable.
optionsPick<ArrayOptions, "signal">

Returns​

ReadableReadableRequired
a stream with limit chunks taken.

Since​

v17.5.0

toArray​

This method allows easily obtaining the contents of a stream.

As this method reads the entire stream into memory, it negates the benefits of streams. It's intended for interoperability and convenience, not as the primary way to consume streams.

Parameters​

optionsPick<ArrayOptions, "signal">

Returns​

PromisePromise<any[]>Required
a promise containing an array with the contents of the stream.

Since​

v17.5.0

uncork​

The writable.uncork() method flushes all data buffered since cork was called.

When using writable.cork() and writable.uncork() to manage the buffering of writes to a stream, defer calls to writable.uncork() usingprocess.nextTick(). Doing so allows batching of allwritable.write() calls that occur within a given Node.js event loop phase.

stream.cork();
stream.write('some ');
stream.write('data ');
process.nextTick(() => stream.uncork());

If the writable.cork() method is called multiple times on a stream, the same number of calls to writable.uncork() must be called to flush the buffered data.

stream.cork();
stream.write('some ');
stream.cork();
stream.write('data ');
process.nextTick(() => {
  stream.uncork();
  // The data will not be flushed until uncork() is called a second time.
  stream.uncork();
});

See also: writable.cork().

Returns​

voidvoid

Since​

v0.11.2

unpipe​

The readable.unpipe() method detaches a Writable stream previously attached using the pipe method.

If the destination is not specified, then _all_ pipes are detached.

If the destination is specified, but no pipe is set up for it, then the method does nothing.

const fs = require('node:fs');
const readable = getReadableStreamSomehow();
const writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second.
readable.pipe(writable);
setTimeout(() => {
  console.log('Stop writing to file.txt.');
  readable.unpipe(writable);
  console.log('Manually close the file stream.');
  writable.end();
}, 1000);

Parameters​

destinationWritableStream
Optional specific stream to unpipe

Returns​

SocketSocketRequired

Since​

v0.9.4

unref​

Calling unref() on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already unrefed callingunref() again will have no effect.

Returns​

SocketSocketRequired
The socket itself.

Since​

v0.9.1

unshift​

Passing chunk as null signals the end of the stream (EOF) and behaves the same as readable.push(null), after which no more data can be written. The EOF signal is put at the end of the buffer and any buffered data will still be flushed.

The readable.unshift() method pushes a chunk of data back into the internal buffer. This is useful in certain situations where a stream is being consumed by code that needs to "un-consume" some amount of data that it has optimistically pulled out of the source, so that the data can be passed on to some other party.

The stream.unshift(chunk) method cannot be called after the 'end' event has been emitted or a runtime error will be thrown.

Developers using stream.unshift() often should consider switching to use of a Transform stream instead. See the API for stream implementers section for more information.

// Pull off a header delimited by \n\n.
// Use unshift() if we get too much.
// Call the callback with (error, header, stream).
const { StringDecoder } = require('node:string_decoder');
function parseHeader(stream, callback) {
  stream.on('error', callback);
  stream.on('readable', onReadable);
  const decoder = new StringDecoder('utf8');
  let header = '';
  function onReadable() {
    let chunk;
    while (null !== (chunk = stream.read())) {
      const str = decoder.write(chunk);
      if (str.includes('\n\n')) {
        // Found the header boundary.
        const split = str.split(/\n\n/);
        header += split.shift();
        const remaining = split.join('\n\n');
        const buf = Buffer.from(remaining, 'utf8');
        stream.removeListener('error', callback);
        // Remove the 'readable' listener before unshifting.
        stream.removeListener('readable', onReadable);
        if (buf.length)
          stream.unshift(buf);
        // Now the body of the message can be read from the stream.
        callback(null, header, stream);
        return;
      }
      // Still reading the header.
      header += str;
    }
  }
}

Unlike push, stream.unshift(chunk) will not end the reading process by resetting the internal reading state of the stream. This can cause unexpected results if readable.unshift() is called during a read (i.e. from within a _read implementation on a custom stream). Following the call to readable.unshift() with an immediate push will reset the reading state appropriately, however it is best to simply avoid calling readable.unshift() while in the process of performing a read.

Parameters​

chunkanyRequired
Chunk of data to unshift onto the read queue. For streams not operating in object mode, chunk must be a string, Buffer, Uint8Array, or null. For object mode streams, chunk may be any JavaScript value.
encodingBufferEncoding
Encoding of string chunks. Must be a valid Buffer encoding, such as 'utf8' or 'ascii'.

Returns​

voidvoid

Since​

v0.9.11

wrap​

Prior to Node.js 0.10, streams did not implement the entire node:streammodule API as it is currently defined. (See Compatibility for more information.)

When using an older Node.js library that emits 'data' events and has a pause method that is advisory only, thereadable.wrap() method can be used to create a Readable stream that uses the old stream as its data source.

It will rarely be necessary to use readable.wrap() but the method has been provided as a convenience for interacting with older Node.js applications and libraries.

const { OldReader } = require('./old-api-module.js');
const { Readable } = require('node:stream');
const oreader = new OldReader();
const myReader = new Readable().wrap(oreader);

myReader.on('readable', () => {
  myReader.read(); // etc.
});

Parameters​

streamReadableStreamRequired
An "old style" readable stream

Returns​

SocketSocketRequired

Since​

v0.9.4

write​

**write**(buffer, cb?): boolean

Sends data on the socket. The second parameter specifies the encoding in the case of a string. It defaults to UTF8 encoding.

Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory.'drain' will be emitted when the buffer is again free.

The optional callback parameter will be executed when the data is finally written out, which may not be immediately.

See Writable stream write() method for more information.

Parameters​

bufferstring | Uint8ArrayRequired
cb(err?: Error) => void

Returns​

booleanboolean

Since​

v0.1.90

**write**(str, encoding?, cb?): boolean

Parameters​

strstring | Uint8ArrayRequired
encodingBufferEncoding
cb(err?: Error) => void

Returns​

booleanboolean

addAbortListener​

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​

signalAbortSignalRequired
resource(event: Event) => voidRequired

Returns​

[dispose]() => voidRequired

Since​

v20.5.0

from​

A utility method for creating duplex streams.

  • Stream converts writable stream into writable Duplex and readable stream to Duplex.
  • Blob converts into readable Duplex.
  • string converts into readable Duplex.
  • ArrayBuffer converts into readable Duplex.
  • AsyncIterable converts into a readable Duplex. Cannot yield null.
  • AsyncGeneratorFunction converts into a readable/writable transform Duplex. Must take a source AsyncIterable as first parameter. Cannot yield null.
  • AsyncFunction converts into a writable Duplex. Must return either null or undefined
  • Object ({ writable, readable }) converts readable and writable into Stream and then combines them into Duplex where the Duplex will write to the writable and read from the readable.
  • Promise converts into readable Duplex. Value null is ignored.

Parameters​

srcstring | Object | Promise<any> | ArrayBuffer | Stream | Blob | Iterable<any> | AsyncIterable<any> | AsyncGeneratorFunctionRequired

Returns​

DuplexDuplexRequired

Since​

v16.8.0

fromWeb​

A utility method for creating a Duplex from a web ReadableStream and WritableStream.

Parameters​

duplexStreamobjectRequired
duplexStream.readableReadableStream<any>Required
duplexStream.writableWritableStream<any>Required
optionsPick<DuplexOptions, "signal" | "allowHalfOpen" | "decodeStrings" | "encoding" | "highWaterMark" | "objectMode">

Returns​

DuplexDuplexRequired

Since​

v17.0.0

getEventListeners​

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​

emitterEventEmitter | _DOMEventTargetRequired
namestring | symbolRequired

Returns​

Function[]Function[]Required

Since​

v15.2.0, v14.17.0

getMaxListeners​

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​

emitterEventEmitter | _DOMEventTargetRequired

Returns​

numbernumber

Since​

v19.9.0

isDisturbed​

Returns whether the stream has been read from or cancelled.

Parameters​

streamReadableStream | ReadableRequired

Returns​

booleanboolean

Since​

v16.8.0

listenerCount​

A class method that returns the number of listeners for the given eventNameregistered on the given emitter.

import { EventEmitter, listenerCount } from 'node:events';

const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2

Parameters​

emitterEventEmitterRequired
The emitter to query
eventNamestring | symbolRequired
The event name

Returns​

numbernumber

Since​

v0.9.12

Deprecated​

Since v3.2.0 - Use listenerCount instead.

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());

Parameters​

emitterEventEmitterRequired
eventNamestringRequired
The name of the event being listened for
optionsStaticEventEmitterOptions

Returns​

AsyncIterableIteratorAsyncIterableIterator<any>Required
that iterates eventName events emitted by the emitter

Since​

v13.6.0, v12.16.0

once​

Static **once**(emitter, eventName, options?): Promise&#60;any[]&#62;

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​

emitter_NodeEventTargetRequired
eventNamestring | symbolRequired
optionsStaticEventEmitterOptions

Returns​

PromisePromise<any[]>Required

Since​

v11.13.0, v10.16.0

Static **once**(emitter, eventName, options?): Promise&#60;any[]&#62;

Parameters​

emitter_DOMEventTargetRequired
eventNamestringRequired
optionsStaticEventEmitterOptions

Returns​

PromisePromise<any[]>Required

setMaxListeners​

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

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

setMaxListeners(5, target, emitter);

Parameters​

nnumber
A non-negative number. The maximum number of listeners per EventTarget event.
eventTargets(EventEmitter | _DOMEventTarget)[]Required

Returns​

voidvoid

Since​

v15.4.0

toWeb​

A utility method for creating a web ReadableStream and WritableStream from a Duplex.

Parameters​

streamDuplexDuplexRequired

Returns​

objectobject
readableReadableStream<any>Required
writableWritableStream<any>Required

Since​

v17.0.0

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