Optional options: SocketConstructorOptsIf 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.
v0.9.4
Readonly bufferThis 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().
v0.3.8
Since v14.6.0 - Use writableLength instead.
Readonly bytesThe amount of received bytes.
v0.5.3
Readonly bytesThe amount of bytes sent.
v0.5.3
Readonly closedIs true after 'close' has been emitted.
v18.0.0
Readonly connectingIf 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.
v6.1.0
Readonly destroyedSee writable.destroyed for further details.
Readonly erroredReturns error if the stream has been destroyed with an error.
v18.0.0
Optional Readonly localThe 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'.
v0.9.6
Optional Readonly localThe string representation of the local IP family. 'IPv4' or 'IPv6'.
v18.8.0, v16.18.0
Optional Readonly localThe numeric representation of the local port. For example, 80 or 21.
v0.9.6
Readonly pendingThis 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).
v11.2.0, v10.16.0
Is true if it is safe to call readable.read(), which means
the stream has not been destroyed or emitted 'error' or 'end'.
v11.4.0
Readonly Experimental readableReturns whether the stream was destroyed or errored before emitting 'end'.
v16.8.0
Readonly Experimental readableReturns whether 'data' has been emitted.
v16.7.0, v14.18.0
Readonly readableGetter for the property encoding of a given Readable stream. The encodingproperty can be set using the readable.setEncoding() method.
v12.7.0
Readonly readableBecomes true when 'end' event is emitted.
v12.9.0
Readonly readableThis property reflects the current state of a Readable stream as described
in the Three states section.
v9.4.0
Readonly readableReturns the value of highWaterMark passed when creating this Readable.
v9.3.0
Readonly readableThis 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.
v9.4.0
Readonly readableGetter for the property objectMode of a given Readable stream.
v12.3.0
Readonly readyThis property represents the state of the connection as a string.
socket.readyState is opening.open.readOnly.writeOnly.v0.5.0
Optional Readonly remoteThe 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).
v0.5.10
Optional Readonly remoteThe string representation of the remote IP family. 'IPv4' or 'IPv6'.
v0.11.14
Optional Readonly remoteThe numeric representation of the remote port. For example, 80 or 21.
v0.5.10
Optional Readonly timeoutThe socket timeout in milliseconds as set by socket.setTimeout().
It is undefined if a timeout has not been set.
v10.7.0
Readonly writableIs true if it is safe to call writable.write(), which means
the stream has not been destroyed, errored, or ended.
v11.4.0
Readonly writableNumber of times writable.uncork() needs to be
called in order to fully uncork the stream.
v13.2.0, v12.16.0
Readonly writableIs true after writable.end() has been called. This property
does not indicate whether the data has been flushed, for this use writable.writableFinished instead.
v12.9.0
Readonly writableIs set to true immediately before the 'finish' event is emitted.
v12.6.0
Readonly writableReturn the value of highWaterMark passed when creating this Writable.
v9.3.0
Readonly writableThis 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.
v9.4.0
Readonly writableIs true if the stream's buffer has been full and stream will emit 'drain'.
v15.2.0, v14.17.0
Readonly writableGetter for the property objectMode of a given Writable stream.
v12.3.0
Static Readonly captureValue: Symbol.for('nodejs.rejection')
See how to write a custom rejection handler.
v13.4.0, v12.16.0
Static captureValue: boolean
Change the default captureRejections option on all new EventEmitter objects.
v13.4.0, v12.16.0
Static defaultBy 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.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 allEventEmitter instances, including those created before
the change is made. However, calling emitter.setMaxListeners(n) still has
precedence over events.defaultMaxListeners.
This is not a hard limit. The EventEmitter instance will allow
more listeners to be added but will output a trace warning to stderr indicating
that a "possible EventEmitter memory leak" has been detected. For any singleEventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners()methods can be used to
temporarily avoid this warning:
import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
// do stuff
emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});
The --trace-warnings command-line flag can be used to display the
stack trace for such warnings.
The emitted warning can be inspected with process.on('warning') and will
have the additional emitter, type, and count properties, referring to
the event emitter instance, the event's name and the number of attached
listeners, respectively.
Its name property is set to 'MaxListenersExceededWarning'.
v0.11.2
Static Readonly errorThis symbol shall be used to install a listener for only monitoring 'error'events. Listeners installed using this symbol are called before the regular'error' listeners are called.
Installing a listener using this symbol does not change the behavior once an'error' event is emitted. Therefore, the process will still crash if no
regular 'error' listener is installed.
v13.6.0, v12.17.0
Optional _constructOptional error: null | ErrorOptional _writevOptional error: null | Errorevents.EventEmitter
Rest ...args: any[]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' }
v0.1.90
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.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.
Optional connectionListener: (() => void)Optional connectionListener: (() => void)Optional connectionListener: (() => void)Optional connectionListener: (() => void)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().
v0.11.2
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().
Optional error: ErrorError which will be passed as payload in 'error' event
v8.0.0
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
Rest ...args: any[]v0.1.26
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.
Optional callback: (() => void)Optional callback for when the socket is finished.
The socket itself.
v0.1.90
Optional callback: (() => void)Optional encoding: BufferEncodingOptional callback: (() => void)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) ]
v6.0.0
Returns the current max listener value for the EventEmitter which is either
set by emitter.setMaxListeners(n) or defaults to defaultMaxListeners.
v1.0.0
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
v0.11.14
Returns the number of listeners listening for the event named eventName.
If listener is provided, it will return how many times the listener is found
in the list of the listeners of the event.
The name of the event being listened for
Optional listener: FunctionThe event handler function
v3.2.0
Returns a copy of the array of listeners for the event named eventName.
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
v0.1.26
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
The name of the event.
The callback function
Rest ...args: any[]v0.1.101
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
The name of the event.
The callback function
Rest ...args: any[]v0.3.0
Optional options: { Optional end?: booleanAdds 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.
The name of the event.
The callback function
Rest ...args: any[]v6.0.0
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.
The name of the event.
The callback function
Rest ...args: any[]v6.0.0
Optional encoding: BufferEncodingReturns a copy of the array of listeners for the event named eventName,
including any wrappers (such as those created by .once()).
import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));
// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];
// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();
// Logs "log once" to the console and removes the listener
logFnWrapper();
emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');
// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
v9.4.0
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.
Optional size: numberOptional argument to specify how much data to read.
v0.9.4
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code,
particularly when the EventEmitter instance was created by some other
component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
Optional event: string | symbolv0.1.26
Removes the specified listener from the listener array for the event namedeventName.
const callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
removeListener() will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified eventName, then removeListener() must be
called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the
time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and before the last listener finishes execution
will not remove them fromemit() in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
const callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
const callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered after the listener
being removed. This will not impact the order in which listeners are called,
but it means that any copies of the listener array as returned by
the emitter.listeners() method will need to be recreated.
When a single function has been added as a handler multiple times for a single
event (as in the example below), removeListener() will remove the most
recently added instance. In the example the once('ping')listener is removed:
import { EventEmitter } from 'node:events';
const ee = new EventEmitter();
function pong() {
console.log('pong');
}
ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);
ee.emit('ping');
ee.emit('ping');
Returns a reference to the EventEmitter, so that calls can be chained.
v0.1.26
Rest ...args: any[]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.
v18.3.0, v16.17.0
The writable.setDefaultEncoding() method sets the default encoding for a Writable stream.
The new default encoding
v0.11.15
Set the encoding for the socket as a Readable Stream. See readable.setEncoding() for more information.
Optional encoding: BufferEncodingThe socket itself.
v0.1.90
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=1TCP_KEEPIDLE=initialDelayTCP_KEEPCNT=10TCP_KEEPINTVL=1Optional enable: booleanOptional initialDelay: numberThe socket itself.
v0.1.92
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.
v0.3.5
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.
Optional noDelay: booleanThe socket itself.
v0.1.90
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.
Optional callback: (() => void)The socket itself.
v0.1.90
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().
v0.11.2
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);
Optional destination: WritableStreamOptional specific stream to unpipe
v0.9.4
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.
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.
Optional encoding: BufferEncodingEncoding of string chunks. Must be a valid Buffer encoding, such as 'utf8' or 'ascii'.
v0.9.11
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.
});
An "old style" readable stream
v0.9.4
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.
Optional cb: ((err?) => void)Optional err: Errorv0.1.90
Optional encoding: BufferEncodingOptional cb: ((err?) => void)Optional err: ErrorStatic fromA 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 undefinedObject ({ 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.v16.8.0
Static fromExperimental
A utility method for creating a Duplex from a web ReadableStream and WritableStream.
Optional options: Pick<DuplexOptions, "encoding" | "highWaterMark" | "objectMode" | "signal" | "decodeStrings" | "allowHalfOpen">v17.0.0
Static getReturns 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] ]
}
v15.2.0, v14.17.0
Static isReturns whether the stream has been read from or cancelled.
v16.8.0
Static listenerA 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
The emitter to query
The event name
v0.9.12
Since v3.2.0 - Use listenerCount instead.
Static onimport { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
Returns an AsyncIterator that iterates eventName events. It will throw
if the EventEmitter emits 'error'. It removes all listeners when
exiting the loop. The value returned by each iteration is an array
composed of the emitted event arguments.
An AbortSignal can be used to cancel waiting on events:
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ac = new AbortController();
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
process.nextTick(() => ac.abort());
The name of the event being listened for
Optional options: StaticEventEmitterOptionsthat iterates eventName events emitted by the emitter
v13.6.0, v12.16.0
Static onceCreates a Promise that is fulfilled when the EventEmitter emits the given
event or that is rejected if the EventEmitter emits 'error' while waiting.
The Promise will resolve with an array of all the arguments emitted to the
given event.
This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event
semantics and does not listen to the 'error' event.
import { once, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
process.nextTick(() => {
ee.emit('myevent', 42);
});
const [value] = await once(ee, 'myevent');
console.log(value);
const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});
try {
await once(ee, 'myevent');
} catch (err) {
console.error('error happened', err);
}
The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the
'error' event itself, then it is treated as any other kind of event without
special handling:
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.error('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
An AbortSignal can be used to cancel waiting for the event:
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
Optional options: StaticEventEmitterOptionsv11.13.0, v10.16.0
Optional options: StaticEventEmitterOptionsStatic setimport { setMaxListeners, EventEmitter } from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
Optional n: numberA non-negative number. The maximum number of listeners per EventTarget event.
Rest ...eventTargets: (EventEmitter | _DOMEventTarget)[]v15.4.0
Static toExperimental
A utility method for creating a web ReadableStream and WritableStream from a Duplex.
v17.0.0
Generated using TypeDoc
This class is an abstraction of a TCP socket or a streaming
IPCendpoint (uses named pipes on Windows, and Unix domain sockets otherwise). It is also anEventEmitter.A
net.Socketcan 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