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 false
.
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.
v8.0.0
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
Optional
Readonly
localThe numeric representation of the local port. For example, 80
or 21
.
v0.9.6
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 encoding
property 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.
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
captureStatic
captureSets or gets the default captureRejection value for all emitters.
Static
defaultStatic
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.
Optional
_constructOptional
_writevevents.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()
.
v8.0.0
Optional
error: ErrorError which will be passed as payload in 'error'
event
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.
const EventEmitter = require('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
v0.1.26
Rest
...args: any[]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.
v0.1.90
The socket itself.
Optional
callback: (() => void)Optional callback for when the socket is finished.
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 Symbol
s.
const EventEmitter = require('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 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 eventName
and 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.
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
v0.1.101
The name of the event.
The callback function
Rest
...args: any[]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.
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
v0.3.0
The name of the event.
The callback function
Rest
...args: any[]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 eventName
and listener
will result in the listener
being added, and called, multiple
times.
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
v6.0.0
The name of the event.
The callback function
Rest
...args: any[]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.
v6.0.0
The name of the event.
The callback function
Rest
...args: any[]Optional
encoding: BufferEncodingReturns a copy of the array of listeners for the event named eventName
,
including any wrappers (such as those created by .once()
).
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.
v0.9.4
Optional
size: numberOptional argument to specify how much data to read.
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.
v0.1.26
Optional
event: string | symbolRemoves 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.
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:
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
The socket itself.
The writable.setDefaultEncoding()
method sets the default encoding
for a Writable
stream.
v0.11.15
The new default encoding
Set the encoding for the socket as a Readable Stream
. See readable.setEncoding()
for more information.
v0.1.90
The socket itself.
Optional
encoding: BufferEncodingEnable/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
v0.1.92
The socket itself.
Optional
enable: booleanOptional
initialDelay: numberBy default EventEmitter
s will print a warning if more than 10
listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. The emitter.setMaxListeners()
method allows the limit to be
modified for this specific EventEmitter
instance. The value can be set toInfinity
(or 0
) to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter
, so that calls can be chained.
v0.3.5
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.
v0.1.90
The socket itself.
Optional
noDelay: booleanSets 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.
v0.1.90
The socket itself.
Optional
callback: (() => void)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('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);
v0.9.4
Optional
destination: WritableStreamOptional specific stream to unpipe
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('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.
v0.9.11
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'
.
Prior to Node.js 0.10, streams did not implement the entire stream
module 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('stream');
const oreader = new OldReader();
const myReader = new Readable().wrap(oreader);
myReader.on('readable', () => {
myReader.read(); // etc.
});
v0.9.4
An "old style" readable stream
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.
v0.1.90
Optional
encoding: BufferEncodingOptional
cb: ((err?: Error) => void)Static
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 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.v16.8.0
Static
fromExperimental
A utility method for creating a Readable
from a web ReadableStream
.
v17.0.0
Optional
options: Pick<ReadableOptions, "encoding" | "highWaterMark" | "objectMode" | "signal">Static
getReturns a copy of the array of listeners for the event named eventName
.
For EventEmitter
s this behaves exactly the same as calling .listeners
on
the emitter.
For EventTarget
s this is the only way to get the event listeners for the
event target. This is useful for debugging and diagnostic purposes.
const { getEventListeners, EventEmitter } = require('events');
{
const ee = new EventEmitter();
const listener = () => console.log('Events are fun');
ee.on('foo', listener);
getEventListeners(ee, 'foo'); // [listener]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
getEventListeners(et, 'foo'); // [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 eventName
registered on the given emitter
.
const { EventEmitter, listenerCount } = require('events');
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2
v0.9.12
Since v3.2.0 - Use listenerCount
instead.
The emitter to query
The event name
Static
onconst { on, EventEmitter } = require('events');
(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')) {
// 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:
const { on, EventEmitter } = require('events');
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());
v13.6.0, v12.16.0
that iterates eventName
events emitted by the emitter
The name of the event being listened for
Optional
options: StaticEventEmitterOptionsStatic
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.
const { once, EventEmitter } = require('events');
async function run() {
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.log('error happened', err);
}
}
run();
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:
const { EventEmitter, once } = require('events');
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.log('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
An AbortSignal
can be used to cancel waiting for the event:
const { EventEmitter, once } = require('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!
v11.13.0, v10.16.0
Optional
options: StaticEventEmitterOptionsOptional
options: StaticEventEmitterOptionsStatic
setconst {
setMaxListeners,
EventEmitter
} = require('events');
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
v15.4.0
Optional
n: numberA non-negative number. The maximum number of listeners per EventTarget
event.
Rest
...eventTargets: (EventEmitter | _DOMEventTarget)[]Static
toExperimental
A utility method for creating a web ReadableStream
from a Readable
.
v17.0.0
Generated using TypeDoc
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 anEventEmitter
.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