Readable

ReadableReadableRequired

Inherited from

addListener(event, listener): Readable

Parameters

event"data"Required

listener(chunk: any) => voidRequired

Returns

ReadableReadableRequired

Inherited from

addListener(event, listener): Readable

Parameters

event"end"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

addListener(event, listener): Readable

Parameters

event"error"Required

listener(err: Error) => voidRequired

Returns

ReadableReadableRequired

Inherited from

addListener(event, listener): Readable

Parameters

event"pause"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

addListener(event, listener): Readable

Parameters

event"readable"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

addListener(event, listener): Readable

Parameters

event"resume"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

addListener(event, listener): Readable

Parameters

eventstring | symbolRequired

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

Returns

ReadableReadableRequired

Inherited from

destroy

destroy(error?): Readable

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

ReadableReadableRequired

Since

v8.0.0

Inherited from

ReadableBase.destroy

emit

emit(event): 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

event"close"Required

Returns

boolean

booleanboolean

Since

v0.1.26

Inherited from

emit(event, chunk): boolean

Parameters

event"data"Required

chunkanyRequired

Returns

boolean

booleanboolean

Inherited from

emit(event): boolean

Parameters

event"end"Required

Returns

boolean

booleanboolean

Inherited from

emit(event, err): boolean

Parameters

event"error"Required

errErrorRequired

Returns

boolean

booleanboolean

Inherited from

emit(event): boolean

Parameters

event"pause"Required

Returns

boolean

booleanboolean

Inherited from

emit(event): boolean

Parameters

event"readable"Required

Returns

boolean

booleanboolean

Inherited from

emit(event): boolean

Parameters

event"resume"Required

Returns

boolean

booleanboolean

Inherited from

emit(event, ...args): boolean

Parameters

eventstring | symbolRequired

argsany[]Required

Returns

boolean

booleanboolean

Inherited from

ReadableBase.getMaxListeners

eventNames

eventNames(): (string | symbol)[]

Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.

import { EventEmitter } from 'node:events';

const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});

const sym = Symbol('symbol');
myEE.on(sym, () => {});

console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]

Returns

(string | symbol)[]

(string \| symbol)[](string | symbol)[]Required

Since

v6.0.0

Inherited from

ReadableBase.eventNames

getMaxListeners

getMaxListeners(): number

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

Returns

number

numbernumber

Since

v1.0.0

Inherited from

isPaused

isPaused(): boolean

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

boolean

booleanboolean

Since

v0.11.14

Inherited from

ReadableBase.isPaused

listenerCount

listenerCount(eventName, listener?): number

Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.

Parameters

eventNamestring | symbolRequired

The name of the event being listened for

listenerFunction

The event handler function

Returns

number

numbernumber

Since

v3.2.0

Inherited from

ReadableBase.listenerCount

listeners

listeners(eventName): Function[]

Returns a copy of the array of listeners for the event named eventName.

server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]

Parameters

eventNamestring | symbolRequired

Returns

Function[]

Function[]Function[]Required

Since

v0.1.26

Inherited from

ReadableBase.listeners

off

off(eventName, listener): Readable

Alias for emitter.removeListener().

Parameters

eventNamestring | symbolRequired

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

Returns

ReadableReadableRequired

Since

v10.0.0

Inherited from

ReadableBase.off

on

on(event, listener): Readable

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

event"close"Required

The name of the event.

listener() => voidRequired

The callback function

Returns

ReadableReadableRequired

Since

v0.1.101

Inherited from

on(event, listener): Readable

Parameters

event"data"Required

listener(chunk: any) => voidRequired

Returns

ReadableReadableRequired

Inherited from

on(event, listener): Readable

Parameters

event"end"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

on(event, listener): Readable

Parameters

event"error"Required

listener(err: Error) => voidRequired

Returns

ReadableReadableRequired

Inherited from

on(event, listener): Readable

Parameters

event"pause"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

on(event, listener): Readable

Parameters

event"readable"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

on(event, listener): Readable

Parameters

event"resume"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

on(event, listener): Readable

Parameters

eventstring | symbolRequired

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

Returns

ReadableReadableRequired

Inherited from

once

once(event, listener): Readable

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

event"close"Required

The name of the event.

listener() => voidRequired

The callback function

Returns

ReadableReadableRequired

Since

v0.3.0

Inherited from

once(event, listener): Readable

Parameters

event"data"Required

listener(chunk: any) => voidRequired

Returns

ReadableReadableRequired

Inherited from

once(event, listener): Readable

Parameters

event"end"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

once(event, listener): Readable

Parameters

event"error"Required

listener(err: Error) => voidRequired

Returns

ReadableReadableRequired

Inherited from

once(event, listener): Readable

Parameters

event"pause"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

once(event, listener): Readable

Parameters

event"readable"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

once(event, listener): Readable

Parameters

event"resume"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

once(event, listener): Readable

Parameters

eventstring | symbolRequired

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

Returns

ReadableReadableRequired

Inherited from

pause

pause(): Readable

The readable.pause() method will cause a stream in flowing mode to stop emitting 'data' events, switching out of flowing mode. Any data that becomes available will remain in the internal buffer.

const readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
  console.log(`Received ${chunk.length} bytes of data.`);
  readable.pause();
  console.log('There will be no additional data for 1 second.');
  setTimeout(() => {
    console.log('Now data will start flowing again.');
    readable.resume();
  }, 1000);
});

The readable.pause() method has no effect if there is a 'readable'event listener.

Returns

ReadableReadableRequired

Since

v0.9.4

Inherited from

ReadableBase.pause

pipe

pipe<T>(destination, options?): T

TWritableStreamRequired

Parameters

destinationTRequired

optionsobject

options.endboolean

Returns

T

Inherited from

ReadableBase.pipe

prependListener

prependListener(event, listener): Readable

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

event"close"Required

The name of the event.

listener() => voidRequired

The callback function

Returns

ReadableReadableRequired

Since

v6.0.0

Inherited from

prependListener(event, listener): Readable

Parameters

event"data"Required

listener(chunk: any) => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependListener(event, listener): Readable

Parameters

event"end"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependListener(event, listener): Readable

Parameters

event"error"Required

listener(err: Error) => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependListener(event, listener): Readable

Parameters

event"pause"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependListener(event, listener): Readable

Parameters

event"readable"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependListener(event, listener): Readable

Parameters

event"resume"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependListener(event, listener): Readable

Parameters

eventstring | symbolRequired

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

Returns

ReadableReadableRequired

Inherited from

prependOnceListener

prependOnceListener(event, listener): Readable

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

event"close"Required

The name of the event.

listener() => voidRequired

The callback function

Returns

ReadableReadableRequired

Since

v6.0.0

Inherited from

prependOnceListener(event, listener): Readable

Parameters

event"data"Required

listener(chunk: any) => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependOnceListener(event, listener): Readable

Parameters

event"end"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependOnceListener(event, listener): Readable

Parameters

event"error"Required

listener(err: Error) => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependOnceListener(event, listener): Readable

Parameters

event"pause"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependOnceListener(event, listener): Readable

Parameters

event"readable"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependOnceListener(event, listener): Readable

Parameters

event"resume"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

prependOnceListener(event, listener): Readable

Parameters

eventstring | symbolRequired

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

Returns

ReadableReadableRequired

Inherited from

ReadableBase.rawListeners

push

push(chunk, encoding?): boolean

Parameters

chunkanyRequired

encodingBufferEncoding

Returns

boolean

booleanboolean

Inherited from

ReadableBase.push

rawListeners

rawListeners(eventName): Function[]

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');

Parameters

eventNamestring | symbolRequired

Returns

Function[]

Function[]Function[]Required

Since

v9.4.0

Inherited from

read

read(size?): any

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

any

anyany

Since

v0.9.4

Inherited from

ReadableBase.read

removeAllListeners

removeAllListeners(event?): Readable

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

ReadableBase.removeAllListeners

ReadableReadableRequired

Since

v0.1.26

Inherited from

removeListener

removeListener(event, listener): Readable

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

ReadableReadableRequired

Since

v0.1.26

Inherited from

removeListener(event, listener): Readable

Parameters

event"data"Required

listener(chunk: any) => voidRequired

Returns

ReadableReadableRequired

Inherited from

removeListener(event, listener): Readable

Parameters

event"end"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

removeListener(event, listener): Readable

Parameters

event"error"Required

listener(err: Error) => voidRequired

Returns

ReadableReadableRequired

Inherited from

removeListener(event, listener): Readable

Parameters

event"pause"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

removeListener(event, listener): Readable

Parameters

event"readable"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

removeListener(event, listener): Readable

Parameters

event"resume"Required

listener() => voidRequired

Returns

ReadableReadableRequired

Inherited from

removeListener(event, listener): Readable

Parameters

eventstring | symbolRequired

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

Returns

ReadableReadableRequired

Inherited from

resume

resume(): Readable

The readable.resume() method causes an explicitly paused Readable stream to resume emitting 'data' events, switching the stream into flowing mode.

The readable.resume() method can be used to fully consume the data from a stream without actually processing any of that data:

getReadableStreamSomehow()
  .resume()
  .on('end', () => {
    console.log('Reached the end, but did not read anything.');
  });

The readable.resume() method has no effect if there is a 'readable'event listener.

Returns

ReadableReadableRequired

Since

v0.9.4

Inherited from

ReadableBase.resume

setEncoding

setEncoding(encoding): Readable

The readable.setEncoding() method sets the character encoding for data read from the Readable stream.

By default, no encoding is assigned and stream data will be returned asBuffer objects. Setting an encoding causes the stream data to be returned as strings of the specified encoding rather than as Bufferobjects. For instance, calling readable.setEncoding('utf8') will cause the output data to be interpreted as UTF-8 data, and passed as strings. Callingreadable.setEncoding('hex') will cause the data to be encoded in hexadecimal string format.

The Readable stream will properly handle multi-byte characters delivered through the stream that would otherwise become improperly decoded if simply pulled from the stream as Buffer objects.

const readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', (chunk) => {
  assert.equal(typeof chunk, 'string');
  console.log('Got %d characters of string data:', chunk.length);
});

Parameters

encodingBufferEncodingRequired

The encoding to use.

Returns

ReadableReadableRequired

Since

v0.9.4

Inherited from

ReadableBase.setEncoding

setMaxListeners

setMaxListeners(n): Readable

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

ReadableBase.setMaxListeners

ReadableReadableRequired

Since

v0.3.5

Inherited from

unpipe

unpipe(destination?): Readable

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

ReadableReadableRequired

Since

v0.9.4

Inherited from

ReadableBase.unpipe

unshift

unshift(chunk, encoding?): void

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

void

voidvoid

Since

v0.9.11

Inherited from

ReadableBase.unshift

wrap

wrap(stream): Readable

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

ReadableReadableRequired

Since

v0.9.4

Inherited from

ReadableBase.wrap

from

Static from(iterable, options?): Readable

A utility method for creating Readable Streams out of iterators.

Parameters

iterableIterable<any> | AsyncIterable<any>Required

optionsReadableOptions

Returns

ReadableReadableRequired

Inherited from

ReadableBase.from

fromWeb

Static fromWeb(readableStream, options?): Readable

A utility method for creating a Readable from a web ReadableStream.

Parameters

readableStreamReadableStream<any>Required

optionsPick<ReadableOptions, "signal" | "encoding" | "highWaterMark" | "objectMode">

Returns

ReadableBase.getEventListeners

ReadableReadableRequired

Since

v17.0.0

getEventListeners

Static getEventListeners(emitter, name): Function[]

Returns a copy of the array of listeners for the event named eventName.

For EventEmitters this behaves exactly the same as calling .listeners on the emitter.

For EventTargets this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.

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

{
  const ee = new EventEmitter();
  const listener = () => console.log('Events are fun');
  ee.on('foo', listener);
  console.log(getEventListeners(ee, 'foo')); // [ [Function: listener] ]
}
{
  const et = new EventTarget();
  const listener = () => console.log('Events are fun');
  et.addEventListener('foo', listener);
  console.log(getEventListeners(et, 'foo')); // [ [Function: listener] ]
}

Parameters

emitterEventEmitter | _DOMEventTargetRequired

namestring | symbolRequired

Returns

Function[]

Function[]Function[]Required

Since

v15.2.0, v14.17.0

Inherited from

isDisturbed

Static isDisturbed(stream): boolean

Returns whether the stream has been read from or cancelled.

Parameters

streamReadableStream | ReadableRequired

Returns

boolean

booleanboolean

Since

v16.8.0

Inherited from

ReadableBase.isDisturbed

listenerCount

Static listenerCount(emitter, eventName): number

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

number

numbernumber

Since

v0.9.12

Deprecated

Since v3.2.0 - Use listenerCount instead.

Inherited from

ReadableBase.listenerCount

on

Static on(emitter, eventName, options?): AsyncIterableIterator<any>

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
  ee.emit('foo', 'bar');
  ee.emit('foo', 42);
});

for await (const event of on(ee, 'foo')) {
  // The execution of this inner block is synchronous and it
  // processes one event at a time (even with await). Do not use
  // if concurrent execution is required.
  console.log(event); // prints ['bar'] [42]
}
// Unreachable here

Returns an AsyncIterator that iterates eventName events. It will throw if the EventEmitter emits 'error'. It removes all listeners when exiting the loop. The value returned by each iteration is an array composed of the emitted event arguments.

An AbortSignal can be used to cancel waiting on events:

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // Emit later on
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo', { signal: ac.signal })) {
    // The execution of this inner block is synchronous and it
    // processes one event at a time (even with await). Do not use
    // if concurrent execution is required.
    console.log(event); // prints ['bar'] [42]
  }
  // Unreachable here
})();

process.nextTick(() => ac.abort());

Parameters

emitterEventEmitterRequired

eventNamestringRequired

The name of the event being listened for

optionsStaticEventEmitterOptions

Returns

AsyncIterableIterator<any>

AsyncIterableIteratorAsyncIterableIterator<any>Required

that iterates eventName events emitted by the emitter

Since

v13.6.0, v12.16.0

Inherited from

once

Static once(emitter, eventName, options?): Promise<any[]>

Creates a Promise that is fulfilled when the EventEmitter emits the given event or that is rejected if the EventEmitter emits 'error' while waiting. The Promise will resolve with an array of all the arguments emitted to the given event.

This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event semantics and does not listen to the 'error' event.

import { once, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

process.nextTick(() => {
  ee.emit('myevent', 42);
});

const [value] = await once(ee, 'myevent');
console.log(value);

const err = new Error('kaboom');
process.nextTick(() => {
  ee.emit('error', err);
});

try {
  await once(ee, 'myevent');
} catch (err) {
  console.error('error happened', err);
}

The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the 'error' event itself, then it is treated as any other kind of event without special handling:

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

const ee = new EventEmitter();

once(ee, 'error')
  .then(([err]) => console.log('ok', err.message))
  .catch((err) => console.error('error', err.message));

ee.emit('error', new Error('boom'));

// Prints: ok boom

An AbortSignal can be used to cancel waiting for the event:

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

const ee = new EventEmitter();
const ac = new AbortController();

async function foo(emitter, event, signal) {
  try {
    await once(emitter, event, { signal });
    console.log('event emitted!');
  } catch (error) {
    if (error.name === 'AbortError') {
      console.error('Waiting for the event was canceled!');
    } else {
      console.error('There was an error', error.message);
    }
  }
}

foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!

Parameters

emitter_NodeEventTargetRequired

eventNamestring | symbolRequired

optionsStaticEventEmitterOptions

Returns

Promise<any[]>

PromisePromise<any[]>Required

Since

v11.13.0, v10.16.0

Inherited from

Static once(emitter, eventName, options?): Promise<any[]>

Parameters

emitter_DOMEventTargetRequired

eventNamestringRequired

optionsStaticEventEmitterOptions

Returns

Promise<any[]>

PromisePromise<any[]>Required

Inherited from