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NDJSONStream

@webda/utils

Class: NDJSONStream

Defined in: packages/utils/src/serializers.ts:40

NDJSONStream is a Readable stream that emits JSON objects separated by newlines.

Extends​

  • Readable

Constructors​

Constructor​

new NDJSONStream(data): NDJSONStream

Defined in: packages/utils/src/serializers.ts:47

Parameters​

data​

any[]

Array of objects to serialize and stream as NDJSON.

Returns​

NDJSONStream

Overrides​

Readable.constructor

Properties​

closed​

readonly closed: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:186

Is true after 'close' has been emitted.

Since​

v18.0.0

Inherited from​

Readable.closed

destroyed​

destroyed: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:181

Is true after readable.destroy() has been called.

Since​

v8.0.0

Inherited from​

Readable.destroyed

errored​

readonly errored: Error

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:191

Returns error if the stream has been destroyed with an error.

Since​

v18.0.0

Inherited from​

GunzipConditional.errored

readable​

readable: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:138

Is true if it is safe to call read, which means the stream has not been destroyed or emitted 'error' or 'end'.

Since​

v11.4.0

Inherited from​

Readable.readable

readableAborted​

readonly readableAborted: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:132

Returns whether the stream was destroyed or errored before emitting 'end'.

Since​

v16.8.0

Inherited from​

Readable.readableAborted

readableDidRead​

readonly readableDidRead: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:143

Returns whether 'data' has been emitted.

Since​

v16.7.0, v14.18.0

Inherited from​

Readable.readableDidRead

readableEncoding​

readonly readableEncoding: BufferEncoding

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:148

Getter for the property encoding of a given Readable stream. The encoding property can be set using the setEncoding method.

Since​

v12.7.0

Inherited from​

GunzipConditional.readableEncoding

readableEnded​

readonly readableEnded: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:153

Becomes true when 'end' event is emitted.

Since​

v12.9.0

Inherited from​

Readable.readableEnded

readableFlowing​

readableFlowing: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:159

This property reflects the current state of a Readable stream as described in the Three states section.

Since​

v9.4.0

Inherited from​

GunzipConditional.readableFlowing

readableHighWaterMark​

readonly readableHighWaterMark: number

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:164

Returns the value of highWaterMark passed when creating this Readable.

Since​

v9.3.0

Inherited from​

Readable.readableHighWaterMark

readableLength​

readonly readableLength: number

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:171

This property contains the number of bytes (or objects) in the queue ready to be read. The value provides introspection data regarding the status of the highWaterMark.

Since​

v9.4.0

Inherited from​

Readable.readableLength

readableObjectMode​

readonly readableObjectMode: boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:176

Getter for the property objectMode of a given Readable stream.

Since​

v12.3.0

Inherited from​

Readable.readableObjectMode

Methods​

_construct()?​

optional _construct(callback): void

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:192

Parameters​

callback​

(error?) => void

Returns​

void

Inherited from​

Readable._construct

_destroy()​

_destroy(error, callback): void

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:655

Parameters​

error​

Error

callback​

(error?) => void

Returns​

void

Inherited from​

Readable._destroy

_read()​

_read(): void

Defined in: packages/utils/src/serializers.ts:55

Push the next JSON-serialized item (followed by \n) or signal end of stream.

Returns​

void

Overrides​

Readable._read

[asyncDispose]()​

[asyncDispose](): Promise<void>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:678

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

Returns​

Promise<void>

Since​

v20.4.0

Inherited from​

Readable.[asyncDispose]

[asyncIterator]()​

[asyncIterator](): AsyncIterator<any>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:672

Returns​

AsyncIterator<any>

AsyncIterator to fully consume the stream.

Since​

v10.0.0

Inherited from​

Readable.[asyncIterator]

[captureRejectionSymbol]()?​

optional [captureRejectionSymbol](error, event, ...args): void

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/events.d.ts:123

The Symbol.for('nodejs.rejection') method is called in case a promise rejection happens when emitting an event and captureRejections is enabled on the emitter. It is possible to use events.captureRejectionSymbol in place of Symbol.for('nodejs.rejection').

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

class MyClass extends EventEmitter {
  constructor() {
    super({ captureRejections: true });
  }

  [captureRejectionSymbol](err, event, ...args) {
    console.log('rejection happened for', event, 'with', err, ...args);
    this.destroy(err);
  }

  destroy(err) {
    // Tear the resource down here.
  }
}

Parameters​

error​

Error

event​

string | symbol

args​

...any[]

Returns​

void

Since​

v13.4.0, v12.16.0

Inherited from​

Readable.[captureRejectionSymbol]

addListener()​

Call Signature​

addListener<E>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:680

Alias for emitter.on(eventName, listener).

Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

listener​

(...args) => void

Returns​

this

Since​

v0.1.26

Inherited from​

Readable.addListener

Call Signature​

addListener(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:684

Parameters​
eventName​

string | symbol

listener​

(...args) => void

Returns​

this

Inherited from​

Readable.addListener

compose()​

compose(stream, options?): Duplex

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:504

import { Readable } from 'node:stream';

async function* splitToWords(source) {
  for await (const chunk of source) {
    const words = String(chunk).split(' ');

    for (const word of words) {
      yield word;
    }
  }
}

const wordsStream = Readable.from(['text passed through', 'composed stream']).compose(splitToWords);
const words = await wordsStream.toArray();

console.log(words); // prints ['text', 'passed', 'through', 'composed', 'stream']

readable.compose(s) is equivalent to stream.compose(readable, s).

This method also allows for an AbortSignal to be provided, which will destroy the composed stream when aborted.

See stream.compose(...streams) for more information.

Parameters​

stream​

WritableStream | WritableStream<any> | TransformStream<any, any> | ((source) => void)

options?​

Abortable

Returns​

Duplex

a stream composed with the stream stream.

Since​

v19.1.0, v18.13.0

Inherited from​

Readable.compose

destroy()​

destroy(error?): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:667

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​

error?​

Error

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

Returns​

this

Since​

v8.0.0

Inherited from​

Readable.destroy

drop()​

drop(limit, options?): Readable

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:627

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

Parameters​

limit​

number

the number of chunks to drop from the readable.

options?​

Abortable

Returns​

Readable

a stream with limit chunks dropped from the start.

Since​

v17.5.0

Inherited from​

Readable.drop

emit()​

Call Signature​

emit<E>(eventName, ...args): boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:685

Synchronously calls each of the listeners registered for the event named eventName, 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
Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

args​

...ReadableEventMap[E]

Returns​

boolean

Since​

v0.1.26

Inherited from​

Readable.emit

Call Signature​

emit(eventName, ...args): boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:686

Parameters​
eventName​

string | symbol

args​

...any[]

Returns​

boolean

Inherited from​

Readable.emit

eventNames()​

eventNames(): (string | symbol)[]

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/events.d.ts:190

Returns an array listing the events for which the emitter has registered listeners.

import { EventEmitter } from 'node:events';

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

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

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

Returns​

(string | symbol)[]

Since​

v6.0.0

Inherited from​

Readable.eventNames

every()​

every(fn, options?): Promise<boolean>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:603

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

Parameters​

fn​

(data, options?) => boolean | Promise<boolean>

a function to call on each chunk of the stream. Async or not.

options?​

Pick<ReadableOperatorOptions, "concurrency" | "signal">

Returns​

Promise<boolean>

a promise evaluating to true if fn returned a truthy value for every one of the chunks.

Since​

v17.5.0

Inherited from​

Readable.every

filter()​

filter(fn, options?): Readable

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:531

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

Parameters​

fn​

(data, options?) => boolean | Promise<boolean>

a function to filter chunks from the stream. Async or not.

options?​

ReadableOperatorOptions

Returns​

Readable

a stream filtered with the predicate fn.

Since​

v17.4.0, v16.14.0

Inherited from​

Readable.filter

find()​

Call Signature​

find<T>(fn, options?): Promise<T>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:586

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

Type Parameters​
T​

T

Parameters​
fn​

(data, options?) => data is T

a function to call on each chunk of the stream. Async or not.

options?​

Pick<ReadableOperatorOptions, "concurrency" | "signal">

Returns​

Promise<T>

a promise evaluating to the first chunk for which fn evaluated with a truthy value, or undefined if no element was found.

Since​

v17.5.0

Inherited from​

Readable.find

Call Signature​

find(fn, options?): Promise<any>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:590

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

Parameters​
fn​

(data, options?) => boolean | Promise<boolean>

a function to call on each chunk of the stream. Async or not.

options?​

Pick<ReadableOperatorOptions, "concurrency" | "signal">

Returns​

Promise<any>

a promise evaluating to the first chunk for which fn evaluated with a truthy value, or undefined if no element was found.

Since​

v17.5.0

Inherited from​

Readable.find

flatMap()​

flatMap(fn, options?): Readable

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:617

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

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

Parameters​

fn​

(data, options?) => any

a function to map over every chunk in the stream. May be async. May be a stream or generator.

options?​

Pick<ReadableOperatorOptions, "concurrency" | "signal">

Returns​

Readable

a stream flat-mapped with the function fn.

Since​

v17.5.0

Inherited from​

Readable.flatMap

forEach()​

forEach(fn, options?): Promise<void>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:550

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

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

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

Parameters​

fn​

(data, options?) => void | Promise<void>

a function to call on each chunk of the stream. Async or not.

options?​

Pick<ReadableOperatorOptions, "concurrency" | "signal">

Returns​

Promise<void>

a promise for when the stream has finished.

Since​

v17.5.0

Inherited from​

Readable.forEach

getMaxListeners()​

getMaxListeners(): number

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/events.d.ts:197

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

Returns​

number

Since​

v1.0.0

Inherited from​

Readable.getMaxListeners

isPaused()​

isPaused(): boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:354

The readable.isPaused() method returns the current operating state of the Readable. This is used primarily by the mechanism that underlies the readable.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

Since​

v0.11.14

Inherited from​

Readable.isPaused

iterator()​

iterator(options?): AsyncIterator<any>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:514

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

Parameters​

options?​

ReadableIteratorOptions

Returns​

AsyncIterator<any>

Since​

v16.3.0

Inherited from​

Readable.iterator

listenerCount()​

Call Signature​

listenerCount<E>(eventName, listener?): number

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:687

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

Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

The name of the event being listened for

listener?​

(...args) => void

The event handler function

Returns​

number

Since​

v3.2.0

Inherited from​

Readable.listenerCount

Call Signature​

listenerCount(eventName, listener?): number

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:691

Parameters​
eventName​

string | symbol

listener?​

(...args) => void

Returns​

number

Inherited from​

Readable.listenerCount

listeners()​

Call Signature​

listeners<E>(eventName): (...args) => void[]

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:692

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] ]
Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

Returns​

(...args) => void[]

Since​

v0.1.26

Inherited from​

Readable.listeners

Call Signature​

listeners(eventName): (...args) => void[]

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:693

Parameters​
eventName​

string | symbol

Returns​

(...args) => void[]

Inherited from​

Readable.listeners

map()​

map(fn, options?): Readable

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:522

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

Parameters​

fn​

(data, options?) => any

a function to map over every chunk in the stream. Async or not.

options?​

ReadableOperatorOptions

Returns​

Readable

a stream mapped with the function fn.

Since​

v17.4.0, v16.14.0

Inherited from​

Readable.map

off()​

Call Signature​

off<E>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:694

Alias for emitter.removeListener().

Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

listener​

(...args) => void

Returns​

this

Since​

v10.0.0

Inherited from​

Readable.off

Call Signature​

off(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:695

Parameters​
eventName​

string | symbol

listener​

(...args) => void

Returns​

this

Inherited from​

Readable.off

on()​

Call Signature​

on<E>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:696

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. The emitter.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
Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

The name of the event.

listener​

(...args) => void

The callback function

Returns​

this

Since​

v0.1.101

Inherited from​

Readable.on

Call Signature​

on(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:697

Parameters​
eventName​

string | symbol

listener​

(...args) => void

Returns​

this

Inherited from​

Readable.on

once()​

Call Signature​

once<E>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:698

Adds a one-time listener 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. The emitter.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
Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

The name of the event.

listener​

(...args) => void

The callback function

Returns​

this

Since​

v0.3.0

Inherited from​

Readable.once

Call Signature​

once(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:702

Parameters​
eventName​

string | symbol

listener​

(...args) => void

Returns​

this

Inherited from​

Readable.once

pause()​

pause(): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:318

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​

this

Since​

v0.9.4

Inherited from​

Readable.pause

pipe()​

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

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:29

Type Parameters​

T​

T extends WritableStream

Parameters​

destination​

T

options?​

PipeOptions

Returns​

T

Since​

v0.9.4

Inherited from​

Readable.pipe

prependListener()​

Call Signature​

prependListener<E>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:703

Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

server.prependListener('connection', (stream) => {
  console.log('someone connected!');
});

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

Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

The name of the event.

listener​

(...args) => void

The callback function

Returns​

this

Since​

v6.0.0

Inherited from​

Readable.prependListener

Call Signature​

prependListener(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:707

Parameters​
eventName​

string | symbol

listener​

(...args) => void

Returns​

this

Inherited from​

Readable.prependListener

prependOnceListener()​

Call Signature​

prependOnceListener<E>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:708

Adds a one-time listener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this listener is removed, and then invoked.

server.prependOnceListener('connection', (stream) => {
  console.log('Ah, we have our first user!');
});

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

Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

The name of the event.

listener​

(...args) => void

The callback function

Returns​

this

Since​

v6.0.0

Inherited from​

Readable.prependOnceListener

Call Signature​

prependOnceListener(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:712

Parameters​
eventName​

string | symbol

listener​

(...args) => void

Returns​

this

Inherited from​

Readable.prependOnceListener

push()​

push(chunk, encoding?): boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:474

Parameters​

chunk​

any

encoding?​

BufferEncoding

Returns​

boolean

Inherited from​

Readable.push

rawListeners()​

Call Signature​

rawListeners<E>(eventName): (...args) => void[]

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:713

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

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

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

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

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

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

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

E extends keyof ReadableEventMap

Parameters​
eventName​

E

Returns​

(...args) => void[]

Since​

v9.4.0

Inherited from​

Readable.rawListeners

Call Signature​

rawListeners(eventName): (...args) => void[]

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:714

Parameters​
eventName​

string | symbol

Returns​

(...args) => void[]

Inherited from​

Readable.rawListeners

read()​

read(size?): any

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:271

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. If size 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 the size 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​

size?​

number

Optional argument to specify how much data to read.

Returns​

any

Since​

v0.9.4

Inherited from​

Readable.read

reduce()​

Call Signature​

reduce<T>(fn): Promise<T>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:649

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

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

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

Type Parameters​
T​

T

Parameters​
fn​

(previous, data, options?) => T

a reducer function to call over every chunk in the stream. Async or not.

Returns​

Promise<T>

a promise for the final value of the reduction.

Since​

v17.5.0

Inherited from​

Readable.reduce

Call Signature​

reduce<T>(fn, initial, options?): Promise<T>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:650

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

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

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

Type Parameters​
T​

T

Parameters​
fn​

(previous, data, options?) => T

a reducer function to call over every chunk in the stream. Async or not.

initial​

T

the initial value to use in the reduction.

options?​

Abortable

Returns​

Promise<T>

a promise for the final value of the reduction.

Since​

v17.5.0

Inherited from​

Readable.reduce

removeAllListeners()​

Call Signature​

removeAllListeners<E>(eventName?): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:716

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.

Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName?​

E

Returns​

this

Since​

v0.1.26

Inherited from​

Readable.removeAllListeners

Call Signature​

removeAllListeners(eventName?): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:717

Parameters​
eventName?​

string | symbol

Returns​

this

Inherited from​

Readable.removeAllListeners

removeListener()​

Call Signature​

removeListener<E>(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:718

Removes the specified listener from the listener array for the event named eventName.

const callback = (stream) => {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.

Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them from emit() 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 indexes of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.

When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:

import { EventEmitter } from 'node:events';
const ee = new EventEmitter();

function pong() {
  console.log('pong');
}

ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);

ee.emit('ping');
ee.emit('ping');

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

Type Parameters​
E​

E extends keyof ReadableEventMap

Parameters​
eventName​

E

listener​

(...args) => void

Returns​

this

Since​

v0.1.26

Inherited from​

Readable.removeListener

Call Signature​

removeListener(eventName, listener): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:722

Parameters​
eventName​

string | symbol

listener​

(...args) => void

Returns​

this

Inherited from​

Readable.removeListener

resume()​

resume(): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:337

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​

this

Since​

v0.9.4

Inherited from​

Readable.resume

setEncoding()​

setEncoding(encoding): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:296

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 as Buffer objects. Setting an encoding causes the stream data to be returned as strings of the specified encoding rather than as Buffer objects. For instance, calling readable.setEncoding('utf8') will cause the output data to be interpreted as UTF-8 data, and passed as strings. Calling readable.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​

encoding​

BufferEncoding

The encoding to use.

Returns​

this

Since​

v0.9.4

Inherited from​

Readable.setEncoding

setMaxListeners()​

setMaxListeners(n): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/events.d.ts:472

By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.

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

Parameters​

n​

number

Returns​

this

Since​

v0.3.5

Inherited from​

Readable.setMaxListeners

some()​

some(fn, options?): Promise<boolean>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:572

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

Parameters​

fn​

(data, options?) => boolean | Promise<boolean>

a function to call on each chunk of the stream. Async or not.

options?​

Pick<ReadableOperatorOptions, "concurrency" | "signal">

Returns​

Promise<boolean>

a promise evaluating to true if fn returned a truthy value for at least one of the chunks.

Since​

v17.5.0

Inherited from​

Readable.some

take()​

take(limit, options?): Readable

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:634

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

Parameters​

limit​

number

the number of chunks to take from the readable.

options?​

Abortable

Returns​

Readable

a stream with limit chunks taken.

Since​

v17.5.0

Inherited from​

Readable.take

toArray()​

toArray(options?): Promise<any[]>

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:562

This method allows easily obtaining the contents of a stream.

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

Parameters​

options?​

Abortable

Returns​

Promise<any[]>

a promise containing an array with the contents of the stream.

Since​

v17.5.0

Inherited from​

Readable.toArray

unpipe()​

unpipe(destination?): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:381

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.

import fs from '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​

destination?​

WritableStream

Optional specific stream to unpipe

Returns​

this

Since​

v0.9.4

Inherited from​

Readable.unpipe

unshift()​

unshift(chunk, encoding?): void

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:447

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).
import { StringDecoder } from '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​

chunk​

any

Chunk of data to unshift onto the read queue. For streams not operating in object mode, chunk must be a {string}, {Buffer}, {TypedArray}, {DataView} or null. For object mode streams, chunk may be any JavaScript value.

encoding?​

BufferEncoding

Encoding of string chunks. Must be a valid Buffer encoding, such as 'utf8' or 'ascii'.

Returns​

void

Since​

v0.9.11

Inherited from​

Readable.unshift

wrap()​

wrap(stream): this

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:473

Prior to Node.js 0.10, streams did not implement the entire node: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, the readable.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.

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

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

Parameters​

stream​

ReadableStream

An "old style" readable stream

Returns​

this

Since​

v0.9.4

Inherited from​

Readable.wrap

from()​

static from(iterable, options?): Readable

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:106

A utility method for creating Readable Streams out of iterators.

Parameters​

iterable​

Iterable<any, any, any> | AsyncIterable<any, any, any>

Object implementing the Symbol.asyncIterator or Symbol.iterator iterable protocol. Emits an 'error' event if a null value is passed.

options?​

ReadableOptions

Options provided to new stream.Readable([options]). By default, Readable.from() will set options.objectMode to true, unless this is explicitly opted out by setting options.objectMode to false.

Returns​

Readable

Since​

v12.3.0, v10.17.0

Inherited from​

Readable.from

fromWeb()​

static fromWeb(readableStream, options?): Readable

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:111

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

Parameters​

readableStream​

ReadableStream

options?​

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

Returns​

Readable

Since​

v17.0.0

Inherited from​

Readable.fromWeb

isDisturbed()​

static isDisturbed(stream): boolean

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:127

Returns whether the stream has been read from or cancelled.

Parameters​

stream​

ReadableStream | ReadableStream<any>

Returns​

boolean

Since​

v16.8.0

Inherited from​

Readable.isDisturbed

toWeb()​

static toWeb(streamReadable, options?): ReadableStream

Defined in: node_modules/.pnpm/@types+node@25.5.0/node_modules/@types/node/stream.d.ts:119

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

Parameters​

streamReadable​

ReadableStream

options?​

ReadableToWebOptions

Returns​

ReadableStream

Since​

v17.0.0

Inherited from​

Readable.toWeb