Web Streams API

[History]

Version	Changes
v21.0.0	No longer experimental.
v18.0.0	Use of this API no longer emit a runtime warning.
v16.5.0	Added in: v16.5.0

[Stable: 2 - Stable]

Stable: 2 Stability: 2 - Stable

An implementation of the WHATWG Streams Standard.

Overview

The WHATWG Streams Standard (or "web streams") defines an API for handling streaming data. It is similar to the Node.js Streams API but emerged later and has become the "standard" API for streaming data across many JavaScript environments.

There are three primary types of objects:

• ReadableStream - Represents a source of streaming data.
• WritableStream - Represents a destination for streaming data.
• TransformStream - Represents an algorithm for transforming streaming data.

Example ReadableStream

This example creates a simple ReadableStream that pushes the current performance.now() timestamp once every second forever. An async iterable is used to read the data from the stream.

ESM

import {
  ReadableStream,
} from 'node:stream/web';

import {
  setInterval as every,
} from 'node:timers/promises';

import {
  performance,
} from 'node:perf_hooks';

const SECOND = 1000;

const stream = new ReadableStream({
  async start(controller) {
    for await (const _ of every(SECOND))
      controller.enqueue(performance.now());
  },
});

for await (const value of stream)
  console.log(value);

CJS

const {
  ReadableStream,
} = require('node:stream/web');

const {
  setInterval: every,
} = require('node:timers/promises');

const {
  performance,
} = require('node:perf_hooks');

const SECOND = 1000;

const stream = new ReadableStream({
  async start(controller) {
    for await (const _ of every(SECOND))
      controller.enqueue(performance.now());
  },
});

(async () => {
  for await (const value of stream)
    console.log(value);
})();

API

Class: ReadableStream

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

new ReadableStream([underlyingSource [, strategy]])

Added in: v16.5.0

• underlyingSource <Object>

  • start <Function> A user-defined function that is invoked immediately when the ReadableStream is created.

  • controller <ReadableStreamDefaultController> | <ReadableByteStreamController>

  • Returns: undefined or a promise fulfilled with undefined.

  • pull <Function> A user-defined function that is called repeatedly when the ReadableStream internal queue is not full. The operation may be sync or async. If async, the function will not be called again until the previously returned promise is fulfilled.

  • controller <ReadableStreamDefaultController> | <ReadableByteStreamController>

  • Returns: A promise fulfilled with undefined.

  • cancel <Function> A user-defined function that is called when the ReadableStream is canceled.

  • reason <any>

  • Returns: A promise fulfilled with undefined.

  • type <string> Must be 'bytes' or undefined.

  • autoAllocateChunkSize <number> Used only when type is equal to 'bytes'. When set to a non-zero value a view buffer is automatically allocated to ReadableByteStreamController.byobRequest. When not set one must use stream's internal queues to transfer data via the default reader ReadableStreamDefaultReader.

• strategy <Object>

  • highWaterMark <number> The maximum internal queue size before backpressure is applied.
  • size <Function> A user-defined function used to identify the size of each chunk of data.
  • chunk <any>
  • Returns: <number>

readableStream.locked

Added in: v16.5.0

• Type: <boolean> Set to true if there is an active reader for this <ReadableStream>.

The readableStream.locked property is false by default, and is switched to true while there is an active reader consuming the stream's data.

readableStream.cancel([reason])

Added in: v16.5.0

• reason <any>
• Returns: A promise fulfilled with undefined once cancelation has been completed.

readableStream.getReader([options])

Added in: v16.5.0

• options <Object>

  • mode <string> 'byob' or undefined

• Returns: <ReadableStreamDefaultReader> | <ReadableStreamBYOBReader>

ESM

import { ReadableStream } from 'node:stream/web';

const stream = new ReadableStream();

const reader = stream.getReader();

console.log(await reader.read());

CJS

const { ReadableStream } = require('node:stream/web');

const stream = new ReadableStream();

const reader = stream.getReader();

reader.read().then(console.log);

Causes the readableStream.locked to be true.

readableStream.pipeThrough(transform[, options])

Added in: v16.5.0

• transform <Object>

  • readable <ReadableStream> The ReadableStream to which transform.writable will push the potentially modified data it receives from this ReadableStream.
  • writable <WritableStream> The WritableStream to which this ReadableStream's data will be written.

• options <Object>

  • preventAbort <boolean> When true, errors in this ReadableStream will not cause transform.writable to be aborted.
  • preventCancel <boolean> When true, errors in the destination transform.writable do not cause this ReadableStream to be canceled.
  • preventClose <boolean> When true, closing this ReadableStream does not cause transform.writable to be closed.
  • signal <AbortSignal> Allows the transfer of data to be canceled using an <AbortController>.

• Returns: <ReadableStream> From transform.readable.

Connects this <ReadableStream> to the pair of <ReadableStream> and <WritableStream> provided in the transform argument such that the data from this <ReadableStream> is written in to transform.writable, possibly transformed, then pushed to transform.readable. Once the pipeline is configured, transform.readable is returned.

Causes the readableStream.locked to be true while the pipe operation is active.

ESM

import {
  ReadableStream,
  TransformStream,
} from 'node:stream/web';

const stream = new ReadableStream({
  start(controller) {
    controller.enqueue('a');
  },
});

const transform = new TransformStream({
  transform(chunk, controller) {
    controller.enqueue(chunk.toUpperCase());
  },
});

const transformedStream = stream.pipeThrough(transform);

for await (const chunk of transformedStream)
  console.log(chunk);
  // Prints: A

CJS

const {
  ReadableStream,
  TransformStream,
} = require('node:stream/web');

const stream = new ReadableStream({
  start(controller) {
    controller.enqueue('a');
  },
});

const transform = new TransformStream({
  transform(chunk, controller) {
    controller.enqueue(chunk.toUpperCase());
  },
});

const transformedStream = stream.pipeThrough(transform);

(async () => {
  for await (const chunk of transformedStream)
    console.log(chunk);
    // Prints: A
})();

readableStream.pipeTo(destination[, options])

Added in: v16.5.0

• destination <WritableStream> A <WritableStream> to which this ReadableStream's data will be written.

• options <Object>

  • preventAbort <boolean> When true, errors in this ReadableStream will not cause destination to be aborted.
  • preventCancel <boolean> When true, errors in the destination will not cause this ReadableStream to be canceled.
  • preventClose <boolean> When true, closing this ReadableStream does not cause destination to be closed.
  • signal <AbortSignal> Allows the transfer of data to be canceled using an <AbortController>.

• Returns: A promise fulfilled with undefined

Causes the readableStream.locked to be true while the pipe operation is active.

readableStream.tee()

[History]

Version	Changes
v18.10.0, v16.18.0	Support teeing a readable byte stream.
v16.5.0	Added in: v16.5.0

• Returns: <ReadableStream[]>

Returns a pair of new <ReadableStream> instances to which this ReadableStream's data will be forwarded. Each will receive the same data.

Causes the readableStream.locked to be true.

readableStream.values([options])

Added in: v16.5.0

• options <Object>
  • preventCancel <boolean> When true, prevents the <ReadableStream> from being closed when the async iterator abruptly terminates. Default: false.

Creates and returns an async iterator usable for consuming this ReadableStream's data.

Causes the readableStream.locked to be true while the async iterator is active.

import { Buffer } from 'node:buffer';

const stream = new ReadableStream(getSomeSource());

for await (const chunk of stream.values({ preventCancel: true }))
  console.log(Buffer.from(chunk).toString());

Async Iteration

The <ReadableStream> object supports the async iterator protocol using for await syntax.

import { Buffer } from 'node:buffer';

const stream = new ReadableStream(getSomeSource());

for await (const chunk of stream)
  console.log(Buffer.from(chunk).toString());

The async iterator will consume the <ReadableStream> until it terminates.

By default, if the async iterator exits early (via either a break, return, or a throw), the <ReadableStream> will be closed. To prevent automatic closing of the <ReadableStream>, use the readableStream.values() method to acquire the async iterator and set the preventCancel option to true.

The <ReadableStream> must not be locked (that is, it must not have an existing active reader). During the async iteration, the <ReadableStream> will be locked.

Transferring with postMessage()

A <ReadableStream> instance can be transferred using a <MessagePort>.

const stream = new ReadableStream(getReadableSourceSomehow());

const { port1, port2 } = new MessageChannel();

port1.onmessage = ({ data }) => {
  data.getReader().read().then((chunk) => {
    console.log(chunk);
  });
};

port2.postMessage(stream, [stream]);

ReadableStream.from(iterable)

Added in: v20.6.0

• iterable <Iterable> Object implementing the Symbol.asyncIterator or Symbol.iterator iterable protocol.

A utility method that creates a new <ReadableStream> from an iterable.

ESM

import { ReadableStream } from 'node:stream/web';

async function* asyncIterableGenerator() {
  yield 'a';
  yield 'b';
  yield 'c';
}

const stream = ReadableStream.from(asyncIterableGenerator());

for await (const chunk of stream)
  console.log(chunk); // Prints: 'a', 'b', 'c'

CJS

const { ReadableStream } = require('node:stream/web');

async function* asyncIterableGenerator() {
  yield 'a';
  yield 'b';
  yield 'c';
}

(async () => {
  const stream = ReadableStream.from(asyncIterableGenerator());

  for await (const chunk of stream)
    console.log(chunk); // Prints: 'a', 'b', 'c'
})();

To pipe the resulting <ReadableStream> into a <WritableStream> the <Iterable> should yield a sequence of <Buffer>, <TypedArray>, or <DataView> objects.

ESM

import { ReadableStream } from 'node:stream/web';
import { Buffer } from 'node:buffer';

async function* asyncIterableGenerator() {
  yield Buffer.from('a');
  yield Buffer.from('b');
  yield Buffer.from('c');
}

const stream = ReadableStream.from(asyncIterableGenerator());

await stream.pipeTo(createWritableStreamSomehow());

CJS

const { ReadableStream } = require('node:stream/web');
const { Buffer } = require('node:buffer');

async function* asyncIterableGenerator() {
  yield Buffer.from('a');
  yield Buffer.from('b');
  yield Buffer.from('c');
}

const stream = ReadableStream.from(asyncIterableGenerator());

(async () => {
  await stream.pipeTo(createWritableStreamSomehow());
})();

Class: ReadableStreamDefaultReader

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

By default, calling readableStream.getReader() with no arguments will return an instance of ReadableStreamDefaultReader. The default reader treats the chunks of data passed through the stream as opaque values, which allows the <ReadableStream> to work with generally any JavaScript value.

new ReadableStreamDefaultReader(stream)

Added in: v16.5.0

• stream <ReadableStream>

Creates a new <ReadableStreamDefaultReader> that is locked to the given <ReadableStream>.

readableStreamDefaultReader.cancel([reason])

Added in: v16.5.0

• reason <any>
• Returns: A promise fulfilled with undefined.

Cancels the <ReadableStream> and returns a promise that is fulfilled when the underlying stream has been canceled.

readableStreamDefaultReader.closed

Added in: v16.5.0

• Type: <Promise> Fulfilled with undefined when the associated <ReadableStream> is closed or rejected if the stream errors or the reader's lock is released before the stream finishes closing.

readableStreamDefaultReader.read()

Added in: v16.5.0

• Returns: A promise fulfilled with an object:
  • value <any>
  • done <boolean>

Requests the next chunk of data from the underlying <ReadableStream> and returns a promise that is fulfilled with the data once it is available.

readableStreamDefaultReader.releaseLock()

Added in: v16.5.0

Releases this reader's lock on the underlying <ReadableStream>.

Class: ReadableStreamBYOBReader

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

The ReadableStreamBYOBReader is an alternative consumer for byte-oriented <ReadableStream>s (those that are created with underlyingSource.type set equal to 'bytes' when the ReadableStream was created).

The BYOB is short for "bring your own buffer". This is a pattern that allows for more efficient reading of byte-oriented data that avoids extraneous copying.

import {
  open,
} from 'node:fs/promises';

import {
  ReadableStream,
} from 'node:stream/web';

import { Buffer } from 'node:buffer';

class Source {
  type = 'bytes';
  autoAllocateChunkSize = 1024;

  async start(controller) {
    this.file = await open(new URL(import.meta.url));
    this.controller = controller;
  }

  async pull(controller) {
    const view = controller.byobRequest?.view;
    const {
      bytesRead,
    } = await this.file.read({
      buffer: view,
      offset: view.byteOffset,
      length: view.byteLength,
    });

    if (bytesRead === 0) {
      await this.file.close();
      this.controller.close();
    }
    controller.byobRequest.respond(bytesRead);
  }
}

const stream = new ReadableStream(new Source());

async function read(stream) {
  const reader = stream.getReader({ mode: 'byob' });

  const chunks = [];
  let result;
  do {
    result = await reader.read(Buffer.alloc(100));
    if (result.value !== undefined)
      chunks.push(Buffer.from(result.value));
  } while (!result.done);

  return Buffer.concat(chunks);
}

const data = await read(stream);
console.log(Buffer.from(data).toString());

new ReadableStreamBYOBReader(stream)

Added in: v16.5.0

• stream <ReadableStream>

Creates a new ReadableStreamBYOBReader that is locked to the given <ReadableStream>.

readableStreamBYOBReader.cancel([reason])

Added in: v16.5.0

• reason <any>
• Returns: A promise fulfilled with undefined.

Cancels the <ReadableStream> and returns a promise that is fulfilled when the underlying stream has been canceled.

readableStreamBYOBReader.closed

Added in: v16.5.0

• Type: <Promise> Fulfilled with undefined when the associated <ReadableStream> is closed or rejected if the stream errors or the reader's lock is released before the stream finishes closing.

readableStreamBYOBReader.read(view[, options])

[History]

Version	Changes
v21.7.0, v20.17.0	Added min option.
v16.5.0	Added in: v16.5.0

• view <Buffer> | <TypedArray> | <DataView>

• options <Object>

  • min <number> When set, the returned promise will only be fulfilled as soon as min number of elements are available. When not set, the promise fulfills when at least one element is available.

• Returns: A promise fulfilled with an object:

  • value <TypedArray> | <DataView>
  • done <boolean>

Requests the next chunk of data from the underlying <ReadableStream> and returns a promise that is fulfilled with the data once it is available.

Do not pass a pooled <Buffer> object instance in to this method. Pooled Buffer objects are created using Buffer.allocUnsafe(), or Buffer.from(), or are often returned by various node:fs module callbacks. These types of Buffers use a shared underlying <ArrayBuffer> object that contains all of the data from all of the pooled Buffer instances. When a Buffer, <TypedArray>, or <DataView> is passed in to readableStreamBYOBReader.read(), the view's underlying ArrayBuffer is detached, invalidating all existing views that may exist on that ArrayBuffer. This can have disastrous consequences for your application.

readableStreamBYOBReader.releaseLock()

Added in: v16.5.0

Releases this reader's lock on the underlying <ReadableStream>.

Class: ReadableStreamDefaultController

Added in: v16.5.0

Every <ReadableStream> has a controller that is responsible for the internal state and management of the stream's queue. The ReadableStreamDefaultController is the default controller implementation for ReadableStreams that are not byte-oriented.

readableStreamDefaultController.close()

Added in: v16.5.0

Closes the <ReadableStream> to which this controller is associated.

readableStreamDefaultController.desiredSize

Added in: v16.5.0

• Type: <number>

Returns the amount of data remaining to fill the <ReadableStream>'s queue.

readableStreamDefaultController.enqueue([chunk])

Added in: v16.5.0

• chunk <any>

Appends a new chunk of data to the <ReadableStream>'s queue.

readableStreamDefaultController.error([error])

Added in: v16.5.0

• error <any>

Signals an error that causes the <ReadableStream> to error and close.

Class: ReadableByteStreamController

[History]

Version	Changes
v18.10.0	Support handling a BYOB pull request from a released reader.
v16.5.0	Added in: v16.5.0

Every <ReadableStream> has a controller that is responsible for the internal state and management of the stream's queue. The ReadableByteStreamController is for byte-oriented ReadableStreams.

readableByteStreamController.byobRequest

Added in: v16.5.0

• Type: <ReadableStreamBYOBRequest>

readableByteStreamController.close()

Added in: v16.5.0

Closes the <ReadableStream> to which this controller is associated.

readableByteStreamController.desiredSize

Added in: v16.5.0

• Type: <number>

Returns the amount of data remaining to fill the <ReadableStream>'s queue.

readableByteStreamController.enqueue(chunk)

Added in: v16.5.0

• chunk: <Buffer> | <TypedArray> | <DataView>

Appends a new chunk of data to the <ReadableStream>'s queue.

readableByteStreamController.error([error])

Added in: v16.5.0

• error <any>

Signals an error that causes the <ReadableStream> to error and close.

Class: ReadableStreamBYOBRequest

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

When using ReadableByteStreamController in byte-oriented streams, and when using the ReadableStreamBYOBReader, the readableByteStreamController.byobRequest property provides access to a ReadableStreamBYOBRequest instance that represents the current read request. The object is used to gain access to the ArrayBuffer/TypedArray that has been provided for the read request to fill, and provides methods for signaling that the data has been provided.

readableStreamBYOBRequest.respond(bytesWritten)

Added in: v16.5.0

• bytesWritten <number>

Signals that a bytesWritten number of bytes have been written to readableStreamBYOBRequest.view.

readableStreamBYOBRequest.respondWithNewView(view)

Added in: v16.5.0

• view <Buffer> | <TypedArray> | <DataView>

Signals that the request has been fulfilled with bytes written to a new Buffer, TypedArray, or DataView.

readableStreamBYOBRequest.view

Added in: v16.5.0

• Type: <Buffer> | <TypedArray> | <DataView>

Class: WritableStream

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

The WritableStream is a destination to which stream data is sent.

import {
  WritableStream,
} from 'node:stream/web';

const stream = new WritableStream({
  write(chunk) {
    console.log(chunk);
  },
});

await stream.getWriter().write('Hello World');

new WritableStream([underlyingSink[, strategy]])

Added in: v16.5.0

• underlyingSink <Object>

  • start <Function> A user-defined function that is invoked immediately when the WritableStream is created.

  • controller <WritableStreamDefaultController>

  • Returns: undefined or a promise fulfilled with undefined.

  • write <Function> A user-defined function that is invoked when a chunk of data has been written to the WritableStream.

  • chunk <any>

  • controller <WritableStreamDefaultController>

  • Returns: A promise fulfilled with undefined.

  • close <Function> A user-defined function that is called when the WritableStream is closed.

  • Returns: A promise fulfilled with undefined.

  • abort <Function> A user-defined function that is called to abruptly close the WritableStream.

  • reason <any>

  • Returns: A promise fulfilled with undefined.

  • type <any> The type option is reserved for future use and must be undefined.

• strategy <Object>

  • highWaterMark <number> The maximum internal queue size before backpressure is applied.
  • size <Function> A user-defined function used to identify the size of each chunk of data.
  • chunk <any>
  • Returns: <number>

writableStream.abort([reason])

Added in: v16.5.0

• reason <any>
• Returns: A promise fulfilled with undefined.

Abruptly terminates the WritableStream. All queued writes will be canceled with their associated promises rejected.

writableStream.close()

Added in: v16.5.0

• Returns: A promise fulfilled with undefined.

Closes the WritableStream when no additional writes are expected.

writableStream.getWriter()

Added in: v16.5.0

• Returns: <WritableStreamDefaultWriter>

Creates and returns a new writer instance that can be used to write data into the WritableStream.

writableStream.locked

Added in: v16.5.0

• Type: <boolean>

The writableStream.locked property is false by default, and is switched to true while there is an active writer attached to this WritableStream.

Transferring with postMessage()

A <WritableStream> instance can be transferred using a <MessagePort>.

const stream = new WritableStream(getWritableSinkSomehow());

const { port1, port2 } = new MessageChannel();

port1.onmessage = ({ data }) => {
  data.getWriter().write('hello');
};

port2.postMessage(stream, [stream]);

Class: WritableStreamDefaultWriter

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

new WritableStreamDefaultWriter(stream)

Added in: v16.5.0

• stream <WritableStream>

Creates a new WritableStreamDefaultWriter that is locked to the given WritableStream.

writableStreamDefaultWriter.abort([reason])

Added in: v16.5.0

• reason <any>
• Returns: A promise fulfilled with undefined.

Abruptly terminates the WritableStream. All queued writes will be canceled with their associated promises rejected.

writableStreamDefaultWriter.close()

Added in: v16.5.0

• Returns: A promise fulfilled with undefined.

Closes the WritableStream when no additional writes are expected.

writableStreamDefaultWriter.closed

Added in: v16.5.0

• Type: <Promise> Fulfilled with undefined when the associated <WritableStream> is closed or rejected if the stream errors or the writer's lock is released before the stream finishes closing.

writableStreamDefaultWriter.desiredSize

Added in: v16.5.0

• Type: <number>

The amount of data required to fill the <WritableStream>'s queue.

writableStreamDefaultWriter.ready

Added in: v16.5.0

• Type: <Promise> Fulfilled with undefined when the writer is ready to be used.

writableStreamDefaultWriter.releaseLock()

Added in: v16.5.0

Releases this writer's lock on the underlying <ReadableStream>.

writableStreamDefaultWriter.write([chunk])

Added in: v16.5.0

• chunk: <any>
• Returns: A promise fulfilled with undefined.

Appends a new chunk of data to the <WritableStream>'s queue.

Class: WritableStreamDefaultController

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

The WritableStreamDefaultController manages the <WritableStream>'s internal state.

writableStreamDefaultController.error([error])

Added in: v16.5.0

• error <any>

Called by user-code to signal that an error has occurred while processing the WritableStream data. When called, the <WritableStream> will be aborted, with currently pending writes canceled.

writableStreamDefaultController.signal

• Type: <AbortSignal> An AbortSignal that can be used to cancel pending write or close operations when a <WritableStream> is aborted.

Class: TransformStream

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

A TransformStream consists of a <ReadableStream> and a <WritableStream> that are connected such that the data written to the WritableStream is received, and potentially transformed, before being pushed into the ReadableStream's queue.

import {
  TransformStream,
} from 'node:stream/web';

const transform = new TransformStream({
  transform(chunk, controller) {
    controller.enqueue(chunk.toUpperCase());
  },
});

await Promise.all([
  transform.writable.getWriter().write('A'),
  transform.readable.getReader().read(),
]);

new TransformStream([transformer[, writableStrategy[, readableStrategy]]])

Added in: v16.5.0

• transformer <Object>

  • start <Function> A user-defined function that is invoked immediately when the TransformStream is created.

  • controller <TransformStreamDefaultController>

  • Returns: undefined or a promise fulfilled with undefined

  • transform <Function> A user-defined function that receives, and potentially modifies, a chunk of data written to transformStream.writable, before forwarding that on to transformStream.readable.

  • chunk <any>

  • controller <TransformStreamDefaultController>

  • Returns: A promise fulfilled with undefined.

  • flush <Function> A user-defined function that is called immediately before the writable side of the TransformStream is closed, signaling the end of the transformation process.

  • controller <TransformStreamDefaultController>

  • Returns: A promise fulfilled with undefined.

  • readableType <any> the readableType option is reserved for future use and must be undefined.

  • writableType <any> the writableType option is reserved for future use and must be undefined.

• writableStrategy <Object>

  • highWaterMark <number> The maximum internal queue size before backpressure is applied.
  • size <Function> A user-defined function used to identify the size of each chunk of data.
  • chunk <any>
  • Returns: <number>

• readableStrategy <Object>

  • highWaterMark <number> The maximum internal queue size before backpressure is applied.
  • size <Function> A user-defined function used to identify the size of each chunk of data.
  • chunk <any>
  • Returns: <number>

transformStream.readable

Added in: v16.5.0

• Type: <ReadableStream>

transformStream.writable

Added in: v16.5.0

• Type: <WritableStream>

Transferring with postMessage()

A <TransformStream> instance can be transferred using a <MessagePort>.

const stream = new TransformStream();

const { port1, port2 } = new MessageChannel();

port1.onmessage = ({ data }) => {
  const { writable, readable } = data;
  // ...
};

port2.postMessage(stream, [stream]);

Class: TransformStreamDefaultController

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

The TransformStreamDefaultController manages the internal state of the TransformStream.

transformStreamDefaultController.desiredSize

Added in: v16.5.0

• Type: <number>

The amount of data required to fill the readable side's queue.

transformStreamDefaultController.enqueue([chunk])

Added in: v16.5.0

• chunk <any>

Appends a chunk of data to the readable side's queue.

transformStreamDefaultController.error([reason])

Added in: v16.5.0

• reason <any>

Signals to both the readable and writable side that an error has occurred while processing the transform data, causing both sides to be abruptly closed.

transformStreamDefaultController.terminate()

Added in: v16.5.0

Closes the readable side of the transport and causes the writable side to be abruptly closed with an error.

Class: ByteLengthQueuingStrategy

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

new ByteLengthQueuingStrategy(init)

Added in: v16.5.0

• init <Object>
  • highWaterMark <number>

byteLengthQueuingStrategy.highWaterMark

Added in: v16.5.0

• Type: <number>

byteLengthQueuingStrategy.size

Added in: v16.5.0

• Type: <Function>
  • chunk <any>
  • Returns: <number>

Class: CountQueuingStrategy

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.5.0	Added in: v16.5.0

new CountQueuingStrategy(init)

Added in: v16.5.0

• init <Object>
  • highWaterMark <number>

countQueuingStrategy.highWaterMark

Added in: v16.5.0

• Type: <number>

countQueuingStrategy.size

Added in: v16.5.0

• Type: <Function>
  • chunk <any>
  • Returns: <number>

Class: TextEncoderStream

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.6.0	Added in: v16.6.0

new TextEncoderStream()

Added in: v16.6.0

Creates a new TextEncoderStream instance.

textEncoderStream.encoding

Added in: v16.6.0

• Type: <string>

The encoding supported by the TextEncoderStream instance.

textEncoderStream.readable

Added in: v16.6.0

• Type: <ReadableStream>

textEncoderStream.writable

Added in: v16.6.0

• Type: <WritableStream>

Class: TextDecoderStream

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v16.6.0	Added in: v16.6.0

new TextDecoderStream([encoding[, options]])

Added in: v16.6.0

• encoding <string> Identifies the encoding that this TextDecoder instance supports. Default: 'utf-8'.
• options <Object>
  • fatal <boolean> true if decoding failures are fatal.
  • ignoreBOM <boolean> When true, the TextDecoderStream will include the byte order mark in the decoded result. When false, the byte order mark will be removed from the output. This option is only used when encoding is 'utf-8', 'utf-16be', or 'utf-16le'. Default: false.

Creates a new TextDecoderStream instance.

textDecoderStream.encoding

Added in: v16.6.0

• Type: <string>

The encoding supported by the TextDecoderStream instance.

textDecoderStream.fatal

Added in: v16.6.0

• Type: <boolean>

The value will be true if decoding errors result in a TypeError being thrown.

textDecoderStream.ignoreBOM

Added in: v16.6.0

• Type: <boolean>

The value will be true if the decoding result will include the byte order mark.

textDecoderStream.readable

Added in: v16.6.0

• Type: <ReadableStream>

textDecoderStream.writable

Added in: v16.6.0

• Type: <WritableStream>

Class: CompressionStream

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v17.0.0	Added in: v17.0.0

new CompressionStream(format)

[History]

Version	Changes
v21.2.0, v20.12.0	format now accepts deflate-raw value.
v17.0.0	Added in: v17.0.0

• format <string> One of 'deflate', 'deflate-raw', or 'gzip'.

compressionStream.readable

Added in: v17.0.0

• Type: <ReadableStream>

compressionStream.writable

Added in: v17.0.0

• Type: <WritableStream>

Class: DecompressionStream

[History]

Version	Changes
v18.0.0	This class is now exposed on the global object.
v17.0.0	Added in: v17.0.0

new DecompressionStream(format)

[History]

Version	Changes
v21.2.0, v20.12.0	format now accepts deflate-raw value.
v17.0.0	Added in: v17.0.0

• format <string> One of 'deflate', 'deflate-raw', or 'gzip'.

decompressionStream.readable

Added in: v17.0.0

• Type: <ReadableStream>

decompressionStream.writable

Added in: v17.0.0

• Type: <WritableStream>

Utility Consumers

Added in: v16.7.0

The utility consumer functions provide common options for consuming streams.

They are accessed using:

ESM

import {
  arrayBuffer,
  blob,
  buffer,
  json,
  text,
} from 'node:stream/consumers';

CJS

const {
  arrayBuffer,
  blob,
  buffer,
  json,
  text,
} = require('node:stream/consumers');

streamConsumers.arrayBuffer(stream)

Added in: v16.7.0

• stream <ReadableStream> | <stream.Readable> | <AsyncIterator>
• Returns: <Promise> Fulfills with an ArrayBuffer containing the full contents of the stream.

ESM

import { arrayBuffer } from 'node:stream/consumers';
import { Readable } from 'node:stream';
import { TextEncoder } from 'node:util';

const encoder = new TextEncoder();
const dataArray = encoder.encode('hello world from consumers!');

const readable = Readable.from(dataArray);
const data = await arrayBuffer(readable);
console.log(`from readable: ${data.byteLength}`);
// Prints: from readable: 76

CJS

const { arrayBuffer } = require('node:stream/consumers');
const { Readable } = require('node:stream');
const { TextEncoder } = require('node:util');

const encoder = new TextEncoder();
const dataArray = encoder.encode('hello world from consumers!');
const readable = Readable.from(dataArray);
arrayBuffer(readable).then((data) => {
  console.log(`from readable: ${data.byteLength}`);
  // Prints: from readable: 76
});

streamConsumers.blob(stream)

Added in: v16.7.0

• stream <ReadableStream> | <stream.Readable> | <AsyncIterator>
• Returns: <Promise> Fulfills with a <Blob> containing the full contents of the stream.

ESM

import { blob } from 'node:stream/consumers';

const dataBlob = new Blob(['hello world from consumers!']);

const readable = dataBlob.stream();
const data = await blob(readable);
console.log(`from readable: ${data.size}`);
// Prints: from readable: 27

CJS

const { blob } = require('node:stream/consumers');

const dataBlob = new Blob(['hello world from consumers!']);

const readable = dataBlob.stream();
blob(readable).then((data) => {
  console.log(`from readable: ${data.size}`);
  // Prints: from readable: 27
});

streamConsumers.buffer(stream)

Added in: v16.7.0

• stream <ReadableStream> | <stream.Readable> | <AsyncIterator>
• Returns: <Promise> Fulfills with a <Buffer> containing the full contents of the stream.

ESM

import { buffer } from 'node:stream/consumers';
import { Readable } from 'node:stream';
import { Buffer } from 'node:buffer';

const dataBuffer = Buffer.from('hello world from consumers!');

const readable = Readable.from(dataBuffer);
const data = await buffer(readable);
console.log(`from readable: ${data.length}`);
// Prints: from readable: 27

CJS

const { buffer } = require('node:stream/consumers');
const { Readable } = require('node:stream');
const { Buffer } = require('node:buffer');

const dataBuffer = Buffer.from('hello world from consumers!');

const readable = Readable.from(dataBuffer);
buffer(readable).then((data) => {
  console.log(`from readable: ${data.length}`);
  // Prints: from readable: 27
});

streamConsumers.json(stream)

Added in: v16.7.0

• stream <ReadableStream> | <stream.Readable> | <AsyncIterator>
• Returns: <Promise> Fulfills with the contents of the stream parsed as a UTF-8 encoded string that is then passed through JSON.parse().

ESM

import { json } from 'node:stream/consumers';
import { Readable } from 'node:stream';

const items = Array.from(
  {
    length: 100,
  },
  () => ({
    message: 'hello world from consumers!',
  }),
);

const readable = Readable.from(JSON.stringify(items));
const data = await json(readable);
console.log(`from readable: ${data.length}`);
// Prints: from readable: 100

CJS

const { json } = require('node:stream/consumers');
const { Readable } = require('node:stream');

const items = Array.from(
  {
    length: 100,
  },
  () => ({
    message: 'hello world from consumers!',
  }),
);

const readable = Readable.from(JSON.stringify(items));
json(readable).then((data) => {
  console.log(`from readable: ${data.length}`);
  // Prints: from readable: 100
});

streamConsumers.text(stream)

Added in: v16.7.0

• stream <ReadableStream> | <stream.Readable> | <AsyncIterator>
• Returns: <Promise> Fulfills with the contents of the stream parsed as a UTF-8 encoded string.

ESM

import { text } from 'node:stream/consumers';
import { Readable } from 'node:stream';

const readable = Readable.from('Hello world from consumers!');
const data = await text(readable);
console.log(`from readable: ${data.length}`);
// Prints: from readable: 27

CJS

const { text } = require('node:stream/consumers');
const { Readable } = require('node:stream');

const readable = Readable.from('Hello world from consumers!');
text(readable).then((data) => {
  console.log(`from readable: ${data.length}`);
  // Prints: from readable: 27
});