Web Streams API | Node.js v18.20.8 Documentation (original) (raw)

API#

Class: ReadableStream#

new ReadableStream([underlyingSource [, strategy]])#

Added in: v16.5.0

• underlyingSource
  • start A user-defined function that is invoked immediately when the ReadableStream is created.
    * controller |
    * Returns: undefined or a promise fulfilled with undefined.
  • pull A user-defined function that is called repeatedly when theReadableStream 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 |
    * Returns: A promise fulfilled with undefined.
  • cancel A user-defined function that is called when theReadableStream is canceled.
    * reason
    * Returns: A promise fulfilled with undefined.
  • type Must be 'bytes' or undefined.
  • autoAllocateChunkSize 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
  • highWaterMark The maximum internal queue size before backpressure is applied.
  • size A user-defined function used to identify the size of each chunk of data.
    * chunk
    * Returns:

readableStream.locked#

Added in: v16.5.0

• Type: Set to true if there is an active reader for this.

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
• Returns: A promise fulfilled with undefined once cancelation has been completed.

readableStream.getReader([options])#

Added in: v16.5.0

• options
  • mode 'byob' or undefined
• Returns: |

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

const stream = new ReadableStream();

const reader = stream.getReader();

console.log(await reader.read()); 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
  • readable The ReadableStream to whichtransform.writable will push the potentially modified data is receives from this ReadableStream.
  • writable The WritableStream to which thisReadableStream's data will be written.
• options
  • preventAbort When true, errors in this ReadableStreamwill not cause transform.writable to be aborted.
  • preventCancel When true, errors in the destinationtransform.writable do not cause this ReadableStream to be canceled.
  • preventClose When true, closing this ReadableStreamdoes not cause transform.writable to be closed.
  • signal Allows the transfer of data to be canceled using an .
• Returns: From transform.readable.

Connects this to the pair of and provided in the transform argument such that the data from this 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.

`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); 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); })();`

readableStream.pipeTo(destination[, options])#

Added in: v16.5.0

• destination A to which thisReadableStream's data will be written.
• options
  • preventAbort When true, errors in this ReadableStreamwill not cause destination to be aborted.
  • preventCancel When true, errors in the destinationwill not cause this ReadableStream to be canceled.
  • preventClose When true, closing this ReadableStreamdoes not cause destination to be closed.
  • signal Allows the transfer of data to be canceled using an .
• Returns: A promise fulfilled with undefined

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

readableStream.tee()#

• Returns: <ReadableStream[]>

Returns a pair of new instances to which thisReadableStream'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
  • preventCancel When true, prevents the from being closed when the async iterator abruptly terminates.Default: false.

Creates and returns an async iterator usable for consuming thisReadableStream'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 object supports the async iterator protocol usingfor 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 until it terminates.

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

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

Transferring with postMessage()#

A instance can be transferred using a .

`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]);`

Class: ReadableStreamDefaultReader#

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 to work with generally any JavaScript value.

new ReadableStreamDefaultReader(stream)#

Added in: v16.5.0

• stream

Creates a new that is locked to the given .

readableStreamDefaultReader.cancel([reason])#

Added in: v16.5.0

• reason
• Returns: A promise fulfilled with undefined.

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

readableStreamDefaultReader.closed#

Added in: v16.5.0

• Type: Fulfilled with undefined when the associated 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
  • done

Requests the next chunk of data from the underlying 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 .

Class: ReadableStreamBYOBReader#

The ReadableStreamBYOBReader is an alternative consumer for byte-oriented s (those that are created withunderlyingSource.type set equal to 'bytes' when theReadableStream 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

Creates a new ReadableStreamBYOBReader that is locked to the given .

readableStreamBYOBReader.cancel([reason])#

Added in: v16.5.0

• reason
• Returns: A promise fulfilled with undefined.

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

readableStreamBYOBReader.closed#

Added in: v16.5.0

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

readableStreamBYOBReader.read(view)#

Added in: v16.5.0

• view | |
• Returns: A promise fulfilled with an object:
  • value
  • done

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

Do not pass a pooled 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 object that contains all of the data from all of the pooled Buffer instances. When a Buffer, , or 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 .

Class: ReadableStreamDefaultController#

Added in: v16.5.0

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

readableStreamDefaultController.close()#

Added in: v16.5.0

Closes the to which this controller is associated.

readableStreamDefaultController.desiredSize#

Added in: v16.5.0

• Type:

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

readableStreamDefaultController.enqueue([chunk])#

Added in: v16.5.0

• chunk

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

readableStreamDefaultController.error([error])#

Added in: v16.5.0

• error

Signals an error that causes the to error and close.

Class: ReadableByteStreamController#

Every has a controller that is responsible for the internal state and management of the stream's queue. TheReadableByteStreamController is for byte-oriented ReadableStreams.

readableByteStreamController.byobRequest#

Added in: v16.5.0

• Type:

readableByteStreamController.close()#

Added in: v16.5.0

Closes the to which this controller is associated.

readableByteStreamController.desiredSize#

Added in: v16.5.0

• Type:

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

readableByteStreamController.enqueue(chunk)#

Added in: v16.5.0

• chunk: | |

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

readableByteStreamController.error([error])#

Added in: v16.5.0

• error

Signals an error that causes the to error and close.

Class: ReadableStreamBYOBRequest#

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/TypedArraythat 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

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

readableStreamBYOBRequest.respondWithNewView(view)#

Added in: v16.5.0

• view | |

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: | |

Class: WritableStream#

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
  • start A user-defined function that is invoked immediately when the WritableStream is created.
    * controller
    * Returns: undefined or a promise fulfilled with undefined.
  • write A user-defined function that is invoked when a chunk of data has been written to the WritableStream.
    * chunk
    * controller
    * Returns: A promise fulfilled with undefined.
  • close A user-defined function that is called when theWritableStream is closed.
    * Returns: A promise fulfilled with undefined.
  • abort A user-defined function that is called to abruptly close the WritableStream.
    * reason
    * Returns: A promise fulfilled with undefined.
  • type The type option is reserved for future use and must be undefined.
• strategy
  • highWaterMark The maximum internal queue size before backpressure is applied.
  • size A user-defined function used to identify the size of each chunk of data.
    * chunk
    * Returns:

writableStream.abort([reason])#

Added in: v16.5.0

• reason
• 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:

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:

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

Transferring with postMessage()#

A instance can be transferred using a .

`const stream = new WritableStream(getWritableSinkSomehow());

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

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

port2.postMessage(stream, [stream]);`

Class: WritableStreamDefaultWriter#

new WritableStreamDefaultWriter(stream)#

Added in: v16.5.0

• stream

Creates a new WritableStreamDefaultWriter that is locked to the givenWritableStream.

writableStreamDefaultWriter.abort([reason])#

Added in: v16.5.0

• reason
• 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: Fulfilled with undefined when the associated 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:

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

writableStreamDefaultWriter.ready#

Added in: v16.5.0

• Type: 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 .

writableStreamDefaultWriter.write([chunk])#

Added in: v16.5.0

• chunk:
• Returns: A promise fulfilled with undefined.

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

Class: WritableStreamDefaultController#

The WritableStreamDefaultController manage's the 's internal state.

writableStreamDefaultController.error([error])#

Added in: v16.5.0

• error

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

writableStreamDefaultController.signal#

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

Class: TransformStream#

A TransformStream consists of a and a 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
  • start A user-defined function that is invoked immediately when the TransformStream is created.
    * controller
    * Returns: undefined or a promise fulfilled with undefined
  • transform 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
    * controller
    * Returns: A promise fulfilled with undefined.
  • flush 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
    * Returns: A promise fulfilled with undefined.
  • readableType the readableType option is reserved for future use and must be undefined.
  • writableType the writableType option is reserved for future use and must be undefined.
• writableStrategy
  • highWaterMark The maximum internal queue size before backpressure is applied.
  • size A user-defined function used to identify the size of each chunk of data.
    * chunk
    * Returns:
• readableStrategy
  • highWaterMark The maximum internal queue size before backpressure is applied.
  • size A user-defined function used to identify the size of each chunk of data.
    * chunk
    * Returns:

transformStream.readable#

Added in: v16.5.0

• Type:

transformStream.writable#

Added in: v16.5.0

• Type:

Transferring with postMessage()#

A instance can be transferred using a .

`const stream = new TransformStream();

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

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

port2.postMessage(stream, [stream]);`

Class: TransformStreamDefaultController#

The TransformStreamDefaultController manages the internal state of the TransformStream.

transformStreamDefaultController.desiredSize#

Added in: v16.5.0

• Type:

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

transformStreamDefaultController.enqueue([chunk])#

Added in: v16.5.0

• chunk

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

transformStreamDefaultController.error([reason])#

Added in: v16.5.0

• reason

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#

new ByteLengthQueuingStrategy(init)#

Added in: v16.5.0

• init
  • highWaterMark

byteLengthQueuingStrategy.highWaterMark#

Added in: v16.5.0

• Type:

byteLengthQueuingStrategy.size#

Added in: v16.5.0

• Type:
  • chunk
  • Returns:

Class: CountQueuingStrategy#

new CountQueuingStrategy(init)#

Added in: v16.5.0

• init
  • highWaterMark

countQueuingStrategy.highWaterMark#

Added in: v16.5.0

• Type:

countQueuingStrategy.size#

Added in: v16.5.0

• Type:
  • chunk
  • Returns:

Class: TextEncoderStream#

new TextEncoderStream()#

Added in: v16.6.0

Creates a new TextEncoderStream instance.

textEncoderStream.encoding#

Added in: v16.6.0

• Type:

The encoding supported by the TextEncoderStream instance.

textEncoderStream.readable#

Added in: v16.6.0

• Type:

textEncoderStream.writable#

Added in: v16.6.0

• Type:

Class: TextDecoderStream#

new TextDecoderStream([encoding[, options]])#

Added in: v16.6.0

• encoding Identifies the encoding that this TextDecoder instance supports. Default: 'utf-8'.
• options
  • fatal true if decoding failures are fatal.
  • ignoreBOM 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:

The encoding supported by the TextDecoderStream instance.

textDecoderStream.fatal#

Added in: v16.6.0

• Type:

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

textDecoderStream.ignoreBOM#

Added in: v16.6.0

• Type:

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

textDecoderStream.readable#

Added in: v16.6.0

• Type:

textDecoderStream.writable#

Added in: v16.6.0

• Type:

Class: CompressionStream#

new CompressionStream(format)#

Added in: v17.0.0

• format One of either 'deflate' or 'gzip'.

compressionStream.readable#

Added in: v17.0.0

• Type:

compressionStream.writable#

Added in: v17.0.0

• Type:

Class: DecompressionStream#

new DecompressionStream(format)#

Added in: v17.0.0

• format One of either 'deflate' or 'gzip'.

decompressionStream.readable#

Added in: v17.0.0

• Type:

decompressionStream.writable#

Added in: v17.0.0

• Type:

Utility Consumers#

Added in: v16.7.0

The utility consumer functions provide common options for consuming streams.

They are accessed using:

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

streamConsumers.arrayBuffer(stream)#

Added in: v16.7.0

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

`` 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}); 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}); }); ``

streamConsumers.blob(stream)#

Added in: v16.7.0

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

`` 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}); 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}); }); ``

streamConsumers.buffer(stream)#

Added in: v16.7.0

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

`` 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}); 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}); }); ``

streamConsumers.json(stream)#

Added in: v16.7.0

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

`` 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}); 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}); }); ``

streamConsumers.text(stream)#

Added in: v16.7.0

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

`` 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}); 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}); }); ``