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|
# Web Streams API
<!--introduced_in=v16.5.0-->
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: Use of this API no longer emit a runtime warning.
-->
> Stability: 1 - Experimental.
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.
```mjs
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('stream/web');
const {
setInterval: every
} = require('timers/promises');
const {
performance
} = require('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`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new ReadableStream([underlyingSource [, strategy]])`
<!-- YAML
added: v16.5.0
-->
<!--lint disable maximum-line-length remark-lint-->
* `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'`.
* `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}
<!--lint enable maximum-line-length remark-lint-->
#### `readableStream.locked`
<!-- YAML
added: 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])`
<!-- YAML
added: v16.5.0
-->
* `reason` {any}
* Returns: A promise fulfilled with `undefined` once cancelation has
been completed.
#### `readableStream.getReader([options])`
<!-- YAML
added: v16.5.0
-->
* `options` {Object}
* `mode` {string} `'byob'` or `undefined`
* Returns: {ReadableStreamDefaultReader|ReadableStreamBYOBReader}
```mjs
import { ReadableStream } from 'node:stream/web';
const stream = new ReadableStream();
const reader = stream.getReader();
console.log(await reader.read());
```
```cjs
const { ReadableStream } = require('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])`
<!-- YAML
added: v16.5.0
-->
* `transform` {Object}
* `readable` {ReadableStream} The `ReadableStream` to which
`transform.writable` will push the potentially modified data
is 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` is not cause this `ReadableStream` to be
canceled.
* `preventClose` {boolean} When `true`, closing this `ReadableStream`
will no 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.
```mjs
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);
```
```cjs
const {
ReadableStream,
TransformStream,
} = require('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)`
<!-- YAML
added: 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 `transform.writable` to be aborted.
* `preventCancel` {boolean} When `true`, errors in the destination
`transform.writable` is not cause this `ReadableStream` to be
canceled.
* `preventClose` {boolean} When `true`, closing this `ReadableStream`
will no cause `transform.writable` 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()`
<!-- YAML
added: 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])`
<!-- YAML
added: v16.5.0
-->
* `options` {Object}
* `preventCancel` {boolean} When `true`, prevents the {ReadableStream}
from being closed when the async iterator abruptly terminates.
**Defaults**: `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.
```mjs
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.
```mjs
import { Buffer } from '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}.
```js
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`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
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)`
<!-- YAML
added: v16.5.0
-->
* `stream` {ReadableStream}
Creates a new {ReadableStreamDefaultReader} that is locked to the
given {ReadableStream}.
#### `readableStreamDefaultReader.cancel([reason])`
<!-- YAML
added: 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`
<!-- YAML
added: 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()`
<!-- YAML
added: v16.5.0
-->
* Returns: A promise fulfilled with an object:
* `value` {ArrayBuffer}
* `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()`
<!-- YAML
added: v16.5.0
-->
Releases this reader's lock on the underlying {ReadableStream}.
### Class: `ReadableStreamBYOBReader`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
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.
```mjs
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)`
<!-- YAML
added: v16.5.0
-->
* `stream` {ReadableStream}
Creates a new `ReadableStreamBYOBReader` that is locked to the
given {ReadableStream}.
#### `readableStreamBYOBReader.cancel([reason])`
<!-- YAML
added: 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`
<!-- YAML
added: 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)`
<!-- YAML
added: v16.5.0
-->
* `view` {Buffer|TypedArray|DataView}
* Returns: A promise fulfilled with an object:
* `value` {ArrayBuffer}
* `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 `fs` module
callbacks. These types of `Buffer`s 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()`
<!-- YAML
added: v16.5.0
-->
Releases this reader's lock on the underlying {ReadableStream}.
### Class: `ReadableStreamDefaultController`
<!-- YAML
added: 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 `ReadableStream`s that are not byte-oriented.
#### `readableStreamDefaultController.close()`
<!-- YAML
added: v16.5.0
-->
Closes the {ReadableStream} to which this controller is associated.
#### `readableStreamDefaultController.desiredSize`
<!-- YAML
added: v16.5.0
-->
* Type: {number}
Returns the amount of data remaining to fill the {ReadableStream}'s
queue.
#### `readableStreamDefaultController.enqueue(chunk)`
<!-- YAML
added: v16.5.0
-->
* `chunk` {any}
Appends a new chunk of data to the {ReadableStream}'s queue.
#### `readableStreamDefaultController.error(error)`
<!-- YAML
added: v16.5.0
-->
* `error` {any}
Signals an error that causes the {ReadableStream} to error and close.
### Class: `ReadableByteStreamController`
<!-- YAML
added: 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 `ReadableStream`s.
#### `readableByteStreamController.byobRequest`
<!-- YAML
added: v16.5.0
-->
* Type: {ReadableStreamBYOBRequest}
#### `readableByteStreamController.close()`
<!-- YAML
added: v16.5.0
-->
Closes the {ReadableStream} to which this controller is associated.
#### `readableByteStreamController.desiredSize`
<!-- YAML
added: v16.5.0
-->
* Type: {number}
Returns the amount of data remaining to fill the {ReadableStream}'s
queue.
#### `readableByteStreamController.enqueue(chunk)`
<!-- YAML
added: v16.5.0
-->
* `chunk`: {Buffer|TypedArray|DataView}
Appends a new chunk of data to the {ReadableStream}'s queue.
#### `readableByteStreamController.error(error)`
<!-- YAML
added: v16.5.0
-->
* `error` {any}
Signals an error that causes the {ReadableStream} to error and close.
### Class: `ReadableStreamBYOBRequest`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
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)`
<!-- YAML
added: v16.5.0
-->
* `bytesWritten` {number}
Signals that a `bytesWritten` number of bytes have been written
to `readableStreamBYOBRequest.view`.
#### `readableStreamBYOBRequest.respondWithNewView(view)`
<!-- YAML
added: 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`
<!-- YAML
added: v16.5.0
-->
* Type: {Buffer|TypedArray|DataView}
### Class: `WritableStream`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
The `WritableStream` is a destination to which stream data is sent.
```mjs
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]])`
<!-- YAML
added: 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])`
<!-- YAML
added: 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()`
<!-- YAML
added: v16.5.0
-->
* Returns: A promise fulfilled with `undefined`.
Closes the `WritableStream` when no additional writes are expected.
#### `writableStream.getWriter()`
<!-- YAML
added: v16.5.0
-->
* Returns: {WritableStreamDefaultWriter}
Creates and creates a new writer instance that can be used to write
data into the `WritableStream`.
#### `writableStream.locked`
<!-- YAML
added: 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}.
```js
const stream = new WritableStream(getWritableSinkSomehow());
const { port1, port2 } = new MessageChannel();
port1.onmessage = ({ data }) => {
data.getWriter().write('hello');
};
port2.postMessage(stream, [stream]);
```
### Class: `WritableStreamDefaultWriter`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new WritableStreamDefaultWriter(stream)`
<!-- YAML
added: v16.5.0
-->
* `stream` {WritableStream}
Creates a new `WritableStreamDefaultWriter` that is locked to the given
`WritableStream`.
#### `writableStreamDefaultWriter.abort([reason])`
<!-- YAML
added: 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()`
<!-- YAML
added: v16.5.0
-->
* Returns: A promise fulfilled with `undefined`.
Closes the `WritableStream` when no additional writes are expected.
#### `writableStreamDefaultWriter.closed`
<!-- YAML
added: 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`
<!-- YAML
added: v16.5.0
-->
* Type: {number}
The amount of data required to fill the {WritableStream}'s queue.
#### `writableStreamDefaultWriter.ready`
<!-- YAML
added: v16.5.0
-->
* type: A promise that is fulfilled with `undefined` when the
writer is ready to be used.
#### `writableStreamDefaultWriter.releaseLock()`
<!-- YAML
added: v16.5.0
-->
Releases this writer's lock on the underlying {ReadableStream}.
#### `writableStreamDefaultWriter.write([chunk])`
<!-- YAML
added: v16.5.0
-->
* `chunk`: {any}
* Returns: A promise fulfilled with `undefined`.
Appends a new chunk of data to the {WritableStream}'s queue.
### Class: `WritableStreamDefaultController`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
The `WritableStreamDefaultController` manage's the {WritableStream}'s
internal state.
#### `writableStreamDefaultController.abortReason`
* Type: {any} The `reason` value passed to `writableStream.abort()`.
#### `writableStreamDefaultController.error(error)`
<!-- YAML
added: 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`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
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.
```mjs
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]]])`
<!-- YAML
added: 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`
<!-- YAML
added: v16.5.0
-->
* Type: {ReadableStream}
#### `transformStream.writable`
<!-- YAML
added: v16.5.0
-->
* Type: {WritableStream}
#### Transferring with postMessage()
A {TransformStream} instance can be transferred using a {MessagePort}.
```js
const stream = new TransformStream();
const { port1, port2 } = new MessageChannel();
port1.onmessage = ({ data }) => {
const { writable, readable } = data;
// ...
};
port2.postMessage(stream, [stream]);
```
### Class: `TransformStreamDefaultController`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
The `TransformStreamDefaultController` manages the internal state
of the `TransformStream`.
#### `transformStreamDefaultController.desiredSize`
<!-- YAML
added: v16.5.0
-->
* Type: {number}
The amount of data required to fill the readable side's queue.
#### `transformStreamDefaultController.enqueue([chunk])`
<!-- YAML
added: v16.5.0
-->
* `chunk` {any}
Appends a chunk of data to the readable side's queue.
#### `transformStreamDefaultController.error([reason])`
<!-- YAML
added: 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()`
<!-- YAML
added: v16.5.0
-->
Closes the readable side of the transport and causes the writable side
to be abruptly closed with an error.
### Class: `ByteLengthQueuingStrategy`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new ByteLengthQueuingStrategy(options)`
<!-- YAML
added: v16.5.0
-->
* `options` {Object}
* `highWaterMark` {number}
#### `byteLengthQueuingStrategy.highWaterMark`
<!-- YAML
added: v16.5.0
-->
* Type: {number}
#### `byteLengthQueuingStrategy.size`
<!-- YAML
added: v16.5.0
-->
* Type: {Function}
* `chunk` {any}
* Returns: {number}
### Class: `CountQueuingStrategy`
<!-- YAML
added: v16.5.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new CountQueuingStrategy(options)`
<!-- YAML
added: v16.5.0
-->
* `options` {Object}
* `highWaterMark` {number}
#### `countQueuingStrategy.highWaterMark`
<!-- YAML
added: v16.5.0
-->
* Type: {number}
#### `countQueuingStrategy.size`
<!-- YAML
added: v16.5.0
-->
* Type: {Function}
* `chunk` {any}
* Returns: {number}
### Class: `TextEncoderStream`
<!-- YAML
added: v16.6.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new TextEncoderStream()`
<!-- YAML
added: v16.6.0
-->
Creates a new `TextEncoderStream` instance.
#### `textEncoderStream.encoding`
<!-- YAML
added: v16.6.0
-->
* Type: {string}
The encoding supported by the `TextEncoderStream` instance.
#### `textEncoderStream.readable`
<!-- YAML
added: v16.6.0
-->
* Type: {ReadableStream}
#### `textEncoderStream.writable`
<!-- YAML
added: v16.6.0
-->
* Type: {WritableStream}
### Class: `TextDecoderStream`
<!-- YAML
added: v16.6.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new TextDecoderStream([encoding[, options]])`
<!-- YAML
added: 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`
<!-- YAML
added: v16.6.0
-->
* Type: {string}
The encoding supported by the `TextDecoderStream` instance.
#### `textDecoderStream.fatal`
<!-- YAML
added: v16.6.0
-->
* Type: {boolean}
The value will be `true` if decoding errors result in a `TypeError` being
thrown.
#### `textDecoderStream.ignoreBOM`
<!-- YAML
added: v16.6.0
-->
* Type: {boolean}
The value will be `true` if the decoding result will include the byte order
mark.
#### `textDecoderStream.readable`
<!-- YAML
added: v16.6.0
-->
* Type: {ReadableStream}
#### `textDecoderStream.writable`
<!-- YAML
added: v16.6.0
-->
* Type: {WritableStream}
### Class: `CompressionStream`
<!-- YAML
added: v17.0.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new CompressionStream(format)`
<!-- YAML
added: v17.0.0
-->
* `format` {string} One of either `'deflate'` or `'gzip'`.
#### `compressionStream.readable`
<!-- YAML
added: v17.0.0
-->
* Type: {ReadableStream}
#### `compressionStream.writable`
<!-- YAML
added: v17.0.0
-->
* Type: {WritableStream}
### Class: `DecompressionStream`
<!-- YAML
added: v17.0.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42225
description: This class is now exposed on the global object.
-->
#### `new DecompressionStream(format)`
<!-- YAML
added: v17.0.0
-->
* `format` {string} One of either `'deflate'` or `'gzip'`.
#### `decompressionStream.readable`
<!-- YAML
added: v17.0.0
-->
* Type: {ReadableStream}
#### `decompressionStream.writable`
<!-- YAML
added: v17.0.0
-->
* Type: {WritableStream}
### Utility Consumers
<!-- YAML
added: v16.7.0
-->
The utility consumer functions provide common options for consuming
streams.
They are accessed using:
```mjs
import {
arrayBuffer,
blob,
buffer,
json,
text,
} from 'node:stream/consumers';
```
```cjs
const {
arrayBuffer,
blob,
buffer,
json,
text,
} = require('stream/consumers');
```
#### `streamConsumers.arrayBuffer(stream)`
<!-- YAML
added: v16.7.0
-->
* `stream` {ReadableStream|stream.Readable|AsyncIterator}
* Returns: {Promise} Fulfills with an `ArrayBuffer` containing the full
contents of the stream.
#### `streamConsumers.blob(stream)`
<!-- YAML
added: v16.7.0
-->
* `stream` {ReadableStream|stream.Readable|AsyncIterator}
* Returns: {Promise} Fulfills with a {Blob} containing the full contents
of the stream.
#### `streamConsumers.buffer(stream)`
<!-- YAML
added: v16.7.0
-->
* `stream` {ReadableStream|stream.Readable|AsyncIterator}
* Returns: {Promise} Fulfills with a {Buffer} containing the full
contents of the stream.
#### `streamConsumers.json(stream)`
<!-- YAML
added: 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()`.
#### `streamConsumers.text(stream)`
<!-- YAML
added: v16.7.0
-->
* `stream` {ReadableStream|stream.Readable|AsyncIterator}
* Returns: {Promise} Fulfills with the contents of the stream parsed as a
UTF-8 encoded string.
[Streams]: stream.md
[WHATWG Streams Standard]: https://streams.spec.whatwg.org/
|