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ReadableStreamDefaultReader

The ReadableStreamDefaultReader API defines a reader for a readable stream. It is designed based on the standard Web APIs ReadableStreamDefaultReader.
Note:
A ReadableStreamDefaultReader object cannot be constructed directly. You can use the ReadableStream.getReader method to construct a ReadableStreamDefaultReader object.

Overview

// Use TransformStream to construct a ReadableStream object.
const { readable } = new TransformStream();

// Use the ReadableStream object to obtain the reader.
const reader = readable.getReader();

Attributes

closed

// reader.closed
readonly closed: Promise<void>;
The closed attribute returns a Promise object. If the stream is closed, the status of the Promise object is fulfilled. If an exception occurs on the stream or the lock on the reader is released, the status of the Promise object is rejected.

Methods

read

reader.read(): Promise<{value: Chunk, done: boolean}>;
The read() method reads data from the stream.
Note:
You cannot initiate the next stream reading operation until the current stream reading operation ends.

Returned values

The reader.read method returns a Promise object that contains the read data Chunk and the reading status.
If a chunk is available, the Promise object is in the fulfilled status and contains an object in the { value: theChunk, done: false } format.
If the stream is closed, the Promise object is in the fulfilled status and contains an object in the { value: undefined, done: true } format.
If an exception occurs on the stream, the Promise object is in the rejected status, and the relevant error information is included.

Chunk

The Chunk parameter indicates the data to be read from the stream.
type Chunk = string | ArrayBuffer | ArrayBufferView;

cancel

reader.cancel(reason?: string): Promise<string>;
The cancel() method closes the stream and ends the reading operation.

releaseLock

reader.releaseLock(): void;
The releaseLock() method cancels the association with the stream and releases the lock on the stream.

References