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ReadableStream DefaultReader

Background

Section titled “Background”

A reader is used when you want to read from a ReadableStream, rather than piping its output to a WritableStream.

A ReadableStreamDefaultReader is not instantiated via its constructor. Rather, it is retrieved from a ReadableStream:

const { readable, writable } = new TransformStream();
const reader = readable.getReader();

Properties

Section titled “Properties”

  • reader.closed : Promise

    • A promise indicating if the reader is closed. The promise is fulfilled when the reader stream closes and is rejected if there is an error in the stream.

Methods

Section titled “Methods”

  • read() : Promise

    • A promise that returns the next available chunk of data being passed through the reader queue.

  • cancel(reasonstringoptional) : void

    • Cancels the stream. reason is an optional human-readable string indicating the reason for cancellation. reason will be passed to the underlying source’s cancel algorithm -- if this readable stream is one side of a TransformStream, then its cancel algorithm causes the transform’s writable side to become errored with reason.

  • releaseLock() : void

    • Releases the lock on the readable stream. A lock cannot be released if the reader has pending read operations. A TypeError is thrown and the reader remains locked.
Section titled “Related resources”