WritableStream

Last updated Apr 23, 2026

Background

A WritableStream is the writable property of a TransformStream. On the Workers platform, WritableStream cannot be directly created using the WritableStream constructor.

A typical way to write to a WritableStream is to pipe a ReadableStream to it.

readableStream
  .pipeTo(writableStream)
  .then(() => console.log('All data successfully written!'))
  .catch(e => console.error('Something went wrong!', e));

To write to a WritableStream directly, you must use its writer.

const writer = writableStream.getWriter();
writer.write(data);

Refer to the WritableStreamDefaultWriter documentation for further detail.

Properties

  • locked boolean
  • A Boolean value to indicate if the writable stream is locked to a writer.

Methods

  • abort(reasonstringoptional) : Promise\<void>
  • Aborts the stream. This method returns a promise that fulfills with a response undefined. reason is an optional human-readable string indicating the reason for cancellation. reason will be passed to the underlying sink’s abort algorithm. If this writable stream is one side of a TransformStream, then its abort algorithm causes the transform’s readable side to become errored with reason.

Warning

Any data not yet written is lost upon abort. - getWriter() : WritableStreamDefaultWriter - Gets an instance of WritableStreamDefaultWriter and locks the WritableStream to that writer instance.

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description: Use WritableStreamDefaultWriter in Workers to write data directly to a WritableStream. title: WritableStream DefaultWriter image: https://developers.cloudflare.com/workers/runtime-apis/streams/writablestreamdefaultwriter/og.png?v=2e492aaffcdb663b

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