ReadableStreamSource : Object

Object that provides the sequence of values for a ReadableStream. Passed to the ReadableStream constructor. Any JavaScript object can be used as a readable stream source. Any of the properties/method can be specified. If a property/method is not provided, the ReadableStream will use a default behavior for the property/method.

Spec

Instance Properties

type : String

If set to 'bytes', the ReadableStream will be a readable byte stream.

Spec

Instance Methods

cancel(reason : Object) : Promise<undefined>

Called when the stream has been canceled, either by ReadableStream.cancel() or Reader.cancel(), with reason as the value passed to that function.

Example:

const stringStream = new ReadableStream({
  start(controller) {
    controller.enqueue('a');
    controller.enqueue('b');
    controller.close();
  },
  cancel(reason) {
    console.log(`cancel reason: ${reason}`);
  }
});

const reader = stringStream.getReader();

let result;
while (!(result = await reader.read()).done) {
  console.log(result.value);
  reader.cancel('xyz');
}

Run

Results:

Spec

pull(controller : ReadableStreamController) : Promise<undefined>

Called each time the stream's internal queue drops below the high water mark, indicating this should enqueue more chunks.

Example:

const stringStream = new ReadableStream({
  i: 1,
  pull(controller) {
    console.log('pull', controller.desiredSize);
    while (controller.desiredSize > 0) {
      controller.enqueue(`chunk_${this.i++}`);
    }
    if (this.i > 5) controller.close();
  }
}, new CountQueuingStrategy({ highWaterMark: 2 }));

const reader = stringStream.getReader();
let result;
while (!(result = await reader.read()).done) {
  console.log('received:', result.value);
}

Run

Results:

Spec

start(controller : ReadableStreamController) : Object

Example:

// Create a stream of strings.
const stringStream = new ReadableStream({
  start(controller) {
    ['a', 'b', 'c'].forEach(s => controller.enqueue(s));
  }
});

const reader = stringStream.getReader();
let result;
while (!(result = await reader.read()).done) {
  console.log(result.value);
}

Run

Results:

Spec

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