The cancel() method of the ReadableStreamBYOBReader interface returns a Promise that resolves when the stream is canceled. Calling this method signals a loss of interest in the stream by a consumer.

reason Optional

A human-readable reason for the cancellation. The underlying source may or may not use it.

A Promise, which fulfills with the value given in the reason parameter.

TypeError

The source object is not a ReadableStreamBYOBReader, or the stream has no owner.

This example code calls the cancel() method when a button is pressed, passing the string "user choice" as a reason. The promise resolves when cancellation completes.

button.addEventListener("click", () => {
  reader.cancel("user choice").then(() => console.log(`cancel complete`));
});

Note that this code can be seen running in the Using readable byte streams example code (press the Cancel stream button).

• ReadableStreamBYOBReader() constructor
• Using readable byte stream