cancel(reason)

The cancel() method of the ReadableStreamDefaultReader interface returns a Promise that resolves when the stream is canceled.

Cancel is used when you’ve completely finished with the stream and don’t need any more data from it, even if chunks are enqueued waiting to be read. That data is lost after cancel is called, and the stream is not readable any more. To close the stream without getting rid of enqueued chunks, use ReadableStreamDefaultController.close().

Arguments

Name	Type	Description
reason	any	An optional human-readable value that represents the reason for canceling the stream.

Returns

A promise that resolves with the provided reason when the stream is canceled.

Exceptions

Exception	Description
TypeError	Thrown when the source object is not a ReadableStreamDefaultReader or the stream has no owner.

Example

import { ReadableStream } from 'k6/experimental/streams';
import { setTimeout } from 'k6/timers';

export default async function () {
  // Define a number stream that emits numbers from 1 to 10 every second
  const stream = numbersStream();

  // We use the getReader method to create a reader and lock the stream to it
  const reader = stream.getReader();

  while (true) {
    const { done, value } = await reader.read();
    if (done) break;
    if (value === 8) {
      // Cancel the stream when the number is 8
      await reader.cancel('cancelling the stream');
      break;
    }

    console.log(`received number ${value} from stream`);
  }
}

function numbersStream() {
  let currentNumber = 0;

  return new ReadableStream({
    start(controller) {
      const fn = () => {
        if (currentNumber < 10) {
          controller.enqueue(++currentNumber);
          setTimeout(fn, 1000);
          return;
        }

        controller.close();
      };
      setTimeout(fn, 1000);
    },
  });
}