This is documentation for the next version of K6. For the latest stable release, go to the latest version.

JavaScript API

k6/experimental

streams

ReadableStream

cancel(reason)

Open source

cancel(reason)

The cancel() method of the ReadableStream 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.

Return value

A promise that resolves with the value undefined when the stream is canceled.

Exceptions

Exception	Description
TypeError	Thrown the stream is locked to a reader.

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();
  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, any enqueued chunks are lost
      await reader.cancel('cancelling the stream');
      break;
    }
  }
}

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);
    },
  });
}