Service worker stream transferring 2

1-service-worker.js

"use strict";

const worker = new Worker("worker.js");

self.onfetch = e => {
  e.respondWith(new Promise(resolve => {
    const guid = generateGUID();
    
    worker.addEventListener("message", function messageListener({ data: { readableStream, messageId } }) {
      if (messageId !== guid) {
        return;
      }
      worker.removeEventListener("message", messageListener);
      resolve(new Response(readableStream));
    });
    worker.postMessage(guid);
  });
};

2-worker.js

"use strict";

self.onmessage = ({ data: messageId, source }) => {
  const readableStream = new ReadableStream({
    start(controller) {
      // These can be done asynchronously if you want.
      controller.enqueue(new Uint8Array([1, 2, 3]));
      controller.close();
    }
  });
  
  source.postMessage({ readableStream, messageId }, [readableStream]);
  // readableStream has now been transferred/neutered/detached.
  // This means that readableStream.getReader() will never work anymore in this thread.
  // However, we as the creator of the stream can still *enqueue data into it*; it's just
  // that the UA has an exclusive lock on reading data out of it, for the purpose of transferring
  // it over to the service worker.
};