content/test/data/workers/shared_fetcher.js

self.addEventListener('connect', (evt) => {
  const port = evt.ports[0];

  port.addEventListener('message', (event) => {
    fetch(event.data)
        .then((response) => port.postMessage({ok: response.ok}))
        .catch((error) => port.postMessage({error: error.name}));
  });
  port.start();

  port.postMessage('ready');
});