electron/spec/fixtures/workers/load_worker.html

<script>
  function loadWorker(url) {
    return new Promise((resolve) => {
      try {
        const w = new Worker(url);
        w.onerror = () => resolve('failed');
        w.onmessage = (m) => resolve(m.data);
        w.postMessage('success');
      } catch {
        resolve('failed');
      }
    });
  }
</script>