<!DOCTYPE html>
<html>
<head>
<title>Service Worker for a background service test</title>
<script>

let sw = null;

async function installSW() {
  sw = await navigator.serviceWorker.register('service-worker.js');
  await navigator.serviceWorker.ready;
  sw.active.postMessage('Posting message!');
}

async function waitForMessageFromSW() {
  return await new Promise(
      resolve => navigator.serviceWorker.onmessage = e => resolve(e.data));
}

</script>
</head>
<body></body>
</html>