Start / Stop interval on Service Worker

index.html

<button onclick="sendMessage('start')">Start Listen</button>
<button onclick="sendMessage('stop')">Stop Listen</button>
<script>
  let se;
  const registration = navigator.serviceWorker.register('/sw.js').then(data => {
    se = data.active;
    console.log('ready');
  });

  function sendMessage(message) {
    se.postMessage(message);
  }
</script>

sw.js

let interval;

function startListen() {
  interval = setInterval(() => {
    console.log(Date.now());
  }, 1000);
}
function stopListen() {
  clearInterval(interval);
}

self.addEventListener('message', ({data}) => {
  switch (data) {
    case 'start':
      startListen();
      break;
    case 'stop':
      stopListen();
      break;
  }
});