window.html

<title>CacheAttack Worker</title>
<h1>CacheAttack Worker</h1>
<p1>This window is used for cache checking.</p1>
<script> 
window.addEventListener("pagehide", event => {
  window.opener.postMessage("pagehide");
});
window.addEventListener('load', (event) => {
  window.opener.postMessage("load");
});
</script>