<!DOCTYPE html>
<html class="reftest-wait">
<head>
<script>
let f = document.createElement('frame');
f.onload = function() {
  let frameDocument = f.contentDocument;
  frameDocument.body.onbeforeunload = function () { frameDocument.write('<p>beforeUnload</p>') };
  frameDocument.write('<p>trigger unload</p>')
  window.stop();
  document.documentElement.className = '';
};
document.documentElement.appendChild(f);
</script>
</head>
<body>
</body>
</html>
