chromium/src/third_party/blink/web_tests/external/wpt/fetch/metadata/resources/unload-with-beacon.html - manifest_repos/chromium_src - Git at Google

 <!DOCTYPE html>
 <script>
   // When told, register an unload handler that will trigger a beacon to the
   // URL given by the sender of the message.
   window.addEventListener('message', e => {
       var url = e.data;
       window.addEventListener('unload', () => {
           navigator.sendBeacon(url, 'blah');
       });
       window.parent.postMessage('navigate-away', '*');
   });
 </script>
	<!DOCTYPE html>
	<script>
	// When told, register an unload handler that will trigger a beacon to the
	// URL given by the sender of the message.
	window.addEventListener('message', e => {
	var url = e.data;
	window.addEventListener('unload', () => {
	navigator.sendBeacon(url, 'blah');
	});
	window.parent.postMessage('navigate-away', '*');
	});
	</script>