sousa-gecko/testing/web-platform/tests/webmessaging/support/postMessage-reload-child.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
Child Window (B)
<script>
'use strict';

// This message is sent from parent's unload handler and because we
// should be not-fully active by the time the queued task runs
// we should never receive this.
window.addEventListener('message', (msg) => {
  window.parent.parent.postMessageTaskRan = true;
});
</script>
</body>
</html>