chromium/third_party/blink/web_tests/external/wpt/html/browsers/windows/nested-browsing-contexts/resources/post-to-parent.html

<script>
const ident = new URL(location).searchParams.get("ident"),
      post = () => parent.postMessage({ name: window.name, ident }, "*");
onmessage = () => post();
post();
</script>