chromium/third_party/blink/web_tests/external/wpt/html/cross-origin-opener-policy/resources/postback.html

<!doctype html>
<meta charset=utf-8>
<script src="/common/dispatcher/dispatcher.js"></script>
<script>
const params = new URL(location).searchParams;
const channelName = params.get("channel");
const responseToken = params.get("responseToken");
const iframeToken = params.get("iframeToken");

// If the channel parameter is set, use the BroadcastChannel-based communication
// method. Otherwise, use the dispatcher (useful in cases where this is embedded
// in a third-party iframe that doesn't share a partition with the top-level
// site).
if (channelName != "null") {
  const bc = new BroadcastChannel(channelName);
  // Handle the close message from the test-cleanup, forwarding it to the
  // top level document, as this iframe and the opening document might not
  // be able to close the popup.
  bc.onmessage = event => {
    if (event.data == "close") {
       top.postMessage("close", "*");
     }
  };

  window.addEventListener("message", event => {
    bc.postMessage(event.data);
  });

} else {
  window.addEventListener("message", event => {
    send(responseToken, JSON.stringify(event.data));
  });

  async function waitToClose() {
    response = await receive(iframeToken);
    // Handle the close message from the test-cleanup, forwarding it to the
    // top level document, as this iframe and the opening document might not
    // be able to close the popup.
    if (response == "close") {
      top.postMessage("close", "*");
    }
  }
  waitToClose();
}
</script>