<!DOCTYPE html>
<script>
  const windowProps = ["innerWidth", "innerHeight"];
  const windowPropsObj = {};
  const channelName = location.search.substr(1);
  const channel = new BroadcastChannel(channelName);
  for (const prop of windowProps) {
    windowPropsObj[prop] = window[prop];
  }
  channel.postMessage(windowPropsObj);

  // Because messages are not delivered synchronously and because closing a
  // browsing context prompts the eventual clearing of all task sources, this
  // document should not be closed until the opener document has confirmed
  // receipt.
  channel.onmessage = () => { window.close() };
</script>
