file_sync_xhr_document_write_with_iframe.html

Enable keyboard shortcuts

<!DOCTYPE HTML>

<body>

<script>

function syncXHR() {

  let xhr = new XMLHttpRequest();

  xhr.open("GET", window.location, false);

  xhr.send(null);

addEventListener('load', () => {

  syncXHR();

  document.open();

  document.write(

    '<body>' +

    '<iframe src="about:blank"></iframe>' +

    // eslint-disable-next-line no-useless-concat

    '<script>window.opener.postMessage("DONE", "*");</' + 'script>' +

    '</body>');

  document.close();

}, { once: true });

</script>

</body>