portal-post-message-before-activate-window.html

Enable keyboard shortcuts

<!DOCTYPE html>

<body>

  <script>

    var portal = document.createElement("portal");

    portal.src = "portal-post-message-before-activate-portal.html";

    document.body.appendChild(portal);

    portal.onload = () => {

      portal.postMessage("message");

      portal.activate();

  </script>

</body>