gdm_service.html

<html>
<meta charset=utf-8>
<div id="div"></div>
<video id="video" width="320" height="200" autoplay></video><br>
<script>
const console = { log: msg => div.innerHTML += msg + "<br>" };

onmessage = async () => {
  try {
    video.srcObject = await navigator.mediaDevices.getDisplayMedia({video: true});
    console.log(video.srcObject.getVideoTracks()[0].label);
  } catch(e) {
    console.log(e);
  }
};

</script>
</html>