logic.js

                const videoElem = document.getElementById("video");
const logElem = document.getElementById("log");
const startElem = document.getElementById("start");
const stopElem = document.getElementById("stop");

// Options for getDisplayMedia()

var displayMediaOptions = {
  video: {
    cursor: "always"
  },
  audio: false
};

// Set event listeners for the start and stop buttons
startElem.addEventListener("click", function(evt) {
  startCapture();
}, false);

stopElem.addEventListener("click", function(evt) {
  stopCapture();
}, false); console.log = msg => logElem.innerHTML += `${msg}<br>`;
console.error = msg => logElem.innerHTML += `<span class="error">${msg}</span><br>`;
console.warn = msg => logElem.innerHTML += `<span class="warn">${msg}<span><br>`;
console.info = msg => logElem.innerHTML += `<span class="info">${msg}</span><br>`; async function startCapture() {
  logElem.innerHTML = "";

  try {
    videoElem.srcObject = await navigator.mediaDevices.getDisplayMedia(displayMediaOptions);
    dumpOptionsInfo();
  } catch(err) {
    console.error("Error: " + err);
  }
} function stopCapture(evt) {
  let tracks = videoElem.srcObject.getTracks();

  tracks.forEach(track => track.stop());
  videoElem.srcObject = null;
} function dumpOptionsInfo() {
  const videoTrack = videoElem.srcObject.getVideoTracks()[0];
 
  console.info("Track settings:");
  console.info(JSON.stringify(videoTrack.getSettings(), null, 2));
  console.info("Track constraints:");
  console.info(JSON.stringify(videoTrack.getConstraints(), null, 2));
}