// get with web apis #fullscren element and on click toggle fullscreen
const fullscreen = document.getElementById('fullscreen');
const elem = document.documentElement;
fullscreen.addEventListener('click', () => {
  if (document.fullscreenElement) {
    closeFullscreen();  
  } else {
    openFullscreen();
  }
});

function openFullscreen() {
  if (elem.requestFullscreen) {
    elem.requestFullscreen();
  } else if (elem.webkitRequestFullscreen) { /* Safari */
    elem.webkitRequestFullscreen();
  } else if (elem.msRequestFullscreen) { /* IE11 */
    elem.msRequestFullscreen();
  }
}

function closeFullscreen() {
  if (document.exitFullscreen) {
    document.exitFullscreen();
  } else if (document.webkitExitFullscreen) { /* Safari */
    document.webkitExitFullscreen();
  } else if (document.msExitFullscreen) { /* IE11 */
    document.msExitFullscreen();
  }
}