requestFullscreen () {
  const docElm = document.documentElement
  if (docElm.requestFullscreen) {
    docElm.requestFullscreen()
  } else if (docElm.msRequestFullscreen) {
    docElm.msRequestFullscreen()
  } else if (docElm.mozRequestFullScreen) {
    docElm.mozRequestFullScreen()
  } else if (docElm.webkitRequestFullScreen) {
    docElm.webkitRequestFullScreen()
  }
}

function isFullscreen () {
  return document.fullscreenElement ||
  document.msFullscreenElement ||
  document.mozFullScreenElement ||
  document.webkitFullscreenElement || false;
}

  exitFullScreen () {
    if(isFullscreen()){
      if (document.exitFullscreen) {
        document.exitFullscreen()
      } else if (document.msExitFullscreen) {
        document.msExitFullscreen()
      } else if (document.mozCancelFullScreen) {
        document.mozCancelFullScreen()
      } else if (document.webkitCancelFullScreen) {
        document.webkitCancelFullScreen()
      }
    }
}