function fullScreenFun() {
    var iFullscreen = false; //當前是否全屏狀態
    var fullscreenEnabled = document.fullscreenEnabled ||
      document.mozFullScreenEnabled ||
      document.webkitFullscreenEnabled ||
      document.msFullscreenEnabled;

    if (fullscreenEnabled) {
      let de = document.documentElement;
      if (iFullscreen) {
        //關閉全屏
        if (document.exitFullscreen) {
          document.exitFullscreen();
        } else if (document.mozCancelFullScreen) {
          document.mozCancelFullScreen();
        } else if (document.webkitCancelFullScreen) {
          document.webkitCancelFullScreen();
        }
      } else {
        //開啟全屏
        if (de.requestFullscreen) {
          de.requestFullscreen();
        } else if (de.mozRequestFullScreen) {
          de.mozRequestFullScreen();
        } else if (de.webkitRequestFullScreen) {
          de.webkitRequestFullScreen();
        }
      }
    } else {
      alert('瀏覽器當前不能全屏');
    }
  }