code: function exitFullscreen() {
          var _doument = document;
          if (document.exitFullscreen) {
              document.exitFullscreen();
          }
          else if (_doument.msExitFullscreen) {
              _doument.msExitFullscreen();
          }
          else if (_doument.mozCancelFullScreen) {
              _doument.mozCancelFullScreen();
          }
          else if (_doument.webkitExitFullscreen) {
              _doument.webkitExitFullscreen();
          }
      }
docs: exit fullscreen mode.