vue 实现网页全屏（大屏）

screen () {
  const element = document.documentElement;
  if (this.fullscreen) {
    // 退出全屏
    if (!document.exitFullscreen && document.exitFullscreen) {
      document.exitFullscreen();
    } else if (document.webkitCancelFullScreen) {
      document.webkitCancelFullScreen();
    } else if (document.mozCancelFullScreen) {
      document.mozCancelFullScreen();
    } else if (document.msExitFullscreen) {
      document.msExitFullscreen();
    }
  } else {
    // 全屏展示
    if (element.requestFullscreen) {
      element.requestFullscreen();
    } else if (element.webkitRequestFullScreen) {
      element.webkitRequestFullScreen();
    } else if (element.mozRequestFullScreen) {
      element.mozRequestFullScreen();
    } else if (element.msRequestFullscreen) {
      // IE11
      element.msRequestFullscreen();
    }
  }
  this.fullscreen = !this.fullscreen;
},