JS 如何判断当前页面是否全屏

   	//  监听全屏事件触发
      fullscreenchange() {
        let isFullScreen = document.fullScreen || document.mozFullScreen || document.webkitIsFullScreen;
        if (isFullScreen) {
          //  进入全屏
        } else {
          //  退出全屏
          
        }
      },