fullScreen() {

    document.getElementById("fullScreen").style.display = "none";

    document.getElementById("exitScreen").style.display = "block";

    let el = document.documentElement as any;

    let rfs = el.requestFullScreen || el.webkitRequestFullScreen || el.mozRequestFullScreen || el.msRequestFullscreen;

    if (typeof rfs != "undefined" && rfs) {

      rfs.call(el);

    };

    return;

  }

  //退出全屏

  exitScreen() {

    document.getElementById("fullScreen").style.display = "block";

    document.getElementById("exitScreen").style.display = "none";

    let cfs = document as any;

    if (cfs.exitFullscreen) {

      cfs.exitFullscreen();

    }

    else if (cfs.webkitCancelFullScreen) {

      cfs.webkitCancelFullScreen();

    }

    else {

      cfs.msExitFullscreen();

    }

  }