全屏，退出全屏

笔记

注意：不能自动调用，必须手动触发

 requestFullScreen() {
    let el = document.documentElement;
    let rfs = el.requestFullScreen || el.webkitRequestFullScreen ||
      el.mozRequestFullScreen || el.msRequestFullScreen;
    if (rfs) { //typeof rfs != "undefined" && rfs
      rfs.call(el);
    } else if (typeof window.ActiveXObject != 'undefined') {
      //for IE，这里其实就是模拟了按下键盘的F11，使浏览器全屏
      let wscript = new ActiveXObject('WScript.Shell');
      if (wscript != null) {
        wscript.SendKeys('{F11}');
      }
    }

  }

cancelFullScreen() {
    let el = document;
    let cfs = el.cancelFullScreen || el.webkitCancelFullScreen ||
      el.mozCancelFullScreen || el.exitFullScreen;
    if (cfs) { //typeof cfs != "undefined" && cfs
      cfs.call(el);
    } else if (typeof window.ActiveXObject != 'undefined') {
      //for IE，这里和fullScreen相同，模拟按下F11键退出全屏
      let wscript = new ActiveXObject('WScript.Shell');
      if (wscript != null) {
        wscript.SendKeys('{F11}');
      }
    }
  }