text: var showNav = document.getElementsByClassName("showNav")[0];
  var nav = document.getElementsByClassName("nav")[0];
  var navLi = nav.getElementsByTagName("li");
  var lastLi = document.getElementsByClassName("lastLi")[0];
  var Icon = lastLi.getElementsByClassName("iconfont")[0];
  var num = navLi.length;
  var onOff = true;
  showNav.onclick = function () {
      if (onOff) {
          onOff = false;
          nav.classList.add("showHidden");
          for (var i = 1; i < num - 1; i++) {
              navLi[i].style.display = "block";
          }
          Icon.innerHTML = "&#xe64a;";
      } else {
          onOff = true;
          nav.classList.remove("showHidden");
          for (var i = 1; i < num - 1; i++) {
              navLi[i].style.display = "";
          }
          Icon.innerHTML = "&#xe653;";
      }
  }
  