code: function removeClassName(el, cls) {
    if (!cls || !(cls = cls.trim())) {
      return;
    }
  
    var clsArr = cls.split(/\s+/);
    if (el.classList) {
      clsArr.forEach(function (c) {
        return el.classList.remove(c);
      });
    } else {
      var curCls = ' ' + el.className + ' ';
      clsArr.forEach(function (c) {
        var tar = ' ' + c + ' ';
        while (curCls.indexOf(tar) !== -1) {
          curCls = curCls.replace(tar, ' ');
        }
      });
      el.className = curCls.trim();
    }
  }
docs: 为HTML元素移除className
  @param {HTMLElement} el 目标元素
  @param {String} cls 要移除的className（多个以空格分割）