code: function Select(selector, opts) {
      var _this = this;
  
      var $selectNative =  _this.$selectNative = $(selector).eq(0);
      if (!$selectNative.length) {
        return;
      }
  
      // 已通过自定义属性实例化过，不再重复实例化
      var oldInst = $selectNative.data('mdui.select');
      if (oldInst) {
        return oldInst;
      }
  
      $selectNative.hide();
  
      _this.options = $.extend({}, DEFAULT, (opts || {}));
  
      // 为当前 select 生成唯一 ID
      _this.uniqueID = $.guid();
  
      _this.state = 'closed';
  
      // 生成 select
      _this.handleUpdate();
  
      // 点击 select 外面区域关闭
      $document.on('click touchstart', function (e) {
        var $target = $(e.target);
        if (
          (_this.state === 'opening' || _this.state === 'opened') &&
          !$target.is(_this.$select) &&
          !$.contains(_this.$select[0], $target[0])
        ) {
          _this.close();
        }
      });
    }
docs: 下拉选择
  @param selector
  @param opts
  @constructor