docs: function __getElements(selector) {
      var self = this;
      //获取容器
      var container = this.options.container;
      if (typeof container == 'string') {
        //如果是字符串，则选择器
        this.container = doc.querySelector(container);
      } else {
        //对象传值
        this.container = container;
      }
      //获取容器内的所有目标元素
      if (this.container == window) {
        var appearWatchElements = doc.querySelectorAll(selector);            
      } else {
        var appearWatchElements = this.container.querySelectorAll(selector);
      }
      var appearWatchElements = [].slice.call(appearWatchElements, null);
  
      appearWatchElements = appearWatchElements.filter(function(ele) {
        // 如果已经绑定过，清除appear状态，不再加入到数组里
        if (ele.dataset['bind'] == '1') {
          delete ele._hasAppear;
          delete ele._hasDisAppear;
          delete ele._appear;      
          ele.classList.remove(self.options.cls);
          return false;
        } else {
          return true;
        }
      });
  
      return appearWatchElements;
    }