code: function (attrName, attrVal) {
              if (!attrName) {
                  delete this.attrs;
                  return;
              }
              if(!this.attrs){
                  this.attrs = {};
              }
              if (utils.isObject(attrName)) {
                  for (var a in attrName) {
                      if (!attrName[a]) {
                          delete this.attrs[a]
                      } else {
                          this.attrs[a.toLowerCase()] = attrName[a];
                      }
                  }
              } else {
                  if (!attrVal) {
                      delete this.attrs[attrName]
                  } else {
                      this.attrs[attrName.toLowerCase()] = attrVal;
                  }
  
              }
          }
docs: 设置当前节点所代表的元素属性，即设置attrs对象下的属性值
  @method setAttr
  @param { String } attrName 要设置的属性名称
  @param { * } attrVal 要设置的属性值，类型视设置的属性而定
  @return { * } 返回attrs对象下的属性值
  @example
  ```javascript
  node.setAttr('title','标题');
  ```