code: function () {
          var enabledAttributes = this._enabledAttributes;
          var attributeList = this._attributeList;
          // Cache
          if (enabledAttributes) {
              return enabledAttributes;
          }
  
          var result = [];
          var nVertex = this.vertexCount;
  
          for (var i = 0; i < attributeList.length; i++) {
              var name = attributeList[i];
              var attrib = this.attributes[name];
              if (attrib.value) {
                  if (attrib.value.length === nVertex * attrib.size) {
                      result.push(name);
                  }
              }
          }
  
          this._enabledAttributes = result;
  
          return result;
      }
docs: Get enabled attributes name list
  Attribute which has the same vertex number with position is treated as a enabled attribute
  @return {string[]}