code: function getLinkedData(dataType) {
      var mainData = this[MAIN_DATA];
      return (dataType == null || mainData == null)
          ? mainData
          : mainData[DATAS][dataType];
  }
docs: Supplement method to List.
  
  @public
  @param {string} [dataType] If not specified, return mainData.
  @return {module:echarts/data/List}