code: function (lineDash) {
          if (lineDash instanceof Array) {
              this._lineDash = lineDash;
  
              this._dashIdx = 0;
  
              var lineDashSum = 0;
              for (var i = 0; i < lineDash.length; i++) {
                  lineDashSum += lineDash[i];
              }
              this._dashSum = lineDashSum;
          }
          return this;
      }
docs: 必须在其它绘制命令前调用
  Must be invoked before all other path drawing methods
  @return {module:zrender/core/PathProxy}