code: function buildAxis() {
              if (isHorizontal) {
                  xAxis = d3Axis.axisBottom(xScale)
                      .ticks(xTicks, valueLabelFormat);
                  yAxis = d3Axis.axisLeft(yScale)
              } else {
                  xAxis = d3Axis.axisBottom(xScale)
                  yAxis = d3Axis.axisLeft(yScale)
                      .ticks(yTicks, valueLabelFormat)
              }
          }
docs: Creates the d3 x and y axis, setting orientations
  @private