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