code: function buildVoronoi() {
              voronoi = d3Voronoi.voronoi()
                  .x((d) => xScale(d.x))
                  .y((d) => yScale(d.y))
                  .extent([
                      [0, 0],
                      [chartWidth, chartHeight]
                  ])(dataPoints);
          }
docs: Draws the voronoi component in the chart.
  @return {void}
  @private