code: function drawHorizontalBars(layersSelection) {
              let layerJoin = layersSelection
                  .data(layers);
  
              layerElements = layerJoin
                  .enter()
                    .append('g')
                      .attr('transform', ({key}) => `translate(0,${yScale(key)})`)
                      .classed('layer', true);
  
              let barJoin = layerElements
                  .selectAll('.bar')
                  .data(({values}) => values);
  
              // Enter + Update
              let bars = barJoin
                      .enter()
                        .append('rect')
                          .classed('bar', true)
                          .attr('x', 1)
                          .attr('y', (d) => yScale2(getGroup(d)))
                          .attr('height', yScale2.bandwidth())
                          .attr('fill', (({group}) => categoryColorMap[group]));
  
              if (isAnimated) {
                  bars.style('opacity', barOpacity)
                      .transition()
                      .delay((_, i) => animationDelays[i])
                      .duration(animationDuration)
                      .ease(ease)
                      .tween('attr.width', horizontalBarsTween);
              } else {
                  bars.attr('width', (d) => xScale(getValue(d)));
              }
          }
docs: Draws the bars along the x axis
  @param  {D3Selection} layersSelection Selection of layers
  @return {void}