highlightBarFunction = (barSelection) =>
                barSelection.attr('fill', ({name}) =>
                    d3Color.color(
                        chartGradientColors
                        ? chartGradientColors[1]
                        : colorMap(name)
                    ).darker()
                )
Bar Chart reusable API class that renders a
simple and configurable bar chart.

@module Bar
@tutorial bar
@requires d3-array, d3-axis, d3-dispatch, d3-scale, d3-selection

@example
var barChart = bar();

barChart
    .height(500)
    .width(800);

d3Selection.select('.css-selector')
    .datum(dataset)
    .call(barChart);