A bar chart displays the percentage of varicella cases in Bolivia by year, with bars colored teal by default and turning coral when clicked to highlight a selected year. The chart loads data from a CSV file, maps it with numeric year and percentage values, and renders axes and bars using d3.scaleBand, d3.scaleLinear, d3.axisBottom, and d3.axisLeft. A unidirectional data flow pattern in udf.js manages state, passing selections between viz.js, setupSVG.js, and renderBarChart.js.