This bar chart visualizes online customer sales, plotting the number of purchases against total revenue for each category. It uses D3.js v4 with an SVG rendering approach, leveraging `d3.scaleBand` for the categorical x-axis and `d3.scaleLinear` for the continuous y-axis. Data is loaded asynchronously from a CSV file via `d3.csv`. The chart positions rectangular bars with a fixed blue fill, rotating the x-axis labels for readability.