This example demonstrates D3’s enter, exit, and update pattern for binding data to SVG rectangles, showing how bars are added, resized, or removed as the dataset changes. The code uses `selection.enter()`, `.merge(selection)`, and `selection.exit().remove()` within a reusable `drawChart` function, and it calls that function twice with different data arrays to illustrate the transitions. It relies on the D3 v5 `select` and `merge` APIs, with SVG rendering in a fixed 960×500 viewport.