This example demonstrates D3’s data join and selection patterns by animating a row of circles whose count and vertical positions oscillate with a sine wave. The code uses `d3.select`, `d3.range`, and `selectAll().data().join()` to update SVG circles at 60 frames per second, while a commented-out version shows the older `enter()`/`merge()`/`exit()` workflow. The visualization renders directly into the browser window via an SVG element sized to `window.innerWidth` and `window.innerHeight`, with no external data source.