Animated circles demonstrate D3’s enter-update-exit cycle through the `join` method, using `selectAll` and `data` with data-derived sine waves to shift positions and radii. The visualization renders in SVG within the browser, updating at 60 frames per second via `setInterval`. Each frame recalculates a dynamic dataset from `d3.range`, illustrating how `join('circle')` automatically creates, updates, and removes nodes as data count fluctuates. The source uses D3 v7’s modular imports (`select`, `range`) and properties like `cx`, `cy`, and `r` to bind values directly to DOM attributes.