This example demonstrates animated circle transitions driven by a continuous data stream. It shows how D3’s data join pattern updates SVG circle positions and radii in real time, with the number of circles and their attributes oscillating sinusoidally. The code uses `d3.select` and `selection.data` with `.join('circle')` to manage enter/update/exit, while `setInterval` triggers a refresh at 60 fps. Data is generated procedurally via `makeData`, which computes varying x, y, and r values based on a time parameter. The visualization highlights the simplicity of binding dynamic data to SVG elements using D3 v6.