This example demonstrates how merge and join functions work in D3 by animating a set of circles whose positions, radii, and count change over time via a `setInterval` timer. It shows how `selectAll`, `data`, and `join('circle')` merge new data with existing SVG elements, while separate `vizData.js` modules use ES6 `import`/`export` syntax to keep the code scalable. The visualization uses `d3.range` to generate data points and `d3.select` to append an SVG to the body, with the animation updating every 200 milliseconds.