This example demonstrates an interactive circular bubble chart that visualizes hierarchical JSON data, with a focus on handling multiple datasets. The visualization uses D3 v3’s `d3.layout.pack` to position and size circles based on nested data values, while a click-to-zoom animation transitions between hierarchy levels. Users can switch between three JSON files via buttons, which are implemented as SVG groups with click handlers that reload and re-render the pack layout. The code uses `d3.json` for asynchronous data loading, `d3.scale.linear` with HCL color interpolation for node coloring, and `d3.interpolateZoom` for smooth zoom transitions.