This example demonstrates D3 data joins with interactive buttons that remove or modify circles in an SVG scatterplot. Clicking "Remove" pops the last item from an array of x/y coordinates, redrawing the remaining circles; clicking "Modify" replaces one random entry with new values. The code uses `select`, `scaleLinear`, and `max` from d3 v5, along with a custom `rand` utility, to update circle positions via enter/merge/exit selections. The visualization highlights how shared update logic handles both new and existing elements.