This example shows how D3’s data join handles dynamic updates to a scatterplot of five circles. Buttons trigger removal or modification of data points, with exiting circles turning red while new and updated circles render in steel blue. The code uses D3 v5’s `select`, `scaleLinear`, and `merge` to bind array data to SVG circles. Updates call the `update` function, which handles enter, update, and exit selections, while random coordinates come from a custom `rand` helper.