Fork of Fade Out Fade In 2
This example shows two sequential sets of circles. First, two blue circles appear briefly; after two seconds, they fade out and are removed. Then, four red circles fade in, each placed at new coordinates. The visualization uses D3 v7 with SVG and animation. The code demonstrates a common D3 pattern where the `transition()` method applies a fade-out effect, followed by a `.delay(2000)` before the new selection fades in. The author notes the timing issue: the new selection is created before the first circles are fully removed, resulting in only two red circles appearing instead of four.