This multi-line chart uses a Voronoi tessellation to handle mouseover; the closest point to the mouse on any line is highlighted. Click the checkbox in the top-right to toggle the visibility of the underlying Voronoi diagram.
The main difference with mbostock‘s original block: Multi-Line Voronoi is that the real action is now happening in voronoi.find().
We don’t need a hidden SVG overlay. We just keep it there to display it on demand, but it’s not used for the animation.