But honestly, I don't see how those 2 lines

   .on('mouseover', this.rolloverOn(args))

   .on('mouseout', this.rolloverOff(args));

For a charting library, yes I would expect this to be easy. But to be fair, D3js is not a charting library. The OP here is showing their version of a charting library based off of D3js.

Remember, D3 = Data Driven Documents, which can be leveraged for extremely fast interactive visualizations

For further clarification here is the goal/definition from D3js.org:

"D3 allows you to bind arbitrary data to a Document Object Model (DOM), and then apply data-driven transformations to the document. For example, you can use D3 to generate an HTML table from an array of numbers. Or, use the same data to create an interactive SVG bar chart with smooth transitions and interaction."

A charting library wouldn't give you the flexibility to do this: http://bl.ocks.org/mbostock/d8e15a0ab7f85818a5bd or this: http://bost.ocks.org/mike/shuffle/

Edit: a must see are the creations from the man himself. Mike Bostock http://bl.ocks.org/mbostock

    1) building a Voronoi tessellation from the given points
    2) at each mouse movement perform point-in-polygon queries on all polygons until found
    3) rebuild Voronoi as data changes

    1) at each mouse movement calculate distance-to-point for each point
    2) select the shortest