For donutchart: http://zeroviscosity.com/d3-js-step-by-step/step-5-adding-tooltips
Event definitions: http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-EventTarget
Bar chart example: http://bl.ocks.org/mbostock/3885304
Tooltip: http://bl.ocks.org/biovisualize/1016860

My Project: https://uofi.box.com/s/iua06pmiaq8lt9xn03ucpkjqs54pu7rw