This is a follow on from the simple d3.js graph used as an example in the book D3 Tips and Tricks.
It demonstrates the loading of new data and updating a graph on a button press. It should be taken in context with the text of the book which can be downloaded for free from Leanpub.
https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js