From the webpage:
These code examples accompany the O’Reilly video course “Intermediate d3.js: Charts, Layouts, and Maps”.
This video is preceded by the introductory video course “An Introduction to d3.js: From Scattered to Scatterplot”. I recommend watching and working through that course before attempting this one.
Some of these examples are adapted from the sample code files for Interactive Data Visualization for the Web (O’Reilly, March 2013).
If you have been looking to step up your d3 skills, here’s the opportunity to do so!
Enjoy!