The same questions as some years back: How to get started with it ?
The good news: There is plenty of material out there about D3, books, websites, tutorials. I purchased a couple of books from Packt Books and O’Reilly as PDF version, I think they have the most books, though most of them based on earlier D3 versions.
I wont recommend a specific one, most follow the same principles, a short intro to the DOM, explain the D3 basics followed by more or less complex samples. As with any other technology or programming language you learn most hands-on, there so many examples and good tutorials available. I never attempted to understand everything, understand the concepts, dissect existing visualizations and get creative !
D3.js Website and
I will revisit some of the old visualizations I created and also try to convert some newer ideas into visualizations. Now tinkering and playing became much easier, I recommend JSFiddleif you want to avoid local web server setup, though JSFiddle does not support version 4.0 yet (at the time of writing this).
I am working with D3 again after experimenting with visualization tools like Tableau and realizing quickly that outstanding visualizations only can be created with the power of D3, though you have to work with sourcecode and understand whats going on under the hood of a modern web browser. Please dont forget D3 is released under the BSD license !