Resources about d3 specifically.
A short introduction into the the d attribute of path elements
Updating your chart in d3.js
How v5 helps clean up your updating code
Learn all the things that are important about projections in d3.
How to create a simple tooltip in d3.js
Learn how to create tooltips in d3. This post shows you actual d3 code and adds explanations to the most important aspects of tooltips in d3 and has a demo as well.
SVG Basics for d3
Three basic elements of SVG you should know if you want to create maps with d3.