It's peculiar how there are a billion beginner-level articles on d3.js, but the people who get stuck usually need something between that and intermediate.

If someone considers writing a d3.js tutorial, I'd urge them to use a real example, since this is where people realize they should use features like line.defined(), figure out how to implement gridlines yourself, and so on.

As great as d3.js, it's really hard to dive into the official wiki/docs as well as hit them for help.