D3 Documentation

Is there any good D3js Documentation?
the official reference doesn’t tell mush details about the usage and the meaning of different functions and methods.
and the documentations I found on the internet are incomplete or for older versions.
I need more details to read, I want to deeply understand D3.
I’m doing the projects of d3js now and I feel that I’m just following steps I found on different examples
without deeply understanding them.
I already finished 3 data visualization projects
so any help, please?

The best reference for the D3 methods is going to be their official API Reference.

the Official API isn’t helpful for me. it doesn’t tell much details.
is n’t there any better one? like MDN for Javascript they explain everything.