At the end of most videos throughout the course, the Treehouse instructor provides additional resources (such as links to documentation or examples) that complement the concepts covered in that video.
The tutorial videos in this course are longer than many of the other Treehouse courses, yet still remain easy to follow and very engaging. The material is presented at a reasonable pace and everything is clearly explained.
This course will give you some idea of what you can do with D3.js, however it doesn't cover many of the useful functionalities. You will have to seek out other resources to complement your learning in order to fully utilize D3.js.
The tutorials are written in a way that makes them clear and informative without being bulky. Due to the tutorials being example-heavy, you are able to see the concepts learned in code after every step.
If you have a specific project in mind, the set-up of these tutorials make it easy to read through the chapters only relevant to what you need, without feeling lost.
These tutorials are a great place for a beginner to start, but if you want to do more advanced things with the library then you'll have to continue with another resource. However Scott Murray has a book, "Interactive Data Visualization for the Web" that extends his online tutorials.
You don't need to have any prior experience with D3.js to understand this book.
The author starts with the basics and introduces new concepts at a good pace.
The free only version is all the material placed on one page. It's quite a bit difficult to follow as the material is quite tightly placed and you have to scroll back to the top any time you want to refer to the table of contents.
The D3 gallery isn't a tutorial, it only shows examples of graphs created with D3.
For someone completely new to D3, this would likely be an overwhelming place to start.
D3js.org provides a long list of examples demonstrating the library in use, and the code for those examples. D3js.org is also where the documentation for the library can be found (such as a list of all the methods available).
Though D3js.org provides some tutorials, the documentation is better suited for developers who have already been introduced to the library and need to reference the official documentation. Someone new to D3.js will most likely find themselves unsure where to start.
Getting Started with D3 is a good starting point for learning about the library. The book takes you through set up, basic concepts and provides examples to reinforce what you're learning.
Getting Started with D3 barely touches on the the functionalities of this powerful library. It does a poor job of giving the reader a feel for the different features and it's possibilities.