I am the author of the tutorial. I created a tool that captures keystrokes and file operations in a popular editor and allows them to be played back in a browser. The author can then add a narrative as the code evolves with text, pictures, and videos.
I have more 'books' on C++, python, SQL, web dev, dart/flutter, clojure, ruby, and more:
I use these for the programming-focused cs courses that I teach instead of having the students buy bloated textbooks. The students prefer them to books (no surprise) and videos (somewhat surprising). The code is searchable and copy/pasteable so the students actually use it.
The tool is free and open.