Thanks for this link. I will be reading it for sure. I also stumbled on the annotated source of Underscore.js a few days ago (http://underscorejs.org/docs/underscore.html). Would love any more stuff like this that anyone knows of.
Docco Source: http://jashkenas.github.io/docco/
Backbone Source: http://backbonejs.org/docs/backbone.html
CoffeeScript Source: http://coffeescript.org/documentation/docs/grammar.html
Generally I think that a linear step-by-step description is often not the best way though, often you would have to explain concepts or the bigger picture first.
https://watchandcode.com/courses/eloquent-javascript-the-ann...