[2mur]

Backbone and Underscore have annotated source code:

http://backbonejs.org/docs/backbone.html

http://underscorejs.org/docs/underscore.html

[adamcw]

This is what I came to suggest as well. I would also say that Express is a good one as well if you're looking to learn Node. Not quite as clear as the annotated source for Backbone, but well commented.

I also liked the "Let's Make a Framework" posts at DailyJS. DailyJS in general was a great blog that is now closed, but the archives are still up.

https://github.com/strongloop/express

http://dailyjs.com/framework-index/

[rememberlenny]

+1 for Backbone. It is very well documented

[teamhappy]

I was about to suggest lodash.