Have you ever checked out jQuery from GitHub?
While I was reading the jQuery source code as it's broken out in the github repository, I discovered that it is really readable. Most of it makes a lot of sense, and you can derive much knowledge and pleasure from the way the different jQuery contributors have created a unified whole out of the various component parts.
Other important learning tools: jQuery's github repository uses node.js for assembly, git for code control, and both jshint and jqunit for catching some bugs. Reading the package.json files, the various git control files, even the editorconfig dot-file are real eye-openers: they make for a consistent experience for all developers, and they work brilliantly. My only complaint, now that I've experimented with editorconfig, is that it marks all files as having changed, even if you don't actually change anything at all.