Have you ever thought before to inspect or learn from the source code of libraries like (JQuery, Underscore, React, etc ..)?

Obviously,

Learning from source of famous frameworks or libraries is particularly instructive.

Developers of this source code are mostly expert in JavaScript, so we can only learn from it. 

In my experience, I like to read source code of Backbone.js, it has a good documentation and architecture.

All JavaScript developers must learn it to be considered as an expert.

Yes.. It is very good to learn from libraries source because it give you detailed information how the current library works.

Yes, if I judge it necessary

yes .. but variable names encoded

yes , if I needed this because the libraries code is so complicated 

Yes It is better to learn from libraries source 

I personally learnt a lot by making my own projects, solving problems encountered and optimising my codes.  ))))

Yes, but only when I required as going through the source codes takes a lot of time. But what I learned mostly from the source code is, the proper way to document source code.

Yes We can learn new things from experts.