And how does this relate to the statement above? How many of this is DOM manipulation code for browser? i'll make a wild guess of 90%?

Part of this though is because web apps are for better or worse increasingly being almost nothing but javascript. And it becomes tedious moving back and forth between javascript and another language. Even if that language is really good. So i think people are just going with javascript for "everything" and rewriting their libraries in it.

HTML is the most popular language on GitHub ;)

I always wonder what percentage of that consists of included dependencies.

Most of our "django projects" are listed as being written in js on GitHub.

A good half of it may just be "we threw jQuery in here instead of making you download it".

How does it calculate the size of the code base for each language? Most people would be using jquery as a minified oneliner. How can that inflate the numbers so much?

GitHub's source code language detection is over there:

https://github.com/github/linguist/tree/master/lib/linguist

It doesn't measure line length, which could be a good way to detect minified JavaScript. It uses file extensions and byte size. There is some exclusion of commonly bundled libraries, but it's a rough heuristic on file paths.

I'd imagine counting by characters would make a lot more sense than counting lines.