I wanted to do exactly what you describe yesterday -- just download the latest stable version of a one-JS-file library to include on one page of a web app where its functionality is relevant. We used to do this by downloading example-1.0.8.min.js from the obvious Download link on www.example.com.
As it turns out, the project from yesterday lives in a GitHub repository with a dozen files scattered across a root and four subdirectories. I honestly have no idea how to build it; it's written in a compiled-to-JS language, the build instructions are a one-liner that refer to a build tool I've heard of but never used, and there are at least half a dozen other files in the project that seem to be there only for some sort of compatibility with various other tools I've heard of but never used/don't use on this project/don't have installed on this workstation.
I find myself reminded almost daily of this now-infamous XKCD: http://xkcd.com/927/
This is not progress. :-(
I've spent about half of my work day today working out npm dependency conflicts... The Einstein quote about insanity comes to mind.