Proprietary Javascript is a way smaller problem than normal proprietary
software for two reasons:
first, it is executed in your webbrowser, which puts it in a sandbox. That
means that the webbrowser limits what javascript can actually do, and if your
webbrowser is free software, everybody can check if it is really doing a
proper job.
Second, most javascript code that you find on smaller websites is visible in
your console, that means everybody can read what it's doing and in principle,
every user can find harmful features and inform others about it.
However, it's true that bigger websites which rely more on javascript mostly
minify and uglify their code, so you get a compressed and non-human-readable
version.
What you should be more concerned with is injected javascript from services
like google analytics, since they can track you. I advice installing noscript
and blocking those sites.
The functionality of the website you want to use will not suffer from this.
My personal opinion is that the fuss about non-free javascript is way, way
too big and exaggerated.
Besides, javascript applications are most of the time deeply connected with
the layout of the webpage and the server as a backend api.
Take both away and the code is basically useless because incomplete.
In general, it's way harder to apply the idea of free software on javascript
(in websites) mainly due to those issues.
Writing a modified version of the
javaschttps://www.youtube.com/watch?v=igDGkpTHuhkript of a website and
sharing it with your friends? Maybe but difficult and mostly unneccesary.
Writing a modified version of the javascript code of a website and realising
a modified version?
In most cases, that makes no sense since the website might change any day,
making your code useless.
Again, big single-page-webapps which are running soley on the client are a
different story.
