jqc is a really small script, just one line, that re-enables $ in the jQuery compatibility mode.
As of January 2021 this repo is archived and no changes will be made. Read more at https://klooven.link/archive.
Sometimes the compatibily mode is activated (eg. in WordPress) even if you don't really need it. This script lets you use $ instead of jQuery in this mode.
If possible, you should of course not use that mode if you don't need it.
jqc is made with the jsDelivr CDN in mind.
Using jsDelivr you can combine files, so you can just combine jqc with any file you want!
Here's how to combine files.
With this I mean this mode.
This is an interesting article about jQuery with WordPress.