It's often in comments in the JS file(s) -- sometimes with the licenses quoted entirely and sometimes in a form abbreviated by an automated code packer. Probably a lot of sites aren't actually compliant with the terms of the licenses doing things that way, but IANAL.
Many licences make a distinction between using software and distributing it
For example in the GPLv3:
To “convey” a work means any kind of propagation that enables other parties to make or receive copies. Mere interaction with a user through a computer network, with no transfer of a copy, is not conveying.
Welcome to the web development community! This is a place to post, discuss, get help about, etc. anything related to web development
Web development is the process of creating websites or web applications
Some webdev blogs
Not sure what to post in here? Want some web development related things to read?
Heres a couple blogs that have web development related content