Does require proprietary javascript?

here is a question from one of our members:

Does use or require proprietary Javascript ?

I am asking because I’ve got a friend who only uses FOSS and very strictly avoids proprietary Javascript, and so refused to communicate via, believing that it requires proprietary Javascript.

I am not technically knowledgeable enough to know if this is true or not.

Many thanks if you can advise me.

I post it here, to have confirmation. Maybe @Yurko @dvdjaco @Jonathan would know.

The frontend is released under the GNU Lesser General Public License v3.0 and so is the backend.