What are the commands for purging all packages from a specific repository only, and removing it?

I added a https://deb.nodesource.com/node_8.x repository to install some npm stuff we were using at a hackathon. I no longer need any of that stuff, and I'd like to purge all packages installed from those repos and remove them. But I can't remember which packages I installed.

I tried using the "Origin" tab in Synaptic, which shows a list of installed packages available from each repo on the system. But for some reason the deb.nodesource repo doesn't show up there (all my other default and added repos are there).

How do I purge all packages installed from this repo and remove it?