client.on sounds like you are using a library, so refer to that libraries documentation. I personally don’t use a library for my bots (beyond WS for connection handling) so to “listen” for a sub I parse the relevant message(s) in chat.
By “listen” I mean “listen/read in chat like how you would as a human reading chat”
So I “listen” for USERNOTICE messages for Subscriber events
Sounds similar to what I do elsewhere so that looks fine.