Maintain communication between two clients even if their IP addresses change

I'm trying to figure out if it is possible to have something like this scenario:

Say we have two people, Alice and Bob. Alice wants to send some data (doesn't matter what this data is) to Bob, and vice versa. I know that WebRTC can be used to serverless-ly exchange messages, but that requires Alice and Bob knowing each other's IP addresses. Now, it's relatively easy for Alice and Bob to share their IP addresses once, to initialize a connection, but what happens if one of them happens to connect to a different network; maybe Bob is in a coffee shop, for instance, and his IP address is thus different? The previously initialized connection wouldn't be to his current IP address, so they'd have to reinitialize the connection; but how?

It would seem to me that there would already need to be some sort of preexisting communication between the two so they could share their IP addresses, but then why not just communicate through the method they communicate their IP addresses instead? Alternatively, there could be a server that connects the two, but that defeats the serverless part of the system.

So, is there any way to maintain communication between two clients even if they happen to change networks, and thus IP addresses? Perhaps there is a more fixed method of identifying devices than their IP addresses, like I've seen in this SO answer, but it's years old, so maybe there's something new? I'd be implementing this in JS, across multiple devices/OSs, so that answer probably wouldn't work. Any ideas/examples would be greatly appreciated; I mainly want to know if this is even possible, and, if so, how.

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