My overall goal is to build in simple chat rooms cross platform.
Your native module would communicate with the React Native app through the RN bridge. At a high level you'd have to implement
sendMessage/joinChannel from RN -> iOS and
receivedMessage/Channel from iOS -> RN.
One example (that I've communicated to the Twilio team) is that their JS SDKs break when npm-V8 centric deps like
crypto can't be ported. I'm guessing there are several other basic libraries that are commonplace in Node that don't get ported over by React Native's build system.
You can track related React Native issues here: (Symptom - node modules are missing): https://github.com/facebook/react-native/issues/4968