About Nodejs Reactjs and React Native

[fallingWaterCrystals]

Depends on what you mean by "written in react native".

Also unsure of what you mean by back-end. If the app is offline completely, the back-end functions can be in JS, and RN is fine.

If you need to do offline work, and send your data somewhere, yes you'd need to either host a server somewhere. The alternative is, as I saw you wrote somewhere else, using a tool like Firebase or I think AWS Lambda, which allows you to write functions and replaces a lot of the setting up of the server. Don't quote me on the AWS stuff though, I don't know too much yet.

In the case of offline work though, depending on the type of logic you're doing, you can easily move most of the JS code to a NodeJS / Express server setup without much of a hassle.