Build an iOS app & Node.js API simultaneously

I'm building an iOS app that communicates to a Node.js API I'm also building. Locally, everything is ok, I've structured my iOS code in a way that I only declare the API base URL in one place (ie. 192.168.0.3:5000 - local).

However, you can imagine where I'm going with this.

Once I deploy the API to Heroku, what's the best way for me to manage the iOS side of things in regard to: 1. testing locally with the local API, 2. deploying the iOS app to the app store (ie. how do I tell it to use a different API URL?)

Any advice would be great on setting up a sane development environment for this...