How do I secure my React Native Expo app from hackers? [closed]

I’d hate to build an entire application to only have it hacked.

I am using Firebase and Expo. I know about security rules for Firebase but is there any rules I need to abide by for the JavaScript within React Native/Expo?

Like, is there anyway a user can just change my javascript code and use it against me? I’ve heard about runtime attacks but I don’t know if people can do that in a mobile app like they can in a browser. I’ve seen where a user/attacker can literally just change variables and turn it into code that sends application data to the attackers server but I don’t know how that works.