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Why do I need to know, how to work with native code in React Native app?​

There are several advantages of having a skill (or at least basic knowledge) in terms of native mobile development. React Native is a great abstraction that allows many JS developers to write mobile apps which:

  • use platform UI elements
  • are at the same time managed with JS code on both platforms
  • can benefit from the JS ecosystem
  • can benefit from features unavailable for natively written apps (e.g. codepush)

However, both Android and iOS have a rich palette of UI elements and platform APIs, while React Native as a core offers only minimal set of primitives like text fields, scroll views, modals, etc. So sooner or later you'll need to somehow bring those missing parts to your app. Some of those can be integrated via 3rd party packages - this has an advantage of using battle-tested logic with an easy interface. The disadvantage is that you lose control over that specific chunk of application's code - if the 3rd party lib doesn't support customization of some platform API, unless you fork, you cannot customize that thing from JS code (while from native code, it would be easy-peasy job). And there are APIs and SDKs that don't have any React Native package - will the client or the user care that you cannot implement some functionality, because nobody else bridged those SDKs before? Ofc not.

The skill of being able to expose any platform element to the React Native JS layer makes huge impact on you as a developer:

  • You're not constrained with a single mindset of leveraging all responsiblity on 3rd party packages, even with the cost of producing non-optimal application
  • You're far ahead on each RN programming interview, because you'll not be surprised/confused with any "did you bridge some native API?" question
  • That knowledge can help you when working with Android & iOS devs (at the end, not every RN project is a greenfield app 😉)

But why even bother with all those weird Javas & Objective-Cs, when I can use Expo?​

Expo is a great framework, no doubt! Not only it simplifies the coding stage, but it also handles the deployment part. It has a rich set of libraries for some common features (e.g. filesystem, audio/video, system web-browser, etc.).

However

It's still an abstraction over the platform you develop on. It won't magically make arbitrary native code available in the JS codebase. That native code still has to be bridged.

Luckily, Expo folks did tremendous job by creating Expo Modules. It's oriented around modern native languages (Swift & Kotlin), with nice DSL and without big boilerplate, it lets you focus on the most important thing - exposing platform code, to the React Native app.

So if you use Expo, you should check Expo Modules' official tutorial. You can also stay here and check following guides to learn some RN + native insights which will give you better overview and you'll appreciate Expo & Expo Modules even more!