Brent Vatne does a good job, in his articles, in describing how to bridge React Native an iOS native code or even enhancing the existing framework.

This time in React Native View Components (1/2) discusses how to wrap existing iOS view components and pass the attributes from JavaScript

for most non-trivial apps, you'll quickly find yourself running into issues such as lack of support for multiline on , accessing an unwrapped API such as the Google Login SDK, needing to display a gradient, presenting a modal window, playing and controlling the playback options of a video or audio file, adding a blur effect and so on. The community is quickly building components to solve these problems but you want to use react-native now.

and in React Native View Components (2/2) tells how to subclass a native iOS UIKit class and override its setters to work regardless of their application order.

When you feel ready to contribute back to the React Native community with your own Component, he shares his experience in writing a whole lot of them in his Packaging a React Native component article.