How much code is React Native and how much code is hand written Objective-C ? can you answer that question ? "Use" doesn't mean 100% without a single line of Objective-C written.

Groups is a mix of native code and React Native, but Ads Manager is pure react native. The app is completely written in Javascript.

No, like GarageBand, OmniFocus, Keynote, or hell even iBooks.

React Native is only the view layer. There is a ton more to an app than just the view layer.

Not just the view. React Native also gives you access to HTTP and full JavaScript logic, so the model, view and controllers can be written using React Native.

I just discovered that. They're using building polyfills to simulate the browser behavior, too. Very cool.