How are sketch designs converted to react native code?

Hey guys,

So I'm a product designer and I've seen a few new tools popping up that convert most designs into production ready react native code, a few examples are:

• supernova.io

• draftbit.com

-extensions.zeplin.io/zeplin/react-native

What is used to make this conversion? I just want a little insight on this? I'm still barely learning the ropes of react native but any insight would be great. Especially what language or library or even the logic used to convert things so easily.

P.S I'm not sure how production ready it is but for example Draftbit actually allows you to run the app in Expo including navigation.

Thanks