Purely informational question, not really a problem but: I remember following the instructions and seeing that there were some steps to get the react-native-fbsdk working. These steps involved messing with my android build.gradle and adding the iOS SDK and the info.plist and whatnot. That aside, why doesn't Facebook utilize the javascript SDK? Is it not possible? If so, why is it not possible for Facebook to do this? If it is possible, why did they opt to utilize the both the android and iOS SDK?
One value prop of React Native is that it's not just an HTML 5 website embedded in a native wrapper. It literally uses the native APIs/components, and the same goes for SDKs. Technically, a pure JS SDK could be optimized for a browser experience, rely on window or document, and while the functionality might be able to be executed natively, the polyfills provided in RN might not be enough to cover the implementation. The way it makes API calls are probably different too. The views are different too (no DOM in RN), so that would apply for any SDK views (button?).
I just finished converting an iOS SDK to a React Native package and I feel that the implementation will be more inline with how the original iOS SDK was designed, since it's using those methods under the covers instead of pure JS. JS is just invoking the native methods, not taking over the methods.
Just my $0.02...