how to catch uncaught exception (globally) in react native

You could possibly override the exception logging that React Native uses for development:

ErrorUtils.setGlobalHandler(function() {
// your handler here
});

https://github.com/facebook/react-native/blob/522fd33d6f3c8fb339b0dde35b05df34c1233306/Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js#L46

You may then need to write some Obj-C which you expose to JS, depending on your exact requirements.