Because targetting javascript has a lot of advantages, being cross platform is a major one of them. You basically get the type-safety of swift, with the ability to target multiple platforms.

The fact that it transpiles to JS is irrelevant, you can provide a safe interface to something unsafe. Take Elm for example, it transpiles to JS and yet guarantees that you will never produce a runtime exception.

The JavaScript toolchain is more than good enough to build the kinds of applications that React Native targets. Most of these applications aren't stellar apps that require critical performance or rigorous type checking, they're just dumb front-ends to REST endpoints. If you're going to build an awesome app, then use better tools.

The reason I would use React over Xamarin is simple: Speed of training and development. I can hire, train and get a React developer up and running and building proof-of-concepts a lot quicker than on Xamarin.

RN supports iOS, Windows, and Android. Plus RN is somewhat close to React, so some code could be reused between the two. Plus you get out-of-band code updates!

Xamarin supports iOS, Windows, and Android. But there is no web story. Or is there?