I show how you using only a browser can do instant React native testing, both in iOS an Android. The app is coded in ES2015 JavaScript using React Native and requires no compiling or building. The code runs and updates as you type, and your can see the result in a free app found at https://expo.io/ which is available for both iOS and Android.
The example app can be seen here: https://snack.expo.io/Sk6H4ayqb
snack.expo.io
react-native-training.github.io/react-native-elements/