Limitations of the react-native JS engine
Can't find variable: Proxy
#What features of ES6 can I use in react?
The documentation provides an official answer here. Having said that, you can theoretically use everything that can be implemented in ES5 by providing polyfills for the unsupported features you want to use. So, for most things you can tell react-native to use your custom babel config with additional babel-plugins to spit out ES5. On the babel website is a list of features that can be transpiled to ES5 with polyfills, unfortunately, Proxies are an "unsupported feature" and there is no (efficient) polyfill for them. Let's hope react-native upgrades to some better JS engine to get full ES6 support.