Accelerating Mobile App development at Zalando with Rendering Engine and React Native

Zalando migrated their mobile app to React Native using a brownfield integration approach. They built a custom framework called Rendering Engine that enables progressive adoption, shares code between web and mobile platforms, and maintains isolation from legacy native code. The architecture packages React Native as an npm module consumed by both a standalone developer app and native SDKs, allowing gradual screen migration while preserving existing capabilities. They use react-strict-dom for cross-platform UI components and StyleX for theming, successfully launching screens including their Discovery Feed.