React Native Brownfield: Lessons from the Trenches

A greenfield app is built from scratch with React Native; a brownfield app uses it for selected views or flows in an existing native app. Tormey says brownfield work adds native language and platform knowledge, toolchains, and the effort of learning an inherited codebase. He estimates it can initially be two to three times harder than a greenfield project.

Tormey frames React Native as an infrastructure investment: learning it costs time, so it should eventually save time or speed development. Brownfield integration is more suitable for larger organizations with multiple mobile teams and an existing React web team, where learning and implementation can be shared. He recommends starting with a simple, measurable project to build confidence and trust, while accounting for organizational concerns as well as technical ones.

Tormey describes an open-source example based on Keepsafe’s subscription upsell screens, which the company wanted to update experiments for using CodePush. Native iOS code launches and hosts the React Native screen; an event bridge sends purchase and dismissal events back to native handlers. A JSON configuration maps screen names to default props, while native code handles existing systems such as payments and navigation.

Tormey’s proposed workflow has native and React Native engineers agree on stub events after reviewing designs, then build their parts in parallel and iterate together with product and design. Once integrated, the team checks whether native code changed. CodePush can ship screens immediately when no native changes are needed; native changes must wait for an iOS or Android app release.

The Keepsafe project used React Native Event Bridge so external web or React Native engineers could build screens without access to, or deep knowledge of, the native code. Tormey says this approach suited that project’s constraints, but is not the only way to integrate React Native. He points to Artsy’s open-source work and Pinterest’s brownfield materials as further examples.