Performance Does Matter - Making Your React-Native App Fast

Bruchim links app speed to retention, ratings, and revenue, citing research that each 1% reduction in startup time can raise retention by 0.27%. He says teams should measure performance on users’ real devices, noting that 35% of Wix’s user base used devices more than two years old.

Bruchim recommends Hermes on Android for faster launches, interactions, and lower memory use; Wix saw startup improve by up to 50% on some devices. He advises inspecting bundle contents, removing unused or oversized dependencies such as Moment when simpler date operations suffice, and using RAM bundles or Metro inline requires to load code as needed. Inline requires improved startup by 20% on iOS in Wix’s case.

He recommends caching data and images, showing cached content while refreshing, and fetching only what a screen needs. For rendering, he suggests preventing avoidable updates and giving users immediate loading feedback with loaders or skeletons. Using the native animation driver can reduce bridge traffic, though its supported properties include transforms and opacity.

Bruchim says JavaScript libraries can add bridge traffic, so teams should consider native implementations where available. He describes JSI as a way for JavaScript and native code to communicate directly without serializing JSON messages, while noting that it was not yet production-ready or well documented at the time of the talk.

He recommends monitoring in production as well as profiling during development, using tools such as Flipper, React DevTools, and React Native Bundle Visualizer. Bruchim describes reporting startup measurements by device, platform, and app version, and checking pull requests for regressions. He also recommends Why Did You Render to identify avoidable renders and removing console logs from production.