Tips & Tricks From the Ultimate Guide to RN Optimization 2025

Kwaśniewski explains that time to interactive (TTI) measures the time from opening the app to seeing meaningful content, and distinguishes cold, warm, hot, and iOS prewarm starts. React Native Performance can track lifecycle events such as `nativeLaunchStart` and `runJSBundleStart`; iOS prewarming can complicate measurements. For frame rate, the Dev Menu shows UI and JavaScript thread FPS, while Flashlight can track performance over time on Android.

Concurrent React can pause or abandon rendering work, and React Native requires the New Architecture to use these features. Kwaśniewski demonstrates `useDeferredValue` with a slow component: deferring its updates keeps text input more responsive while the component still renders.

The React Compiler is a Babel plugin that memoizes values and can reduce unnecessary renders, provided the code follows React’s rules. In the Expensify app, enabling it resulted in up to 4.3% faster TTI; apps that are already heavily memoized may see smaller gains. For heavy JavaScript-thread computation, he cites React Native Quick Crypto as up to 58 times faster than CryptoJS by using C++.

View flattening merges layout-only nodes to simplify the native hierarchy, but can change how many children a native component receives. Setting `collapsable={false}` on a view preserves it when the expected child count matters. Kwaśniewski also recommends disabling Android bundle compression so Hermes can use memory mapping; this is the default from React Native 0.79, and older versions can add `noCompress` in `build.gradle` for around 12% faster TTI, as stated in the transcript.