React Native uses a JavaScript bridge to communicate with native components, which can cause slight delays and affect frame rates, especially in complex animations. Flutter compiles to native ARM code, offering smoother 60fps or higher animations with less CPU overhead. Both frameworks consume moderate memory, but Flutter apps tend to have more consistent performance due to direct rendering.
For React Native, minimize bridge communication by batching updates and using native modules for heavy tasks. Use FlatList for large lists and avoid unnecessary re-renders with memoization. For Flutter, leverage widget rebuilding wisely, use const constructors, and avoid heavy work in build methods. Both benefit from profiling tools to find bottlenecks and optimize rendering.
React Native apps typically have smaller initial bundle sizes because they rely on native UI components, but require bundling JavaScript code which can increase size. Flutter apps include the entire rendering engine, leading to larger app sizes (usually 5-10MB more). Startup time is generally faster in React Native due to native UI, while Flutter's startup can be slightly longer but improves with app warm-up.
React Native uses native UI components on both platforms, so UI looks native but may differ slightly between iOS and Android. Flutter renders its own UI consistently across platforms, so apps look the same but may feel less native. iOS requires code signing and uses Xcode for React Native and Flutter. Android uses Gradle and APK/AAB signing for both. Flutter's single codebase reduces platform-specific UI tweaks.
Both React Native and Flutter apps must comply with Apple App Store and Google Play policies. Ensure apps do not use private APIs, handle user data securely, and provide accessibility features. React Native apps must include proper JavaScript bundle signing and Flutter apps must optimize for app size to meet store limits. Both require proper app icons, launch screens, and privacy disclosures.
If your React Native or Flutter app takes 5 seconds to load a screen, likely causes include heavy JavaScript processing or widget rebuilding, large image assets, or blocking synchronous code. Check for excessive bridge calls in React Native or expensive build methods in Flutter. Use profiling tools to identify slow operations and optimize asset loading and rendering.