Expo React Native Performance Best Practices

Comprehensive performance optimization guide for Expo React Native applications. Contains 42 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

• Writing new React Native components or screens
• Implementing lists with FlatList or FlashList
• Adding animations or transitions
• Optimizing images and asset loading
• Reviewing code for performance issues

Rule Categories by Priority

Quick Reference

1. App Startup & Bundle Size (CRITICAL)

• startup-enable-hermes – Enable Hermes JavaScript engine
• startup-remove-console-logs – Remove console logs in production
• startup-splash-screen-control – Control splash screen visibility
• startup-preload-assets – Preload critical assets during splash
• startup-async-routes – Use async routes for code splitting
• startup-cherry-pick-imports – Use direct imports instead of barrel files

2. List Virtualization (CRITICAL)

• list-use-flashlist – Use FlashList instead of FlatList
• list-estimated-item-size – Provide accurate estimatedItemSize
• list-get-item-type – Use getItemType for mixed lists
• list-stable-render-item – Stabilize renderItem with useCallback
• list-get-item-layout – Provide getItemLayout for fixed heights
• list-memoize-items – Memoize list item components

3. Re-render Optimization (HIGH)

• rerender-use-memo-expensive – Memoize expensive computations
• rerender-use-callback-handlers – Stabilize callbacks with useCallback
• rerender-functional-setstate – Use functional setState updates
• rerender-lazy-state-init – Use lazy state initialization
• rerender-split-context – Split context by update frequency
• rerender-derive-state – Derive state instead of syncing

4. Animation Performance (HIGH)

• anim-use-native-driver – Enable native driver for animations
• anim-use-reanimated – Use Reanimated for complex animations
• anim-layout-animation – Use LayoutAnimation for simple transitions
• anim-transform-not-dimensions – Animate transform instead of dimensions
• anim-interaction-manager – Defer heavy work during animations

5. Image & Asset Loading (MEDIUM-HIGH)

• asset-use-expo-image – Use expo-image for image loading
• asset-prefetch-images – Prefetch images before display
• asset-optimize-image-size – Request appropriately sized images
• asset-use-webp-format – Use WebP format for images
• asset-recycling-key – Use recyclingKey in FlashList images

6. Memory Management (MEDIUM)

• mem-cleanup-subscriptions – Clean up subscriptions in useEffect
• mem-clear-timers – Clear timers on unmount
• mem-abort-fetch – Abort fetch requests on unmount
• mem-avoid-inline-objects – Avoid inline objects in props
• mem-limit-list-data – Limit list data in memory

7. Async & Data Fetching (MEDIUM)

• async-parallel-fetching – Fetch independent data in parallel
• async-defer-await – Defer await until value needed
• async-batch-api-calls – Batch related API calls
• async-cache-responses – Cache API responses locally
• async-refetch-on-focus – Refetch data on screen focus

8. Platform Optimizations (LOW-MEDIUM)

• platform-android-overdraw – Reduce Android overdraw
• platform-ios-text-rendering – Optimize iOS text rendering
• platform-android-proguard – Enable ProGuard for Android release
• platform-conditional-render – Platform-specific optimizations

How to Use

Read individual reference files for detailed explanations and code examples:

• Section definitions – Category structure and impact levels
• Rule template – Template for adding new rules

Full Compiled Document

For the complete guide with all rules expanded, see AGENTS.md.

Reference Files