Expo React Native Performance

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

2. List Virtualization (CRITICAL)

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

3. Re-render Optimization (HIGH)

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

4. Animation Performance (HIGH)

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

5. Image & Asset Loading (MEDIUM-HIGH)

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

6. Memory Management (MEDIUM)

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

7. Async & Data Fetching (MEDIUM)

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

8. Platform Optimizations (LOW-MEDIUM)

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

How to Use

Read individual reference files for detailed explanations and code examples:

• Section definitions [blocked] - Category structure and impact levels
• Rule template [blocked] - Template for adding new rules

Full Compiled Document

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

Reference Files