react-native-builder

name	react-native-builder
description	Expert React Native development covering navigation, state management, native modules, performance optimization, platform-specific code, Expo vs bare workflow, animations, testing, debugging, and OTA updates. Use when the user asks about react native builder, react native builder best practices, or needs guidance on react native builder implementation. Do NOT use when the user needs a different specialized skill or is asking about an unrelated technology domain.
license	Apache-2.0
metadata	{"author":"foundry-skills","version":"1.0.0","tags":"mobile best-practices javascript design","category":"software-engineering","subcategory":"mobile-development","depends":"","disclaimer":"none","difficulty":"intermediate"}

React Native Builder

Overview

This skill provides comprehensive expertise in building production-grade React Native applications. It covers the full spectrum from project initialization through deployment, including architectural decisions, performance tuning, and cross-platform strategies that deliver native-quality experiences on both iOS and Android.

Project Initialization Decision Tree

New React Native Project?
├── Prototyping / MVP / No native modules needed?
│   └── Use Expo Managed Workflow
│       ├── `npx create-expo-app@latest my-app`
│       ├── Benefits: OTA updates, EAS Build, managed signing
│       └── Constraint: Limited native module access (use expo-dev-client to escape)
├── Need custom native modules / full control?
│   └── Use Bare Workflow (React Native CLI)
│       ├── `npx react-native init MyApp`
│       ├── Benefits: Full native access, custom build configs
│       └── Cost: Manual signing, manual native dependency linking
└── Migrating from Expo Managed?
    └── `npx expo prebuild` (Continuous Native Generation)
        └── Generates ios/ and android/ dirs while keeping Expo config

Navigation Architecture (React Navigation)

Stack + Tab + Drawer Composition

// navigation/RootNavigator.tsx
import { createNativeStackNavigator } from '@react-navigation/native-stack';
import { createBottomTabNavigator } from '@react-navigation/bottom-tabs';

// Define type-safe route params
export type RootStackParamList = {
  Auth: undefined;
  Main: undefined;
  Modal: { itemId: string };
};

export type MainTabParamList = {
  Home: undefined;
  Search: { query?: string };
  Profile: { userId: string };
};

const Stack = createNativeStackNavigator<RootStackParamList>();
const Tab = createBottomTabNavigator<MainTabParamList>();

function MainTabs() {
  return (
    # ... (condensed) ...
          </Stack.Group>
        </>
      ) : (
        <Stack.Screen name="Auth" component={AuthNavigator} />
      )}
    </Stack.Navigator>
  );
}

Deep Linking Configuration

const linking = {
  prefixes: ['myapp://', '[reference URL]'],
  config: {
    screens: {
      Main: {
        screens: {
          Home: 'home',
          Profile: 'profile/:userId',
        },
      },
      Modal: 'item/:itemId',
    },
  },
};

// In App.tsx
<NavigationContainer linking={linking} fallback={<LoadingScreen />}>
  <RootNavigator />
</NavigationContainer>

State Management Strategy

Decision Matrix

Criteria	Zustand	Redux Toolkit	Jotai	React Query
Learning curve	Low	Medium	Low	Medium
Boilerplate	Minimal	Moderate	Minimal	Low
DevTools	Basic	Excellent	Basic	Excellent
Server state	Manual	RTK Query	Manual	Built-in
Bundle size	~1KB	~11KB	~3KB	~13KB
Best for	Simple-medium apps	Large enterprise	Atomic state	Server-heavy apps

Recommended Architecture: Zustand + React Query

// stores/useAppStore.ts
import { create } from 'zustand';
import { persist, createJSONStorage } from 'zustand/middleware';
import AsyncStorage from '@react-native-async-storage/async-storage';

interface AppState {
  theme: 'light' | 'dark' | 'system';
  onboardingComplete: boolean;
  setTheme: (theme: AppState['theme']) => void;
  completeOnboarding: () => void;
}

export const useAppStore = create<AppState>()(
  persist(
    (set) => ({
      theme: 'system',
      onboardingComplete: false,
      setTheme: (theme) => set({ theme }),
      completeOnboarding: () => set({ onboardingComplete: true }),
    }),
    {
      name: 'app-storage',
      # ... (condensed) ...
export function () {
   ({
    : [, categoryId],
    :  api.(categoryId),
    :  *  * , 
    :  *  * ,   
  });
}

Native Modules

Turbo Modules (New Architecture)

// specs/NativeDeviceInfo.ts
import type { TurboModule } from 'react-native';
import { TurboModuleRegistry } from 'react-native';

export interface Spec extends TurboModule {
  getDeviceId(): Promise<string>;
  getBatteryLevel(): Promise<number>;
  getFreeDiskSpace(): Promise<number>;
}

export default TurboModuleRegistry.getEnforcing<Spec>('DeviceInfo');

Platform-Specific Code

// components/DatePicker/index.ios.tsx
export function DatePicker({ value, onChange }: Props) {
  return <DateTimePicker display="spinner" value={value} onChange={onChange} />;
}

// components/DatePicker/index.android.tsx
export function DatePicker({ value, onChange }: Props) {
  const [show, setShow] = useState(false);
  return (
    <>
      <Pressable onPress={() => setShow(true)}>
        <Text>{format(value, 'PP')}</Text>
      </Pressable>
      {show && (
        <DateTimePicker display="default" value={value} onChange={(e, d) => {
          setShow(false);
          if (d) onChange(d);
        }} />
      )}
    </>
  );
}

// Usage: import { DatePicker } from './components/DatePicker';
// Metro bundler auto-resolves .ios.tsx / .android.tsx

Performance Optimization

Critical Performance Rules

1. Memoize expensive renders: Use React.memo, useMemo, useCallback
2. Flatten lists: Use FlatList or FlashList, never .map() for long lists
3. Avoid bridge serialization: Minimize JS-to-native data transfer
4. Use Hermes engine: Enabled by default in RN 0.70+; verify in build logs
5. Image optimization: Use expo-image or FastImage with caching

FlatList / FlashList Optimization

import { FlashList } from '@shopify/flash-list';

function ProductList({ products }: { products: Product[] }) {
  const renderItem = useCallback(({ item }: { item: Product }) => (
    <ProductCard product={item} />
  ), []);

  const keyExtractor = useCallback((item: Product) => item.id, []);

  return (
    <FlashList
      data={products}
      renderItem={renderItem}
      keyExtractor={keyExtractor}
      estimatedItemSize={120}
      // FlashList handles recycling automatically
      // For FlatList, also set:
      // windowSize={5}
      // maxToRenderPerBatch={10}
      // removeClippedSubviews={true}
      // getItemLayout for fixed-height items
    />
  );
}

JS Thread Profiling

// Enable in dev: React DevTools Profiler
// Production monitoring:
import { PerformanceObserver } from 'react-native-performance';

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    if (entry.duration > 16) { // Dropped frame threshold
      analytics.track('slow_render', {
        name: entry.name,
        duration: entry.duration,
      });
    }
  });
});

Animations with Reanimated

Shared Element Transitions

import Animated, {
  useSharedValue,
  useAnimatedStyle,
  withSpring,
  withTiming,
  interpolate,
  Extrapolation,
} from 'react-native-reanimated';
import { Gesture, GestureDetector } from 'react-native-gesture-handler';

function SwipeableCard({ onDismiss }: { onDismiss: () => void }) {
  const translateX = useSharedValue(0);
  const opacity = useSharedValue(1);

  const gesture = Gesture.Pan()
    .onUpdate((e) => {
      translateX.value = e.translationX;
    })
    .onEnd((e) => {
      if (Math.abs(e.translationX) > 150) {
        translateX.value = withTiming(Math.sign(e.translationX) * 500);
        opacity.value = withTiming(0, {}, () => {
          # ... (condensed) ...
  return (
    <GestureDetector =>
      
        {/* Card content */}
      
    
  );
}

Scroll-Driven Animations

function CollapsibleHeader() {
  const scrollY = useSharedValue(0);

  const headerStyle = useAnimatedStyle(() => ({
    height: interpolate(scrollY.value, [0, 100], [200, 60], Extrapolation.CLAMP),
    opacity: interpolate(scrollY.value, [0, 80], [1, 0], Extrapolation.CLAMP),
  }));

  const scrollHandler = useAnimatedScrollHandler({
    onScroll: (event) => {
      scrollY.value = event.contentOffset.y;
    },
  });

  return (
    <>
      <Animated.View style={[styles.header, headerStyle]} />
      <Animated.ScrollView onScroll={scrollHandler} scrollEventThrottle={16}>
        {/* Content */}
      </Animated.ScrollView>
    </>
  );
}

Testing Strategy

Unit Tests (Jest + React Native Testing Library)

// __tests__/ProductCard.test.tsx
import { render, fireEvent, waitFor } from '@testing-library/react-native';
import { ProductCard } from '../components/ProductCard';

describe('ProductCard', () => {
  const mockProduct = {
    id: '1',
    name: 'Widget',
    price: 29.99,
    image: '[reference URL]',
  };

  it('renders product details', () => {
    const { getByText } = render(<ProductCard product={mockProduct} />);
    expect(getByText('Widget')).toBeTruthy();
    expect(getByText('$29.99')).toBeTruthy();
  });

  it('calls onPress with product id', () => {
    const onPress = jest.fn();
    const { getByTestId } = render(
      <ProductCard product={mockProduct} onPress={onPress} />
    );
    fireEvent.(());
    (onPress).();
  });
});

E2E Tests (Detox)

// e2e/login.test.ts
describe('Login Flow', () => {
  beforeAll(async () => {
    await device.launchApp({ newInstance: true });
  });

  it('should login with valid credentials', async () => {
    await element(by.id('email-input')).typeText('[e-mail]');
    await element(by.id('password-input')).typeText('password123');
    await element(by.id('login-button')).tap();
    await waitFor(element(by.id('home-screen')))
      .toBeVisible()
      .withTimeout(5000);
  });
});

Debugging Techniques

Tool	Purpose	When to Use
Flipper	Network, layout, DB inspection	General debugging
React DevTools	Component tree, props, state	UI debugging
Hermes debugger	JS breakpoints, profiling	Logic debugging
Xcode Instruments	Memory leaks, CPU profiling	iOS performance
Android Profiler	Memory, CPU, network	Android performance
console.warn + LogBox	Quick debug logging	Rapid iteration

OTA Updates

Expo Updates (EAS Update)

// app.json
{
  "expo": {
    "updates": {
      "url": "[reference URL]",
      "fallbackToCacheTimeout": 3000
    },
    "runtimeVersion": {
      "policy": "sdkVersion"
    }
  }
}

// App.tsx - Manual update check
import * as Updates from 'expo-updates';

async function checkForUpdates() {
  if (__DEV__) return;
  try {
    const update = await Updates.checkForUpdateAsync();
    if (update.isAvailable) {
      await Updates.fetchUpdateAsync();
      await Updates.reloadAsync(); // Restarts the app with new bundle
    }
  } catch (e) {
    console.error('Update check failed:', e);
  }
}

Update Strategy Decision

OTA Update Strategy:
├── Critical bug fix → Force update on next launch
├── Minor improvement → Background download, apply on next cold start
├── Feature behind flag → Download silently, enable via remote config
└── Native code change → Full binary release (App Store / Play Store)

Expo vs Bare Workflow Comparison

Feature	Expo Managed	Bare / Prebuild
Native module access	Via expo-dev-client	Full access
Build service	EAS Build (cloud)	Local or CI
OTA updates	EAS Update	CodePush or custom
Push notifications	expo-notifications	Direct APNs/FCM
Config management	app.json / app.config.js	Native project files
Upgrade path	expo upgrade	Manual or rn-upgrade-helper

Production Checklist

• Enable Hermes on both platforms
• Configure ProGuard rules for Android release
• Set up crash reporting (Sentry / Crashlytics)
• Configure deep linking and universal links
• Test on physical devices (not just simulators)
• Verify offline behavior and error boundaries
• Set up CI/CD with EAS Build or Fastlane
• Configure app signing for both platforms
• Test accessibility with screen readers
• Profile memory usage and fix leaks
• Set up analytics and performance monitoring
• Configure OTA update strategy
• Verify bundle size (use react-native-bundle-visualizer)
• Test on minimum supported OS versions

When to Use

Use this skill when:

• Designing or implementing react native builder solutions
• Reviewing or improving existing react native builder approaches
• Making architectural or implementation decisions about react native builder
• Learning react native builder patterns and best practices
• Troubleshooting react native builder-related issues

Do NOT use this skill when:

• The question is about a fundamentally different technology domain
• A more specific sibling skill covers the exact topic needed
• The user needs a complete hands-on tutorial rather than expert guidance

Output Format

# React Native Builder Analysis

## Context Assessment
[Situation summary and constraints]

## Recommended Approach
[Primary recommendation with rationale]

## Implementation Steps
1. [Step with specific details]
2. [Step with specific details]
3. [Step with specific details]

## Trade-offs and Considerations
- [Key trade-off 1]
- [Key trade-off 2]

## Next Steps
- [Immediate action item]
- [Follow-up action item]

Example

Input: "Help me implement react native builder for a medium-scale production application"

Output: A structured analysis covering current state assessment, recommended react native builder approach with specific patterns, implementation roadmap with milestones, and risk mitigation strategies tailored to the application scale and constraints.

Edge Cases

• Legacy system integration: When react native builder must coexist with legacy approaches, provide a gradual migration path rather than a complete rewrite
• Scale mismatch: When the solution complexity exceeds the project scale, recommend a simpler approach and note when to revisit
• Team skill gaps: When the team lacks experience with the recommended approach, include learning resources and simpler alternatives
• Conflicting requirements: When constraints conflict (e.g., performance vs. maintainability), explicitly state the trade-off and recommend based on stated priorities