React Native Expo (0.76-0.82+ / SDK 52+)

CRITICAL:

• React Native 0.82+ requires New Architecture - legacy architecture completely removed
• If migrating from 0.75 or earlier, upgrade to 0.76-0.81 first to use the interop layer
• Never try to disable New Architecture in 0.82+ (build will fail)

3. Start Development Server

# Start Expo dev server
npx expo start

# Press 'i' for iOS simulator
# Press 'a' for Android emulator
# Press 'j' to open React Native DevTools (NOT Chrome debugger!)

CRITICAL:

• Old Chrome debugger removed in 0.79 - use React Native DevTools instead
• Metro terminal no longer streams console.log() - use DevTools Console
• Keyboard shortcuts 'a'/'i' work in CLI, not Metro terminal

Critical Breaking Changes (Dec 2024+)

🔴 New Architecture Mandatory (0.82+)

What Changed:

• 0.76-0.81: New Architecture default, legacy frozen (no new features)
• 0.82+: Legacy Architecture completely removed from codebase

Impact:

# This will FAIL in 0.82+:
# gradle.properties (Android)
newArchEnabled=false  # ❌ Ignored, build fails

# iOS
RCT_NEW_ARCH_ENABLED=0  # ❌ Ignored, build fails

Migration Path:

1. Upgrade to 0.76-0.81 first (if on 0.75 or earlier)
2. Test with New Architecture enabled
3. Fix incompatible dependencies (Redux, i18n, CodePush)
4. Then upgrade to 0.82+

🔴 propTypes Removed (React 19 / RN 0.78+)

What Changed: React 19 removed propTypes completely. No runtime validation, no warnings - silently ignored.

Before (Old Code):

import PropTypes from 'prop-types';

function MyComponent({ name, age }) {
  return <Text>{name} is {age}</Text>;
}

MyComponent.propTypes = {  // ❌ Silently ignored in React 19
  name: PropTypes.string.isRequired,
  age: PropTypes.number
};

After (Use TypeScript):

type MyComponentProps = {
  name: string;
  age?: number;
};

function MyComponent({ name, age }: MyComponentProps) {
  return <Text>{name} is {age}</Text>;
}

Migration:

# Use React 19 codemod to remove propTypes
npx @codemod/react-19 upgrade

🔴 forwardRef Deprecated (React 19)

What Changed: forwardRef no longer needed - pass ref as a regular prop.

Before (Old Code):

import { forwardRef } from 'react';

const MyInput = forwardRef((props, ref) => {  // ❌ Deprecated
  return <TextInput ref={ref} {...props} />;
});

After (React 19):

function MyInput({ ref, ...props }) {  // ✅ ref is a regular prop
  return <TextInput ref={ref} {...props} />;
}

🔴 Swift iOS Template Default (0.77+)

What Changed: New projects use Swift AppDelegate.swift instead of Objective-C AppDelegate.mm.

Old Structure:

ios/MyApp/
├── main.m              # ❌ Removed
├── AppDelegate.h       # ❌ Removed
└── AppDelegate.mm      # ❌ Removed

New Structure:

// ios/MyApp/AppDelegate.swift ✅
import UIKit
import React

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
  func application(_ application: UIApplication, ...) -> Bool {
    // App initialization
    return true
  }
}

Migration (0.76 → 0.77): When upgrading existing projects, you MUST add this line:

// Add to AppDelegate.swift during migration
import React
import ReactCoreModules

RCTAppDependencyProvider.sharedInstance()  // ⚠️ CRITICAL: Must add this!

Source: React Native 0.77 Release Notes

🔴 Metro Log Forwarding Removed (0.77+)

What Changed: Metro terminal no longer streams console.log() output.

Before (0.76):

# console.log() appeared in Metro terminal
$ npx expo start
> LOG  Hello from app!  # ✅ Appeared here

After (0.77+):

# console.log() does NOT appear in Metro terminal
$ npx expo start
# (no logs shown)  # ❌ Removed

# Workaround (temporary, will be removed):
$ npx expo start --client-logs  # Shows logs, deprecated

Solution: Use React Native DevTools Console instead (press 'j' in CLI).

Source: React Native 0.77 Release Notes

🔴 Chrome Debugger Removed (0.79+)

What Changed: Old Chrome debugger (chrome://inspect) removed. Use React Native DevTools instead.

Old Method (Removed):

# ❌ This no longer works:
# Open Dev Menu → "Debug" → Chrome DevTools opens

New Method (0.76+):

# Press 'j' in CLI or Dev Menu → "Open React Native DevTools"
# ✅ Uses Chrome DevTools Protocol (CDP)
# ✅ Reliable breakpoints, watch values, stack inspection
# ✅ JS Console (replaces Metro logs)

Limitations:

• Third-party extensions not yet supported (Redux DevTools, etc.)
• Network inspector coming in 0.83 (late 2025)

Source: React Native 0.79 Release Notes

🔴 JSC Engine Moved to Community (0.79+)

What Changed: JavaScriptCore (JSC) moved out of React Native core, Hermes is default.

Before (0.78):

• Both Hermes and JSC bundled
• JSC available in Expo Go

After (0.79+):

// If you still need JSC (rare):
{
  "dependencies": {
    "@react-native-community/javascriptcore": "^1.0.0"
  }
}

Expo Go:

• JSC completely removed from Expo Go (SDK 52+)
• Hermes only

Note: JSC will eventually be removed entirely from React Native.

🔴 Deep Imports Deprecated (0.80+)

What Changed: Importing from internal paths will break.

Before (Old Code):

// ❌ Deep imports deprecated
import Button from 'react-native/Libraries/Components/Button';
import Platform from 'react-native/Libraries/Utilities/Platform';

After:

// ✅ Import only from 'react-native'
import { Button, Platform } from 'react-native';

Source: React Native 0.80 Release Notes

New Features (Post-Dec 2024)

CSS Properties (0.77+ New Architecture Only)

React Native now supports many CSS properties previously only available on web:

1. display: contents

Makes an element "invisible" but keeps its children in the layout:

<View style={{ display: 'contents' }}>
  {/* This View disappears, but Text still renders */}
  <Text>I'm still here!</Text>
</View>

Use case: Wrapper components that shouldn't affect layout.

2. boxSizing

Control how width/height are calculated:

// Default: padding/border inside box
<View style={{
  boxSizing: 'border-box',  // Default
  width: 100,
  padding: 10,
  borderWidth: 2
  // Total width: 100 (padding/border inside)
}} />

// Content-box: padding/border outside
<View style={{
  boxSizing: 'content-box',
  width: 100,
  padding: 10,
  borderWidth: 2
  // Total width: 124 (100 + 20 padding + 4 border)
}} />

3. mixBlendMode + isolation

Blend layers like Photoshop:

<View style={{ backgroundColor: 'red' }}>
  <View style={{
    mixBlendMode: 'multiply',  // 16 modes available
    backgroundColor: 'blue'
    // Result: purple (red × blue)
  }} />
</View>

// Prevent unwanted blending:
<View style={{ isolation: 'isolate' }}>
  {/* Blending contained within this view */}
</View>

Available modes: multiply, screen, overlay, darken, lighten, color-dodge, color-burn, hard-light, soft-light, difference, exclusion, hue, saturation, color, luminosity

4. outline Properties

Visual outline that doesn't affect layout (unlike border):

<View style={{
  outlineWidth: 2,
  outlineStyle: 'solid',      // solid | dashed | dotted
  outlineColor: 'blue',
  outlineOffset: 4,           // Space between element and outline
  outlineSpread: 2            // Expand outline beyond offset
}} />

Key difference: Outline doesn't change element size or trigger layout recalculations.

Source: React Native 0.77 Release Notes

Android XML Drawables (0.78+)

Use native Android vector drawables (XML) as Image sources:

// Load XML drawable at build time
import MyIcon from './assets/my_icon.xml';

<Image
  source={MyIcon}
  style={{ width: 40, height: 40 }}
/>

// Or with require:
<Image
  source={require('./assets/my_icon.xml')}
  style={{ width: 40, height: 40 }}
/>

Benefits:

• Scalable vector graphics (resolution-independent)
• Smaller APK size vs PNG
• Off-thread decoding (better performance)

Constraints:

• Build-time resources only (no network loading)
• Android only (iOS still uses SF Symbols or PNG)

Source: React Native 0.78 Release Notes

React 19 New Hooks

1. useActionState (replaces form patterns)

import { useActionState } from 'react';

function MyForm() {
  const [state, submitAction, isPending] = useActionState(
    async (prevState, formData) => {
      // Async form submission
      const result = await api.submit(formData);
      return result;
    },
    { message: '' }  // Initial state
  );

  return (
    <form action={submitAction}>
      <TextInput name="email" />
      <Button disabled={isPending}>
        {isPending ? 'Submitting...' : 'Submit'}
      </Button>
      {state.message && <Text>{state.message}</Text>}
    </form>
  );
}

2. useOptimistic (optimistic UI updates)

import { useOptimistic } from 'react';

function LikeButton({ postId, initialLikes }) {
  const [optimisticLikes, addOptimisticLike] = useOptimistic(
    initialLikes,
    (currentLikes, amount) => currentLikes + amount
  );

  async function handleLike() {
    addOptimisticLike(1);  // Update UI immediately
    await api.like(postId);  // Then update server
  }

  return (
    <Button onPress={handleLike}>
      ❤️ {optimisticLikes}
    </Button>
  );
}

3. use (read promises/contexts during render)

import { use } from 'react';

function UserProfile({ userPromise }) {
  // Read promise directly during render (suspends if pending)
  const user = use(userPromise);

  return <Text>{user.name}</Text>;
}

Source: React 19 Upgrade Guide

React Native DevTools (0.76+)

Access:

• Press j in CLI
• Or open Dev Menu → "Open React Native DevTools"

Features:

• ✅ Reliable breakpoints (unlike old Chrome debugger)
• ✅ Watch values, call stack inspection
• ✅ JS Console (replaces Metro logs)
• ✅ Chrome DevTools Protocol (CDP) based
• ⏳ Network inspector (coming in 0.83)
• ❌ Third-party extensions not yet supported

Source: React Native DevTools Announcement

Known Issues Prevention

This skill prevents 12 documented issues:

Issue #1: propTypes Silently Ignored

Error: No error - propTypes just doesn't work Source: React 19 Upgrade Guide Why It Happens: React 19 removed runtime propTypes validation Prevention: Use TypeScript instead, run npx @codemod/react-19 upgrade to remove

Issue #2: forwardRef Deprecated Warning

Error: Warning: forwardRef is deprecated Source: React 19 Upgrade Guide Why It Happens: React 19 allows ref as a regular prop Prevention: Remove forwardRef wrapper, pass ref as prop directly

Issue #3: New Architecture Cannot Be Disabled (0.82+)

Error: Build fails with newArchEnabled=false Source: React Native 0.82 Release Notes Why It Happens: Legacy architecture completely removed from codebase Prevention: Migrate to New Architecture before upgrading to 0.82+

Issue #4: "Fabric component descriptor not found"

Error: Fabric component descriptor provider not found for component Source: New Architecture Migration Guide Why It Happens: Component not compatible with New Architecture (Fabric) Prevention: Update library to New Architecture version, or use interop layer (0.76-0.81)

Issue #5: "TurboModule not registered"

Error: TurboModule '[ModuleName]' not found Source: New Architecture Migration Guide Why It Happens: Native module needs New Architecture support (TurboModules) Prevention: Update library to support TurboModules, or use interop layer (0.76-0.81)

Issue #6: Swift AppDelegate Missing RCTAppDependencyProvider

Error: RCTAppDependencyProvider not found Source: React Native 0.77 Release Notes Why It Happens: When migrating from Objective-C to Swift template Prevention: Add RCTAppDependencyProvider.sharedInstance() to AppDelegate.swift

Issue #7: Metro Logs Not Appearing

Error: console.log() doesn't show in terminal Source: React Native 0.77 Release Notes Why It Happens: Metro log forwarding removed in 0.77 Prevention: Use React Native DevTools Console (press 'j'), or --client-logs flag (temporary)

Issue #8: Chrome Debugger Not Working

Error: Chrome DevTools doesn't connect Source: React Native 0.79 Release Notes Why It Happens: Old Chrome debugger removed in 0.79 Prevention: Use React Native DevTools instead (press 'j')

Issue #9: Deep Import Errors

Error: Module not found: react-native/Libraries/... Source: React Native 0.80 Release Notes Why It Happens: Internal paths deprecated, strict API enforced Prevention: Import only from 'react-native', not deep paths

Issue #10: Redux Store Crashes with New Architecture

Error: App crashes on Redux store creation Source: Redux Toolkit Migration Guide Why It Happens: Old redux + redux-thunk incompatible with New Architecture Prevention: Use Redux Toolkit (@reduxjs/toolkit) instead

Issue #11: i18n-js Unreliable with New Architecture

Error: Translations not updating, or app crashes Source: Community reports (GitHub issues) Why It Happens: i18n-js not fully compatible with New Architecture Prevention: Use react-i18next instead

Issue #12: CodePush Crashes on Android

Error: Android crashes looking for bundle named null Source: CodePush GitHub Issues Why It Happens: Known incompatibility with New Architecture Prevention: Avoid CodePush with New Architecture, or wait for official support

Migration Guide: 0.72-0.75 → 0.82+

Step 1: Upgrade to Interop Layer First (0.76-0.81)

Why: Can't skip directly to 0.82 if using legacy architecture - you'll lose the interop layer.

# Check current version
npx react-native --version

# Upgrade to 0.81 first (last version with interop layer)
npm install [email protected]
npx expo install --fix

Step 2: Enable New Architecture (if not already)

# Android (gradle.properties)
newArchEnabled=true

# iOS
RCT_NEW_ARCH_ENABLED=1 bundle exec pod install

# Rebuild
npm run ios
npm run android

Step 3: Fix Incompatible Dependencies

Common incompatibilities:

# Replace Redux with Redux Toolkit
npm uninstall redux redux-thunk
npm install @reduxjs/toolkit react-redux

# Replace i18n-js with react-i18next
npm uninstall i18n-js
npm install react-i18next i18next

# Update React Navigation (if old version)
npm install @react-navigation/native@latest

Step 4: Test Thoroughly

# Run on both platforms
npm run ios
npm run android

# Test all features:
# - Navigation
# - State management (Redux)
# - API calls
# - Deep linking
# - Push notifications

Step 5: Migrate to React 19 (if upgrading to 0.78+)

# Run React 19 codemod
npx @codemod/react-19 upgrade

# Manually verify:
# - Remove all propTypes declarations
# - Remove forwardRef wrappers
# - Update to new hooks (useActionState, useOptimistic)

Step 6: Upgrade to 0.82+

# Only after testing with New Architecture enabled!
npm install [email protected]
npx expo install --fix

# Rebuild
npm run ios
npm run android

Step 7: Migrate iOS to Swift (if new project)

New projects (0.77+) use Swift by default. For existing projects:

# Follow upgrade helper
# https://react-native-community.github.io/upgrade-helper/
# Select: 0.76 → 0.77

# CRITICAL: Add this line to AppDelegate.swift
RCTAppDependencyProvider.sharedInstance()

Common Patterns

Pattern 1: Conditional Rendering with New Hooks

import { useActionState } from 'react';

function LoginForm() {
  const [state, loginAction, isPending] = useActionState(
    async (prevState, formData) => {
      try {
        const user = await api.login(formData);
        return { success: true, user };
      } catch (error) {
        return { success: false, error: error.message };
      }
    },
    { success: false }
  );

  return (
    <View>
      <form action={loginAction}>
        <TextInput name="email" placeholder="Email" />
        <TextInput name="password" secureTextEntry />
        <Button disabled={isPending}>
          {isPending ? 'Logging in...' : 'Login'}
        </Button>
      </form>
      {!state.success && state.error && (
        <Text style={{ color: 'red' }}>{state.error}</Text>
      )}
    </View>
  );
}

When to use: Form submission with loading/error states

Pattern 2: TypeScript Instead of propTypes

// Define prop types with TypeScript
type ButtonProps = {
  title: string;
  onPress: () => void;
  disabled?: boolean;
  variant?: 'primary' | 'secondary';
};

function Button({ title, onPress, disabled = false, variant = 'primary' }: ButtonProps) {
  return (
    <Pressable
      onPress={onPress}
      disabled={disabled}
      style={[styles.button, styles[variant]]}
    >
      <Text style={styles.text}>{title}</Text>
    </Pressable>
  );
}

When to use: Always (propTypes removed in React 19)

Pattern 3: New CSS for Visual Effects

// Glowing button with outline and blend mode
function GlowButton({ title, onPress }) {
  return (
    <Pressable
      onPress={onPress}
      style={{
        backgroundColor: '#3b82f6',
        padding: 16,
        borderRadius: 8,
        // Outline doesn't affect layout
        outlineWidth: 2,
        outlineColor: '#60a5fa',
        outlineOffset: 4,
        // Blend with background
        mixBlendMode: 'screen',
        isolation: 'isolate'
      }}
    >
      <Text style={{ color: 'white', fontWeight: 'bold' }}>
        {title}
      </Text>
    </Pressable>
  );
}

When to use: Visual effects without affecting layout (New Architecture only)

Using Bundled Resources

Scripts (scripts/)

check-rn-version.sh - Detects React Native version and warns about architecture requirements

Example Usage:

./scripts/check-rn-version.sh
# Output: ✅ React Native 0.82 - New Architecture mandatory
# Output: ⚠️ React Native 0.75 - Upgrade to 0.76+ recommended

References (references/)

react-19-migration.md - Detailed React 19 breaking changes and migration steps

new-architecture-errors.md - Common build errors when enabling New Architecture

expo-sdk-52-breaking.md - Expo SDK 52+ specific breaking changes

When Claude should load these: When encountering migration errors, build failures, or detailed React 19 questions

Assets (assets/)

new-arch-decision-tree.md - Decision tree for choosing React Native version

css-features-cheatsheet.md - Complete examples of new CSS properties

Expo SDK 52+ Specifics

Breaking Changes

JSC Removed from Expo Go:

// This no longer works in Expo Go (SDK 52+):
{
  "jsEngine": "jsc"  // ❌ Ignored, Hermes only
}

Google Maps Removed from Expo Go (SDK 53+):

# Must use custom dev client for Google Maps
npx expo install expo-dev-client
npx expo run:android

Push Notifications Warning: Expo Go shows warnings for push notifications - use custom dev client for production testing.

New Features (SDK 52)

expo/fetch (WinterCG-compliant):

import { fetch } from 'expo/fetch';

// Standards-compliant fetch for Workers/Edge runtimes
const response = await fetch('https://api.example.com/data');

React Navigation v7:

npm install @react-navigation/native@^7.0.0

Official Documentation

• React Native: https://reactnative.dev
• Expo: https://docs.expo.dev
• React 19: https://react.dev/blog/2024/04/25/react-19-upgrade-guide
• New Architecture: https://reactnative.dev/docs/new-architecture-intro
• Upgrade Helper: https://react-native-community.github.io/upgrade-helper/
• Context7 Library ID: /facebook/react-native

Package Versions (Verified 2025-11-22)

{
  "dependencies": {
    "react": "^19.1.0",
    "react-native": "^0.82.0",
    "expo": "~52.0.0",
    "@react-navigation/native": "^7.0.0",
    "@reduxjs/toolkit": "^2.0.0",
    "react-i18next": "^15.0.0"
  },
  "devDependencies": {
    "@types/react": "^19.0.0",
    "typescript": "^5.7.0"
  }
}

Troubleshooting

Problem: Build fails with "Fabric component descriptor not found"

Solution: Library not compatible with New Architecture. Check library docs for New Architecture support, or use interop layer (0.76-0.81 only).

Problem: "propTypes is not a function" error

Solution: React 19 removed propTypes. Use TypeScript for type checking instead. Run npx @codemod/react-19 upgrade.

Problem: console.log() not showing in Metro terminal

Solution: Metro log forwarding removed in 0.77. Use React Native DevTools Console (press 'j') or npx expo start --client-logs (temporary workaround).

Problem: Swift AppDelegate errors during iOS build

Solution: Add RCTAppDependencyProvider.sharedInstance() to AppDelegate.swift. See Swift migration section.

Problem: Redux store crashes on startup

Solution: Use Redux Toolkit instead of legacy redux + redux-thunk. Install @reduxjs/toolkit.

Problem: Can't disable New Architecture in 0.82+

Solution: New Architecture is mandatory in 0.82+. If you need legacy, stay on 0.81 or earlier (not recommended).

Complete Setup Checklist

Use this checklist to verify your setup:

• React Native 0.76+ or Expo SDK 52+ installed
• New Architecture enabled (automatic in 0.82+)
• Hermes engine enabled (default)
• React 19 migration complete (no propTypes, no forwardRef)
• TypeScript configured for type checking
• React Native DevTools accessible (press 'j')
• No deep imports (react-native/Libraries/*)
• Redux Toolkit (not legacy redux)
• react-i18next (not i18n-js)
• iOS builds successfully (Swift template if new project)
• Android builds successfully
• Dev server runs without errors
• All navigation/state management working

Questions? Issues?

1. Check references/new-architecture-errors.md for build errors
2. Check references/react-19-migration.md for React 19 issues
3. Check official docs: https://reactnative.dev/docs/new-architecture-intro
4. Ensure New Architecture is enabled (mandatory in 0.82+)
5. Verify all dependencies support New Architecture

Knowledge Gap Filled: This skill covers React Native updates from December 2024+ that LLMs won't know about. Without this skill, Claude would suggest deprecated APIs, removed features, and outdated patterns.