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**Why this matters:**
- Expo SDK 52+ uses React Native 0.76+ with New Architecture enabled by default
- New Architecture is **mandatory** in React Native 0.82+ (cannot be disabled)
- Hermes is the only supported JavaScript engine (JSC removed from Expo Go)

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**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)

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**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

---

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**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+

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
};

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

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

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import { forwardRef } from 'react';

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

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

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

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

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

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

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

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**After (0.77+):**
```bash

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

**Source:** [React Native 0.77 Release Notes](https://reactnative.dev/blog/2025/01/14/release-0.77)

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**New Method (0.76+):**
```bash

**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](https://reactnative.dev/blog/2025/04/release-0.79)

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

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

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

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

// 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)
}} />

<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>

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

// 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 }}
/>

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>
  );
}

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>
  );
}

import { use } from 'react';

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

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

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---

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>
  );
}

// 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>
  );
}

// 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>
  );
}

./scripts/check-rn-version.sh

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

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

import { fetch } from 'expo/fetch';

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

npm install @react-navigation/native@^7.0.0

{
  "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"
  }
}