React Native

React Native allows you to build native mobile apps using React and JavaScript/TypeScript. It renders veritable native UI components (not webviews), offering performance close to native apps while maintaining the React developer experience.

When to Use

Building iOS and Android apps with a shared codebase.
Teams with existing React/Web expertise.
Apps requiring Over-the-Air (OTA) updates (via Expo Updates or CodePush).
Prototyping cross-platform mobile experiences rapidly.

Quick Start

Using Expo (Recommended for 2024/2025):

npx create-expo-app@latest my-app
cd my-app
npx expo start

// app/index.tsx (Expo Router)
import { useState } from "react";
import { View, Text, Button, StyleSheet } from "react-native";
import { Link } from "expo-router";

export default function Home() {
  const [count, setCount] = useState(0);

  return (
    <View style={styles.container}>
      <Text style={styles.text}>Count: {count}</Text>
      <Button title="Increment" onPress={() => setCount((c) => c + 1)} />

      <Link href="/details" style={styles.link}>
        Go to Details
      </Link>
    </View>
  );
}

const styles = StyleSheet.create({
  container: { flex: 1, justifyContent: "center", alignItems: "center" },
  text: { fontSize: 24, marginBottom: 20 },
  link: { marginTop: 20, color: "blue" },
});

Core Concepts

Native Components vs Web

React Native works by bridging JavaScript to Native UI components.

<View> maps to UIView (iOS) / android.view.View (Android).
<Text> maps to UITextView / TextView.
New Architecture (Fabric/TurboModules): Removes the async bridge for synchronous, direct C++ communication (JSI), improving performance.

Flexbox Layout

Layouts use Flexbox (like CSS), but defaults to flexDirection: 'column' (unlike row on web). Everything needs strict dimensions or flex grow capabilities.

Fast Refresh

React Native preserves local state while reloading components instantly on file save, significantly speeding up the dev loop.

Common Patterns

Expo Router (File-based Routing)

Modern React Native apps use expo-router which mimics Next.js.

app/index.tsx -> Home screen
app/(tabs)/_layout.tsx -> Tab navigation
app/[id].tsx -> Dynamic routes

Server State (React Query)

Avoid Redux for API state. Use TanStack Query (React Query).

Caches data, handles loading/error states, and manages refetching.

Client State (Zustand)

For global app state (theme, auth token), Zustand is preferred over Redux/Context for its simplicity and performance (selectors).

Best Practices

Do:

Use Expo for new projects unless you have strict native code dependency needs that Config Plugins can't handle.
Use TypeScript for type safety.
Use FlashList (by Shopify) instead of FlatList for long lists performance.
Use Reanimated for complex animations (runs on UI thread).

Don't:

Don't leave console.log in production builds (it slows down the bridge).
Don't do heavy calculations in the JS thread during animations/gestures.
Don't define styles inside the render function (recreates objects every render).

Troubleshooting

Error	Cause	Solution
`Metro Bundler process exited with code 1`	Port in use or bad cache.	`npx expo start -c` (clear cache).
`Invariant Violation: View config not found`	Import issues or upgrading RN versions.	Check node_modules, clear watchman.
`CocoaPods could not find compatible versions`	iOS dependency conflict.	`cd ios && pod install --repo-update`.
`Text strings must be rendered within a <Text> component`	Raw text directly inside View.	Wrap all strings in `<Text>`.

react-native