Before writing any code, it’s crucial to understand how React Native works under the hood. This knowledge will help you debug issues, optimize performance, and make better architectural decisions throughout your React Native journey.What You’ll Learn:
What React Native is and how it differs from other solutions
React Native is an open-source framework created by Meta (Facebook) in 2015 that allows developers to build truly native mobile applications using JavaScript and React. Unlike hybrid frameworks that use WebViews, React Native renders actual native UI components.
True Native
Renders to real native components (UIView, TextView), not web views
Cross-Platform
One codebase for iOS and Android with 90%+ code reuse
Hot Reloading
See changes instantly without rebuilding the entire app
JavaScript
Use the language and ecosystem you already know
Large Ecosystem
Access to npm packages and React libraries
Active Community
Backed by Meta with millions of developers worldwide
The legacy bridge has several limitations that can impact performance:
Asynchronous Only: All communication is async, causing delays for time-sensitive operations
Serialization Overhead: Data must be serialized to JSON, adding CPU overhead
Single Bottleneck: All communication goes through one bridge
No Direct Access: JavaScript can’t directly call native methods
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// Example: Bridge latency issue with animations// This animation might feel janky because each frame// requires a round-trip through the bridgeconst opacity = useRef(new Animated.Value(0)).current;Animated.timing(opacity, { toValue: 1, duration: 300, useNativeDriver: true, // This helps! Runs animation on native thread}).start();
JSI is the foundation of the new architecture—a lightweight C++ layer that allows JavaScript to hold references to native objects and call methods directly:
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// Conceptual example of JSI benefits// Old Bridge: Async, serializedbridge.call('NativeModule', 'getData', { id: 123 }) .then(data => console.log(data));// New JSI: Direct, can be syncconst data = NativeModule.getData({ id: 123 }); // Direct call!
JSI Benefits:
No Serialization: Objects are passed by reference, not serialized to JSON
Synchronous Calls: When needed, JS can call native code synchronously
Lazy Loading: Native modules load only when first accessed
Multiple Engines: JSI abstracts the JS engine, enabling Hermes, JSC, or V8
✅ Your team knows JavaScript/TypeScript and React✅ You need to ship iOS and Android apps quickly✅ You want near-native performance with code reuse✅ You need access to the npm ecosystem✅ You’re building a startup MVP or enterprise app✅ You want to share code with a React web app✅ You need over-the-air updates (CodePush/EAS Update)
✅ You need absolute best performance (games, AR/VR)✅ You’re building complex animations/graphics✅ Your app requires cutting-edge platform features immediately✅ You have separate iOS and Android teams✅ You’re building platform-specific experiences✅ App size is critical (React Native adds ~10MB)
✅ You want pixel-perfect custom UI everywhere✅ Your team doesn’t have JavaScript experience✅ You need excellent animation performance out of the box✅ You’re building from scratch (no existing React code)✅ You prefer strongly-typed languages (Dart)✅ You want a single rendering engine across platforms
┌─────────────────────────────────────────────────────────────────────────────┐│ Technology Decision Framework │├─────────────────────────────────────────────────────────────────────────────┤│ ││ Question 1: Does your team know React/JavaScript? ││ ├── Yes ──► Strong candidate for React Native ││ └── No ──► Consider Flutter or Native ││ ││ Question 2: Do you need to share code with web? ││ ├── Yes ──► React Native + React Native Web ││ └── No ──► Any option works ││ ││ Question 3: Is performance absolutely critical? ││ ├── Yes (games, AR) ──► Native or Flutter ││ └── No (most apps) ──► React Native is fine ││ ││ Question 4: Do you need OTA updates? ││ ├── Yes ──► React Native (CodePush/EAS Update) ││ └── No ──► Any option works ││ ││ Question 5: Timeline and budget? ││ ├── Fast & Limited ──► React Native or Flutter ││ └── Flexible ──► Any option works ││ │└─────────────────────────────────────────────────────────────────────────────┘
// This runs on JS threadconst handlePress = () => { // This computation blocks the JS thread const result = heavyComputation(); // ❌ Bad - blocks UI updates // Better: Use native module or InteractionManager InteractionManager.runAfterInteractions(() => { const result = heavyComputation(); // ✅ Runs after animations complete });};// Even better: Use useNativeDriver for animationsAnimated.timing(opacity, { toValue: 1, duration: 300, useNativeDriver: true, // ✅ Animation runs on UI thread, not JS thread}).start();
Q1: What makes React Native different from hybrid frameworks like Ionic?
Answer: React Native renders to actual native UI components (UIView, TextView), while hybrid frameworks render to WebViews. This gives React Native near-native performance and platform-specific look and feel.
Q2: What are the three main components of the new architecture?
Answer:
JSI (JavaScript Interface): Direct C++ bindings between JS and native
Fabric: New rendering system with synchronous layout
Answer: Hermes compiles JavaScript to bytecode at build time (ahead-of-time compilation), while JSC compiles at runtime. This means Hermes apps start faster because they skip parsing and compilation at launch.
Q4: When should you NOT choose React Native?
Answer: Avoid React Native for:
Performance-critical apps (games, AR/VR)
Apps requiring immediate access to cutting-edge platform features
