Mocking native modules in React Native - Build, Publish & Deploy

Build & Publish - Mocking native modules

Performance Impact

Mocking native modules in React Native is mainly a development and testing technique. It does not affect the app's runtime frame rate or battery usage in production because mocks are replaced by real native modules when the app runs on devices.

During testing, mocks help speed up test execution by avoiding calls to slow native code. This reduces memory use and CPU load in test environments, but these benefits do not apply to the released app.

Optimization Tips

To keep your app running smoothly at 60fps, ensure that native modules are efficiently implemented and avoid heavy work on the JavaScript thread.

Mocks should only be used in test code, never in production builds. Use tools like Jest with proper mock setup to isolate native module behavior during tests.

Keep native module interfaces simple and asynchronous to prevent blocking the UI thread.

App Bundle Size and Startup Time

Mocking native modules does not increase your app bundle size because mocks are only included in test environments, not in production bundles.

Startup time is unaffected by mocks since the real native modules load normally in the released app.

iOS vs Android Differences

Both iOS and Android use native modules to bridge platform-specific code to React Native.

Mocking native modules works similarly on both platforms in JavaScript test environments.

However, native module implementations differ: iOS uses Objective-C or Swift, Android uses Java or Kotlin. Mocks abstract these differences during testing.

Store Review Guidelines

• Ensure your app does not include test mocks in production builds to avoid unexpected behavior.
• Follow Apple's Human Interface Guidelines and Google Play policies for native module usage, especially regarding permissions and user data.
• Sign your app properly with valid certificates (iOS) and keys (Android) to pass store reviews.
• Test your app thoroughly on real devices to confirm native modules work as expected before publishing.

Self-Check Question

Your app takes 5 seconds to load this screen. What's likely wrong?

• You might be calling native modules synchronously on the main thread, blocking UI rendering.
• Heavy native module initialization or expensive bridging calls could delay startup.
• Mocks are not used in production, so check if native modules are optimized and asynchronous.

Key Result

Mocking native modules improves test speed and reliability without affecting app performance or size in production. Always separate mocks from production code and optimize native module implementations for smooth UI and fast startup.