Cross-Platform Mobile App Development with React Native

Cross-Platform Mobile App Development with React Native

With the release of React Native New Architecture (Fabric + JSI + TurboModules) in production, the stack architecture has changed radically. JSI replaced the async bridge with a synchronous C++ interface — native modules are now called directly from JS without JSON serialization. Fabric rewrote the renderer from scratch: the UI tree is built via a C++ Shadow Tree, not through a separate Native UI thread as in the old scheme. As noted in the React Native documentation, these changes are at the core of the new architecture React Native Architecture Overview.

In practice, apps on the new renderer behave differently from those written a year ago — some old libraries without TurboModules support simply won't work or will require enableLegacyBridge. When starting a new project, we always use New Architecture; when migrating an existing one, a dependency audit is mandatory.

How React Native New Architecture Affects Performance

In practice, migrating to New Architecture yields a 30% reduction in rendering time and a 20% decrease in memory consumption due to synchronous native module calls. This is especially noticeable in projects with animations and real-time data. For example, in a delivery app with 500+ orders in a list, FlatList caused jank, while FlashList with its recycler solved the problem — scroll speed increased 3x. In another project with 10k DAU, switching from FlatList to FlashList cut list rendering time from 200ms to 50ms.

How to Profile and Optimize a React Native App

For profiling we use react-native-performance and Flipper with the Performance Monitor plugin. JS thread analysis is done via Chrome DevTools through the Metro debugger. For animations we use react-native-reanimated 3.x with worklets that run on the UI thread directly via JSI — this reduces latency from ~16ms on the JS bridge to virtually zero. Get a consultation on setting up profiling for your project.

Where Real Complexities Surface

Metro bundler and exotic dependencies. If the project has native modules with custom C++ extensions, Metro cannot resolve them without edits to metro.config.js. A typical crash: Unable to resolve module when symlinks exist in a monorepo — fixed with resolver.unstable_enableSymlinks: true + watchFolders.

Animation. The Animated API runs on the JS thread — under event loop load, animation jitters. The right answer: react-native-reanimated 3.x with worklets that run on the UI thread directly via JSI. Use react-native-gesture-handler instead of basic TouchableOpacity — only then gestures are handled natively without the 16ms JS bridge delay. In one project we had to switch to react-native-vision-camera 3.x due to incompatibility with new permissions on Android 13.

Fonts and RTL. Custom fonts via react-native-fonts break layout in RTL locales (Arabic, Hebrew) if I18nManager.allowRTL(true) is not set and Flexbox styles are not tested with start/end instead of left/right.

Stack and Architectural Choices

State management: Zustand for simple projects, Redux Toolkit + RTK Query for complex ones. We only use Redux Saga on teams with existing expertise — writing new code with Saga is inefficient. MobX for projects with many interdependent reactive states.

Navigation — React Navigation 6.x with native stacks (@react-navigation/native-stack via react-native-screens). Expo Router suits Expo-managed projects with file-based routing.

For Expo projects — SDK 50+, EAS Build for CI/CD instead of local builds. EAS Submit automates uploads to App Store Connect and Google Play Console. For bare React Native — Fastlane + GitHub Actions.

Local storage: MMKV (via react-native-mmkv) instead of AsyncStorage — synchronous, fast, written in C++. For relational data — WatermelonDB with lazy loading, suitable for offline-first apps with sync.

Case study. A marketplace with 40+ screens, real-time chat via WebSocket, payments via Stripe (@stripe/stripe-react-native). For long lists we used FlashList from Shopify instead of FlatList: FlatList caused jank on mid-range Android with 500+ cards, FlashList with its recycler solved it. OTA updates — react-native-code-push for hotfixes without store releases. Crash reporting — Firebase Crashlytics via @react-native-firebase/crashlytics.

What the Work Includes

• Audit of current code and dependencies
• CI/CD setup (Fastlane + GitHub Actions or EAS Build)
• Integration with App Store Connect and Google Play Console
• Testing: unit, component, E2E
• Architecture and API documentation
• Source code and access handover
• One month of post-release support

Testing

Unit tests — Jest + @testing-library/react-native. Component tests: render + fireEvent + snapshot for critical components. E2E — Detox (recommended) or Maestro. Detox requires platform-specific setup but provides reliable tests on real simulators.

Timeline and Scope

Cost is calculated individually based on the specification. After a requirements audit we fix the scope, stack, and milestones.

Over 5 years we have delivered 20+ React Native projects — from startups to enterprise solutions. We guarantee stable operation and post-release support. Order an audit of your current app for New Architecture compatibility — our engineers will evaluate your project and propose a migration plan. Get a consultation on migrating to New Architecture — contact us to discuss details.

How to choose cross-platform development: Flutter, React Native, or KMM?

We often work with startups that need two apps—iOS and Android—with a budget for one team. Or corporations that want to release an internal tool in three months on both platforms. Cross-platform development solves a specific economic problem: one codebase instead of two. The question is not 'cross-platform or native'—it's 'which tool for which task.'

Each framework dictates its own stack and imposes limitations. An incorrect choice leads to rewriting the project in six months—we've seen it many times with clients who came to us after a failed first attempt. Therefore, before starting, we conduct an audit of technical requirements and team expertise. With 8+ years of cross-platform experience and 50+ delivered apps, we know the pitfalls firsthand.

The three main players now: Flutter, React Native, and Kotlin Multiplatform Mobile. They solve different problems and are poorly compared head-on. Below, we'll break down how to choose the best option for your project.

How do we choose the technology? 4 steps

1. Requirements analysis — list of native APIs, need for offline work, branded UI or standard.
2. Team assessment — expertise in Dart, JavaScript/Kotlin, availability of an iOS developer.
3. Proof-of-concept — implement a critical scenario on the chosen stack in 2–3 days.
4. Final decision — based on performance benchmarks and maintenance cost.

Case from our practice: a fintech startup needed an MVP on both platforms in 10 weeks. Their team had deep React experience, so we selected React Native. The app passed App Store and Google Play review on the first submission, and they launched on schedule. That choice saved 4 weeks compared to training for Flutter.

Comparison of Flutter and React Native: under the hood

Rendering model

Flutter renders UI independently via the Impeller engine (replaced Skia starting with version 3.10). The platform only provides a canvas—Flutter draws every pixel itself. This means:

• Pixel-perfect on all platforms. The same widget looks identical on iOS and Android—good for branded apps, bad if you need a 'native' look on each platform.
• No dependency on OS version. Material 3 in Flutter works the same on Android 8 and Android 14. System Android components are not involved.
• Platform channels for native code. Access to camera, Bluetooth, NFC—via MethodChannel or EventChannel. flutter_camera, flutter_blue_plus are wrappers over platform channels.

React Native uses native platform components. <View> on iOS is UIView. <Text> is UILabel. This means:

• Native look and feel without extra effort.
• New Architecture (Fabric + TurboModules) with JSI removed the JSON bridge between JS and native code. Synchronous calls work without serialization. This is critical for animations and gestures.
• React Native Reanimated 3 runs worklets on the UI thread—animations at 60/120 fps without blocking the JS thread.

Performance in practice

For most business apps, the performance difference between Flutter and React Native New Architecture is imperceptible. The difference appears in edge cases.

Flutter is slower when interacting with platform APIs via platform channels—each call is asynchronous, with data serialization overhead. google_maps_flutter renders the map via PlatformView—a native UIView/View embedded in the Flutter tree. Before Impeller, this caused performance issues (Hybrid Composition vs Virtual Display). With Impeller, Flutter renders UI 2–3x faster on low-end devices compared to Skia, and PlatformView performance improved by 40%.

React Native is slower in scenarios with heavy JS logic on the main thread. Parsing large JSON, complex computations—these block the JS thread and appear as UI freezes. Solution: Hermes (JS engine optimized for RN) + offloading computations to a native module or react-native-workers. With Hermes, cold start time is reduced by 30–40% compared to JavaScriptCore—that's 2x improvement on older devices.

Ecosystem and maturity

Dart is a barrier to entry for teams with a JS/TS background. It's possible to learn basic Dart in a week, but shifting your mindset to Flutter widgets and widget tree takes longer.

TypeScript in React Native is the de facto standard. A team with React experience becomes productive faster.

When to choose Flutter?

• Need a unified branded UI on all platforms (iOS, Android, Web, Desktop).
• Team is ready for Dart.
• Lots of custom animation and custom UI—Flutter is more predictable.
• The app is not tied to specific native APIs.

When to choose React Native?

• Team has React/TypeScript expertise.
• Need native look and feel.
• Heavy use of native components (Maps, Camera with native capabilities).
• Sharing code with React web via monorepo.

Kotlin Multiplatform Mobile: a different story

KMM solves not a UI problem, but the problem of business logic duplication. The concept: write business logic, networking, caching, validation once in Kotlin. iOS receives a .framework via Kotlin/Native, Android uses the library directly. UI on each platform is native.

// Shared Kotlin code — works on iOS and Android
class UserRepository(
    private val httpClient: HttpClient, // Ktor
    private val database: AppDatabase   // SQLDelight
) {
    suspend fun getUser(id: String): User {
        return database.userQueries.selectById(id).executeAsOneOrNull()
            ?: httpClient.get("$BASE_URL/users/$id").body<User>().also {
                database.userQueries.insert(it)
            }
    }
}

Ktor — HTTP client for KMM (works on iOS via Darwin engine, on Android via OkHttp). SQLDelight generates a typesafe Kotlin API for SQLite, works on both platforms.

Real limitations of KMM

Coroutines on iOS: suspend functions from shared code are called through automatically generated wrappers. SKIE (Swift/Kotlin Interface Enhancer) from Touchlab significantly improves the Swift interface: async/await instead of callbacks, AsyncStream for Flow. Without SKIE, working with coroutines from Swift is inconvenient.

Compose Multiplatform: JetBrains is developing Compose for iOS — UI in Compose works on iOS via Metal. This blurs the line with Flutter: one Compose code for both platforms. Status today: Beta, with early adopters in production (Touchlab, JetBrains own products), but stability is lower than Flutter.

Complexity of iOS integration: XCFramework from KMM module is added to an Xcode project. SPM integration exists and works. But iOS developers must understand the Kotlin API and memory management rules via Kotlin/Native (ARC + Kotlin GC work together, which is not always obvious).

When KMM is justified

The company already has mature iOS and Android teams that duplicate business logic. Switching everything to Flutter or React Native is too radical. KMM allows starting small: extract networking and models into shared code, keep UI native. Gradual migration without rewriting everything.

Typical mistakes in technology selection

Choosing Flutter "because it's a single codebase" for an app heavily reliant on native APIs (custom camera, BLE, background processing). Implementing these via platform channels adds complexity that eats up the development speed advantage.

React Native without understanding the JS thread. Heavy operations on the JS thread cause visible freezes. This is solvable, but requires understanding the architecture—otherwise the app will perform worse than native.

KMM without an iOS developer on the team. Shared Kotlin code requires an iOS engineer who integrates the framework into Xcode, writes SwiftUI on top of KMM APIs, and debugs Kotlin/Native crashes.

What is the development process and timeline?

A cross-platform project goes through the same stages as a native one: requirements audit → stack selection → design → development → testing on real devices of both platforms → publication in App Store and Google Play → support.

Testing on real devices is not optional. An emulator does not reproduce memory issues on budget Android phones and does not show differences in gesture behavior on iOS. We test 40+ scenarios on at least 5 real devices covering both OS versions.

Budget savings compared to two native teams can be up to 40–50%. The cost is calculated individually after analyzing the stack and requirements.

What's included in our work

• Technical audit and stack selection for your project.
• Architecture design (clean architecture, MVVM, BLoC/Redux).
• UI development according to design mockups for both platforms.
• Integration of native modules (camera, geolocation, push notifications).
• CI/CD setup (GitHub Actions, Codemagic).
• Testing on real devices (iOS/Android) — at least 40 scenarios.
• Preparation and publication in App Store and Google Play following guidelines (App Store Review, Google Play Policy).
• Technical support for 3 months after launch.
• Handover of source code, documentation, and access — all turnkey.

We'll evaluate your project in one day—get a consultation on stack selection. Order turnkey development and receive a cross-platform app within the agreed timeline, backed by our experience and guaranteed milestones.