Build Apps for iOS & Android
— From Idea to App Store

Arrow functions, destructuring, spread/rest, optional chaining, Promises, async/await, event loop, closures, ES modules. The full JS foundation needed for React Native development, including TypeScript-ready code patterns.

Static typing, interfaces, generics, utility types (Partial, Pick, Omit, Record), strict mode config, typing React Native component props & navigation params, declaration files. Catching mobile-specific bugs at compile time before they crash on a user's phone.

Git internals, branching (GitFlow for mobile releases — feature/develop/release/hotfix/main), interactive rebase, cherry-pick, pull requests, semantic versioning for app releases, GitHub Actions basics, conventional commits for changelog automation.

iOS HIG vs Android Material Design 3. Touch target sizing, gesture vocabulary, safe areas, Dynamic Island, dark mode, keyboard avoidance. Reading Figma files — spacing, typography, component states, exporting assets at 1x/2x/3x. Accessibility — VoiceOver, TalkBack, Dynamic Type, contrast ratios (WCAG AA).

Old Bridge vs New Architecture (JSI, Fabric, TurboModules — performance implications). Expo managed vs bare workflow. Metro bundler internals, Fast Refresh. Android Studio (AVD, SDK, signing keys) and Xcode (simulators, provisioning). Running on physical devices — USB debugging (Android), Developer Mode (iOS). Common setup errors across all OS platforms.

View, Text, Image, ScrollView, FlatList (keyExtractor, getItemLayout, initialNumToRender, windowSize — tuning lists of 1000+ items), SectionList, TextInput, Modal, Pressable. StyleSheet.create vs inline performance differences. Flexbox — direction, justify, align, flex, gap. Dimensions API, useWindowDimensions. SafeAreaView, KeyboardAvoidingView. Platform.select for OS-specific code.

All React hooks in depth: useState (batching, functional updates), useEffect (dependency array pitfalls, cleanup, race conditions), useCallback, useMemo (the over-optimisation trap), useRef, useReducer. Custom hooks — useDebounce, useFetch. Redux Toolkit — createSlice, createAsyncThunk, RTK Query (caching, invalidation, optimistic updates). Zustand — minimal boilerplate, persist middleware. React Query — queries, mutations, infinite queries, stale-while-revalidate.

Stack, Bottom Tab, Material Top Tab, Drawer navigators — nesting patterns. Passing params, deep linking (Universal Links on iOS, App Links on Android, testing with Expo). Auth flow — splash → auth check → login or main app, protecting routes. Custom header components, header transparency. Navigation ref for navigating from Redux thunks and notification handlers. TypeScript-safe navigation with typed route params.

Axios — instances, request/response interceptors, AbortController, global error handling, automatic retry. JWT — SecureStore (not AsyncStorage), token refresh with interceptor queue preventing 401 races. REST pagination (cursor vs offset), file uploads with progress. WebSockets with socket.io-client. Apollo Client — queries, mutations, subscriptions, cache normalisation. WatermelonDB for offline-first. NetInfo for connectivity detection.

Camera: expo-image-picker + react-native-vision-camera (real-time ML frame processors, barcode scanning). GPS: expo-location (foreground/background/geofencing) + react-native-maps (markers, callouts, polylines, Supercluster clustering). Push Notifications: APNs (iOS) & FCM (Android) setup via Expo, notification channels, handling press in all app states. Biometrics: Face ID/Fingerprint + keychain. Sensors (expo-sensors), haptics, Share API, Clipboard, Bluetooth basics.

AOT vs JIT compilation (why Dart = fast startup + hot reload). Null safety: ?, ?., ??, ??=, !, late. OOP: classes, named constructors, factory constructors, inheritance, mixins (multiple inheritance alternative), abstract classes, interfaces (implements). Async: Future, Stream, StreamController, await, isolates for CPU-intensive tasks. Extension methods, generics, callable classes, cascade (..), collection operators (map, where, fold, expand). Key differences from JavaScript that trip developers up.

Flutter's 3 trees: Widget (blueprint) → Element (lifecycle) → RenderObject (paint). StatelessWidget vs StatefulWidget — lifecycle methods (initState, didUpdateWidget, dispose). InheritedWidget (foundation of all state solutions). Material 3: ThemeData, ColorScheme, NavigationBar, FilledButton, TextField. Layout: Column, Row, Stack/Positioned, Expanded, Flexible, SizedBox. Scroll: ListView.builder, GridView.builder, CustomScrollView + Slivers (SliverAppBar collapse, SliverList, SliverGrid). Responsive: LayoutBuilder, MediaQuery, OrientationBuilder. CustomPaint for canvas drawing. Custom widget composition patterns.

Provider: ChangeNotifier, Consumer, Selector (granular rebuilds), MultiProvider, ProxyProvider (DI). Riverpod 2.x (why it fixes Provider's limitations): StateNotifierProvider, FutureProvider, StreamProvider, AsyncNotifierProvider — ref.watch vs ref.read vs ref.listen, scoped providers, testing overrides. BLoC with flutter_bloc: Events → States, Cubit (simplified), BlocBuilder (buildWhen), BlocListener, BlocConsumer, Hydrated BLoC (persistence). GetX for rapid prototyping. Trade-off analysis: when to choose which solution.

FlutterFire CLI setup. Firebase Auth: email/password, Google Sign-In, Apple Sign-In (required for App Store), phone OTP (reCAPTCHA + silent APNs). Cloud Firestore: CRUD, real-time snapshots, compound queries, transactions, batch writes, security rules (user-based access, field validation, rate limits). Firebase Storage: upload with UploadTask progress, getDownloadURL. FCM: foreground/background/terminated state handling, notification channels. Firebase Analytics (custom events, user properties), Crashlytics (crash reports, custom keys), Remote Config for feature flags & A/B testing paywall copy.

Implicit animations (AnimatedContainer, AnimatedOpacity, AnimatedCrossFade, AnimatedSwitcher). Explicit: AnimationController, Tween, CurvedAnimation (spring physics). Hero shared-element transitions. Staggered list animations. Lottie (lottie / rive packages for loading, success, error states). CustomPainter canvas — drawArc for progress rings, custom charts, drawing paths. RepaintBoundary for performance isolation. Sliver animations — parallax scrolling. Draggable + DragTarget — sortable lists. Custom gesture recognizers. FragmentShader (Flutter 3.7+) for GPU-accelerated effects.

SharedPreferences (settings). Hive: TypeAdapters (generated), encrypted boxes, lazy loading. SQLite with sqflite & floor ORM (entities, DAOs, reactive DB streams). Offline-first: optimistic UI, sync queue with timestamps, last-write-wins conflict resolution. Connectivity detection (connectivity_plus). WorkManager (Android) & BGTaskScheduler (iOS) for background sync. Platform Channels — writing Kotlin/Swift native code and calling from Dart (use case: native SDKs with no Flutter plugin). Method channels, event channels.

Mobile-optimised Node.js + Express APIs: pagination (cursor vs offset), filtering, rate limiting, Sharp for image resizing, Cloudinary CDN. GraphQL with Apollo Server: schema design, DataLoader (N+1 fix), subscriptions. Firebase Cloud Functions: auth triggers, Firestore triggers, HTTP, scheduled. Socket.io: rooms, presence indicators, typing indicators. Webhook handling. Background sync — queuing offline operations, processing on reconnect.

Razorpay: order creation, webhook verification, UPI deeplink, EMI, payment links. Stripe: PaymentSheet (best UX), 3D Secure, webhook. Apple IAP (StoreKit 2): consumable/non-consumable/auto-renewable subscriptions, grace period, billing retry, server-side validation. Google Play Billing v6: purchase tokens, subscription management. RevenueCat: unified cross-platform entitlements, paywalls, A/B test pricing. AdMob: banner, interstitial, rewarded — mediation setup. Monetisation strategy: freemium vs subscription vs IAP vs ads.

React Native: Jest unit tests (mocking, async, snapshots), React Native Testing Library (component rendering, user events). Detox E2E — writing stable, flake-free device automation. Flutter: unit tests, widget tests (pump, find, expect), integration tests with patrol. Debugging: Flipper (RN network + layout + Redux), Flutter DevTools (widget inspector, memory, performance profiler). Performance: JS thread vs UI thread profiling, InteractionManager, reducing re-renders, image optimisation. Fastlane — gym, gradle, match (code signing), pilot (TestFlight), supply (Play Store). GitHub Actions on macOS runners. EAS Build. Firebase App Distribution for beta.

OpenAI GPT-4o: chat completions, streaming responses in chat UI, function calling for tool use. Google Gemini API (multimodal: text + image). TensorFlow Lite (tflite_flutter): on-device object detection, custom models. ML Kit: text recognition, face detection, barcode scanning, language ID — all on-device, zero API costs. Google Play Console: keystore management (NEVER lose it), release tracks (internal→closed→open→production), store listing, data safety form. App Store Connect: provisioning profiles, TestFlight (10,000 testers), Privacy Manifest (2024 requirement), App Review common rejection reasons, phased release. ASO — keyword research, A/B testing screenshots. Capstone: build, review-pass, and publish your own app.