Interview questions in React Native, page 7
Unit testing a custom hook with renderHook
Render the hook, read result.current, fire actions inside act, assert updated state.
Layered testing strategy for a large RN app
Many fast Jest unit tests, fewer RNTL component tests on behavior, few Detox/Maestro E2E on critical flows.
Build flavors and schemes for RN environments
Android productFlavors with distinct applicationId and resources, iOS schemes plus configurations and targets, environment config injection.
Web DOM elements vs React Native core components
View maps to UIView/ViewGroup, Text to native text, no HTML or CSS, all text must be inside Text.
The legacy React Native Bridge architecture
JS, native, and shadow threads communicate via an async, batched, JSON-serialized Bridge.
Adding native code to Expo without ejecting
Use prebuild with config plugins to inject native changes, build a custom development client with EAS, keep native folders generated not hand-edited.
Composing tap and pan gestures together
Declare both gestures and relate them with simultaneous or exclusive composition, using Gesture.Race or simultaneousHandlers so a small move stays a tap.
Passing params between Stack Navigator screens
Navigate to the route with a params object, read it via route.params on the target, pass an id not a huge object.
Android-only native module called safely from JS
Write a ReactContextBaseJavaModule with an exported method, register it in a package, then guard the JS call with Platform.OS or a null check on the module.
Platform-specific typography in a global theme
Define one theme with Platform.select for fontFamily, expose semantic text styles, and reuse them everywhere rather than per-screen overrides.
Unifying divergent native video player props
A JS component accepts a unified source prop, then uses Platform.OS to map it into each native view's expected props before rendering.
Offline data storage and sync strategy
Persist locally in SQLite or WatermelonDB, queue mutations with a pending flag, detect reconnection with NetInfo, then replay the queue and resolve conflicts.
Creating a native module with a sync method
Extend the RN base class, mark the method exported and synchronous, register in a package or bridging file.
Purpose of RCTBridgeModule and ReactContextBaseJavaModule
These declare a class as a discoverable native module, provide the JS-facing name, and let RN export methods to JavaScript.
Threading of native module methods
Methods run on a dedicated native module queue, not the UI thread; long blocking work stalls other module calls; offload to a background executor or override methodQueue, returning results via promise.
TurboModules and lazy loading benefits
TurboModules use JSI for direct, synchronous, type-safe calls and are loaded lazily on first use instead of all at startup, cutting init time.
What JSI is and how it replaces the Bridge
JSI is a lightweight C++ layer letting JS hold references to native host objects and call them directly and synchronously, with no JSON serialization or async batched queue.
TurboModule lazy loading vs eager startup
Legacy modules are instantiated eagerly at launch; TurboModules initialize only when JS first accesses them, so unused modules cost nothing at startup.
Fabric UI update lifecycle vs old architecture
Render builds an immutable C++ shadow tree, commit diffs trees and runs Yoga layout, mount applies mutations to native views; JSI shares the tree, enabling synchronous and concurrent rendering unlike the…
Generating a signed release APK or AAB
Create a keystore, reference its credentials via gradle.properties (gitignored), wire a release signingConfig in build.gradle, then assembleRelease or bundleRelease.
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