Mobile App Development Interview Questions for 5 Years Experience
40 questions with answers for candidates with 5 years of experience — 2 easy, 25 medium, 13 hard.
What interviewers expect: 5 years experience
At five years, you are interviewed as a senior engineer. Expect deep discussions on app architecture for large teams, offline sync, security, modular codebases and migrations such as adopting a new React Native architecture or moving state libraries. Leadership questions on mentoring, code reviews and cross-team collaboration carry significant weight in the final decision.
This set is weighted towards App Store and Play Store Publishing (8), Mobile Backend, APIs and Firebase (7), Mobile Development Fundamentals (6), React Native Navigation, State and Native Modules (6).
Large-scale app architecture Security and store compliance Migrations and tech debt Mentoring and code review
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01
What is App Store Optimisation and what can a developer influence?
App Store Optimisation improves an app's visibility and conversion in store search. Key factors are the app title, subtitle or short description, keywords, long description, screenshots, preview videos, ratings and reviews. Developers influence it by keeping app size small, crash rates low and performance high, since store algorithms consider quality signals, by adding in-app review prompts at good moments, and by supporting localisation for regional languages.
02
When would you choose a cross-platform framework over native development?
Choose cross-platform when you need both Android and iOS quickly with a small team, the app is mostly forms, lists, content and API-driven screens, and design consistency across platforms is desired. Choose native when the app needs heavy graphics, deep hardware integration, advanced background processing, newest platform features on day one, or very tight performance. Many companies mix both, using native modules inside a cross-platform app.
03
What are over-the-air updates and what are their limits?
Over-the-air updates push new JavaScript bundles and assets to React Native apps without a store release, using services like EAS Update. They fix bugs quickly but can only change JavaScript and assets, not native code, permissions or SDK versions, which need a new build. Store policies allow them only if the app's core purpose does not change. Use runtime versions to ensure updates match compatible native builds, and roll out gradually.
04
Write an EAS configuration for development, preview and production builds.
An error boundary is a class component, or a library like react-error-boundary, that catches rendering errors in its child tree and shows a fallback UI instead of crashing the whole app. Place one at the app root and around risky screens. They do not catch errors in event handlers or async code, so use try-catch there. Report caught errors to a crash reporting tool with context for debugging.
06
How would you migrate a large React Native app from JavaScript to TypeScript?
Enable TypeScript with allowJs so both coexist, start with a relaxed tsconfig, and convert shared code first: API types, models, utilities and navigation param lists. Then convert screens feature by feature, tightening strict options gradually. Add type checks to CI so new files must be TypeScript. Avoid using any to silence errors; use unknown and narrow. Track progress and celebrate milestones to keep momentum.
Maestro is an open-source mobile UI testing framework where flows are written in simple YAML, such as launchApp, tapOn "Login" and assertVisible "Welcome". It works with native, Flutter and React Native apps on Android and iOS, handles waiting automatically, and reduces flakiness compared to many older tools. Teams use it for smoke tests of critical journeys in CI because tests are quick to write and readable by QA.
08
How do you handle pressure when a production issue affects many users?
I stay calm and focus on reducing impact first: confirm the issue, communicate status to the team, and look for the fastest safe mitigation such as a remote config switch, server-side fix or pausing a rollout. Then I find the root cause, ship a proper fix and write a short postmortem. Clear, regular updates to stakeholders reduce panic and let others plan around the issue.
09
Integration tests pass locally but fail randomly in CI. How do you make them reliable?
Flaky tests usually come from timing assumptions, shared state, network dependence or slow emulators. Replace fixed delays with waiting for specific conditions, mock or stub network calls with predictable responses, reset app data between tests, and use stable selectors like keys or test IDs instead of text that changes. Give CI emulators enough resources, retry only as a temporary measure, and track flaky tests separately to fix them.
10
How do you detect and fix memory leaks in cross-platform apps?
Leaks usually come from subscriptions, timers, controllers and listeners that are never disposed, or global caches that grow without limits. In Flutter, dispose controllers and cancel stream subscriptions in dispose, and check the DevTools memory view for growing instances. In React Native, return cleanup functions from useEffect and remove event listeners. Repeatedly open and close a screen while profiling to confirm memory returns to baseline.
11
Write a custom hook that fetches data with loading and error states.
Read the reviewer's message in App Store Connect carefully. Guideline 5.1.1 issues often involve requesting permissions without clear purpose strings, requiring sign-up for features that do not need an account, or missing account deletion. Fix the specific problem, for example improving usage description text or adding in-app account deletion, and reply in Resolution Center explaining the changes. Ask for clarification if the rejection is unclear.
13
Tell me about a technical decision you made that you later regretted, and what you learned.
Situation: on an earlier project I chose a lesser-known state management package because it looked simpler. Task: support the app as it grew. Action: when the package stopped being maintained, I led a migration to Riverpod feature by feature with tests. Result: the migration took three sprints. I learned to evaluate packages by maintenance activity, community size and testing support, not just initial simplicity, and to document decisions.
freezed generates immutable data classes with copyWith, equality, toString and union types or sealed classes, and integrates with json_serializable for fromJson and toJson. It removes boilerplate when modelling state such as loading, data and error variants. You annotate a class, run build_runner, and get generated code in a part file. With Dart 3 sealed classes and records, some teams need it less, but it is still widely used.
15
The client wants the app to look exactly like iOS on iPhones and like Material on Android. How do you approach this in a cross-platform app?
Identify which elements truly need platform-specific behaviour: navigation transitions, back gestures, date pickers, switches and dialogs. In Flutter, use adaptive constructors like Switch.adaptive or Cupertino widgets based on Theme.of(context).platform. In React Native, many components are native already, and Platform.select handles differences. Keep shared business logic and most layout common, and limit platform branches to a component library so they stay manageable.
16
Write a Dart sealed class for API results and handle it with an exhaustive switch.
The app registers with the platform push service, FCM on Android and APNs on iOS, often both through FCM, and receives a device token. The app sends this token to your backend, linked to the user. When an event happens, the backend sends a message to FCM or APNs with the token, which delivers it to the device. The app requests notification permission, handles taps to open the right screen, and refreshes tokens when they change.
18
Store review is delaying your launch date. How do you plan releases to avoid this?
Submit builds early, a few days before the planned date, and use manual release so you can publish the approved build at launch time. Ship the code behind a remote feature flag so the feature can be enabled on launch day without a new review. Keep a pre-approved build ready, follow store guidelines closely and include clear review notes and demo login details for reviewers.
19
Write a React Native function that uploads an image with progress using Expo FileSystem.
JavaScript, including React rendering and business logic, runs on the JS thread, while the native UI thread draws views and handles touches. If the JS thread is busy with heavy computation or large re-renders, taps and JS-driven animations lag even though the UI thread is free. Keep heavy work off the JS thread, move animations to the UI thread with Reanimated, and split expensive tasks into smaller chunks.
21
How do you communicate a delayed release to stakeholders?
I inform them as soon as I know, not on the release day. I explain the reason briefly, such as a store rejection or critical bug, the impact, the new estimated date, and what we are doing to avoid repeating it. I offer options, like releasing other features first. Regular short updates until release keep trust, and I note learnings in the release retrospective.
22
A payment shows success in the app but the order is not created on the server. How would you fix the flow?
The app is probably treating the SDK's success callback as final and the verification call failed or was never sent, for example when the app was killed. Make the backend the source of truth: verify payments with the gateway's signature on the server and use webhooks to update orders even if the app never reports back. The app should poll order status after payment and show a pending state until confirmed.
23
What is a performance budget and how do you enforce it?
A performance budget sets limits on metrics like cold start time, app download size, frame rendering time and memory usage. Enforce it by measuring in CI, for example tracking release build size per pull request and running startup benchmarks on a reference device, and failing or flagging builds that exceed limits. Budgets make performance a shared responsibility rather than something fixed only after users complain.
24
How do native modules work, and when do you write one?
A native module exposes platform code written in Kotlin, Java, Swift or Objective-C to JavaScript. With the New Architecture, you define a typed TypeScript spec, Codegen generates interfaces, and the TurboModule implements them natively. Expo Modules API offers a simpler way using Swift and Kotlin. You write one when no library supports a needed SDK or device feature, such as a specific payment or biometric SDK.
25
An animation stutters whenever the screen fetches data. How do you fix it?
The animation likely runs on the JS thread, and data parsing or re-renders block it. Move the animation to the UI thread with Reanimated or Animated with useNativeDriver, reduce the work done when data arrives by memoising components and normalising state updates, and delay heavy processing with InteractionManager or requestIdleCallback-style scheduling until the animation finishes. Profile with React Native DevTools to confirm.
Expo Router is a file-based router built on React Navigation. Files in the app directory become routes, so app/product/[id].tsx maps to /product/42. Layout files define stacks and tabs, and every screen is deep-linkable automatically on mobile and web. It supports typed routes, protected routes for auth, and API routes. It reduces navigation boilerplate and makes URL-based linking consistent across platforms.
27
What is accessibility in mobile apps and how do you implement it?
Accessibility makes apps usable by people with disabilities. Provide labels for icons and images so screen readers like TalkBack and VoiceOver can announce them, keep touch targets at least 44 to 48 points, support dynamic text sizes, ensure colour contrast, and avoid conveying information only by colour. Flutter uses Semantics widgets, and React Native uses accessibilityLabel and accessibilityRole. Test with screen readers enabled.
28
How do you integrate a payment gateway in a mobile app safely?
Create the order on your backend with the amount, get an order ID, and open the gateway's SDK checkout in the app with that ID. After payment, the SDK returns a payment ID and signature, which the app sends to the backend to verify with the secret key before marking the order paid. Rely on server-side webhooks as the final truth. Never keep secret keys in the app or trust client-side success alone.
29
What is Supabase and how does it compare to Firebase?
Supabase is an open-source backend platform built on PostgreSQL, offering authentication, a relational database with auto-generated APIs, row level security, storage, edge functions and real-time subscriptions. Firebase uses NoSQL databases like Firestore. Supabase suits apps with relational data and SQL needs, and can be self-hosted, while Firebase has a richer mobile ecosystem including Crashlytics, Remote Config and FCM. Many apps combine them.
30
Tell me about a time you had to learn a new framework under a deadline.
Situation: my team decided to build a client app in Flutter, and I had only React Native experience. Task: deliver the login and dashboard screens in three weeks. Action: I completed the official codelabs in the first week, mapped concepts I knew like components and hooks to widgets and state, and asked for early code reviews. Result: the screens shipped on time, and I later wrote a short guide for other React Native developers moving to Flutter.
31
How do you automate store submissions with fastlane?
fastlane defines lanes in a Fastfile, such as beta and release. A lane can increment build numbers, build the app with gradle or gym, sign with match, which stores iOS certificates encrypted in a private repository, upload to TestFlight with pilot or Play testing tracks with supply, and upload metadata and screenshots. Running lanes from CI makes releases repeatable and removes manual steps on a developer's machine.
32
How do animations work in React Native and why use Reanimated?
The built-in Animated API can run animations on the native thread with useNativeDriver for transform and opacity, but not for layout properties. Reanimated runs animation logic in worklets on the UI thread, so animations stay smooth even if JavaScript is busy, and supports gestures, layout animations and shared element transitions. Combined with react-native-gesture-handler, it is the standard for complex interactive animations.
Provider is simple and built on InheritedWidget but depends on BuildContext and can throw provider-not-found errors at runtime. Riverpod, from the same author, is compile-safe, independent of the widget tree, supports async providers and easy overrides for testing. Bloc uses events and states with streams, enforcing strict separation and traceability, popular in large teams and enterprises. Choose based on team familiarity and app complexity.
34
What is a WebView and when is it appropriate to use one?
A WebView embeds a browser engine in your app to show web content. It suits help pages, terms, payment gateway pages or quickly reusing an existing web flow. It is not ideal for core app screens because it feels slower and less native. Restrict navigation to trusted domains, avoid exposing powerful JavaScript bridges to untrusted content, and handle back navigation. Flutter uses webview_flutter and React Native uses react-native-webview.
35
What are useMemo, useCallback and React.memo used for?
React.memo skips re-rendering a component when its props are shallowly equal. useCallback keeps the same function reference between renders, and useMemo caches a computed value, both only changing when dependencies change. They help when passing callbacks to memoised list items or computing expensive values. Overusing them adds complexity with little gain; the React Compiler can now apply such memoisation automatically in supported projects.
36
A security audit finds that the app stores the access token in plain shared preferences. How do you fix it?
Move tokens to secure storage backed by Keychain on iOS and Keystore on Android, such as flutter_secure_storage or expo-secure-store. Migrate existing users by reading the old value once, writing it securely and deleting the plain copy. Shorten access token lifetime, use refresh tokens, exclude sensitive files from backups, and clear tokens on logout. Retest with the audit team to confirm the issue is closed.
37
A Flutter animation is smooth on a flagship phone but janky on a budget phone. How do you fix it?
Profile on the budget device in profile mode. Common fixes: wrap frequently repainting areas in RepaintBoundary, avoid expensive effects like Opacity on large subtrees, clipping and shadows in scrolling lists, use AnimatedBuilder with child so static parts do not rebuild, precache images and decode them at display size, and move heavy computation to isolates. Reduce animation complexity on low-end devices if needed.
Store data in a local database and render the UI from it, so the app works without network. Queue user changes locally with a pending status and sync them in the background when connectivity returns, using retries with backoff. Fetch server changes using timestamps or sync tokens and merge them. Resolve conflicts with clear rules like last write wins or server authority, and show sync status to users.
39
Users say the app does not work properly on foldable phones and tablets. What do you check?
Check whether orientation is locked, layouts use fixed widths, and screens assume phone dimensions. Make layouts adapt by width breakpoints with two-pane layouts on wide screens, handle configuration and size changes without losing state, and avoid hardcoding aspect ratios. Recent Android versions ignore orientation locks on large screens, so locking is no longer a fix. Test with resizable emulators, foldable postures and split-screen mode.
40
A critical bug reaches production in a React Native app. How do you fix it quickly?
If the bug is in JavaScript, fix it, test on a preview channel, and publish an over-the-air update to production with a staged rollout, keeping it compatible with the current runtime version. If it needs native changes, build a hotfix release, submit it, and request expedited review on iOS if justified. Meanwhile disable the feature with a remote config flag if possible, and halt the store rollout.
Frequently asked questions
What is asked in Mobile App Development interviews for 5 years of experience?
At five years, you are interviewed as a senior engineer. Expect deep discussions on app architecture for large teams, offline sync, security, modular codebases and migrations such as adopting a new React Native architecture or moving state libraries. Leadership questions on mentoring, code reviews and cross-team collaboration carry significant weight in the final decision.
How many questions should I practise before a Mobile App Development interview?
Work through all 40 questions here, then the company-wise sets for the employers you are targeting. Quality matters more than count: be able to explain why each answer is right.
Which topics matter most for 5 years of experience?
Focus first on Large-scale app architecture, Security and store compliance, Migrations and tech debt, Mentoring and code review.