Interview practice

Mobile Developer (React Native)

2–5 years · Mid — React Native · JavaScript · Native modules · Offline storage · App release · Performance

technical Debugging 1 of 6

A user reports that the app crashes intermittently in production without any visible error. What methodical approach do you take to diagnose and fix the issue?

What a strong answer covers

Enables logging and error tracking in the app; reproduces the issue on a local environment with similar data; checks for third-party library updates; reviews the last changes made before the issue surfaced; isolates problematic components for further testing.

The follow-up you would get

If logs don’t provide enough information, what additional tools can you employ?

Could you have answered that?

scenario Performance 2 of 6

The app's launch time has increased significantly in the latest build, and users are complaining. What steps do you take initially to diagnose the issue?

What a strong answer covers

Profiles the app's startup time using performance tools; checks for heavy imports or synchronous calls in the launch sequence; evaluates the size of assets and resources being loaded; examines the initial state management; considers using code splitting or lazy loading.

The follow-up you would get

If you identify a large asset causing the delay, how would you go about optimising it without sacrificing quality?

Could you have answered that?

ownership A decision that improved performance 3 of 6

Can you describe a performance-related decision you made that significantly enhanced the app's responsiveness?

What a strong answer covers

Names a specific performance issue and the decision made; details the analysis process that led to the decision; describes the implementation and its effects on app performance; quantifies improvements with metrics; discusses user feedback following the change.

The follow-up you would get

What alternatives did you consider before making that decision?

Could you have answered that?

scenario Debugging production issues 4 of 6

A critical bug is reported just before a major release, causing the app to crash on launch for certain users. What do you do in the first thirty minutes?

What a strong answer covers

Reproduces the crash on a device with similar specs; checks recent code changes related to the launch; identifies and isolates the feature causing the issue; assesses the severity and impact on the release; decides whether to rollback or patch.

The follow-up you would get

If the bug stems from a third-party library, how do you address the dependencies while still meeting the release deadline?

Could you have answered that?

technical Native Modules 5 of 6

You need to access a device's camera functionality through a native module in React Native. What steps do you follow to implement this feature?

What a strong answer covers

Creates a new native module in Android/iOS; exposes the camera API using React Native's bridge; handles permissions accurately in both platforms; tests the module in various scenarios to ensure reliability; documents the module for future developers.

The follow-up you would get

What challenges might you face when bridging native code with JavaScript?

Could you have answered that?

ownership A migration that didn't go as planned 6 of 6

Describe a migration you managed that encountered significant issues, and what you learned from it.

What a strong answer covers

Identifies a specific migration with context; details the initial expectations and the unexpected challenges faced; explains the resolution process and the impact on users; notes changes made to prevent future issues; reflects on lessons learned and adjustments to the migration strategy.

The follow-up you would get

What warning signs could you have spotted earlier?

Could you have answered that?

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