A screen in your React Native app is slow. How do you investigate and fix it?

Summary

Reproduce in a release build, profile to find what re-renders or blocks the JS thread, then fix the cause: memoise rows and stabilise props, move expensive computations out of render, tune lists, right-size images, and move animations to the UI thread.

Longer Answer

Tools: the React DevTools profiler (which components rendered and why), the performance monitor (JS vs UI frame rates), and platform profilers for native issues. Typical culprits: inline functions defeating React.memo, filtering large arrays on every keystroke, full-resolution images in lists, and JSON parsing during interactions.

Key Points

• Measure in release builds first.
• Fix re-renders: memo + useCallback/useMemo.
• Defer heavy work; tune lists and images.

Deep dive: Mobile Apps with React Native and Expo: Performance

What interviewers look for

A measurement-first approach and concrete causes, not a list of random optimisations.