Question 1

How do you approach React performance work?

Accepted Answer

Measure first (Profiler), then fix state location, reduce work, memoize hotspots, virtualize. Don't sprinkle memo/useMemo blindly. Network and bundle size matter too.

Question 2

What does React.lazy + Suspense do for bundles?

Accepted Answer

Code-splits components into separate chunks loaded on demand. Great for routes/modals. Provide meaningful fallbacks. Prefetch when likely needed.

Question 3

Windowing/virtualization — when?

Accepted Answer

Long lists where DOM node count dominates cost. Libraries like react-window. Combine with stable keys and measured row heights.

Question 4

How can Context hurt performance and how to fix?

Accepted Answer

Broad value changes re-render all consumers—split context or use external store subscriptions. useSyncExternalStore powers many modern stores efficiently.

Question 5

startTransition for expensive filtered lists?

Accepted Answer

Keep input state urgent; mark filtered list updates as transition for smoother typing. Show isPending UI. Don't transition every tiny update.

Question 6

Images and React perf?

Accepted Answer

Use modern formats, sizing, lazy loading; avoid layout shift; consider CDN. UI jank isn't always JS—assets matter. Next/Image-like patterns help.

Question 7

Lead: set performance budgets for a React SPA.

Accepted Answer

Define CWV targets, bundle size limits, CI checks, and profiling rituals for major features. Own regressions. Educate on state architecture as the main lever.

Performance React Interview Questions

Other React interview topics