React Developer interview questions
The 7 questions that actually come up, each with what a strong answer covers. These are not scripts to memorise — interviewers can tell — they are the shape of the answer that gets a yes.
7 questionsReact Developer career guide →
When does a React component re-render, and how do you stop wasteful ones?
What a strong answer coversParent renders, state, context. Then: composition first, memo/useMemo where measured, and why the React Compiler changes this answer.
Server components vs client components — how do you split a page?
What a strong answer coversData and markup on the server; interactivity islands on the client. Explain what CANNOT cross the boundary and why.
useEffect: what belongs in it, and what does not?
What a strong answer coversSynchronising with external systems only. Deriving state, transforming data or handling events in effects is the era's most common bug.
Two sibling components need the same server data. Options?
What a strong answer coversLift to a shared server parent, request deduplication (cache/React Query), or context — with the trade-offs of each stated.
Your bundle is 2MB. Reduce it.
What a strong answer coversAnalyse first (source maps), then route-level code splitting, dynamic imports for heavy libs, tree-shaking checks, and image/font discipline.
A form input lags on every keystroke. Why?
What a strong answer coversControlled input re-rendering an expensive tree: isolate state low, defer non-urgent updates (useDeferredValue), virtualise big lists.
How do you make a modal accessible?
What a strong answer coversFocus trap and restore, aria-modal/labelledby, Escape to close, inert background. A concrete checklist beats vibes.