Use this guide to interview a React Developer. Pick eight to twelve questions per session, keep the set consistent across candidates, and prioritize the rendering and state groups — a correct mental model of how React renders is the strongest predictor of quality in this role, and it cannot be faked with memorized answers once you follow up. Anchor scenarios in {{Your product or domain}}.

React fundamentals and rendering

• Explain how React decides to re-render a component, and how you prevent renders that should not happen.
• When do you reach for useEffect, and what are the signs it is being misused?
• Explain the rules of hooks and the problem they solve. When have you built a custom hook worth reusing?
• What are keys in lists actually for, and what breaks when they are wrong?
• How do Server Components change how you structure an app, and where do client components still earn their place?
• Controlled versus uncontrolled components: what is the difference, and when do you choose each for forms?

What good looks like: listen for a correct mental model — props and state identity, reconciliation, why effects run — expressed in the candidate's own words rather than memorized rules. The useEffect question is the best signal in this group: strong candidates describe deriving state during render and treating effects as synchronization with external systems, not as a lifecycle hammer.

State management and data fetching

• How do you decide where a piece of state lives — component, context, an external store, or the URL?
• Compare state libraries you have used — Redux Toolkit, Zustand, Jotai, or context alone. What makes you pick one today?
• How do you handle server state — caching, revalidation, optimistic updates? What do tools like TanStack Query actually solve?
• Walk me through implementing an optimistic update that can fail. How do you roll it back?
• How do you avoid request waterfalls when a page needs several pieces of data?
• Tell me about a state bug that was hard to find. What was the actual cause?

What good looks like: strong candidates separate server cache from client state cleanly, treat the URL as legitimate state, and justify library choices by the problem at hand instead of fashion. Watch for candidates who reach for a global store by default — that pattern creates most of the state bugs this group is probing for.

Performance

• A React page is slow to interact with. Walk me through diagnosing it with the profiler.
• When do memo, useMemo, and useCallback help — and when are they just noise?
• How do you keep bundle size under control? What have you actually cut from a real app?
• How do you render a list of ten thousand rows without wrecking the frame rate?
• Which Core Web Vitals have you improved on a real product, and how?

Testing and quality

• What do you test in a React app, and with what tools? Where do component tests stop and end-to-end tests start?
• How do you write tests that survive refactors? What makes a test brittle?
• How do you test a complex custom hook?
• A flaky test fails one run in ten. How do you approach it?

Styling, accessibility, and UX

• Compare styling approaches you have used — CSS modules, Tailwind, CSS-in-JS. What drives your choice?
• How do you build an accessible dropdown or modal from scratch? Which keyboard and ARIA details matter?
• How do you catch accessibility regressions before users do?
• How do you design a shared component so it stays flexible without becoming a prop soup?

Architecture and collaboration

• How do you structure a large React codebase — by feature, by layer? What has scaled best for you?
• How do you review a React pull request? What do you look for beyond "it works"?
• Tell me about disagreeing with a designer over an interaction's cost or feasibility. How did it resolve?
• How do you keep a team writing consistent React when hooks allow so many styles?
• What recent change in the React ecosystem do you find most significant, and how has it changed your work?