React Developer interview questions & mock practice

Common React Developer interview questions include: What is the virtual DOM, and how does React's reconciliation and diffing work? Explain useState and useEffect, and the rules of hooks. What is the difference between props and state? What does the useEffect dependency array do, and what happens if you omit it? Interviews usually run across 4 rounds — JavaScript round, React core round, Machine coding, State & performance. Practise them with the free timed practice on this page.

A typical React Developer interview has 4 rounds: JavaScript round (Closures, async, the event loop and ES6+ features.); React core round (Hooks, rendering, reconciliation and component patterns.); Machine coding (Build a React component live — search, pagination or a form.); State & performance (Redux/Context, memoisation and optimisation.).

To prepare for a React Developer interview: Know hooks deeply: useState, useEffect, useRef, useMemo, useCallback and the rules that govern them. Understand the render cycle: what triggers a re-render, reconciliation, keys and how to avoid wasted renders. Practice machine coding: build an autocomplete, paginated list or form with validation from scratch. Then rehearse every question out loud with the timed practice on this page before the real thing.

Core React Developer skills tested in interviews include React, JavaScript, Hooks, Redux, TypeScript, Web Performance, CSS. OnJob shows you exactly which of these skills stand between you and a 100% match on every live React Developer job.

Yes. The questions, the answer guidance and the timed practice on this page are free and need no signup. With a free OnJob account you can also take timed role tests and free certification tests. Personalised AI role and skill tests are part of the paid plans.