Top 30 Most Common React Js Interview Questions You Should Prepare For

most common interview questions to prepare for

Written by

James Miller, Career Coach

Written on

Jun 27, 2025

💡 If you ever wish someone could whisper the perfect answer during interviews, Verve AI Interview Copilot does exactly that. Now, let’s walk through the most important concepts and examples you should master before stepping into the interview room.

What core React concepts should I master for interviews?

Direct answer: Focus on React’s purpose (building component-driven UIs), JSX, Virtual DOM, props vs state, lifecycle (or effects), and hooks — these form the foundation most interviewers test.

Expand: Explain how JSX compiles to JavaScript, why the Virtual DOM reduces DOM updates, and the practical difference between props (immutable inputs) and state (component-owned data). Know class vs functional components: functional components + hooks are now standard. Understand key lifecycle equivalents (componentDidMount → useEffect with empty deps, etc.) and common hooks (useState, useEffect, useRef, useContext).

Example: Be ready to explain how lifting state up solves sibling communication, and why keys help reconciliation.

Takeaway: Mastering these fundamentals gives you confidence in both basic and follow-up technical questions during interviews.

What are the top 30 React interview questions you should prepare for?

Direct answer: Prepare a balanced list of 30 questions across fundamentals, coding, advanced topics, and behavioral scenarios — with concise, testable answers.

Expand (Top 30 questions with short answers):

What is React and how does it work?

React is a library for building UI components; it uses a Virtual DOM to batch and efficiently apply UI updates.
What is JSX?
JSX is a syntax extension that looks like HTML but compiles to React.createElement calls.
What is the Virtual DOM and how does it differ from the real DOM?
Virtual DOM is an in-memory representation; React diffs it against previous trees and patches the real DOM minimally.
What are props and state?
Props: read-only inputs from parents. State: internal, mutable, component-specific data.
Difference between class and functional components?
Class components use lifecycle methods and this; functional components use hooks and are now recommended.
What are React hooks? Give examples.
Hooks let you use state and lifecycle in functions. Examples: useState, useEffect, useMemo, useCallback, useRef.
How does useEffect compare to lifecycle methods?
useEffect replaces componentDidMount/Update/WillUnmount depending on dependency array management.
How do you pass data between components?
Parent-to-child via props, child-to-parent via callbacks, sibling via lifted state or Context/Redux.
What is reconciliation?
The process React uses to diff Virtual DOM trees and decide minimal updates to the real DOM.
Explain keys in lists and why they matter.
- Keys identify list items across renders to preserve identity and optimize updates.
Controlled vs uncontrolled components?
- Controlled components have their state managed by React; uncontrolled rely on the DOM (refs).
What is Context API and when to use it?
- Context provides a way to pass data through the component tree without props drilling; use for themes, auth, etc.
Context vs Redux?
- Context is for simple shared state; Redux offers predictable global state management with middleware for complex needs.
What is lifting state up?
- Moving shared state to the nearest common ancestor to coordinate child components.
How do you optimize React performance?
- Techniques: memoization (React.memo, useMemo, useCallback), code-splitting, virtualization, avoiding unnecessary re-renders.
Explain React.memo, useMemo, and useCallback.
- React.memo memoizes components; useMemo memoizes computed values; useCallback memoizes functions.
What is Suspense and Concurrent Mode?
- Suspense lets components wait for async resources; Concurrent Mode (experimental) improves responsiveness by interruptible rendering.
How do you handle side effects in React?
- useEffect for effects; cleanup functions for unmounting; avoid side effects during render.
How does error boundary work?
- Error boundaries catch render-time errors in child components using lifecycle methods in class components (componentDidCatch).
How do you test React components?
- Unit tests with Jest and React Testing Library for behavior; Enzyme for some legacy cases.
What are Higher-Order Components (HOC) and render props?
- Patterns to reuse logic: HOC returns a new component; render props pass a function prop to render something.
How do you handle forms and validation?
- Use controlled components or form libraries (Formik, React Hook Form) for complex validation.
What is server-side rendering (SSR) and how does it differ from CSR?
- SSR renders HTML on the server for initial load/SEO; CSR renders in the browser after JS loads.
How do you do code splitting in React?
- Use dynamic import() and React.lazy with Suspense or bundler-level splitting.
Explain authentication flows in a React app.
- Use tokens or cookies, store securely (prefer httpOnly cookies), and protect routes with guards or HOCs.
How do you debug performance issues?
- Use React DevTools profiler, browser performance tab, and measure render counts and expensive renders.
Describe a common memory leak in React and how to fix it.
- Setting state after unmount by async callbacks; fix with cleanup in useEffect or abort controllers.
What is the purpose of refs in React?
- Refs access DOM nodes or persist mutable values without causing re-renders.
How would you implement pagination or infinite scroll in React?
- Use intersection observers or scroll listeners, fetch next pages lazily, and manage loading state.
How to handle accessibility (a11y) in React?
- Use semantic HTML, ARIA attributes where necessary, keyboard navigation, and tools like axe or Lighthouse.

Takeaway: Memorize concise answers and be prepared to code short examples or explain trade-offs—both prove depth and practical experience.

Citations: For deeper question banks and examples, see resources like the React interview lists on CoderPad’s React interview questions and curated Q&A on GeeksforGeeks for React.

How should I practice React coding exercises and fix-the-code interview tasks?

Direct answer: Practice by solving targeted coding tasks (components, state, events, API calls) and doing timed “fix-the-bug” exercises while explaining your reasoning aloud.

Expand: Start with small problems: build a counter, controlled input, or a Todo list. Move to intermediate tasks: debounced search, paginated list, or optimizing a large list with virtualization. For debugging exercises, replicate the bug locally, add console logs or breakpoints, and use React DevTools to inspect props and component tree. Learn to explain trade-offs: why you chose useReducer over multiple useState hooks or when to lift state.

Example: Given a list re-rendering on every parent update, show how React.memo + useCallback reduces unnecessary renders and measure it using the Profiler.

Timeboxed kata: 20–40 minutes per problem.
Mock interviews with peers or platforms like CoderPad.
Read failing tests or code comments first to find intent.
Practice tips:

Takeaway: Frequent, explained practice of coding problems builds the muscle memory and communication skills interviewers look for.

What advanced React topics should I expect for senior roles?

Direct answer: Expect questions on performance optimization, reconciliation internals, concurrent features, complex state architecture, and scaling patterns.

Expand: Senior interviews probe your ability to architect apps and diagnose issues. Be ready to explain the reconciliation algorithm, fiber architecture, and how React schedules updates. Discuss advanced hooks usage, custom hooks patterns, memoization strategies, and when to optimize. Know server-side rendering nuances (Next.js patterns), streaming SSR, and hydration pitfalls. Demonstrate familiarity with profiling tools, build optimization (tree-shaking, lazy loading), and state management trade-offs (Context vs Redux vs Zustand).

Example deep-dive: Walk an interviewer through reducing Time to Interactive: code-split routes, defer nonessential scripts, memoize expensive computations, and lazy-load images.

Takeaway: For senior roles, emphasize systems thinking, measurable performance improvements, and trade-offs rather than just API knowledge.

Citations: For deeper advanced topic reading, review comprehensive collections like GreatFrontend’s interview questions from ex-interviewers.

How do I prepare for behavioral and interview-process questions for React roles?

Direct answer: Use structured stories (STAR: Situation, Task, Action, Result), rehearse role-specific examples, and learn the common interview formats at target companies.

Expand: Behavioral competence matters: teamwork, conflict resolution, code ownership, and learning from mistakes. Prepare 6–8 STAR stories tailored to technical work: leading a refactor, resolving a production bug, mentoring juniors, shipping a performance fix, or handling architecture trade-offs. Know the company’s interview stages: phone screen, coding interview, system design (for senior roles), and onsite behavioral rounds. Practice explaining technical impact in business terms (e.g., reduced load time by X% leading to Y outcomes).

Resources: Curated behavioral question lists and STAR examples can sharpen answers and delivery. See repositories of behavioral patterns and examples for engineers and interview playbooks.

Takeaway: Structured, metric-backed stories make behavioral answers memorable and show your operational value.

Citations: Check practical behavioral frameworks at GitHub’s awesome-behavioral-interviews and technique guides like the one on I Got A Offer’s behavioral interview advice.

How do React interview questions differ by experience level (junior, mid, senior)?

Direct answer: Juniors face fundamentals and small coding tasks; mid-level developers get integration and architecture problems; seniors face system design, performance, and leadership scenarios.

Junior: Expect questions about JSX, state vs props, basic hooks, and small implementation tasks (build a form, event handler). Emphasize correctness and clarity.
Mid-level: Expect component design, state management patterns, async data fetching, and code quality discussions (testing). You’ll be asked to extend features and optimize.
Senior: Expect architecture discussions (scaling components, CI/CD impacts), performance bottlenecks, cross-team communication, and hiring/mentorship examples. System design questions may include frontend architecture for large-scale apps, SSR strategies, and observability.
Expand:

Junior: Build several small apps, read official docs, and practice debugging.
Mid: Contribute to larger projects, learn state patterns, unit/integration tests, and performance tuning.
Senior: Lead architectural design, present case studies of technical decisions, and mentor others.
Preparation suggestions by level:

Takeaway: Tailor study time to role expectations and prepare examples showing impact corresponding to your experience level.

How Verve AI Interview Copilot Can Help You With This

Verve AI acts as a quiet, context-aware co‑pilot during prep and live interviews — analyzing the question, suggesting structured phrasing (STAR, CAR, or technical step-by-step), and offering concise code snippets or debugging steps. It helps you stay calm by providing on-the-fly outlines and follow-up prompts so you can answer clearly and confidently. Use Verve AI Interview Copilot in mock interviews to practice phrasing and time your responses; Verve AI also suggests improvements to answers and highlights gaps to study next.

What Are the Most Common Questions About This Topic

Q: Can Verve AI help with behavioral interviews?
A: Yes — it uses STAR and CAR frameworks to guide real-time answers.

Q: How long should I study React before interviewing?
A: Varies by role—2–3 months basic prep, longer for senior-level mastery.

Q: Best way to practice React coding problems?
A: Timeboxed exercises, pair programming, and live mocks on platforms like CoderPad.

Q: Should I memorize API signatures?
A: Understand patterns; memorize common hooks and lifecycle equivalents.

Q: How important is testing knowledge for React roles?
A: Very — unit and integration tests are often required, especially mid/senior roles.

Q: Are performance optimizations commonly asked?
A: Yes for mid and senior interviews—know profiling tools and memoization techniques.

Conclusion

Recap: Cover fundamentals, practice coding and debugging, prepare advanced architecture topics if you’re targeting senior roles, and rehearse structured behavioral stories. Use real coding platforms, the React docs, and curated question lists to build depth.

Final note: Preparation and structured answers create confidence. When you want live, context-aware help in practice or during interviews, try Verve AI Interview Copilot to feel confident and prepared for every interview.