React.js and Next.js have rapidly become the cornerstone technologies for building powerful, scalable, and user-friendly web applications. As companies increasingly demand modern full-stack skills, proficiency in React and Next.js is becoming a must-have for frontend and full-stack developers alike.
In this guide, we’ve carefully compiled the top 50 React.js and Next.js interview questions and answers that hiring managers are actively asking in 2025. Whether you’re a fresher stepping into your first React job or an experienced engineer aiming for a senior developer position, this resource will equip you with the essential knowledge to succeed.
Let’s dive deep and master the core concepts and real-world practicalities of React and Next.js!
Table of Contents
React.js Basic Interview Questions
1. What is React.js?
Answer: React.js is an open-source JavaScript library developed by Facebook for building fast and interactive user interfaces for web and mobile applications. It uses a component-based architecture and enables developers to create reusable UI components efficiently.
2. What are the main features of React?
Answer: Key features include:
- JSX (JavaScript XML)
- Component-Based Architecture
- Virtual DOM for faster rendering
- Unidirectional Data Flow
- Hooks for state and lifecycle management
3. What is JSX?
Answer: JSX stands for JavaScript XML. It allows developers to write HTML structures directly within JavaScript code, making the code easier to understand and maintain.
4. What are components in React?
Answer: Components are the building blocks of a React application. They are JavaScript functions or classes that accept inputs (props) and return React elements describing what should appear on the screen.
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5. What is the difference between Functional and Class components?
Answer:
- Functional Components: Simple functions that return JSX. Introduced hooks to manage state and lifecycle.
- Class Components: ES6 classes that extend
React.Componentand can manage state and lifecycle using methods.
6. What is the Virtual DOM in React?
Answer: The Virtual DOM is an in-memory representation of the real DOM. React uses it to optimize updates by comparing the virtual DOM with a previous snapshot and updating only the parts that changed.
7. What are props in React?
Answer: Props (short for properties) are read-only inputs passed from parent components to child components to configure them or pass dynamic data.
8. What is state in React?
Answer: State is a built-in React object used to contain data or information about a component. State changes trigger UI updates dynamically.
9. What is the difference between state and props?
Answer:
- Props: Passed from parent to child components. Immutable inside the child.
- State: Managed within the component and can change over time based on user interaction or other factors.
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10. What are lifecycle methods in React?
Answer: Lifecycle methods are functions that get called at different stages of a component’s existence, such as mounting, updating, and unmounting. Examples include
componentDidMount(), shouldComponentUpdate(), and componentWillUnmount().11. What is useState Hook?
Answer:
useState is a React Hook that allows functional components to maintain internal state without converting them to class components.12. What is useEffect Hook?
Answer:
useEffect lets you perform side effects (data fetching, DOM manipulation, etc.) inside functional components. It replaces lifecycle methods like componentDidMount and componentDidUpdate.13. What is lifting state up in React?
Answer: Lifting state up refers to moving shared state to a common ancestor component to synchronize the state across multiple child components.
14. What is React Router?
Answer: React Router is a standard routing library for React applications that allows navigation between different views or pages without refreshing the browser.
15. What is conditional rendering in React?
Answer: Conditional rendering allows React components to render different UI elements based on certain conditions using JavaScript operators like
if, ternary, or logical operators.Related Read: 100+ Node.js Interview Questions and Answers [ 2025 ]
React.js Intermediate Interview Questions
16. What is the Context API in React?
Answer: The Context API allows you to share global state or values across a React application without prop drilling. It consists of a Context object created with
React.createContext() and accessed using the Provider and useContext hook.17. What is useContext Hook in React?
Answer:
useContext is a Hook that simplifies accessing data from a Context provider. It avoids the need to wrap components manually and allows direct consumption of context values inside functional components.18. What is useReducer Hook in React?
Answer:
useReducer is a React Hook used for managing complex state logic by dispatching actions. It’s ideal when the next state depends heavily on the previous state or when dealing with multiple sub-values in a state object.19. What is the difference between useState and useReducer?
Answer:
- useState: Simpler for basic state management.
- useReducer: Preferred for complex state transitions, multiple states, or centralized state management using actions and reducers.
20. What are controlled and uncontrolled components in React?
Answer:
- Controlled Components: Form elements like input or select whose values are controlled by React state.
- Uncontrolled Components: Form elements that manage their own state internally and rely on refs to access their current values.
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21. What is the useRef Hook in React?
Answer:
useRef returns a mutable ref object whose .current property persists for the full lifetime of the component. It’s commonly used for accessing DOM nodes or storing persistent values across renders without causing re-renders.22. What is memoization in React?
Answer: Memoization is an optimization technique where expensive function results are cached so they are not recalculated unless inputs change. In React, functions like
React.memo(), useMemo(), and useCallback() provide memoization.23. How does React.memo work?
Answer:
React.memo is a higher-order component that prevents re-rendering if props haven’t changed. It’s used to optimize performance for functional components by memoizing the rendered output.24. What is useCallback Hook?
Answer:
useCallback returns a memoized version of the callback function that only changes if one of its dependencies changes. It’s useful when passing callbacks to optimized child components.25. What is useMemo Hook?
Answer:
useMemo returns a memoized value. It recomputes the value only when dependencies change, preventing unnecessary expensive calculations on every render.Related Read: Front End Developer Interview Questions and Answers [ 2025 ]
26. What is code splitting in React?
Answer: Code splitting is the practice of breaking up a large bundle into smaller chunks so they can be loaded on demand. React supports code splitting through dynamic
import() and libraries like React.lazy and Loadable Components.27. What is React.lazy and Suspense?
Answer:
- React.lazy: Allows dynamic import of components, enabling code splitting at the component level.
- Suspense: Provides a declarative way to “wait” for some code to load before rendering a fallback UI (e.g., a spinner).
28. How can you optimize the performance of a React application?
Answer:
- Use React.memo, useCallback, and useMemo
- Code splitting with dynamic imports
- Windowing or list virtualization using libraries like react-window
- Lazy loading images and components
- Optimizing bundle size and dependencies
29. What is error boundary in React?
Answer: Error Boundaries are React components that catch JavaScript errors anywhere in their child component tree and display a fallback UI instead of crashing the application. Implemented using
componentDidCatch and getDerivedStateFromError.30. What is a Higher-Order Component (HOC) in React?
Answer: A Higher-Order Component (HOC) is a function that takes a component and returns a new component with enhanced behavior. Commonly used for reusing logic across multiple components.
Related Read: JavaScript ES6+ Features You Must Know for Interviews in [ 2025 ]
Next.js Fundamentals Interview Questions
31. What is Next.js?
Answer: Next.js is a React framework that enables server-side rendering, static site generation, and dynamic routing out-of-the-box. It simplifies building production-ready React applications with performance optimizations built-in.
32. What are the main features of Next.js?
Answer:
- Server-Side Rendering (SSR)
- Static Site Generation (SSG)
- API Routes
- Built-in CSS and Sass support
- Image Optimization
- Incremental Static Regeneration (ISR)
33. What is the difference between SSR and SSG in Next.js?
Answer:
- SSR (Server-Side Rendering): HTML is generated at request time.
- SSG (Static Site Generation): HTML is generated at build time, resulting in faster load times.
34. What is getStaticProps in Next.js?
Answer:
getStaticProps is an async function used in Next.js pages to fetch data at build time. It enables static site generation with dynamic data.Related Read: HTML and CSS Interview Questions & Answers [ 2025 ]
35. What is getServerSideProps in Next.js?
Answer:
getServerSideProps is an async function used to fetch data on every request. It enables server-side rendering where fresh data is needed at runtime.36. What is getStaticPaths in Next.js?
Answer:
getStaticPaths works with getStaticProps to generate dynamic routes during the build process. It defines a list of paths that need to be statically generated.37. How does file-based routing work in Next.js?
Answer: Next.js uses a file-system-based router where the file structure under the
/pages directory automatically maps to corresponding routes in the application.38. How do you create dynamic routes in Next.js?
Answer: Dynamic routes are created by adding square brackets to filenames inside the
/pages directory, such as [id].js, to capture dynamic segments in the URL.39. What are API Routes in Next.js?
Answer: API Routes allow building backend endpoints directly in a Next.js app under the
/pages/api directory without needing a separate server.40. How do you perform image optimization in Next.js?
Answer: Next.js provides a built-in
next/image component that automatically optimizes images on-demand for faster load times and better performance, including resizing, lazy loading, and serving in modern formats like WebP.Related Read: Full Stack Developer Skills You Can Add to Your Resume
Conclusion
If you’re preparing for a React.js or Next.js interview in 2025, you’re already investing in two of the most in-demand and future-proof skills in tech. Frontend and full-stack development are evolving fast — and companies aren’t just hiring coders anymore. They’re looking for engineers who understand architecture, performance, and user experience.
Mastering the core concepts of React.js and Next.js will give you an edge that many candidates still lack. And it’s not just about knowing the syntax — it’s about knowing when, where, and why to use these technologies.
Our advice? Go beyond theory. Build small projects. Debug stubborn bugs. Get your hands dirty with server-side rendering, dynamic routes, and performance tuning. Interviews today often mirror the real-world challenges developers face, and showing practical thinking can set you apart.
We hope these React.js and Next.js interview questions help you think deeper, answer smarter, and ultimately land the opportunity you’re aiming for.
FAQs on React.js and Next.js Interviews
1. How important is Next.js knowledge for React developers?
Answer: Very important. Next.js extends React’s capabilities by adding server-side rendering, static generation, and advanced performance optimizations that many modern projects now require.
2. Which companies actively hire React.js and Next.js developers?
Answer: Companies like Netflix, TikTok, Uber, GitHub, Shopify, and many startups prioritize candidates with strong React.js and Next.js expertise.
3. What is the learning curve for Next.js if you know React?
Answer: The learning curve is moderate. If you know React basics, picking up Next.js (routing, SSR, SSG, API routes) is relatively straightforward.
4. Can I use Next.js without a backend server?
Answer: Yes, Next.js can serve fully static websites using Static Site Generation (SSG) without a custom backend. For dynamic functionalities, you can leverage API routes within Next.js itself.
5. How to prepare for coding rounds in React interviews?
Answer: Practice common coding challenges involving React Hooks, component design, state management patterns, form handling, and real-world small projects.
6. What is better for SEO: React or Next.js?
Answer: Next.js is superior for SEO because it provides server-side rendering (SSR) and static generation (SSG), allowing better crawlability for search engines compared to client-side-only React apps.
7. Is Next.js suitable for large enterprise applications?
Answer: Absolutely. Next.js scales well and supports enterprise-grade features like internationalization, incremental builds, middleware, and advanced caching strategies.
8. What additional skills complement React and Next.js expertise?
Answer: Skills like TypeScript, GraphQL, REST APIs, serverless architectures, CI/CD pipelines, and performance optimization greatly enhance a React and Next.js developer’s profile.
