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?
2. What are the main features of React?
- JSX (JavaScript XML)
- Component-Based Architecture
- Virtual DOM for faster rendering
- Unidirectional Data Flow
- Hooks for state and lifecycle management
3. What is JSX?
4. What are components in React?
Related Read: Coding and Programming Interview Questions [ 2025 ]
5. What is the difference between Functional and Class components?
- Functional Components: Simple functions that return JSX. Introduced hooks to manage state and lifecycle.
- Class Components: ES6 classes that extend
React.Component
and can manage state and lifecycle using methods.
6. What is the Virtual DOM in React?
7. What are props in React?
8. What is state in React?
9. What is the difference between state and props?
- 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.
Related Read: Top 10 Programming Languages to Learn in 2025
10. What are lifecycle methods in React?
componentDidMount()
, shouldComponentUpdate()
, and componentWillUnmount()
.11. What is useState Hook?
useState
is a React Hook that allows functional components to maintain internal state without converting them to class components.12. What is useEffect Hook?
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?
14. What is React Router?
15. What is conditional rendering in React?
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?
React.createContext()
and accessed using the Provider
and useContext
hook.17. What is useContext Hook in React?
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?
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?
- 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?
- 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.
Related Read: 100+ JavaScript Interview Questions and Answers [ 2025 ]
21. What is the useRef Hook in React?
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?
React.memo()
, useMemo()
, and useCallback()
provide memoization.23. How does React.memo work?
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?
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?
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?
import()
and libraries like React.lazy and Loadable Components.27. What is React.lazy and Suspense?
- 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?
- 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?
componentDidCatch
and getDerivedStateFromError
.30. What is a Higher-Order Component (HOC) in React?
Related Read: JavaScript ES6+ Features You Must Know for Interviews in [ 2025 ]
Next.js Fundamentals Interview Questions
31. What is Next.js?
32. What are the main features of Next.js?
- 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?
- 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?
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?
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?
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?
/pages
directory automatically maps to corresponding routes in the application.38. How do you create dynamic routes in Next.js?
/pages
directory, such as [id].js
, to capture dynamic segments in the URL.39. What are API Routes in Next.js?
/pages/api
directory without needing a separate server.40. How do you perform image optimization in Next.js?
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.