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Top 81 React.js Interview Questions & Answers (2026)

81 Questions 39 Beginner 28 Intermediate 14 Advanced

About React.js

React is the most popular JavaScript library for building user interfaces, developed and maintained by Meta. Used by Facebook, Instagram, Airbnb, Netflix, Dropbox, and tens of thousands of companies, React has transformed how web interfaces are built. The React ecosystem (Next.js, React Query, Zustand, React Router) is the dominant stack for modern web applications.

What to Expect in a React.js Interview

React interviews cover component architecture, hooks (useState, useEffect, useContext, useRef, useMemo, useCallback, custom hooks), state management patterns, React 18 features (concurrent rendering, Suspense, useTransition), performance optimization (memoization, virtualization, code splitting), and testing strategies.

How to Use This Guide

React interview questions frequently involve writing or debugging code. As you read through answers, implement the examples in a sandbox like StackBlitz or CodeSandbox. Hooks — especially their rules and common pitfalls — account for the majority of React interview questions at every level.

Curated by Tech Baithak Editorial Team · Last updated: May 2026

Beginner 39 questions

Core concepts every React.js developer must know.

01 What is React? 02 What is JSX? 03 What is the Virtual DOM? 04 What is a React component? 05 What are props in React? 06 What is state in React? 07 What is the useState hook? 08 What is the useEffect hook? 09 What is the difference between controlled and uncontrolled components? 10 What is the useRef hook? 11 What is the useContext hook? 12 What is prop drilling and how do you solve it? 13 What are React keys and why are they important? 14 What is the React reconciliation algorithm? 15 What are React fragments? 16 What is conditional rendering in React? 17 What is the difference between state and props? 18 What is lifting state up in React? 19 What is the useReducer hook? 20 What is the useMemo hook? 21 What is the useCallback hook? 22 What is React.memo? 23 What are React lifecycle methods? 24 What is an error boundary in React? 25 What is the difference between class components and function components? 26 What is the children prop in React? 27 What is React Strict Mode? 28 What is a higher-order component (HOC) in React? 29 What are render props in React? 30 What is the React context API? 31 What is lazy loading in React? 32 What is Suspense in React? 33 What is React.StrictMode double invocation? 34 What is event handling in React? 35 What is form handling in React? 36 What is the difference between React.Component and React.PureComponent? 37 What is the reconciliation algorithm and Fiber? 38 What is the difference between defaultProps and default parameter values? 39 What is the difference between findDOMNode and ref?

Intermediate 28 questions

Practical knowledge for developers with hands-on experience.

01 What are custom hooks in React? 02 What are the rules of hooks in React? 03 What is the useLayoutEffect hook and how does it differ from useEffect? 04 What is the useImperativeHandle hook? 05 What is the useDeferredValue hook in React 18? 06 What is useTransition in React 18? 07 What is React Server Components? 08 What is the difference between useState and useReducer? 09 How does React batch state updates? 10 What is React Concurrent Mode? 11 What are React portals? 12 What is the useId hook in React 18? 13 What is the useSyncExternalStore hook? 14 What is React.forwardRef and when do you use it? 15 What is the difference between React.cloneElement and React.createElement? 16 What are compound components in React? 17 What is the React.Children API? 18 What is the purpose of shouldComponentUpdate? 19 What is server-side rendering (SSR) in React? 20 What is hydration in React? 21 What is code splitting in React? 22 What is the difference between useEffect cleanup and componentWillUnmount? 23 What is memoization in React and how do you implement it? 24 What is the Context API performance issue and how do you fix it? 25 What are React Portals use cases? 26 What is the React Profiler API? 27 What is the difference between client-side routing and server-side routing? 28 What is React Testing Library?

Advanced 14 questions

Deep expertise questions for senior and lead roles.

01 How does React's reconciliation algorithm handle keys? 02 What is the React Fiber architecture in depth? 03 What are React rendering optimizations beyond React.memo? 04 How do you implement an undo/redo system in React? 05 What are React's concurrent features and how do Transitions work? 06 How does React handle forms at scale? 07 What is the React Compiler (React Forget)? 08 What are the patterns for sharing logic between components in React? 09 How does React handle accessibility (a11y)? 10 What is React's use() hook in React 19? 11 What is the React Activity (Offscreen) API? 12 How does React Server Actions work in React 19? 13 What are micro-frontends in the context of React? 14 What is state management at scale and which library should you choose?

Back to All Topics 81 questions total