Top 40 React Interview Questions with Answers Updated (2025)

The intent behind this question is to assess your understanding of React's purpose and basic concept.

Sample Answer:

React is a JavaScript library developed by Facebook for building user interfaces, especially single-page applications. It helps Developers create reusable UI components and efficiently update the DOM using a virtual DOM. React promotes component-based architecture and a unidirectional data flow, making applications easier to manage and scale.

This question assesses your knowledge of event handling in React components.

Sample Answer:

Events in React are created using camelCase syntax and passed as props. For example, I handle a button click like this:

The handleClick function contains the event logic. React uses synthetic events to normalise event behaviour across browsers.

This question will evaluate your familiarity with what makes React unique and effective.

Sample Answer:

Key features of React include the virtual DOM, reusable components, JSX syntax, unidirectional data flow, and lifecycle methods. It also supports hooks for functional component state and side effects. React's ability to efficiently update and render only changed components improves performance.

The intent of this question is to check your understanding of how React identifies and manages dynamic lists.

Sample Answer:

Keys in React are unique identifiers used when rendering lists of elements. They help React detect which items have changed, been added, or removed. Without keys, React may re-render entire lists unnecessarily, which can reduce efficiency. Keys should be stable, unique, and consistent.

This question assesses your knowledge of rendering dynamic data collections. 

Sample Answer:

I can create a list in React by using the map() function to iterate across an array and return JSX for each item. Each element must include a unique key. For example:

The intent of this question is to gauge your understanding of React class component structure.

Sampe Answer:

In class components, the render() method is used to describe what the UI should look like. It returns React elements (JSX) that React then renders to the DOM. It gets called during mounting and updating to reflect state or prop changes.

This question will help assess your knowledge of how React handles operations outside rendering.

Sample Answer:

Side effects in React include data fetching, subscriptions, manual DOM manipulation, timers, and logging. These operations are handled using useEffect in functional components or lifecycle methods in class components. They are separated from rendering to maintain predictable UI behaviour.

The intent behind this question is to see if you can identify React’s drawbacks alongside its strengths.

Sample Answer:

For beginners React has a steep learning curve, especially with JSX and hooks. It only handles the view layer, requiring other libraries for routing or state management. Also, frequent updates can lead to compatibility issues and a need for constant learning.

This question will test your understanding of how state is managed in class components.

Sample Answer:

this.setState is used in class components to update the component’s state. It schedules a re-render and merges the new state with the current state. Unlike direct state mutation, setState ensures that the component behaves predictably and updates efficiently.

The purpose behind this question is to assess your understanding of how React describes UI components.

Sample Answer:

JSX stands for JavaScript XML. It helps me write HTML-like syntax in JavaScript, which gets transformed into React elements. JSX makes the code more readable and concise but must be transpiled using tools like Babel to become browser-compatible.

Your answer to this question will help the interviewer evaluate your understanding of JSX compilation.

Sample Answer:

Browsers don’t understand JSX directly. During the build process, JSX is transpiled by tools like Babel into React.createElement() calls, which return JavaScript objects representing DOM nodes. These objects are then rendered into actual DOM elements by React’s renderer.

The intent behind this question is to assess your knowledge of React’s performance optimisation strategy.

Sample Answer:

The virtual DOM is an in-memory representation of the real DOM. When state changes, React updates the virtual DOM first, compares it with the previous version using a diffing algorithm, and applies only the changed parts to the real DOM. This boosts performance.

The purpose of this question is to evaluate your understanding of React’s position in the web framework landscape.

Sample Answer:

React is a library focused solely on building UIs, while Angular is a full-fledged MVC framework. React uses JSX and unidirectional data flow, whereas Angular uses TypeScript and two-way binding. While React is flexible, it requires additional libraries for routing and state.

This question is designed to test your knowledge of component Data Management.

Sample Answer:

Props are read-only inputs passed from parent to child components, while state is a local, mutable data store managed within a component. Props enable component reuse, while state handles dynamic data that affects rendering and interaction within the component.

This question will assess your knowledge of functional component capabilities.

Sample Answer:

React Hooks are important functions that allow me to use state and lifecycle features in functional components. Common hooks include useState, useEffect, useContext, and useRef. They simplify component logic, reduce boilerplate, and eliminate the need for class components in many cases.

The intent behind this question is to test your understanding of React's data flow.

Sample Answer:

One-way data binding means that data flows in a single direction, from parent to child components via props. This ensures predictable behaviour, making it easier to debug and maintain. Child components cannot modify parent data directly, encouraging better separation of concerns.

This question is posed to evaluate your knowledge of state management and prop drilling solutions.

Sample Answer:

The Context API enables me to share state across components without passing props manually at every level. It’s useful for global data like themes, authentication, or user preferences. It includes React.createContext, Provider, and useContext to distribute and consume data efficiently.

The purpose behind asking this question is to test your understanding of handling raw HTML content.

Sample Answer:

dangerouslySetInnerHTML is a React attribute used to inject raw HTML into components. It should be used cautiously as it bypasses React’s sanitisation and can expose my app to XSS attacks if the HTML is not properly validated or escaped.

This question will assess your ability to display content based on conditions.

Sample Answer:

Conditional rendering in React allows me to display components or elements based on a condition. This is done using JavaScript logical operators or ternary expressions directly in JSX. For example: {isLoggedIn ? : } renders components based on user state.

The intent behind this question is to assess your understanding of how state is modified in React components.

Sample Answer:

In class components, I update state using this.setState(), which schedules a re-render and merges the new state with the old one. In functional components, I use the useState hook's updater function, like setCount(count + 1). Direct state mutation is avoided for consistent UI rendering.

This question is designed to evaluate your ability to implement navigation in a React application.

Sample Answer:

I create a switching component using React Router by defining Routes and Route components. Each route corresponds to a different component or page. The Switch or updated Routes element renders only the first match, helping me display the correct page based on the URL.

The purpose behind asking this question is to check your knowledge of client-side routing in React applications.

Sample Answer:

React Router is a standard library for handling routing in React. It enables navigation between views of different components, changing the URL without reloading the page. It uses components like BrowserRouter, Routes, and Route to manage navigation in single-page applications.

This question will help your interviewer test your understanding of state management and whether hooks can be a Redux alternative.

Sample Answer:

React Hooks, like useState and useContext, can replace Redux for small to medium applications with less complex state needs. However, for larger apps requiring centralised, predictable state management and middleware, Redux remains more powerful and scalable than using hooks alone.

This question is posed to assess your understanding of React’s event handling mechanism.

Sample Answer:

Synthetic events are React’s cross-browser wrapper around native DOM events. They normalise event behaviour so I don't have to handle inconsistencies between browsers. React automatically pools and reuses these events for performance, although this behaviour can be opt-out in recent versions.

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Your answer to this question will help assess your understanding of organising and reusing code effectively in React.

Sample Answer:

I modularise code by splitting my React application into reusable components, each in its own file.  can further use utility functions, custom hooks, and separate folders for routes, assets, and services. This improves readability, scalability, and maintainability of my codebase.

The purpose behind asking this question is to check your knowledge of returning multiple elements from a component.

Sample Answer:

React Fragments let me group multiple elements without adding extra nodes to the DOM. Instead of a wrapper

This question will help test your understanding of development tools and best practices in React.

Sample Answer:

React.StrictMode is a wrapper component that helps identify potential issues in an app during development. It highlights unsafe lifecycles, legacy APIs, and unexpected side effects. It doesn’t render anything to the DOM and is used only for development, not production.

My response to this question will help the interviewer assess how well I manage user input and form state in React.

Sample Answer:

Forms in React are usually handled using controlled components, where input values are bound to state via useState or this.state. Changes are tracked with onChange events, allowing real-time validation and data handling. Libraries like Formik can simplify complex form logic.

The intent behind this question is to evaluate your awareness of best practices for performance.

Sample Answer:

React code can be optimised using techniques like memoisation with React.memo, useMemo, and useCallback. Lazy loading components, using keys effectively in lists, and avoiding unnecessary re-renders also help. Tools like React Profiler assist in identifying performance bottlenecks.

This question will help your interviewer to assess how well you understand communication between unrelated components.

Sample Answer:

Sibling components can share data through a common parent by lifting state up or using a global store like Redux or Context API. React Router itself handles navigation but not data sharing, so the state must be maintained outside the route-specific components.

This will help you showcase your understanding of Form State Management styles.

Sample Answer:

Controlled components are form elements whose value is managed by React state. Uncontrolled components rely on the DOM to maintain their state using refs. Controlled components offer better control and validation, while uncontrolled components are simpler but harder to manage for complex logic.

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This question will help the interviewer gauge how well you understand code reuse patterns.

Sample Answer:

HOC refers to a function that takes a component and returns a new component with improved capabilities. It's often used to share logic across components, like access control or theming. HOCs follow the pattern: const Enhanced = withLogic(Component);.

Your response to this question will give the interviewer a sense of your understanding of web security and API interaction.

Sample Answer:

Cross-origin Resource Sharing is a security feature which restricts requests between different origins. React apps often call APIs from different domains, and if the server doesn't allow it, I’ll get a CORS error. The server must set appropriate headers to allow cross-origin requests.

With this question, the interviewer wants to verify your ability to use React state and events.

Sample Answer:

The intent behind this question is to assess your understanding of React’s motivation.

Sampel Answer:

React aimed to solve problems like complex data flow, tight coupling between UI and logic, and inefficient DOM updates in traditional MVC. It introduced a component-based architecture with unidirectional data flow and a virtual DOM, which simplified UI development and improved performance.

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With this question, your interviewer will gauge your grasp of Redux architecture.

Sample Answer:

Data in Redux flows in a unidirectional cycle: actions are dispatched, reducers handle the actions to produce new state, and the updated state is passed to components via connect() or useSelector. Middleware can intercept actions for side effects like async calls.

The intent of this question is to make you compare functional and class components.

Sample Answer:

Hooks offer cleaner, more readable code and better performance in many cases due to reduced boilerplate. They enable reusing logic without nesting or inheritance. However, poor hook usage (like overuse of useEffect) can harm performance if not handled carefully, just like class components.

With this question, the interviewer will evaluate your foundational understanding of Redux.

Sample Answer:

Redux is based on three principles:

1) Single Source of Truth: The state is stored in one central object.

2) State is Read-only: State can only be changed by dispatching actions.

3) Pure Functions: Reducers specify how the state changes based on actions.

The intent of this question is to test your understanding of performance optimisations.

Sample Answer:

A PureComponent in React is a component that does a shallow comparison of props and state to determine if it should re-render. If neither has changed, React skips re-rendering, improving performance. It’s mainly used to prevent unnecessary renders in class components.

With this question, the interviewer will assess your understanding of modern React development.

Sample Answer:

Hooks allow functional components to use state and lifecycle features without writing classes. They lead to more concise and modular code. While class-based components are still supported, hooks simplify reusability and logic sharing, making them the preferred choice in modern React development.