React Interview Questions and Answers are essential for anyone preparing for React job interviews. React is a widely used JavaScript library for building user interfaces, and understanding its core concepts can help you secure a role as a frontend developer.
In this guide, we have compiled a list of React Interview Questions and Answers covering fundamental and advanced topics such as JSX, Virtual DOM, state and props, React hooks, performance optimization, and state management with Redux. Whether you’re a beginner or an experienced developer, this resource will help you confidently tackle React-related interview questions and improve your understanding of best practices.
1. What are the key features of React?
Answer:
- React uses JSX for writing UI elements. Moreover, it has a Virtual DOM for efficient updates.
- Uses a component-based architecture.
- Follows a unidirectional data flow for predictable state management.
- Provides hooks for managing state and lifecycle in functional components.
2. What is the difference between functional and class components?
Answer:
- Functional components are simple JavaScript functions. In addition, they use hooks for state and side effects.
- Class components use lifecycle methods and this.state for state management.
- Functional components are preferred due to better performance and readability.
3. What is JSX and why is it used in React?
Answer:
- JSX is a syntax extension of JavaScript that allows writing HTML-like code inside JavaScript.
- It improves code readability and makes it easier to visualize UI structure.
4. What is the Virtual DOM and how does it work?
Answer:
- The Virtual DOM is a lightweight copy of the real DOM. As a result, React updates the Virtual DOM first.
- This process improves performance and minimizes unnecessary re-renders.
5. What are props in React?
Answer:
- Props (short for properties) are read-only data passed from a parent component to a child component.
- They allow components to be dynamic and reusable.
6. What is state in React?
Answer:
- State is a mutable object that holds component-specific data.
- When the state changes, the component re-renders with the new data.
7. What is the difference between state and props?
Answer:
- Props are immutable and used to pass data from a parent to a child component.
- State is mutable and managed within the component itself.
8. What is React Router?
Answer:
- React Router is a navigation library that enables client-side routing in React applications.
- It allows switching between views without refreshing the page.
9. What is the difference between controlled and uncontrolled components?
Answer:
- Controlled components manage form data using React state (useState).
- Uncontrolled components store form data in the actual DOM (using ref).
10. What are React hooks?
Answer:
- Hooks allow functional components to use state and lifecycle features.
- Common hooks include useState, useEffect, useContext, useMemo, and useCallback.
11. What is useEffect and how does it work?
Answer:
- useEffect is a hook that manages side effects in functional components, such as data fetching, event listeners, or subscriptions.
- It can run on mount, update, or unmount depending on dependencies.
12. What is useMemo and when should you use it?
Answer:
- useMemo optimizes performance by memoizing expensive computations.
- It prevents unnecessary recalculations on every render.
13. What is useCallback and how is it different from useMemo?
Answer:
- useCallback memoizes a function so that it does not get re-created on every render.
- useMemo memoizes a computed value rather than a function.
14. What is React Context API?
Answer:
- The Context API is a state management solution that allows passing global data without prop drilling.
- It is useful for themes, authentication, and global settings.
15. What is Redux and why is it used?
Answer:
- Redux is a state management library used for managing application-wide state.
- It follows a unidirectional data flow and consists of actions, reducers, and a store.
16. What is React.memo and how does it help performance?
Answer:
- React.memo is a higher-order component that prevents unnecessary re-renders by memoizing a component.
- It only re-renders if the component’s props change.
17. What are Higher-Order Components (HOCs)?
Answer:
- HOCs are functions that wrap components to add additional functionality.
- They enable code reuse, such as authentication handling and logging.
18. What is lazy loading in React?
Answer:
- Lazy loading is a performance optimization technique that defers loading components until they are needed.
- It reduces the initial load time of an application.
19. What is reconciliation in React?
Answer:
- Reconciliation is React’s diffing algorithm that updates only the changed parts of the real DOM efficiently.
- It compares the new Virtual DOM with the previous one and updates only necessary elements.
20. What is Concurrent Mode in React?
Answer:
- Concurrent Mode is an experimental feature that improves rendering performance by allowing React to work on multiple UI updates at the same time.
- It enhances responsiveness and user experience.
Learn more about React and explore advanced concepts on our websitte DesignWithRehana platform while also checking out in-depth video tutorials on our YouTube channel.