React.js is one of the most sought-after JavaScript libraries for building dynamic and responsive user interfaces. As the demand for React.js professionals grows, being well-prepared for interviews is crucial. Here are some of the top React.js interview questions and answers to help you ace your next interview.
1. What is React.js?
React.js is a JavaScript library developed by Facebook for building user interfaces, particularly for single-page applications. It allows developers to create reusable UI components and manage the view layer of an application efficiently. A well-structured React js course in Pune covers fundamental to advanced concepts,
2. What are the features of React.js?
JSX: A syntax extension that combines HTML with JavaScript.
Virtual DOM: Improves performance by minimizing direct manipulation of the real DOM.
Component-Based Architecture: Encourages reusable and maintainable code.
Unidirectional Data Flow: Ensures better data control and debugging.
3. What is the Virtual DOM, and how does it work?
The Virtual DOM is a lightweight copy of the actual DOM. When a component’s state changes, React updates the Virtual DOM first. It then compares the updated Virtual DOM with the previous version using a process called “diffing.” Finally, React updates only the changed elements in the real DOM, optimizing performance.
4. What are props in React.js?
Props (short for properties) are read-only data passed from a parent component to a child component. They help make components reusable by allowing dynamic data to be rendered. React js classes in Pune provides hands-on experience and project-based learning to make you job-ready.

5. What is the difference between state and props in React.js?
State: Manages data that changes within a component.
Props: Pass data from parent to child components and are immutable.
6. What are React Hooks?
React Hooks are functions introduced in React 16.8 that allow developers to use state and other React features in functional components. Common hooks include:
useState: For managing state.
useEffect: For handling side effects like API calls.
useContext: For accessing context without using props.
7. What is Redux, and how is it used with React?
Redux is a state management library used with React to handle complex application states. It provides a single source of truth and ensures predictable state transitions through actions and reducers.
8. What are Higher-Order Components (HOCs)?
HOCs are functions that take a component as input and return a new component with enhanced functionality. They are used for code reuse and implementing features like authentication.
9. How do you optimize performance in a React application?
Using React.memo to prevent unnecessary re-renders.
Implementing lazy loading for components and assets.
Using the useCallback and useMemo hooks.
Keeping component hierarchies shallow to minimize Virtual DOM updates.
10. What are keys in React, and why are they important?
Keys are unique identifiers used in lists to help React identify and manage elements efficiently during updates. They ensure proper rendering and avoid issues with dynamic lists.
Learn React.js Effectively
For those looking to excel in React.js, joining React js classes in Pune is an excellent choice.
Conclusion
Preparing for a React.js interview requires a solid understanding of its core concepts, features, and practical applications. By familiarizing yourself with these commonly asked questions, you can approach your interview with confidence. Investing in professional training is also a great way to strengthen your knowledge and skill set, paving the way for a successful career in React.js development.