React JS has become one of the most popular JavaScript libraries for building user interfaces, particularly for single-page applications. With many companies, including Wipro, seeking skilled React developers, it’s crucial to prepare for the interview process. In this blog, we present the top 20 React JS interview questions along with comprehensive answers to help you succeed.
1. What is React?
React is an open-source JavaScript library developed by Facebook for building user interfaces, particularly for single-page applications. It allows developers to create reusable UI components, making it easier to manage and render dynamic data efficiently.
2. What are the key features of React?
Some key features of React include:
- Virtual DOM: Enhances performance by minimizing direct manipulation of the DOM.
- Component-based architecture: Encourages reusability and separation of concerns.
- One-way data binding: Simplifies debugging by ensuring a clear data flow.
- JSX: A syntax extension that allows writing HTML-like code within JavaScript.
3. Explain the concept of props in React.
Props, short for properties, are read-only attributes passed from a parent component to a child component. They allow for data transfer and configuration of child components, enabling dynamic rendering of UI based on the data provided.
4. What is the difference between state and props?
- Props: Passed to components from a parent, immutable, and used to configure child components.
- State: Managed within a component, mutable, and used to control the component’s behavior and render dynamic data.
5. What are React Hooks?
React Hooks are functions that let developers use state and other React features without writing a class. Common hooks include:
- useState: For managing state.
- useEffect: For handling side effects such as data fetching and subscriptions.
- useContext: For accessing context in functional components.
6. Explain the use of the useEffect hook.
The useEffect hook allows developers to perform side effects in functional components, such as data fetching, subscriptions, or manually changing the DOM. It can be configured to run on specific state changes or on component mount/unmount.
7. What is the Virtual DOM, and how does it work?
The Virtual DOM is an in-memory representation of the actual DOM. React updates the Virtual DOM instead of the real DOM, minimizing direct manipulations. When changes occur, React computes the differences and updates only the parts of the DOM that have changed, improving performance.
8. What is JSX?
JSX (JavaScript XML) is a syntax extension for JavaScript that allows developers to write HTML-like code within JavaScript. It makes it easier to create and visualize UI components while keeping JavaScript logic intact.
9. What are controlled components in React?
Controlled components are form elements whose value is controlled by React state. The component’s state is the single source of truth, and the form elements update their values based on state changes.
10. What is the significance of keys in React?
Keys are unique identifiers assigned to elements in a list to help React identify which items have changed, been added, or removed. They improve performance by enabling React to optimize rendering and update processes.
11. Explain the concept of context in React.
Context provides a way to share values between components without passing props through every level of the tree. It is useful for managing global data such as themes, user authentication, or settings.
12. What is the difference between class components and functional components?
- Class components: ES6 classes that can hold state and lifecycle methods.
- Functional components: Simpler, stateless functions that can use hooks to manage state and lifecycle without needing classes.
13. How do you handle events in React?
Events in React are handled using camelCase syntax. The event handler functions can be passed as props to elements. For example:
<button onClick={this.handleClick}>Click me</button>
14. What is React Router?
React Router is a library for routing in React applications. It enables navigation between different components based on the URL, allowing for the creation of single-page applications with dynamic routing.
15. Explain the lifecycle methods of a React component.
Lifecycle methods are special methods that get called at specific points in a component's life. They include:
- componentDidMount: Invoked after the component is mounted.
- componentDidUpdate: Invoked after the component updates.
- componentWillUnmount: Invoked before the component is unmounted and destroyed.
16. What are higher-order components (HOCs)?
Higher-order components are functions that take a component as an argument and return a new component. They are used for code reuse, enhancing components with additional functionality, such as adding state or data fetching capabilities.
17. What is Redux, and how does it relate to React?
Redux is a state management library commonly used with React. It provides a centralized store for managing application state, enabling predictable state transitions and facilitating debugging. Redux can be integrated into React applications using the React-Redux library.
18. How can you optimize the performance of a React application?
To optimize performance, consider the following techniques:
- Code splitting: Load components only when needed.
- Memoization: Use
React.memoanduseMemoto prevent unnecessary re-renders. - Lazy loading: Load images and components only when they enter the viewport.
19. Explain the concept of lazy loading in React.
Lazy loading is a technique to defer the loading of components until they are needed. This can be achieved using the React.lazy() function and Suspense component, improving initial load time and overall performance.
20. Why do you want to work for Wipro?
In this question, express your admiration for Wipro’s commitment to innovation, its diverse work culture, and how the company's values align with your career goals. Highlight your eagerness to contribute to and grow within the organization.
Conclusion
Preparing for a React JS interview requires a solid understanding of both the fundamental concepts and advanced features of the library. Familiarizing yourself with these questions and answers will equip you to face your interview at Wipro with confidence.
Good luck!
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