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💥React Interview Questions and Answer💥
1. What is React?
Answer: React is a JavaScript library for building user interfaces. It was developed by Facebook and has become one of the most popular libraries for front-end web development.
2. What is JSX?
Answer: JSX is a syntax extension for JavaScript that allows you to write HTML-like code in your JavaScript files. It is used in React to define the structure and layout of components.
3. What is a component in React?
Answer: A component is a reusable piece of code that defines the structure and behavior of a part of a user interface. Components can be nested within each other to create complex interfaces.
4. What is the difference between props and states in React?
Answer: Props are used to pass data from a parent component to a child component, while the
state is used to manage data within a component. Props are read-only, while the state can be modified using setState().
5. What is the significance of the virtual DOM in React?
Answer: The virtual DOM is a lightweight representation of the actual DOM in memory. React uses the virtual DOM to optimize updates by only updating the parts of the actual DOM that have changed.
6. What is the purpose of keys in React?
Answer: Keys are used to helping React identify which items in a list have changed, been added, or been removed. They should be unique within a list and help React maintain the correct component state.
7. What are higher-order components in React?
Answer: Higher-order components are functions that take a component as an argument and return a new component with additional functionality. They are commonly used for code reuse and to add cross-cutting concerns like logging or authentication.
8. What is a lifecycle method in React?
Answer: A lifecycle method is a method that is called at specific points during a component's lifecycle. They can be used to perform actions like fetching data, updating the component's state, or cleaning up after the component has been removed from the DOM.
9. What is Redux and how does it work with React?
Answer: Redux is a state management library that is commonly used with React. It provides a centralized store for managing the application's state and allows components to access and modify that state using actions and reducers.
10. What is the significance of the context API in React?
Answer: The context API is a feature that allows data to be passed down the component tree without having to manually pass it through each level. It is commonly used for sharing data like a user's authentication status or theme across multiple components.
11. What are the differences between stateful and stateless components in React?
Answer: Stateful components are components that have a state and can change over time. They are created using ES6 classes and can modify their own state using setState(). In contrast, stateless components are functional components that don't have a state and only render based on the props they receive. They are simpler to write and test and are recommended whenever possible as they can improve the performance of your application.
12. What are controlled components in React?
Answer: Controlled components are input components like text fields, checkboxes, and radio buttons that are controlled by React. Their values are managed by React's state, and any changes made to the input are reflected in the state.
13. What is the purpose of React Router?
Answer: React Router is a library that allows you to add routing to a React application. It provides a way to manage the navigation between different views in a single-page application and enables you to create dynamic and user-friendly interfaces.
14. What is the significance of the componentDidMount() method in React?
Answer: The componentDidMount() method is a lifecycle method in React that is called once the component has been mounted and rendered on the page. It is commonly used to fetch data from an API or perform other setup tasks that require access to the DOM.
15. What is the difference between server-side rendering and client-side rendering in React?
Answer: Server-side rendering is the process of rendering the React components on the server and sending the resulting HTML to the client. It can improve the performance and SEO of your application but requires additional setup and configuration. In contrast, client-side rendering is the default approach in React, where the components are rendered on the client side using JavaScript.
16. What is the purpose of Redux Thunk middleware?
Answer: Redux Thunk is a middleware that allows you to write asynchronous logic in Redux. It provides a way to dispatch async actions that return functions instead of plain objects, allowing you to perform tasks like API calls or handling complex logic.
17. What is the difference between React and Angular?
Answer: React is a JavaScript library for building user interfaces, while Angular is a full-featured framework for building web applications. React uses a virtual DOM for performance optimization, while Angular uses a two-way data binding approach for managing state. React has a larger ecosystem and is more flexible, while Angular provides more structure and out-of-the-box features.
18. What is the significance of the shouldComponentUpdate() method in React?
Answer: The shouldComponentUpdate() method is a lifecycle method in React that allows you to control whether a component should re-render or not. It can be used to optimize performance by preventing unnecessary re-renders.
19. What are React Hooks?
Answer: React Hooks are a new feature introduced in React 16.8 that allow you to use state and other React features in functional components. They provide a simpler and more efficient way to manage component state and lifecycle methods.
20. What is the purpose of the useEffect() Hook in React?
Answer: The useEffect() Hook is a built-in Hook in React that allows you to perform side effects in functional components. It replaces the componentDidMount(), componentDidUpdate(), and componentWillUnmount() lifecycle methods, and can be used to fetch data, set up event listeners, or perform other tasks.
21. What is the difference between a presentational component and a container component in React?
Answer: Presentational components are components that are focused on the UI and rendering logic, while container components are components that are focused on managing data and state. Container components typically use presentational components to render the UI, and may also contain business logic or handle user interactions.
22. What is the purpose of the useMemo() Hook in React?
Answer: The useMemo() Hook is a built-in Hook in React that allows you to memoize the result of a function, preventing unnecessary re-computation. It can be used to optimize performance by only re-computing the result when the input values have changed.
23. What is the purpose of the useCallback() Hook in React?
Answer: The useCallback() Hook is a built-in Hook in React that allows you to memoize a function, preventing unnecessary re-renders of components that use it as a prop. It can be used to optimize performance by only creating a new function when the input values have changed.
24. What is the purpose of the useContext() Hook in React?
Answer: The useContext() Hook is a built-in Hook in React that allows you to access context values without needing to pass them down through intermediate components. It can simplify the code and make it easier to manage global state or other shared data.
25. What is the difference between props and state in React?
Answer: Props are data passed down from a parent component to a child component, while state is data managed within a component. Props are read-only and cannot be modified by the child component, while state can be modified using setState().
26. What is the purpose of the forwardRef() function in React?
Answer: The forwardRef() function is a built-in function in React that allows you to forward refs from a child component to a parent component. It can be used to pass refs to DOM elements or to other components that need to access the DOM.
27. What is the purpose of the useReducer() Hook in React?
Answer: The useReducer() Hook is a built-in Hook in React that allows you to manage complex state using a reducer function. It can be used as an alternative to useState() for managing state in more complex scenarios.
28. What is the significance of the componentWillUnmount() method in React?
Answer: The componentWillUnmount() method is a lifecycle method in React that is called before a component is unmounted and removed from the page. It is commonly used to clean up any resources that were created in the componentDidMount() method or in other lifecycle methods.
29. What is the purpose of the useMemo() Hook in React?
Answer: The useMemo() Hook is a built-in Hook in React that allows you to memoize the result of a function, preventing unnecessary re-computation. It can be used to optimize performance by only re-computing the result when the input values have changed.
30. What is the difference between server-side rendering and client-side rendering in React?
Answer: Server-side rendering is the process of rendering the React components on the server and sending the resulting HTML to the client. It can improve the performance and SEO of your application but requires additional setup and configuration. In contrast, client-side rendering is the default approach in React, where the components are rendered on the client side using JavaScript.
31. What is the purpose of the React Developer Tools extension for Chrome?
Answer: The React Developer Tools extension is a browser extension for Google Chrome that allows developers to inspect and debug React applications. It provides a tree view of the component hierarchy, a visualization of the props and state of each component, and a timeline view of the component lifecycle.
32. What is the Virtual DOM in React?
Answer: The Virtual DOM is a concept in React that represents a lightweight copy of the actual DOM tree. React uses the Virtual DOM to perform efficient updates to the UI, by comparing the current Virtual DOM with a previous version and only updating the parts of the tree that have changed.
33. What is the purpose of the PropTypes library in React?
Answer: The PropTypes library is a library in React that allows you to specify the expected types and values of the props passed to a component. It can help catch errors early and improve the maintainability of your code.
34. What is the purpose of the React Router library in React?
Answer: The React Router library is a library in React that allows you to manage the routing and navigation of your application. It provides a declarative way to define routes and render different components based on the current URL.
35. What is JSX in React?
Answer: JSX is a syntax extension for JavaScript that allows you to write HTML-like code inside your JavaScript files. It is used in React to define the structure and appearance of the UI, and is converted to regular JavaScript code at build time.
36. What is the purpose of the key prop in React?
Answer: The key prop is a special prop in React that helps React identify which elements in a list have changed or been added or removed. It is used to improve the performance and efficiency of updating lists and should be unique for each element.
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