Preparing for a React interview? Here’s a curated list of advanced React interview questions along with detailed answers to help you ace your next technical interview.
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1. What are React Hooks? Explain their advantages.
Answer: React Hooks are functions that let you use state and other React features without writing a class component. Advantages include cleaner code, reusability of logic, and easier code organization.
2. Explain the concept of virtual DOM in React.
Answer: Virtual DOM is a lightweight copy of the real DOM. React uses it to perform efficient DOM updates by comparing the virtual DOM with the previous state, identifying differences, and updating only what has changed.
3. What are controlled components in React?
Answer: Controlled components in React are those where form data is handled by React components. They maintain their state in the state property and update it with setState() method.
4. What are the differences between React components and Angular components?
Answer: React components use JSX for templating, virtual DOM, and are easier to learn. Angular components use HTML for templating, real DOM, and have a steeper learning curve.
5. Explain the concept of higher-order components (HOCs) in React.
Answer: Higher-order components are functions that take a component as an argument and return a new component. They are used to share common functionality between components without repeating code.
6. How does React Router work? Explain its main components.
Answer: React Router is a popular routing library for React applications. It provides dynamic routing, allowing navigation between different views/components. Main components include <Router>, <Route>, <Switch>, and <Link>.
7. What are PureComponent and React.memo() in React?
Answer: PureComponent is a class component in React that implements shouldComponentUpdate with a shallow prop and state comparison. React.memo() is a higher-order component that memoizes a functional component, preventing unnecessary re-renders.
8. What are the lifecycle methods in React? Explain each phase briefly.
Answer: React has three main lifecycle phases: Mounting, Updating, and Unmounting. Key methods include componentDidMount(), componentDidUpdate(), and componentWillUnmount().
9. How does React handle forms? Explain controlled vs. uncontrolled components.
Answer: React handles forms using controlled and uncontrolled components. Controlled components use state to manage form data, while uncontrolled components use refs to access form values.
10. Explain the use of context in React.
Answer: Context provides a way to pass data through the component tree without having to pass props down manually at every level. It’s useful for sharing global data like themes or user authentication.
11. What are React Fragments? Why are they useful?
Answer: React Fragments allow grouping multiple elements in a component without adding extra nodes to the DOM. They improve code readability and performance.
12. Describe the purpose of keys in React lists.
Answer: Keys are special string attributes used by React to identify which items have changed, are added, or are removed. They help React efficiently update the UI.
13. How does error handling work in React?
Answer: React uses error boundaries to catch JavaScript errors during rendering, component lifecycle methods, and in constructors of the whole tree below them. Error boundaries are components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI instead of crashing the whole application.
14. What are the differences between class components and functional components?
Answer: Class components are ES6 classes that extend from React.Component and use a render method to return React elements. Functional components are simpler and rely on JavaScript functions to render UI based on props.
15. How does Redux work with React? Explain the basic principles.
Answer: Redux is a predictable state container for JavaScript apps. It helps manage application state and makes data flow more predictable by enforcing unidirectional data flow and centralizing state management.
16. What are React hooks? List some built-in hooks and their purposes.
Answer: React hooks are functions that let you use state and other React features without writing a class component. Examples include useState() for managing state, useEffect() for handling side effects, and useContext() for consuming context.
17. Explain the concept of lazy loading in React. How can you implement lazy loading?
Answer: Lazy loading is a technique where components are loaded only when they are needed. React.lazy() and Suspense allow you to implement lazy loading in React applications, improving performance by reducing initial load times.
18. How can you optimize performance in React applications?
Answer: Performance optimization techniques in React include using memoization, optimizing render methods, minimizing unnecessary re-renders with PureComponent or React.memo(), and code splitting with lazy loading.
19. What is the role of PropTypes library in React?
Answer: PropTypes is a library used to type-check props passed to React components. It helps catch bugs early by validating props against expected types.
20. Explain the concept of server-side rendering (SSR) in React.
Answer: Server-side rendering is the process of rendering React components on the server-side and sending the fully rendered HTML page to the client. It improves initial load times and SEO.
21. How does React handle events? Explain event delegation in React.
Answer: React handles events using SyntheticEvent, a cross-browser wrapper around the browser’s native event. Event delegation in React involves attaching a single event listener to a parent element and using event.target to handle events on child elements.
22. Describe how you can optimize React applications for SEO.
Answer: To optimize React applications for SEO, use server-side rendering (SSR) or prerendering to ensure search engines can crawl and index content. Implement meta tags, canonical URLs, and ensure clean HTML structure.
23. What are React hooks rules? List some common rules to follow when using hooks.
Answer: Rules for using React hooks include:
- Only call hooks at the top level of your functional component or custom hook.
- Only call hooks from React functional components or custom hooks, not regular JavaScript functions.
- Ensure hooks are called in the same order on every render.
24. How can you handle state management in large React applications?
Answer: In large React applications, manage state using context API, Redux, or other state management libraries. Use component composition and separation of concerns to maintain a scalable architecture.
25. Explain the purpose of the React Developer Tools extension.
Answer: React Developer Tools is a browser extension that allows developers to inspect React component hierarchies, inspect component props and state, and debug React applications more efficiently.
26. How does React differ from Angular and Vue.js?
Answer: React is a JavaScript library for building user interfaces, focusing on component-based architecture and virtual DOM. Angular is a full-fledged framework with a focus on dependency injection and TypeScript. Vue.js is a progressive framework known for its simplicity and two-way data binding.
27. What are the advantages of using Redux with React?
Answer: Redux provides a centralized state management solution for React applications, making it easier to manage complex application state and enabling predictable data flow. It also facilitates debugging and testing.
28. Describe the React Context API. When would you use it?
Answer: React Context API provides a way to pass data through the component tree without having to pass props down manually at every level. Use it for sharing global data like themes, user authentication, or preferences across components.
29. How does React handle forms and form validation?
Answer: React handles forms using controlled components, where form data is handled by React components and managed through state. Form validation can be implemented using built-in HTML5 form validation or libraries like Formik or Yup.
30. Explain the use of React portals.
Answer: React portals provide a way to render children into a DOM node that exists outside the DOM hierarchy of the parent component. They are useful for rendering modals, tooltips, or other UI components that need to break out of the parent component’s DOM boundaries.
31. What are the advantages of using JSX in React?
Answer: JSX is a syntax extension for JavaScript that allows you to write HTML elements and React components in the same file. Advantages include easier integration of UI components, improved code readability, and reduced syntax errors.
32. How can you implement code splitting in React?
Answer: Code splitting in React can be implemented using dynamic import() statements, React.lazy() for lazy loading components, and React Suspense to handle loading states. It helps reduce initial bundle size and improve application performance.
33. Describe the differences between React.memo() and useMemo().
Answer: React.memo() is a higher-order component that memoizes a functional component based on its props, preventing unnecessary re-renders. useMemo() is a hook that memoizes the result of a function so that it is only recomputed when its dependencies change, optimizing performance.
34. How can you handle authentication and authorization in React applications?
Answer: Implement authentication and authorization in React using techniques like JWT tokens, OAuth, or session-based authentication. Use protected routes, role-based access control (RBAC), and secure API calls to enforce access control.
35. What are some best practices for writing performant React code?
Answer: Best practices include:
- Minimizing re-renders by using PureComponent or React.memo().
- Using keys correctly in lists to optimize updates.
- Implementing code splitting and lazy loading for better performance.
- Optimizing images and assets.
- Avoiding unnecessary state changes and side effects.
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n conclusion, mastering these advanced React interview questions and concepts is crucial for anyone aiming to excel in React development roles. By understanding the intricacies of React Hooks, virtual DOM, state management with Redux, and optimizing performance through code splitting and memoization, developers can build scalable, efficient, and maintainable applications. Additionally, familiarity with React’s ecosystem, including tools like React Router, Context API, and React Developer Tools, enhances one’s ability to tackle real-world challenges effectively.
