Top 50 React Interview Questions and Answers To Prepare

React is a popular and powerful library that allows you to create interactive and dynamic web applications. It has many features and concepts that you need to master, such as components, hooks, state, props, routing, data fetching, performance, testing, and debugging. If you are preparing for a React Developer interview, you need to practice some common React interview questions and answers that can help you create an impact on the interviewer and land your dream job. You can acquire a better understanding of React by pursuing the best JavaScript courses.

This Story also Contains

1. Explore Full Stack Development Certification Courses by Top Providers
2. Explore Javascript Certification Courses by Top Providers
3. Conclusion

In this article, we have compiled a list of 50 React interview questions for freshers and experienced developers, covering various topics and levels of difficulty. These interview questions can help you ace your next React interviews and get placed in top companies.

Also Read: 16+ Courses in React Native for Beginners

1. What is React?

This is one of the most common React interview questions you should prepare for. React is a JavaScript library for building user interfaces. React uses a declarative and component-based approach to create reusable and composable UI elements. It also uses a virtual DOM to efficiently update the UI based on the state changes.

2. What are the advantages of using React?

Some of the advantages of using React are:

• It is easy to learn and use

• It improves the performance of the web applications by using virtual DOM and diffing algorithm

• It supports server-side rendering and code splitting for better SEO and user experience

• It has a large and active community and ecosystem of tools and libraries

3. What are the main features of React?

Some of the main features of React are virtual DOM, JSX, hooks, functional components, and one-way data flow. This is another one of the common React interview questions for experienced and new developers.

4. What are components in React?

Components are the building blocks of React applications. They are self-contained pieces of code that can accept inputs (props) and return elements that describe what to display on the screen. React interview questions for freshers and experienced developers often test your knowledge of components and their types, props, state, and hooks.

5. What are props in React?

This is one of the important React interview questions and answers to be prepared for. Props are the inputs that a component can receive from its parent component or from the default props. They are read-only and should not be modified by the component. Props are one of the common topics for React interview questions and answers, as they are essential for communication between components.

6. What is State in React?

State is the internal data that a component can manage and update. It is usually initialised in the constructor or with the useState() hook and updated with the setState() method or the setter function returned by the useState() hook. State is one of the important concepts for interview questions for React developer, as it determines how your component behaves and renders.

7. What are Hooks in React?

Hooks are special functions that let you use state and other React features in functional components. They start with the word “use” and follow some rules, such as only calling them at the top level and not inside loops or conditions. Hooks are one of the new and advanced features for React interview questions and answers for freshers and experienced developers.

Also Read: 20+ Online Courses to Learn ReactJS

8. What is the difference between State and Props in React?

The difference between State and Props is that State is managed by the component itself and can change over time, while Props are passed from the parent component and are fixed throughout the component’s lifetime.

9. What is the difference between functional and class components in React?

The difference between functional and class components is that functional components are simpler and easier to write and test, while class components have more features such as lifecycle methods and state management.

10. What are some of the lifecycle methods in React class components?

This is one of the most-asked React interview questions for experienced individuals as well as freshers. Some of the lifecycle methods in React class components are constructor(), render(), componentDidMount(), componentDidUpdate(), componentWillUnmount(), shouldComponentUpdate(), getDerivedStateFromProps(), and getSnapshotBeforeUpdate().

Explore Full Stack Development Certification Courses by Top Providers

11. How do you create a custom hook in React?

To create a custom hook in React, you need to define a function that starts with “use” and returns a value or an array of values. You can also use other hooks inside your custom hook, but follow the same rules as for regular hooks.

12. How do you implement routing in React?

To implement routing in React, you need to use a library such as React Router, which provides components such as BrowserRouter, Route, Switch, Link, and useHistory to create dynamic navigation in your application.

13. How do you fetch data from an API in React?

This is a common topic for React interview questions and answers for freshers and experienced developers. To fetch data from an API in React, you can use the built-in fetch() method or a library such as axios to make HTTP requests. You can also use hooks such as useEffect() and useState() to handle the loading, error, and data states of your request.

14. What is JSX in React?

JSX is a syntax extension that allows you to write HTML-like code in your JavaScript files. JSX makes it easier to create and render React elements in your web application. JSX is one of the basic concepts for React interview questions and answers for freshers and experienced developers.

15. How do you use conditional rendering in React?

This type of React developer interview questions are important to practice. Conditional rendering is a technique that allows you to render different UI elements based on some condition. Conditional rendering can be done by using JavaScript operators, such as if-else, ternary, and logical, in your JSX code. Conditional rendering is one of the common topics for interview questions for React Developers, as it tests your logic and creativity.

16. How do you use lists and keys in React?

For lists and keys in React, you can use the map() method to iterate over an array of data and return an element for each item. You also need to provide a unique key prop to each element to help React identify which items have changed or been added or removed. Lists and keys are one of the important concepts for React interview questions and answers for freshers and experienced developers.

17. How do you use forms and controlled components in React?

To use forms and controlled components in React, you need to store the form values in the state of your component and update them with onChange handlers on each input element. You also need to provide an onSubmit handler on the form element to handle the form submission. Forms and controlled components are one of the common topics for interview questions for React Developers, as they test your knowledge of state management and event handling.

18. How do you use refs and the useRef() hook in React?

To use refs and the useRef() hook in React, you need to create a ref object with useRef() and assign it to a DOM element with the ref attribute. You can then access the current value of the ref object with ref.current in your component. Refs and the useRef() hook are one of the advanced topics for React interview questions and answers for freshers and experienced developers.

19. How do you use context and the useContext() hook in React?

To use context and the useContext() hook in React, you need to create a context object with createContext() and provide a value for it with a Provider component at the top level of your component tree. You can then access the value of the context object with useContext() in any child component that needs it. Context and the useContext() hook are one of the new and advanced topics for interview questions for React developer, as they test your knowledge of data flow and performance optimisation.

20. How do you use reducers and the useReducer() hook in React?

This type of interview questions for React developers are frequently asked. To use reducers and the useReducer() hook in React, you need to define a reducer function that takes the current state and an action as arguments and returns a new state based on the action type and payload. You also need to create an initial state object and pass it along with the reducer function to useReducer(), which returns a state value and a dispatch function that you can use to update the state with actions. Reducers and the useReducer() hook are one of the advanced topics for React interview questions and answers for freshers and experienced developers.

Also Read: Top 10 Companies Hiring ReactJS Developers in India

21. How do you use custom hooks in React?

To use custom hooks in React, you need to define a function that starts with “use” and returns a value or an array of values. You can also use other hooks inside your custom hook, but follow the same rules as for regular hooks. You can then use your custom hook in any functional component that needs it. Custom hooks are one of the new and advanced topics for interview questions for React Developers, as they test your knowledge of hooks and code organisation.

22. How do you use prop types and default props in React?

To use prop types and default props in React, you need to install the prop-types library and import it in your component file. You can then use the PropTypes object to specify the type and required status of each prop that your component expects. You can also use the defaultProps object to provide default values for props that are not passed by the parent component. Prop types and default props are one of the basic topics for React interview questions and answers for freshers and experienced developers.

23. How do you use higher-order components (HOCs) in React?

To use higher-order components (HOCs) in React, you need to define a function that takes a component as an argument and returns a new component that wraps the original component and adds some additional functionality or props to it. You can then use the HOC function to enhance any component that needs it. HOCs are one of the advanced topics for interview questions for React Developers, as they test your knowledge of components and composition.

24. How do you use render props in React?

To use render props in React, you need to define a component that accepts a function as a prop and calls it with some arguments inside its render method. You can then pass any function that returns an element as the render prop to the component and use the arguments to customise the rendering. Render props are one of the advanced topics for React interview questions and answers for freshers and experienced developers.

25. How do you use portals in React?

This type of React interview questions and answers are common.To use portals in React, you need to import the createPortal() method from react-dom and use it to render a child element into a different DOM node than its parent component. You can then use portals to render modals, tooltips, or other UI elements that need to break out of the normal DOM hierarchy. Portals are one of the new and advanced topics for interview questions for React Developers, as they test your knowledge of DOM manipulation and UI design.

26. How do you use fragments in React?

To use fragments in React, you need to use the <></> syntax or the Fragment component to wrap multiple elements without adding an extra node to the DOM. You can then use fragments to return multiple elements from a component without creating unnecessary wrappers. Fragments are one of the new and basic topics for React interview questions and answers for freshers and experienced developers.

Also Read: Online Full End Development Certification Courses

27. How do you use error boundaries in React?

To use error boundaries in React, you need to define a class component that implements the static getDerivedStateFromError() or the componentDidCatch() lifecycle methods and use them to catch errors thrown by any of its child components. You can then use error boundaries to display a fallback UI or log the error information when something goes wrong in your application. Error boundaries are one of the new and advanced topics for interview questions for React developer, as they test your knowledge of error handling and lifecycle methods.

28. How do you use suspense and lazy loading in React?

To use suspense and lazy loading in React, you need to import the lazy() and Suspense components from react and use them to dynamically load components that are not needed immediately. You can then use suspense to display a loading indicator or a fallback UI while the component is being loaded. Suspense and lazy loading are one of the new and advanced topics for React interview questions and answers for freshers and experienced developers.

29. How do you use hooks in React?

To use hooks in React, you need to import them from React and follow some rules such as only calling them at the top level of your functional components and not inside loops or conditions. You can then use hooks such as useState(), useEffect(), useRef(), useContext(), and useReducer() to add state, effects, refs, context, and reducers to your functional components. Hooks are one of the new and important topics for interview questions for React Developers, as they test your knowledge of state management, side effects, and data flow.

30. How do you use routing in React?

This is one of the important React interview questions and answers you must practice. To use routing in React, you need to install and import a library such as React Router and use its components such as BrowserRouter, Route, Switch, Link, and useHistory to create dynamic navigation in your application. You can then use routing to render different components based on the URL path or parameters. Routing is one of the common topics for React interview questions and answers for freshers and experienced developers, as it tests your knowledge of navigation and UI design.

Explore Javascript Certification Courses by Top Providers

31. What is the significance of the virtual DOM in React?

The virtual DOM is a virtual representation of the actual DOM in memory. React uses it to optimise UI updates by calculating the minimal changes required and then updating the real DOM accordingly, reducing the overall rendering time.

32. How does React handle events?

React handles events through synthetic events that wrap native browser events. Event handlers are written in camelCase and attached to JSX elements, ensuring consistent behaviour across different browsers.

33. What is JSX transformation and why is it used?

JSX transformation is the process of converting JSX syntax to regular JavaScript code that browsers can understand. It allows developers to write HTML-like code in their JavaScript files, enhancing readability and making UI creation more intuitive.

34. What are keys used for in React lists?

Keys are used to provide a stable identity to elements in a list. React uses these keys to efficiently update, reorder, or remove elements in a list, improving performance and avoiding unnecessary re-rendering.

35. What is the purpose of the shouldComponentUpdate() method?

This is one of the frequently asked React interview questions for experienced professionals. The shouldComponentUpdate() method allows you to optimise component rendering by controlling whether a component should re-render when its props or state change. By returning true or false, you can prevent unnecessary re-renders and improve performance.

36. How does React handle forms and input elements?

React manages form data using controlled components. Each form input element has its value controlled by React's state. When the user interacts with the input, it triggers an onChange event that updates the state, reflecting the user's input.

37. What is the role of the useEffect() hook?

The useEffect() hook is used to manage side effects in functional components. It can be used to perform tasks such as data fetching, subscriptions, or manual DOM manipulations after the component has rendered.

38. How do you optimise performance in React applications?

Performance optimisation in React can be achieved by minimising unnecessary re-renders, using memorisation techniques like React.memo, implementing lazy loading, code splitting, and using tools like React DevTools to identify bottlenecks.

39. What is the significance of the React Developer Tools extension?

React Developer Tools is a browser extension that helps developers inspect and debug React component hierarchies, state, and props. It provides insights into the virtual DOM, allowing for efficient debugging and development.

40. What are controlled and uncontrolled components in React?

This is one of the common React interview questions for freshers and professionals alike. Controlled components have their state controlled by React. Their values are stored in the component's state, and updates are handled through state changes. Uncontrolled components store their state in the DOM and are accessed using refs.

41. How can you prevent prop drilling in React?

Prop drilling, where props are passed through multiple intermediate components, can be mitigated by using context or by lifting state to a common parent component, allowing data to be shared without the need for extensive prop passing.

42. What is the role of React.memo() in functional components?

React.memo() is a higher-order component that memorises functional components. It prevents unnecessary re-renders by only updating the component if its props have changed, improving performance.

43. How do you handle CSS in React?

CSS in React can be managed through regular CSS files, inline styles, or CSS-in-JS libraries like styled-components. The choice depends on the project's needs, modularity, and styling complexity.

44. What is the purpose of the PureComponent class in React?

The PureComponent class is an optimised version of the standard Component class. It performs shallow prop and state comparisons to determine if a re-render is necessary, leading to performance improvements in certain scenarios.

45. How can you handle errors in React component trees?

This is one of the important React Developer interview questions. You can use the ErrorBoundary component to catch errors in the component tree and display a fallback UI. This prevents the entire application from crashing and allows you to handle errors gracefully.

46. What are hooks rules and why are they important?

Hooks have rules that ensure their proper usage, like calling them at the top level of functional components and not inside loops or conditions. These rules maintain the consistency and predictability of React's behaviour.

47. How do you pass data between sibling components?

Data can be passed between sibling components through a common parent component. The parent component holds the data in its state and passes it as props to the siblings.

48. What is the purpose of the React.Fragment component?

React.Fragment is used as a wrapper around multiple JSX elements when you want to return adjacent elements without adding an extra node to the DOM. This helps improve the structure of your component tree.

49. How can you optimise the performance of rendering long lists in React?

For long lists, you can use techniques like virtualisation (with libraries like react-virtualized or react-window) to render only the visible items, reducing the rendering time and improving performance.

50. How do you perform server-side rendering (SSR) in React?

This type of interview questions for React Developers are often asked in interviews. Server-side rendering is achieved by rendering React components on the server before sending them to the client. Libraries like Next.js simplify the process and provide benefits like improved SEO and initial load times.

Also Read: Top Networking Interview Questions and Answers To Crack Interviews

Conclusion

React is one of the most popular and powerful front-end frameworks for web development. React interview questions and answers for freshers and experienced developers can help you prepare for your next React job interview and test your knowledge of React concepts, features, and best practices. In this article, we have covered some of the frequently asked React interview questions and answers, ranging from basic to advanced topics. We hope this article has helped you learn something new and boost your confidence for your next React job interview