Top React Interview Questions and Answers for TCS

Introduction

Are you preparing for a React interview at TCS? React is one of the most popular JavaScript libraries for building dynamic user interfaces. TCS frequently asks fundamental React questions to assess a candidate’s proficiency in React concepts, components, hooks, state management, and performance optimization.

This blog provides a comprehensive list of basic React interview questions that will help both freshers and experienced professionals succeed in their TCS technical interview.

✔ Covers key React concepts
✔ Includes real-world examples
✔ Ideal for freshers and experienced developers

📌 Bookmark this page and go through these questions before your TCS React interview! 🚀

Top React Interview Questions and Answers

Here are some common React.js interview questions that might be asked in a TCS (Tata Consultancy Services) interview or any other technical interview. These questions cover fundamental concepts, best practices, and advanced topics in React.js:

Basic React.js Interview Questions

1. What is React.js?

– React is a JavaScript library for building user interfaces, particularly single-page applications (SPAs). It is maintained by Facebook and a community of developers.

2. What are the key features of React?

– Virtual DOM
– Component-based architecture
– One-way data binding
– JSX (JavaScript XML)
– React Hooks (for functional components)

3. What is JSX?

– JSX is a syntax extension for JavaScript that allows you to write HTML-like code in JavaScript. It makes the code more readable and easier to write.

4. What is the difference between Real DOM and Virtual DOM?

– Real DOM: Represents the actual HTML structure of a webpage. Updating it is slow because it directly manipulates the browser’s DOM.

– Virtual DOM: A lightweight copy of the Real DOM. React uses it to optimize updates by comparing the Virtual DOM with the Real DOM and applying only the necessary changes.

5.  What are components in React?

– Components are reusable, independent pieces of UI. They can be functional or class-based.

6. What is the difference between functional and class components?

– Functional Components: Stateless, simpler, and use hooks for state and lifecycle methods.

– Class Components: Stateful, use `this.state` and lifecycle methods like `componentDidMount`.

7. What are props in React?

– Props (short for properties) are used to pass data from a parent component to a child component. They are read-only.

8. What is state in React?

– State is a built-in React object used to store data or information about the component. It is mutable and can be updated using `setState` (in class components) or `useState` (in functional components).

9. What are React Hooks?

– Hooks are functions that allow you to use state and other React features in functional components. Examples include `useState`, `useEffect`, and `useContext`.

10. What is the purpose of `useEffect`?

– `useEffect` is used to perform side effects in functional components, such as fetching data, updating the DOM, or subscribing to events. It replaces lifecycle methods like `componentDidMount`, `componentDidUpdate`, and `componentWillUnmount`.

Intermediate React.js Interview Questions

11. What are keys in React, and why are they important?

– Keys are unique identifiers used to identify which items have changed, been added, or been removed in a list. They help React optimize rendering performance.

12. What is the difference between controlled and uncontrolled components?

– Controlled Components: Form data is handled by React state.
– Uncontrolled Components: Form data is handled by the DOM itself.

13. What is React Router?

– React Router is a library used for routing in React applications. It allows you to navigate between different components without reloading the page.

14. What is Redux, and why is it used?

– Redux is a state management library for JavaScript applications. It is used to manage the global state of an application in a predictable way.

15. What is the difference between React context and Redux?

– React Context: Built-in API for sharing state across components without prop drilling.
– Redux: External library for managing global state with a centralized store and middleware support.

16. What is the significance of `shouldComponentUpdate`?

– `shouldComponentUpdate` is a lifecycle method used to optimize performance by preventing unnecessary re-renders of a component.

17. What is the purpose of `useMemo` and `useCallback`?

– `useMemo`: Memoizes a value to avoid expensive calculations on every render.
– `useCallback`: Memoizes a function to prevent unnecessary re-creations.

18. What is React Fragments?

– React Fragments allow you to group multiple elements without adding an extra node to the DOM. Syntax: `<></>` or `<React.Fragment></React.Fragment>`.

19. What is the difference between `useState` and `useReducer`?

– `useState`: Used for managing simple state.
– `useReducer`: Used for managing complex state logic, similar to Redux.

20. What is code splitting in React?

– Code splitting is a technique to split your code into smaller bundles, which are loaded on demand. This improves the performance of your application.

Advanced React.js Interview Questions

21. What is the difference between `componentDidMount` and `useEffect`?

– `componentDidMount` is a lifecycle method in class components that runs after the component is mounted.
– `useEffect` with an empty dependency array (`[]`) mimics `componentDidMount` in functional components.

22. What are Higher-Order Components (HOCs)?

– HOCs are functions that take a component and return a new component with additional props or functionality.

23. What are React Portals?

– Portals allow you to render a child component outside the DOM hierarchy of the parent component. Useful for modals, tooltips, etc.

24. What is the difference between `useRef` and `useState`?

– `useRef`: Used to persist values across renders without causing re-renders.
– `useState`: Used to manage state and triggers re-renders when updated.

25. What is the purpose of `React.memo`?

– `React.memo` is a higher-order component used to memoize a functional component, preventing unnecessary re-renders.

26. What is the difference between server-side rendering (SSR) and client-side rendering (CSR)?

– **SSR**: Renders the React app on the server and sends the HTML to the client.
– **CSR**: Renders the React app in the browser using JavaScript.

27. What is the significance of `Error Boundaries` in React?

– Error boundaries are React components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI.

28. What is the purpose of `React.lazy`?

– `React.lazy` is used to lazily load components, improving performance by loading components only when needed.

29. What is the difference between `useLayoutEffect` and `useEffect`?

– `useLayoutEffect`: Runs synchronously after all DOM mutations.
– `useEffect`: Runs asynchronously after the render is committed to the screen.

30. How do you optimize performance in a React application?

– Use `React.memo`, `useMemo`, and `useCallback`.
– Implement code splitting and lazy loading.
– Optimize re-renders with `shouldComponentUpdate` or `React.PureComponent`.
– Use a state management library like Redux or Context API effectively.

Behavioral and Scenario-Based Questions

1. Explain a project where you used React. What challenges did you face, and how did you overcome them?

2. How do you handle state management in large-scale applications?

3. How do you ensure code reusability in React?

4. What is your approach to debugging React applications?

5. How do you handle API calls in React?

Tips for TCS React.js Interview

– Focus on fundamental concepts like components, props, state, and lifecycle methods.
– Be prepared to explain your thought process and problem-solving approach.
– Practice coding problems related to React, such as creating components, handling forms, and managing state.
– Familiarize yourself with TCS’s tech stack and how React fits into it.

Good luck with your interview! 🚀