React Interview Questions for Freshers and Experienced Developers

React Interview Questions for Freshers and Experienced Developers

React is one of the most popular JavaScript libraries for building user interfaces, and its demand has risen significantly in the developer community. Whether you’re preparing for your first React interview or an experienced developer looking to level up, this guide covers the most frequently asked React interview questions for both freshers and experienced developers. This article is your ultimate resource to ace your interview with confidence!

React Interview Questions for Freshers

Freshers or entry-level developers are expected to have a strong understanding of React’s core concepts. Here are some key React questions that will likely come up in interviews:

1. What is React?

React is a JavaScript library developed by Facebook that helps developers build user interfaces, particularly single-page applications (SPAs). It allows for the creation of reusable UI components and efficiently updates and renders the right components when your data changes.

2. What are the advantages of using React?

React offers several advantages, including:

• Reusable Components: You can create reusable UI components that make development faster and easier.
• Virtual DOM: React uses a virtual DOM to optimize rendering, improving app performance.
• Strong Community Support: React is widely used and has a large community, ensuring a wealth of tutorials, libraries, and tools.
• Unidirectional Data Flow: React’s data flow ensures consistency and ease of debugging.

3. What are the limitations of React?

While React is a powerful library, it has a few limitations:

• JSX Syntax: React uses JSX, which may seem unusual to beginners.
• SEO Challenges: React’s client-side rendering may present SEO issues (though this can be mitigated with server-side rendering).
• Learning Curve: React’s complexity increases when you dive into advanced concepts like hooks, context, and state management.

4. What is useState() in React?

useState() is a React Hook that allows you to add state to functional components. It returns a state variable and a function to update that state.

5. What are keys in React?

In React, keys help identify which items in a list are changed, added, or removed. They should be unique and stable to help React efficiently update the UI.

6. What is JSX?

JSX (JavaScript XML) is a syntax extension for JavaScript that allows you to write HTML-like code inside your JavaScript code. It’s a core feature of React that simplifies UI development.

7. What are the differences between functional and class components?

• Functional Components: These are simple JavaScript functions that accept props and return JSX.
• Class Components: These are ES6 classes that extend React.Component and have lifecycle methods.

8. What is the virtual DOM? How does React use the virtual DOM to render the UI?

The Virtual DOM is a lightweight copy of the actual DOM. React uses it to improve app performance by updating only the parts of the UI that have changed, rather than re-rendering the entire UI.

9. What are the differences between controlled and uncontrolled components?

• Controlled Components: Form elements whose values are controlled by React state.
• Uncontrolled Components: Form elements whose values are handled by the DOM.

10. What are props in React?

Props (short for properties) are used to pass data from a parent component to a child component. Props are immutable in the child component.

11. Explain React state and props.

State is a mutable data structure that is owned by a component, while props are immutable data passed down from a parent component.

12. Explain about types of side effects in React component.

Side effects in React can include data fetching, subscriptions, or manually changing the DOM. useEffect() is used to handle side effects.

13. What is prop drilling in React?

Prop drilling refers to the process of passing props through multiple layers of components until they reach the component that needs them.

14. What are error boundaries?

Error boundaries are React components that catch JavaScript errors in their child components and display a fallback UI instead of crashing the whole app.

15. What is React Hooks?

React Hooks are functions that let you “hook into” React state and lifecycle features from functional components.

16. Explain React Hooks.

React Hooks, like useState, useEffect, useContext, and others, allow developers to use React features in functional components without needing to write class components.

17. What are the rules that must be followed while using React Hooks?

• Hooks must be called at the top level.
• They must be called from React function components or custom hooks.

18. What is the use of useEffect React Hooks?

useEffect is a Hook used for handling side effects in functional components, such as data fetching, subscriptions, and DOM manipulation.

19. Why do React Hooks make use of refs?

Refs are used in React to reference DOM elements directly without causing re-renders.

20. What are Custom Hooks?

Custom Hooks are JavaScript functions that allow you to reuse stateful logic across multiple components.

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React Interview Questions for Experienced Developers

Experienced React developers should be well-versed in advanced topics such as performance optimization, routing, and state management. Here’s a list of questions for more experienced developers:

1. How to perform automatic redirect after login?

You can use React Router’s useNavigate hook to navigate to a different route after a successful login.

2. How to pass data between sibling components using React Router?

You can pass data between sibling components using React context or by managing the shared state in a parent component.

3. How to re-render the view when the browser is resized?

You can use the useState and useEffect hooks to track the window size and update the state when the browser is resized.

4. How to create a switching component for displaying different pages?

You can use React Router to create dynamic routing and switch between components based on the current route.

5. Explain how to create a simple React Hooks example program.

You can create a simple React program using useState and useEffect hooks to manage state and handle side effects in functional components.

6. Explain conditional rendering in React.

Conditional rendering in React is done by using JavaScript operators like if, ternary operator, or logical && inside JSX to render different components based on certain conditions.

7. Can React Hook replace Redux?

React Hooks can manage local component state and context, but Redux is still preferred for managing complex global state across many components.

8. What is React Router?

React Router is a library for handling routing in React applications. It allows for navigation between different views without reloading the page.

9. Do Hooks cover all the functionalities provided by the classes?

Yes, React Hooks offer the same functionalities as class components, such as managing state and lifecycle methods.

10. How does the performance of using Hooks differ in comparison with classes?

Hooks generally lead to cleaner and more efficient code in functional components. They enable better performance optimizations like memoization with useMemo and useCallback.

11. Differentiate React Hooks vs Classes.

Class components are based on ES6 classes and have lifecycle methods, whereas Hooks offer a way to use state and side effects in functional components.

12. Explain about types of Hooks in React.

Common hooks include:

• useState
• useEffect
• useContext
• useReducer
• useRef
• useMemo
• useCallback

13. Does React Hook work with static typing?

Yes, React Hooks can be used with TypeScript for static typing, which helps in maintaining type safety across your React components.

14. What are the lifecycle methods of React?

Lifecycle methods in class components include componentDidMount, componentDidUpdate, and componentWillUnmount. Functional components use hooks like useEffect to replicate lifecycle behaviors.

15. What are the different phases of the component lifecycle?

The component lifecycle includes:

• Mounting: The component is being created and inserted into the DOM.
• Updating: The component is being re-rendered due to changes in state or props.
• Unmounting: The component is being removed from the DOM.

16. What are Higher Order Components?

Higher Order Components (HOCs) are functions that take a component and return a new component with additional props or functionality.

17. How to pass data between React components?

Data can be passed between components using props, state, or React context.

18. Name a few techniques to optimize React app performance.

• Memoization: Use React.memo to prevent unnecessary re-renders.
• Code splitting: Load only necessary code using dynamic imports.
• Lazy loading: Load components only when required.
• Pure components: Use React.PureComponent for optimization.

19. What are the different ways to style a React component?

You can style React components using:

• Inline styles
• CSS Modules
• Styled-components
• SASS/SCSS

20. How to prevent re-renders in React?

Use React.memo for functional components, shouldComponentUpdate in class components, and hooks like useMemo and useCallback for memoization.

21. Explain Strict Mode in React.

Strict Mode is a tool for highlighting potential problems in an application. It helps identify components with unsafe lifecycle methods, side effects, and other potential issues.