If you’re getting ready for a React JS interview, you’re in the right place. Whether you’re a frontend developer polishing your skills or a beginner aiming for your first React developer role, understanding the most commonly asked React JS interview questions can make all the difference.
In this guide, we’ll explore top React JS interview questions and answers, from basic concepts to advanced techniques, helping you confidently face technical interviews in 2025.
Why React JS Is a Must-Know for Modern Developers
Before diving into the questions, it’s essential to understand why React JS remains one of the most in-demand skills in web development.
React, developed by Facebook (now Meta), is a JavaScript library used for building fast, interactive user interfaces. Its component-based structure, React Hooks, and virtual DOM make it a top choice for modern frontend interviews.
Key Advantages of React JS
- Reusable UI components
- Improved performance through Virtual DOM
- Easy integration with other JavaScript libraries
- Strong developer community and ecosystem
Employers love developers who can build scalable, efficient apps — and that’s where your React JS interview preparation comes in.
Top React JS Interview Questions and Answers
This section covers a mix of beginner, intermediate, and advanced React JS questions, ensuring you’re ready for any challenge.
1. What Is React JS?
React JS is an open-source JavaScript library used for building user interfaces, especially for single-page applications (SPAs). It enables developers to build reusable components that update efficiently with data changes.
2. Explain the Virtual DOM in React
A frequent question in React interviews is about the Virtual DOM — a core concept that makes React fast.
The Virtual DOM is a lightweight copy of the real DOM. When data changes, React compares the virtual DOM with the previous version using a process called “diffing,” and only updates the parts of the real DOM that have changed.
3. What Are React Components?
React components are the building blocks of a React application. There are two main types:
- Class Components: Use ES6 classes and have lifecycle methods.
- Functional Components: Use plain JavaScript functions and can use React Hooks.
Example:
function Welcome(props) {
return <h1>Hello, {props.name}</h1>;
}
4. What Are React Hooks?
React Hooks were introduced in version 16.8 to simplify state management and side effects in functional components.
Common Hooks include:
- useState() – Manages state in functional components.
- useEffect() – Handles side effects like fetching data.
- useContext() – Accesses context without prop drilling.
5. Explain Props and State
This is a staple in React JS developer interview questions.
- Props: Short for “properties,” they’re used to pass data from parent to child components.
- State: Represents local data managed inside a component.
Difference: Props are immutable, while state is mutable and managed internally.
6. What Is JSX in React?
JSX (JavaScript XML) is a syntax extension that allows you to write HTML-like code in JavaScript. It makes the code more readable and expressive.
Example:
const element = <h1>Welcome to React!</h1>;
7. How Does React Handle Events?
React normalizes events using its own event system called Synthetic Events, ensuring consistent behavior across browsers.
Example:
<button onClick={handleClick}>Click Me</button>
8. What Is the Purpose of Keys in React?
Keys help React identify which items have changed, been added, or removed in lists. Always use unique keys like IDs when rendering arrays.
Bad:
<li key={index}>Item</li>
Better:
<li key={item.id}>Item</li>
9. What Is Lifting State Up in React?
When multiple components need to share state, the state should be lifted up to their nearest common ancestor. This ensures unidirectional data flow, a key React principle.
10. How to Optimize React App Performance
An advanced React interview question for experienced developers focuses on performance optimization.
Strategies include:
- Using React.memo() to prevent unnecessary re-renders
- Splitting code with React.lazy() and Suspense
- Avoiding inline functions in render methods
- Using the Profiler API
Intermediate to Advanced React JS Interview Questions
Once you’ve mastered the basics, interviewers often move into deeper, scenario-based React JS questions.
11. What Is Context API and When Should You Use It?
The Context API helps manage global state without prop drilling. It’s best used for themes, user authentication, or localization.
Example:
const ThemeContext = React.createContext();
12. What Are Higher-Order Components (HOC)?
A Higher-Order Component is a function that takes a component and returns a new one with added functionality.
Used for code reuse and cross-cutting concerns like logging or authorization.
13. Explain React Router
React Router is used to handle navigation in single-page applications.
Example:
<Route path="/home" element={<Home />} />
14. What Are Controlled and Uncontrolled Components?
- Controlled Components: Managed by React via state.
- Uncontrolled Components: Managed by the DOM directly using refs.
Example of Controlled Input:
<input value={name} onChange={(e) => setName(e.target.value)} />
15. What Are Error Boundaries in React?
Error boundaries are React components that catch JavaScript errors in their child components and display fallback UIs. Implemented using componentDidCatch().
Practical React JS Coding Interview Examples
In many React coding interviews, you’ll be asked to write or debug short snippets. Here are some sample tasks:
- Build a counter app using Hooks
- Fetch data from an API using useEffect()
- Create a simple todo list with add/remove functionality
- Implement dark mode using Context API
Tip: Practice on platforms like CodeSandbox or LeetCode to improve your speed and confidence.
React JS Interview Questions for Experienced Developers
For senior roles, expect questions around React architecture, state management, and performance tuning.
Advanced Topics to Review
- Redux / Zustand / Recoil state management
- Server-Side Rendering (Next.js)
- React Performance Profiling
- Testing with Jest and React Testing Library
- TypeScript with React
How to Prepare for a React JS Interview
Here’s a React JS interview preparation guide to streamline your study process.
Step 1: Strengthen Core JavaScript
React heavily relies on JavaScript fundamentals — closures, async/await, destructuring, and ES6 features.
Step 2: Build Small Projects
Create mini-projects like:
- Weather app (API integration)
- Movie search app
- To-do list with Hooks
Step 3: Revise React Concepts
Go over React Hooks, props/state, and component lifecycle.
Step 4: Practice Mock Interviews
Simulate interviews with friends or use online coding challenge sites.
Step 5: Stay Updated
React evolves quickly. Follow the official React blog and GitHub discussions for the latest updates.
Common Mistakes to Avoid in React Interviews
- Confusing props and state
- Forgetting to add keys to lists
- Overusing useEffect() and causing infinite loops
- Ignoring React performance optimization techniques
Conclusion: Your Next Steps to Ace a React JS Interview
Preparing for a React JS interview doesn’t have to be intimidating. With consistent practice, a clear understanding of React components, hooks, and state management, you’ll be ready to handle even the most challenging React interview questions.
Keep building, experimenting, and learning — React rewards curiosity and hands-on experience.
If this React JS interview preparation guide helped you, share it with fellow developers or drop your favorite React JS question in the comments. Let’s grow together as React developers!
