Top Interview Questions for React.js Developers in 2025
React.js has become one of the most popular JavaScript libraries for building user interfaces, and its demand in the tech industry continues to grow. Whether you’re a seasoned React developer or a beginner, preparing for an interview is essential. In this blog, we will cover the top interview questions for React.js developers in 2025 and provide you with tips to ace them.
WEB DEVELOPMENTINTERVIEW PREPARATION
1/9/20254 min read


1. What Is React.js and How Does It Work?
One of the most fundamental questions you can expect in any React.js interview is an explanation of what React.js is and how it works. Interviewers want to assess your basic understanding of the framework.
React is a JavaScript library used for building user interfaces, primarily for single-page applications. React breaks UIs into components, which are reusable and can manage their own state. It uses a virtual DOM to optimize performance by minimizing direct manipulations of the actual DOM, leading to faster rendering.
2. What Is the Virtual DOM and How Does It Improve Performance?
React’s virtual DOM is a key concept that distinguishes it from other JavaScript libraries and frameworks. Interviewers may ask this question to assess your understanding of React’s performance optimization.
The Virtual DOM is an in-memory representation of the real DOM elements. When a component’s state changes, React first updates the virtual DOM. It then compares the updated virtual DOM with the previous version using a diffing algorithm. The changes are then reflected in the actual DOM, minimizing the number of direct updates and improving performance.
3. What Are Components in React, and What Is the Difference Between Class and Functional Components?
Components are the building blocks of React applications. You can expect an interview question that checks your understanding of React components.
Class Components: These are ES6 classes that extend React.Component. They can hold state and have lifecycle methods.
Functional Components: These are simpler components that are created using JavaScript functions. With the introduction of Hooks, functional components can now manage state and lifecycle events.
You should explain that functional components are now more commonly used due to their simplicity and the powerful capabilities provided by React Hooks.
4. What Are React Hooks, and How Do They Work?
React Hooks were introduced in React 16.8, and they allow developers to manage state and side effects in functional components. Interviewers will likely ask about your experience with Hooks.
useState: Allows functional components to have a state.
useEffect: Allows side effects such as data fetching, subscriptions, or manually updating the DOM.
useContext: Used to manage and share state across multiple components without passing props.
useRef: A hook that allows you to persist values across renders without causing re-renders.
Explain how you’ve used these hooks in your projects to simplify state management and side effects in functional components.
5. What Is the Concept of “State” in React?
State is a crucial concept in React, and interviewers often ask about it to understand your ability to manage and manipulate data within components.
In React, state refers to data that is specific to a component and can change over time. When the state of a component changes, React re-renders the component to reflect the updated state. State can be managed in both class components (using this.state) and functional components (using the useState hook).
6. What Are Props in React?
Props (short for "properties") are used to pass data from one component to another in React. Understanding how props work is essential for any React developer.
Props are immutable and passed from a parent component to a child component.
They can be any JavaScript value (string, number, array, object, function, etc.) and help customize components.
React uses props to create dynamic and reusable components.
Provide an example of how props are passed from parent to child components to illustrate their importance.
7. What Is JSX and How Does It Work in React?
JSX (JavaScript XML) is a syntax extension for JavaScript that allows you to write HTML-like code within your JavaScript code. This is an essential concept for React developers, and interviewers may ask about it.
JSX is not required for writing React components but is widely used because it simplifies writing components and makes the code more readable. Under the hood, JSX is transformed into React.createElement() calls.
Example:
jsx
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const element = <h1>Hello, React!</h1>;
8. What Is the React Component Lifecycle?
Understanding the component lifecycle is important for managing the behavior of your application at various stages. This question tests your knowledge of class components, although with the introduction of Hooks, functional components also have lifecycle features.
For class components, the lifecycle includes methods like:
componentDidMount: Called once the component is mounted (ideal for data fetching).
componentDidUpdate: Called after the component updates.
componentWillUnmount: Called just before the component is removed from the DOM.
For functional components, the useEffect hook serves a similar purpose.
9. How Do You Handle Forms in React?
Forms are a key feature of many web applications, and React provides various ways to manage form data. Interviewers often want to test your ability to handle form inputs and submission events.
Controlled Components: In controlled components, form data is managed by the component's state. The value of the input is tied to the component state, and any changes to the form fields update the state.
Uncontrolled Components: These are form elements where React doesn’t control the state of the input fields. Instead, you use refs to access the input values directly.
Explain your experience with both approaches and the scenarios where each one is appropriate.
10. What Are Higher-Order Components (HOCs) in React?
Higher-Order Components (HOCs) are a pattern in React used to enhance the functionality of a component. HOCs are functions that take a component and return a new component with additional props.
You can explain that HOCs are often used for tasks such as:
Adding authentication checks
Fetching data
Handling error boundaries
An example of an HOC might look like:
javascript
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function withLoading(Component) { return function LoadingComponent({ isLoading, ...props }) { if (isLoading) return <div>Loading...</div>; return <Component {...props} />; }; }
11. What Is Redux and How Does It Work with React?
Redux is a predictable state container for JavaScript applications. It is commonly used with React to manage the global state of the application.
Redux works by using a store to hold the entire state of the application. Actions are dispatched to modify the state, and reducers define how the state should change in response to those actions.
You should explain how Redux helps manage complex state logic and keeps components decoupled from one another.
Conclusion
React.js continues to be a powerful and popular tool for building dynamic web applications. By preparing for these common interview questions, you’ll be able to confidently answer React.js-related inquiries in 2025. Keep practicing, stay updated with the latest React features, and refine your skills to stand out in the competitive job market.
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