React JS has become one of the most in-demand JavaScript libraries for building interactive and dynamic user interfaces. Created by Facebook, React has taken front-end development by storm, especially with its component-based architecture and virtual DOM.

If you're a fresher preparing for your first job in web development, it's crucial to be ready for React JS interview questions. At DigiSnare Technologies, we’ve put together a beginner-friendly list of top React JS interview questions and answers to help you crack your next interview.

What is React JS?

React JS is a front-end JavaScript library used to build user interfaces, especially for single-page applications. It allows developers to create reusable UI components.

What are the features of React?

• Virtual DOM
• JSX (JavaScript XML)
• Component-based architecture
• One-way data binding
• Fast rendering
• Reusable components

What is JSX?

JSX stands for JavaScript XML. It allows you to write HTML-like code inside JavaScript. It helps make code more readable and easier to write React components.

const element = 
Hello, World!
;

What is the difference between a class component and a functional component?

What is a component in React?

A component is a reusable piece of code that represents a part of the UI. React has two types of components:

• Functional Components
• Class Components

What are props in React?

Props (short for properties) are used to pass data from one component to another. They are read-only and help create dynamic content.

function Welcome(props) {
    return 
Hello, {props.name}
;
}

What is state in React?

State is an object used to store component-specific data that can change over time. When the state changes, React re-renders the component.

What is the use of useState hook?

useState is a React hook that lets you add state to functional components.

const [count, setCount] = useState(0);

What is the Virtual DOM?

Virtual DOM is a lightweight copy of the real DOM. React uses it to update only the changed parts of the DOM, improving performance.

What is the useEffect hook in React?

useEffect allows you to perform side effects like data fetching, subscriptions, or manually changing the DOM from within a functional component.

useEffect(() => {
        console.log("Component mounted");
}, []);

What are React lifecycle methods?

These are special methods in class components that are automatically invoked at different stages of a component’s life:

• componentDidMount()
• componentDidUpdate()
• componentWillUnmount()

How does routing work in React?

React uses React Router for client-side routing. It allows developers to navigate between components/pages without reloading the page.

import { BrowserRouter as Router, Route } from "react-router-dom";

How do you pass data between components in React?

• From parent to child: via props
• From child to parent: via callback functions
• Between unrelated components: via context API or state management libraries

How do you handle forms in React?

You can use controlled components with state to handle form input:

 setName(e.target.value)} />

• Understand the basics of JavaScript and ES6
• Practice with small projects (To-do app, calculator, etc.)
• Be confident in explaining React hooks and component lifecycle
• Keep updated with the latest React features and versions

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