1. What is React, and why is it so popular?

React is basically a JavaScript library that helps build UIs generally for client-side single page applications where database records keep changing. Component-based architecture also makes it a very efficient system for the developers to reuse codes and adapt to state changes smoothly. Yet another reason React stands such tall is its virtue of carrying a virtual DOM. When a change occurs, React, rather than updating the whole web page at once, simply updates any part of the DOM that absolutely requires it. In this concern, React performs speedier and smoother. Thus, it manifests itself in a form of efficiency, reusability, and developer-friendly building of web applications.

2. What’s the Key features in React interview guide 2025?

When you’re quizzed on React’s prime compilations, you also have a chance to tend to its strengths. Here are several features that you would want to consider:

Virtual DOM: React machetes all updates with a virtual DOM, ensuring that only those sections of the app affected by the updates re-render.
Component-based architecture: React applications can be described as reusable component collections that incorporate many aspects for easy management and convenience over time.
Unidirectional Data Flow: Through application structure, it makes evident how data flows throughout an application, from parent to child.
JSX (JavaScript XML): Use JSX when you need to code HTML elements inside JavaScript using React, thereby making it all a lot readable and more efficient.

In fact, these few features among others make React a preferred choice for a developer’s modern web application.

3. What is Virtual DOM in React interview guide 2025?

VDOM is a very important concept in React. It is where the real DOM elements are represented in memory. Changes would first happen in the virtual DOM rather than the real one.

Then, React compares the virtual DOM that has changes against the previous version, finds the best updates to apply to the real DOM directly, and consequently increases performance doing so.

4. What are props in React?

Props are the properties through which a parent component passes information to a child component in React. This allows for some reusability of the components while letting the data flow between the components. Once the prop is given to a component, the component cannot change it; props are read-only. I feel that the concept is actually of core essence to any individual expecting ever to follow the React interview guide 2025.

Take for example a UserProfile component that takes a name prop from the parent:

<UserProfile name="John Doe" />

Inside the UserProfile component, you would access the prop like this:

const UserProfile = (props) => {
  return <h1>{props.name}</h1>;
};

One of the most critical and surefire ways, if not the most pivotal tool, to make React flexible and teach it to scale up to large applications is to adjust well to the plethora of props.

5. What are state and its importance in React?

Props maintain the relation that forces the movement of data from parent to child, whereas states store data relative to a particular component. Dynamic data held by state constantly changes and thus determines the render of its corresponding component. State is mutable, which means a component can update its own state with the help of the setState function.

For instance, in a form component, the control over input fields might be in the hands of the state:

const [inputValue, setInputValue] = useState('');

const handleChange = (e) => {
  setInputValue(e.target.value);
};

return <input value={inputValue} onChange={handleChange} />;

State is crucial to creating interactive and dynamic UI because it enables components to respond to user events.

6. What is JSX?

JSX stands for JavaScript XML; it is a very syntax-with extension for JavaScript, which is closer to being like HTML syntax-c. Using this, an industry can write HTML-like directly into JavaScript files. React then compiles JSX to the JavaScript understandable by browser.

JSX compromise examples look similar to HTML; but there are a few differences seen in JSX like usage of className instead of class so as to avoid confusion with the keyword class of JavaScript as shonned in the example of using JSX in:

const Greeting = () => {
  return <h1>Hello, world!</h1>;
};

7. What are functional components vs. class components?

Even though both component types can technically meet the same purpose in React, there is a lot of distinction, such as in syntax and behavior, as well as purpose. Class components are defined using ES6 class syntax and manage their own state and lifecycle methods. Class components provide more power and flexibility for use when preestablished functionality is insufficient.

In contrast, for formulating functional components, a developer will need a JavaScript function and, before the advent of Hooks, was a stateless construct. The ability to manage state and side effects in a function will be at par with class components because of Hooks. As most developers lean toward functional components with cleaner and more compact syntax, it is their most preferred form.

Indeed, React has taken a progressive path toward functional components since the introduction of Hooks. However, class components are still quite prevalent in old React code bases, as well as working with legacy systems. Therefore, learning about the differences of these two component types becomes an essential aspect because class components are not completely obsolete in certain cases.

Functional Components: Simple JavaScript functions, which take props as an argument and return JSX. Functional components are now able to use state and side effects thanks to the introduction of React Hooks.

const Welcome = (props) => {
  return <h1>Hello, {props.name}!</h1>;
};

Class Components: They are ES6 classes that extend React.Component and are expected to implement a render which returns JSX. Class components employ lifecycle methods like componentDidMount, shouldComponentUpdate, etc.

class Welcome extends React.Component {
  render() {
    return <h1>Hello, {this.props.name}!</h1>;
  }
}

Hooks do most of the groundwork by giving each piece a definitive matter to concentrate upon.

8. What are React hooks, and why do developers find them useful?

With React Hooks introduced for state and lifecycle method handling inception into functional components, life used to be somewhat more difficult since the latter offered only class component support for state and lifecycle methods. The hooks empower the functional component field by offering the same features, hereby increasing their possibilities. This makes them an essential part of any React interview guide 2025.

Some common React Hooks are:

useState: This hook allows functional components to have their own states.
useEffect: After rendering, invoking side-effects like data fetching or event listener attachment.
useContext: Helps you to consume contexts in functional components.
useReducer: Can be considered an advanced state management mechanism for handling complex state logic, almost like useState.

Here’s an example using useState:

const Counter = () => {
  const [count, setCount] = useState(0);
  
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
};

Another advantage of hooks are that they facilitate the handling of state and side effects within React components, thereby providing a more simple and readable alternative to class components. For more detailed questions and explanations, explore this ReactJS Interview Questions GitHub repository.

9. What is the dissimilarity existing between a controlled component and uncontrolled component?

Controlled components are those where the value of the input form elements is controlled by the component in React, using React state to store and update the value from the setState.

For example:

const NameForm = () => {
  const [name, setName] = useState('');

  return (
    <form>
      <input type="text" value={name} onChange={(e) => setName(e.target.value)} />
    </form>
  );
};

The DOM handles the component’s state that is not under its control. Instead of utilizing a state component, your value will be available via a ref in your component.

const NameForm = () => {
  const inputRef = useRef();

  const handleSubmit = (e) => {
    e.preventDefault();
    alert('Name: ' + inputRef.current.value);
  };

  return (
    <form onSubmit={handleSubmit}>
      <input type="text" ref={inputRef} />
      <button type="submit">Submit</button>
    </form>
  );
};

Another term for these is “creepy algorithms”, given that they watch individuals conscientiously whether they are aware someone is watching or not.

10. What is React Router and how does it operate?

React developers use React Router to manage the navigation in their React applications. In fact, it would be that layer through which you will be able to create single-page applications (SPAs) with the so-called navigation without reloading pages.

This will be the declarative way towards specifying those routes as well as handling changes in URLs. You declare those routes by using the Route component itself and the navigation will be managed through the Link component.

Hence, here is an example for a simple implementation of React Router:

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

const App = () => (
  <Router>
    <nav>
      <Link to="/">Home</Link>
      <Link to="/about">About</Link>
    </nav>
    <Route path="/" exact component={Home} />
    <Route path="/about" component={About} />
  </Router>
);

const Home = () => <h1>Home Page</h1>;
const About = () => <h1>About Page</h1>;

React Router helps in easy implementation of multi-page navigation in a single-page application, which has a great effect on improving user experience.

Conclusion

It is mandatory for an aspirant to be competent in Render, JSX, functional components, and hooks in a 2023 interview on React. These concepts are not arbitrary, but constitute form the framework of React, while also enabling developers to create efficient, clean, and scalable applications.

Understanding how the Virtual DOM performs optimizations in rendering, how JSX compiles into a human-readable UI, and how Hooks simplified functional components shows depth. State management? It is the secret ingredient that keeps it all dynamic and responsive.

It is a euphoria in itself, experienced by a beginner or a professional programmer, to experience the component-oriented programming in React. So go and build that application, get some real-world practice, and step into that interview all set to blow away your interviewer when the talk is about React! This React interview guide 2025 will help you feel more confident and prepared.

If you want to ace the React interview in 2025 then you need to study very hard upon the Virtual DOM, JSX, Hooks, and State Management. These are not mere terms; instead, they use an understanding cater way in which you will learn about React and learn how to build clean, efficient scalable applications. For deeper insights, check out this React Native Performance Optimization guide.