🎉 Introduction to React (React 18 & 19 Updates)

React, an efficient, flexible, and open-source JavaScript library 🛠️, continues to evolve with versions 18 and 19, offering powerful new features. Developed by Jordan Walke at Facebook, React was first deployed on Facebook’s news feed in 2011 and on Instagram in 2012.

Why is React popular?

• Component-based development 🏗️
• Virtual DOM for improved performance ⚡
• Easy integration with other libraries 📚

New in React 18 & 19:

• Concurrent Rendering: Better app responsiveness by breaking rendering into smaller, non-blocking tasks.
• Automatic Batching: Multiple state updates within a single event handler are now automatically batched.
• React Server Components: Streamlined data fetching and SSR optimizations 🌐.

✨ React Interview Questions for Freshers (React 18 & 19 Ready)

1. What is React?

React is a front-end, open-source JavaScript library designed to build user interfaces for single-page applications 🖼️. It enables developers to create reusable UI components.

Key Features (React 18+):

• Server-side rendering with Suspense 🖥️
• Virtual DOM 🏎️
• Concurrent rendering 🔄
• Component-based architecture 🏗️

2. What are the advantages of React?

🟢 Advantages:

• Virtual DOM: Enhances performance by reducing expensive DOM updates ⚡.
• Gentle learning curve: Easier to learn than other frameworks like Angular 🧑‍📚.
• SEO-friendly: Server-side rendering boosts search engine optimization 📈.
• Reusable components: Promotes faster development through modular code 🏗️.
• Rich ecosystem: Access to numerous tools and libraries 🌐.
• React 18/19 Features: Concurrent rendering and automatic batching for smoother user experience.

3. What are the limitations of React?

🔴 Limitations:

• React is a library, not a complete framework 🔧.
• Learning all components and features can take time 🕰️.
• Difficult for beginners to fully grasp 🤯.
• JSX and inline templating may increase complexity 🛠️.

4. What is useState() in React?

The useState() Hook enables state management in functional components 🛠️. It returns an array with two elements: the current state and a function to update it.

Example:

const [count, setCounter] = useState(0);
const increment = () => setCounter(count + 1);

5. What are keys in React?

Keys are special attributes in lists to help React identify elements that have changed, are added, or removed 🔑.

Example:

const ids = [1, 2, 3];
const listItems = ids.map(id => <li key={id}>{id}</li>);

Importance of keys:

• Enables efficient rendering ⚡
• Provides unique identity for elements 🔍

6. What is JSX?

JSX (JavaScript XML) allows HTML-like syntax inside JavaScript 📜. It improves code readability and maintainability.

Example:

const element = <h1>Hello, JSX!</h1>;

7. Functional vs. Class Components

Hooks have made functional components equivalent to class components in terms of state and lifecycle management 🌀.

Example Functional Component:

function Greeting({ name }) {
  return <h1>Hello, {name}!</h1>;
}

8. What is the Virtual DOM?

The Virtual DOM is a lightweight representation of the Real DOM 🏗️. React updates the Virtual DOM, compares it to the previous state, and efficiently updates the Real DOM.

Why Virtual DOM?

• Faster updates ⚡
• Reduces unnecessary re-rendering 🚀

9. Controlled vs. Uncontrolled Components

Example of Controlled Component:

function Form() {
  const [inputValue, setInputValue] = useState("");
  return <input value={inputValue} onChange={e => setInputValue(e.target.value)} />;
}

10. What are props in React?

Props are inputs passed from a parent component to a child component 📦.

Example:

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

11. State vs. Props

12. What are Error Boundaries?

Error boundaries catch rendering errors and prevent the entire app from crashing 🚨.

Example:

class ErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }

  static getDerivedStateFromError() {
    return { hasError: true };
  }

  render() {
    if (this.state.hasError) return <h1>Something went wrong!</h1>;
    return this.props.children;
  }
}

13. What is prop drilling in React?

Prop drilling happens when data is passed from a parent to a deeply nested component through intermediate components 🔄.

Disadvantage: Tight coupling between components.

14. What is the use of React Hooks?

Hooks are built-in functions that enable state and lifecycle management without class components ⚙️.

Popular Hooks:

• useState: Manages state.
• useEffect: Handles side effects.
• useRef: Accesses DOM elements.
• React 18+: Concurrent rendering hooks for better performance.

Example:

function Counter() {
  const [count, setCount] = useState(0);
  return <button onClick={() => setCount(count + 1)}>Count: {count}</button>;
}

💡 Final Thoughts: React remains at the forefront of modern front-end development. These questions, updated for React 18 and 19, will prepare you for interviews. Good luck! 🍀