ReactJS

React.js – A Powerful JavaScript Library for Modern Web Development

Introduction

React.js is an open-source JavaScript library developed and maintained by Meta (formerly Facebook). It is widely used for building interactive and efficient user interfaces (UIs), particularly for single-page applications (SPAs) and mobile applications. React’s component-based architecture enables developers to create reusable UI elements, leading to scalable and maintainable codebases.

Why Use React.js?

React has become one of the most popular front-end libraries due to its:

• Component-Based Architecture – Encourages reusability and modularity in code.

• Virtual DOM (VDOM) – Optimizes rendering for better performance.

• Unidirectional Data Flow – Ensures predictable application behavior.

• Rich Ecosystem – Supported by a vast community with libraries like React Router, Redux, and Next.js.

• Cross-Platform Support – Can be used in web applications, mobile apps (React Native), and even desktop applications (Electron).

Key Features of React.js

1. JSX (JavaScript XML)

React uses JSX, a syntax extension that allows developers to write UI components using an HTML-like structure inside JavaScript.

const HelloWorld = () => {
  return <h1>Hello, World!</h1>;
};

2. Components and Props

React applications are built using components, which can be either functional or class-based. These components accept props to make them dynamic.

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

3. State Management

React provides useState() for handling component-level state. For larger applications, state management libraries like Redux, Recoil, or Zustand can be used.

import { useState } from "react";

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

4. React Hooks

Hooks allow functional components to have state and lifecycle methods. Popular hooks include:

• useState – Manages state in functional components.

• useEffect – Handles side effects such as API calls.

• useContext – Provides global state without prop drilling.

Example of useEffect for fetching data:

import { useEffect, useState } from "react";

const FetchData = () => {
  const [data, setData] = useState([]);

  useEffect(() => {
    fetch("https://jsonplaceholder.typicode.com/posts")
      .then((response) => response.json())
      .then((json) => setData(json));
  }, []);

  return (
    <ul>
      {data.map((item) => (
        <li key={item.id}>{item.title}</li>
      ))}
    </ul>
  );
};

5. React Router

React Router enables client-side navigation without reloading the page.

import { BrowserRouter as Router, Route, Routes } from "react-router-dom";
import Home from "./Home";
import About from "./About";

const App = () => {
  return (
    <Router>
      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/about" element={<About />} />
      </Routes>
    </Router>
  );
};

Advanced Topics in React.js

• Next.js – A React framework for server-side rendering (SSR) and static site generation (SSG).

• React Native – Builds mobile apps using React components.

• State Management Solutions – Redux, MobX, Recoil, Zustand.

• Performance Optimization – Lazy loading, memoization (React.memo), and code splitting.