What is React?

React is a JavaScript library for building user interfaces, created by Facebook (now Meta) in 2013. It revolutionized web development by introducing a component-based architecture and the concept of the Virtual DOM.

What Makes React Special

• Component-Based Architecture: Instead of building pages, you build components that can be reused anywhere

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

// Use it anywhere
<Welcome name="Alice" />
<Welcome name="Bob" />

• Declarative UI: You describe what the UI should look like, not how to manipulate it

function TodoList({ todos }) {
  return (
    <ul>
      {todos.map(todo => (
        <li key={todo.id} className={todo.completed ? 'done' : ''}>
          {todo.text}
        </li>
      ))}
    </ul>
  )
}

• Efficient Updates:

React's Virtual DOM ensures only the parts that actually changed get updated in the real DOM

React Hooks: The Game Changer

React Hooks (introduced in React 16.8) allow you to use state and other React features in functional components:

import React, { useState, useEffect } from 'react'

function UserProfile({ userId }) {
  const [user, setUser] = useState(null)
  const [loading, setLoading] = useState(true)

  useEffect(() => {
    fetch(`/api/users/${userId}`)
      .then(res => res.json())
      .then(userData => {
        setUser(userData)
        setLoading(false)
      })
  }, [userId])

  if (loading) return <div>Loading...</div>
  return <div>Welcome, {user.name}!</div>
}

The React Ecosystem

React isn't just a library—it's an entire ecosystem:

• Routing: React Router for navigation
• State Management: TanStack Query, Zustand, or built-in Context API
• Styling: CSS Modules, Styled Components, or Tailwind CSS
• Frameworks: Next.js or React Router v7 for full-stack applications
• Testing: Vitest, React Testing Library
• DevTools: React Developer Tools browser extension

Why React Became So Popular

• Large Community: Millions of developers and thousands of libraries
• Industry Adoption: Used by Facebook, Netflix, Uber, and countless others
• Job Market: High demand for React developers worldwide
• Constant Innovation: Regular updates and new features
• Learning Resources: Excellent documentation and tutorials
• Flexibility: Works well with other libraries and frameworks