What is React?

React is a JavaScript library for building user interfaces. Created by Facebook (now Meta) in 2013, it has become the most popular front-end library in the world.

Why React?

React solves a fundamental problem in web development: keeping the UI in sync with application state. Before React, developers had to manually manipulate the DOM, which was error-prone and hard to maintain.

Key Concepts

1. Declarative: You describe what the UI should look like, not how to update it
2. Component-Based: Build encapsulated components that manage their own state
3. Learn Once, Write Anywhere: Use React for web, mobile (React Native), and more

How React Works

React introduces a concept called the Virtual DOM:

User Action → State Change → Virtual DOM Update → Diff → Real DOM Update

Instead of updating the real DOM directly, React:

1. Creates a virtual representation of the UI
2. When state changes, creates a new virtual DOM
3. Compares (diffs) the old and new virtual DOM
4. Updates only the parts that actually changed

This makes updates efficient and predictable.

A Simple Example

Here's what a React component looks like:

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

// Usage
<Welcome name="World" />

This might look like HTML, but it's actually JSX - a syntax extension that lets you write HTML-like code in JavaScript.

What You'll Learn

In this course, you'll learn:

• How to create and compose components
• Managing state and props
• Handling events and forms
• Working with hooks
• Building a complete project

Let's get started!