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KIRAN RAJ
KIRAN RAJ

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React

  1. What is React?
  2. React (also called React.js) is a JavaScript library used to build user interfaces, especially for single-page applications (SPAs).
  3. It was developed and maintained by Facebook (Meta).
  4. In simple words: React helps you build fast, interactive, and modern web applications.

2.Why React?

  • In traditional websites, when you move from one page to another, the entire page reloads.
  • React avoids this and updates only what is needed.

Reasons to Use React:
1️⃣ Component-Based Architecture:
React applications are built using components.

Examples:

  • Header component
  • Footer component
  • Button component

Components are reusable and easy to maintain.

2️⃣ Virtual DOM (High Performance):

  • React uses a Virtual DOM, which is a lightweight copy of the real DOM.
    When data changes:

  • React compares the old Virtual DOM with the new one

  • Updates only the changed parts in the real DOM

This makes React very fast and efficient.

3️⃣ Single Page Application (SPA)

React applications do not reload the page.

  • Only content changes
  • Page feels smooth and responsive

Example apps: Facebook, Instagram, Netflix

4️⃣ Strong Community & Career Opportunities

  • Huge developer community
  • Many tutorials and libraries
  • High demand for React developers

2.How React Works?

Let’s understand React’s working step by step.

🧠 Step 1: Components

Everything in React is a component.

function Hello() {
  return <h1>Hello World</h1>;
}
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🧠 Step 2: JSX

React uses JSX, which looks like HTML but works inside JavaScript.

const name = "Kiran";
<h1>Hello {name}</h1>
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JSX makes code easier to read and write.

🧠 Step 3: State and Props

🔹 State
State is data that belongs to a component.

const [count, setCount] = useState(0);
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When state changes, the UI updates automatically.

🔹 Props
Props are used to pass data from one component to another.

<Child name="React" />
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🧠 Step 4: Virtual DOM Update

When state or props change:

  • Virtual DOM updates
  • React finds the difference
  • Only required changes are applied to the real DOM

This keeps the app fast and smooth.

  1. Where is React Used?
  • Social media platforms
  • E-commerce websites
  • Dashboards
  • Web applications
  • Mobile apps (using React Native)

Popular companies using React:

  • Facebook
  • Instagram
  • Netflix
  • WhatsApp Web

Conclusion:

React is:

  • A powerful library for building UI
  • Fast, scalable, and reusable
  • One of the most popular tools in modern web development

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