03 Express Framework

Node.js ka http module basic hai. Real-world apps ke liye hum use karte hain Express.js. Ye Node.js ke liye sabse popular Framework hai jo development ko super fast aur easy banata hai.

1. Setup & Hello World 🌍

Sabse pehle project initialize karein aur Express install karein:

npm init -y
npm install express

Ab server.js banayein:

const express = require('express');
const app = express();
const port = 3000;

// Basic Route
app.get('/', (req, res) => {
  res.send('Hello from Express! 🚀');
});

// Server Start
app.listen(port, () => {
  console.log(`Server chal raha hai port ${port} par...`);
});

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2. Routing (Rasta Dikhana) 🗺️

Routing ka matlab hai decide karna ki user jab kisi URL par jaye to kya hona chahiye.

HTTP Methods (CRUD Basics)

• GET: Data maangna (Read)
• POST: Naya data bhejna (Create)
• PUT/PATCH: Data update karna (Update)
• DELETE: Data uda dena (Delete)

// GET Request
app.get('/users', (req, res) => {
  res.json({ name: "Aditya", role: "Developer" });
});

// POST Request (Data receive karna)
// Note: Iske liye JSON parser middleware chahiye!
app.use(express.json());

app.post('/users', (req, res) => {
  const newUser = req.body; // Body se data nikala
  console.log(newUser);
  res.send('User add ho gaya!');
});

Dynamic Routes (Params)

URL me values pass karna (jaise /users/123).

app.get('/users/:id', (req, res) => {
  const userId = req.params.id;
  res.send(`User ID: ${userId} ka data ye raha...`);
});

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3. Middleware (Gatekeepers) 🛡️

Middleware wo functions hote hain jo Request aur Response ke beech me aate hain. Ye kisi request ko modify kar sakte hain, rok sakte hain, ya log kar sakte hain.

Request (req) -> Middleware -> Response (res)

Example: Logger Middleware

Har request aane par time log karna.

// Middleware define kiya
const logger = (req, res, next) => {
  console.log(`[${new Date().toISOString()}] ${req.method} request aayi: ${req.url}`);
  next(); // Agle function/route par jane do (Zaroori hai!)
};

// App me lagaya
app.use(logger);

// Ab ye '/secret' route par bhi chalega
app.get('/secret', (req, res) => {
  res.send('Ye secret data hai!');
});

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Summary

Express.js Node.js ka backbone hai.

• app.get/post: Routes banane ke liye.
• req.body: Form data lene ke liye (parsing zaroori hai).
• req.params: URL se ID nikalne ke liye.
• Middleware: Request ko beech me rokne ya check karne ke liye (Auth, Logging).

Next Up: Ab dekhte hain security! Authentication kaise karein (Login/Signup)? 🔐