Backend with Node.js

In This Section, You Will Learn:

• • What backend development is
• • Node.js – JavaScript on the server
• • Express.js – the most popular framework
• • REST APIs – how frontend talks to backend
• • Creating your first API endpoints
• • Handling requests and responses

What is Backend Development?

• The backend is everything the user DOESN'T see.
• Backend Handles:
• • User authentication (login/signup)
• • Database operations (saving/fetching data)
• • Business logic (calculations, validations)
• • File uploads
• • Payment processing
• • Email sending
• Frontend vs Backend:
• • Frontend: 'Show the login form'
• • Backend: 'Check if password is correct'
• • Frontend: 'Display user profile'
• • Backend: 'Fetch user data from database'
• Full-stack = Frontend + Backend = Build complete applications

Node.js – JavaScript on Servers

• Node.js lets you run JavaScript OUTSIDE the browser.
• Why Node.js:
• • Same language (JS) for frontend AND backend
• • Very fast (non-blocking I/O)
• • Huge ecosystem (npm packages)
• • Used by: Netflix, LinkedIn, PayPal, Uber
• Setting Up:
• 1. Install Node.js from nodejs.org
• 2. Create a project folder
• 3. Run: npm init -y
• 4. Create index.js
• Simple Node Server:
• “`
• const http = require('http');
• const server = http.createServer((req, res) => {
• res.end('Hello World!');
• });
• server.listen(3000);
• // Visit: http://localhost:3000
• “`

Express.js – The Popular Framework

• Express makes building APIs MUCH easier than raw Node.
• Installing Express:
• “`
• npm install express
• “`
• Basic Express Server:
• “`
• const express = require('express');
• const app = express();
• app.get('/', (req, res) => {
• res.send('Hello World!');
• });
• app.listen(3000, () => {
• console.log('Server running on port 3000');
• });
• “`
• Key Express Features:
• • Routing (handle different URLs)
• • Middleware (process requests)
• • Static files (serve images, CSS)
• • Easy JSON handling

REST APIs – How Data Moves

• REST API = Rules for how frontend and backend communicate.
• HTTP Methods:
• • GET: Fetch data
• • POST: Create new data
• • PUT/PATCH: Update existing data
• • DELETE: Remove data
• Example API Routes:
• “`
• // Get all users
• app.get('/api/users', (req, res) => {…});
• // Get one user
• app.get('/api/users/:id', (req, res) => {…});
• // Create user
• app.post('/api/users', (req, res) => {…});
• // Update user
• app.put('/api/users/:id', (req, res) => {…});
• // Delete user
• app.delete('/api/users/:id', (req, res) => {…});
• “`
• JSON: Data format used for API communication

Handling Requests and Responses

• Request (req): What the client sends
• Response (res): What the server returns
• Getting Data from Requests:
• “`
• // URL parameters: /users/123
• app.get('/users/:id', (req, res) => {
• const userId = req.params.id;
• });
• // Query strings: /search?q=hello
• app.get('/search', (req, res) => {
• const query = req.query.q;
• });
• // Body data (POST)
• app.use(express.json());
• app.post('/users', (req, res) => {
• const { name, email } = req.body;
• });
• “`
• Sending Responses:
• “`
• res.json({ message: 'Success' });
• res.status(404).json({ error: 'Not found' });
• “`