Working with Express.js Framework

Express.js is a lightweight and flexible web framework built on top of Node.js.
It simplifies building web servers, APIs, and backend applications by providing a clean structure and powerful features.

1. Why Use Express.js?

Without Express:

• Complex routing logic

• Repetitive code for handling requests

• Hard-to-maintain server setup

With Express:

• Minimal code

• Easy routing

• Built-in middleware support

• High performance

2. Installing Express

npm install express

3. Creating a Basic Express Server

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

app.get('/', (req, res) => {
  res.send('Welcome to Express.js');
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

4. Handling Routes

GET Request

app.get('/users', (req, res) => {
  res.send('User list');
});

POST Request

app.post('/users', (req, res) => {
  res.send('User created');
});

5. Request and Response Objects

Request (req)

• req.params – URL parameters

• req.query – Query strings

• req.body – Request data

Response (res)

• res.send() – Send response

• res.json() – Send JSON

• res.status() – Set HTTP status

6. Middleware in Express

Middleware functions execute between request and response.

Built-in Middleware

app.use(express.json());

Custom Middleware

app.use((req, res, next) => {
  console.log(req.method, req.url);
  next();
});

7. Serving Static Files

app.use(express.static('public'));

8. Route Parameters

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

9. Error Handling

app.use((err, req, res, next) => {
  res.status(500).send('Server Error');
});

10. Express Project Structure (Typical)

project/
│── routes/
│── controllers/
│── models/
│── app.js
│── package.json

11. Advantages of Express.js

• Fast and unopinionated

• Easy to learn

• Large ecosystem

• Widely used

12. Express vs Node HTTP Module

13. Summary

• Express.js simplifies Node.js development

• Provides routing and middleware

• Ideal for REST APIs and web apps

• Forms the base of many Node frameworks