Express.js for Building Web Applications

Express.js for Building Web Applications

npm install express

2. Creating an Express Application:

To create an Express application, require the Express module and create an instance of the application.

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

3. Defining Routes:

Express allows you to define routes for handling HTTP requests. You can specify the HTTP method (GET, POST, PUT, DELETE, etc.) and the URL path that each route should match.

app.get('/', (req, res) => {
  res.send('Hello, World!');
});

app.get('/about', (req, res) => {
  res.send('About Us');
});

4. Middleware:

Middleware functions are essential in Express.js. They can be used to perform tasks such as logging, authentication, and data parsing. Middleware functions are executed in the order they are added to the application.

// Example middleware function
app.use((req, res, next) => {
  console.log('Request received at:', new Date());
  next(); // Call the next middleware or route handler
});

5. Request and Response Objects:

Express provides request (req) and response (res) objects that carry information about the HTTP request and allow you to send a response back to the client.

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

6. Template Engines:

Express can work with template engines like EJS, Handlebars, or Pug to dynamically render HTML templates and serve dynamic content.

app.set('view engine', 'ejs'); // Example with EJS

app.get('/profile', (req, res) => {
  res.render('profile', { username: 'john_doe' });
});

7. Static Files:

You can serve static files (e.g., CSS, JavaScript, images) using the built-in express.static middleware.

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

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

const port = process.env.PORT || 3000;

app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});