Express.js Framework

Introduction to Express.js

Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.

Key Features:

Robust routing
Focus on high performance
Super-high test coverage
HTTP helpers (redirection, caching, etc)
View system supporting 14+ template engines
Content negotiation
Executable for generating applications

Why Express.js?

Express.js is one of the most popular web frameworks for Node.js, known for its simplicity, flexibility, and large ecosystem of middleware.

Getting Started

Installation

# Create a new directory
mkdir my-express-app
cd my-express-app

# Initialize package.json
npm init -y

# Install Express
npm install express

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

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

app.listen(port, () => {
  console.log(`App listening at http://localhost:${port}`);
});

Project Structure

my-express-app/
  ├── node_modules/
  ├── public/
  │   ├── css/
  │   ├── js/
  │   └── img/
  ├── routes/
  │   ├── index.js
  │   └── users.js
  ├── views/
  │   ├── layouts/
  │   └── partials/
  ├── app.js
  ├── package.json
  └── README.md

Routing

Basic Routing

// Basic routes
app.get('/', (req, res) => {
  res.send('Home page');
});

app.post('/submit', (req, res) => {
  res.send('Got a POST request');
});

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

// Query strings
app.get('/search', (req, res) => {
  const query = req.query.q;
  res.send(`Search query: ${query}`);
});

Router Module

// routes/users.js
const express = require('express');
const router = express.Router();

router.get('/', (req, res) => {
  res.send('Users list');
});

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

module.exports = router;

// app.js
const usersRouter = require('./routes/users');
app.use('/users', usersRouter);

Middleware

Built-in Middleware

// Body parser middleware
app.use(express.json());
app.use(express.urlencoded({ extended: true }));

// Static files middleware
app.use(express.static('public'));

// Cookie parser
const cookieParser = require('cookie-parser');
app.use(cookieParser());

Custom Middleware

// Logger middleware
const logger = (req, res, next) => {
  console.log(`${req.method} ${req.url} ${new Date()}`);
  next();
};

// Error handling middleware
const errorHandler = (err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
};

app.use(logger);
app.use(errorHandler);

Template Engines

EJS Setup

// Install EJS
// npm install ejs

// Set up EJS
app.set('view engine', 'ejs');
app.set('views', './views');

// Render template
app.get('/', (req, res) => {
  res.render('index', {
    title: 'Home Page',
    message: 'Welcome to Express'
  });
});

EJS Template





    
    
    

  <%= title %>




  <%= message %>
  <% if (users.length) { %>
    
      <% users.forEach(user => { %>
        <%= user.name %>
      <% }); %>
    
  <% } %>

Database Integration

MongoDB with Mongoose

// Install Mongoose
// npm install mongoose

// Connect to MongoDB
const mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/myapp', {
  useNewUrlParser: true,
  useUnifiedTopology: true
});

// Define Schema
const userSchema = new mongoose.Schema({
  name: String,
  email: { type: String, required: true, unique: true },
  password: { type: String, required: true },
  createdAt: { type: Date, default: Date.now }
});

const User = mongoose.model('User', userSchema);

Database Operations

// Create
app.post('/users', async (req, res) => {
  try {
    const user = new User(req.body);
    await user.save();
    res.status(201).send(user);
  } catch (error) {
    res.status(400).send(error);
  }
});

// Read
app.get('/users', async (req, res) => {
  try {
    const users = await User.find({});
    res.send(users);
  } catch (error) {
    res.status(500).send(error);
  }
});

Authentication

Passport.js Setup

// Install required packages
// npm install passport passport-local express-session

const passport = require('passport');
const LocalStrategy = require('passport-local').Strategy;
const session = require('express-session');

// Session setup
app.use(session({
  secret: 'your-secret-key',
  resave: false,
  saveUninitialized: false
}));

app.use(passport.initialize());
app.use(passport.session());

Authentication Logic

passport.use(new LocalStrategy(
  async (username, password, done) => {
    try {
      const user = await User.findOne({ username });
      if (!user) {
        return done(null, false);
      }
      const isValid = await user.validatePassword(password);
      if (!isValid) {
        return done(null, false);
      }
      return done(null, user);
    } catch (error) {
      return done(error);
    }
  }
));

// Protected route
app.get('/profile',
  isAuthenticated,
  (req, res) => {
    res.render('profile', { user: req.user });
  }
);

Deployment

Deployment Checklist:

Set environment variables
Configure error handling
Set up logging
Enable HTTPS
Set up monitoring

Production Setup

// Environment variables
require('dotenv').config();

// Production error handler
if (process.env.NODE_ENV === 'production') {
  app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send('Server Error');
  });
}

// Start server
const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});