Express.js Cheat Sheet

Here’s a cheat sheet for Express.js:

Installation

# Install Express globally
npm install -g express

# Create a new Express app
express myapp

# Install dependencies
cd myapp
npm install

Basic Server Setup

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

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

Routing

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

// Handling POST requests
app.post('/api/data', (req, res) => {
  // Handle POST data
  res.send('Data received!');
});

Middleware

// Custom middleware
const myMiddleware = (req, res, next) => {
  // Your logic here
  next();
};

app.use(myMiddleware);

// Built-in middleware
app.use(express.json()); // Parse JSON in requests
app.use(express.urlencoded({ extended: true })); // Parse URL-encoded data

Route Parameters

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

Static Files

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

Template Engines (Example: EJS)

# Install EJS
npm install ejs

// Set EJS as the view engine
app.set('view engine', 'ejs');

// Render EJS views
app.get('/profile', (req, res) => {
  res.render('profile', { username: 'JohnDoe' });
});

Error Handling

// Custom error handling middleware
app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something went wrong!');
});

Express Router

// Create a router
const router = express.Router();

// Use the router in your app
app.use('/api', router);

// Define routes in the router
router.get('/data', (req, res) => {
  res.json({ message: 'API data' });
});

Middleware Chain

// Middleware chain
app.use(middleware1);
app.use(middleware2);
app.use(middleware3);

Express Generator

# Install Express Generator
npm install -g express-generator

# Create a new app using the generator
express myapp
cd myapp
npm install
npm start

Additional Resources

• Express.js Documentation

This cheat sheet covers basic Express.js setup, routing, middleware, static files, template engines, error handling, Express Router, and more.