Express

Introduction Getting Started Installation Basic Configuration Server Setup Basic Server Health Check Routing Basic Routes Route Parameters Middleware Custom Logger Middleware Built-in Middleware Request & Response Request Object Response Object Error Handling Custom Error Handler Best Practices Project Structure Route Organization Security Best Practices Performance Tips

Introduction

Express.js is a minimal, unopinionated web framework for Node.js that provides a robust set of features for building web applications and APIs. Unlike opinionated frameworks like Nest.js, Fastify, or Django, Express gives developers more flexibility in structuring their applications.

Getting Started

Installation


npm init -y
npm install express@5
npm install nodemon --save-dev

Basic Configuration

Update package.json:


{
  "type": "module",
  "scripts": {
    "dev": "nodemon --watch --env-file=.env main.js",
    "deploy": "node main.js"
  }
}

Server Setup

Basic Server


import express from "express";

const app = express();
const PORT = process.env.PORT || 3000;

// Parse JSON bodies
app.use(express.json());
// Parse URL-encoded bodies
app.use(express.urlencoded({ extended: false }));

app.get("/", (req, res) => {
  res.send("API is active");
});

app.listen(PORT, () => {
  console.log(`Server started on ${PORT}`);
});

Health Check


app.get("/health", (req, res) => {
  res.status(200).json({ status: "healthy" });
});

Routing

Basic Routes


// GET request
app.get("/api/items", (req, res) => {
  res.json({ items: [] });
});

// POST request
app.post("/api/items", (req, res) => {
  res.status(201).json({ message: "Item created" });
});

// Dynamic routes
app.get("/api/items/:id", (req, res) => {
  const id = parseInt(req.params.id);
  res.json({ id });
});

Route Parameters

URL Parameters: req.params

Query Parameters: req.query

Request Body: req.body

Middleware

Custom Logger Middleware


const requestLogger = (req, res, next) => {
  console.log(`${req.method} ${req.path} at ${new Date().toISOString()}`);
  next();
};

app.use(requestLogger);

Built-in Middleware


// JSON Parser
app.use(express.json());

// URL-encoded Parser
app.use(express.urlencoded({ extended: false }));

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

// Compression: npm install compression
import compression from 'compression';
app.use(compression());

Request & Response

Request Object

req.params: URL parameters

req.query: Query string parameters

req.body: Request body (for POST/PUT)

req.headers: Request headers

req.path: Request path

req.method: HTTP method

Response Object


// Send JSON
res.json({ data: "value" });

// Send Status
res.status(200).send("Success");

// Send File
import path from 'path';
res.sendFile(path.join(process.cwd(), 'public', 'index.html'));

Error Handling

Custom Error Handler


const errorHandler = (err, req, res, next) => {
  const statusCode = err.statusCode || 500;
  res.status(statusCode).json({
    error: {
      message: err.message,
      stack: process.env.NODE_ENV === 'production' ? '🥞' : err.stack
    }
  });
};

// 404 Handler
const notFound = (req, res, next) => {
  const error = new Error(`Not Found - ${req.originalUrl}`);
  res.status(404);
  next(error);
};

// Use handlers
app.use(notFound);
app.use(errorHandler);

Best Practices

Project Structure


project/
├── controllers/    # Route handlers
├── middleware/     # Custom middleware
├── models/         # Data models
├── routes/         # Route definitions
├── public/         # Static files
├── main.js         # Entry point
└── package.json

Route Organization


// routes/items.js
import express from 'express';
const router = express.Router();

router.get('/', (req, res) => {
  res.json({ items: [] });
});

export default router;

// main.js
import itemsRouter from './routes/items.js';
app.use('/api/items', itemsRouter);

Security Best Practices

Always validate input

Use CORS middleware for cross-origin requests

Set security headers

Rate limit requests

Use HTTPS in production

Implement proper authentication/authorization

Performance Tips

Use compression middleware

Implement caching

Use async/await for asynchronous operations

Proper error handling

Load balancing for production

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