express-docs

---
name: "express-docs"
description: "Express is a fast, unopinionated, minimalist web framework for Node.js. It provides a robust set of features for web and mobile applications, including routing, middleware, template rendering, and API development."
license: "MIT"
---

# Express Expert (v5.x)

**Official Documentation:** https://expressjs.com/
**GitHub:** https://github.com/expressjs/express

## What is Express?

Express is a fast, unopinionated, minimalist web framework for Node.js. It provides a robust set of features for web and mobile applications, including routing, middleware, template rendering, and API development.

## Quick Reference

| Topic | File |
|------|------|
| Getting Started (install, hello world, generator, static files, FAQ) | `getting-started.md` |
| Routing (methods, paths, params, handlers, app.route, Router) | `routing.md` |
| Middleware (writing, using, app-level, router-level, error, built-in, third-party) | `middleware.md` |
| Error Handling (catching errors, handlers, async patterns) | `error-handling.md` |
| API: express() & Application Object | `api-app.md` |
| API: Request Object (req properties & methods) | `api-request.md` |
| API: Response Object (res properties & methods) | `api-response.md` |
| API: Router Object (router methods) | `api-router.md` |
| Template Engines (using, developing, rendering) | `template-engines.md` |
| Debugging (DEBUG env var, debugging routes, views) | `debugging.md` |
| Database Integration (MongoDB, MySQL, PostgreSQL, Redis) | `database.md` |
| Security (best practices, helmet, CORS, rate limiting) | `security.md` |
| Performance (best practices, caching, clustering) | `performance.md` |
| Production (healthcheck, graceful shutdown, behind proxies) | `production.md` |
| Migration (to Express 4, to Express 5, breaking changes) | `migration.md` |
| Overriding Express API (methods, properties, TypeScript) | `overriding-api.md` |
| Security Updates (CVEs, vulnerabilities, patches) | `security-updates.md` |

## Hello World

```js
import express from 'express';
const app = express();
const port = 3000;

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

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});
```

## Project Structure

```
myapp/
  app.js              # Main application file
  routes/
    index.js          # Route handlers
    users.js
    api/
      v1.js
  middleware/
    auth.js
    logger.js
  public/             # Static assets
    images/
    css/
    js/
  views/              # Template files
    index.ejs
    layout.ejs
  package.json
```

## Key Concepts

- **Middleware** — Functions that execute during the request-response cycle
- **Routing** — Maps HTTP methods and URLs to handler functions
- **Application Object** — The `app` object created by `express()`
- **Request Object** — `req` represents the HTTP request
- **Response Object** — `res` represents the HTTP response
- **Router** — Isolated instance of middleware and routes (modular routing)
- **Template Engines** — Server-side rendering with EJS, Pug, Handlebars, etc.
- **Error Handling** — Centralized error handling via error middleware
- **Express 5** — Async error support, path-to-regexp v8, removed deprecated APIs

## Prerequisites

- Node.js (v18+ recommended for Express 5)
- JavaScript fundamentals
- HTTP basics (methods, headers, status codes)
- npm/pnpm/yarn package management

## Installation

```bash
# Create a new project
mkdir myapp && cd myapp
npm init -y
npm install express

# Using Express generator
npx express-generator myapp
cd myapp && npm install
```

## References

- [Express Docs](https://expressjs.com/)
- [Express GitHub](https://github.com/expressjs/express)
- [Express 5.x API](https://expressjs.com/en/5x/api.html)
- [Express GitHub Wiki](https://github.com/expressjs/express/wiki)
- [Express Community](https://github.com/expressjs/express/wiki#community)
- [Awesome Express](https://github.com/expressjs/express/wiki#middleware--modules)