Express

Express is a fast, unopinionated, minimalist web framework for Node.js created by TJ Holowaychuk in 2010 and now maintained by the OpenJS Foundation, serving as the most widely adopted Node.js web framework with over thirty million weekly npm downloads, powering web applications and APIs for companies including Uber, IBM, Accenture, and Intuit, and serving as the foundation for popular higher-level frameworks including NestJS, Keystone, and Sails. The routing system provides flexible pattern matching for HTTP methods and URL paths with parameterized routes, regular expression routes, route parameters with optional regex constraints, and route grouping through Express Router for modular application organization, supporting middleware chains that process requests sequentially through logging, body parsing, cookie handling, authentication, compression, static file serving, and error handling layers. The middleware architecture enables the ecosystem of over ten thousand npm packages that extend functionality, with application-level middleware applied to all requests, router-level middleware for specific route groups, error-handling middleware for centralized exception processing, and built-in middleware for serving static files, JSON body parsing, and URL-encoded form data processing. The template engine support enables server-side HTML rendering through integration with Pug, EJS, Handlebars, Mustache, and dozens of other template engines, while the response API provides methods for JSON responses, file downloads, redirects, cookie management, and custom status codes. The production best practices include process management through PM2, clustering for multi-core utilization, and reverse proxy configuration with NGINX. Designed for Node.js backend developers and API engineers.