Express

Express is a minimal and flexible Node.js web application framework that provides a thin layer of fundamental features for building web servers and APIs. It simplifies HTTP request handling through a routing system that maps URL patterns and HTTP methods to handler functions, and a middleware pipeline that processes requests through a chain of functions for parsing, authentication, and logging.

The framework is deliberately unopinionated, providing core routing and middleware capabilities without dictating project structure, database choice, or templating engine. Developers compose their stack from individual packages. A typical Express application might use body-parser for JSON, cors for cross-origin requests, helmet for security headers, and passport for authentication, each added as middleware in the request pipeline.

For web development, Express is the most widely used Node.js server framework and serves as the foundation many higher-level frameworks build upon. While newer alternatives like Fastify offer better performance and Hono provides edge-runtime compatibility, Express remains dominant due to its massive ecosystem, extensive documentation, and volume of existing knowledge. Understanding its middleware pattern is foundational for server-side JavaScript development.