Express

Express is a fast, minimal, and unopinionated web framework for Node.js. First released in 2010, it became the default starting point for Node.js web development and remains one of the most downloaded npm packages in history.

Express adds a thin, composable layer on top of Node's built-in http module: a router for mapping HTTP methods and URL patterns to handler functions, a middleware system for processing requests in a pipeline, and a set of HTTP utilities for tasks like setting headers, redirecting, and caching.

The middleware model is Express's core abstraction. Every piece of functionality — body parsing, authentication, logging, CORS, rate limiting, static file serving — is a middleware function with the signature (req, res, next). Third-party middleware packages like passport, multer, morgan, helmet, and cors plug into this pipeline, making Express highly composable without dictating the architecture of your application.

Routing supports parameterised paths (/users/:id), query string parsing, HTTP method chaining, and route-level middleware, providing enough structure for simple APIs while staying out of the way for complex ones.

Express is completely unopinionated about database access, authentication strategy, template engine, or project structure. This flexibility has made it the underlying engine for many higher-level frameworks: NestJS, LoopBack, Feathers, and Keystone all run on Express (or can be configured to). It is also frequently embedded as the HTTP layer in microservice architectures.

Express 5 (stable v5.x released 2024) modernised the framework with native Promise support in middleware and route handlers, eliminating the need for express-async-errors wrappers, and introduced breaking changes around error handling and router API.

Express is maintained under the OpenJS Foundation umbrella.