Express

Express (also known as Express.js) is a minimal and flexible web application framework for Node.js designed for building web applications and APIs. It provides a thin layer of fundamental web application features, including a robust routing system, a modular middleware pattern, and support for rendering templates, serving static files, and handling HTTP requests and responses. Its middleware architecture allows developers to compose small components that process requests, perform actions such as authentication or data parsing, and either pass control to the next middleware or terminate the response.

Express is part of the Node.js ecosystem and is widely used to create RESTful services and single-page applications. It emphasizes simplicity and unopinionated design, enabling developers to choose additional libraries and architectures. The framework uses an application object and a Router to organize routes; middleware can be mounted globally or per-route, enabling features like logging, body parsing, cookie handling, and error management. It supports various template engines and can integrate with databases and other services.

Developed by TJ Holowaychuk in 2010 and maintained by a large community of contributors, Express has become one of the most popular Node.js frameworks. It has a large ecosystem of middleware packages and extensions and is commonly used in platforms and stacks such as MEAN and MERN. While alternative frameworks exist, Express's balance of simplicity, extensibility, and performance makes it a common choice for building production web servers and APIs on Node.js.