Express.js Web Framework

Express.js (commonly referred to as Express) is a free and open-source web application framework for Node.js, designed for building web applications and APIs. Originally created by TJ Holowaychuk in 2010 (first commit on June 26, 2010), Express is the de facto standard web framework for Node.js and is part of the MEAN, MERN, and MEVN stacks. It is currently maintained by the OpenJS Foundation. Key features: minimal and flexible: Express provides a thin layer of fundamental web application features without obscuring Node.js features. It does not impose an application structure, leaving developers free to organize their code as they see fit. Routing: powerful routing system using HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS) and URL patterns. Routes can be defined with string patterns, regular expressions, and route parameters. Router-level middleware for modular route mounting. Middleware: the core design pattern. Middleware functions have access to the request (req), response (res), and next function. Middleware can execute code, modify request/response objects, end the request-response cycle, or call the next middleware. Express ships with built-in middleware (express.static, express.json, express.urlencoded). Over 10,000 third-party middleware packages available. Template engines: supports server-side rendering with template engines including Pug (Jade), EJS, Handlebars, Nunjucks, and Mustache via app.set('view engine'). Static files: express.static middleware serves static assets (HTML, CSS, JS, images). Error handling: dedicated error-handling middleware. Security: integrates with helmet, cors, express-rate-limit. API development: RESTful and GraphQL APIs. Testing: integrates with Supertest, Jest, and Mocha. Used by IBM, Uber, Accenture, and many others. JavaScript. MIT.