Express

Express is a fast, unopinionated, minimalist web framework for Node.js. It provides a thin layer of HTTP server features on top of Node's built-in http module: routing, middleware, request and response helpers, view rendering, and a small set of body-parsing and static-file middlewares re-exported from sister packages.

The repository at https://github.com/expressjs/express ships a single npm package, express, currently at version 5.2.1. The whole library is implemented in roughly 2,800 lines of JavaScript split across six files in lib/. Most heavy lifting (routing, body parsing, file sending) is delegated to dedicated packages in the expressjs/ org.

What's in this wiki

• Architecture — how the pieces fit together, with diagrams
• Getting started — install, build, test, run
• Glossary — Express-specific vocabulary

Then continue into:

• By the numbers — codebase stats snapshot
• Lore — the timeline from 2009 to today
• Systems — internal building blocks (application, request, response, view, utils)
• Features — cross-cutting capabilities (routing, middleware, body parsing, static files, templating)
• How to contribute — workflow, testing, debugging, conventions
• Reference — configuration settings and dependencies

At a glance

Item	Value
Package name	express
Version (master)	5.2.1
Language	JavaScript (CommonJS)
Minimum Node	Node.js 18+ (engines.node: ">= 18" in package.json)
Source files (lib/)	6 files, ~2,800 LOC
Test framework	Mocha + supertest, run via npm test
License	MIT
Default branch	master

Hello World

import express from 'express';

const app = express();

app.get('/', (req, res) => {
  res.send('Hello World');
});

app.listen(3000);

express() is the factory exported from lib/express.js. It returns a callable application — a function (req, res, next) that can be passed straight to http.createServer (and app.listen() does this for you). See Application for the full lifecycle.