Express.js
noun · backend framework
A minimalist and flexible web framework for Node.js that provides a robust set of features for building web applications and REST APIs — considered the de facto standard for backend JavaScript development thanks to its simplicity, performance, and extensible middleware ecosystem.
A lightweight abstraction layer on top of Node.js's native HTTP module that simplifies route, request, and response management — enabling you to create a complete backend server in just a few lines of code while retaining full control over the application architecture.
The technical foundation upon which major frameworks like NestJS, Sails.js, and LoopBack are built — Express.js is used in production by Uber, IBM, Accenture, and thousands of companies to serve millions of API requests daily with proven reliability and scalability.
Express.js is an open-source backend framework for Node.js that enables you to create web servers and RESTful APIs quickly and in a structured manner. It provides a powerful routing system, middleware management, and native integration with template engines. Express.js is the most widely used Node.js framework in the world with over 30 million weekly downloads on NPM. Our agency uses it as the backend foundation for our Full-stack JavaScript architectures.
Express.js is used because it offers the best balance between simplicity and power for backend JavaScript development. Its minimalist architecture allows you to start an API server in minutes, while its extensible middleware system handles authentication, validation, logging, and CORS without bloating the framework. Express.js integrates seamlessly with MongoDB, PostgreSQL, and Redis databases, and is the ideal companion to React and Next.js for building high-performance Full-stack applications.
To install Express.js, make sure you have Node.js and NPM installed, then initialize a project with `npm init -y`. Next, install Express with `npm install express`. Create an `app.js` file with the minimal code: `const express = require('express'); const app = express(); app.listen(3000)`. Your Express server is ready. For a professional setup, we recommend immediately adding essential middleware: `cors`, `helmet` for security, and `morgan` for request logging.
NPM configuration is done through the `package.json` file, which centralizes project metadata, dependencies, and execution scripts. Create it with `npm init`, which guides you through the options, or `npm init -y` for default values. Then configure your custom scripts in the `scripts` section: `"start": "node app.js"`, `"dev": "nodemon app.js"`. For global settings (proxy, private registry), use `npm config set`. Proper NPM configuration is the foundation of any structured and reproducible professional project.
To install an NPM package, use the command `npm install package-name` (or `npm i package-name`), which downloads the package and automatically adds it to your `package.json` dependencies. Add the `--save-dev` (or `-D`) flag for development-only dependencies (linters, testing tools). To install a specific version: `npm install express@4.18.2`. Always verify a package's reliability before installation by checking its download count, last update date, and number of open issues on GitHub.
A middleware in Node.js is a function that executes between receiving an HTTP request and sending the response, with access to the `req` (request), `res` (response), and `next` (function to pass to the next middleware) objects. Middlewares form a processing chain that can modify the request, validate data, verify authentication, log access, or handle errors. This architectural pattern is at the heart of Express.js's philosophy and enables building modular applications where each layer has a single, testable responsibility.
An Express middleware is a function specific to the Express.js framework that intercepts each incoming request to perform processing before it reaches the final route. Express uses middlewares for everything: request body parsing (`express.json()`), static file serving (`express.static()`), security (`helmet`), CORS (`cors`), and error handling. They stack via `app.use()` and execute in declaration order. At Async Code, we architect our middlewares in layers (security, validation, business logic, response) for optimal maintainability.
Choosing Express.js means opting for the proven stability of the world's most popular backend JavaScript framework, backed by a massive community and an ecosystem of over 50,000 middleware packages. Its learning curve is gentle for JavaScript developers, its unopinionated architecture offers complete design freedom, and its performance is excellent for high-load REST APIs. Express.js is also the foundation for more structured frameworks like NestJS, ensuring that the skills acquired remain relevant in the long term.
Body-parser is a Node.js middleware that parses the body of incoming HTTP requests and makes the data accessible via `req.body`. It supports JSON (`bodyParser.json()`), URL-encoded (`bodyParser.urlencoded()`), and raw/text formats. Historically a separate package, body-parser has been built directly into Express.js since version 4.16 via `express.json()` and `express.urlencoded()`. It remains essential for any server that receives form data or JSON payloads from frontend applications like React or Next.js.
Yes, Express.js remains in 2025 the most widely used backend Node.js framework in the world with over 30 million weekly downloads on NPM and a presence in the majority of professional JavaScript stacks. While alternatives like Fastify (more performant in benchmarks) or NestJS (more structured) are gaining popularity, Express.js maintains its dominant position thanks to its simplicity, maturity, and unmatched ecosystem. At Async Code, we use it in production for our backend APIs alongside our Next.js applications, and it continues to prove its reliability at scale.