/noʊd dʒeɪ ɛs/
noun … “a runtime environment that executes JavaScript on the server side.”
Node.js is a cross-platform, event-driven runtime built on the V8 JavaScript engine that allows developers to run JavaScript outside the browser. It provides an asynchronous, non-blocking I/O model, making it highly efficient for building scalable network applications such as web servers, APIs, real-time messaging systems, and microservices. By extending JavaScript to the server, Node.js enables full-stack development with a single language across client and server environments.
The core of Node.js includes a runtime for executing JavaScript, a built-in library for handling networking, file system operations, and events, and a package ecosystem managed by npm. Its non-blocking, event-driven architecture allows concurrent handling of multiple connections without creating a new thread per connection, contrasting with traditional synchronous server models. This makes Node.js particularly well-suited for high-throughput, low-latency applications.
Node.js integrates naturally with other technologies. For example, it works with async functions and callbacks for event handling, uses Fetch API or WebSocket for network communication, and interoperates with databases through client libraries. Developers often pair it with Express.js for routing and middleware, or with Socket.IO for real-time bidirectional communication.
In practical workflows, Node.js is used to build RESTful APIs, real-time chat applications, streaming services, serverless functions, and command-line tools. Its lightweight event loop and extensive module ecosystem enable rapid development and high-performance deployment across diverse environments.
An example of a simple Node.js HTTP server:
const http = require('http');
const server = http.createServer((req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello, Node.js!');
});
server.listen(3000, () => {
console.log('Server running at [http://localhost:3000/](http://localhost:3000/)');
}); The intuition anchor is that Node.js acts like a “JavaScript engine for servers”: it brings the language and event-driven model of the browser to backend development, enabling fast, scalable, and asynchronous handling of data and connections.