What is Node.js?

Node.js is a free, open-source, cross-platform JavaScript runtime environment that lets developers run JavaScript code outside a web browser. Before Node.js existed, JavaScript was confined to the browser. Node.js changed that permanently.

A Brief History

JavaScript was created in 1995 to run inside browsers. For over a decade it lived exclusively there. In 2009, Ryan Dahl released Node.js by embedding Google's V8 JavaScript engine — the same engine that powers Chrome — into a C++ program and exposing low-level operating system APIs to JavaScript code. Suddenly, JavaScript could read files, open network sockets, and talk to databases, just like Python or Java.

Node.js became popular quickly because:

• Web developers already knew JavaScript, so they could reuse skills on the server
• Its event-driven, non-blocking model proved excellent for I/O-heavy tasks
• The npm package registry grew rapidly into the largest open-source ecosystem in the world

What Node.js Is Used For

Node.js is especially well-suited for:

• Web servers and REST APIs — handling many concurrent requests efficiently
• Real-time applications — chat applications, live dashboards, collaborative tools
• Command-line tools — build tools, code generators, scripts
• Microservices — small, independently deployable services
• Streaming applications — processing large files or media without loading them fully into memory

Large companies including Netflix, LinkedIn, Uber, PayPal, and NASA have adopted Node.js for production workloads.

JavaScript on the Server vs the Browser

Running JavaScript in Node.js is different from running it in the browser:

Feature	Browser	Node.js
DOM / window	Available	Not available
File system	Not available	Available via fs module
HTTP server	Not available	Available via http module
Module system	ES Modules	CommonJS + ES Modules
Global object	window	global / globalThis

Your First Node.js Program

After installing Node.js from nodejs.org, you can run a JavaScript file directly from the terminal:

// hello.js
console.log("Hello from Node.js!");

node hello.js
# Hello from Node.js!

The node command invokes the Node.js runtime, which reads the file, compiles it with V8, and executes it. There is no browser involved — this runs entirely on your machine or server.

The Node.js Ecosystem

Node.js ships with a standard library (called core modules) covering file I/O, networking, streams, cryptography, and more. Beyond that, the npm registry hosts over two million packages that you can install and use in seconds.

Understanding Node.js opens the door to server-side development, full-stack JavaScript, build tooling, and a huge category of modern software. This course walks you through the fundamentals step by step.