What is Node.js and how does it work?

What is Node.js?

Node.js is a server-side JavaScript runtime built on Chrome's V8 JavaScript engine. It allows you to run JavaScript outside the browser — on servers, desktops, and command-line tools.

Key Characteristics

Feature	Description
Runtime	Built on V8 (Google Chrome's JS engine)
Non-blocking I/O	Handles many connections without waiting
Single-threaded	One main thread + event loop
Event-driven	Callbacks/Promises react to events
Cross-platform	Runs on Linux, macOS, Windows

How Node.js Works

Your JS Code
     ↓
  Node.js APIs (fs, http, crypto…)
     ↓
   libuv (C++ library)
     ↓
  OS (file system, network, timers…)

V8 compiles your JavaScript to native machine code
libuv provides the event loop and async I/O via a thread pool
Node.js Core APIs bridge JS and the OS

Simple HTTP Server Example

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');
});

Why Node.js?

Fast — V8 + non-blocking I/O handles thousands of concurrent connections
Unified language — JavaScript on both frontend and backend
Huge ecosystem — npm has over 2 million packages
Great for real-time apps — chat, notifications, streaming
Microservices-friendly — lightweight and fast to start

Node.js is not ideal for CPU-intensive tasks (heavy computation, video encoding, image processing) because it runs on a single thread. For those, consider Go, Rust, or use Node.js Worker Threads.

Summary

Node.js = JavaScript runtime + V8 engine + libuv event loop + non-blocking I/O. It excels at I/O-bound tasks (APIs, real-time apps, microservices) and is the foundation of the modern JavaScript backend ecosystem.

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What is Node.js and how does it work?

#What is Node.js?

#Key Characteristics

#How Node.js Works

#Simple HTTP Server Example

#Why Node.js?

#When NOT to Use Node.js

#Summary