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Introduction to Node.js · learncode.live

What is Node.js?

Node.js is an open-source, cross-platform JavaScript runtime that lets you run JavaScript outside the browser. Built on Chrome’s V8 engine, it brings JavaScript to the server, command line, and even IoT devices.

┌──────────────┐
│  JavaScript  │
│   (your      │
│    code)     │
├──────────────┤
│  Node.js     │
│  APIs        │
├──────────────┤
│  V8 Engine   │
├──────────────┤
│  OS Layer    │
└──────────────┘

Why Node.js?

Before Node.js (2009), JavaScript was trapped in the browser. Developers had to learn a different language (PHP, Python, Ruby, Java) to write backend code. Node.js changed that by:

  • Unifying language - use JavaScript everywhere
  • Non-blocking I/O - handle thousands of concurrent connections with a single thread
  • NPM ecosystem - the largest package registry on earth

Who Uses Node.js?

CompanyUse Case
NetflixFaster startup & rendering
UberHigh-throughput data processing
PayPalUnified frontend/backend stacks
LinkedInMobile server architecture
WalmartReal-time inventory

Your First Node.js Script

Create a file hello.js:

// hello.js
console.log('Hello, Node.js!');
console.log('Running on', process.version);

Run it:

node hello.js
# Output:
# Hello, Node.js!
# Running on v22.x.x

Note: The exact version depends on what you have installed. This is fine - all code in this tutorial works across modern Node.js versions.

Node.js is Event-Driven

Node.js uses an event-driven, non-blocking I/O model. Instead of waiting for a file to read or a database to respond, it registers a callback and moves on:

// non-blocking.js
const fs = require('fs');

console.log('1. Start reading file...');

fs.readFile('hello.js', 'utf8', (err, data) => {
  if (err) throw err;
  console.log('3. File read complete');
});

console.log('2. Done! (but file read is still in progress)');

Output:

1. Start reading file...
2. Done! (but file is still in progress)
3. File read complete

Node.js vs Traditional Servers

Traditional (PHP, Python, Ruby)Node.js
Concurrency modelMulti-threaded (one thread per request)Single-threaded + event loop
Blocking I/OYes - thread waitsNo - callback is queued
Memory usageHigher (many threads)Lower (single thread)
Best forCPU-heavy tasksI/O-heavy apps (APIs, real-time)

Key Takeaways

  • Node.js is a JavaScript runtime for the server, not a framework
  • Built on the V8 JavaScript engine
  • Uses non-blocking, event-driven I/O for high concurrency
  • npm provides access to over 2 million packages
  • Perfect for APIs, real-time apps, CLIs, and microservices
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