Node.js Lesson 2: Install & Your First Script

Let’s install Node.js and run your first server-side JavaScript file.

Installation

# Go to nodejs.org → Download LTS version
# Verify installation:
node --version   # v20.x.x or higher
npm --version    # comes with Node

Your First Node.js Script

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

const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce((a, b) => a + b, 0);
console.log("Sum:", sum);

// Run in terminal:
// node hello.js

Node.js vs Browser JavaScript

// Browser JS has:
// document, window, localStorage, fetch (sort of), DOM

// Node.js has:
// process, __filename, __dirname, require(), module
// NO document or window!

console.log(__filename);  // full path to this file
console.log(__dirname);   // directory containing this file
console.log(process.version);  // Node version
console.log(process.platform);  // "win32", "darwin", "linux"

REPL — Interactive Node.js

# In terminal, just type:
node

# Now you can type JS directly:
> 2 + 2
4
> "hello".toUpperCase()
"HELLO"
> .exit   # to quit