Node.js Modules & NPM

CommonJS vs ES Modules

// CommonJS (default in Node.js)
// utils.js
function add(a, b) {
  return a + b;
}

module.exports = { add };
// or: exports.add = add;

// app.js
const { add } = require('./utils');
console.log(add(2, 3));

// ES Modules (requires "type": "module" in package.json)
// utils.mjs (or .js with "type": "module")
export function add(a, b) {
  return a + b;
}

export default function multiply(a, b) {
  return a * b;
}

// app.mjs
import multiply, { add } from './utils.mjs';
console.log(add(2, 3));
console.log(multiply(2, 3));

NPM Package Management

# Initialize project
npm init -y

# Install dependencies
npm install express
npm install -D typescript @types/node

# Install specific version
npm install lodash@4.17.21

# Update packages
npm update
npm update express

# Remove package
npm uninstall express

# List installed packages
npm list
npm list --depth=0

# Run scripts
npm run dev
npm start
npm test