Node.js — Modules

CommonJS

// math.js
function add(a, b) { return a + b; }
function subtract(a, b) { return a - b; }

module.exports = { add, subtract };

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

ES Modules

// math.mjs
export function add(a, b) { return a + b; }
export function subtract(a, b) { return a - b; }

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

package.json for ES Modules

{
  "type": "module"
}

Built-in Modules

Module	Description
fs	File system
path	File paths
http	HTTP server
https	HTTPS server
url	URL parsing
os	Operating system
events	Event emitter
stream	Streams

const fs = require('fs');
const path = require('path');
const http = require('http');

Export Patterns

// Single export
module.exports = function() {};

// Multiple exports
module.exports = {
    func1: function() {},
    func2: function() {}
};

// Export class
module.exports = class MyClass {};

Mini Practice

1. Create a module with CommonJS
2. Create a module with ES Modules
3. Use built-in modules
4. Export functions and classes

Up Next

Continue with NPM — package management.