L2. Node.js Modules & Import/Export

1. Initializing a Project

npm init -y

• Automatically generates package.json without asking for details.

2. What are Modules?

• Functions saved in different files and imported where needed.

• Helps organize code better.

3. Writing and Using Modules

Creating a Module (util.js)

// Define functions
export const sub = (a, b) => a + b;  
export const mul = (a, b) => a * b;

• Export functions directly using export.

Importing in index.js

import { sub, mul } from "./util.js";  

console.log("Subtraction:", sub(2, 1));

• Use ES Module Import (import {}) instead of require().

4. Switching to ES Modules

• In package.json, add:

"type": "module"

• Enables ES Module syntax (import/export).

5. Alternative (CommonJS Syntax)

If using CommonJS (default in Node.js):

Exporting in util.js

const sub = (a, b) => a + b;  
const mul = (a, b) => a * b;  

module.exports = { sub, mul };

Importing in index.js

const { sub, mul } = require("./util");