Import

// main.js
import add, { subtract, multiply, duplicate } from './myMath.js';
console.log(add(6, 2)); // 8 
console.log(subtract(6, 2)) // 4
console.log(multiply(6, 2)); // 12
console.log(duplicate(5)) // 10
// index.html
<script type="module" src="main.js"></script>