Basics of using ES Modules

includes.js

export const add = (a, b) => a + b;
export const subtract = (a, b) => a - b;

export default { add, subtract };

index.js

import mainModule, { add, subtract } from "./includes.js";

console.log(add(1, 2));
// 3
console.log(mainModule.add(1, 2));
// 3

console.log(subtract(1, 2));
// -1
console.log(mainModule.subtract(1, 2));
// -1

setup.sh

npm init -y
npm install --save-dev esm
node -r esm index.js