JavaScript Modules & Tooling

ES Modules (ESM)

// math.js
export const add = (a, b) => a + b;
export default function multiply(a, b) { return a * b; }

// main.js
import multiply, { add } from './math.js';
import * as math from './math.js';

// Dynamic import (lazy loading)
const { add } = await import('./math.js');

CommonJS (Node.js)

// module.js
module.exports = { add: (a, b) => a + b };
// or
exports.add = (a, b) => a + b;

// main.js
const { add } = require('./module');

Key Differences: ESM vs CJS

Modern Toolchain

• Bundlers: Webpack, Vite, Rollup, esbuild
• Transpilers: Babel (ES6+ → ES5), TypeScript
• Package manager: npm, yarn, pnpm
• Linters: ESLint
• Formatters: Prettier