ES Modules vs. CommonJS: The JS Module System

JavaScript modules allow developers to break up codebases into reusable, self-contained files. Historically, the language had no native module syntax, which led to the creation of **CommonJS** for Node.js and eventually **ES Modules** as the official standard.

CommonJS (CJS)

CommonJS uses require() to load modules synchronously and module.exports to export. It is the default in older Node.js environments.

// math.js
module.exports.add = (a, b) => a + b;

// index.js
const { add } = require('./math');

ES Modules (ESM)

ES Modules are the official standard. They use import and export and operate asynchronously, enabling static analysis and optimizations like tree-shaking (removing unused code during build).

// math.js
export const add = (a, b) => a + b;

// index.js
import { add } from './math.js';