Modules: CommonJS & ES Modules

A module is a file whose variables and functions are private unless exported. Modules keep code organised, reusable and testable: a pricing.js module, a db.js module, a routes/ folder.

Node supports two module systems: • CommonJS (CJS) — require() and module.exports; the traditional Node style. • ES Modules (ESM) — import and export; the JavaScript standard, also used in browsers.