JavaScript Modules — ES Modules, CommonJS, and the Modern Module Ecosystem

hello@ghafoorsblog.com (AG Sayyed) — Mon, 15 Sep 2025 08:00:00 +0000

The problem a module system solves

For most of its history JavaScript had no module system. Every script shared one global namespace. The solutions were progressively cleverer hacks:

IIFE — an immediately-invoked function expression wrapping the code in a private scope, exposing a single global.
The Module Pattern — var MyLib = (function () { ... })() — closures emulating private members.
AMD (RequireJS) — asynchronous loading designed for the browser.
CommonJS — synchronous require() born inside Node.js, became the npm standard.
UMD — a wrapper that detects whether AMD, CommonJS, or a bare global is in scope and adapts.

In 2015 the language finally added ES Modules (ESM) — a standard, statically analysable, asynchronous module system that works in both browsers and Node.

Esm on Ghafoor's Personal Blog

JavaScript Modules — ES Modules, CommonJS, and the Modern Module Ecosystem

The problem a module system solves