DevMata / cjs-vs-esm

A brief look into CJS vs ESM

cjs-vs-esm

A brief look into CJS vs ESM.

Description

Common JS(CJS) and EcmaScript Modules (ESM) are not the only module systems in the JS ecosystem. But we can consider them the two most important ones.

CJS is the most known system. But with the arrival of ESM we need to start checking its differences.

TL;DR

CJS

• uses require and module.exports as API
• works synchronously
• can use ESM files if these have .mjs extension
• you can use import only as dynamic import

Faux ESM

• looks like ESM
• uses export and import as API
• translates/compiles to CJS in Node.js
  • transpiled code with Babel
  • Typescript sometimes 😅

ESM

• uses export and import as API
• works asynchronously
• can use CJS files if these have .cjs extension

Resources

What Are CJS, AMD, UMD, and ESM in Javascript?

ES6 In Depth Articles

ES modules: A cartoon deep-dive

Dynamic import()