Table of Contents
1. Historical Development
- CommonJS (CJS):
- Introduced in 2009 for Node.js.
- Designed to work in server environments where synchronous loading of modules was acceptable.
- Uses
require()to import modules andmodule.exportsto export them. - Example:
const fs = require('fs'); module.exports = function() { /* ... */ };
- ES Modules (ESM):
- Introduced in ECMAScript 2015 (ES6) to standardize modules in JavaScript.
- Designed to work both in browsers and servers.
- Supports static analysis (better for tree-shaking, optimization).
- Uses
import/exportsyntax. - Example:
import { readFile } from 'fs'; export default function() { /* ... */ };
2. Key Differences
| Feature | CommonJS (CJS) | ES Modules (ESM) |
|---|---|---|
| Loading | Synchronous | Asynchronous (can be dynamic) |
| Syntax | require(), module.exports | import, export |
| Compatibility | Node.js only (initially) | Browsers + Node.js |
| Static Analysis | Limited | Full static analysis (tree-shaking) |
| Dynamic Imports | Not natively supported | Supported with import() |
3. Why Both Exist
- Legacy Support: Node.js started with CommonJS, and many libraries are built with it. Migrating everything to ESM isn’t instant.
- Different Use Cases:
- CJS is great for synchronous server-side code.
- ESM is ideal for browser environments where async loading and modular bundling are common.
- Gradual Adoption: Node.js now supports ESM, but CommonJS is still widely used. Developers can choose based on their needs.
4. The Future?
With the rise of ES Modules, the ecosystem is slowly shifting toward ESM even in Node.js. However, CommonJS is unlikely to disappear completely soon, especially for existing projects.
If you’re starting new projects, ESM is the recommended approach unless you have a specific need for CommonJS.
