CommonJS

CommonJS is a module system and module format that was originally designed for Node.js, allowing you to split JavaScript code into separate files and requiring them using the require() function. While it has been widely used in Node.js applications and was essential for the early development of the Node.js ecosystem, we recommend using ECMAScript Modules (ESM) instead for new projects.

Reasons for Hold Status

1. ESM is the Standard: ECMAScript Modules is the official standardized module system for JavaScript, supported by modern browsers and Node.js. It provides a more consistent development experience across different environments.

2. Better Static Analysis: ESM's static module structure enables better tree-shaking (dead code elimination) and optimization by bundlers, while CommonJS's dynamic nature makes these optimizations more difficult.

3. Asynchronous by Design: ESM supports both synchronous and asynchronous module loading, while CommonJS is synchronous by nature, which can lead to performance bottlenecks.

4. Interoperability Issues: Using CommonJS alongside ESM can lead to interoperability challenges, especially in projects that use both module systems. Some tools and libraries may require additional configuration or transpilation steps.

Working with ESM

When working with existing CommonJS projects:

1. Use the .cjs extension for CommonJS files and .mjs for ESM files to make the module system explicit

2. Add "type": "module" to your package.json to use ESM by default

3. For new modules within existing projects, prefer using ESM syntax:

   // Instead of CommonJS
   const { foo } = require("bar");
   module.exports = { baz };
   
   // Use ESM
   import { foo } from "bar";
   export { baz };

Reference of usage in our organization

While we still maintain some legacy projects using CommonJS, all new TypeScript/JavaScript projects should use ESM. For existing projects using CommonJS, consider gradually migrating to ESM when making substantial changes to the codebase.