Node.js Module System

Node.js has two module systems:

1. CommonJS Modules:

2. ECMAScript Modules (ESM):

CommonJS Modules:

• This is the traditional module system in Node.js.

• Files with .cjs extension are treated as CommonJS modules.

• Files with .js extension are treated as CommonJS modules unless the nearest package.json file has "type": "module".

• You use require() to import modules and module.exports to export functionality.

  example -

    // math.js
    function add(a, b) {
      return a + b;
    }
  
    module.exports = { add }; 
  
    // app.js
    const math = require('./math');
    console.log(math.add(2, 3)); // 5
  

  ECMAScript Modules (ESM):

  • This is the modern module system, aligned with the browser's module system.

  • Files with .mjs extension are treated as ES modules.

  • Files with .js extension are treated as ES modules if the nearest package.json file has "type": "module".

  • You use import to import modules and export to export functionality.

•   // math.mjs
    export function add(a, b) {
      return a + b;
    }
  
    // app.mjs
    import { add } from './math.mjs';
    console.log(add(2, 3)); // 5
  

  Key Differences:

• Syntax: ESM uses import and export, while CommonJS uses require and module.exports.

• Asynchronous: ESM is asynchronous by nature, allowing for better performance.

• Compatibility: ESM is the future standard, while CommonJS is still widely used.

  Choosing the Right Module System:

• For new projects, ESM is recommended.

• For existing projects using CommonJS, you can gradually migrate to ESM.

• If you need to support older Node.js versions, CommonJS is your only option.

Thank you !