Module

A module is a self-contained unit of code that encapsulates related functionality and can be imported and reused across different parts of an application.

ES6 Modules

Modern JavaScript uses the ES6 module system:

javascript
// math.js - Exporting
export const add = (a, b) => a + b
export const subtract = (a, b) => a - b
export default multiply = (a, b) => a * b

// app.js - Importing
import multiply, { add, subtract } from './math.js'

Benefits

Encapsulation Keep code organized and prevent naming conflicts.

Reusability Use the same code in multiple places.

Maintainability Easier to update and debug isolated units.

Dependency Management Clear dependencies between code units.

Module Formats

ES6 Modules (ESM) Native JavaScript modules, supported in modern browsers.

CommonJS Node.js module system using require() and module.exports.

AMD (Asynchronous Module Definition) Older format for browser-based modules.

UMD (Universal Module Definition) Works in both browser and Node.js environments.

Example

javascript
// user.js
export class User {
  constructor(name) {
    this.name = name
  }

  greet() {
    return `Hello, ${this.name}`
  }
}

// app.js
import { User } from './user.js'
const user = new User('Alice')
console.log(user.greet())

Learn More

• MDN: JavaScript Modules