Module Pattern Implementation

Introduction

The Module pattern uses an IIFE (Immediately Invoked Function Expression) to create a closure that encapsulates private state and exposes a controlled public API.

Basic IIFE Module

const UserModule = (function() {
  // Private state
  const users = [];
  let nextId = 1;

  function validateUser(user) {
    return user.name && user.email;
  }

  // Public API
  return {
    add(name, email) {
      if (!name || !email) throw new Error('Name and email required');
      const user = { id: nextId++, name, email };
      users.push(user);
      return user;
    },

    getAll() {
      return [...users];
    },

    getById(id) {
      return users.find(u => u.id === id);
    },

    remove(id) {
      const index = users.findIndex(u => u.id === id);
      if (index !== -1) return users.splice(index, 1)[0];
    }
  };
})();

UserModule.add('Alice', 'alice@email.com');
UserModule.getAll(); // [{ id: 1, name: 'Alice', email: 'alice@email.com' }]

Revealing Module Pattern

const Calculator = (function() {
  // Private
  let result = 0;

  function validate(num) {
    if (typeof num !== 'number') throw new Error('Invalid number');
  }

  // Public references
  return {
    add(num) { validate(num); result += num; return this; },
    subtract(num) { validate(num); result -= num; return this; },
    multiply(num) { validate(num); result *= num; return this; },
    getResult() { return result; },
    reset() { result = 0; return this; }
  };
})();

Calculator.add(5).multiply(2).getResult(); // 10

ES Module Alternative

Modern ES modules provide the same encapsulation natively:

// 📁 userModule.js (private by default)
const users = [];
let nextId = 1;

export function createUser(name, email) {
  const user = { id: nextId++, name, email };
  users.push(user);
  return user;
}

export function getUsers() { return [...users]; }

Summary

IIFE creates a closure for private state
Return an object with only the public methods
Private variables and functions stay hidden
ES modules make the pattern less necessary today

Module Pattern Implementation

Module Pattern Implementation

Introduction

Basic IIFE Module

Revealing Module Pattern

ES Module Alternative

Summary

Further Reading