Day 41

Design Patterns — Module Pattern

11 min

JavaScript 100 Days

Design patterns reusable solutions hain common programming problems ke liye. Module pattern se code ko private aur public parts mein organize karte hain — encapsulation ka practical implementation.

Module Pattern (IIFE)

Immediately Invoked Function Expression se private scope banao.

module.js

javascript

const ShoppingCart = (() => {
  // Private — bahar se accessible nahi
  let items = [];
  let discount = 0;
  
  function calculateTotal() {
    return items.reduce((sum, item) => sum + item.price, 0) * (1 - discount);
  }
  
  // Public API
  return {
    addItem(item) {
      items.push(item);
      console.log(`Added: ${item.name}`);
    },
    removeItem(id) {
      items = items.filter(i => i.id !== id);
    },
    setDiscount(pct) { discount = pct / 100; },
    getTotal() { return calculateTotal(); },
    getItems() { return [...items]; } // copy — original safe!
  };
})();

ShoppingCart.addItem({ id: 1, name: "Shirt", price: 1500 });
console.log(ShoppingCart.getTotal()); // 1500
// ShoppingCart.items — undefined (private!)

🎯 Practice Challenge

BankAccount module banao with private balance. deposit(), withdraw(), getBalance() public methods. Overdraft protection add karo.

Project: Expense TrackerDesign Patterns — Observer