cart-manager

Cart Utilities

A lightweight ES module for managing shopping cart operations using localStorage. This library provides a simple and intuitive API for adding, removing, updating, and managing cart items in browser-based applications.

Features

• 🚀 Simple and intuitive API
• 💾 Persistent storage using localStorage
• 🔒 Safe data handling with built-in validation
• 📦 Zero dependencies
• 🎯 TypeScript-friendly structure
• ⚡ Lightweight and fast

Installation

Browser (ES Modules)

Include the module in your HTML file:

  import {
    addToCart,
    removeFromCart,
    getCart,
    updateQuantity,
    getPrice,
    clearCart
  } from "./cart-utils.js";

API Reference

addToCart(data, id)

Adds a new item to the cart. If an item with the same ID already exists, the operation is skipped.

Parameters:

• data (Object): The item object containing product details
  • id (Number|String): Unique identifier for the item
  • name (String): Product name
  • price (Number): Product price
  • quantity (Number): Quantity to add
• id (Number|String): The ID of the item (must match data.id)

Example:

addToCart(
  { 
    id: 1, 
    name: "Ergonomic Chair", 
    price: 1200, 
    quantity: 1 
  },
  1
);

Important Notes:

• The item must include an id property
• The second parameter should match the item's ID
• Duplicate IDs will not be added to prevent conflicts

removeFromCart(id)

Removes an item from the cart by its unique identifier.

Parameters:

• id (Number|String): The ID of the item to remove

Example:

removeFromCart(1);

Important Notes:

• Removing a non-existent ID performs no action
• No error is thrown for invalid IDs

getCart()

Retrieves the current cart contents.

Returns:

• Array: Cart items, or null if the cart is empty

Example:

const cart = getCart();

if (cart) {
  console.log("Current cart:", cart);
} else {
  console.log("Cart is empty");
}

Important Notes:

• Returns null (not an empty array) when cart is empty
• Always check for null before iterating

updateQuantity(id, quantity)

Updates the quantity of a specific item in the cart.

Parameters:

• id (Number|String): The ID of the item to update
• quantity (Number): The new quantity value

Example:

updateQuantity(1, 3);

Important Notes:

• If the item doesn't exist, a message is logged but no error is thrown
• Ensure quantity is a positive number
• Setting quantity to 0 does not remove the item

getPrice(tax = 0, deliveryCharges = 0)

Calculates the total cart price including optional tax and delivery charges.

Parameters:

• tax (Number, optional): Tax amount to add (default: 0)
• deliveryCharges (Number, optional): Delivery fee to add (default: 0)

Returns:

• Number: Total cart value

Example:

const subtotal = getPrice();
const total = getPrice(50, 30);

console.log("Subtotal:", subtotal);
console.log("Total with tax and delivery:", total);

Important Notes:

• Items without a quantity property default to 1
• Ensure all prices are numeric values
• Tax and delivery charges are added to the subtotal

clearCart()

Removes all items from the cart and clears localStorage.

Example:

clearCart();

Important Notes:

• This action is irreversible
• Consider asking for user confirmation before clearing
• Use after successful checkout or explicit cart reset

Data Structure

Cart data is stored in localStorage with the following structure:

[
  {
    "id": 1,
    "name": "Ergonomic Chair",
    "price": 1200,
    "quantity": 2
  },
  {
    "id": 2,
    "name": "Standing Desk",
    "price": 3500,
    "quantity": 1
  }
]

Best Practices

Unique IDs

Always ensure each item has a unique identifier:

// Good
addToCart({ id: Date.now(), name: "Product", price: 100, quantity: 1 }, Date.now());

// Avoid duplicate IDs

Quantity Management

Use updateQuantity() instead of adding the same item multiple times:

// Recommended
updateQuantity(1, 3);

// Not recommended
addToCart(item, 1);
addToCart(item, 1);
addToCart(item, 1);

Type Safety

Ensure numeric values are properly typed:

const price = Number(item.price);
const quantity = parseInt(item.quantity, 10);

Error Handling

Always validate cart data before operations:

const cart = getCart();

if (cart && Array.isArray(cart)) {
  // Safe to process cart
  cart.forEach(item => {
    console.log(item.name, item.price);
  });
}

Common Pitfalls

Issue	Solution
Cart returns null	Check for null before accessing cart data
Quantities not updating	Ensure ID exists and quantity is valid
Price calculation errors	Verify all prices are numbers, not strings
LocalStorage quota exceeded	Clear cart periodically or limit items
Duplicate items	Use updateQuantity() instead of addToCart()

Browser Compatibility

This library uses localStorage and ES6 modules, which are supported in:

• Chrome 61+
• Firefox 60+
• Safari 10.1+
• Edge 16+

License

MIT License - feel free to use in personal and commercial projects.

Contributing

Contributions are welcome! Please ensure all changes maintain backward compatibility and include appropriate documentation.

Need help? Open an issue or submit a pull request on GitHub.