@commerce-atoms/cart

Pure cart line math engine for Shopify products.

Purpose

Provides utilities for cart operations and calculations that are framework-agnostic:

• Adding/merging/updating cart items
• Computing subtotal, totalQuantity, and discounts
• Normalizing cart structure
• Line-by-line math operations

Non-goals

This package explicitly does NOT:

• ❌ Store cart state in localStorage or sessions
• ❌ Provide UI components (<CartSummary />)
• ❌ Fetch cart data from Shopify
• ❌ Include routing logic
• ❌ Manage React state or context

API

Core Functions

// Calculate cart subtotal from line items
import { calculateSubtotal } from "@commerce-atoms/cart/totals/calculateSubtotal";

const subtotal = calculateSubtotal(cartLines);
// Returns: 199.97

// Add a new line to cart
import { addCartLine } from "@commerce-atoms/cart/line/addCartLine";

const updatedLines = addCartLine(lines, {
  id: "123",
  quantity: 2,
  price: 10.0,
});

// Update line quantity
import { updateCartLine } from "@commerce-atoms/cart/line/updateCartLine";

const updatedLines = updateCartLine(lines, "line-id", { quantity: 5 });

// Remove line from cart
import { removeCartLine } from "@commerce-atoms/cart/line/removeCartLine";

const updatedLines = removeCartLine(lines, "line-id");

// Merge duplicate lines
import { mergeCartLines } from "@commerce-atoms/cart/line/mergeCartLines";

const mergedLines = mergeCartLines(lines1, lines2);

Types

import type { CartLine } from "@commerce-atoms/cart/types/cartLine";
import type { Cart } from "@commerce-atoms/cart/types/cart";