cart-logic

To merge a guest cart into a user account on login, apply upsert semantics to line items and resolve max-quantity conflicts. This ensures adding the same variant increments quantity instead of creating duplicates, while preserving audit history for guest carts.

Client-side cart totals often differ due to stale pricing data. You should capture the unit price at add time and always recalculate subtotals, discounts, and totals server-side to ensure checkout consistency and prevent mispriced items.

Yes, this cart logic works with headless storefronts, Shopify, WooCommerce, and BigCommerce. It provides practical guidance for managing cart state, persistent guest sessions, and server-side subtotal recalculation across these specific ecommerce platforms.

The best way to persist a guest shopping cart across sessions is using an httpOnly guest token cookie paired with server-side cart storage. This ensures shoppers' intended purchases are reliably tracked across page loads and devices without disappearing.

To validate stock and handle add-to-cart operations correctly, you must validate stock availability on add and apply correct upsert semantics. This tracks items reliably so intended purchases are not lost, duplicated, or mispriced at checkout.

You should use server-side cart state management when you need to prevent inconsistent totals, ensure reliable persistence across devices, and handle guest-to-user merge scenarios. This approach avoids missing persistence and guest carts disappearing after login.