Case Study: Transforming Shopify Collection Filters for True Inventory Accuracy
Overview
A Shopify merchant using a premium theme approached me with a recurring pain point: the default "Availability" filters and product stock messaging on collection pages did not reflect the real-time inventory situation. Their goal was to offer a more transparent shopping experience and give customers better tools to find what's actually in stock.
The Challenge
- Shopify's native availability filter treats products with "Continue selling when out of stock" enabled as in-stock—even when inventory is zero.
- Product pages showed accurate inventory messages, but collection pages didn't.
- The merchant wanted consistent messaging across product and collection pages and a truly accurate "In Stock"/"Out of Stock" filter.
- The solution needed to be fast, scalable, and integrate seamlessly with their heavily customized Shopify theme.
Solution Design
To overcome Shopify's limitations, I proposed a hybrid approach combining theme customization, Shopify's Storefront API, and a lightweight JavaScript app.
Key Features Delivered:
- Accurate stock messaging on collection pages using the same logic as product pages.
- Custom inventory filter that ignores the "Continue selling" flag and uses true inventory counts.
- Real-time UI updates on filter selection, reflecting correct product counts.
- Pagination and filter persistence using cookies for consistent UX across browsing sessions.
Technical Highlights
- Storefront API Integration: Fetched complete product lists to determine actual inventory levels.
- Custom Filtering Logic: Overrode Shopify's default logic to reflect only real stock.
- Dynamic Messaging: Matched collection page stock messages to those on the product pages (e.g., "Currently out of stock", "We have 3 in stock").
- Filter Persistence: Used cookies to retain filter state across pagination and filter selections.
- Search Template Extension: Later extended this functionality to the search results page for consistency across the storefront.
- Edge Case Handling: Resolved issues with Vendor Collection pages, variant inventory mismatches, and dynamic product counts.
Tech Stack
| Component | Purpose |
|---|---|
| Shopify Liquid | Theme templating |
| JavaScript (ES6+) | Frontend logic |
| Shopify Storefront API (GraphQL) | Data fetching |
| Custom theme app using app blocks | Integration |
| Cookie-based state management | Filter persistence |
Results
- Fully accurate "In Stock" and "Out of Stock" filters based on live inventory.
- Consistent and clear stock messages across collection and product pages.
- Improved customer trust and reduced friction in product discovery.
- Seamless integration with the merchant's theme and future-proof architecture.
- Follow-on work from the client to replicate the same filters on their second store.
Why It Matters to eCommerce Managers
As an eCommerce Manager, you're constantly looking for ways to:
- Increase trust and reduce returns from stock-related surprises
- Streamline the product discovery process
- Improve site usability without sacrificing theme integrity
This project proves that it's possible to overcome Shopify's default limitations and build a more transparent, conversion-optimized storefront—without waiting for a feature update from Shopify.