To add new content requiring custom backend functionality, what is the best approach?

Building a private app using a script resource is the most effective approach when you need to add new content that requires custom backend functionality. This method allows for the creation of a secure and tailored solution that can interact with Shopify's API, enabling you to manipulate data, perform operations, and integrate features that are not achievable through Liquid or front-end scripting alone.

Private apps have the ability to access Shopify’s backend infrastructure and can manage complex tasks, such as data processing and storage, offering a robust way to handle custom functionality that is beyond standard Liquid capabilities. This allows developers to leverage the vast API capabilities of Shopify without being restricted by the limitations that come with just using Liquid templates or JavaScript on the front end. The application can also maintain critical security protocols, as private apps authenticate requests and ensure that sensitive data remains protected.

In contrast, other approaches like returning data as JSON with Liquid or using Liquid and JavaScript for display might not provide the necessary backend support. While these methods can enhance customer-facing aspects of a Shopify store, they cannot effectively implement complex operations or manage new data requirements without the backend support that a private app can offer.