How do I integrate a Builder product box with an AJAX cart in Shopify?

Unfortunately, since each Shopify theme handles the AJAX cart (slide out cart, javascript cart) functionality differently, there is not a built in way to trigger the cart to open automatically when making a product box in Builder. There are a few options to get it to work though.

The first on is to use the built in refresh page functionality to ensure that when a product is added, the cart icon on your site updates: Why does the cart icon on my store not update when someone adds a product to cart from a Builder product widget?

The second approach is to find out what code triggers the slide out cart in your theme code, and then within builder add a click handler to the product box add to cart button. Since each theme is different, you will need to check with your theme developer or search online forums to determine if your theme supports function calls that will a) update the contents of the cart, and b) trigger the cart slide out. Once you determine those functions, you can then call them within a Builder element event by choosing click, and then choosing custom code as the action:

and then calling the function(s) necessary to trigger the cart