Using the Spiffy Ajax API
From Spiffy Stores Knowledge Base
You can access the Spiffy Ajax API from your theme to enhance your customers' experience on your store.
The Spiffy Ajax API allows your customer to add items to the cart, update quantities in the cart and fetch information about the cart, all without requiring a page refresh.
The Spiffy Ajax API also allows you to directly fetch information about a particular product using its handle.