Shopify doesn’t have an API to verify discounts, however, I have found a little workaround.
By making an AJAX call to
/discount/(code), Shopify will set a cookie telling the checkout to auto-apply a discount on a visit to the checkout page.
Next, making an AJAX call to
/checkout, we’re able to parse the HTML and determine if the discount code worked!
Here’s an example of it in action:
For the source code of this script, please see this repository.