fix(storefront): STRF-12475 Use fetch when updating variants in cart

assets/js/theme/cart.js

@@ -151,6 +151,28 @@ export default class Cart extends PageManager {
                 this.$modal.one(ModalEvents.opened, optionChangeHandler);
             }
 
+            const modalForm = this.$modal.find('form');
+
+            // Create block scoped reference to this.refreshContent, so it can be accessed via onSubmit
+            const refreshContent = () => this.refreshContent();
+
+            async function onSubmit(event) {
+                event.preventDefault();
+                const formData = new FormData(this);
+                const resp = await fetch('/cart.php', {
+                    method: 'POST',
+                    credentials: 'include',
+                    body: formData,
+                });
+
+                if (resp.ok) {
+                    modal.close();
+                    refreshContent();
+                }
+            }
+
+            modalForm.on('submit', onSubmit);
+
             this.productDetails = new CartItemDetails(this.$modal, context);
 
             this.bindGiftWrappingForm();