Overview

Function API allows developers to customize and extend the cart and checkout processes by injecting their own pricing logic. To ensure compatibility, the function must adhere to a strict input and output structure.

Cart Input and Output Rules

Cart Input Structure

The function receives structured input data when triggered by the cart or checkout process.

Field	Type	Required	Description
cart	object	Yes	The shopping cart object
cart.line_items	array	Yes	The list of items in the cart
product	object	Yes	The product information
product.product_id	string	Yes	Product ID
product.variant_id	string	Yes	Variant ID
product.price	string	Yes	Product price
product.product_title	string	Yes	Product title
product.metafields	array of object	Yes	A list of metafields associated with the product Allows users to store additional custom data
id	string	Yes	Line item ID
quantity	string	Yes	Quantity of the item
properties	string	Yes	Custom attributes defined by the user

Metafield Definition

Metafield is optional but plays a crucial role in the price adjustment function.

Product Metafields can be used to store custom pricing rules, discount strategies, and other extended information.
Since functions cannot directly request data from the developer’s own server, using Metafields as a storage method is essential.

Field	Type	Required	Description
namespace	string	Yes	A container for a set of metafields. Grouping metafields within a namespace prevents conflicts with other metafields that have the same key name.
key	string	Yes	The key of the metafield.
value	mixed	Yes	The data stored in the metafield.

Cart-Transform Input Example

{
    "cart": {
        "line_items": [
            {
                "product": {
                    "product_id": "1231",
                    "variant_id": "1231",
                    "price": "10.00",
                    "title": "test product",
                    "metafields": [
                        {
                            "namespace": "custom-option",
                            "key": "adjust-10-price",
                            "value": "true"
                        }
                    ]
                },
                "id": "1",
                "quantity": 1,
                "properties": "{\"Color\":\"Red\"}"
            }
        ]
    }
}

Cart Output Structure

Overview

The output of a Function API execution determines how the system should update relevant data. This is returned in a structured JSON format containing an operations object. The operations define changes such as modifying prices, adjusting inventory, or updating order statuses.

General Output Structure

Note:

If multiple operations are performed on the same cart line ID, the system only executes the first operation in the list.
Any subsequent update operations for the same ID will be discarded.

Fields Definition

Field	Type	Required	Description
operations	array of operation object	Yes	Shopping cart operation
operations.update	array of update object	No	List of update operations
operations.update.id	string	Yes	Cart line ID
operations.update.price	Price object	Yes	If `adjustment_fixed_price` is less than 0, the update will not be applied. If the specified cart line ID does not exist, the update will not be applied.
operations.update.price. adjustment_fixed_price	string	Yes	Custom price: Must be within the range `[0, 999999999]`. The specified amount is added to the product price for price adjustment.

Cart-Transform Output Example

{
    "operations": {
        "update": [
            {
                "id": "1",
                "price": {
                    "adjustment_fixed_price": "10.00"
                }
            }
        ]
    }
}