Pass session variables through the cart

How to set it up

Add any parameter prefixed with h: to a cart link or form:

https://YOURSTORE.foxycart.com/cart?name=Product+Name&price=10.00&h:customer_id=12345

Multiple session variables can be added in the same request:

https://YOURSTORE.foxycart.com/cart?name=Product+Name&price=10.00&h:customer_id=12345&h:affiliate_id=ABC

The same works in a form:

<form action="https://YOURSTORE.foxycart.com/cart" method="post">
  <input type="hidden" name="name" value="Product Name" />
  <input type="hidden" name="price" value="10.00" />
  <input type="hidden" name="h:customer_id" value="12345" />
  <input type="submit" value="Buy Now" />
</form>

Accessing session variables in JavaScript

Session variables are available in FC.json.custom_fields:

FC.client.on('ready.done', function() {
  console.log(FC.json.custom_fields.customer_id);
});

custom_fields sits at the top level of the cart JSON — it is not nested under individual items, even if the h: parameter was added alongside a specific product.

Accessing session variables in Twig

Session variables are also available as custom_fields in Twig, for use in templates like the web receipt or email receipt:

{{ custom_fields.customer_id.value }}

Adding session variables without adding a product

Use cart=view to add session variables to the cart without adding a product:

FC.client.on('ready.done', function() {
  FC.client.request('https://' + FC.settings.storedomain + '/cart?h:foo=bar');
});

Notes

• Session variables are not tied to products — they persist for the life of the session regardless of what products are in the cart.

• Session variables are never displayed to the customer, at any point in the cart, checkout, or receipt.

• Maximum value length is 700 characters.

• Do not sign h: values if using link and form validation.

• After a transaction is completed, session variables are accessible via the transaction XML datafeed or the API.

• This is different from the session cookie itself (fcsid) — see Configure the session domain and cookie path if you need to control where that cookie is set, or JavaScript events reference for the full list of events available on FC.client.