jilt.setCustomer() which accepts an object with:
last_name. There is no return value but when an integration has debug mode enabled, it will write the results to the console. This method saves the data to the respective integration's session and will send the data to Jilt when the visitor adds an item to their cart.
By using this method, you can set an email for a customer much earlier than the checkout, which increases the overall number of abandoned carts available to email. This works best if you have an existing popup or newsletter signup that the visitor may enter their email address in prior to adding an item to the cart.