Keep a shopping cart updated without relying on an 'Update Cart' button

Question

Am in the process of implementing a fairly conventional shopping checkout flow. Currently it steps thru like:

1. User adds an item to the cart and is presented with Step1 (login or register as new customer)
2. User is presented with summary of current the order and a handful of controls that modify the order. After confirming the desired configuration, the user has to click 'Proceed' to see Step 3 which amounts to nothing more than redisplaying the summary and offering 2 methods of payment.
3. Re-confirm order and choose 'Bill Me' or 'Pay By Credit Card'.

I don't like 'Update Cart' buttons. Currently we use onBlur to update the cart without user interaction.

I also don't like asking the user read an order summary twice and would like to merge Steps 2 & 3. So i'd like to place the 2 payment option buttons at the bottom of Step 2. Relying onBlur is going to cause problems with synchronization between the displayed state of the order user changes.

I _think we could trap onFocus for those controls that modify the order, disable the payment buttons until the order is re-rendered to screen and the insert some text to the effect 'your changes have been recorded, please re-confirm your order and then choose your preferred form of payment.'

The page is jQuerfied & Ajax-able so these interactions seem reasonable. But it would be the first time this team has implemented anything of the sort and we are leery of the unknowns.

thx

Answer 1

Update Cart is the conventional way of doing this. If your page is ajaxed then it is better to update the back end using ajax, but giving the button will lessen the chances of error and misbehaving on the part of the cart.