I'm creating a simple shopping cart. The cart itself is on the same page as the items a visitor would order. I would like the cart to reflect changes made to pull-down menus which allow users to order from 0-10 of each item on a list of items without their needing to click an "update" or "add to cart" button. If you are on OS X, iPhoto's interface for ordering prints from Kodak does exactly what I want.
Someone orders 5 of Widget #1 using a pulldown form object and the cart immediately displays 5
They then order 3 of Widget #2 the same way and the cart updates to show a total of 8.
Bonus question - can this value then be passed on to use in a PHP script?
You can put code in the drop down's onChange event to set the other field.
When to send your variables you, as long as they are set in a form field for the current form they will be sent in the POST header. If not you have to make your own code and use the OnSubmit event to set them to hidden fields and send that way.