Sterling Rose Design Blog

In my project, I have orders, and each order can have an unlimited number of line_items. Line_items are created by the user clicking on a button, which appends (via RJS) a new row to the line_items tabled form. So far, so good.

But I needed the extended price (quantity * price_per) of each line_item to be calculated every time the user tabbed out or clicked away from the price_per field. Further, I needed the subtotal, tax, total, and balance fields to be automatically re-calculated.

I messed around with it for several hours, trying Javascript, Prototype, and even jQuery, before I finally settled on a Prototype approach that worked. The real struggle was that using Rails 2.3’s nested forms functionality meant that each line_item would have an index key embedded in the middle of the text field’s name and id, and I could not come up with a good way to extract it, to pass it to the Javascript function.

Luckily...