[development] Form API and Javascript stuck

Earl Miles merlin at logrus.com
Sun Feb 21 21:22:36 UTC 2010

Karyn Cassio wrote:
> Hi Everyone,
> I hope you are enjoying your weekend and not working too hard.
> I'm still trying to get my head around js, and was hoping someone may 
> have some insights to help me with the next steps on a form I am creating.
> I have an order form that is going to be dynamically created.
> I am able to successfully pass the quantity value upon user input for 
> field 1.
> Basically I'm using onchange() to pass the quantity value to the script.
> The id of the price field is of the format unit-price-0, unit-price-1, etc.
> Each line item's subtotal should update before going onto the next line 
> item.
> Here's the js function. Each line item has its own unit-cost, quantity, 
> and subtotal.
> Any help would be so appreciated.

Let's assume that you've set up the ids so that they all match:

1) Each line item has a unique, probably numeric id.
2) The id of all the form fields for each line item is carefully
    crafted such that the quantity will be "edit-quantity-ID", the
    price will be "edit-price-ID" and the subtotal will be
3) The quantity is a textfield. The price is either a disabled textfield
    so that the user cannot change it, or a hidden field. The subtotal
    is similar.
4) Each line item quantity has this class: 'line-item-quantity'.

You would then create a .js file using this code. Note that I am using 
jQuery to create simpler code, so if you're not familiar with jQuery it 
may not be immediately understandable, but it would be very valuable to 
learn some as use of jQuery significantly increases javascript productivity.

For example's sake I am butchering the calculation to be as simple as 
possible. Judging from your code it needs to be a touch more complex 
than this, but you can handle that I am sure.

// You would put this inside a Drupal behavior:
Drupal.behaviors.myBehaviorFunction = function() {
     .addClass('line-item-processed') // Ensures we do only process once
     .change(function() {
       // The id of this should be edit-quantity-ID so we use replace
       // to get the base id:
       var id = $(this).attr('id').replace('edit-quantity-', '');
       var price = $('edit-price-' + id).val();

       var subTotal = id * price; // Do your actual calculation here.

       $('edit-subtotal-' + id).val(subTotal);

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