Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.javascript > #15769

Re: How to do calculation with dynamic form field names?

Show all headers | View raw

On 07/09/2012 05:07, justaguy wrote:

[snip]

> <form>
> <input type="text" id="item1">, <input type="text" id="qty1">, <input
> type="text" id="price1">, fieldX1 t1

[snip]

> a) t{n} = subtotal field.
> b) number of rows is unknown, it could be 1 to 30.
>
> What I'd like to do is: calculate subtotal and total.
> each subtotal = qty{n} * parseFloat(price{n})
>
> My attempt is to loop through the entire form, I'm able to retrieve
> all the values for the qty{n} field,
> but I don't know how to retrieve the value of its Corresponding
> Price{n}.

[snip]

What you're looking for is bracket notation; the ability to construct 
property names through string concatenation. This is described in the 
FAQ (and elaborated in the notes): 
<http://jibbering.com/faq/#propertyAccessAgain>

As you don't know the number of rows, you can leverage the fact that a 
nonexistent property will return null to simplify your loop (no need to 
use String.prototype.indexOf):

   var i = 0,
       element;

   // 'item' may be a better choice below if that's always
   // present in a row and 'qty' isn't, in which case the
   // condition below should become a null comparison instead
   // of an assignment expression/boolean type-conversion.
   while ((element = form.elements['qty' + i])) {
     var subtotal = form.elements['qty' + i]
       * form.elements['price' + i];
     // ...
     i++;
   }

Alternatively, you could of course inject a script element that contains 
a variable initialised with the number of rows when the page is generated.

Hope that helps,
-- 
Mike Winter
Replace ".invalid" with ".uk" to reply by e-mail.

Back to comp.lang.javascript | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

Re: How to do calculation with dynamic form field names? Mike Winter <usenet@michael-winter.me.invalid> - 2012-09-07 15:26 +0100
  Re: How to do calculation with dynamic form field names? justaguy <lichunshen84@gmail.com> - 2012-09-07 08:03 -0700
    Re: How to do calculation with dynamic form field names? Gene Wirchenko <genew@ocis.net> - 2012-09-07 10:05 -0700
      Re: How to do calculation with dynamic form field names? justaguy <lichunshen84@gmail.com> - 2012-09-07 11:39 -0700
        Re: How to do calculation with dynamic form field names? SAM <stephanemoriaux.NoAdmin@wanadoo.fr.invalid> - 2012-09-07 21:56 +0200
    Re: How to do calculation with dynamic form field names? Mike Winter <usenet@michael-winter.me.invalid> - 2012-09-07 20:05 +0100
      Re: How to do calculation with dynamic form field names? justaguy <lichunshen84@gmail.com> - 2012-09-07 12:36 -0700
        Re: How to do calculation with dynamic form field names? justaguy <lichunshen84@gmail.com> - 2012-09-07 12:51 -0700
        Re: How to do calculation with dynamic form field names? Mike Winter <usenet@michael-winter.me.invalid> - 2012-09-07 20:57 +0100

csiph-web