How Can I Count The Total Number Of Results Displayed?

I'm currently working on a javascript form validator and have run into a problem. The validator is used to make sure that the customer has entered a number in the quantity input box of the item they wish to purchase.

Code:

function validateRE(fieldToCheck, strRegExp, msg, min, max) {
if (!min) { min = 0 }
if (!max) { max = 100 }

for (i=0;i<15;i++)
{
if (fieldToCheck[i].value) {
var re_pattern = strRegExp;
if (!re_pattern.test(fieldToCheck[i].value) || fieldToCheck[i].value.length < min || fieldToCheck[i].value.length > max) {
alert(msg);
fieldToCheck[i].focus();
fieldToCheck[i].select();
return false;
}
}
}
return true;
}
Used with:

Code:
<form method="post" action="../some_URL"
onsubmit="return (

validateRE(this.quantity, /^[1-9]{1}$|^[0-9]{2,3}$/,
'Please enter a Quantity.', 1, 3)

);">
The part in question is the red highlighted section.
The number of items that is under a specific product is generated dynamically and can range from 2-20. How can I get javascript to count the total number of items and run "for i=0;i<total number" instead so it is different for each product page?