Not allowing a certain number of items in cart

I'm needing to modify the cart to NOT allow 13 items. Any other number of items can be sold, just not 13.

Does anyone have any ideas where to start on this? Could it be a validation rule using the Validation Tool kit?

Any ideas would be great.

13 items of the cart total quantity, or 13 of just one item in the cart?

what should happen if the quantity is at 13? Adjust the quantity up? or down? show a message?

Both, it shouldn't allow 13 items in the cart, or 13 of one item.

Ideally a message would come up saying quantities of 13 are not allowed, or something like that.

you would need to use a javascript function on the onClick event of the add to cart button.

this example assumes that:
1: the cart object is named "eCart1"
2: the add to cart button form is named "eCart1_1_ATC_1"
3: the quantity element is named "eCart1_1_Quantity_Add"

you will need to make modifications to the javascript if your code uses different names

the on click event for the button would be:


onClick="return if13(<?php echo $eCart1->TotalColumn("Quantity"); ?>,document.eCart1_1_ATC_1.eCart1_1_Quantity_Add.value);"

the javascript function would look like:
<script type="text/javascript">
function if13(alreadyIn, qtyAdded) {
//alert(parseInt(alreadyIn)+parseInt(qtyAdded));
if(parseInt(alreadyIn)+parseInt(qtyAdded) == 13) {
alert('no');
return false;
}
}
</script>


keep in mind that this is really not something that is supported in eCart and we will not be able to offer extensive support for it

If a customer edits the quantities whilst on the cart page, then the number of items in the cart could be also be changed to 13.

in this instance, you could count the number of items in the cart, and if it is equal to 13, disable the checkout button and show a suitable message