function updateQty()
{
  var old_qty = parseInt($('cart_qty').innerHTML);
  if($('qty').value!="")
  $('cart_qty').innerHTML = old_qty+parseInt($('qty').value); 
}

function checkQuantity()
{
    var qty = parseInt($('qty').value);
    if(qty <= 0)
    {
        alert("Quantity must be bigger than 0");
        return false;
    }
    if(qty > 9999)
    {
        alert("9999 is the maximum amount of quantity allowed");
        return false;
    }
    return true;
}