ช่วยดู Javascript ให้ทีครับ มันไม่คำนวณให้ ถ้ามีสินค้าตัวเดียว

 $cnt=count($_SESSION['pro_in_cart']);
                for($i=0;$i<$cnt;$i++){
                    $sql_sp=mysqL_query("SELECT * FROM supplier_product WHERE sp_id='".$_SESSION['pro_in_cart'][$i]."'");
                    $rs_sp=mysql_fetch_array($sql_sp);

                    $sql_pro=mysql_query("SELECT * FROM product WHERE Product_ID='$rs_sp[product_id]'");
                    $rs_pro=mysql_fetch_array($sql_pro);
                    
                    echo "<tr>
                            <td class='border_order_data' align='center'>$rs_pro[Product_ID]<input type='hidden' name='pro_id' value='$rs_pro[Product_ID]'></td>
                            <td class='border_order_data' align='center'>$rs_pro[Product_Name]</td>
                            <td class='border_order_data' align='center'><input type='text' name='amount' id='amount$i' style='width:1.5cm' onblur='JavaScript:fnccal();'></td>
                            <td class='border_order_data' align='center'>".number_format($rs_sp['price_per_unit'], 2,'.',',')."<input type='hidden' name='price_per_unit' id='price_per_unit$i' value='$rs_sp[price_per_unit]'></td>
                            <td class='border_order_data' align='center'><input type='text' name='sum' id='sum$i' style='width:2cm' onblur='JavaScript:fnccal();'></td>
                            <td class='border_order_data' align='center'><a href='add2cart.php?del=$i'>ลบ</a></td>
                        </tr>";
                    //$all_total+=$rs_sp['total_price'];
                }

<script language="javascript">
function fnccal(){

    var sum =0;
    var tot =0;
    for(i=0;i<document.form1.cnt.value;i++){
        sum=parseFloat(eval("document.form1.amount"+i+".value"))*parseFloat(eval("document.form1.price_per_unit"+i+".value"));
         document.form1.sum[i].value=sum;
        tot=tot+sum;
        document.form1.total_price.value=tot;
    
    }
}
</script>