การส่งค่าระหว่าง PHP javascipt โดยใช้ document.getElementById(''+i) มาคำนวนในช่อง input

function  doMath() {
 		var i = 1; 
       var nValue; var amount;
       var price=100;
       nValue = document.getElementById("message"+i).value;
    if(i<nValue.length){

       	amount=(nValue*price);
       	 console.log("จำนวนรวม"+amount);
      	 document.getElementById("total"+i).value=amount ;
         i++;
         
   		}
    }

<?php
 echo "เลขใบสั่งซื้อ&nbsp;"  .$fetched_row["page_num"];
$result_set=mysql_query($sql_query);
	if(mysql_num_rows($result_set)>0)
	{

		$i=0;
		while($row = mysql_fetch_row($result_set))
		{

			$i = $i+1;
			
			?>
				<tr>
			<td><input type="text" name="message<?php echo $i ?>" id="message<?php echo $i ?>" value="<?php echo $row[6]; ?>"  onkeyup="doMath()"maxlength="60">message</td>
			<td><input type="text" name="total<?php echo $i ?>" id="total<?php echo $i ?>" maxlength="60"> amount</td>
		</tr>
<?php
		}
	}
	else
	{
		?>
		 <tr>
        <th colspan="3">ไม่พบข้อมูล</th>
        </tr>
        <?php
	}
?>