TalkPHP - Ajax + Javascript + DIV problem

Not so much or a problem, just I don't know...

Ok, so ajax select to create a table with a few fields in it is working fine, obviously puts the table in a DIV...

Now the problem I have is I want to do a calculation on a field in the table, the issue I have is I don't know where to do the javascript calc (if that makes sense)...

Code:

<html>

<head>

<META HTTP-EQUIV="Pragma" CONTENT="no-cache">

<META HTTP-EQUIV="Expires" CONTENT="-1">

<script type="text/javascript">



function calcMargin(margin)

{



do I do this here ??????



}





function showProduct(str)

{



// use correct code for Browser Type

if (window.XMLHttpRequest)

  {// code for IE7+, Firefox, Chrome, Opera, Safari

  xmlhttp=new XMLHttpRequest();

  }

else

  {// code for IE6, IE5

  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");

  }



// Check for state change and fill the "div" with the sql data and table html bollocks



xmlhttp.onreadystatechange=function()

  {

  if (xmlhttp.readyState==4 && xmlhttp.status==200)

    {

    document.getElementById("txtHint").innerHTML=xmlhttp.responseText;

    }

  }

xmlhttp.open("GET","getProd.php?q="+str,true);

xmlhttp.send();

}

</script>



</head>





<?









$con = mysql_connect('localhost', 'user', 'pass');

if (!$con)

  {

  die('Could not connect: ' . mysql_error());

  }



mysql_select_db("database", $con);



/*

Grab the ID's and the product names from the db, only going to use the id_prd value for the form value

but going to show the ID and product name for ease of use.

*/





$sql="SELECT id_prd, name_prd FROM products_prdV2 order by id_prd asc";

$result = mysql_query($sql);

?>





<body>

Please select a Product from the List

<form>

<select name="id_prd" onchange="showProduct(this.value)">



<?

while($row = mysql_fetch_array($result))

        {

        echo "<option value=" . $row['id_prd'] .">" . $row['id_prd'] . " " . $row['name_prd'] . "</option>\n";

        }

?>





</select>

</form>



<br />

<div id="txtHint"></div>

</body>

<HEAD>

<META HTTP-EQUIV="Pragma" CONTENT="no-cache">

</HEAD>

</HTML>

This is the form processor (yes it is rough, just throwing it together to get it working then will tidy and sort it properly, just want funtionality first)

Code:

<?php



$q=$_GET["q"];



?>



<script type="text/javascript">



function calcMargin(margin)

{



Or do I do this here ????





}

</script>



<?



$con = mysql_connect('localhost', 'user', 'pass');

if (!$con)

  {

  die('Could not connect: ' . mysql_error());

  }



mysql_select_db("database", $con);

$sql="SELECT id_prd, sku_prd, price_prd, prd_discounts.discount_sum  FROM products_prdV2, prd_discounts WHERE id_prd = $q  and discount_prd_id = $q";



$result = mysql_query($sql);



echo "<table border='1'>";

echo "<tr>";

echo "<th>Product ID</th>";

echo "<th>Product name</th>";

echo "<th>Price</th>";

echo "<th>Discount Percentage</th>";

echo "<th>Price after discount</th>";

echo "<th>Cost Price</th>";

echo "<th>Margin</th>";

echo "</tr>";



while($row = mysql_fetch_array($result))

  {

  echo "<tr>";

  echo "<td>" . $row['id_prd'] . "</td>";

  echo "<td>" . $row['sku_prd'] . "</td>";

  echo "<td>&pound;" . $row['price_prd'] . "</td>";

  echo "<td>" . $row['discount_sum'] . "%</td>";

  echo "<td>&pound;" . round(($row['price_prd'] - (($row['price_prd'] / 100) * $row['discount_sum'])), 2) . "</td>";

  echo "<td><input type='text' name='cost_price' onChange='calcMargin(this.value)'></td>";

  echo "<td><input type='text' name='margin' value='margin' readonly='readonly' /></td>";

  echo "</tr>";



  }

echo "</table><br><br>";





mysql_close($con);

?>

Thanks :D