javascript - Computing for the value of the last column cell -- involves dynamic table rows -

consider following html table:

<table id="mytable1">     <tr id="tr1">         <td><input type="text" id="quantity1" name="quantity1" /></td>         <td><input type="text" id="weight1" name="weight1" /></td>         <td><input type="text" id="sub_total1" name="sub_total1" /></td>     </tr> </table> 

what i'm trying accomplish here need update value sub_total field on every row based on values typed in quantity , weight fields on same row every time keyup() triggered.

now believe manageable task if table i'm working on static only. inclusion of dynamic adding of table rows caused me troubles.

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jquery dynamic addition of rows:

$(document).ready(function() {  var counter = 2;  $("#addbutton").click(function() {      $('#mytable1 tr:last').after(         '<tr id="tr"><td><input type="text" name="quantity' + counter +              '" id="quantity' + counter + '" value=""></input></td>' +          '<td><input type="text" name="weight' + counter +              '" id="weight' + counter + '" value=""></input></td>' +          '<td><input type="text" name="sub_total' + counter +              '" id="sub_total' + counter + '" value=""></input></td></tr>'     );      counter++; }); }); 

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here have formula used in computing sub_total:

var sub_total  = ((170 * first 10 kilos) + (70 * remaining weight)) * (quantity); 

so given sample values: quantity = 10 weight = 15, should have

var sub_total  = ((170 * 10) + (70 * 5)) * (10); 

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i have following start ' not quite sure place inside these functions

$('#mytable1 input[id^=\'quantity\'], #mytable1 input[id^=\'weight\']').live('keyup',function() {      $('#mytable1 input[id^=\'quantity\'], #mytable1 input[id^=\'weight\']').each(function(index, value) {     }); }); 

you can use closest() match parent table row of modified element. there, it's easier locate quantity, weight , sub_total elements:

$("#mytable1 [id^=quantity], #mytable1 [id^=weight]").live("keyup", function() {     var $tr = $(this).closest("tr");     var quantity = parseint($("[id^=quantity]", $tr).val());     var weight = parseint($("[id^=weight]", $tr).val());      var firstten;     if (weight <= 10) {         firstten = weight;         weight = 0;     } else {         firstten = 10;         weight -= 10;     }      $("[id^=sub_total]", $tr).val((170 * firstten + 70 * weight) * quantity); });