php - How to sum ​​with javascript if data form while()? -

i have code

<script> function select(val, item) { var prize = $(".prize"+item).val(); var prize = prize*val; $(".dollar"+item).html(prize);  //----- code error --------// $sub_total=$(".dollar1").val()+$(".dollar2").val()+$(".dollar3").val()+..... etc; $(".total").html($sub_total); // ---------------------------- //  } </script>  <input type="hidden" value="140" class="prize1"> <select class="quantity" id="quant2" value="1" onchange="select(this.value, 1)"> src="1"> <option value="1" selected>1</option> <option value="2">2</option> <option value="3">3</option> </select> prize : <span class="dollar1" value="140">140</span> <br> <input type="hidden" class="prize2" value="150"> <select class="quantity" id="quant2" value="2" onchange="select(this.value, 2)"> src="2"> <option value="1">1</option> <option value="2" selected>2</option> <option value="3">3</option> </select> prize : <span class="dollar2" value="300">300</span>  ...... etc  <br><br> <label> total </label> : <span class="total">?????</span> 

how make total element , can compute amounts on price? how if after onchange select, on dollar1 dollar2 dollar3 ... etc summed , because use while() on script. should in script ?

$sub_total=dollar1+dollar2+dollar3+..... etc; $(".total").html($sub_total); 

if php code

<?php while($loll = $resultu->fetch_array(mysqli_both)){ $id_item= $loll['id_item']; $prize=$loll['prize'];     <input type="hidden" value="<?php echo $prize ?>" class="prize<?php echo $id_item ?> ">     <select class="quantity" value="<?php echo $id_item ?>" onchange="select(this.value, <?php echo $id_item ?>)"> src="<?php echo $id_item ?>">     <option value="1" selected>1</option>     <option value="2">2</option>     <option value="3">3</option>     </select>     prize : <span class="dollar<?php echo $id_item ?>" value="<?php echo $prize ?>"><?php echo $prize ?></span>     <br> }     ...... etc      <br><br>     <label> total </label> : <span class="total">?????</span> 

how can summed $sub_total= --> $(".dollar<?php echo $id_item ?>")?

here simple jquery example run sum calculation when user changes select elements:

html

<select id="select1">             <option value="1">1</option>             <option value="2">2</option>             <option value="3">3</option>         </select>         <select id="select2">             <option value="1">1</option>             <option value="2">2</option>             <option value="3">3</option>         </select>         <input id="result" type="text"/> 

javascript

$(document).ready(function () {     $('#select1, #select2').change(function () {         var num1 = number($('#select1').val());         var num2 = number($('#select2').val());         var sum = num1 + num2;         $('#result').val("$" + sum);     });  });