row total

HTML

<form name="panierform" id="panierform" method="post" action="">
  <table width="80%" border="2" id="myTable">
    <tr>
      <th scope="col">Product</th>
      <th scope="col">Price</th>
      <th scope="col">Qty</th>
      <th scope="col">Product Total</th>
    </tr>
    <tr>
      <td>
        <label for="article"></label>
        <input type="text" name="article" id="article" class="article" value="1" />
      </td>
      <td>
        <label for="prix"></label>
        <input name="prix" type="text" id="prix" class="prix" value="10" />
      </td>
      <td>
        <label for="quantity"></label>
        <input name="quantity" type="number" id="quantity" class="quantity" value="" />
      </td>
      <td>
        <label for="ptotal"></label>
        <input type="text" name="ptotal" id="ptotal" class="ptotal" value="" />
      </td>
    </tr>
    <tr>
      <td>
        <label for="article"></label>
        <input type="text" name="article" id="article" class="article" value="2" />
      </td>
      <td>
        <label for="prix"></label>
        <input name="prix" type="text" id="prix" class="prix" value="40" />
      </td>
      <td>
        <label for="quantity"></label>
        <input name="quantity" type="number" id="quantity" class="quantity" value="" />
      </td>
      <td>
        <label for="ptotal"></label>
        <input type="text" name="ptotal" id="ptotal" class="ptotal" value="" />
      </td>
    </tr>
  </table>
</form>

JavaScript

function calculatePtotal() {
  $("tr", "#myTable").each(function(i, row) {
    $row = $(row);
    var value = parseFloat($('.prix', $row).val());
    var quantity = parseFloat($(".quantity", $row).val());
    var shipping = parseFloat($(".shipping", $row).val());
    var ptotal = (value * quantity);
    $(".ptotal", $row).val(parseFloat(ptotal).toFixed(2));
  });
}

calculatePtotal();

$(".quantity, .shipping").change(function() {
  calculatePtotal();
});