Number Formatting in JQuery

Question

Good day to all, 

 

I just started developing a program in MVC (very newbie in both MVC and JQuery). In my front-end, I need to add two textbox and show the result in the 3rd textbox. Below is my JQuery code:

 

function Comma(Num) {
        Num += '';
        Num = Num.replace(',', ''); Num = Num.replace(',', ''); Num = Num.replace(',', '');
        Num = Num.replace(',', ''); Num = Num.replace(',', ''); Num = Num.replace(',', '');
        x = Num.split('.');
        x1 = x[0];
        x2 = x.length > 1 ? '.' + x[1] : '';
        var rgx = /(\d+)(\d{3})/;
        while (rgx.test(x1))
            x1 = x1.replace(rgx, '$1' + ',' + '$2');
        return x1 + x2;
    }

    $(function () {

        var total_amount = function () {
            var sum = 0;
            $('.amount').each(function () {
                var num = $(this).val().replace(',', '');
                if (num != 0) {
                    sum += parseFloat(num);
                }
            });
            $('#total_amount').val(sum);
        }


        $('.amount').keyup(function () {
            total_amount();
        });
    });

 Below is my mark-up also:

 

@Html.LabelFor(model => model.laborCost, htmlAttributes: new { @class = "control-label col-md-1" })
                            <div class="col-md-2">
                                @Html.EditorFor(model => model.laborCost, new { htmlAttributes = new { @class = "form-control text-right amount", @onkeyup = "javascript:this.value=Comma(this.value);" } })
                                @Html.ValidationMessageFor(model => model.laborCost, "", new { @class = "text-danger" })
                            </div>
                            @Html.LabelFor(model => model.partsCost, htmlAttributes: new { @class = "control-label col-md-1" })
                            <div class="col-md-2">
                                @Html.EditorFor(model => model.partsCost, new { htmlAttributes = new { @class = "form-control text-right amount", @onkeyup = "javascript:this.value=Comma(this.value);" } })
                                @Html.ValidationMessageFor(model => model.partsCost, "", new { @class = "text-danger" })
                            </div>
                            <div class="col-sm-1">
                                <b>
                                    Total
                                </b>
                            </div>
                            <div class="col-sm-2">
                                <input type="text" name="totalCost" class="form-control text-right" readonly="readonly" value="0" id="total_amount" />
                            </div>

My problem is that, whenever the number goes more than 6 0's,  the result is no long correct. see sample:

 

 

 My country is Laos so transaction amount usually exceeds a million. Thanks a lot for any assistance.