添加订单总计的输入时出错

Question

我正在尝试使用jQuery一起添加“total”类的输入，然后在#total_price字段中显示它。问题是我的代码只是简单地连接数字而不是将它们加在一起，所以代替2和2导致4导致22。如果有人能解释我哪里出错了将不胜感激！感谢

HTML片段给你一个想法：

<tr>
                            <td>
                                <select id="Board_D" class="service">
                                    <option value="select">Board Pickets</option>
                                    <option value="1">Board Pickets on 1X4 6' Tall</option>
                                    <option value="2">Board Pickets on 1X6 6' Tall</option>
                                    <option value="3">Board Pickets on 1X4 8' Tall</option>
                                    <option value="4">Board Pickets on 1X6 8' Tall</option>
                                </select>
                            </td>
                            <td>$<input id="Board_C" /></td>
                            <td><input id="Board_Q" class="service" /></td>
                            <td>$<input id="Board_A" class="total" /></td>
                        </tr>

JS：

$(document.body).on('keypress keydown keyup change', '#manualOverrideNo, [class="total"], [class="standard"], [class="service"]', function(){
    if($('#manualOverrideNo').prop('checked')) {

        /*total_cost = 9;
        $("#total_price").val(total_cost);*/
        var sum = '';
            /*Go through each input with class of 'total'*/

        $(".total").each(function() {
            /*Add only if value is a number*/
            if(!isNaN(this.value) && this.value.length !== 0) {
                sum += parseFloat(this.value);
            }
        });
        $("#total_price").val(sum);
    }
});