javascript 有条件地禁用按钮

Question

为什么我收到警报，但在从选择更新总计后将负值更改为正值后按钮未启用。这是不起作用的部分:

    if ($('.grand_total').val() < 0) {
   $('#submit').prop('disabled', true);
   alert('negative number found');

} else if ($('.grand_total').val() > 0) {
   $('#submit').prop('disabled', false);
   alert('positive number found');
}  

这是完整的代码:

 <script language="javascript">
 $(".add_to_total").on('change', function() {
var total = 0;
var grand_total = 0; 
$(".dynamic_row").each(function() {
    var row = $(this);

    var start_hour_am = parseFloat(row.find(".start_hour_am").val()) || 0;
    var start_minute_am = parseFloat(row.find(".start_minute_am").val()) || 0;

    var end_hour_am = parseFloat(row.find(".end_hour_am").val()) || 0;
    var end_minute_am = parseFloat(row.find(".end_minute_am").val()) || 0;        

    var start_hour_pm = parseFloat(row.find(".start_hour_pm").val()) || 0;
    var start_minute_pm = parseFloat(row.find(".start_minute_pm").val()) || 0;          

    var end_hour_pm = parseFloat(row.find(".end_hour_pm").val()) || 0;
    var end_minute_pm = parseFloat(row.find(".end_minute_pm").val()) || 0;

    total = ( (Number(end_hour_am) + (Number(end_minute_am))) - (Number(start_hour_am) + Number(start_minute_am)) + (Number(end_hour_pm) + Number(end_minute_pm)) - (Number(start_hour_pm) + Number(start_minute_pm)));
    row.find(".total").val(total);
    grand_total = Number(grand_total) + Number(total);  

}); 
    $("#grand_total").val(grand_total);


if ($('.grand_total').val() < 0) {
   $('#submit').prop('disabled', true);
   alert('negative number found');

} else if ($('.grand_total').val() > 0) {
   $('#submit').prop('disabled', false);
   alert('positive number found');
}  

 });
 </script>

任何想法将不胜感激。

更新这是总计的 html:

<input type="text" class="grand_total" name="grand_total" id="grand_total" data-role="none" value="0" size="3" readonly="true">

这是我试图禁用的按钮:

<button type="submit" data-theme="e" data-mini="true" data-inline="true" name="submit" id="submit" class="submit" data-icon="check" value="submit-value">Submit</button>

按照 Nick N 的建议，按钮禁用/启用仍然遇到同样的问题。

<script language="javascript">
$(".add_to_total").on('change', function() {
    var total = 0;
    var grand_total = 0; 
    $(".dynamic_row").each(function() {
        var row = $(this);

        var start_hour_am = parseFloat(row.find(".start_hour_am").val()) || 0;
        var start_minute_am = parseFloat(row.find(".start_minute_am").val()) || 0;

        var end_hour_am = parseFloat(row.find(".end_hour_am").val()) || 0;
        var end_minute_am = parseFloat(row.find(".end_minute_am").val()) || 0;        

        var start_hour_pm = parseFloat(row.find(".start_hour_pm").val()) || 0;
        var start_minute_pm = parseFloat(row.find(".start_minute_pm").val()) || 0;          

        var end_hour_pm = parseFloat(row.find(".end_hour_pm").val()) || 0;
        var end_minute_pm = parseFloat(row.find(".end_minute_pm").val()) || 0;

        total = ( (Number(end_hour_am) + (Number(end_minute_am))) - (Number(start_hour_am) + Number(start_minute_am)) + (Number(end_hour_pm) + Number(end_minute_pm)) - (Number(start_hour_pm) + Number(start_minute_pm)));
        row.find(".total").val(total);
        grand_total = Number(grand_total) + Number(total);  

    }); 
        $("#grand_total").val(grand_total);


    //if (parseFloat($('.grand_total').val()) < 0) {
    //   $('#submit').prop('disabled', true);
    //   alert('negative number found');

    //} else if (parseFloat($('.grand_total').val()) > 0) {
    //   $('#submit').prop('disabled', false);
    //   alert('positive number found');
    //}


    var total = parseFloat($('#grand_total').val());
    if(total < 0){
       $('#submit').prop('disabled', true);
       alert('negative number found...');
    }
    else {
       $('#submit').prop('disabled', false);
       alert('positive number found...');
    }     

});
</script>

更新好吧，看起来问题是因为该按钮是 jquery mobile 生成的按钮，当发现负值时，它不会更新按钮的状态，如果我刷新整个表单，按钮状态就会改变。我通过将数据 Angular 色设置为无来测试这一点，以便提交按钮成为标准表单按钮并且禁用/启用功能有效。我有什么想法可以解决这个问题吗？

Answer 1

这应该有效:

var total = parseFloat($('.grand_total').val());
if(total < 0){
   $('#submit').attr("disabled", "disabled");
   alert('negative number found');
}
else {
   $('#submit').removeAttr("disabled"); 
   alert('positive number found');
}

<小时/>

Jquery Mobile:不要刷新整个表单，而只刷新按钮:

$('#submit').button('refresh');

<小时/>

请注意:我将“#”更改为“.”。根据您的 HTML，您还可以更改此行:

 $(".grand_total").val(grand_total);

至:

$("#grand_total").val(grand_total);