javascript - jQuery 数学不工作

Question

<分区>

Answer 1

您必须使用 unary 运算符强制结果为数字。

var $plus = +$old + 1;

另一种解决方案是使用parseInt 方法。

var $plus =parseInt($old,10) + 1;

解决方案

$('.ddd-plus').click(function(){
        var $old = $('.quntity-input').val();
        var $plus =+$old +1;
        $('input').val($plus);
    });
$('.ddd-minus').click(function(){
        var $old = $('.quntity-input').val();
        var $plus =$old -1;
        if($plus<0){
          return;
        }
        $('input').val($plus);
});

.sp-quantity {
    width:124px;
    height:42px;
    font-family:"ProximaNova Bold", Helvetica, Arial;
}
.sp-minus {
    width:40px;
    height:40px;
    border:1px solid #e1e1e1;
    float:left;
    text-align:center;
}
.sp-input {
    width:40px;
    height:40px;
    border:1px solid #e1e1e1;
    border-left:0px solid black;
    float:left;
}
.sp-plus {
    width:40px;
    height:40px;
    border:1px solid #e1e1e1;
    border-left:0px solid #e1e1e1;
    float:left;
    text-align:center;
}
.sp-input input {
    width:30px;
    height:34px;
    text-align:center;
    font-family:"ProximaNova Bold", Helvetica, Arial;
    border: none;
}
.sp-input input:focus {
    border:1px solid #e1e1e1;
    border: none;
}
.sp-minus a, .sp-plus a {
    display: block;
    width: 100%;
    height: 100%;
    padding-top: 5px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="sp-quantity">
        <div class="sp-minus fff"> <a class="ddd-minus" href="#">-</a></div>
        <div class="sp-input">
            <input type="text" class="quntity-input" value="1">
        </div>
        <div class="sp-plus fff"> <a class="ddd-plus" href="#">+</a></div>
    </div>