购物车数字加减

效果图

html

<ul class="btn-numbox">
    <li>
        <ul class="count">
            <li style="margin-left: 40px;"><span id="num-jian" class="num-jian">-</span></li>
            <li><input type="text" class="input-num" id="input-num" value="0"></li>
            <li><span id="num-jia" class="num-jia">+</span></li>
        </ul>
    </li>
</ul>

css

* {padding: 0;margin: 0;border: 0;outline: 0}
ul,li {list-style: none;}
a {text-decoration: none;}
a:hover {cursor: pointer;text-decoration: none;}
a:link {text-decoration: none;}
img {vertical-align: middle;}
.btn-numbox {overflow: hidden;margin-top: 20px;margin-left: 40px;}
.btn-numbox li {float: left;}
.btn-numbox li .number,.kucun {
    display: inline-block;
    font-size: 12px;
    color: #808080;
    vertical-align: sub;
}
.btn-numbox .count {
    overflow: hidden;
    margin: 0 16px 0 -20px;
}
.btn-numbox 
.count .num-jian,
.input-num,
.num-jia {
    display: inline-block;
    width: 28px;
    height: 28px;
    line-height: 28px;
    text-align: center;
    font-size: 18px;
    color: #999;
    cursor: pointer;
    border: 1px solid #e6e6e6;
}
.btn-numbox .count .input-num {
    width: 58px;
    height: 28px;
    color: #333;
    border-left: 0;
    border-right: 0;
}

js

jquery实现
$('.num-jian').click(function(e) {
        //closest() 获得匹配选择器的第一个祖先元素
        console.log($(this).find('.input-num'));
        var obj = $(this).closest('ul').find('.input-num');
        if (obj.val() <= 0) {
            obj.val(0);
        } else {
            obj.val(parseInt(obj.val()) - 1);
        }
        obj.change();
    });

    $('.num-jia').click(function(m) {
        var obj = $(this).closest('ul').find('.input-num');
        obj.val(parseInt(obj.val()) + 1);
        obj.change();
    });

原生js实现
var num_jia = document.getElementById('num-jia');
    var num_jian = document.getElementById('num-jian');
    var input_num = document.getElementById('input-num');

    num_jia.onclick = function() {
        input_num.value = parseInt(input_num.value) + 1;
    }

    num_jian.onclick = function() {
        if(input_num <= 0) {
            input_num.value = 0;
        } else {
            input_num.value = parseInt(input_num.value) - 1;
        }
    }