JQ购物车+1-1

//购物车-
        function Jian(obj) {
            var n = $(obj).prev().val();
            var num = parseInt(n) - 1;
            if (num == 0) {
                layer.msg("购物数量不能小于0");
                return false;
            }
            $(obj).prev().val(num);

        }

//购物车+
        function Jia(obj) {
            var n = $(obj).next().val();
            var num = parseInt(n) + 1;
            if (num == 0) {
                return;
            }
            $(obj).next().val(num);
        }