施用js验证年龄是否有18岁

使用js验证年龄是否有18岁
 <div class="renzhenglx_div">
                            <div class="renzheng_left_div" style="line-height: 20px">
                                生日：</div>
                            <div class="renzheng_right_div">
                                <select name="Date_Year" id="Date_Year" class="select_b_div" style="width: auto;">
                                </select>&nbsp;年&nbsp;&nbsp;
                                <select name="birthday_m" id="birthday_m" class="select_b_div" style="width: auto;">
                                </select>&nbsp;月&nbsp;&nbsp;
                                <select name="birthday_d"" id="birthday_d" class="select_b_div" style="width: auto;">
                                </select>&nbsp;日
                            </div>
                        </div>
[解决办法]

 var date = new Date();
 var sYear = $("#Date_Year").val();
 var sMonth = $("#birthday_m").val();
 var sDay = $("#birthday_d").val();
 var dYear = date.getFullYear();
 var dMonth = date.getMonth()+1;
 var dDay = date.getDate();

 if((Number(dDay)-Number(sDay))<0)
 {
     dMonth -= 1;
 }
 if((Number(dMonth)-Number(sMonth))<0)
 {
     dYear -= 1;
 }
 if((Number(dYear)-Number(sYear))>=18)
 {
     alert("已满18岁");
  }
 else
 {
      alert("未满18岁");
  }