引用css和js文件

<link rel="stylesheet" type="text/css" href="css/style.css">
<script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js" charset="utf-8"></script>

css样式

* {margin: 0;padding: 0;}
html {width: 100%;font: normal 100% Helvetica, Arial, sans-serif;font-family: '微软雅黑';font-size:10px;}

.paymentOrder{height: 7.5rem;text-align: center; line-height: 7.5rem;font-size: 1.5rem;}
.paymentOrder span{font-size: 3rem;color: #8582ff;vertical-align: sub;}
.btn{overflow: hidden;text-align: center;}
button{width:8rem;text-align: center; font-size: 1.3rem;height: 3.5rem; line-height: 3.5rem;padding:0; text-indent:0;color: #FFFFFF; background: #8582ff;border-radius: .3rem;border: none;outline: none;margin: 0 1rem;display: inline-block;cursor: pointer;font-family: '微软雅黑'}

js代码

var t=new Timer(119999);
t.inTime();

function Timer(intSecond){
  var _this=this,m,flag=true;
  this.second=intSecond;
  this.inTime=function(){
    m=setInterval(function(){
          var day=0,hour=0,minute=0,second=0;
          if(intSecond > 0){
              day = Math.floor(intSecond / (60 * 60 * 24));
              hour = Math.floor(intSecond / (60 * 60)) - (day * 24);
              minute = Math.floor(intSecond / 60) - (day * 24 * 60) - (hour * 60);
              second = Math.floor(intSecond) - (day * 24 * 60 * 60) - (hour * 60 * 60) - (minute * 60);
          }
          if (day <= 9) day = '0' + day;
          if (hour <= 9) hour = '0' + hour;
          if (minute <= 9) minute = '0' + minute;
          if (second <= 9) second = '0' + second;
          $('#J_Day').html(day);
          $('#j_Hour').html(hour);
          $('#J_Minute').html(minute);
          $('#J_Second').html(second);
          _this.second=intSecond--;
          if(intSecond == -2){
            alert("超时！");
            clearInterval(m);
          }
      }, 1000);
  }

  this.stopTime=function(){
    clearInterval(m);
    flag=false;
  }

  this.startTime=function(){
    if(flag){
      alert("兄弟，你点击暂停了吗？不要搞事情！");
      return
    }
    clearInterval(m);
    this.inTime();
    flag=true;
  }

}

使用方法： t.inTime(); //创建一个倒计时函数 t.stopTime(); //停止倒计时 t.startTime(); //开始倒计时