微信小程序js倒計時功能

//倒計時方法

var that=this;
    this.data.intervarID= setInterval(function () {
      var leftTime = (new Date(2017, 6-1, 28, 17, 40, 0)) - (new Date()); //計算剩余的毫秒數 
      var days = parseInt(leftTime / 1000 / 60 / 60 / 24, 10); //計算剩余的天數 
      var hours = parseInt(leftTime / 1000 / 60 / 60 % 24, 10); //計算剩余的小時 
      var minutes = parseInt(leftTime / 1000 / 60 % 60, 10);//計算剩余的分鍾 
      var seconds = parseInt(leftTime / 1000 % 60, 10);//計算剩余的秒數 
      days = checkTime(days);
      hours = checkTime(hours);
      minutes = checkTime(minutes);
      seconds = checkTime(seconds);
      that.setData({
        clock: days + "天" + hours + "小時" + minutes + "分" + seconds + "秒"
      })
      if (days == '00' && hours == '00' && minutes == '00' && seconds=='00')
      {
        clearInterval(that.data.intervarID);

        that.setData({
          btnname: '立即搶購'
        })
      }
    }, 1000
    )