小程序倒计时，已知过期时间实现倒计时

话不多说，直接贴代码 

    /**
   * 页面的初始数据
   */
  data: {
    pastDate:'2019-03-05 17:27:34',//过期时间
    timer: "00:30:00",
    },
  /**
   * 生命周期函数--监听页面加载
   */
  onLoad: function(options) {
   var timerInterval= setInterval(that.countDown, 1000);
    
  },
  //定时触发方法
  countDown(){
    let pastDate = this.data.pastDate;
    let nowPastTime = new Date(pastDate.replace(/-/g, '/')).getTime();
    let now = new Date().getTime();
    let secs = (nowPastTime - now) / 1000;
    let mesc = this.dateformate(secs);
    if (mesc == "00:00:00"){
      clearInterval(timerInterval);
      // console.log(12312);
    }else{
      this.setData({
        timer: mesc
      })
    }
  },
   // 时间格式化输出，将时间戳转为 倒计时时间
  dateformate(micro_second) {
    var second = micro_second; //总的秒数
    // 天数位   
    var day = Math.floor(second / 3600 / 24);
    var dayStr = day.toString();
    if (dayStr.length == 1) dayStr = '0' + dayStr;
    // 小时位   
    //var hr = Math.floor(second / 3600 % 24);
    var hr = Math.floor(second / 3600); //直接转为小时 没有天 超过1天为24小时以上
    var hrStr = hr.toString();
    if (hrStr.length == 1) hrStr = '0' + hrStr;
    // 分钟位  
    var min = Math.floor(second / 60 % 60);
    var minStr = min.toString();
    if (minStr.length == 1) minStr = '0' + minStr;
    // 秒位  
    var sec = Math.floor(second % 60);
    var secStr = sec.toString();
    if (secStr.length == 1) secStr = '0' + secStr;
    return hrStr + ":" + minStr + ":" + secStr;
  },