计算时间差开始倒计时

// 声明

// 页面引用
  <p class="cp-main-tip">剩余时间{{countDown}}<button id="hand-btn" class="hand-btn">交卷</button></p>

 timeFn(d1) {
    var t = "2018-02-03T14:30:00Z"; 
    setInterval(()=>{
      var endTime = new Date(t);
      var ss = (endTime.getTime() - (new Date()).getTime()) / 1000 ;
      var hour = Math.floor(ss / 60 / 60);
      var mins = Math.floor((ss / 60 % 60));
      var scds = Math.floor(ss % ( 60));
      this.countDown = ‘‘;
      if(hour > 0){
        this.countDown += (hour < 10 ? (‘0‘ + hour) : hour) + ‘:‘;
      }
      this.countDown += (mins < 10 ? (‘0‘ + mins) : mins) + ‘:‘;
      this.countDown += (scds < 10 ? (‘0‘ + scds) : scds);

    },1000)
};