计算时间差开始倒计时

// 声明

countDown = "00:00";

// 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)
};

// // 倒计时
    timeFn() {
        const params = {
            'endTimeStr': this.endTime   // 03:03:25
        };
        this.dataService
            .CountDown(params)
            .then((data) => {
                let timeArray = data.endTime.split(':');
                this.hour = parseInt(timeArray[0]);
                this.mins = parseInt(timeArray[1]);
                this.scds = parseInt(timeArray[2]);
                let timeCountScd = this.hour * 60 * 60 + this.mins * 60 + this.scds;
              this.allTimeCount = setInterval(() => {
                    this.countDown = '';
                    // 时间为负值时跳出考试
                    if (timeCountScd  < 0) {
                        this.countDown = '考试时间已截止';
                        this._hiddenPaper = true;
                        // 跳转到列表页
                        clearInterval(this.allTimeCount);
                        setTimeout(() => {
                            this.router.navigate(['main/student']);
                        }, 10000);
                    }else {
                        timeCountScd -- ;
                        if ( timeCountScd === 0) {
                            this._message.create('success', `试卷已提交，考试结束！`, {nzDuration: 5000});
                            this.handlePage();
                            // 保存成功后跳转到列表页
                            clearInterval(this.allTimeCount);
                            setTimeout(() => {
                                this.router.navigate(['main/student']);
                            }, 5000);
                        }
                        this.hour = Math.floor(timeCountScd / 60 / 60);
                        this.mins = Math.floor(timeCountScd / 60 % 60);
                        this.scds = Math.floor( timeCountScd % 60);
                        this.countDown += ( this.hour < 10 ? ('0' + this.hour) : this.hour) + ':';
                        this.countDown += ( this.mins < 10 ? ('0' + this.mins) : this.mins) + ':';
                        this.countDown += ( this.scds < 10 ? ('0' + this.scds) : this.scds);
                    }

                }, 1000)

            });

    };