倒数计时器结束后设定秒表计时器

Question

我的程序中有一个倒数计时器，我想启动一个秒表计时器，该计时器跟踪倒计时完成后每隔一秒，一分钟和一小时，即使用户不在网站中，它也持续计数，只有在用户点击按钮后才能停止

  var countDownDate = new Date().getTime();

  var x = setInterval(function(){
    var currentDate = new Date().getTime();

    var distance = countDownDate - currentDate;

    var days = Math.floor(distance / (1000 * 60 * 60 * 24));
    var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
    var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
    var seconds = Math.floor((distance % (1000 * 60)) / 1000);


    if(days == 0 && hours == 0){
      document.getElementById("due").innerHTML = "due date";
      document.getElementById("demo").innerHTML = minutes + "m " + seconds + "s ";
    }else if(hours == 0){
      document.getElementById("due").innerHTML = "due date";
      document.getElementById("demo").innerHTML = hours + "h" + minutes + "m " + seconds + "s ";
    }

    if (distance < 0) {
      clearInterval(x);
      document.getElementById("due").innerHTML = "overdue by";
      document.getElementById("demo").innerHTML = "The timer has run out";
    }

  },1000);

倒计时后，秒表应自动启动，并持续跟踪经过的每一秒，即使不在网站中也是如此，除非已停止