Calcular countdown y countup

countdown (tiempo que falta para una fecha y hora concreta):
<p id="tiempo"></p>
<p id="demo"></p>
<script>
var countDownDate = new Date("Jan 18, 2018 11:11:00").getTime();
var x = setInterval(function() {
  var now = new Date().getTime();
  var distance = countDownDate - now;
 
  document.getElementById("tiempo").innerHTML = distance + " milisegundos en total";
 
  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);

  document.getElementById("demo").innerHTML = days + "d " + hours + "h "
  + minutes + "m " + seconds + "s ";

  if (distance < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "EXPIRED";
  }
}, 1000);
</script>

countup (tiempo que ha transcurrido desde una fecha y hora concreta):
<p id="tiempo"></p>
<p id="demo"></p>
<script>
var countDownDate = new Date("Jan 18, 2018 7:50:00").getTime();
var x = setInterval(function() {
  var now = new Date().getTime();
  var distance = now - countDownDate;
 
  document.getElementById("tiempo").innerHTML = distance + " milisegundos en total";
 
  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);

  document.getElementById("demo").innerHTML = days + "d " + hours + "h "
  + minutes + "m " + seconds + "s ";

  if (distance < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "EXPIRED";
  }
}, 1000);
</script>