Update Input field value with javascript

I am trying to build a javascript function that will update an input field every second with a new number. This is essentially what I'm hoping my function can do, and hopefully someone can give me a pointer about what I'm doing wrong.

<script>
   var myVar = setInterval(function(){ getNumber() }, 1000);

   function getNumber() {
     var x = round(microtime(true) * 1000);;
     document.getElementById("displaynum").value = x;

</script>

<input type="text" id="displaynum">

Couple of issues you have:

• Closing bracket for the function
• It is Math.round() and not just round()
• What is microtime()? I have replaced it with Math.random() to generate a random number.

var myVar = setInterval(function() {
  getNumber()
}, 1000);

function getNumber() {
  var ts = new Date().getTime();
  var x = Math.round(ts*Math.random());
  document.getElementById("displaynum").value = x;
}

<input type="text" id="displaynum">

Update:

Use new Date().getTime() to get the current time stamp and couple it with Math.random() to get a random number with least probability to get repeated.