Countdown on JavaScript

Question

I want to make a countdown that starts on 5 minutes and goes to 0 with the pass of the time.

Here is my code:

var x = setInterval(function() {
  var t = 300;
  var minutes = Math.floor(t / 60);
  var seconds = Math.floor(t / 5; 
  document.getElementById("demo").innerHTML = minutes + ":" + seconds;
  if (t < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "EXPIRED";
  }
},1000);

<p id="demo"></p>

It doesn't work. I know how to do it with a specific date, but it doesn't work with an established amount of time.

Can someone help me?

Answer 1

New code, that works (thanks to FZs and Flori Bruci):

	<p id="demo"></p>
	<script> 
		var t = 27; 
	    var x = setInterval(function() {
	    var minutes = Math.floor(t / 60); 
	    var seconds = Math.floor(t / 5); 
	    document.getElementById("demo").innerHTML = minutes + ":" + seconds; 
	    t--;
	        if (t < 0) { 
	            clearInterval(x); 
	            document.getElementById("demo").innerHTML = "EXPIRED"; 
	        } 
	    }, 200); 
	</script>