Untitled

<!DOCTYPE html>
<html lang="en">

<head>
<meta charset="utf-8" />
<title>JS</title>

<script>

	var seconds=10;
	var s;
	var timer;

	function decreaseSeconds() {
		seconds--;
		s.innerHTML=seconds;
	}

	timer = setInterval(decreaseSeconds, 1000);

	function setup() {
		s=document.getElementById("seconds");
		s.innerHTML=90;
		s.innerHTML=seconds;
	}

</script>

</head>

<body onload="setup()">

<h1>Quiz on line</h1>

<p>Mancano <em id="seconds">90</em> secondi al termine del quiz.</p>

</body>

</html>