Untitled

<!DOCTYPE html>
<html>
<head>
	<title></title>

</head>
<body>
	<div id="chrono"></div>
	<button id="test">Test</button>
	<script>
		var time = new Date();

		function getMillisecondeFor(minute){
				return minute*60*1000;

			}

		var btn = document.getElementById("test");
		btn.addEventListener("click", function(){
			if(confirm("Cette action supprimera votre réservation actuelle, souhaitez-vous continuez ?") === true){
			var time = new Date();
			var dateFutur = time.getTime() + getMillisecondeFor(20);
			localStorage.setItem("futur_date", dateFutur);
		}
		})

		function hasReservation(){

		return(localStorage.getItem("futur_date") > time.getTime());
}

		function logTime(){
			if(hasReservation()){
		var actualTime = new Date().getTime();
		var calcul = Math.round((localStorage.getItem("futur_date") - actualTime) /1000);
		console.log(Math.round(calcul/60) -1);
		console.log(Math.round(calcul%60));
		var minutes = Math.round(calcul/60) -1;
		var secondes = Math.round(calcul%60);

		if(minutes <= 0){
			alert("Votre réservation est terminé")
			clearInterval(intervalId);
		}
		var myDiv = document.getElementById("chrono");
		myDiv.innerHTML = "Min : "+minutes +" Secondes "+ secondes;

	}
	}

		var intervalId = setInterval(logTime,1000);

	</script>

</body>
</html>