Decompte de jours - Javascript

var delais=0;  

function getDelay(){  
 var dateEvent = new Date('2013', '07', '31');  
 var dateNow = new Date();  
 var d = dateEvent.getTime() - dateNow.getTime();  
 return d;  
}  

delais = getDelay();  

function startCompteur(delais){  
 setInterval(bip, 1000);  
}  

function bip()  
{  
 var nBJour = Math.floor(delais/86400000);  
 var resteJour = delais%86400000;  
 var nbHeure = Math.ceil(resteJour/3600000);  
 var resteHeure = resteJour%3600000;  
 var nbMinute = Math.ceil(resteHeure/60000);  
 var resteMinute = resteHeure%60000;  
 var nbSeconde = Math.ceil(resteMinute/1000);  
 document.getElementById("bip").innerHTML = nbJour+"jours, "+nbHeure+"h"+nbMinute+"min"+nbSeconde+"s";  
}