« Calculer les heures, la journée, la menthe, les secondes » Réponse du code

var dateFuture = new Date(new Date().getFullYear() +1, 0, 1);
var dateNow = new Date();

var seconds = Math.floor((dateFuture - (dateNow))/1000);
var minutes = Math.floor(seconds/60);
var hours = Math.floor(minutes/60);
var days = Math.floor(hours/24);

hours = hours-(days*24);
minutes = minutes-(days*24*60)-(hours*60);
seconds = seconds-(days*24*60*60)-(hours*60*60)-(minutes*60);