You may checkout this code:
var today = new Date();
var Christmas = new Date("2012-12-25");
var diffMs = (Christmas - today); // milliseconds between now & Christmas
var diffDays = Math.floor(diffMs / 86400000); // days
var diffHrs = Math.floor((diffMs % 86400000) / 3600000); // hours
var diffMins = Math.round(((diffMs % 86400000) % 3600000) / 60000); // minutes
alert(diffDays + " days, " + diffHrs + " hours, " + diffMins + " minutes until Christmas 2009 =)");
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…