Date.prototype.dateDiff = function(interval,objDate){
	var dtEnd = new Date(objDate);
	if(isNaN(dtEnd)) return undefined;
	switch (interval) {
	case "s":return parseInt((dtEnd - this) / 1000);
	case "n":return parseInt((dtEnd - this) / 60000);
	case "h":return parseInt((dtEnd - this) / 3600000);
	case "d":return parseInt((dtEnd - this) / 86400000);
	case "w":return parseInt((dtEnd - this) / (86400000 * 7));
	case "m":return (dtEnd.getMonth()+1)+((dtEnd.getFullYear()-this.getFullYear())*12) - (this.getMonth()+1);
	case "y":return dtEnd.getFullYear() - this.getFullYear();
	}
	}
	
	Date.prototype.format = function(format) {
		var returnStr = '';
		var replace = Date.replaceChars;
		for (var i = 0; i < format.length; i++) {
			var curChar = format.charAt(i);
			if (i - 1 >= 0 && format.charAt(i - 1) == "\\") { 
				returnStr += curChar;
			}
			else if (replace[curChar]) {
				returnStr += replace[curChar].call(this);
			} else if (curChar != "\\"){
				returnStr += curChar;
			}
		}
		return returnStr;
	};
	 
	Date.replaceChars = {
		shortMonths: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
		longMonths: ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'],
		shortDays: ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'],
		longDays: ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'],
		
		// Day
		d: function() { return (this.getDate() < 10 ? '0' : '') + this.getDate(); },
		D: function() { return Date.replaceChars.shortDays[this.getDay()]; },
		j: function() { return this.getDate(); },
		l: function() { return Date.replaceChars.longDays[this.getDay()]; },
		N: function() { return this.getDay() + 1; },
		S: function() { return (this.getDate() % 10 == 1 && this.getDate() != 11 ? 'st' : (this.getDate() % 10 == 2 && this.getDate() != 12 ? 'nd' : (this.getDate() % 10 == 3 && this.getDate() != 13 ? 'rd' : 'th'))); },
		w: function() { return this.getDay(); },
		z: function() { var d = new Date(this.getFullYear(),0,1); return Math.ceil((this - d) / 86400000); }, // Fixed now
		// Week
		W: function() { var d = new Date(this.getFullYear(), 0, 1); return Math.ceil((((this - d) / 86400000) + d.getDay() + 1) / 7); }, // Fixed now
		// Month
		F: function() { return Date.replaceChars.longMonths[this.getMonth()]; },
		m: function() { return (this.getMonth() < 9 ? '0' : '') + (this.getMonth() + 1); },
		M: function() { return Date.replaceChars.shortMonths[this.getMonth()]; },
		n: function() { return this.getMonth() + 1; },
		t: function() { var d = new Date(); return new Date(d.getFullYear(), d.getMonth(), 0).getDate() }, // Fixed now, gets #days of date
		// Year
		L: function() { var year = this.getFullYear(); return (year % 400 == 0 || (year % 100 != 0 && year % 4 == 0)); },	// Fixed now
		o: function() { var d  = new Date(this.valueOf());  d.setDate(d.getDate() - ((this.getDay() + 6) % 7) + 3); return d.getFullYear();}, //Fixed now
		Y: function() { return this.getFullYear(); },
		y: function() { return ('' + this.getFullYear()).substr(2); },
		// Time
		a: function() { return this.getHours() < 12 ? 'am' : 'pm'; },
		A: function() { return this.getHours() < 12 ? 'AM' : 'PM'; },
		B: function() { return Math.floor((((this.getUTCHours() + 1) % 24) + this.getUTCMinutes() / 60 + this.getUTCSeconds() / 3600) * 1000 / 24); }, // Fixed now
		g: function() { return this.getHours() % 12 || 12; },
		G: function() { return this.getHours(); },
		h: function() { return ((this.getHours() % 12 || 12) < 10 ? '0' : '') + (this.getHours() % 12 || 12); },
		H: function() { return (this.getHours() < 10 ? '0' : '') + this.getHours(); },
		i: function() { return (this.getMinutes() < 10 ? '0' : '') + this.getMinutes(); },
		s: function() { return (this.getSeconds() < 10 ? '0' : '') + this.getSeconds(); },
		u: function() { var m = this.getMilliseconds(); return (m < 10 ? '00' : (m < 100 ?
	'0' : '')) + m; },
		// Timezone
		e: function() { return "Not Yet Supported"; },
		I: function() { return "Not Yet Supported"; },
		O: function() { return (-this.getTimezoneOffset() < 0 ? '-' : '+') + (Math.abs(this.getTimezoneOffset() / 60) < 10 ? '0' : '') + (Math.abs(this.getTimezoneOffset() / 60)) + '00'; },
		P: function() { return (-this.getTimezoneOffset() < 0 ? '-' : '+') + (Math.abs(this.getTimezoneOffset() / 60) < 10 ? '0' : '') + (Math.abs(this.getTimezoneOffset() / 60)) + ':00'; }, // Fixed now
		T: function() { var m = this.getMonth(); this.setMonth(0); var result = this.toTimeString().replace(/^.+ \(?([^\)]+)\)?$/, '$1'); this.setMonth(m); return result;},
		Z: function() { return -this.getTimezoneOffset() * 60; },
		// Full Date/Time
		c: function() { return this.format("Y-m-d\\TH:i:sP"); }, // Fixed now
		r: function() { return this.toString(); },
		U: function() { return this.getTime() / 1000; }
	};
	
	function datediff(){
		var sDT = new Date(document.getElementById("departure_date").value);
		var eDT = new Date(document.getElementById("arrivalDate").value);
		var df  = sDT.dateDiff("d",eDT);
		document.getElementById("nights").value = df;
	}
	


	function addday(){
		if (document.getElementById("departure_date").value != "") {
			var sDT = new Date(document.getElementById("departure_date").value);
			var nights = document.getElementById("nights").value;
			var eDT = new Date(sDT);
			eDT.setDate(eDT.getDate()+(nights*1));
			//alert(eDT.format('Y/m/d'));
			document.getElementById("arrivalDate").value = eDT.format('Y/m/d');
		}
	}