Pure Javascript Calendar

--Calendar.js
var _panelID="CalendarPanel";
var _currentYear=0;
var _currentMonth=-1;
function OpenCalendar(defYear, defMonth, defDay) {
	var now=new Date();
	if ((typeof defYear == "undefined")||(isNaN(defYear)))
		defYear = now.getFullYear();
	if ((typeof defMonth == "undefined")||(isNaN(defMonth)))
		defMonth = now.getMonth();
	else
		defMonth--;
	if ((typeof defDay == "undefined")||(isNaN(defDay)))
		defDay = now.getDate();
	FillCalendar(defYear, defMonth+1, defDay);
	
	var objPanel = document.getElementById(_panelID);
	objPanel.style.display = "block";
	var panelWidth = GetElementWidth(objPanel);
	var panelHeight = GetElementHeight(objPanel);
	var bodyWidth = document.body.clientWidth;
	var bodyHeight = document.body.clientHeight;
	var panelLeft = parseInt((bodyWidth/2)-(panelWidth/2));
	var panelTop = parseInt((bodyHeight/2)-(panelHeight/2));
	objPanel.style.left = panelLeft+"px";
	objPanel.style.top = panelTop+"px";
}

function FillCalendar(year, month, day) {
	//var date=new Date();
	//date.setFullYear(year+1, month, day);
	//alert(date);
	
	_currentYear = year;
	_currentMonth = month-1;
	
	var daysCount=DaysInMonth(year, month);
	var objPanel = document.getElementById(_panelID);
	if (!objPanel) {
		objPanel = document.createElement("div");
		objPanel.id = _panelID;
		objPanel.style.position = "absolute";
		objPanel.style.display = "none";
		objPanel.style.border = _calenderBorderSize+"px solid "+_calenderBorderColor;
		objPanel.style.backgroundColor = _calendarBackground;
		objPanel.onclick = new Function("HideCalendar()");
		document.body.appendChild(objPanel);
	}
	
	while (objPanel.childNodes.length > 0)
		objPanel.removeChild(objPanel.childNodes[0]);

	BuildCalendarDetails(objPanel, _currentMonth, _currentYear);
	
	var cellWidth=50;
	var cellHeight=50;
	var currentDay=1;
	var objTable=document.createElement("table");
	objTable.setAttribute("border", "0");
	objTable.setAttribute("cellpadding", "0");
	objTable.setAttribute("cellspacing", "0");
	var objRow=0;
	while (currentDay <= daysCount) {
		if (((currentDay-1)%7) == 0) {
			objRow=objTable.insertRow(objTable.rows.length);
		}
		for (var i=1; i<=7; i++) {
			if (currentDay > daysCount)
				break;
			var objCell=objRow.insertCell(objRow.cells.length);
			objCell.setAttribute("width", cellWidth+"");
			objCell.setAttribute("height", cellHeight+"");
			objCell.style.border = "1px solid black";
			objCell.style.textAlign = "center";
			objCell.style.backgroundColor = _calenderCellColor;
			objCell.style.fontFamily = _calenderCellFontName;
			objCell.style.fontSize = _calenderCellFontSize;
			objCell.style.cursor = "pointer";
			objCell.onmouseover = new Function("PutMoreLight(this)");
			objCell.onmouseout = new Function("RestoreColor(this)");
			objCell.onclick = new Function("CalenderCellClick(this);");
			objCell.innerHTML = currentDay+"";
			currentDay++;
		}
	}
	objPanel.appendChild(objTable);
	//window.resizeTo(objTable.clientWidth, objPanel.offsetHeight);
}

function BuildCalendarDetails(objContainer, month, year) {
	var btnPreviousMonth=BuildCalendarButton((_rightToLeft  )?">>":"<<");
	btnPreviousMonth.onclick = PreviousMonthClick;
	
	var btnNextMonth=BuildCalendarButton((_rightToLeft)?"<<":">>");
	btnNextMonth.onclick = NextMonthClick;
	
	var objMonthSpan=BuildCalendarSpan(_monthNames[month]);
	var objYearSpan=BuildCalendarSpan(year+"");
	
	var objSpan=document.createElement("div");
	objSpan.id = _panelID+"_details";
	objSpan.style.textAlign = "center";
	objSpan.appendChild(BuildCalendarSpan("&nbsp;"));
	if (_rightToLeft) {
		objSpan.appendChild(btnNextMonth);
		objSpan.appendChild(BuildCalendarSpan("&nbsp;"));
		objSpan.appendChild(objMonthSpan);
		objSpan.appendChild(BuildCalendarSpan("&nbsp;&nbsp;&nbsp;"));
		objSpan.appendChild(objYearSpan);
		objSpan.appendChild(BuildCalendarSpan("&nbsp;"));
		objSpan.appendChild(btnPreviousMonth);
	}
	else {
		objSpan.appendChild(btnPreviousMonth);
		objSpan.appendChild(BuildCalendarSpan("&nbsp;"));
		objSpan.appendChild(objYearSpan);
		objSpan.appendChild(BuildCalendarSpan("&nbsp;&nbsp;&nbsp;"));
		objSpan.appendChild(objMonthSpan);
		objSpan.appendChild(BuildCalendarSpan("&nbsp;"));
		objSpan.appendChild(btnNextMonth);
	}
	objSpan.appendChild(BuildCalendarSpan("&nbsp;"));
	//objSpan.appendChild(BuildCalendarSpan("<br />"));
	objContainer.appendChild(objSpan);
}

function BuildCalendarButton(strText) {
	var result=document.createElement("button");
	result.setAttribute("type", "button");
	result.style.fontSize = "18px";
	result.innerHTML = strText;
	return result;
}

function BuildCalendarSpan(strText) {
	var result=document.createElement("span");
	result.style.fontFamily = _calenderTextFontName;
	result.style.fontSize = _calenderTextFontSize;
	result.style.color = _calenderTextColor;
	result.innerHTML = strText;
	return result;
}

function CalenderCellClick(objCell) {
	//hide:
	HideCalendar();
	
	//set date:
	var date=new Date();
	date.setFullYear(_currentYear, _currentMonth, parseInt(objCell.innerHTML));
	
	//activate callback function:
	eval(_calendarCallbackFunction+"('"+date+"')");
}

function HideCalendar() {
	var objPanel = document.getElementById(_panelID);
	objPanel.style.display = "none";
}

function PreviousMonthClick() {
	_currentMonth--;
	if (_currentMonth < 0) {
		_currentMonth = 11;
		_currentYear--;
	}
	FillCalendar(_currentYear, _currentMonth+1, 1);
}

function NextMonthClick() {
	_currentMonth++;
	if (_currentMonth > 11) {
		_currentMonth = 0;
		_currentYear++;
	}
	FillCalendar(_currentYear, _currentMonth+1, 1);
}

function DaysInMonth(year, month) {
	var date=new Date();
	var result=0;
	date.setFullYear(year, month-1, 1);
	while ((date.getFullYear() <= year)&&(date.getMonth() <= (month-1))) {
		result++;
		if (result > 31) {
			alert("error getting days in month!\nyear: "+year+", month: "+month);
			return 0;
		}
		date.setFullYear(year, month-1, date.getDate()+1);
	}
	return result;
}

function GetElementWidth(element) {
	return element.clientWidth;
}

function GetElementHeight(element) {
	return element.clientHeight;
}

var arrColoredControls=new Array();
function PutMoreLight(objControl, color, lightAmount) {
	var cancelAddLight=objControl.getAttribute("cancel_add_light");
	if (cancelAddLight == "1")
		return true;
	
	if (typeof color == "undefined")
		color = _calenderCellColor;
	
	if (typeof lightAmount == "undefined")
		lightAmount = _calendarAddLight;
	
	arrColoredControls[objControl] = color;
	
	var R=HexToInt(color.substring(1, 3));
	var G=HexToInt(color.substring(3, 5));
	var B=HexToInt(color.substring(5, 7));
	
	R = SafeAdd(R, lightAmount, 0, 255);
	G = SafeAdd(G, lightAmount, 0, 255);
	B = SafeAdd(B, lightAmount, 0, 255);
	
	var lightedColor=BuildColor(R, G, B);
	objControl.style.backgroundColor = lightedColor;
}

function RestoreColor(objControl) {
	var cancelAddLight=objControl.getAttribute("cancel_add_light");
	if (cancelAddLight == "1")
		return true;
	objControl.style.backgroundColor = arrColoredControls[objControl];
}

function IntToHex(num) {
	if (num < 10)
		return (num+"");
	
	switch (num) {
		case 10: return "a";
		case 11: return "b";
		case 12: return "c";
		case 13: return "d";
		case 14: return "e";
		case 15: return "f";
	}
	
	return IntToHex(parseInt(num/16))+IntToHex(parseInt(num%16));
}

function HexToInt(strHex) {
	return parseInt(strHex, 16);
}

function SafeAdd(num, addition, min, max) {
	num += addition;
	if (num > max)
		num = max;
	if (num < min)
		num = min;
	return num;
}

function BuildColor(r, g, b) {
	var R=IntToHex(r);
	var G=IntToHex(g);
	var B=IntToHex(b);
	R=(R.length == 1)?("0"+R):R;
	G=(G.length == 1)?("0"+G):G;
	B=(B.length == 1)?("0"+B):B;
	return "#"+R+G+B;
}

--CalendarTest.html
<html>
<head>
<meta http-equiv="Content-Type" context="text/html; charset=windows-1255" />
<title>Calendar Test</title>
<script type="text/javascript">
//var _monthNames=new Array("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December");
var _monthNames=new Array("ינואר", "פברואר", "מרץ", "אפריל", "מאי", "יוני", "יולי", "אוגוסט", "ספטמבר", "אוקטובר", "נובמבר", "דצמבר");
var _rightToLeft=true;
var _calendarBackground="#B5C3C3";
var _calenderBorderSize=3;
var _calenderBorderColor="blue";
var _calenderCellColor="#F6B853";
var _calenderCellFontName="Tahoma";
var _calenderCellFontSize="21px";
var _calenderTextFontName="Tahoma";
var _calenderTextFontSize="22px";
var _calenderTextColor="white";
var _calendarAddLight=30;
var _calendarCallbackFunction="CalendarCallback";
</script>
<script type="text/javascript" src="Calendar.js"></script>
<script type="text/javascript">
function BrowseDate() {
	var strDate = document.forms[0].elements["Date"].value;
	var arrParts=strDate.split("/");
	OpenCalendar(parseInt(arrParts[2]), parseInt(arrParts[1]), parseInt(arrParts[0]));
}

function CalendarCallback(strSelectedDate) {
	var date=new Date(strSelectedDate);
	document.forms[0].elements["Date"].value = date.getDate()+"/"+(date.getMonth()+1)+"/"+date.getFullYear();
}
</script>
</head>
<body>
Hello World!
<form>
Date: <input type="text" name="Date" /><button type="button" onclick="BrowseDate();">...</button>
</form>
</body>
</html>

//var _monthNames=new Array("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December");
var _monthNames=new Array("ינואר", "פברואר", "מרץ", "אפריל", "מאי", "יוני", "יולי", "אוגוסט", "ספטמבר", "אוקטובר", "נובמבר", "דצמבר");

var _monthNames=new Array("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December");
//var _monthNames=new Array("ינואר", "פברואר", "מרץ", "אפריל", "מאי", "יוני", "יולי", "אוגוסט", "ספטמבר", "אוקטובר", "נובמבר", "דצמבר");