Javascript calendar

A javascript calendar.

<html>
<body>

	<style type="text/css">
		span.label {color:black;width:30;height:16;text-align:center;margin-top:0;background:#ffF;font:bold 13px Arial}
		span.c1 {cursor:hand;color:black;width:30;height:16;text-align:center;margin-top:0;background:#ffF;font:bold 13px Arial}
		span.c2 {cursor:hand;color:red;width:30;height:16;text-align:center;margin-top:0;background:#ffF;font:bold 13px Arial}
		span.c3 {cursor:hand;color:#b0b0b0;width:30;height:16;text-align:center;margin-top:0;background:#ffF;font:bold 12px Arial}
	</style>

	<script type="text/javascript">
		function maxDays(mm, yyyy){
			var mDay;
			if((mm == 3) || (mm == 5) || (mm == 8) || (mm == 10)){
				mDay = 30;
			}
			else{
				mDay = 31
				if(mm == 1){
					if (yyyy/4 - parseInt(yyyy/4) != 0){
						mDay = 28
					}
					else{
						mDay = 29
					}
				}
			}
			return mDay;
		}
		function changeBg(id){
			if (eval(id).style.backgroundColor != "yellow"){
				eval(id).style.backgroundColor = "yellow"
			}
			else{
				eval(id).style.backgroundColor = "#ffffff"
			}
		}
		function writeCalendar(){
			var now = new Date
			var dd = now.getDate()
			var mm = now.getMonth()
			var dow = now.getDay()
			var yyyy = now.getFullYear()
			var arrM = new Array("January","February","March","April","May","June","July","August","September","October","November","December")
			var arrY = new Array()
			for (ii=0;ii<=4;ii++){
				arrY[ii] = yyyy - 2 + ii
			}
			var arrD = new Array("Sun","Mon","Tue","Wed","Thu","Fri","Sat")

			var text = ""
			text = "<form name=calForm>"
			text += "<table border=1>"
			text += "<tr><td>"
			text += "<table width=100%><tr>"
			text += "<td align=left>"
			text += "<select name=selMonth onChange='changeCal()'>"
			for (ii=0;ii<=11;ii++){
				if (ii==mm){
					text += "<option value= " + ii + " Selected>" + arrM[ii] + "</option>"
				}
				else{
					text += "<option value= " + ii + ">" + arrM[ii] + "</option>"
				}
			}
			text += "</select>"
			text += "</td>"
			text += "<td align=right>"
			text += "<select name=selYear onChange='changeCal()'>"
			for (ii=0;ii<=4;ii++){
				if (ii==2){
					text += "<option value= " + arrY[ii] + " Selected>" + arrY[ii] + "</option>"
				}
				else{
					text += "<option value= " + arrY[ii] + ">" + arrY[ii] + "</option>"
				}
			}
			text += "</select>"
			text += "</td>"
			text += "</tr></table>"
			text += "</td></tr>"
			text += "<tr><td>"
			text += "<table border=1>"
			text += "<tr>"
			for (ii=0;ii<=6;ii++){
				text += "<td align=center><span class=label>" + arrD[ii] + "</span></td>"
			}
			text += "</tr>"
			aa = 0
			for (kk=0;kk<=5;kk++){
				text += "<tr>"
				for (ii=0;ii<=6;ii++){
					text += "<td align=center><span id=sp" + aa + " onClick='changeBg(this.id)'>1</span></td>"
					aa += 1
				}
				text += "</tr>"
			}
			text += "</table>"
			text += "</td></tr>"
			text += "</table>"
			text += "</form>"
			document.write(text)
			changeCal()
		}
		function changeCal(){
			var now = new Date
			var dd = now.getDate()
			var mm = now.getMonth()
			var dow = now.getDay()
			var yyyy = now.getFullYear()
			var currM = parseInt(document.calForm.selMonth.value)
			var prevM
			if (currM!=0){
				prevM = currM - 1
			}
			else{
				prevM = 11
			}
			var currY = parseInt(document.calForm.selYear.value)
			var mmyyyy = new Date()
			mmyyyy.setFullYear(currY)
			mmyyyy.setMonth(currM)
			mmyyyy.setDate(1)
			var day1 = mmyyyy.getDay()
			if (day1 == 0){
				day1 = 7
			}
			var arrN = new Array(41)
			var aa
			for (ii=0;ii<day1;ii++){
				arrN[ii] = maxDays((prevM),currY) - day1 + ii + 1
			}
			aa = 1
			for (ii=day1;ii<=day1+maxDays(currM,currY)-1;ii++){
				arrN[ii] = aa
				aa += 1
			}
			aa = 1
			for (ii=day1+maxDays(currM,currY);ii<=41;ii++){
				arrN[ii] = aa
				aa += 1
			}
			for (ii=0;ii<=41;ii++){
				eval("sp"+ii).style.backgroundColor = "#FFFFFF"
			}
			var dCount = 0
			for (ii=0;ii<=41;ii++){
				if (((ii<7)&&(arrN[ii]>20))||((ii>27)&&(arrN[ii]<20))){
					eval("sp"+ii).innerHTML = arrN[ii]
					eval("sp"+ii).className = "c3"
				}
				else{
					eval("sp"+ii).innerHTML = arrN[ii]
					if ((dCount==0)||(dCount==6)){
						eval("sp"+ii).className = "c2"
					}
					else{
						eval("sp"+ii).className = "c1"
					}
					if ((arrN[ii]==dd)&&(mm==currM)&&(yyyy==currY)){
						eval("sp"+ii).style.backgroundColor="#90EE90"
					}
				}
				dCount += 1
				if (dCount>6){
					dCount=0
				}
			}
		}
	</script>

	<script type="text/javascript">writeCalendar()</script>


</body>
</html>

References

html javascript