请教各位大侠一个封装htc,combobox事件问题。

[Spr_Perfei]

<public:component tagname="ComboBox">
	<public:defaults viewLinkContent="true" canHaveHTML="true"/>
	<public:property name="value" get="getValue" put="setValue"/>
	<public:attach event="oncontentready" onevent="f_CreateComboBox()" />
	<public:method name="add"/>
	<public:method name="removeAll"/>
</public:component>
<SCRIPT LANGUAGE="JScript">
var oPopup = null;
var ComboBox = null;
var ComboBoxIpt = null;
var DropDown = null;
var DropList = null;
var aNodes = new Array();
var cValue="";
var ScrollBar=null;
var flag=0;				
function getValue()
{
	return ComboBoxIpt.value;
}
function setValue(val)
{
	if(val!=null)
	{
		cValue=val;
	}
}
function add(text)
{
	aNodes.push(text);
}
function removeAll()
{
	ComboBoxIpt.value = "";
	while(true)
	{
		if(aNodes.pop()==undefined)
			return;
	}
}
function f_CreateComboBox()
{
	aNodes = f_CreateNodes(element.innerHTML);
	DropList = f_PublicCreateDropList();
	ScrollBar = f_PublicCreateScrollBar();
	f_PublicCreateDropListData(aNodes);
	ComboBox = f_PublicCreateComboBox();
	ComboBoxIpt = f_PublicCreateComboBoxIpt();
	DropDown = f_PublicCreateDropDown();
	oPopup = f_PublicCreatePopup();
	if(aNodes.length==2)									
	  ComboBoxIpt.value=aNodes[0]
	if(cValue=="")
		ComboBoxIpt.value="--------";
	DropDown.attachEvent("onmousedown",fnMousedown);
	ComboBoxIpt.attachEvent("onfocus",ComboBoxFocus);
	ComboBoxIpt.attachEvent("onpropertychange",ComboBoxChange);
	ComboBoxIpt.attachEvent("onblur",ComboBoxIptBlur);                
	ComboBoxIpt.attachEvent("onkeydown",ComboBoxIptCancel)		   //添加代码，取消键盘事件
	element.document.attachEvent("onclick", chkstat);
}
function f_PublicCreateComboBox()
{
	var oTable = element.document.createElement("TABLE");
	oTable.cellSpacing = 0;
	oTable.cellPadding = 0;
	oTable.id = "AXTeamComboBox"+uniqueID;
	oTable.style.display = "inline";
	oTable.border = 0;
	oTable.bgColor = "#FFFFFF";
	element.insertAdjacentElement("BeforeBegin",oTable);
	oTable.ComboBoxFocus = false;
	return oTable;
}
function f_PublicCreateComboBoxIpt()
{
	var oInput = element.document.createElement("INPUT");
	oInput.type = "text";
	oInput.name=element.name;
	oInput.style.cssText="border-right-style:none";
	oInput.style.width = element.width;
	oInput.id = "AXTeamComboBoxIpt"+uniqueID;
	oInput.value=cValue;
	ComboBox.insertRow().insertCell().appendChild(oInput);
	ComboBox.rows[0].bgColor = "#FFFFFF";
	//oInput.value="--------"
	return oInput;
}
function f_PublicCreateDropDown()
{
	var oTable = element.document.createElement("TABLE");
	oTable.cellSpacing = 0;
	oTable.cellPadding = 0;
	oTable.id = "AXTeamDropDown"+uniqueID;
	oTable.border = 0;
	oTable.bgColor="#DBD8D1";
	oTable.style.cssText = "display:inline;cursor:default;border:1px;border-style:solid;border-top-color:#404040;border-right-color:#D4D0C8;border-left-color:#D4D0C8;border-bottom-color:#D4D0C8";
	//oTable.attachEvent("onselectstart", fnCancel);
	var otd = oTable.insertRow().insertCell();
	var oButton = element.document.createElement("INPUT");
	oButton.type = "button";
	oButton.value = "6";
	oButton.id = "AXTeamDropDownButton"+uniqueID;
	oButton.attachEvent("onselectstart", fnCancel);
	oButton.style.cssText = "font-family: webdings;font-size:8px;text-align:center;width:16px;height:18px";
	otd.appendChild(oButton);
	ComboBox.rows[0].insertCell().appendChild(oTable);
	return oTable;
}
function f_PublicCreateDropList()
{
	var oTable = element.document.createElement("TABLE");
	oTable.cellSpacing = 1;
	oTable.cellPadding = 0;
	oTable.border = 0;
	oTable.bgColor="#FFFFFF";
	oTable.style.cssText = "font-size:9pt;cursor:default";
	oTable.attachEvent("onselectstart", fnCancel);
	return oTable;
}
function f_PublicCreateDropListData(aNodes,redata)
{
	try{
		if(!redata)
			var re=new RegExp("^");
		else
			var re=new RegExp(redata,"i");
		var otd = null;
		var No=DropList.rows.length;
		for(i=0;i<No;i++)DropList.deleteRow();	
		for(var i=0;i<aNodes.length;i++)
		{
			if(re.test(aNodes[i]))
			{
				otd = DropList.insertRow().insertCell();
				otd.style.height = "12px";
				otd.style.fontSize = "9pt";
				otd.innerHTML = aNodes[i];
				otd.attachEvent("onmouseover",DropListOver);
				otd.attachEvent("onmouseout",DropListOut);
				otd.attachEvent("onclick",DropListClick);
				otd.attachEvent("onmousedown",flag_set);				
			}
			
		}
	}
	catch(e)
	{
	}
}
function flag_set()
{
flag=1;
}
function f_PublicCreatePopup()
{
	var oSpan = element.document.createElement("span");
	oSpan.style.cssText = "position:absolute;display:none;cursor:default;z-index:100;border:1px solid #666666;";
	element.parentElement.appendChild(oSpan);
	return oSpan;
}
function f_PublicCreateScrollBar()
{
	var oDiv = element.document.createElement("div");
	oDiv.style.cssText = "overflow-x:hidden;overflow-y:auto";
	return oDiv;
}
function f_CreateNodes(htmlText)
{
	var oSpan = element.document.createElement("span");
	oSpan.innerHTML = htmlText;
	oSpan.style.cssText="font-size:9pt";
	var xNodes = oSpan.childNodes;
	var Nodes = new Array();
	var nNumNodes = (xNodes == null) ? 0 : xNodes.length;
	for (var nIndex = 0; nIndex < nNumNodes; nIndex++)
	{
		var node = xNodes[nIndex];
		if (node != null)
			Nodes = Nodes.concat(f_CreateDropListItems(node));
	}
	return Nodes;
}
function f_CreateDropListItems(oNode)
{
	var rNodes;
	var szTagName = (oNode.tagName == null) ? "" : oNode.tagName.toLowerCase();
	if(szTagName == "option")
	{
		var szText = oNode.innerText;
		rNodes = new Array(szText);
	}
	else
		rNodes = new Array();
	return rNodes;
}
function fnMousedown()
{
	
	if(event.srcElement != ComboBoxIpt)
	{
		if(oPopup.style.display == '')
		{
			oPopup.style.display = 'none';
			return;
		}
		f_PublicCreateDropListData(aNodes)
		ComboBoxIpt.select();
	}
	//oPopup.appendChild(DropList);
	ScrollBar.appendChild(DropList);
	oPopup.appendChild(ScrollBar);
	oPopup.style.width = ((oPopup.offsetWidth < ComboBox.offsetWidth) ? ComboBox.offsetWidth : oPopup.offsetWidth)-2;
	ScrollBar.style.width=oPopup.style.width;
	ScrollBar.style.height = (DropList.rows.length<=7) ? "100%" : 103;
	oPopup.style.left = getx(ComboBox);
	oPopup.style.top = gety(ComboBox)+22;
	oPopup.style.display = 'inline';
	ScrollBar.children[0].width = "100%";
	ComboBox.ComboBoxFocus = true;
}

function DropListOver()
{
	obj = event.srcElement;
	obj.bgColor='highlight';obj.style.color='#FFFFFF';obj.style.cursor='default';
}
function DropListOut()
{
	obj = event.srcElement;
	obj.bgColor='#FFFFFF';obj.style.color='#000000';
}
function DropListClick()
{
	obj = event.srcElement;
	ComboBoxIpt.value = obj.innerText;
	oPopup.style.display = "none";
	ComboBoxIpt.select();
	flag=0;										
	DropDown.style.color = '#000000';
}
function ComboBoxFocus()
{
	if(ComboBox.ComboBoxFocus) return;
	
	ComboBox.ComboBoxFocus = true;
}
function ComboBoxChange()
{
	f_PublicCreateDropListData(aNodes,ComboBoxIpt.value);
	fnMousedown();
	addOption();
}
///，用于当下拉列表为空时，取消键盘输入事件
function ComboBoxIptCancel()
{
  if((aNodes.length==0)||(aNodes[0].indexOf("--")>-1))
    return false;
  if((aNodes.length==1)&&(aNodes[0].indexOf("")>-1))
    return false;
}
//结束
function addOption(){
 if(event.keyCode==13)
 {
	 for(var i=0;i<aNodes.length;i++)
	 {
		node = aNodes[i];
		if(node == ComboBoxIpt.value)
			return;
	 }
	aNodes[aNodes.length] = ComboBoxIpt.value;
 }
}
添加ComboBoxIpt函数。作用ComboBox控件内容判断
function ComboBoxIptBlur()
{
	var str=ComboBoxIpt.value;
	if(flag)
	  return;
	
	if(str==""){ComboBoxIpt.value="--------"
	   return;
	}
	if(str=="--------") return;
	if(aNodes.length==0){
	   if(str!="")  ComboBoxIpt.value="--------";
	   return;
	}	
	if(aNodes[0].indexOf("--")>-1){
	   if(str!="")  ComboBoxIpt.value="--------";
	   return;
	}	
	
	for(var i=0;i<aNodes.length;i++)
	{
		node=aNodes[i];	
		var j=node.indexOf(str)		
		if(node==str)
			return;
		else if(j>-1)
		{	 
			alert("请选择下拉列表中选择存在的项目！");
			ComboBoxIpt.value=str;
			return;
		}
	}
	alert("请选择下拉列表中选择存在的项目！");
	ComboBoxIpt.value="";
	ComboBoxIpt.focus()
	return;			
}
function chkstat()
{
	var oEl = event.srcElement;
	while( null != oEl && oEl != ComboBox)
	{
		oEl = oEl.parentElement;
	}
	if(oEl == null)
	{
		ComboBox.ComboBoxFocus = false;		
		oPopup.style.display = "none";
	}
}
function fnCancel()
{
	return false;
}
function getx(e)
{
	var l=e.offsetLeft;
	while(e=e.offsetParent){
		l+=e.offsetLeft;
	}
	return l;
}
function gety(e)
{
	var t=e.offsetTop;
	while(e=e.offsetParent){
		t+=e.offsetTop;
	}
	return t;
}
</SCRIPT>

这是个封装的 combobox，但是好像没有 Change事件，怎么加个Change事件，然后我asp里，再怎么调Change。
谢谢了。
我不太懂，请各位大侠详细点。