DropDownList三级联动

<script type="text/javascript">
			window.onload = function()
			{
			    branchOne = document.getElementById("<%=ddlBranchOne.ClientID %>");
			    branchTwo = document.getElementById("<%=ddlBranchTwo.ClientID %>");
			    branchThree = document.getElementById("<%=ddlBranchThree.ClientID %>");
			    //加载一级机构信息
				loadBranchOne();
			}
			var loadBranchOne = function()
			{
			    //请求URL
			    reqUrl = "/TheOneHRWeb/handler/GetBranchOne.aspx?ocaID=" + new Date().getTime();
			    //回调函数
			    var fnCallBack = function(oResult)
			    {
			        //将Json格式的字符串转换为JS对象
			        var result = eval(oResult);
			        //读取数据
			        exportDropDownList(branchOne, result);
			        branchOne.onchange = function()
			        {
			            if(branchOne.value != "-1")
			            {
			                //加载二级机构信息
			                loadBranchTwo(branchOne.value);
			            }
			            //选中项为"请选择"
			            else
			            {
			                //清空二级机构下拉菜单
			                clearDropDownList(branchTwo);
			                //添加一项"请选择"
			               branchTwo.options.add(new Option("请选择", "-1"));
			              //清空三级机构下拉菜单
			              clearDropDownList(branchThree); 
			              branchThree.options.add(new Option("请选择", "-1"));
			            }     
			        }
			    }
			    oHttp.Get(reqUrl, fnCallBack, null);
			}
			
			var loadBranchTwo = function(branchId)
			{
			    //请求的URL
			    var reqUrl = "/TheOneHRWeb/handler/GetBranchTwo.aspx?ocaID=" + new Date().getTime() +"&branchID="+branchId;
			    //回调函数
			    var fnCallBack = function(oRequest)
			    {
			        //将Json格式的字符串转换为JS对象
			        var result = eval(oRequest);
			        exportDropDownList(branchTwo, result);
			        branchTwo.onchange = function()
			        {
			            if(branchTwo.value != "-1")
			            {
			                loadBranchThree(branchTwo.value);
			            }
			            else
			            {
			               //清空三级机构下拉菜单
			              clearDropDownList(branchThree); 
			              branchThree.options.add(new Option("请选择", "-1"));
			            }
			        }
			    }
			    //alert(reqUrl);
			    oHttp.Get(reqUrl, fnCallBack, null);
			}
			
			var loadBranchThree = function(branchId)
			{
			    //请求的URL
			    var reqUrl = "/TheOneHRWeb/handler/GetBranchThird.aspx?ocaID=" + new Date().getTime() +"&branchID=" + branchId;
			    //回调函数
			    var fnCallBack = function(oResult)
			    {
			        var result = eval(oResult);
			        exportDropDownList(branchThree, result);
			    }
			    oHttp.Get(reqUrl, fnCallBack, null);
			}
			
			//导入下拉菜单数据
			function exportDropDownList(ddl, oResult)
			{
			    //清空select
			    clearDropDownList(ddl);
			    //创建一个option对象
			    var oOption = document.createElement("option");
			    //创建一项"请选择"
		        var oSelect = document.createTextNode("请选择");
		        //给select添加value值
		        oOption.setAttribute("value", "-1");
			    oOption.appendChild(oSelect);
			    ddl.appendChild(oOption);
			    //遍历Json数据,添加每项
			    for(var i = 0; i < oResult.length; i++)
			    {
			        //文本
			        var brName = oResult[i].branchName;
			        //值
			        var brID = oResult[i].branchID;
			        var brOption = document.createElement("option");
			        brOption.setAttribute("value", brID);
			        brOption.appendChild(document.createTextNode(brName));
			        ddl.appendChild(brOption);
			    }
			}
			
			//清空下拉菜单(select)
			function clearDropDownList(ddl)
			{
			    for(var i = ddl.options.length - 1; i>=0; i--)
			    {
			        ddl.remove(i);
			    }
			}
</script>