JS写了一棵树，出现了问题，代码已经贴出，请大家看看有什么问题？

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

<html>

	<head>

		<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

		<title>emp</title>

		<script type="text/javascript" src="prototype-1.6.0.3.js">

    	</script>

		<script type="text/javascript">

			var xmlHttp;

			//获得对象

			function initRequest() {

				if(window.ActiveXObject) {

					xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");

				}else if(window.XMLHttpRequest) {

					xmlHttp = new XMLHttpRequest();

				}

			}

			//将查出的结果进行显示

			function listEmpAction() {

				initRequest();

				var url = "http://localhost/AjaxProject/findAllEmp.jsp";

				xmlHttp.open("GET", url, true);

				xmlHttp.onreadystatechange = listEmpCallback;

				xmlHttp.send(null);

			}

			//向查出的表中添加新员工

			function insertEmpAction(){

				initRequest();

				var id = document.getElementById("id").value;

				var name = document.getElementById("name").value;

				var salary = document.getElementById("salary").value;

				var url = "http://localhost/AjaxProject/insertEmp.jsp?id="+id+"&name="+name+"&salary="+salary;

				xmlHttp.open("GET", url, true);

				xmlHttp.onreadystatechange = insertEmpCallback;

				xmlHttp.send(null);

			}

			

			function listEmpCallback() {

				clearEmpList();

				if(xmlHttp.readyState == 4) {

					var empList = xmlHttp.responseXML;

					//appendEmp(response);

					var emps = empList.getElementsByTagName("emp");

					//alert(emps.length);

					for(var i=0; i<emps.length; i++) {

						var emp = emps.item(i);

						var id = emp.getElementsByTagName("id").item(0).firstChild.text;

						var name = emp.getElementsByTagName("name").item(0).firstChild.text;

						var salary = emp.getElementsByTagName("salary").item(0).firstChild.text;

						appendEmp(Emp(id, name, salary));

					}

				}

			}

			

			function insertEmpCallback() {

				listEmpAction();

				$("empForm");

			}

			

			 function Emp(id, name, salary){

                    return {

                        "id": id,

                        "name": name,

                        "salary": salary

                    };

                }

			

			function appendEmp(emp){

				//var info = document.getElementById("empForm");

				//info.innerHTML = response;

				  var tr = document.createElement("tr");

                    

                  var td1 = document.createElement("td");

                  var td2 = document.createElement("td");

                  var td3 = document.createElement("td");

                    

                  td1.appendChild(document.createTextNode(emp.id));

                  td2.appendChild(document.createTextNode(emp.name));

                  td3.appendChild(document.createTextNode(emp.salary));

					                    

                  tr.appendChild(td1);

                  tr.appendChild(td2);

                  tr.appendChild(td3);

                    

                  $("empList").appendChild(tr);

			}

			

			function clearEmpList() {

				var empList = $("empList").childNodes;

				for(var i=empList.length-1; i>=0; i--) {

					$("empList").removeChild(empList.item(i));

				}

			}

		</script>

	</head>

	<body>

		<table id="t1" border="1" width="80%">

			<thead>

				<tr>

					<td>

						ID

					</td>

					<td>

						Name

					</td>

					<td>

						Salary

					</td>

				</tr>

			</thead>

			<tbody id="empList">

			</tbody>

		</table>

		<input type="button" value="List" onclick="listEmpAction();" />

		

		<div id="empForm">

		<table id="t1" border="1" width="80%">

			<thead>

				<tr>

					<td>ID</td>

					<td><input type="text" id="id"/></td>

				</tr>

				<tr>

					<td>Name</td>

					<td><input type="text" id="name"/></td>

				</tr>

				<tr>

					<td>Salary</td>

					<td><input type="text" id="salary"/></td>

				</tr>

			</thead>

		</table>

		<input type="submit" value="Insert" onclick="insertEmpAction();" />

		</div>

	</body>

</html>