关于JAVACRIPT的小问题

<body id="body1">
<script language="javascript" type="text/javascript">
<!--
       var ele_table= document.createElement("table");
    var ele_tbody=document.createElement("tbody");
    var ele_tr1= document.createElement("tr");
    var ele_td1= document.createElement("td");
    var ele_td2= document.createElement("td");
    var ele_tr2= document.createElement("tr");
    var ele_td3= document.createElement("td");
    var ele_td4= document.createElement("td");
    var ele_tr3= document.createElement("tr");
    var ele_td5= document.createElement("td");
    var text_td1= document.createTextNode("第一个单元格");
    var text_td2= document.createTextNode("第二个单元格");
    var text_td3= document.createTextNode("第三个单元格");
    var text_td4= document.createTextNode("第四个单元格");
    var text_td5= document.createTextNode("第五个单元格");
    //添加节点到页面中
    ele_td1.appendChild(text_td1);
    ele_td2.appendChild(text_td2);
    ele_td3.appendChild(text_td3);
    ele_td4.appendChild(text_td4);
    ele_td5.appendChild(text_td5);
    ele_tr1.appendChild(ele_td2);
    ele_tr1.insertBefore(ele_td1,ele_td2);
    ele_tr2.appendChild(ele_td4);
    ele_tr2.insertBefore(ele_td3,ele_td4);
    ele_tr3.appendChild(ele_td5);
    ele_tbody.appendChild(ele_tr3);
       ele_tbody.insertBefore(ele_tr2,ele_tr3);
    ele_tbody.insertBefore(ele_tr1,ele_tr2);
    //ele_tbody.removeChild(ele-tr1);
    ele_table.appendChild(ele_tbody);
    var ele_body=document.getElementById("body1");
    ele_body.appendChild(ele_table);