table对象 的 appendChild()的问题

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<link  rel="stylesheet" href="createTab.css"  />
<script type="text/javascript">
function sortTab(){
var tabNode=document.getElementsByTagName("table")[0];
var rows=tabNode.rows;
var arr=new Array();
for(var s=1;s<=rows.length-1;s++){
arr[s-1]=rows[s]; }for(var x=0;x<arr.length;x++){   }
for(var x=0;x<arr.length;x++){
  for(var y=x+1;y<arr.length;y++){
if(arr[x].cells[1].innerText>=arr[y].cells[1].innerText)
{
var temp=arr[x];
arr[x]=arr[y];
arr[y]=temp;
}
  }   
}
   
for(var x=2;x>=1;x--){    // 这里的x赋2，3，4，5，都行，为什么会这样的，所以觉得appendChild()很奇怪？
  tabNode.deleteRow(x); 
    
}
alert(tabNode.rows.length)
for(var y=0;y<arr.length;y++){
      tabNode.appendChild(arr[y]);
}
    alert(tabNode.rows.length)
}
</script>
</head><body>
<table>
       <tr>
           <th>姓名</th>
           <th onclick="sortTab()"><a href="javascript:void(0)">年龄</a></th>
           <th>性别</th>
       </tr>
       <tr>
           <td>ads</td>
           <td>22</td>
           <td>fdgd</td>
       </tr>
       <tr>
           <td>sdf</td>
           <td>23</td>
           <td>fgdx</td>
       </tr>
       <tr>
           <td>dsf</td>
           <td>13</td>
           <td>sdfd</td>
       </tr>
       <tr>
           <td>dsfg</td>
           <td>11</td>
           <td>sfds</td>
       </tr>
       <tr>
           <td>gdg</td>
           <td>34</td>
           <td>dsf</td>
       </tr>
       <tr>
           <td>erf</td>
           <td>45</td>
           <td>fsf</td>
       </tr>
</table>
</body>
</html>