سوال مفهومی از ajax در این کد

کد پی‌اچ‌پی:
[color=#800000]<script type=[color=#0000FF]"text/javascript"[/color] language=[color=#0000FF]"javascript"[/color]>[/color]
var pageurl="del.php?code=";
var xmlhttp;
var nid=0;
function answer()
{
if(xmlhttp.readyState == 4)
{
var result=xmlhttp.responseText;
del(nid);
}
}
function sendfordel(id)
{
var strcode;
createXMLHttpRequest();
strcode = id;
nid=id;
xmlhttp.open("GET", pageurl + strcode, true);
xmlhttp.onreadystatechange=answer;
xmlhttp.send(null);
}
function createXMLHttpRequest()
{
if (window.ActiveXObject)
{
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
else if (window.XMLHttpRequest)
{
xmlhttp = new XMLHttpRequest();
}
}
function del(nid)
{
var tab=document.getElementById("tbl");
var tr=document.getElementById("tr"+nid);
tab.deleteRow(tr.rowIndex);
}
[color=#800000]</script>[/color]
[color=#000080]</head>[/color]
[color=#000080]<body>[/color]
[color=#008080]<table width=[color=#0000FF]"500"[/color] id=[color=#0000FF]"tbl"[/color] border=[color=#0000FF]"0"[/color] cellspacing=[color=#0000FF]"0"[/color] cellpadding=[color=#0000FF]"5"[/color]>[/color]
[color=#008080]<tr>[/color]
[color=#008080]<td width=[color=#0000FF]"99"[/color] bgcolor=[color=#0000FF]"#00CC66"[/color]>[/color]ID[color=#008080]</td>[/color]
[color=#008080]<td width=[color=#0000FF]"112"[/color] bgcolor=[color=#0000FF]"#00CC66"[/color]>[/color]Name[color=#008080]</td>[/color]
[color=#008080]<td width=[color=#0000FF]"171"[/color] bgcolor=[color=#0000FF]"#00CC66"[/color]>[/color]Phone Number[color=#008080]</td>[/color]
[color=#008080]<td width=[color=#0000FF]"78"[/color] bgcolor=[color=#0000FF]"#00CC66"[/color]>[/color]Operation[color=#008080]</td>[/color]
[color=#008080]</tr>[/color]
[color=#000080]<?php
$s=mysql_connect("127.0.0.1","root","");
if(!$s)
echo "error in connect to mysql server";
$db=mysql_select_db("tellbook");
$result=mysql_query("select * from tbl");
$row="";
while($row=mysql_fetch_assoc($result))
{?>[/color]
[color=#000080]<?php $id=$row["id"]; ?>[/color]
[color=#008080]<tr id=[color=#0000FF]"tr<?php print($id);?>"[/color]>[/color]
[color=#008080]<td>[/color][color=#000080]<?php print($row["id"]); ?>[/color][color=#008080]</td>[/color]
[color=#008080]<td>[/color][color=#000080]<?php print($row["name"]); ?>[/color][color=#008080]</td>[/color]
[color=#008080]<td>[/color][color=#000080]<?php print($row["telephone"]); ?>[/color][color=#008080]</td>[/color]
[color=#008080]<td>[/color][color=#FF8000]<input type=[color=#0000FF]"button"[/color] value=[color=#0000FF]" delete "[/color] name=[color=#0000FF]"clk"[/color] onclick=[color=#0000FF]"sendfordel(<?php print($id);?>;);"[/color]/>[/color][color=#008080]</td>[/color]
[color=#008080]</tr>[/color]
[color=#000080]<?php
}
mysql_close($s);
?>[/color]
[color=#008080]</table>[/color]
[color=#000080]</body>[/color]