PHP与ajax遇到的问题，第一次接触ajax

大家看下我哪里写的有问题了老报如下错误：
“完成该操作所需要的数据还不可使用”
以下是js程序代码var xmlHttp;
function S_xmlhttprequest(){
if(window.ActiveXObject){
xmlHttp=new ActiveXObject('Microsoft.XMLHTTP');
}else if(window.XMLHttpRequest){
xmlHttp=new XMLHttpRequest();
}
}function funphp100(url){
S_xmlhttprequest();
xmlHttp.open("GET","for.php?id="+url,true); //传值
xmlHttp.onreadystatechange= byphp; //调用byphp这个方法
xmlHttp.send(null);
}function byphp(){
var byphp100 = xmlHttp.responseText;
document.getElementById('php100').innerHTML = byphp100;

}以下是PHP程序代码：index.php<script type="text/javascript" src="ajax.js"></script>
<a href="#" onclick="funphp100('q')">q</a>
<a href="#" onclick="funphp100('t')">t</a>
<a href="#" onclick="funphp100('x')">x</a><div id="php100"></div>以下是循环显示页面：for.php<?php
if ($o= $_GET['id']) {
for ($i=1;$i<=10;$i++){
echo $o;
}
}
?>

解决方案 »

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实例代码
<?
  session_start();
  $myCxmis = new Cxmis;
  if($mysubmit =="确定"){
    $result = $myCxmis->register($username,$password);
    if($result==2){
$uid=$username;
session_register('uid'); ?>
<script language="javascript">
alert("注册成功");
window.location='ywsljj.php';
</script>
<?
    }else if($result==1){
?>
<script language="javascript">
alert("此用户名已经存在，请重新注册");
window.location='javascript:history.back(-1)';
</script>
<?
    }else{
?>
<script language="javascript">
alert("注册失败，请重新注册");
window.location='javascript:history.back(-1)';
</script>
<?
  }}else {
?>
<html> <head>
<meta http-equiv="Content-Language" content="zh-cn">
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title> </title>
</head>
<script language="Javascript" src="/script/checkpassword.js"> </script>
<script language="Javascript" src="/script/ajaxreg.js"> </script>
<body topmargin="0" leftmargin="0" rightmargin="0" bottommargin="0"> <div align="left">
<table border="0" width="100%" cellspacing="0" cellpadding="0" id="table1"> <?
require("./include/top.inc");
?> <tr>
<td align="left" valign="top">
<table border="0" width="100%" id="table3" cellspacing="0" cellpadding="0">
<tr>
<td align="left" valign="top" width="235">
<table border="0" width="100%" id="table19" cellspacing="0" cellpadding="0">
<tr>
<td align="left" valign="top"> </td>
</tr>
<tr>
<td>
<img border="0" src="images/zjcx_ml_11_01.gif" width="235" height="166"> </td>
</tr>
</table>
</td>
<td align="left" valign="top">
<table border="0" width="100%" id="table14" cellspacing="0" cellpadding="0">
<tr>
<td width="22">
<img border="0" src="images/zjcx_07_01.gif" width="22" height="16"> </td>
<td background="images/zjcx_07_02.gif">
<img border="0" src="images/zjcx_07_02.gif" width="745" height="16"> </td>
</tr>
<tr>
<td background="images/zjcx_07_03.gif" height="380" width="22">
<img border="0" src="images/zjcx_07_03.gif" width="22" height="50"> </td>
<td align="left" valign="top">
<table border="0" width="100%" id="table15" cellspacing="0" cellpadding="0">
<tr>
<td>
<p align="center">帐 号 注 册
 </td>
</tr>
<tr>
<td>
<table border="0" width="100%" id="table16" cellspacing="0" cellpadding="0">
<tr>
<td width="363">
<img border="0" src="images/zjcx_07_08_01.gif" width="363" height="17"> </td>
<td background="images/zjcx_07_08_02.gif">
<img border="0" src="images/zjcx_07_08_02.gif" width="9" height="17"> </td>
<td width="373">
<img border="0" src="images/zjcx_07_08_03.gif" width="373" height="17"> </td>
</tr>
</table>
</td>
</tr>
<tr>
<td align="center">
<table border="0" width="98%" id="table18" cellspacing="0" cellpadding="0">
<tr>
<td>
<form name=reg method=post action="/register.php" onsubmit="return checkpwd(this)">
<table  border="0" cellspacing="1" cellpadding="5" bgcolor="#9ad0eb">
<table  border="0" cellspacing="1" cellpadding="5" bgcolor="#9ad0eb" width="100%">
<tr bgcolor="#e4f2fa"> <td colspan=3>帐号注册 </td> </tr>
( * 为必填项)
<tr bgcolor="#e4f2fa">
                      <td >
                        <div align="center">用户名 <font color="#FF0000">* </font> </div>
                      </td>
                      <td >
                        <input type="text" name="username" id="username" size="25" maxlength="15" onBlur="return usercheck('check')">

                      </td>
<td align="left" bgcolor="#FFFFFF">  <span id="check"> 3-16个字符，英文小写、汉字、数字、最好不要全部是数字。 </span> </td>                     </tr>
<tr bgcolor="#e4f2fa">
                      <td >
                        <div align="center">密码 <font color="#FF0000">* </font> </div>
                      </td>
                      <td >
                        <input type="password" name="password" id="userpwd" onBlur="pwdcheck('pwd')">

                      </td>
<td align="left" bgcolor="#FFFFFF" id="pwd"> 密码字母有大小写之分。6-16位（包括6、16），限用英文、数字。 </td>                     </tr>
                    <tr bgcolor="#e4f2fa">
                      <td >
                        <div align="center">确认密码 <font color="#FF0000">* </font> </div>
                      </td>
                      <td >
                        <input type="password" name="checkpassword" id="reuserpwd" onBlur="pwdrecheck('repwd')">
                      </td>
<td align="left" bgcolor="#FFFFFF" id="repwd"> 请再次输入登录密码。 </td>
                    </tr>
<tr bgcolor="#e4f2fa"> <td colspan=3 align="center">
<input type="submit" name=mysubmit value="确定">
<input type=reset value="重填">
</td> </tr>
</table>
</form>  </td>
</tr>
</table>
</td>
</tr>
<tr>
<td>
<table border="0" width="100%" id="table17" cellspacing="0" cellpadding="0">
<tr>
<td width="363">
<img border="0" src="images/zjcx_07_08_01.gif" width="363" height="17"> </td>
<td background="images/zjcx_07_08_02.gif">
<img border="0" src="images/zjcx_07_08_02.gif" width="9" height="17"> </td>
<td width="373">
<img border="0" src="images/zjcx_07_08_03.gif" width="373" height="17"> </td>
</tr>
</table>
</td>
</tr>
</table>
</td>
</tr>
</table>
</td>
</tr>
</table>
</td>
</tr> <?
require("./include/bottom.inc");
?> </table>
</div> </body> </html>
<?
}
$myCxmis->Destroy();
?>
ajaxreg.js代码如下：
var http_request=false;
  function send_request(url){//初始化，指定处理函数，发送请求的函数
    http_request=false;
        //开始初始化XMLHttpRequest对象
        if(window.XMLHttpRequest){//Mozilla浏览器
        http_request=new XMLHttpRequest();
        if(http_request.overrideMimeType){//设置MIME类别
          http_request.overrideMimeType("text/xml");
        }
        }
        else if(window.ActiveXObject){//IE浏览器
        try{
          http_request=new ActiveXObject("Msxml2.XMLHttp");
        }catch(e){
          try{
          http_request=new ActiveXobject("Microsoft.XMLHttp");
          }catch(e){}
        }
    }
        if(!http_request){//异常，创建对象实例失败
        window.alert("创建XMLHttp对象失败！");
        return false;
        }
        http_request.onreadystatechange=processrequest;
        //确定发送请求方式，URL，及是否同步执行下段代码
    http_request.open("GET",url,true);
        http_request.send(null);
  }
  //处理返回信息的函数
  function processrequest(){
  var mess
  if(http_request.readyState==4){//判断对象状态     if(http_request.status==200){//信息已成功返回，开始处理信息
  if(http_request.responseText=='exist')
mess=" <font color=red>此用户名已经存在，请更换用户名！ </font>";
  else if(http_request.responseText=='ok')
mess=" <font color=red>此用户名可以注册 </font>";
  else if(http_request.responseText=='right')
mess=" <font color=red>旧密码正确 </font>";
  else if(http_request.responseText=='error')
mess=" <font color=red>旧密码不正确 </font>";
          document.getElementById(reobj).innerHTML=mess;
        }
        else{//页面不正常
          alert("您所请求的页面不正常！");
        }
  }
  }
  function usercheck(obj){
  var f=document.reg;
  var username=f.username.value;
  if(username==""){         document.getElementById(obj).innerHTML=" <font color='#ff0000'>用户名不能为空！ </font>";
        //f.username.focus();
        //return false;
  }
  else if(username.replace(/[^\x00-\xff]/g,'##').length>16){
          document.getElementById(obj).innerHTML=" <font color=red>用户名长度不能大于16位（汉字不能超过8个）！ </font>";
          //f.userpwd.focus();
          return false;
  }
  else{
  document.getElementById(obj).innerHTML="正在读取数据...";
  send_request('checkuserreg.php?username='+username);
  reobj=obj;
  }
  }
  function userpwdcheck(obj){
  var f=document.reg;
  var oldpassword=f.oldpassword.value;
  if(oldpassword==""){         document.getElementById(obj).innerHTML=" <font color='#ff0000'>旧密码不能为空！ </font>";
        //f.username.focus();
        //return false;
  }
  else{
  document.getElementById(obj).innerHTML="正在读取数据...";
  send_request('checkuserpwd.php?oldpassword='+oldpassword);
  reobj=obj;
  }
  }
  function pwdcheck(obj){
    var f=document.reg;
        var pwd=f.userpwd.value;
        if(pwd==""){
          document.getElementById(obj).innerHTML=" <font color=red>用户密码不能为空！ </font>";
          //f.userpwd.focus();
          return false;
        }
        else if(f.userpwd.value.length <6){
          document.getElementById(obj).innerHTML=" <font color=red>密码长度不能小于6位！ </font>";
          //f.userpwd.focus();
          return false;
        }
        else{
          document.getElementById(obj).innerHTML=" <font color=red>密码符合要求！ </font>";
        }
  }
  function pwdrecheck(obj){
    var f=document.reg;
        var repwd=f.reuserpwd.value;
        if (repwd==""){
          document.getElementById(obj).innerHTML=" <font color=red>请再输入一次密码！ </font>";
          //f.reuserpwd.focus();
          return false;
        }
        else if(f.userpwd.value!=f.reuserpwd.value){
          document.getElementById(obj).innerHTML=" <font color=red>两次输入的密码不一致！ </font>";
          //f.reuserpwd.focus();
          return false;
        }
        else{
          document.getElementById(obj).innerHTML=" <font color=red>密码输入正确！ </font>";
        }
  }
<script type="text/javascript" src="ajax.js"></script>
<a href="#" onclick="funphp100('q')">q</a>
<a href="#" onclick="funphp100('t')">t</a>
<a href="#" onclick="funphp100('x')">x</a>
<div id="php100"></div>funphp100('q')函数参数是否正确？我自己人认为应该是数字，要不然$o= $_GET['id']赋值为0，所以循环就不执行，也就没返回信息
//其实这个问题很简单，你把这个byphp()函数改一下就可以了。
function byphp(){
    if(xmlHttp.readyState==4){
    var byphp100 = xmlHttp.responseText;
    document.getElementById('php100').innerHTML = byphp100;
    }
}