ajax传值给php

test.php

<script type="text/javascript">

function selectInput(oSelect) {
var value= oSelect.value;
var url = "2.php";
var postStr   = "value="+ value ;

//--------------------------------------------------------------------------------
//实例化Ajax
//var ajax = InitAjax();
          var ajax = false;
         //开始初始化XMLHttpRequest对象
         if(window.XMLHttpRequest) { //Mozilla 浏览器
                 ajax = new XMLHttpRequest();
                 if (ajax.overrideMimeType) {//设置MiME类别
                         ajax.overrideMimeType("text/xml");
                 }
         }
         else if (window.ActiveXObject) { // IE浏览器
                 try {
                         ajax = new ActiveXObject("Msxml2.XMLHTTP");
                 } catch (e) {
                         try {
                                 ajax = new ActiveXObject("Microsoft.XMLHTTP");
                         } catch (e) {}
                 }
         }
         if (!ajax) { // 异常，创建对象实例失败
                 window.alert("不能创建XMLHttpRequest对象实例.");
                 return false;
         }
//--------------------------------------------------------------------------------------------                

ajax.open("POST", url, true);
ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
ajax.send(postStr);

//----------------------------------------------------------------------------------------------
ajax.onreadystatechange = function() {
   //如果执行状态成功，那么就把返回信息写到指定的层里
   if (ajax.readyState == 4 && ajax.status == 200) {
    msg.innerHTML = ajax.responseText; //写入到id为msg的div里
   }
}
//-------------------------------------------------------------------------------------------------
}
</script> 

<div id="msg"></div>  

<?php $cnx = new PDO("odbc:Driver={SQL Server};Server=(local);Database=DBCT_Dev;",'sa','123456'); //连接数据库 ?>

<select onchange="selectInput(this)"">
<?php
$Province=$cnx->query("select ProvinceName,ProvinceId from S_Province");
foreach($Province as $sheng){
    echo "<option value='".$sheng['ProvinceId']."'>".$sheng['ProvinceName']."</option>";
    }?>
</select>

2.php

<?php
     print_r ($_POST['value']);
?>