php+jquery+ajax表单提交数据

HTML：

<div id="msg"></div>
<form name="user_info" method="post" action="">
姓名：<input type="text" id="user_name"name="user_name" /><br />
年龄：<input type="text" name="user_age" /><br />
性别：<input type="text" name="user_sex" /><br />
<input type="button" value="提交表单" onClick="saveUserInfo()">
</form>

js：

<script language="javascript">
function saveUserInfo()
{
//获取接受返回信息层
var msg = document.getElementByIdx_xx_x("msg");
//获取表单对象和用户信息值
var f = document.user_info;
var userName = f.user_name.value;
var userAge = f.user_age.value;
var userSex = f.user_sex.value;
//接收表单的URL地址
var url = "./ajax_output.php";
//需要POST的值，把每个变量都通过&来联接
var postStr    = "user_name="+ userName +"&user_age="+ userAge +"&user_sex="+ userSex;
//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;
          }
               
               
               
//通过Post方式打开连接
ajax.open("POST", url, true);
//定义传输的文件HTTP头信息
ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
//发送POST数据
ajax.send(postStr);
//获取执行状态
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;
    }
}
alert (userName);
}
</script>

PHP：

 

ajax_output.php:
<?php
      $username = $_POST['user_name'];
      $userage = $_POST['user_age'];
      $usersex = $_POST['user_sex'];
   echo "$username <br>";
   echo "$userage <br>";
   echo "$usersex <br>";
   $db = new mysqli('localhost','root','123456','test');
   if(!$db){
    echo "连接失败！";
   }
   $db->query("set names utf8");
   $query = "insert into userinfo(uname,uage,usex) values ('".$username."','".$userage."','".$usersex."')";
   $result = $db->query($query);
   if ($result){
    echo "上传成功！";
   }
   else {
    echo "失败！";
   }
   $db->close();

?>