ajax实现分页

ajax.js代码:
 
var http_request=false;
function send_request(url)
{
 http_request=false;
 //开始初始化XMLHttp对象
 if(window.XMLHttpRequest){//MOILLA浏览器
  
    http_request=new XMLHttpRequest();
    if(http_request.overrideMimeType){
       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){
    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);
 
}
//处理返回信息函数
function processrequest(){
    if(http_request.readyState==4){
       if(http_request.status==200){
       document.getElementById(reobj).innerHTML=http_request.responseText;
     }else{
        alert("您所请求的页面不正常");
      }
     }
 }
 function dopage(obj,url){
     document.getElementById(obj).innerHTML="正在读取数据.....";
     send_request(url);
     reobj=obj;
  }
 
myajax.php代码：
 
 
<?php
 header("Content-type:text/html;charset=gb2312");
?>
<html>
 <head>
    <title>ajax分页</title>
 <script src="ajax.js"></script>
<style>
  .d{font-size:13px}
  table{font-size:14px}
  a{ text-decoration:none}
</style>
 </head>
 <body>
    <div id="result" class="d">
   <?php
      $page=isset($_GET["page"])?intval($_GET["page"]):1;
   $num=3;   //每页显示3条数据
   $link=mysql_connect("localhost","root","8821") or die("数据库连接失败".mysql_error());
   mysql_select_db("page") or die("数据库选择失败".mysql_error());
   mysql_query("set names 'gb2312'");
   $result=mysql_query("select * from student");
   $total=mysql_num_rows($result);//查询所有数据
   $url="myajax.php";  //获取本页url
   //页码计算
   $pagenum=ceil($total/$num);  //获得总页数,也是最后一页
   $page=min($pagenum,$page); //获得首页
   $prepg=$page-1;//上一页
   $nextpg=($page==$pagenum?0:$page+1);//下一页
   $offset=($page-1)*$num;
   //开始分页导航代码
   $pagenav="显示第<b>".($total?($offset+1):0)."<b>-<b>".min($offset+3,$total)."<b>条记录，共".$total."条记录$nbsp;";
   //如果只有一页则跳出函数
   if($pagenum<=1) return false;
   $pagenav.="<a href=javascript:dopage('result','$url?page=1');>首页</a>--";
   if($prepg)$pagenav.="<a href=javascript:dopage('result','$url?page=$prepg');>前页--</a>";else $pagenav.="前页--";
   if($nextpg)$pagenav.="<a href=javascript:dopage('result','$url?page=$nextpg');>后页--</a>";else $pagenav.="后页--";
   $pagenav.="<a href=javascript:dopage('result','$url?page=$pagenum');>尾页</a> ";
   $pagenav.="</select>共".$pagenum."页";
   if($page>$pagenum){  //假如传入的页面参数大于总页数  则现实错误信息
       echo "can not found the page".$page;
    exit;
   }
   $info=mysql_query("select * from student limit $offset,$num");
   echo "<table border=3>";
   while($it=mysql_fetch_array($info)){
     echo "<tr>";
     echo "<td>".$it["id"]."</td>";
     echo "<td>".$it["name"]."</td>";
     echo "<td>".$it["age"]."</td>";
     echo "<td>".$it["email"]."</td>";
     echo "</tr>";
   }
   echo "</table>";
   echo "<br>";
   echo $pagenav;
   ?>
 </div>
 </body>
</html>