ajax的创建 ajax.js

//创建ajax对象function c_xmlhttp(){  var xmlhttp=null;   if(window.XMLHttpRequest){                  xmlhttp= new XMLHttpRequest;          //如果请求的不是xml 则将它转为xml           if(xmlhttp.overrideMime Type){                xmlhttp.overrideMime Type("text/html")               }   }  else if(window.ActiveXObiect){          try{                             xmlhttp=new ActiveXobject(Wsxml2.XMLHTTP);        }catch(e){                try{                                             xmlhttp=new ActiveXObject(Microsoft.XNLHTTP);                   }catch(e){}            }  }return xmlhttp;}xmlhttp=c_xmlhttp();function getdata(id){      xmlhttp.open('GET','index.php?id='+id,true);      xmlhttp.onreadystatechange=handle;      xmlhttp.send();}function handle(){     if(xmlhttp.readystate==4){           if(xmlhttp.status==200){                    var text=xmlhttp.responseText;                    document.getElementById('content').innerHTML=text;             }    }}

inddex.html

                                 名称:    
     
 

index.php

     query("select *from user where name=".$id);  if(is_array(mysqli_fetch_row($query))){        echo "该用户已存在";  }else          echo "可以使用";}?>