Checking for Unique Usernames

Chardee MacDennis

right so i have written a registration form which validates fine using JS, I just added a username field and want to ensure the username is unique. This is how i attempted to do it:

Javascript

if (window.xmlhttprequest) {
        xmlhttp = new xmlhttprequest();
    } 
    
    else if (window.ActiveXObject) {
        xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }

    xmlhttp.open('GET', 'test.php?username='+username, false);
    xmlhttp.send('');
        
   if (xmlhttp.status == 200) {
       return xmlhttp.responseText.indexOf('true') == -1;
   } else return false; }

PHP

<?php
    include ('../includes/connectionManagerClass.php');
    $openDb=new MYSQLDB;
    if (isset($_REQUEST['username']) && !empty($_REQUEST['username'])) {
        $username=$_REQUEST['username'];
        $query="SELECT * FROM USERS WHERE USERNAME = '".$username."'";
        $result=mysql_query($query);
        
        if(mysql_num_rows($result)==0){
            echo("true");
        }
        
        else {
            echo("false");
        }
        
    } else {
        echo("false");
    }
?>

since i added in the JS above to my validation class it now doesnt validate at all and i can register with none of the fields filled out. The php file definitely works.

anyone have any suggestions as to what i am doing wrong, i really dont know much about the xmlhttp stuff so it could be horribly wrong.

any help would be great!

Chardee MacDennis

not sure what i did wrong but i got it figured, here's the working code in case it comes in use for someone!

xmlhttp=null;
    if (window.XMLHttpRequest) {// all modern browsers
      xmlhttp=new XMLHttpRequest();
    }
    
    else if (window.ActiveXObject) {// for IE5, IE6
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
     }
     
    if (xmlhttp!=null) {
          xmlhttp.open('GET', 'test.php?username='+username, false);
          xmlhttp.send(null);
    }
    
      if (xmlhttp.status==200) {
        if(xmlhttp.responseText.indexOf('true') == -1) {
            document.myform.Name.focus();
            showError("errorRegister","That username is already in use, please choose another",0,0);
            return false;
        }
    }