jQuery JSON validation for username before continuing with Facebook registration...

[akhileshbc]

    //...

    if(sql_num_rows($result,$dbi)>0){
        $data['username'] = "Taken";
        
    } else {
        $data['username'] = "Free";
        
    }
    header("Content-Type: application/json");
    echo json_encode($data);  
    exit;

   //.... 

See if this helps.