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public function check_member_available($username)
  {
     $query = $this->db->get_where('members',array('username'=> $username));
      $HTML='';
     if($query->num_rows() == FALSE)
     {
        $HTML='not exists';
     }
     else 
     {
        $HTML='user exists';
     }
     echo $HTML;
  }

public function check_members()
  {
     $this->load->model('users');
     if($this->input->post('username'))
     {
         $username = $this->input->post('username');
         $this->users->check_member_available($username);
     }
     
     
      
     $this->load->view('cajax');
  }

<div id="container">
    <div id="wrapper">
         <div id="form">
             <label>Choose Your Username</label>
      <input type="text" autocomplete="off" name="user_name" id="user_id" class="user_name" >
             <span class="check"></span> <br><br> 
         </div>
    </div>

</div>

[removed][removed]
<link rel="stylesheet" type="text/css" href="<?php echo base_url();?>css/css/style.css" />
[removed]
$(function()
{
  $('.user_name').keyup(function()
  {
  var checkname=$(this).val();
 var availname=remove_whitespaces(checkname);
  if(availname!=''){
  $('.check').show();
  $('.check').fadeIn(400).html('<?php echo base_url();?>images/image/ajax-loading.gif ');

  var String = 'username='+ availname;
  $.ajax({
          type: "POST",
          url: "<?php echo site_url();?>/home/check_members",
          data: String,
          cache: false,
          success: function(result){
               var result=remove_whitespaces(result);
               if(result==''){
                       $('.check').html('<?php echo base_url();?>images/image/accept.png This Username Is Avaliable');
                       $(".check").removeClass("red");
             $('.check').addClass("green");
                       $(".user_name").removeClass("yellow");
                       $(".user_name").addClass("white");
               }else{
                       $('.check').html('<?php echo base_url();?>images/image/error.png This Username Is Already Taken');
                       $(".check").removeClass("green");
        $('.check').addClass("red")
                       $(".user_name").removeClass("white");
                       $(".user_name").addClass("yellow");
               }
          }
      });
   }else{
       $('.check').html('');
    
   }
  });

});

function remove_whitespaces(str){
     var str=str.replace(/^\s+|\s+$/,'');
     return str;    
}
[removed]

public function check_members()
  {
     $this->load->model('users');
     if($this->input->post('username'))
     {
         $username = $this->input->post('username');
         $this->users->check_member_available($username);
     }
     
     
      
     $this->load->view('cajax');
  }

public function check_members()
  {      
     $this->load->view('cajax');
  }  

public function ajax_check_members()
{
     $this->load->model('users');
     if($this->input->post('username'))
     {
         $username = $this->input->post('username');
         $this->users->check_member_available($username);
     }
}

class Ajax_post extends CI_Controller {
  
  public function getwhere(){
        //$this->load->library('javascript');
        if($this->input->post('username', TRUE)){
        $username = $this->input->post('username', TRUE);
        $query = $this->db->get_where('members',array('username'=>$username));
        if ($query->num_rows() == 1){
           echo '<font color="red">The nickname <strong>'.$username.'</strong> is already in use.</font>';
        }else {
                echo "OK";
        }
    } 
    
     
 }
  public function check_members(){
    
     $this->load->view('ajax_view');
  }
 
}

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js">
</script>

$(document).ready(function(){

$("#username").change(function() { 

var usr = $("#username").val();

if(usr.length >= 4)
{
$("#status").html('http://www.d4yd.com/mycode/images/loader.gif Checking availability…');
    $.ajax({  
    type: "POST",  
    url: "http://www.d4yd.com/mycode/ajax_post/getwhere",  
    data: { username: usr }  
  }).done(function(msg){
      if(msg == 'OK')
 { 
        $("#username").removeClass('object_error'); // if necessary
  $("#username").addClass("object_ok");
  $(#status).html(' http://www.d4yd.com/mycode/images/tick.gif');
 }  
 else  
 {  
  $("#username").removeClass('object_ok'); // if necessary
  $("#username").addClass("object_error");
  $(#status).html(msg);
 }  
  }) 

}
else
 {
 $("#status").html('<font color="red">The username should have at least <strong>4</strong> characters.</font>');
 $("#username").removeClass('object_ok'); // if necessary
 $("#username").addClass("object_error");
 }

});

});