CodeIgniter - Ajax Json call to controller not working

I am current using CodeIgniter 2.2.2 I have the following controller code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class switchLang extends CI_Controller {
    public function __construct()
    {
        parent::__construct();

                $this->load->helper('url');
    }
    public function changeLang()
    {
            log_message('debug', 'INSIDE');
            //echo "test";

            $data = array("STATUS"=>"true");
            //echo "HI";
            echo json_encode($data) ;   
    }

    public function index(){
        }   
}

And inside my view I have the following ajax call:

<script  type="text/javascript">
            $(document).ready(function() {      
                                var base_url = '<?php echo site_url('switchLang/changeLang');?>';

                                $('#lang').click(function(event) {
                                        console.log(5 + 6);
                                        $.ajax({
                    'async': false,
                    'url' : base_url,
                    'type' : 'POST', 
                    'dataType': 'json',
                    'data' : 'data',
                    'success' : function(data){ 
                                console.log(data);
                                 if(data){
                                    location.reload(); 
                                }
                             }
                                    });

                                });
                        });
</script>

I am trying to reload page on success jax call. However I am getting only the following response in my Chrome debugger and nothing happens.

What exactly is mock post and how come my ajax isn't calling my controller function? Note: But when I try manually typing url inside my browser((myhostname)/switchLang/changeLang), my controller seems to be working perfectly.