Codeigniter Ajax网址错误

I have a problem when sending data with ajax,in the URL it adds .php to my controller

need help :(

this is the AJAX script to make call to Welcome controller:

<script>
$(document).ready(function () {
$('#palier').change(function(){
   var idf=$(this).val();
 console.log(idf);
    $.ajax({
       url : "<?php echo base_url(); ?>"+"Welcome/affectation_exam",
       type : "POST",
       data:{idf:idf},
       datatype:"text",
       success:function(data){
           $('#specialite').html(data); 
          // console.log(data);
       }


    });

});
})

</script>

in the controller i have :

public function affectation_exam($page='affectation des examens')
  {

    $data['title']=$page;

      $this->load->model('Palier');
      $this->load->model('Specialite');
      $data['records']=$this->Specialite->get_specialite();
      $data['palier']=$this->Palier->get_palier();
      $this->load->view('template/main',$data);
      echo $_POST["idf"];


  }

Try this

$.ajax({      
  url  : "<?php echo base_url(); ?>/welcome/affectation_exam";
  ...
});

If you have not removed index.php then use it as

$.ajax({      
  url  : "<?php echo base_url(); ?>/index.php/welcome/affectation_exam";
  ...
});

Edited

Change your controller code like

public function affectation_exam($page='affectation des examens')
{

    $data['title']=$page;
    $this->load->model('Palier');
    $this->load->model('Specialite');
    $data['records']=$this->Specialite->get_specialite();
    $data['palier']=$this->Palier->get_palier();
    $result = $this->load->view('template/main',$data, TRUE);
    //$_POST["idf"];
    echo $result; exit;

}

1) There is no requirement for concatenation of URL string.

2) The controller name needs to be in lower-case.

$.ajax({
       url : "<?php echo base_url(); ?>welcome/affectation_exam",
       .....
     });