Ajax Post with JSON to PHP

Ajax Post with JSON to PHP

This code works successfully without green-shaded codes.
But if green codes are uncommented, nothing happens.

Why????

[ json_encode.php ]

      require_once('connectvars.php');
//$wtype = $_POST['jenre'];


       $dbc = mysqli_connect(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
  
  $query1 = "SELECT eng, id_num FROM words Limit 10";
   
 if ($result1=mysqli_query($dbc, $query1)){ 
$engrow = array();

 while ($row1=mysqli_fetch_array($result1))
   {                
$engrow[] = $row1;  
            }//while
           $js_array =   json_encode($engrow);
                           echo $js_array;    
  }



############           jQuery Ajax Post           ###############
[ajax.php]
$(document).ready(function () {
                  var jenres = 'n';
                  var querynum = 100;
  var data_json = {'jenre':jenres, 'querynum':q_num};

             $.ajax({
                                  // type: "POST",
   url: " json_encode.php",
    //  data: data_json,
   dataType: " JSON",
   success: function( json){
       
       for(var i=0;i<json.length;i++){
           $('#items_container').append (json[i].eng);
       }
   }
})
});//document
...
....