how to pass js function variable to ajax

Question

This is my javascript function which accepts id as a signature and alert the selected text of dropdown

function sendata(id) {
            $(document).ready(function () {
                $(id).on('change', function () {
                    var ctlevel = $(id).find("option:selected").text();
                    var selectedValue = $(id).val();
                    alert("Selected Text: " + ctlevel + " Value: " + selectedValue);


                });
            });
        }

here ,i called the function but it didn't work and it did not alert the text message of dropdown also the data is not sent to controller .but when i replace the senddata function with the inner code of that function it works ??

 $(document).ready(function () {
            senddata('#ddtname');
               $.ajax({
                    url:'@Url.Action("Getdata", "ConfigClass")',
                    type: "GET",
                     data: {'ctname':ctlevel},
                   dataType: "text",

                    //Response carry bunch of data from controller
                     success: function (response) {
                         alert(response);

                         //parse json obj to js
                         var obj = JSON.parse(response)
                         var ele = document.getElementById('sel');
                         $('#sel').empty();

                         //append default value to dropdown
                         var s = '<option value="-1">SubjectName</option>';

                         //using loop for populating dropdown ,values retrive through ajax
                         for (var i = 0; i < obj.length; i++) {
                             // POPULATE SELECT ELEMENT WITH JSON.
                             
                            s+='<option value="' + obj[i]['aid'] + '">' + obj[i]['assignsubject'] + '</option>';
                         } 
                         $('#sel').html(s);
                   },
                    error: function () {
                        alert('not working :(');
                    }
                });
            });