add edit button to datatable

$(document).ready(function(){

  // DataTable
  var userDataTable = $('#userTable').DataTable({
     'processing': true,
     'serverSide': true,
     'serverMethod': 'post',
     'ajax': {
        'url':'ajaxfile.php'
     },
     'columns': [
        { data: 'name' },
        { data: 'email' },
        { data: 'gender' },
        { data: 'city' },
        { data: 'action' },
     ]
  });

  // Update record
  $('#userTable').on('click','.updateUser',function(){
     var id = $(this).data('id');

     $('#txt_userid').val(id);

     // AJAX request
     $.ajax({
        url: 'ajaxfile.php',
        type: 'post',
        data: {request: 2, id: id},
        dataType: 'json',
        success: function(response){
           if(response.status == 1){

             $('#name').val(response.data.name);
             $('#email').val(response.data.email);
             $('#gender').val(response.data.gender);
             $('#city').val(response.data.city);

             userDataTable.ajax.reload();
           }else{
             alert("Invalid ID.");
           }
        }
     });

  });

  // Save user 
  $('#btn_save').click(function(){
     var id = $('#txt_userid').val();

     var name = $('#name').val().trim();
     var email = $('#email').val().trim();
     var gender = $('#gender').val().trim();
     var city = $('#city').val().trim();

     if(name !='' && email != '' && city != ''){

       // AJAX request
       $.ajax({
         url: 'ajaxfile.php',
         type: 'post',
         data: {request: 3, id: id,name: name, email: email, gender: gender, city: city},
         dataType: 'json',
         success: function(response){
            if(response.status == 1){
               alert(response.message);

               // Empty and reset the values
               $('#name','#email','#city').val('');
               $('#gender').val('male');
               $('#txt_userid').val(0);

               // Reload DataTable
               userDataTable.ajax.reload();

               // Close modal
               $('#updateModal').modal('toggle');
            }else{
               alert(response.message);
            }
         }
      });

    }else{
       alert('Please fill all fields.');
    }
  });

  // Delete record
  $('#userTable').on('click','.deleteUser',function(){
     var id = $(this).data('id');

     var deleteConfirm = confirm("Are you sure?");
     if (deleteConfirm == true) {
        // AJAX request
        $.ajax({
          url: 'ajaxfile.php',
          type: 'post',
          data: {request: 4, id: id},
          success: function(response){
             if(response == 1){
                alert("Record deleted.");

                // Reload DataTable
                userDataTable.ajax.reload();
             }else{
                alert("Invalid ID.");
             }
          }
        });
     } 

  });
});