osem-fcy/app/assets/javascripts/osem-datatables.js

$(function () {
  $('.datatable').DataTable({
    // ajax: ...,
    stateSave: true,
    autoWidth: false,
    pagingType: 'full_numbers',
    "lengthMenu": [[25, 50, 100, -1], [25, 50, 100, "All"]],
  });
});