select2 behind swal2 problem code example

Example: swal2 with select2

use HTML tag in swal and onOpen for initiating Select2                   
swal({
  title: "Messaggio",
  html: html,
  confirmButtonColor: '#26C281',
  confirmButtonText: 'Salva',
  confirmButtonColor: '#26C281',
  showCancelButton: true,
  cancelButtonText: 'Chiudi',
  cancelButtonColor: '#EF4836',
  focusConfirm: false,
  onOpen: function () {
    $('.select2').select2({
      minimumResultsForSearch: 15,
      width: '100%',
      placeholder: "Seleziona",
      language: "it"
    });
  },