<!-- Style -->
<link href="https://cdn.jsdelivr.net/npm/select2@4.1.0-beta.1/dist/css/select2.min.css" rel="stylesheet" />
<!-- Script -->
<script src="https://cdn.jsdelivr.net/npm/select2@4.1.0-beta.1/dist/js/select2.min.js"></script>
<script>
// In your Javascript (external.js resource or <script> tag)
$(document).ready(function() {
$('.js-example-basic-single').select2();
});
</script>