my js file order in head is like this
<script src="../js/jquery.min.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/select2.min.css" />
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/select2.min.js"></script>
jquery version is jQuery v2.1.3