Wait to load defer scripts.

More real example

    <script>
    function defer(method) {
        if (window.inputmask) // Important! Wait loading last script!
            method();
        else
            setTimeout(function() { defer(method) }, 50);
    }
    <script>
    <script type="text/javascript" defer src="js/jquery-3.2.1.min.js"></script>
    <script type="text/javascript" defer src="js/bootstrap-3.3.7.min.js"></script>
    <script type="text/javascript" defer src="js/jquery.inputmask.3.3.4.min.js"></script>
    
    
    <script>
      defer(function () {
          alert("jQuery is now loaded");
          // CODE
      });
    </script>  
    

simple exapmle

<script>
    function defer(method) {
        if (window.jQuery)
            method();
        else
            setTimeout(function() { defer(method) }, 50);
    }
<script>
    
<script>
  defer(function () {
      alert("jQuery is now loaded");
      // CODE
  });
</script>