Bootstrap modal restores button focus on close

You can use this method, to make the modal-trigger loose focus when you close the modal:

$('#myModal').on('shown.bs.modal', function (e) {
    $('#modalTrigger').one('focus', function (e) {
        $(this).blur();
    });
});

Example:

$(document).ready(function() {
    $('#myModal').on('shown.bs.modal', function (e) {
        $('#modalTrigger').one('focus', function (e) {
            $(this).blur();
        });
    });
});
<!DOCTYPE html>
<html lang="en">
<head>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.2.1/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.6/umd/popper.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.2.1/js/bootstrap.min.js"></script>
</head>
<body>
  <button id="modalTrigger" type="button" class="btn btn-primary" data-toggle="modal" data-target="#myModal">
    Open modal
  </button>

  <!-- The Modal -->
  <div class="modal" id="myModal">
    <div class="modal-dialog">
      <div class="modal-content">
      
        <!-- Modal Header -->
        <div class="modal-header">
          <h4 class="modal-title">Modal</h4>
          <button type="button" class="close" data-dismiss="modal">&times;</button>
        </div>
        
        
        <!-- Modal footer -->
        <div class="modal-footer">
          <button type="button" class="btn btn-danger" data-dismiss="modal">Close</button>
        </div>
      </div>
    </div>
  </div>
</body>
</html>

Blur buttons when modal closes.

$('body').on('hidden.bs.modal', '.modal', function() {
    $('.btn').blur();
});