bootstrap modal close due to activity on mobile code example

Example: static modal bootstrap 4

<!-- Button trigger modal -->
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#exampleModalScrollable">
  
  nch demo modal
</button>

<!-- Modal -->
<div class="modal fade" id="exampleModalScrollable" tabindex="-1" role="dialog" aria-labelledby="exampleModalScrollableTitle" aria-hidden="true">
  <div class="modal-dialog modal-dialog-scrollable" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <h5 class="modal-title" id="exampleModalScrollableTitle">Modal title</h5>
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">×</span>
        </button>
      </div>
      <div class="modal-body">
        ...
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary">Save changes</button>
      </div>
    </div>
  </div>
</div>