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

<!-- Modal -->
<div class="modal fade" id="exampleModal" tabindex="-1" aria-labelledby="exampleModalLabel" aria-hidden="true">
  <div class="modal-dialog">
    <div class="modal-content">
      <div class="modal-header">
        <h5 class="modal-title" id="exampleModalLabel">Modal title</h5>
        <button type="button" class="btn-close" data-coreui-dismiss="modal" aria-label="Close"></button>
      </div>
      <div class="modal-body">
        ...
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-coreui-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary" onclick="closeModal()">Save changes</button>
      </div>
    </div>
  </div>
</div>

<script>
function closeModal(){
const myModal = new coreui.Modal('#exampleModal');
myModal.hide();
}
</script>