Bootstrap 3 跳出式視窗 modal 如何做？

參考：

https://getbootstrap.com/docs/3.3/javascript/#modals

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

<!-- Modal -->
<div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        <h4 class="modal-title" id="myModalLabel">Modal title</h4>
      </div>
      <div class="modal-body">
        ...
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary">Save changes</button>
      </div>
    </div>
  </div>
</div>

然後，如何讓這個 modal 在載入網頁時，自動彈出？

 <script type="text/javascript">
    $(document).ready(function(){
        $('#myModal').modal('show');
    });
  </script>

透過這段 javascript 讓網頁一開啟時，就自動 show出來。