如何从HTML的父元素获取子元素？

Question

我的HTML页面中有一个元素可以打开引导程序模式。模态启动div内还有一个按钮，单击后显示警报。问题是单击按钮后，弹出警报，并在关闭后打开模态。我需要从按钮中退出模式启动功能，而该功能仍位于模式启动div中，以便可以分别单击“外部舔”按钮。我想我是否可以像更改z-index一样从div中获得按钮，它将解决，但是我不知道该怎么做。<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous"><script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script><script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script><!-- Button trigger modal --><div type="button" class="btn btn-primary" data-toggle="modal" data-target="#exampleModalCenter">  Launch demo modal  <button onclick="alert('clicked!');">External click</button></div><!-- Modal --><div class="modal fade" id="exampleModalCenter" tabindex="-1" role="dialog" aria-labelledby="exampleModalCenterTitle" aria-hidden="true">  <div class="modal-dialog modal-dialog-centered" role="document">    <div class="modal-content">      <div class="modal-header">        <h5 class="modal-title" id="exampleModalLongTitle">Modal title</h5>        <button type="button" class="close" data-dismiss="modal" aria-label="Close">          <span aria-hidden="true">&times;</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>