drop-down-menu - 强制引导下拉菜单始终显示在底部并允许它离开屏幕

Question

当视口(viewport)底部没有空间容纳下拉菜单时，它会显示在其下拉按钮的顶部。是否有可能改变这种行为并使下拉菜单始终出现在底部？

    <div class="dropdown">
  <button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Dropdown button
  </button>
  <div class="dropdown-menu" aria-labelledby="dropdownMenuButton">
    <a class="dropdown-item" href="#">Action</a>
    <a class="dropdown-item" href="#">Another action</a>
    <a class="dropdown-item" href="#">Something else here</a>
  </div>
</div>

Answer 1

对于 Bootstrap 5 (≥ 5.0)
通过设置 data-bs-display="static" 完全禁用 Popper.js 动态定位在 dropdown-toggle元素(按钮或链接)。
来自 Bootstrap 5 Docs > Dropdowns: Options :

By default, we use Popper.js for dynamic positioning. Disable this with static.

.window {
    height: 8em;
    overflow: auto;
    margin: 1em;
    padding: 1em;
    border: 10px solid #DFEAF2;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/js/bootstrap.bundle.min.js" integrity="sha384-ka7Sk0Gln4gmtz2MlQnikT1wXgYsOg+OMhuP+IlRH9sENBO0LRn5q+8nbTov4+1p" crossorigin="anonymous"></script>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css" rel="stylesheet"/>

<div class="window">
    <div class="dropdown">
        <button data-bs-display="static" class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton1" data-bs-toggle="dropdown" aria-expanded="false">
            Dropdown dropdown-toggle with data-bs-display="static"
        </button>
        <ul class="dropdown-menu" aria-labelledby="dropdownMenuButton1">
            <li><a class="dropdown-item" href="#">Action</a></li>
            <li><a class="dropdown-item" href="#">Another action</a></li>
            <li><a class="dropdown-item" href="#">Something else here</a></li>
            <li><a class="dropdown-item" href="#">Action</a></li>
            <li><a class="dropdown-item" href="#">Another action</a></li>
            <li><a class="dropdown-item" href="#">Something else here</a></li>
        </ul>
    </div>
</div>

对于 Bootstrap 4 (4.1 - 4.6)
通过设置 data-display="static" 完全禁用 Popper.js 动态定位在 dropdown-toggle元素(按钮或链接)。
来自 Bootstrap 4 Docs > Dropdowns: Options :

By default, we use Popper.js for dynamic positioning. Disable this with static.

.window {
  height: 8em;
  overflow: auto;
  margin: 1em;
  padding: 1em;
  border: 10px solid #DFEAF2;
}

<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"></script>
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" rel="stylesheet" />
<div class="window">
  <div class="dropdown">
    <button data-display="static" class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
      Dropdown dropdown-toggle with data-display="static"
    </button>
    <div class="dropdown-menu" aria-labelledby="dropdownMenuButton">
      <a class="dropdown-item" href="#">Action</a>
      <a class="dropdown-item" href="#">Another action</a>
      <a class="dropdown-item" href="#">Something else here</a>
      <a class="dropdown-item" href="#">Action</a>
      <a class="dropdown-item" href="#">Another action</a>
      <a class="dropdown-item" href="#">Something else here</a>
    </div>
  </div>
</div>