在bootstrap下拉列表中下拉切换类的目的是什么？

Question

无论是否将dropdown-toggle引导类应用于<button>元素，

下拉菜单都能正常工作，那么为什么要在第一时间使用它呢？

Answer 1

dropdown-toggle类会在outline: 0;上添加:focus到该按钮，因此当您点击该按钮时，它将没有“active”元素的周围蓝色​​边框。< / p>

检查接下来的两个句子：

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

<div class="container">
  <h2>Dropdowns</h2>
  <p>The .divider class is used to separate links inside the dropdown menu with a thin horizontal line:</p>
  <div class="dropdown">
    <button class="btn btn-default dropdown-toggle" type="button" data-toggle="dropdown">Tutorials - no border
      <span class="caret"></span></button>
    <ul class="dropdown-menu">
      <li><a href="#">HTML</a></li>
      <li><a href="#">CSS</a></li>
      <li><a href="#">JavaScript</a></li>
      <li class="divider"></li>
      <li><a href="#">About Us</a></li>
    </ul>
  </div>
</div>

<div class="container">
  <h2>Dropdowns</h2>
  <p>The .divider class is used to separate links inside the dropdown menu with a thin horizontal line:</p>
  <div class="dropdown">
    <button class="btn btn-default" type="button" data-toggle="dropdown">Tutorials - with border
      <span class="caret"></span></button>
    <ul class="dropdown-menu">
      <li><a href="#">HTML</a></li>
      <li><a href="#">CSS</a></li>
      <li><a href="#">JavaScript</a></li>
      <li class="divider"></li>
      <li><a href="#">About Us</a></li>
    </ul>
  </div>
</div>

Answer 2

它添加了以下CSS属性，但它们会在显示下拉按钮的内容时产生影响：

button以及box-shadow，.open，color和background-color基本上是border-color内部outline （在:focus）删除。这里两者比较：

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<!-- Single button -->
<div class="btn-group">
  <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    With .dropdown-toggle <span class="caret"></span>
  </button>
  <ul class="dropdown-menu">
    <li><a href="#">Action</a>
    </li>
    <li><a href="#">Another action</a>
    </li>
    <li><a href="#">Something else here</a>
    </li>
    <li role="separator" class="divider"></li>
    <li><a href="#">Separated link</a>
    </li>
  </ul>
</div>

<!-- Single button -->
<div class="btn-group">
  <button type="button" class="btn btn-default" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Without .dropdown-toggle <span class="caret"></span>
  </button>
  <ul class="dropdown-menu">
    <li><a href="#">Action</a>
    </li>
    <li><a href="#">Another action</a>
    </li>
    <li><a href="#">Something else here</a>
    </li>
    <li role="separator" class="divider"></li>
    <li><a href="#">Separated link</a>
    </li>
  </ul>
</div>

在Chrome，Opera＆amp; Safari浏览器：