aria-label
正常情况下，form表单的input组件都有对应的label.当input组件获取到焦点时，屏幕阅读器会读出相应的label里的文本。
<!DOCTYPE html>
<html>
<head>
<meta charset = "utf-8">
<title>demo</title>
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="external nofollow" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
<script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdn.bootcss.com/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
<script src="https://cdn.bootcss.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
<style type="text/css">
body{padding: 20px;}
</style>
</head>
<body>
<form role = "form">
<div class="form-group col-lg-3 form-horizontal">
<label for = "idCard" class="control-label col-lg-5">身份证号：</label>
<div class="col-lg-7">
<input type = "text" id = "idCard" class="form-control">
</div>
</div>
</form>
</body>
</html>
但是如果我们没有给输入框设置label时，当其获得焦点时，屏幕阅读器会读出aria-label属性的值，aria-label不会在视觉上呈现效果。
<body>
<form role = "form">
<div class="form-group col-lg-3 form-horizontal">
<div class="col-lg-7">
<input type = "text" id = "idCard" class="form-control" aria-label = "身份证号">
</div>
</div>
</form>
</body>
aria-labelledby
<body>
<div class="dropdown">
<button type="button" class="btn dropdown-toggle" id="dropdownMenu1"
data-toggle="dropdown">
选择您的职位
<span class="caret"></span>
</button>
<ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
<li role="presentation">
<a role="menuitem" tabindex="-1" href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" >测试工程师</a>
</li>
<li role="presentation">
<a role="menuitem" tabindex="-1" href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" >开发工程师</a>
</li>
<li role="presentation">
<a role="menuitem" tabindex="-1" href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" >销售工程师</a>
</li>
</ul>
</div>
</body>
注：
如果一个元素同时有aria-labelledby和aria-label，读屏软件会优先读出aria-labelledby的内容
总结
以上所述是小编给大家介绍的Bootstrap的aria-label和aria-labelledby属性实例详解，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对北冥有鱼网站的支持！
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