把浏览器缩小后 出现一个折叠按钮 但是点击后没有反应是怎么回事？
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Bootstrap 实例 - 默认的导航栏</title>
<link href="bootstrap.css" rel="stylesheet">
<script src="jquery.min.js"></script>
<script src="bootstrap.js"></script>
</head>
<body>
<nav class="navbar navbar-default" >
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
<span class="sr-only">daohang</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="#">W3Cschool</a>
</div>
<div class="collapse navbar-collapse" id="example-navbar-collapse">
<ul class="nav navbar-nav">
<li class="active"><a href="#">iOS</a></li>
<li><a href="#">SVN</a></li>
<li><a href="#">AAAA</a></li>
</ul>
</div>
</div>
</nav>
</body>
</html>这样修改，修改id值，和botton对应：
就会出现你想要的效果了：