<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.2/jquery.min.js"></script>
<script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<h2>Dropdown Example</h2>
<p>The <strong>show.bs.dropdown</strong> event occurs when the dropdown is about to be shown.</p>
<p>The <strong>shown.bs.dropdown</strong> event occurs when the dropdown is fully shown.</p>
<p>The <strong>hide.bs.dropdown</strong> event occurs when the dropdown is about to be hidden.</p>
<p>The <strong>hidden.bs.dropdown</strong> event occurs when the dropdown is fully hidden.</p>
<div class="dropdown">
<button class="btn btn-primary dropdown-toggle" id="menu1" type="button" data-toggle="dropdown">Toggle this Dropdown
<span class="caret"></span></button>
<ul class="dropdown-menu" role="menu" aria-labelledby="menu1">
<li role="presentation"><a role="menuitem" tabindex="-1" href="tryit.asp-filename=trybs_ref_js_dropdown_events&stacked=h.html#">HTML</a></li>
<li role="presentation"><a role="menuitem" tabindex="-1" href="tryit.asp-filename=trybs_ref_js_dropdown_events&stacked=h.html#">CSS</a></li>
<li role="presentation"><a role="menuitem" tabindex="-1" href="tryit.asp-filename=trybs_ref_js_dropdown_events&stacked=h.html#">JavaScript</a></li>
<li role="presentation" class="divider"></li>
<li role="presentation"><a role="menuitem" tabindex="-1" href="tryit.asp-filename=trybs_ref_js_dropdown_events&stacked=h.html#">About Us</a></li>
</ul>
</div><br>
<p><strong>Note:</strong> For dropdowns, you should always include the data-toggle="dropdown" attribute. Do not rely solely on the toggle method, as it may not work as expected in all browsers.</p>
</div>
<script>
$(document).ready(function(){
$('.dropdown').on('show.bs.dropdown', function(){
alert('The dropdown is about to be shown.');
});
$('.dropdown').on('shown.bs.dropdown', function(){
alert('The dropdown is now fully shown.');
});
$('.dropdown').on('hide.bs.dropdown', function(e){
alert('The dropdown is about to be hidden.');
});
$('.dropdown').on('hidden.bs.dropdown', function(){
alert('The dropdown is now fully hidden.');
});
});
</script>
</body>
</html>