Adds the specified class if it is not present, and removes the specified class if it is present, using an optional transition.
$("p").click(function () {
$(this).toggleClass("selected", 1000);
});
<!DOCTYPE html>
<html>
<head>
<link type="text/css" href="http://jqueryui.com/latest/themes/base/ui.all.css" rel="stylesheet" />
<script type="text/javascript" src="http://jqueryui.com/latest/jquery-1.3.2.js"></script>
<script src="http://ui.jquery.com/latest/ui/effects.core.js"></script>
<style type="text/css">
p { cursor: pointer; font-size: 1.2em; }
.selected { color:red; }
</style>
<script type="text/javascript">
$(document).ready(function(){
$("p").click(function () {
$(this).toggleClass("selected", 1000);
});
});
</script>
</head>
<body style="font-size:62.5%;">
<p>Click me to toggle 'selected' class.</p>
<p class="selected">Click me to toggle 'selected' class.</p>
<p>Click me to toggle 'selected' class.</p>
</body>
</html>