<!DOCTYPE html>
<html>
<head>
<script src="/lib/jquery-1.12.2.min.js"></script>
<script>
$(document).ready(function(){
$("button").click(function(){
$("li").toggleClass(function(n){
return "listitem_" + n;
});
});
});
</script>
<style>
.listitem_1, .listitem_3 {
color: red;
}
.listitem_0, .listitem_2 {
color: blue;
}
</style>
</head>
<body>
<h1>This is a heading</h1>
<ul>
<li>Peter</li>
<li>Lois</li>
<li>Chris</li>
<li>Stewie</li>
</ul>
<button>Add/remove classes to list items</button>
</body>
</html>