<!DOCTYPE html>
<html>
<head>
<script src="/lib/jquery-1.12.2.min.js"></script>
<script>
$(document).ready(function(){
$("button").click(function(){
$("p").fadeTo(2000, 0.2, function(){
alert("The fadeTo effect is finished!");
});
});
});
</script>
</head>
<body>
<button>Gradually change the opacity of the p element</button>
<p>This is a paragraph.</p>
</body>
</html>