<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script src="custom.js"></script>
</head>
<body>
<button id="b1">ALERT</button>
<button id="b2">Unload</button>
<script>
$(document).ready(function(){
$('#b2').click(function(){
alert("clicked.");
$('head script[src*="custom.js"]').remove();
});
});
</script>
</body>
</html>
