В html документе:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=windows-1251">
<title>Hello, world!</title>
</head>
<body>
<script type="text/javascript">
alert('Hello, world!');
</script>
</body>
</html>