customised pop up message

<!-- this script got from www.javascriptfreecode.com - Coded by: Krishna Eydat -->

<html>
<head>
<script language="javascript" type="text/javascript">
alert("Hello welcome to my site")
</script>
</head>
</html>

<a target="_blank" href="https://www.javascriptfreecode.com/" style="font-size: 8pt; text-decoration: none;font-family:Tahoma">Javascript Free Code</a>