Simple, Ben, as follows:
<head>
<script language="JavaScript" src="/my_global_dir/my_global_js_file.
js"></script>
</head>
Within your external JavaScript file, you do not use the <script> tag, but simply type the code without the opening and closing <script> tags.
And by the way, most developers recommend using external
JS files when you are re-using many of the functions.