Sending A Different Arguments To A Function Depending On The PHP Script?

Using a simple example lets say there is this function in an external script:

Code:

function showmessage(arg){
alert(arg);
}

If we have different scripts eg page1.php, page2.php, page3.php etc

If each one of those scripts calls the function showmessage using different arguments eg page1.php calls it like this :

Code:

<script language="JavaScript" type="text/javascript">
showmessage("page1");
</script>

The above code would have to be embedded into the PHP file.

how can we go about doing that unobtrusively? Ie by not putting the code into the PHP files how can a different argument be passed to that function depending on what page is loaded?