You need to pass a javascript variable to a php function?
You could do this:
<script type="text/javascript">
var c="this is my variable";
document.write("<script type='text/javascript' src='myphpfile.php?c="+c+"'></s"+"cript>");
</script>

Then, in your php file:
$c=$_GET['c'];

And then you play with your variable =D