Sane

A cryptic question... "The opposite of this code"?

I'm going to take a wild stab in the dark, and guess you're trying to do something like...

<?php $my_variable = <Something Coming From Javascript> ?>

So rather than in the code you posted, where JS obtains a value from PHP. Instead, you want PHP to obtain a value from JS?

Look into "AJAX". It's used to send data from Javascript to PHP. It's not as straightforward as the inverse in your first post, but it will get the job done.