Back in 2006 when I worked for Yahoo!, and they had a CMS / template management system called Jake that statically generated templates for the PHP-based frontend servers to evaluate at request time. The idea was that you put as much of your logic as possible into the template generation layer, leaving the request-time logic to handle the stuff that changed request by request.
Now, that all sounds quite reasonable, but the two layers were written in different languages. The pre-template-generation logic was written as inline Perl (plus a little custom syntax, because why not), while the dynamic frontend logic was written in PHP. Perl was frequently used to generate chunks of PHP code to be executed by the frontend servers, and sometimes this PHP code wrote chunks of inline JavaScript. To say that debugging said JS was fun would be an understatement.