Where is page JS generated?

Hi,

What code should I be looking at to find where the Javascript at the bottom of each page is generated?

I'm trying to track down a bug with restricting file uploads with accepted_types in Assignment (2.2) - the bug may be mine, or maybe Moodle's. It looks like changing accepted_types from "*" to an an array results in a JSON object, when it should be a JSON array.