Adding a Header Note section to reuse Javascript

I use Javascript in my notes to add functionality like formatting card tags, slightly modifying a card’s contents, etc. When a note has more than one card type and I want to reuse javascript functionality, I need to copy-paste code but that is very error-prone. It would also make it easier to maintain my notes if I can put all the javascript in one place and it’s separate from HTML, like I do now with CSS (Styling).

Would it be possible to add a “Shared Header Template” section to the Card Types editor whose contents would be wrapped around tags and rendered before the Front Template of a card at render time, a bit like how the Styling section works?

One thing you can do now is putting JavaScript in a separate file in your media folder, then referencing it like this:

<script src="_file.js"></script>

You then only have to duplicate this line in other templates.
Note that the filename should start with an underscore.

You could try using Asset Manager, which basically does what you want: every note type is given an asset collection, and for each asset (might it be JS, HTML, or whatever) you can choose where and how to insert it into a card template.