Because HTMX is declarative and the declaration is in HTML, people have weirdly extended the "no need for js+json+rendering for ajax" to "don't use js".

This is making your life needlessly difficult.

HTMX is just a fancy ajax layer with a little event handling sprinkled on top. You can and should script to your heart content even if you use it, when you need so.

I use js in all most of my HTMX powered pages. Sometimes just a few lines. Sometimes a whole lot. Sometimes vanilla, sometimes alpine. I even have one where I load react for one single page because I want a community widget while the rest of the site is pure HTMX.

You can do whatever you want.