> So, I have HTMX firing when people save their changes via a button, then I need to use the JS API for conditional logic e.g., if valid, then update table. If invalid, then display some kind of message or whatever.

Couldn't that be handled server-side as well? I have my validation logic server-side, and it either returns the updated table row (or other element), or it returns the form again with validation/error messages, fields highlighted where the error occurred, etc.