I’m sorry but I would like to report that I also have a trouble import js_files locally.
I’m working for using the sortable list (please see here Sortable Widget - #16 by Marc)
This does work
pn.extension(js_files={'sortablelist': "https://raw.githack.com/SortableJS/Sortable/master/Sortable.js"})
This does not work
pn.extension(js_files={'sortablelist': "Sortable.js"})
The Sortable.js is in the same folder as my python script notebook file.