Inserting Javascript modified dropdown menu

I’ve been looking through the forums here and at other resources online trying to insert a custom dropdown menu.

I have two dropdown menus. BOX A contains different categories. Depending on which category you choose, BOX B is then populated with different options.

I have everything running on JSFiddle (link below) but I can’t get it to function on my site at all. I have uploaded the javascript as an external file to the /js/ folder in my directory, and tried enqueueing it using the wp_enqueue_scripts function in my theme’s functions.php file, but to no avail.
I’ve even tried just blindly adding it to the page (in the text area of the page editor) out of desperation. Please help!

https://jsfiddle.net/flyingscot1989/3t3p9tvx/

(ps – I generally keep my site locked down to registered users only, because it is part of my company’s intranet)