[Plugin: Category Chained Selects] trying to update

I’m using WordPress 4.1.1 and am trying to update an old plugin: Category Chained Selects.

I’ve placed the two files (php and js) in https://pastebin.com/qCq9cb0i I have made a couple of small modifications from the original.

The instructions for using this plugin are on this site

This is the code I placed in the page template:
chainselect_getcategories( 'location', 3, array('Select Continent', 'Select Country', 'Select State/Province'), array('Select Continent', 'Select Country', 'Select State/Province'), 'Submit', '', 0 );

I’m working on localhost, so I don’t have a link to the actual site.

The first argument “location” is a custom hierarchical taxonomy with 3 levels.

When the page is first loaded, the first dropdown is correctly populated. The second and third are greyed-out as they should be.

If I select a continent, the second field almost disappears and remains empty although there are terms to display.

According to reviews, this plugin used to work very well but not with the most recent version of WP. The plugin seems to have been abandoned.

I went through all the WP functions and checked them against the codex. I can’t see a problem. The PHP looks OK to me but I’m far from being an expert. And the JS seems OK to me.

I did a var_dump($_POST) in the template file right after the line that calls chainselect_getcategories and it’s empty. I don’t know where else I can use the var_dump().

Firebug console does not give any JS errors.

I’ve tried comparing this code to other examples I’ve found, but as inexperienced as I am, I can’t make heads or tales of it.

Is there anyone who can give me a hand? I’d appreciate it so much!