native-slide-toggle | Vanilla JS mobile friendly version of jQuery.slideToggle | Animation library

I'm implementing the a slide toggle for a nested menu in AngularJS. I've been using the code from the following page: https://blog.assaf.co/native-slide-toggle-for-angularjs-1-4-x/

I'm having only one problem with it though. I'm trying to implement this on a sidenav menu with nested submenues, built with

and
• elements. After having toggled a menu item that has submenu, and I later toggle the submenu of that same menu button, the
  element of that menu button doesn't slide in. The height remains the same.

  Also, if I keep the submenu closed, and open only the top menu item, the height of the

  element remains the same when I toggle the submenu, meaning that the submenu doesn't show until I toggle it open (though remaining invisible), then close the top menu button, then open it again.

  Please see it in action here: https://codepen.io/marcus-edensky/pen/MBoWZJ

  Here's my JavaScript code:

  ...