$(document).ready(function(){
  $('.fa-caret-down').click(toggle_menu_items(e));
});


function toggle_menu_items(e){
  e.preventDefault();
  submenu = $(e.currentTarget).next();
  $(submenu).slideToggle(500, function(e){
    if($(submenu).is(":visible")){
      $(e.currentTarget).removeClass('fa-caret-left');
      $(e.currentTarget).addClass('fa-caret-down');
    }
    else{
      $(e.currentTarget).removeClass('fa-caret-down');
      $(e.currentTarget).addClass('fa-caret-left');
    }
  });
}