Navbar menu input

7. Define the subscribe method to tell Shiny when to change the current input value. Here it’s the events applied by Bootstrap in order:

• hide.bs.tab (on the current active tab).
• show.bs.tab (on the to-be-shown tab).
• hidden.bs.tab (on the previous active tab).
• shown.bs.tab (on the newly-active just-shown tab).

subscribe: function(el, callback) {
  // important to use shown.bs.tab and not show.bs.tab!
  $(el).on('shown.bs.tab.navbarMenuBinding', function(e) {
    callback();
  });
},
  
unsubscribe: function(el) {
  $(el).off('.navbarMenuBinding');
}