https://members2.ascrs.org/resource/1782205760000/nc__Resources/DropDownButton.js

1/**
2 * Activates the two separate javascript functions for drop down buttons on page load.
3 **/
4$(document).ready(function(){
5    selectFirstElement();
6    deselectFirstElement();
7});
8
9/**
10 * When a dropdown menu button is opened this function will autoselect the first element in the list.
11 */
12function selectFirstElement() {
13    $(document).on('shown.bs.dropdown', function(event) {
14            var dropdown = $(event.target);
15
16            // Set aria-expanded to true
17            dropdown.find('.dropdown-menu').attr('aria-expanded', true);
18
19            // Set focus on the first link in the dropdown
20            setTimeout(function() {
21                dropdown.find('.dropdown-menu li:first-child a').focus();
22            }, 10);
23    });
24}
25
26/**
27 * When a dropdown menu is closed this function will deselect the selected element in the list.
28 */
29function deselectFirstElement() {
30    $(document).on('hidden.bs.dropdown', function(event) {
31        var dropdown = $(event.target);
32
33        // Set aria-expanded to false
34        dropdown.find('.dropdown-menu').attr('aria-expanded', false);
35
36        // Set focus back to dropdown toggle
37        dropdown.find('.dropdown-toggle').focus();
38    });
39}