https://www.remodelista.com/wp-content/plugins/big-bite-conditional-selects/hub-menus.js?ver=1.1

1var arr = [];
2
3if(typeof SELECT_DATA == 'undefined') {
4	SELECT_DATA = [];
5}
6
7for(var i in SELECT_DATA) {
8    // Copy to avoid referencing.
9    var item = SELECT_DATA[i].item;
10
11    arr[i] = SELECT_DATA[i];
12    arr[i].item = [];
13
14    for(var x in item) {
15        arr[i].item[x] = item[x];
16    }
17}
18
19SELECT_DATA = arr;
20
21function selectActions() {
22    var select_base = document.querySelector('#select-base');
23
24    select_base.onchange = function (event) {
25        var select = event.target;
26        var selected = select.options[select.selectedIndex];
27        var index = selected.dataset.index;
28        var items = SELECT_DATA[index].item;
29
30        var secondaryElement = document.querySelector('#select-secondary');
31        secondaryElement.innerHTML = '';
32
33        items.unshift({
34            id: null,
35            name: 'Choose a field guide.'
36        });
37
38        for (var i in items) {
39            var option = document.createElement('option');
40            option.text = items[i].name.replace(/&/g, '&').replace(/&/g, '&').replace(/$#8217;/g, '\'');
41            option.value = items[i].id;
42            option.dataset.index = i;
43
44            secondaryElement.appendChild(option);
45        }
46    };
47}
48
49function selectSubmission() {
50    document.querySelector('button.cs-submit').onclick = function (event) {
51        event.preventDefault();
52
53        var items = SELECT_DATA;
54        var targetUrl = '';
55        var hubEl = document.querySelectorAll('select[name=choose_hub]');
56
57        for (var i in hubEl) {
58            if (typeof hubEl[i] !== 'object') {
59                break;
60            }
61
62            if (hubEl[i].selectedOptions.length <= 0) {
63                continue;
64            }
65
66            var index = hubEl[i].selectedOptions[0].dataset.index;
67
68            if (typeof index === 'undefined') {
69                continue;
70            }
71
72            if (typeof items[index].permalink !== 'undefined') {
73                targetUrl = items[index].permalink;
74            }
75
76            if (typeof items[index].item !== 'undefined') {
77                items = items[index].item;
78            }
79        }
80
81        window.location.replace(targetUrl);
82    };
83}
84
85function init() {
86    var select_base = document.querySelector('#select-base');
87
88    if (!select_base) {
89        return;
90    }
91
92    selectActions();
93    selectSubmission();
94};
95
96init();