handleLiveSearch() error

[lucianobapo]

resources/assets/administrator/js/theme.js line 209
function with error handleLiveSearch()

Error: $(...).selectize is not a function

static handleLiveSearch() {
        $('[data-type="livesearch"]').selectize({
            valueField: 'id',
            labelField: 'name',
            searchField: ['name'],
            create: false,
            loadThrottle: 500,
            maxOptions: 100,
            load: function(query, callback) {
                if (!query.length >= 3) return callback();

                let selectize = $($(this)[0].$input);

                let baseUrl = selectize.data('url');
                let url = baseUrl + (-1 === baseUrl.indexOf('?') ? '?' : '&');
                url += 'query=' + query;

                $.ajax({
                    url: url,
                    type: 'GET',
                    error: callback,
                    success: function(res) {
                        if (!res.hasOwnProperty('items')) {
                            console.error(
                                'Livesearch response should have "items" collection. ' +
                                'Each element in collection must have at least 2 keys: "id" and "name"',
                            );

                            return false;
                        }

                        return callback(res.items);
                    },
                });
            },
        });