For TypeScript

knockout-chosen.js

ko.bindingHandlers.chosen = {
    init: (element, valueAccessor, allBindings, viewModel, bindingContext) => {
        var $element = $(element);
        var options = ko.unwrap(valueAccessor());

        if (typeof options === 'object')
            $element.chosen(options);

        ['options', 'selectedOptions'].forEach(propName => {
            if ((<any>allBindings).has(propName)) {
                var prop = (<any>allBindings).get(propName);
                if (ko.isObservable(prop)) {
                    prop.subscribe(() => {
                        $element.trigger('chosen:updated');
                    });
                }
            }
        });
    },
    update: (element, valueAccessor, allBindingsAccessor,
        viewModel, bindingContext) => {
        $(element).chosen().trigger('chosen:updated');
    }
}

Added update method