knockout way of building a recaptcha

knockout.recaptcha.js

/**
 * Make sure your page is using <script type="text/javascript" src="http://www.google.com/recaptcha/api/js/recaptcha_ajax.js"></script>
 * or if you're using <script src="https://www.google.com/recaptcha/api.js" async defer></script> then comment out
 * Recaptcha.create and uncomment the grecaptcha.render.
 * based on http://jsfiddle.net/jaGWY/
 * docs: https://developers.google.com/recaptcha/intro & http://recaptchamvc.apphb.com/Home/Document
 */

var app = app || {};
app.knockout = app.knockout || {};
app.knockout.recaptcha = (function ($) {

    var key = app.recaptchaPublicKey;

    var widgetId = null;

    ko.bindingHandlers['recaptcha'] = {
        'init': function (element, valueAccessor, allBindingsAccessor, viewModel) {

            var val = ko.utils.unwrapObservable(valueAccessor()),
                response = val.response;

            $(function () {
                $(app).on("createCaptcha", function (event, theme) {
                    widgetId = grecaptcha.render("recaptcha",
                    {
                        'sitekey': key,
                        'theme': theme,
                        'callback': function () {
                            var responseId = "g-recaptcha-response";
                            responseElement = document.getElementById(responseId);
                            if (ko.isObservable(response))
                                response(responseElement.value);
                            else
                                response = responseElement.value;
                        },
                        'expired-callback': function () {
                            grecaptcha.reset(widgetId);
                        }
                    });

                    //Recaptcha.create(key,
                    //    element.id,
                    //    {
                    //        theme: "clean",
                    //        callback: function (/*none supplied by google, thanks*/) {
                    //            var responseId = 'recaptcha_response_field', challengeId = 'recaptcha_challenge_field',
                    //                challengeElement = document.getElementById(challengeId),
                    //                responseElement = document.getElementById(responseId);

                    //            if (ko.isObservable(challenge))
                    //                challenge(challengeElement.value);
                    //            else
                    //                challenge = challengeElement.value;

                    //            $(responseElement).on("change", function () {
                    //                if (ko.isObservable(response))
                    //                    response(this.value);
                    //                else
                    //                    response = this.value;
                    //            });
                    //        }
                    //    }
                    //  );
                });
            });
        }
    };

    var model = {};

    model.reset = function () {
        grecaptcha.reset(widgetId);
    };

    return model;

})(jQuery);

var onloadCallback = function () {
    jQuery(app).trigger("createCaptcha"); // pass 2nd arg as ["dark"] to make captcha black
};