Marketo event listener for GTM

<script>
/**
 * push Marketo form events and values to Google Tag Manager via the data layer
 * uses the Marketo Forms 2.0 API
 */
(function marketoFormListener (MktoForms2) {
    "use strict";
    /**
     * helper function to push invalid Marketo field errors to GTM
     * @returns {undefined}
     */
    function waitForError () {
        var element, input, mktoErrorMsg;
        // check for error message
        element = document.querySelector(".mktoErrorMsg");
        if (element) {
            mktoErrorMsg = element.textContent || element.innerText;
            // look for invalid input
            input = document.querySelector("input.mktoInvalid, .mktoInvalid input");
            window.dataLayer.push({
                "event": "mkto.form.error",
                "mkto.form.error.message": mktoErrorMsg,
                "gtm.element": input,
                "gtm.elementClasses": input && input.className || "",
                "gtm.elementId": input && input.id || "",
                "gtm.elementName": input && input.name || "",
                "gtm.elementTarget": input && input.target || ""
            });
        }
    }

    if (MktoForms2) {
        MktoForms2.whenReady(function handleReady (form) {
            window.dataLayer.push({
                "event": "mkto.form.ready",
                "mkto.form.id": form.getId(),
                "mkto.form.submittable": form.submittable(),
                "mkto.form.allFieldsFilled": form.allFieldsFilled(),
                "mkto.form.values": form.getValues()
            });

            form.onValidate(function handleValidate (valid) {
                window.dataLayer.push({
                    "event": "mkto.form.validate",
                    "mkto.form.valid": valid
                });
                // wait for the error message to appear
                setTimeout(waitForError, 0);
            });

            form.onSubmit(function handleSubmit (thisForm) {
                var button;
                button = form.getFormElem().find("button[type=\"submit\"]");
                window.dataLayer.push({
                    "event": "mkto.form.submit",
                    "mkto.form.id": form.getId(),
                    "mkto.form.submittable": form.submittable(),
                    "mkto.form.allFieldsFilled": form.allFieldsFilled(),
                    "mkto.form.values": form.getValues(),
                    "mkto.form.button": {
                        "classes": button.attr("class"),
                        "text": button.text(),
                        "type": "submit"
                    }
                });
            });

            form.onSuccess(function handleSuccess (values, followUpUrl) {
                window.dataLayer.push({
                    "event": "mkto.form.success",
                    "mkto.form.id": form.getId(),
                    "mkto.form.values": values,
                    "mkto.form.followUpUrl": followUpUrl,
                    "eventCallback": function () {
                      document.location.href = followUpUrl;
                    },
                    "eventTimeout" : 3000
                  });
                  return false;
             });

        });

        MktoForms2.whenRendered(function handleRendered (form) {
            window.dataLayer.push({
                "event": "mkto.form.rendered",
                "mkto.form.id": form.getId(),
                "mkto.form.submittable": form.submittable(),
                "mkto.form.allFieldsFilled": form.allFieldsFilled(),
                "mkto.form.values": form.getValues()
            });
        });
    }
})(window.MktoForms2);
  </script>