public function getInvisibleWidget($formId, $buttonLabel = 'Submit', $buttonClass ='')
    {
        $hash = md5(uniqid($formId, true));

        return sprintf(
'<script>
       function onSubmit%s(token) {
         document.getElementById("%s").submit();
       }
</script>
<button class="g-recaptcha %s" data-sitekey="%s" data-callback=\'onSubmit%s\'>%s</button>
', $hash, $formId, $buttonClass, $this->siteKey, $hash, $buttonLabel);
    }