Show message on same page after successful form submission.

marketo-form-confirmation.html

<div class="container">
<script src="//app-abc.marketo.com/js/forms2/js/forms2.min.js"></script>
<form id="mktoForm_27"></form>
<script>MktoForms2.loadForm("//app-abc.marketo.com", "123-ABC-456", 1);</script>
<div id="confirmation" aria-hidden="true" style="display:none;">
<p>This is a sample thank you message. Thanks for viewing.</p>
</div>
</div>
<script>
MktoForms2.whenReady(function (form){
     form.onSuccess(function(vals, page){
          form.getFormElem().hide();
          var confirm = document.getElementById('confirmation');
          confirm.style.display = 'inline-block';
          confirm.setAttribute('aria-hidden', false);
          return false;
     });
});
</script>