Feather Icons v4.29.0 add custom svg icons

Question

I would like to add a custom icon to feather icons in javascript. I haven't found anything about it on github. Is it possible to do it?

<!-- Include il file feather.js -->
<script src="https://unpkg.com/feather-icons"></script>

<!-- Inserisci il tuo file SVG personalizzato -->
<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" id="custom-icon">
  <!-- Il contenuto del tuo file SVG -->
</svg>

<!-- Inserisci il codice per sostituire l'icona -->
<script>
  feather.replace({
    'width': 20,
    'height': 20,
    'class': 'custom-icon',
    'contents': document.getElementById('custom-icon').outerHTML
  });
</script>

I tried like this but it doesn't work.