whatsapp.html

<style>
  html:not(.is-phone) .whatsapp-link {
    display: none;
  }
</style>
<a class="whatsapp-link" href="whatsapp://send?text=url-encoded-text-goes-here">
  Share with Whatsapp
</a>
<script>
  ;(function(navigator, document) {
    var isPhone = /(iPhone)|android.*(?=mobile)/gi.test(navigator.userAgent);
    document.documentElement.classList.toggle('is-phone', isPhone);
  })(navigator, document);
</script>