HTML5 Forms

html5Form.html

<style>
  .ProFeature {
    display: none;
  }
</style>

<form action="/episodes" method="POST" data-is-pro="<%= user.pro %>">
  <input type="email" name="email" />
  <input type="email" name="alternate_email" class="ProFeature" disabled />
</form>

<script>
  var proFeatures;
  if ($('form').data('is-pro')) {
    proFeatures = $('.ProFeature');
    proFeatures.prop('disabled', false);
    proFeatures.show();
  }
</script>