JSFiddle - React, Tailwind, and code Playground
HTML
<ul class="customList">
<li data-featured="1">First item</li>
<li data-featured="0">Another item</li>
<li data-featured="0">Last item..</li>
</ul>
JavaScript
if($('li[data-featured="1"]').val() != null){
$('li[data-featured="1"]').append(" <li data-featured='222'>NEW ITEM</li>");
}
else{
$('ul').append("<li data-featured='222'>NEW ITEM</li>");
}