$("ul").empty()
works fine. Is there some other error?
$('input').click(function() {_x000D_
$('ul').empty()_x000D_
});
_x000D_
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>_x000D_
<ul>_x000D_
<li>test</li>_x000D_
<li>test</li>_x000D_
</ul>_x000D_
_x000D_
<input type="button" value="click me" />
_x000D_