JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>not empty</li>
    <li><!-- comment (should be considered empty --><!-- test --></li>
    <li> </li>
    <li></li>
    <li><span> </span></li>
</ul>

CSS

li {
    display: block;
    height: 20px;
    background-color: red;
    margin-bottom: 2px;
}
li.empty {
    background-color: green;
}

JavaScript

(function($){
    $.isBlank = function(html, obj){
        return $.trim(html) === "" || obj.length == 0;
    };

    $('li').each(function() {
        if($.isBlank(
            $(this).html(), 
            $(this).contents().filter(function() {
            	return (this.nodeType !== Node.COMMENT_NODE);
        	})
        )) {
            $(this).addClass('empty');
        }
    });
})(jQuery);