JSFiddle - React, Tailwind, and code Playground

HTML

<div id="sidemenu">
	<ul>
	    <li id="welcomeLi" class="selected"><span>Welcome</span><a href="#home">&bull;</a></li>
	    <li id="mantraLi"><span>Our mantra</span><a href="#mantra">&bull;</a></li>
	    <li id="softwareLi"><span>Our software</span><a href="#software">&bull;</a></li>
	    <li id="involvedLi"><span>Get involved</span><a href="#involved">&bull;</a></li>
	    <li id="contactLi"><span>Contact us</span><a href="#contact">&bull;</a></li>
	</ul>
</div>

JavaScript

$('#sidemenu ul li:not(.selected) span').hide();

$(window).scroll(function() {
    clearTimeout($.data(this, 'scrollTimer'));
    $.data(this, 'scrollTimer', setTimeout(function() {
        $('#sidemenu ul li:not(.selected) span').hide();
        $('#sidemenu ul li.selected span').show();
    }, 250));
});