JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li class="active">li 1</li>
    <li>li 2</li>
    <li>li 3</li>
</ul>

CSS

li.active
{
    font-weight: bold;
}

JavaScript

setInterval(function()
{
    // Remove .active class from the active li, select next li sibling.
    var next = $('ul li.active').removeClass('active').next('li');

    // Did we reach the last element? Of so: select first sibling
    if (!next.length) next = next.prevObject.siblings(':first');

    // Add .active class to the li next in line.
    next.addClass('active');
}, 2000);