JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="menu">
    <li><a href="#" id="parent-one">One</a></li>
    <li><a href="#" id="parent-two">Two</a></li>
    <li><a href="#" id="parent-three">Three</a></li>
    <li><a href="#" id="parent-four" class="active">Four</a></li>
</ul>

<ul class="show-me">
    <li id="child-one">Show One</li>
    <li id="child-two">Show Two</li>
    <li id="child-three">Show Three</li>
    <li id="child-four">Show Four</li>
</ul>

CSS

ul {
    margin-bottom: 1.5em;
}
.show-me li {
    display: none;
}

JavaScript

$(function() {
    // Within .menu, find .active, and do this:
    var new_id = $('.menu').find('.active').attr('id').replace('parent', 'child');

    // Select element with this id, and show it.
    $('#' + new_id).show();
});