JSFiddle - React, Tailwind, and code Playground
HTML
<div class="content">
<div class="tlcontent">
<div class="sideon" id="sideline0">
somethings
</div>
<div class="trackon" id="trackline0">
somethings
</div>
<div class="sideon" id="sideline1">
somethings
</div>
<div class="sideon" id="sideline2">
somethings
</div>
</div>
</div>
JavaScript
alert($('.content :last').attr('id'))