JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="timeline" id="timeline">

            <li id="timelineLI-1A4">

                <div class="timelineIcon letter"></div>

                <div class="dateContainer"></div>

            </li>


            <li id="timelineLI-2">

                <div class="timelineIcon mail"></div>

                <div class="dateContainer"></div>




            </li>

        </ul>

JavaScript

function getNext(id) {
    return $("#" + id).next("li").attr("id");
}

console.log(getNext("timelineLI-1A4"));