JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li class="list" data-id="123">One</li>
    <li class="list" data-id="124">Two</li>
    <li class="list" data-id="125">Three</li>
    <li class="list" data-id="126">Four</li>
</ul>

JavaScript

var dataList = $(".list").map(function() {
    return $(this).data("id");
}).get();

console.log(dataList.join('|'));