JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <span id="a">1</span>
    <span id="a">2</span>
    <span>3</span>
</div>

JavaScript

$(function() {
    var w = $("div");
    console.log($("#a").length);
    console.log($("body #a").length);
    console.log($("#a", w).length);
});