JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>
        <p>item</p>
        <span class="spn">empty span</span>
    </li>
    <li>
        <p>item 2</p>
    </li>
    <li>
        <p>item 2</p>
    </li>
<ul>
<hr>
<a class="add-span"href="#">check</a>

JavaScript

$(document).ready( function () {
$("a.add-span").click(function() {
    $("li:not(:has(span))").each(function(index) {
        $(this).append('<span class="spn">new span<\/span>');
    });
});
    });