JSFiddle - React, Tailwind, and code Playground

HTML

<div id='elementID'>
    <span class='elementClass'>Some text</span> <!-- already present -->
    <span class='elementClass'>Some text</span> <!-- already present -->
    <span class='elementClass'>Some text</span> 
</div>

CSS

span{
 display: block;   
}

JavaScript

$('#elementID').click(function() {
    $('span:first', this).clone().text('Some text' + (+$('span:last',this).index() + 1) ).appendTo(this);
});

$('#elementID').on('DOMNodeInserted', function(e) {
    console.log($(e.target).text());
});