JSFiddle - React, Tailwind, and code Playground

HTML

<div class="one"></div>
<div class="two"></div>
<div class="three"></div>

JavaScript

$('.one').append($('<div class="messages"><p>Just a test.</p></div><div class="messages">Another test</div>')
    .find('div.messages').length);

$('.two').append($('<div><div class="messages"><p>Just a test.</p></div></div><div>testing 123</div>')
    .find('div.messages').length);

// from an answer
$('.three').append($('<div class="messages"><p>Just a test.</p></div><div class="messages">Another test</div>')
    .filter('div.messages').length);