JSFiddle - React, Tailwind, and code Playground
HTML
<div class="note-row" id="10"></div>
<div class="note-row" id="21"></div>
<div class="note-row" id="4"></div>
<div class="note-row" id="5"></div>
<div class="note-row" id="6"></div>
JavaScript
var max = $('.note-row').sort(function(a, b) { return +a.id < +b.id })[0].id;
alert(max);