JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Olá mundo!</h1>
<h2>Olá StackOverflow!</h2>

JavaScript

var lengthH1 = document.querySelector('h1').innerHTML.length;
var lengthH2 = document.querySelector('h2').innerHTML.length;

alert(lengthH1 + ' ' + lengthH2);