JSFiddle - React, Tailwind, and code Playground

by André Albson

HTML

<span class="caracteres">255</span> Restantes <br>
<textarea id="TxtObservacoes"></textarea>

JavaScript

$(document).on("keydown", "#TxtObservacoes", function () {
            var caracteresRestantes = 255;
            var caracteresDigitados = parseInt($(this).val().length);
            var caracteresRestantes = caracteresRestantes - caracteresDigitados;
            
            $(".caracteres").text(caracteresRestantes);
        });