JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="field"></textarea>
<div id="charNum">0</div>

JavaScript

$("#field").keyup(function() {
  el = $(this);
  if (el.val().length >= 500) {
    el.val(el.val().substr(0, 500));
  } else {
    $("#charNum").text(500 - el.val().length);
  }
});