JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="textarea" maxlength="20" placeholder="Enter some text..."></textarea>
<div id="show_counter"></div>

CSS

textarea {
  padding: 10px;
  border: 2px solid #ccc;
  border-radius: 10px;
  height: 90px;
  width: 400px;
}

JavaScript

const textarea = document.getElementById('textarea');
const show_counter = document.getElementById('show_counter');
const max_length = textarea.getAttribute('maxlength');

textarea.addEventListener('input', function (e) {
    const counts = this.value.length;
    show_counter.innerHTML = `${counts}/${max_length}`;
});