JSFiddle - React, Tailwind, and code Playground

HTML

<input id="input" type="text" />
<p>The text box contains: <span id="counter"></span></p>

JavaScript

var input   = document.getElementById("input"),
    counter = document.getElementById("counter");

function count (event) {
    console.debug(event);
    counter.textContent = input.value.length;
}

input.addEventListener('keypress', count);
input.addEventListener('keyup', count);