JSFiddle - React, Tailwind, and code Playground

HTML

<div id="pie">Type a number</div>
<input type="text" name="item1" size="5">

JavaScript

document.getElementsByName('item1')[0].addEventListener('input', function () {
    var value = document.getElementsByName('item1')[0].value;
    document.getElementById('pie').innerHTML = !isNaN(value) ? +value : "Not a number";
});