JSFiddle - React, Tailwind, and code Playground
HTML
<textarea id="field" onkeyup="countChar(this)"></textarea>
<div id="charNum">500 Characters left</div>
JavaScript
function countChar(val) {
var len = val.value.length;
if (len >= 500) {
val.value = val.value.substring(0, 500);
} else {
$('#charNum').text(500 - len+" Characters left");
}
};