JSFiddle - React, Tailwind, and code Playground

HTML

<textarea rows="5" id="content_txt" name="TextArea1" runat="server" maxlength="50"></textarea>
<p id="message"></p>

JavaScript

var area = document.getElementById("content_txt");
var message = document.getElementById("message");
var maxLength = 50;
var checkLength = function() {
    if(area.value.length < maxLength) {
        message.innerHTML = (maxLength-area.value.length) + " characters remainging";
    }
}
setInterval(checkLength, 300);