JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="input" rows="4" cols="50"  maxlength="10">
</textarea>
<span id="output"></span>

JavaScript

var maxWords = 500;
var input = document.getElementById('input');
var output = document.getElementById('output');

output.innerHTML = maxWords + " words left";

input.onkeyup = function() {
    var words = input.value.split(" "); // Convert string into words
    var diff = maxWords - words.length; // Subtract words from maxWords
    console.log(diff)
    console.log(words.length);
    if (diff) { // If words < maxWords
        output.innerHTML = diff + " words left"; // Tell user new word count
    } else { // Prevent user from inputting more than maxWords
        words.length = maxWords; // Remove words over limit
        input.value = words.join(" "); // Fill input
    }
}