JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="input1" maxlength="100"></textarea>
<p><span id="charsLeft1">100</span> characters left</p>
<textarea id="input2" maxlength="100"></textarea>
<p><span id="charsLeft2">100</span> characters left</p>
<textarea id="input3" maxlength="100"></textarea>
<p><span id="charsLeft3">100</span> characters left</p>

JavaScript

var maxLen = 100;
$('input1').observe('keyup', function(evt) {
  $('charsLeft1').update(maxLen - $('input1').value.length);
});
var maxLen = 100;
$('input2').observe('keyup', function(evt) {
  $('charsLeft2').update(maxLen - $('input2').value.length);
});
var maxLen = 100;
$('input3').observe('keyup', function(evt) {
  $('charsLeft3').update(maxLen - $('input3').value.length);
});