JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="myTextarea" length="500"></textarea>
<span id="textareaLength"></span>

CSS

#myTextarea {
    width: 300px;
    height: 300px;
}

#textareaLength {
    position: absolute;
}

JavaScript

var theCounter = $('#textareaLength'),
    textarea = $('#myTextarea'),
    maxLength = textarea.attr('length');

theCounter.text('0 / '+maxLength);
theCounter.css({  
    'top': (textarea.offset().top + textarea.height()) - theCounter.height(),
    'left': (textarea.offset().left + textarea.width()) - theCounter.width()
});

textarea.on('keydown', function() {  
    var theLength = $(this).val().length;
    theCounter.text($(this).val().length+' / '+maxLength)
              .css({  
                  'left': (textarea.offset().left + textarea.width()) - theCounter.width()
              });
});