JSFiddle - React, Tailwind, and code Playground

HTML

<div id="selectmodelediv">
    <select>
        <option value=""></option>
        <option value="1111">test1</option>
        <option value="222">test2</option>
    </select>
    <br/>
    <textarea id="targetText" name="targetText" class="champ_tel_txtarea" rows="6" cols="50"></textarea>
    <div id="compteur" class="compteur"></div>
</div>

JavaScript

function UpdateCharactersLeft(element) {
    var max = 255;
    var len = $(element).val().length;
    
    if (len >= max) {
        $('#compteur').text(' you have reached the limit');
    } 
    else {
        var ch = max - len;
        $('#compteur').text(ch + ' characters left');
    }
}

$('select').change(function () {
    $('#targetText').val($('#selectmodelediv select').val());
    UpdateCharactersLeft(this);
});

$('#targetText').on('keyup', function() {
    UpdateCharactersLeft(this);
});