JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <textarea class="boring"></textarea>
    <textarea class="new" id="id1"></textarea>
    <textarea class="new" id="id2"></textarea>
</div>

CSS

.new {
    height:20px;
}
.new:focus, .new.notEmpty {
    height:80px;
}

JavaScript

$('.container').on('change', 'textarea.new', function () {
    var notEmpty = $(this).val().length > 0;
    $(this).toggleClass('notEmpty', notEmpty);
});