JSFiddle - React, Tailwind, and code Playground

HTML

<textarea></textarea>

CSS

body { margin: 50px; }
textarea {
    height: 100px;
    width: 200px;
    resize: none;
    font-size: 18px;
    overflow-y: hidden;
}

JavaScript

$('textarea').keypress(function(){
    if ( $(this).get(0).scrollHeight > $(this).height() ) {
        $(this).css('font-size', '-=1');
    }
});