JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="a" onkeyup="changeHeigth()">
    line 1
    line 2
    line 3
    ...
    line n
</textarea>

CSS

textarea{
    overflow:hidden
}

JavaScript

window.addEventListener('DOMContentLoaded', changeHeigth);
function changeHeigth()
{
    var textarea = document.getElementById('a');
    var this_val = textarea.value;
    var matches = this_val.match(/\n/g);
	var breaks = matches ? matches.length : 1;
	textarea.setAttribute('rows',breaks);
}