JSFiddle - React, Tailwind, and code Playground

HTML

<textarea name="my-textarea" id="my-textarea"></textarea>
<input type="button" id="btn-undo" value="Undo">
<input type="button" id="btn-redo" value="Redo">

JavaScript

const textarea = document.getElementById('my-textarea');
const btnUndo = document.getElementById('btn-undo');
const btnRedo = document.getElementById('btn-redo');
let contentSave = '';

btnUndo.addEventListener('click', (e) => {
	contentSave = textarea.value;
  textarea.value = '';
});

btnRedo.addEventListener('click', (e) => {
	if (contentSave != '') {
  	textarea.value = contentSave;
  	contentSave = '';
  }
});