How to add undo/redo buttons

This example shows how to add Undo and Redo buttons to the right toolbar (extrabar) of the editor.

<h1>Exploring the mysteries of space</h1>
<p>Space, the final frontier, stretches infinitely beyond the confines of Earth, a vast expanse of darkness speckled with stars, planets, and <b>galaxies</b>. It is a place of profound mystery and beauty, where the laws of physics manifest in ways that challenge our understanding. The cosmos is <a href="https://example/com">a cosmic dance</a> of celestial bodies moving in the silent echo of the universe, from the fiery birth of stars in nebulae to the enigmatic pull of black holes.</p>
<figure>
  <img src="/assets/redactor4/photo.jpg" alt="Blue and purple galaxy">
  <figcaption>Jeremy Thomas <a href="https://unsplash.com/photos/blue-and-purple-galaxy-digital-wallpaper-E0AHdsENmDg">unsplash.com</a></figcaption>
</figure>
<h2>Humanity's Journey Beyond Earth</h2>
<p>Exploring space has pushed humanity to its limits, revealing not just the universe's grandeur, but also the fragility of our own planet. Satellites orbiting Earth provide crucial data for communication, weather forecasting, and global positioning, while telescopes peer deep into the cosmos, uncovering the universe's age and composition. Each discovery in space leads us to new questions about our place in the universe, driving our insatiable curiosity to explore the unknown.</p>

Code

<!-- element -->
<textarea id="entry">...</textarea>

<!-- call -->
<script>
let app = Redactor('#entry', {
    buttons: {
        extrabar: ['undo', 'redo', 'hotkeys']
    }
});
</script>