document.registerElement() deprecated

See here: https://developer.mozilla.org/en-US/docs/Web/API/Document/registerElement (says it's depreciated but scroll down to the 'Browser compatibility' section to see that no browser currently supports it).

Use customElements.define() method instead. Unfortunately the syntax is quite different:

class MyElement extends HTMLElement{
connectedCallback(){
this.innerHTML = "<h2>Pluralsight Comment</h2><textarea></textarea></br><input type='submit'>";
}
}
customElements.define('pluralsight-comment', MyElement);

This site helped me: https://css-tricks.com/an-introduction-to-web-components/