What advantages provide document.registerElement()?

Question

Using own custom tag directly in HTML document without using document.registerElement('my-tag') seems to works fine. It can be styled as usual etc.

Answer 1

registerElement has two advantages:

1. It returns a constructor for that tag, meaning you can instantiate it via Javascript, e.g:
   var myTag = document.registerElement("my-tag"); document.body.appendChild(new myTag())
2. It provides a second parameter which allows you to select a prototype for your element, e.g.
   var customImg = document.registerElement("custom-img", { prototype: Object.create(HTMLImageElement.prototype) });

The second one is actually a general options object where an additional prototype can be extended or an existing tag be extended (like <img is="custom-img">)