By using Templates and Shadow DOM in a custom element, you can make the element easier to handle and resusable. Customized built-in elements – extending built-in elements, like a customized button, based on HTMLButtonElement etc. This allows for a very modern, WebComponents-like way to organize your code, while retaining support for even very old browsers (see custom elements and IE 6 to 8). All custom elements must in some way extend an HTMLElement in order to be registered with the browser. Custom elements are a new web standard which let developers create their own HTML Elements. The command generates custom-button-element.js that you can include in