https://github.com/w3c/webcomponents/issues/563

 

https://github.com/w3c/webcomponents/issues/563

Upgrade runs connectedCallback on an element with a throwing constructor. After executing the following code log contains 'connected'.

let element = document.createElement('a-a');
let log = [];
w.customElements.define('a-a', class extends w.HTMLElement {
  constructor() {
    throw new Error();
  }
  connectedCallback() {
    log.push('connected');
  }
});
document.body.appendChild(element);
https://html.spec.whatwg.org/#concept-upgrade-an-element
enqueueing attributeChangedCallback, connectedCallback after custom element`s state check in Step 2 is not enough when the the element`s state is changed in Step 9.