keeping-track.ts

class MySelectElement extends HTMLElement {
  constructor() {
    super();
    
    const observer = new MutationObserver((records) => {
      for (let record of records) {
        this.addItem(record.addedNodes);
        this.removeItem(record.removedNodes);
      }
    });

    customElements.whenDefined("my-option").then(() => {
      this.addItems(this.children);
      observer.observe(this, { childList: true });
    });
  }
    
  addItems(nodes: Iterable<MyOptionElement>) {}
  removeItems(nodes: Iterable<MyOptionElement>) {}
}