scrap - image loading in webcomponent test

test.html

<script>
  (function(window, document, undefined) {

    //document = document.currentScript.ownerDocument;

    class ImageOnLoadExample extends HTMLElement {

      constructor() {
        super();
        this.attachShadow({mode: 'open'});
        this.shadowRoot.innerHTML = "<h1>ImageOnLoadExample WebComponent</h1>";
      }

      async getImageWidthByUrl(imgUrl) {
        const imgEl = document.createElement("img");
        let untilImgLoaded = new Promise((resolve, reject) => {
          imgEl.onload = resolve;
          imgEl.onerror = reject;
        });
        imgEl.src = imgUrl;
        await untilImgLoaded;
        return imgEl.naturalWidth;
      }

    }
    window.customElements.define('image-on-load-example', ImageOnLoadExample);

  })(window, document);
</script>