Simple HTML Import with custom element that replaces itself with imported content

import.html

        <script>
            window.customElements.define('get-import', class extends HTMLElement {
                constructor() {
                    super();
                    if (this.hasAttribute('url'))
                        window.fetch(this.attributes.url.value)
                                .then(res => res.text())
                                .then(txt => this.outerHTML = txt);
                }
            });
        </script>
<!-- This element will replace itself with the document specified in url attribute -->
<get-import url="folder/page.html"></get-import>