url-route.js

import regexparam from 'https://unpkg.com/regexparam@1/dist/regexparam.mjs';

/**
 * <url-route href="/profile/:user">
 *   <div>some content here</div>
 * </url-route>
 */
customElements.define('url-route', class UrlRoute extends HTMLElement {
  connectedCallback() {
    this.route = regexparam(this.getAttribute('href'));
    const show = this.route.pattern.test(location.pathname);
    this.children.forEach(c => c.style.display = show ? '' : 'none');
  }
});