A basic lit js modern hash router thats so simple you dont need a library for it

HashRouter.js

export class HashRouter {
  #baseURL;
  #host;
  #routes;

  constructor(host, routes) {
    this.#baseURL = `${location.protocol}//${location.host}`;
    this.#host = host;
    this.#routes = routes.map(([p, render]) => [
      new URLPattern(p, this.#baseURL),
      render,
    ]);
    this.#host.addController(this);
  }

  #onHashChange = () => this.#host.requestUpdate();

  hostConnected() {
    window.addEventListener('hashchange', this.#onHashChange);
  }

  hostDisconnected() {
    window.removeEventListener('hashchange', this.#onHashChange);
  }

  render() {
    const path = window.location.hash.substring(1) || '/';
    const url = new URL(path, this.#baseURL).href;

    for (const [pattern, render] of this.#routes) {
      const result = pattern.exec(url);
      if (result) return render(result.pathname.groups);
    }

    return null;
  }
}

HashRouterExample.js

import { LitElement, html } from 'lit';
import { HashRouter } from './HashRouter.js';

class Example extends LitElement {
  #router = new HashRouter(this, [
    ['/', () => html`<h1>hello world</h1>`],
    ['/a', () => html`<h1>A</h1>`],
    ['/:id', (result) => html`<h1>${result.pathname.groups.id}</h1>`],
  ]);

  render() {
    return this.#router.render();
  }
}

customElements.define('example', Example);