hash路由的实现

<div class="container">
    <nav>
        <p><a href="#/">home</a></p>
        <p><a href="#/article">article</a></p>
        <p><a href="#/archive#a=1">archive#a=1</a></p>
        <p><a href="#/about">about</a></p>
    </nav>
    <div id="app"></div>
</div>
<script type="text/babel">
const { useState, useEffect, useMemo } = React;

const Home = () => {
  const [count, setCount] = useState(0);
  const [nowtime, setNowtime] = useState(0);
  const sum = useMemo(() => ((1 + count) * count) / 2 + " ,random: " + Math.random(), [count]);

  return (
      <div>
          <h1>Home Page</h1>
          <p> count: {count}</p>
          <p> sum: {sum}</p>
          <p> nowtime: {nowtime}</p>
          <button onClick={() => setCount(count + 1)}> add 1 </button>
          <button onClick={() => setNowtime(Date.now())}> set now time </button>
      </div>
  );
};
const About = () => {
  return (
      <div>
          <h1>About Page</h1>
      </div>
  );
};
const NotFound404 = () => {
  return (
      <div>
          <h1>404 Page</h1>
      </div>
  );
};
// ReactDOM.render(<Home />, document.getElementById("app"));
const routes = [
  {
      path: "/",
      name: "home",
      component: <Home />,
  },
  {
      path: "/about",
      name: "about",
      component: <About />,
  },
  {
      path: "*",
      name: "404",
      component: <NotFound404 />,
  },
];
const router = new HashRouter();
router.on("change", (currentUrl, lastUrl) => {
  console.log(currentUrl, lastUrl);
  let route = null;
  for (let i = 0, len = routes.length; i < len; i++) {
      const item = routes[i];
      if (currentUrl === item.path) {
          route = item;
          break;
      }
  }
  if (!route) {
      route = routes[routes.length - 1];
  }
  ReactDOM.render(route.component, document.getElementById("app"));
});
</script>

class HashRouter {
  currentUrl = "";
  handlers = {};

  constructor() {
      // this.hashChange();
      this.refresh = this.refresh.bind(this);
      window.addEventListener("load", this.refresh, false);
      window.addEventListener("hashchange", this.refresh, false);
  }
  getHashPath(url) {
      const index = url.indexOf("#");
      if (index >= 0) {
          return url.slice(index + 1);
      }
      return "/";
  }
  refresh(event) {
      let curURL = "",
          oldURL = null;
      if (event.newURL) {
          oldURL = this.getHashPath(event.oldURL || "");
          curURL = this.getHashPath(event.newURL || "");
      } else {
          curURL = this.getHashPath(window.location.hash);
      }
      this.currentUrl = curURL;
      this.emit("change", curURL, oldURL);
  }
  on(evName, listener) {
      this.handlers[evName] = listener;
  }
  emit(evName, ...args) {
      const handler = this.handlers[evName];
      if (handler) {
          handler(...args);
      }
  }
}