`checkValidServiceWorker()` currently doesn't cover the case where I forget to start local server

[ZYinMD]

If I forget to start the local server to serve my build, but visit it in the browser anyway, the old sw can still serve the old assets, and I may not notice. I thought part of the intention of checkValidServiceWorker() was to cover this scenario, but seems it doesn't.

something like this will cover that:

export function register() {
  if (process.env.NODE_ENV === "production" && "serviceWorker" in navigator) {
    const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
    window.addEventListener("load", async () => {
      if (isLocalhost) await validateLocalServer(swUrl);
      registerSW(swUrl);
    });
  }
}

async function validateLocalServer(swUrl: string) {
  try {
    const res = await fetch(swUrl, { headers: { "Service-Worker": "script" } }); // this throws if server isn't running
    if (res.status === 404) throw new Error("404");
  } catch (err) {
    alert(`Local server is not running, or running but no sw found. \n${err.message}`);
    return Promise.reject();
  }
}

async function registerSW(swUrl: string) {
  //...
}