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Create a PWA with Sveltekit | Svelte

Navin Kodag on June 27, 2021

I've been using sveltekit and svelte for over a year now. I'm also waiting for it to be matured enough to beat NextJs in terms of community. But I ...

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Justin Golden • Jan 26 '22

Hi, wondering if it's possible to simply cache everything rather than just what the user sees. It seems if they install with this sw and then open the app the first time offline, they don't have anything cached. Also, if they navigate to another page or load a font, it fails if offline. My whole app is < 1mb and I'd love to just cache it all on install. Thanks in advance.

Love this article by the way

SwiftWinds • May 1 '22 • Edited

I've modified Navin's service worker to do just that:

import { build, files, version } from "$service-worker";

const worker = self as unknown as ServiceWorkerGlobalScope;
const STATIC_CACHE_NAME = `cache${version}`;
const APP_CACHE_NAME = `offline${version}`;

// hard-coded list of app routes we want to preemptively cache
const routes = ["/"];

// hard-coded list of other assets necessary for page load outside our domain
const customAssets = [
  "https://fonts.googleapis.com/css2?family=Inter:wght@400;700;800&display=swap",
  "https://unpkg.com/ress/dist/ress.min.css",
  "https://fonts.gstatic.com/s/inter/v11/UcC73FwrK3iLTeHuS_fvQtMwCp50KnMa1ZL7W0Q5nw.woff2",
];

// `build` is an array of all the files generated by the bundler,
// `files` is an array of everything in the `static` directory
// `version` is the current version of the app

const addDomain = (assets: string[]) =>
  assets.map((f) => self.location.origin + f);

// we filter the files because we don't want to cache logos for iOS
// (they're big and largely unused)
// also, we add the domain to our assets, so we can differentiate routes of our
// app from those of other apps that we cache
const ourAssets = addDomain([
  ...files.filter((f) => !/\/icons\/(apple.*?|original.png)/.test(f)),
  ...build,
  ...routes,
]);

const toCache = [...ourAssets, ...customAssets];
const staticAssets = new Set(toCache);

worker.addEventListener("install", (event) => {
  event.waitUntil(
    caches
      .open(STATIC_CACHE_NAME)
      .then((cache) => {
        return cache.addAll(toCache);
      })
      .then(() => {
        worker.skipWaiting();
      })
  );
});

worker.addEventListener("activate", (event) => {
  event.waitUntil(
    caches.keys().then(async (keys) => {
      // delete old caches
      for (const key of keys) {
        if (key !== STATIC_CACHE_NAME && key !== APP_CACHE_NAME) {
          await caches.delete(key);
        }
      }

      worker.clients.claim();
    })
  );
});

/**
 * Fetch the asset from the network and store it in the cache.
 * Fall back to the cache if the user is offline.
 */
async function fetchAndCache(request: Request) {
  const cache = await caches.open(APP_CACHE_NAME);

  try {
    const response = await fetch(request);
    cache.put(request, response.clone());
    return response;
  } catch (err) {
    const response = await cache.match(request);
    if (response) {
      return response;
    }

    throw err;
  }
}

worker.addEventListener("fetch", (event) => {
  if (event.request.method !== "GET" || event.request.headers.has("range")) {
    return;
  }

  const url = new URL(event.request.url);

  // don't try to handle e.g. data: URIs
  const isHttp = url.protocol.startsWith("http");
  const isDevServerRequest =
    url.hostname === self.location.hostname && url.port !== self.location.port;
  const isStaticAsset = staticAssets.has(url.href);
  const skipBecauseUncached =
    event.request.cache === "only-if-cached" && !isStaticAsset;

  if (isHttp && !isDevServerRequest && !skipBecauseUncached) {
    event.respondWith(
      (async () => {
        // always serve static files and bundler-generated assets from cache.
        // if your application has other URLs with data that will never change,
        // set this variable to true for them, and they will only be fetched once.
        const cachedAsset =
          isStaticAsset && (await caches.match(event.request));

        return cachedAsset || fetchAndCache(event.request);
      })()
    );
  }
});

Simply set the routes array to a list of all routes you want to cache and add URLs to fonts, external CSS, etc. that you want to cache to the customAssets array.

Note that I use a cache-only strategy, so upon updating your app, you'll have to refresh the app twice to see the new content. You can fix this by either employing an instant force refresh (see codyanhorn.tech/blog/pwa-reload-pa...) or notify the user that an update is available (see medium.com/progressive-web-apps/pw...)

Justin Golden • Jun 1 '22

Awesome! Thanks : )

SwiftWinds • Jun 1 '22

No prob! :)

m1212e • Jan 25 '22

Hi, are we allowed to use the service worker snippet? Under which license does your project stand?

Navin Kodag • Feb 5 '22

You can use it to your liking

Dan Tavelli • Oct 22 '21

hey good article. i used this setup for a sveltekit app and it works great but i was having issue with subsequent updates. it would never pick up the new deploy because the index.html was cached i believe? i am also using the static prerender sveltekit adapter so possibly that is related. i ended up having to modify app.html for it to detect a change and then it would pick up the new service worker. have you run into this issue?

Navin Kodag • Oct 23 '21 • Edited

I use the vercel adapter when deploying. I haven't used ssg with sveltekit yet. But I do have an issue whenever I upgrade the packages. Sveltekit throws module not defined errors if i don't set the version to "next" instead of something like "^1.0.0". Have you joined their discord server?

SwiftWinds • May 2 '22

I was having the same issue, but I modified his script slightly and it worked again. See my comment above :)

Eastcoast7624 • Jan 7 '23

I tried to follow your tutorial but I got an error:

RollupError: "timestamp" is not exported by ".svelte-kit/generated/service-worker.js", imported by "src/service-worker.ts".

Do you know anything about this? I'm at a loss as how to fix this.

Kevin Williams • May 26 '24

If you still need an answer, change timestamp to version. I followed the Svelte docs for service workers. Be sure to change timestamp anywhere it appears in your code as well.

Ade • Feb 9 '22

Navin, used your code but the serviceworker is not being registered. It's giving me a 404 error. I added the serviceworker to src folder, manifest in static as in your code.

Is your code still working after their latest update? In the sveltekit doc, they mentioned that vite register the serviceworker. Is there any configuration for vite registering the service worker?