Create a PWA with Sveltekit | Svelte

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 like them both.

So, on this weekend I wanted to turn one of my SvelteKit projects into a PWA. When I wanted to do the same with NextJs projects there were a lot of tutorials. But I couldn't find many guides for svelte beginners.

That's because svelte has pwa functionality built into it.

Note !

Basic things for all PWAs

A website
manifest.json [ basic icons,names,shortcuts]
service-worker [ for offline cache ]

So let's get on with it.

First:

We'll create a demo Sveltekit project:

npm init svelte@next my-app

Then we'll choose a simple config in vite for the sake of this article:

Choose typescript because #typescriptgang:

Now we have a demo project set up with typescript, it will be straight-forward from here on:

Let's get into our directory:

cd my-app

And run:

yarn

After that,

In the /static directory, We'll create a manifest.json.
When svelte compiles the whole application, it copies static files over to the build folder.

	{
	"short_name": "svelte-pwa",
	"name": "svelte-test-pwa",
	"start_url": "/",
	"icons": [
	{
	"src": "logo_512.png",
	"type": "image/png",
	"sizes": "512x512"
	}
	],
	"background_color": "#3367D6",
	"display": "standalone",
	"scope": "/",
	"theme_color": "#3367D6",
	"shortcuts": [
	{
	"name": "How's weather today?",
	"short_name": "Today",
	"description": "View weather information for today",
	"url": "/today?source=pwa",
	"icons": [{ "src": "/icons/logo_192.png", "sizes": "192x192" }]
	},
	{
	"name": "How's weather tomorrow?",
	"short_name": "Tomorrow",
	"description": "View weather information for tomorrow",
	"url": "/tomorrow?source=pwa",
	"icons": [{ "src": "/icons/logo_192.png", "sizes": "192x192" }]
	}
	],
	"description": "Lofi to lofi beats, while using the scratchpad to list down tasks and thoughts"
	}

view raw manifest.json hosted with ❤ by GitHub

Then we'll refer our manifest.json in src/app.html.

And finally we'll create our src/service-worker.ts

Svelte will automatically detect the service-worker in the src folder's root and then register our service worker during build.
Isn't that neat?

	/// <reference lib="webworker" />

	import { build, files, timestamp } from '$service-worker';

	const worker = (self as unknown) as ServiceWorkerGlobalScope;
	const FILES = `cache${timestamp}`;

	// `build` is an array of all the files generated by the bundler,
	// `files` is an array of everything in the `static` directory
	const to_cache = build.concat(files);
	const staticAssets = new Set(to_cache);

	worker.addEventListener('install', (event) => {
	event.waitUntil(
	caches
	.open(FILES)
	.then((cache) => cache.addAll(to_cache))
	.then(() => {
	worker.skipWaiting();
	})
	);
	});

	worker.addEventListener('activate', (event) => {
	event.waitUntil(
	caches.keys().then(async (keys) => {
	// delete old caches
	for (const key of keys) {
	if (key !== FILES) 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(`offline${timestamp}`);

	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 = url.host === self.location.host && staticAssets.has(url.pathname);
	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);
	})()
	);
	}
	});