Name: Convert Svelte to PWA.
Rating: 4.1 (3808 reviews)
Author: alishgiri

Step 1

Create a folder called service-worker inside src/ folder.

Step 2

Create a new file called index.ts or index.js inside src/service-worker/ folder with the following contents.

/// <reference types="@sveltejs/kit" />

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

const CACHE = `cache-${version}`;

const ASSETS = [
    ...build, // the app itself
    ...files // everything in `static`
];

self.addEventListener('install', (event) => {
    // Create a new cache and add all files to it
    async function addFilesToCache() {
        const cache = await caches.open(CACHE);
        await cache.addAll(ASSETS);
    }
    event.waitUntil(addFilesToCache());
});

self.addEventListener('activate', (event) => {
    // Remove previous cached data from disk
    async function deleteOldCaches() {
        for (const key of await caches.keys()) {
            if (key !== CACHE) await caches.delete(key);
        }
    }
    event.waitUntil(deleteOldCaches());
});

self.addEventListener('fetch', (event) => {
    // ignore POST  requests, etc
    if (event.request.method !== 'GET') return;

    async function respond() {
        const url = new URL(event.request.url);
        const cache = await caches.open(CACHE);

        // `build`/`files` can always be served from the cache
        if (ASSETS.includes(url.pathname)) {
            return cache.match(url.pathname);
        }

        // for everything else, try the network first, but
        // fall back to the cache if we're offline
        try {
            const response = await fetch(event.request);

            if (response.status === 200) {
                cache.put(event.request, response.clone());
            }

            return response;
        } catch {
            return cache.match(event.request);
        }
    }

    event.respondWith(respond());
});

Step 3

Create manifest.json file inside static/ folder with the following contents.

Logos and screenshots should be placed inside static/ folder. For this tutorial I have used static/pwa-assets/ folder.

{
    "name": "app_name",
    "description": "app_description",
    "display": "standalone",
    "start_url": "/",
    "orientation": "portrait-primary",
    "prefer_related_applications": false,
    "icons": [
        {
            "src": "pwa-assets/logo-144.png",
            "sizes": "144x144",
            "type": "image/png"
        },
        {
            "src": "pwa-assets/logo-512.png",
            "sizes": "512x512",
            "type": "image/png",
            "purpose": "maskable"
        }
    ],
    "screenshots": [
        {
            "src": "pwa-assets/app-screenshot.png",
            "sizes": "1280x720",
            "type": "image/png",
            "form_factor": "wide",
            "label": "screenshot_description_here"
        }
    ]
}

Step 4

Add the following to the head tag on the src/app.html file.

<link rel="manifest" href="/manifest.json" />

Enjoy your Svelte Progressive Web App (PWA)! 🫡