sw.js

const PRECACHE = 'rle-sprite-editor-001';
const PRECACHE_URLS = [
    './',
    'index.html'
];

let createCacheBustedRequest = url => {
    let request = new Request(url, { cache: 'reload' });
    if ('cache' in request) {
        return request;
    }
    let bustedUrl = new URL(url, self.location.href);
    bustedUrl.search += (bustedUrl.search ? '&' : '') + 'cachebust=' + Date.now();
    return new Request(bustedUrl);
}

self.addEventListener('install', event => {
    event.waitUntil(
        caches.open(PRECACHE)
        .then(cache => cache.addAll(PRECACHE_URLS))
        .then(self.skipWaiting())
    );
});

self.addEventListener('activate', event => {
    const currentCaches = [PRECACHE];
    event.waitUntil(
        caches.keys().then(cacheNames => {
            return cacheNames.filter(cacheName => !currentCaches.includes(cacheName));
        }).then(cachesToDelete => {
            return Promise.all(cachesToDelete.map(cacheToDelete => {
                return caches.delete(cacheToDelete);
            }));
        }).then(() => self.clients.claim())
    );
});

self.addEventListener('fetch', event => {
    if (
        event.request.mode === 'navigate' ||
        (event.request.method === 'GET' && event.request.headers.get('accept').indexOf('text/html') > -1)
    ) {
        event.respondWith(fetch(createCacheBustedRequest(event.request.url)).then(response => {
            caches.open(PRECACHE).then(cache => cache.put(event.request.url, response.clone()));
            return response.clone();
        }).catch(error => {
            return caches.match(event.request.url);
        }));
    }
});