sw.js

const MAIN_CACHE = 'main';

self.addEventListener("install", async (event) => {
    event.waitUntil((async () => {
        const cacheKeys = await caches.keys()
        await Promise.all(cacheKeys.map(name => caches.delete(name)))

        const cache = await caches.open(MAIN_CACHE)
        await cache.addAll(['.'])
    })())
});
  
const cacheFirst = (event) => {

    if (event.request.method.toLowerCase() != 'get') return
    if (event.request.headers.get('Range') != null) return
    
    const requestUrl = new URL(event.request.url)
    
    if (requestUrl.protocol != 'http:' && requestUrl.protocol != 'https:') return;

    event.respondWith((async ()=>{
        const cache = await caches.open(MAIN_CACHE)

        const responsePromise = fetch(event.request).then((response) => {
            if (response.ok) cache.put(event.request, response.clone())
            return response
        })

        let cacheResponse = await caches.match(event.request)

        return cacheResponse || await responsePromise
    })())
};

self.addEventListener('fetch', cacheFirst);