service-worker.js

self.addEventListener("install", (event) => {
  console.info("Service worker installed.", event)
})

self.addEventListener("activate", (event) => {
  console.info("Service worker activated.", event)
})

const CACHE_NAME = "APP-V0"
const FILES_TO_CACHE = ["/index.html", "/js/app.js", "/manifest.json"]
const FILE_ALIASES = new Map([["/", "/index.html"]])

const normalizeUrl = (url) => {
  const url_ = new URL(url)
  url_.pathname = url_.pathname.replace(/\/+/g, "/").replace(/\/$/, "")
  if (FILE_ALIASES.has(url_.pathname)) {
    url_.pathname = FILE_ALIASES.get(url_.pathname)
  }
  return url_.href
}

self.addEventListener("install", async () => {
  const cache = await caches.open(CACHE_NAME)
  const additions = cache.addAll(FILES_TO_CACHE)
  await additions
  console.info(`Files cached: [\n  ${FILES_TO_CACHE.join(`,\n  `)}\n]`)
})

self.addEventListener("activate", async () => {
  const oldCacheKeys = (await caches.keys()).filter((key) => key != CACHE_NAME)
  oldCacheKeys.forEach((key) => caches.delete(key))
})

self.addEventListener("fetch", (event) => {
  const normalizedUrl = normalizeUrl(event.request.url)
  let response = fetch(event.request)
  if (FILES_TO_CACHE.includes(normalizedUrl)) {
    response = response
      .then(async (response) => {
        const cache = await caches.open(CACHE_NAME)
        await cache.put(normalizedUrl, response.clone())
        return response
      })
      .catch(() => caches.match(normalizedUrl))
      .catch(() => null)
  }
  event.respondWith(response)
})