sw.js

const CACHE_NAME = 'c25k-cache-v1';
const ASSETS = [
  './',
  './index.html',
  './style.css',
  './nav.css',
  './settings.css',
  './app.js',
  './manifest.json'
];
self.addEventListener('install', e => {
  e.waitUntil(caches.open(CACHE_NAME).then(c=>c.addAll(ASSETS)));
});
self.addEventListener('activate', e => {
  e.waitUntil(caches.keys().then(keys=>Promise.all(keys.filter(k=>k!==CACHE_NAME).map(k=>caches.delete(k)))));
});
self.addEventListener('fetch', e => {
  if(e.request.method !== 'GET') return;
  e.respondWith(
    caches.match(e.request).then(res=> res || fetch(e.request).then(netRes=>{
      if(netRes.status===200 && netRes.type==='basic'){
        const clone = netRes.clone();
        caches.open(CACHE_NAME).then(c=>c.put(e.request, clone));
      }
      return netRes;
    }).catch(()=> caches.match('./index.html')))
  );
});