sw.js

const CACHE_NAME = 'html-parser-pwa-v1';
const OFFLINE_URL = '.';

self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(CACHE_NAME).then(cache => 
      cache.addAll([
        '.',
        './index.html',
        './manifest.json',
        './sw.js',
        './icons/icon-192.png',
        './icons/icon-512.png'
      ])
    )
  );
});

self.addEventListener('activate', event => {
  event.waitUntil(
    caches.keys().then(keys => Promise.all(
      keys.filter(k => k !== CACHE_NAME).map(k => caches.delete(k))
    ))
  );
});

self.addEventListener('fetch', event => {
  event.respondWith(
    fetch(event.request)
      .catch(() => caches.match(event.request).then(r => r || caches.match(OFFLINE_URL)))
  );
});