service-worker.js

const CACHE_NAME = 'timer-app-v1';
const urlsToCache = [
    './',
    './index.html',
    './index.css',
    './index.js',
    './manifest.json'
];

// Install event
self.addEventListener('install', event => {
    event.waitUntil(
        caches.open(CACHE_NAME).then(cache => {
            return cache.addAll(urlsToCache);
        })
    );
});

// Activate event
self.addEventListener('activate', event => {
    event.waitUntil(
        caches.keys().then(cacheNames => {
            return Promise.all(
                cacheNames.map(cacheName => {
                    if (cacheName !== CACHE_NAME) {
                        return caches.delete(cacheName);
                    }
                })
            );
        })
    );
});

// Fetch event - Network first, then cache
self.addEventListener('fetch', event => {
    event.respondWith(
        fetch(event.request)
            .then(response => {
                // Clone the response
                const responseClone = response.clone();
                
                // Update cache with new response
                caches.open(CACHE_NAME).then(cache => {
                    cache.put(event.request, responseClone);
                });
                
                return response;
            })
            .catch(() => {
                // Offline: return from cache
                return caches.match(event.request).then(response => {
                    return response || caches.match('./index.html');
                });
            })
    );
});