sw.js

const CACHE = 'v1';

self.addEventListener('install', function (event) {
    console.log('The service worker is being installed.');
    event.waitUntil(precache());
});

self.addEventListener('fetch', function (event) {
    console.log('The service worker is serving the assets.');
    event.respondWith(fromProxy(event.request));
});

function precache() {
    return caches.open(CACHE).then(function (cache) {
        return cache.addAll([
            '/',
            '/index.html',
            '/assets/script.js',
            '/assets/style.css',
            '/data/conf.json',
        ]);
    });
}

function fromProxy(request) {
    return caches.open(CACHE).then(function (cache) {
        return cache.match(request).then(function (matching) {
            return matching || fetch(request);
        });
    });
}