sw.js

var CACHE_NAME = 'my-site-cache-v1';
var urlsToCache = [
    '/app.html',
    '/app.js',
    '/app.css',
    '/index.html',
    '/index.js'
];


self.addEventListener('install', function (event) {
    event.waitUntil(
        caches.open(CACHE_NAME)
            .then(function (cache) {
                console.log('Opened cache');
                return cache.addAll(urlsToCache);
            })
    );
});

self.addEventListener('activate', function (event) {
    event.waitUntil(
        caches.keys().then((keyList) => {
            return Promise.all(keyList.map((key) => {
                if (key !== CACHE_NAME) {
                    console.log('Removing old cache', key);
                    return caches.delete(key);
                }
            }));
        })
    );
})

self.addEventListener('fetch', function (event) {
    event.respondWith(
        caches.match(event.request)
            .then(function (response) {
                if (response) {
                    return response;
                }

                return fetch(event.request).then(
                    function (response) {
                        if (!response || response.status !== 200 || response.type !== 'basic') {
                            return response;
                        }
                        var responseToCache = response.clone();

                        caches.open(CACHE_NAME)
                            .then(function (cache) {
                                cache.put(event.request, responseToCache);
                            });

                        return response;
                    }
                );
            })
    );
});