service-worker.js

self.addEventListener("install", function (event) {
    event.waitUntil(preLoad());
});

self.addEventListener("fetch", function (event) {
    event.respondWith(checkResponse(event.request).catch(function () {
        console.log("Fetch from cache successful!")
        return returnFromCache(event.request);
    }));
    console.log("Fetch successful!")
    event.waitUntil(addToCache(event.request));
});
self.addEventListener('sync', event => {
    if (event.tag === 'Sync from cache') {
        console.log("Sync successful!")
    }
});
self.addEventListener('push', function (event) {
    if (event && event.data) {
        var data = event.data.json();
        if (data.method == "PushMessageData") {
            console.log("Push notification sent");
            event.waitUntil(self.registration.showNotification("RED STORE", {body: data.message}))
        }
    }
})

var filesToCache = [
    '/index.html',
    '/checkout.html',
    '/contact.html',
    '/cart.html',
    '/detail.html',
    '/shop.html'
];

var preLoad = function () {
    return caches.open("offline").then(function (cache) { // caching index and important routes
        return cache.addAll(filesToCache);
    });
};

self.addEventListener("fetch", function (event) {
    event.respondWith(checkResponse(event.request).catch(function () {
        return returnFromCache(event.request);
    }));
    event.waitUntil(addToCache(event.request));
});

var checkResponse = function (request) {
    return new Promise(function (fulfill, reject) {
        fetch(request).then(function (response) {
            if (response.status !== 404) {
                fulfill(response);


            } else {
                reject();
            }
        }, reject);
    });
};

var addToCache = function (request) {
    return caches.open("offline").then(function (cache) {
        return fetch(request).then(function (response) {
            return cache.put(request, response);
        });
    });
};

var returnFromCache = function (request) {
    return caches.open("offline").then(function (cache) {
        return cache.match(request).then(function (matching) {
            if (! matching || matching.status == 404) {
                return cache.match("index.html");
            } else {
                return matching;
            }
        });
    });
};