I'm building an PWA with limited offline capability, I'm using this code to save page content to dynamic cache every time user visits a new url:
self.addEventListener('fetch', function(event) {
event.respondWith(
fetch(event.request)
.then(function(res) {
return caches.open('cache')
.then(function(cache) {
cache.put(event.request.url, res.clone());
return res;
})
})
.catch(function(err) {
console.log( err );
return caches.match(event.request);
})
);
});
This works great, after a page is loaded all of it assets are cached and can be seen in offline mode.
But, I would also like to add the option to automatically cache some of the more important urls when the user comes back online.
I do that by putting the list of urls in the array, loop through it and send a fetch request to each url, so those pages can be cached without user visiting/revisiting the page.
Problem is that when I do that some of the assets on some pages are not cached, for example google map on one page, is there a way to simulate real visit to a page, that gets all of the assets from an url with fetch request?
Fetch code:
function fillDynamicCache(user_id = false) {
let urls = [
'/homepage',
'/someotherpage',
'/thirdpage',
'/...',
];
urls.map((url, id) => (
fetch(url)
.then(
function(response) {
if (response.status !== 200) {
console.log('Looks like there was a problem. Status Code: ' +
response.status);
return;
}
console.log( 'in fetch: ' + url );
}
)
.catch(function(err) {
console.log('Fetch Error :-S', err);
})
));
}
self.addEventListener('message', (event) => {
// refresh cache when user comes back online
if (event.data == 'is_online') {
fillDynamicCache();
} else if (event.data == 'is_updated') {
self.skipWaiting();
Typically if you have important assets you want to provide the users, even when they are offline, you should consider an offline first strategy, meaning you prefetch those resources while the service worker is installing.
This way the matching requests will be served from the cache, improving the performance because you skip the relative network calls entirely.
In case the target resources tend to update/change frequently on the server, then you can opt for a stale while revalidate strategy (after the data is provided from the cache, the SW will update its value with a newer one from the network, if available) or even network first, fallback to cache, the latter if you want to provide always the latest values and provide cache data only if the network connection times out or is unavailable.
I wrote an article about service worker and caching strategies, in case you want to go deeper into the topic.
Related
Although I see similar questions regarding the subject, there are not the same. So, I have a pwa app that is basically a simple form that users must fill out. The service worker catch the resources and serves to the app, as usual. The strategy is 'cache first, then network'. All is ok, when is onLine, BUT in offLine mode, the cached resources are not used by the app, I mean, in spite that (you can see) in the cache are the resources(fetch requests) that the app needs, it anyway try to fetch to the web and obviously because there is offLine, the fetch fail and the app crash. So, the code lines ...
caches.match(e.request)
.then( res => {
if (res ){
return res;
}
...
is not working. My question....Why???.
I will appreciate you help/comments.
You should add some more context and code, to let others better understand your situation.
Do you serve data from the cache like the following example?
self.addEventListener('fetch', function(event) {
event.respondWith(
caches.open('mysite-dynamic').then(function(cache) {
return cache.match(event.request).then(function (response) {
return response || fetch(event.request).then(function(response) {
cache.put(event.request, response.clone());
return response;
});
});
})
);
});
I transformed my React application into a PWA and it is working partially fine.
I followed this tutorial: https://medium.com/#toricpope/transform-a-react-app-into-a-progressive-web-app-pwa-dea336bd96e6
However this article only shows how to cache static data and I also need to store data stemming from the server, I could do this following the instruction of the first answer of this post: How can I cache data from API to Cache Storage in React PWA? and inserting the firebase adresses where the data is stored into the array urlsToCache, populated by the files that should be stored into the cache.
So far so good, however after the data be stored into the cache, the application stops fetching data from the server and loads the page only with data from the cache, even if the server is updated. This is what I need to fix.
In short, I need to fetch the data from the server, store it into the cache in order to use it when the application is offline and update the cache every time the server is reached.
I am trying to follow this guide, but without success: https://developers.google.com/web/fundamentals/instant-and-offline/offline-cookbook/#serving-suggestions
This is my worker.js file:
var CACHE_NAME = 'pwa-task-manager';
var urlsToCache = [
'/',
'/completed',
'/index.html',
'/static/js/main.chunk.js',
'/static/js/0.chunk.js',
'/static/js/1.chunk.js',
'/static/js/bundle.js',
'/calculadora',
'https://calc-marmo.firebaseio.com/clientes.json',
'https://calc-marmo.firebaseio.com/adm.json',
];
// Install a service worker
self.addEventListener('install', event => {
// Perform install steps
event.waitUntil(
caches.open(CACHE_NAME)
.then(function(cache) {
console.log('Opened cache');
return cache.addAll(urlsToCache);
})
);
});
// Cache and return requests
self.addEventListener('fetch', event => {
event.respondWith(
caches.match(event.request)
.then(function(response) {
// Cache hit - return response
if (response) {
return response;
}
return fetch(event.request);
}
)
);
});
// Update a service worker
self.addEventListener('activate', event => {
var cacheWhitelist = ['pwa-task-manager'];
event.waitUntil(
caches.keys().then(cacheNames => {
return Promise.all(
cacheNames.map(cacheName => {
if (cacheWhitelist.indexOf(cacheName) === -1) {
return caches.delete(cacheName);
}
})
);
})
);
});
Any help would be much appreciated.
This sound like you need a Network First strategy which is not mention in the cookbook. This strategy is similar to Network falling back to cache but additionally stores the response always in the cache.
Explanation: https://developers.google.com/web/tools/workbox/modules/workbox-strategies#network_first_network_falling_back_to_cache
Code sample (if you don't use workbox): https://gist.github.com/JMPerez/8ca8d5ffcc0cc45a8b4e1c279efd8a94
I have this one-page app with a dynamic URL built with a token, like example.com/XV252GTH and various assets, like css, favicon and such.
Here is how I register the Service Worker:
navigator.serviceWorker.register('sw.js');
And in said sw.js, I pre-cache the assets while installing:
var cacheName = 'v1';
var cacheAssets = [
'index.html',
'app.js',
'style.css',
'favicon.ico'
];
function precache() {
return caches.open(cacheName).then(function (cache) {
return cache.addAll(cacheAssets);
});
}
self.addEventListener('install', function(event) {
event.waitUntil(precache());
});
Note that the index.html (that registers the Service Worker) page is just a template, that gets populated on the server before being sent to the client ; so in this pre-caching phase, I'm only caching the template, not the page.
Now, in the fetch event, any requested resource that is not in the cache gets copied to it:
addEventListener('fetch', event => {
event.respondWith(async function() {
const cachedResponse = await caches.match(event.request);
if (cachedResponse) return cachedResponse;
return fetch(event.request).then(updateCache(event.request));
}());
});
Using this update function
function updateCache(request) {
return caches.open(cacheName).then(cache => {
return fetch(request).then(response => {
const resClone = response.clone();
if (response.status < 400)
return cache.put(request, resClone);
return response;
});
});
}
At this stage, all the assets are in the cache, but not the dynamically generated page. Only after a reload, can I see another entry in the cache: /XV252GTH. Now, the app is offline-ready ; But this reloading of the page kind of defeats the whole Service Worker purpose.
Question: How can I send the request (/XV252GTH) from the client (the page that registers the worker) to the SW? I guess I can set up a listener in sw.js
self.addEventListener('message', function(event){
updateCache(event.request)
});
But how can I be sure that it will be honored in time, ie: sent by the client after the SW has finished installing? What is a good practice in this case?
OK, I got the answer from this page: To cache the very page that registers the worker at activation time, just list all the SW's clients, and get their URL (href attribute).
self.clients.matchAll({includeUncontrolled: true}).then(clients => {
for (const client of clients) {
updateCache(new URL(client.url).href);
}
});
Correct me if I understood you wrong!
You precache your files right here:
var cacheAssets = [
'index.html',
'app.js',
'style.css',
'favicon.ico'
];
function precache() {
return caches.open(cacheName).then(function (cache) {
return cache.addAll(cacheAssets);
});
}
It should be clear that you cache the template since you cache it before the site gets build and this approach is not wrong, at least not for all types of files.
Your favicon.ico for example is a file that you would probably consider as static. Also, it does not change very often or not at all and it isn't dynamic like your index.html.
Source
It should also be clear why you have the correct version after reloading the page since you have an update function.
The solution to this problem is the answer to your question:
How can I send the request (/XV252GTH) from the client (the page that registers the worker) to the SW?
Instead of caching it before the service-worker is installed you want to cache it if the back end built your web page. So here is how it works:
You have an empty cache or at least a cache without your index.html.
Normally a request would be sent to the server to get the index.html. Instead, we do a request to the cache and check if the index.html is in the cache, at least if you load the page for the first time.
Since there is no match in the cache, do a request to the server to fetch it. This is the same request the page would do if it would load the page normally. So the server builds your index.html and sends it back to the page.
After receiving the index.html load it to the page and store it in the cache.
An example method would be Stale-while-revalidate:
If there's a cached version available, use it, but fetch an update for next time.
self.addEventListener('fetch', function(event) {
event.respondWith(
caches.open('mysite-dynamic').then(function(cache) {
return cache.match(event.request).then(function(response) {
var fetchPromise = fetch(event.request).then(function(networkResponse) {
cache.put(event.request, networkResponse.clone());
return networkResponse;
})
return response || fetchPromise;
})
})
);
});
Source
Those are the basics for your problem. Now you got a wide variety of options you can choose from that use the same method but have some additional features. Which one you choose is up to you and without knowing your project in detail no one can tell you which one to choose. You are also not limited to one option. In some cases you might combine two or more options together.
Google wrote a great guide about all the options you have and provided code examples for everything. They also explained your current version. Not every option will be interesting and relevant for you but I recommend you to read them all and read them thoroughly.
This is the way to go.
I have a React app created by using create-react-app. By default, this tool creates a serviceWorker.js file for us and I am using this to register a service-worker. Furthermore, the documents suggest using google's workbox wizard to create a service-worker.js used to manage my website for offline purposes. The goal is for me to store an offline.html page in the browsers cache and whenever there is no online connection, render the cached offline.html page.
I am successful in storing the offline.html in cache and as you can see below, it is stored in the precached URLS (check last two rows).
I can also manually navigate to the offline.html if i change the URL in my browser.
However, I am having trouble automatically grabbing this file and rendering it whenever there isn't a connection.
In the serviceWorker.js code that is generated for me from CRA theres a function called checkValidServiceWorker:
function checkValidServiceWorker(swUrl, config) {
// Check if the service worker can be found. If it can't reload the page.
fetch(swUrl)
.then(response => {
// Ensure service worker exists, and that we really are getting a JS file.
const contentType = response.headers.get('content-type');
if (
response.status === 404 ||
(contentType != null && contentType.indexOf('javascript') === -1)
) {
// No service worker found. Probably a different app. Reload the page.
navigator.serviceWorker.ready.then(registration => {
registration.unregister().then(() => {
window.location.reload();
});
});
} else {
// Service worker found. Proceed as normal.
registerValidSW(swUrl, config);
}
})
.catch(() => {
console.log(
'No internet connection found. App is running in offline mode.'
);
const OFFLINE_URL = '/.offline/offline.html';
return caches.match(OFFLINE_URL).then((response) => {
console.log(response)
});
});
}
So in the catch part of the function, I want to do my redirect because thats the logic that runs when we are offline. I read a lot of docs and my current solution doesn't work. Any ideas on how to redirect in my serviceWorker?
I'm currently considering adding service workers to a Web app I'm building.
This app is, essentially, a collection manager. You can CRUD items of various types and they are usually tightly linked together (e.g. A hasMany B hasMany C).
sw-toolbox offers a toolbox.fastest handler which goes to the cache and then to the network (in 99% of the cases, cache will be faster), updating the cache in the background. What I'm wondering is how you can be notified that there's a new version of the page available. My intent is to show the cached version and, then, if the network fetch got a newer version, to suggest to the user to refresh the page in order to see the latest edits. I saw something in a YouTube video a while ago but the presenter gives no clue of how to deal with this.
Is that possible? Is there some event handler or promise that I could bind to the request so that I know when the newer version is retrieved? I would then post a message to the page to show a notification.
If not, I know I can use toolbox.networkFirst along with a reasonable timeout to make the pages available even on Lie-Fi, but it's not as good.
I just stumbled accross the Mozilla Service Worker Cookbooj, which includes more or less what I wanted: https://serviceworke.rs/strategy-cache-update-and-refresh.html
Here are the relevant parts (not my code: copied here for convenience).
Fetch methods for the worker
// On fetch, use cache but update the entry with the latest contents from the server.
self.addEventListener('fetch', function(evt) {
console.log('The service worker is serving the asset.');
// You can use respondWith() to answer ASAP…
evt.respondWith(fromCache(evt.request));
// ...and waitUntil() to prevent the worker to be killed until the cache is updated.
evt.waitUntil(
update(evt.request)
// Finally, send a message to the client to inform it about the resource is up to date.
.then(refresh)
);
});
// Open the cache where the assets were stored and search for the requested resource. Notice that in case of no matching, the promise still resolves but it does with undefined as value.
function fromCache(request) {
return caches.open(CACHE).then(function (cache) {
return cache.match(request);
});
}
// Update consists in opening the cache, performing a network request and storing the new response data.
function update(request) {
return caches.open(CACHE).then(function (cache) {
return fetch(request).then(function (response) {
return cache.put(request, response.clone()).then(function () {
return response;
});
});
});
}
// Sends a message to the clients.
function refresh(response) {
return self.clients.matchAll().then(function (clients) {
clients.forEach(function (client) {
// Encode which resource has been updated. By including the ETag the client can check if the content has changed.
var message = {
type: 'refresh',
url: response.url,
// Notice not all servers return the ETag header. If this is not provided you should use other cache headers or rely on your own means to check if the content has changed.
eTag: response.headers.get('ETag')
};
// Tell the client about the update.
client.postMessage(JSON.stringify(message));
});
});
}
Handling of the "resource was updated" message
navigator.serviceWorker.onmessage = function (evt) {
var message = JSON.parse(evt.data);
var isRefresh = message.type === 'refresh';
var isAsset = message.url.includes('asset');
var lastETag = localStorage.currentETag;
// ETag header usually contains the hash of the resource so it is a very effective way of check for fresh content.
var isNew = lastETag !== message.eTag;
if (isRefresh && isAsset && isNew) {
// Escape the first time (when there is no ETag yet)
if (lastETag) {
// Inform the user about the update.
notice.hidden = false;
}
//For teaching purposes, although this information is in the offline cache and it could be retrieved from the service worker, keeping track of the header in the localStorage keeps the implementation simple.
localStorage.currentETag = message.eTag;
}
};