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.
Related
I am trying to add a serviceworker to an existing React app with this filesystem layout:
Filesystem
Basically a bit of initialization code is stored in the public folder, and all code of importance is in the src folder. In the serviceWorker.js file, I made an array of filenames to cache and call that array in the 'install' event listener, and if I check DevTools I can see that the filenames are present in the cache: when I preview the data in Chrome DevTools however, I see that the code inside the cached files is all from index.html. In fact, I can add anything I want to the filename array and I will find it in cached storage only to find that it is storing the index.html code. It seems like no matter what file I try to add to the cache, only index.html gets loaded.
ServiceWorker.js:
let CACHE_NAME = "MG-cache-v2";
const urlsToCache = [
'/',
'/index.html',
'/src/App.js',
'/monkey'
];
self.addEventListener('install', function (event) {
//perform install steps
event.waitUntil(
caches.open(CACHE_NAME).then(function (cache) {
console.log('Opened MG_Cache');
return cache.addAll(urlsToCache);
}).catch(function (error) {
console.error("Error loading cache files: ", error);
})
);
self.skipWaiting();
});
self.addEventListener('fetch', function (event) {
event.respondWith(caches.match(event.request).then(function (response) {
if (response) {
return response;
}
return fetch(event.request);
})
);
});
self.addEventListener('activate', (event) => {
event.waitUntil(async function () {
const cacheNames = await caches.keys();
await Promise.all(
cacheNames.filter((cacheName) => {
//Return true if you want to remove this cache,
//but remember that caches are shared across the whole origin
return;
}).map(cacheName => caches.delete(cacheName))
);
})
})
Portion of index.html:
<script>
if ('serviceWorker' in navigator)
{
window.addEventListener('load', function () {
navigator.serviceWorker.register('serviceWorker.js').then(function (registration) {
// Registration was successful
console.log("ServiceWorker registration successful with scope: ", registration.scope);
}, function (err) {
// registration failed :
(console.log('ServiceWorker registration failed: ', err));
});
});
}
</script>
Google Devtools Preview:
All files are the same
I have tried a variety of naming strategies in the filename array but all have ended with the same result. At this point I'm at a complete loss.
EDIT: While this does not solve my problem, I found an answer to another problem that gives a little guidance. It seems like the server never finds the file I request and thus returns index.html. I tried placing the serviceWorker.js file in the src folder and moving the service worker registration to App.js and got an error:
`DOMException: Failed to register a ServiceWorker for scope ('http://localhost:3000/src/') with script ('http://localhost:3000/src/serviceWorker.js'): The script has an unsupported MIME type ('text/html'). `
This suggests that the server somehow doesn't have access to the src folder, only public. Any idea why that may be?
An important piece of information I left out it that I'm using Create-React-App. Because of the enforced layout of the filesystem, the serviceWorker must be placed in the public folder: at the same time, the scope of service workers by default is the folder that they are placed in. According to this answer, changing the scope of the service worker to be a level above the folder that it is in requires adding to the HTTP header response of the service worker (not entirely sure what that means), and doing something like that assumes you have some form of a local server set up. Alas, thus far I have just been using npm start to test my app and pushing onto nsmp to make the site live, thus have negleted to do any form of server implementation myself (I know, not very smart of me).
My hotfix was to create a new temporary app with the npx create-react-app my-app --template cra-template-pwa command, copy all files pertaining to service workers from that app (serviceWorkerRegistration.js, service-worker.js, index.js, potentially setupTests.js), and paste them into my app. Then I could simply follow this tutorial. Now my site works offline.
Basically, I have an online app that uses a htaccess file to silently redirect all requests in a given /folder/ to the same html. Then, to decide what to show the user, the page calls
var page_name = location.href.split('/').pop();
This works well online, but could I use a ServiceWorker to support this folder/file model while the page is offline? Or will I always get the page cannot be found error unless I explicitly cache the URLs?
What you describe can be accomplished using the App Shell model.
Your service worker's exact code might look a little different, and tools like Workbox can automate some of this for you, but a very basic, "vanilla" example of a service worker that accomplishes this is:
self.addEvenListener('install', (event) => {
const cacheShell = async () => {
const cache = await caches.open('my-cache');
await cache.add('/shell.html');
};
event.waitUntil(cacheShell());
});
self.addEventListener('fetch', (event) => {
// If this is a navigation request...
if (event.request.mode === 'navigate') {
// ...respond with the cached shell HTML.
event.respondWith(caches.match('/shell.html'));
return;
}
// Any other caching/response logic can go here.
});
Regardless of what the location.href value is, when this service worker is in control, the App Shell HTML will be used to fulfill all navigation requests.
I've got static site (generated with Pelican) with a multilingual structure, e.g.
www.example.com/
www.example.com/index.html
www.example.com/page1.html
www.example.com/es/
www.example.com/es/index.html
www.example.com/es/page1.html
I've cached the JS and CSS and the index files with a service worker install event:
const staticCacheName = 'static-cache-v5';
const filesToCache = [
'/',
'/index.html',
'/es/index.html',
'/offline.html',
'static/js/main..js',
'static/css/styles.css',
]
self.addEventListener('install', (event) => {
event.waitUntil(
caches.open(staticCacheName).then((cache) => {
return cache.addAll(filesToCache);
})
);
self.skipWaiting();
});
and I'm using a cache, falling back to network strategy:
self.addEventListener('fetch', function(event) {
event.respondWith(
caches.match(event.request).then(function(response) {
return response || fetch(event.request);
})
);
});
The issue I have is when the www.example.com/es/index.html or es/offline.html is accessed offline and loading the CSS and JS files. The problem is that since the es/index.html files references the CSS and JS as ../static/css/styles.css and ../static/js/main.js, they can't find the files in the cache. I've tried to find a way to alter the request and response but so far I've failed. Any help?
Well, you can write some logic in your code where the caches.match(event.request) is changed to something like caches.match(event.request) || caches.match(*canonical-url*) (in pseudo-code). You have possibly had a bug in your code if you tried this already. Another option would be to cache the files twice – with their root-relative paths and their canonical "../" paths. This of course isn't optimal since cache is used twice.
I think the best option would be to generate your site so that it always uses root-relative static asset paths. Replace all "../static/bla" with "/static/bla" and everything should work out of the box very neatly :)
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.
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;
}
};