Progressive Web Apps

Now THAT'S What I Call Service Worker!

Weekly Timber is a client of mine that provides logging services in central Wisconsin. For them, a fast website is vital. Their business is located in Waushara County, and like many rural stretches in the United States, network quality and reliability isn’t great.

[…]

Wisconsin has farmland for days, but it also has plenty of forests. When you need a company that cuts logs, Google is probably your first stop. How fast a given logging company’s website is might be enough to get you looking elsewhere if you’re left waiting too long on a crappy network connection.

I initially didn’t believe a Service Worker was necessary for Weekly Timber’s website. After all, if things were plenty fast to start with, why complicate things? On the other hand, knowing that my client services not just Waushara County, but much of central Wisconsin, even a barebones Service Worker could be the kind of progressive enhancement that adds resilience in the places it might be needed most.

The first Service Worker I wrote for my client’s website—which I’ll refer to henceforth as the “standard” Service Worker—used three well-documented caching strategies:

  1. Precache CSS and JavaScript assets for all pages when the Service Worker is installed when the window’s load event fires.
  2. Serve static assets out of CacheStorage if available. If a static asset isn’t in CacheStorage, retrieve it from the network, then cache it for future visits.
  3. For HTML assets, hit the network first and place the HTML response into CacheStorage. If the network is unavailable the next time the visitor arrives, serve the cached markup from CacheStorage.

These are neither new nor special strategies, but they provide two benefits:

  • Offline capability, which is handy when network conditions are spotty.
  • A performance boost for loading static assets.

[…]

A better, faster Service Worker

The web loves itself some “innovation,” which is a word we equally love to throw around. To me, true innovation isn’t when we create new frameworks or patterns solely for the benefit of developers, but whether those inventions benefit people who end up using whatever it is we slap up on the web. The priority of constituencies is a thing we ought to respect. Users above all else, always.

[…]

There are certainly other challenges, but it’ll be up to you to weigh the user-facing benefits versus the development costs. In my opinion, this approach has broad applicability in applications such as blogs, marketing websites, news websites, ecommerce, and other typical use cases.

All in all, though, it’s akin to the performance improvements and efficiency gains that you’d get from an SPA. Only the difference is that you’re not replacing time-tested navigation mechanisms and grappling with all the messiness that entails, but enhancing them. That’s the part I think is really important to consider in a world where client-side routing is all the rage.

Apple's subtle anti-competitive practices and the web

Apple has a history of stunting the web’s progress on its platforms. On iOS, Apple doesn’t allow fully independent third-party browsers, requiring all apps to leverage its Safari browser when rendering web-based content. While browsers like Chrome and Opera are available in the App Store, they must use Apple’s Safari browser behind the scenes to render web pages, rather than their own. That means Apple has a monopoly on how iPhone and iPad users access the web. To push developers toward building native apps on iOS rather than using web technologies, Apple ignores popular parts of the open web specification that other browsers implement, to its own benefit.

A technology called WebRTC, for example, allows video calling in a web browser without additional software. It powers tools like Google Meet. But Apple was incredibly slow to implement the specification, leaving out key pieces of functionality, and the technology didn’t work when embedded inside apps.

Apple also handicapped an emerging standard called Progressive Web Apps (PWAs) — which, like Electron, allows developers to build native-like apps for both desktop and mobile — by partially implementing it in a way that makes it too inconsistent to rely on. PWA doesn’t have the same problem if users open apps in Chrome or Firefox, but iPhone and iPad users can’t install third-party browsers, which makes PWA-based technology a non-starter.

[…]

Apple’s subtle, anti-competitive practices don’t look terrible in isolation, but together they form a clear strategy: Make it so painful to build with web-based technology on Apple platforms that developers won’t bother. Now that the App Store is not accepting apps built using Electron, developers will likely find creative ways to work around it, but Apple is setting up for a continual cat-and-mouse game as it plans to exert more control over which apps can run on the platform in the future.

When 7 KB Equals 7 MB

While testing a progressive web app for one of our clients, I bumped into a suspicious error in the browser console:

DOMException: Quota exceeded.

After browsing the app a few more times, it became clear the error would occur after a small number of images were added to the cache storage by the service worker. Looking in the Chrome DevTools Application tab, the cache storage was indeed over capacity.

Chrome DevTools showing over-capacity cache storage.
Chrome DevTools showing over-capacity cache storage.

How could this be? There were only ~15 images in the cache storage. Something was off.

What I found could significantly impact your progressive web app—particularly if you use a CDN on a different domain for your assets.

[…]

If you are building a progressive web app and are experiencing bloated cache storage when your service worker caches static assets served from CDNs, make sure the proper CORS response header exists for cross-origin resources, you do not cache opaque responses with your service worker unintentionally, you opt-in cross-origin image assets into CORS mode by adding the crossorigin attribute to the <img> tag.

See the source link for more details.

Using notifications responsibly

We see an increasing number of websites using notifications irresponsibly. The moment you visit the site, you get prompted by the browser to sign up for notifications. Not only is it annoying to be asked immediately, but it is unlikely to be effective.

We wanted to set a good example for responsible use of push notifications. So we don’t ask for permission to send push notifications until the user selects the button asking to turn notifications on. And we only provide the option to subscribe at the bottom of articles.

Screenshot of Cloud Four's options to subscribe to new articles via either web notifications or email

Once someone selects that button, then we trigger the browser alert asking for permission to send notifications. If the person signs up, we send a quick notification thanking them and update the button to indicate how they can turn off notifications.

Cloud Four's Get Notifications button turns into a Turn Off Notifications button after turning on notifications.

For more on using web notifications responsibly, we recommend Best Practices for Push Notifications Permissions UX by Owen Campbell-Moore.