Application Cache is—as Jake so infamously described—not a good API. It was specced and shipped before developers had a chance to figure out what they really needed, and so AppCache turned out to be frustrating at best and downright dangerous in some situations. Its over-zealous caching combined with its byzantine cache invalidation ensured it was never going to become a mainstream technology.
There are very few use-cases for AppCache, but I think I hit upon one of them. Six years ago, A Book Apart published HTML5 For Web Designers. A year and a half later, I put the book online. The contents are never going to change. There’s a second edition of the book out now but if you want to read all the extra bits that Rachel added, you’re going to have to buy the book. The website for the original book is static and unchanging. That’s what made it such a good candidate for using AppCache. I could just set it and forget.
Except that’s no longer true. AppCache is being deprecated and browsers are starting to withdraw support. Chrome is already making sure that AppCache—like geolocation—no longer works on sites that aren’t served over HTTPS. That’s for the best. In retrospect, those APIs should never have been allowed over unsecured HTTP.
I mentioned that I spent the weekend switching all my book websites over to HTTPS, so AppCache should continue to work …for now. It’s only a matter of time before AppCache is removed completely from many of the browsers that currently support it.
Seeing as I’ve got the HTML5 For Web Designers site running on HTTPS now, I might as well go all out and make it a progressive web app. By far the biggest barrier to making a progressive web app is that first step of setting up HTTPS. It’s gotten cheaper—thanks to
Let’s Encrypt —but it still involves mucking around in the command line with root access; I never wanted to become a sysadmin. But once that’s finally all set up, the other technological building blocks—a Service Worker and a manifest file—are relatively easy.
In this case, the Service Worker is using a straightforward bit of logic:
- On installation, cache absolutely everything: HTML, CSS, images.
- When anything is requested, grab it from the cache.
- If it isn’t in the cache, try the network.
- If the network doesn’t work, show an offline page (or image).
Basically I’m reproducing AppCache’s overzealous approach. It works for this site because the content is never going to change. I hope that this time, I really can just set it and forget it. I want the site to be an historical artefact, available at the same URL for at least my lifetime. I don’t want to have to maintain it or revisit it every few years to swap out one API for another.
Which brings me back to the way AppCache is being deprecated…
The Firefox team are very eager to ditch AppCache as soon as possible. On the one hand, that’s commendable. They’re rightly proud of shipping Service Workers and they want to encourage people to use the better technology instead. But it sure stings for the suckers (like me) who actually went and built stuff using AppCache.
In a weird way, I think this rush to deprecate AppCache might actually hurt the adoption of Service Workers. Let me explain…
At last year’s Edge Conference, Nolan Lawson gave a great presentation on storing data in the browser. He enumerated the many ways—past and present—that we could store data locally: WebSQL, Local Storage, IndexedDB …the list goes on. He also posed the question: why aren’t more people using insert-name-of-latest-API-here? To me it seemed obvious why more people weren’t diving into using the latest and greatest option for local data storage. It was because they had been burned before. The developers who rushed into trying previous solutions end up being mocked for their choice. “Still using that ol’ thing? Pffftt!”
You can see that same attitude on display from Mozilla as they push towards removing AppCache. Like in a comment that refers to developers using AppCache in production as “the angry hordes”. Reminds me of something Tom said:
Developer relations is like 20% telling people about what’s new and 80% building trust and making people feel heard.— Tom Dale (@tomdale) April 3, 2016
In that same Mozilla thread, Soledad echoes Tom’s point:
As a member of the devrel team: I think that this should be better addressed in a blog post that someone from the team responsible for switching AppCache off should write, so everyone can understand the reasons and ask questions to those people.
I’d rather warn people beforehand, pointing them to that post and help them with migration paths than apply emergency mitigation strategies when a lot of people find their stuff stopped working in the newer Firefox…
Bravo! That same approach should have also been taken by the Chrome team when it came to their thread about punishing
display:browser in manifest files. There was absolutely no communication with developers about this major decision. I only found out about it because Paul happened to mention it to me.
I was genuinely shocked by this:
Withholding the “add to home screen” prompt like that has a whiff of blackmail about it.
I can confirm that smell. When I was making the manifest file for HTML5 For Web Designers, I really wanted to put
display: browser because I want people to be able to copy and paste URLs (for the book, for individual chapters, and for sections within chapters). But knowing that if I did that, Android users would never see the “add to home screen” prompt made me question that decision. I felt strong-armed into declaring
display: standalone. And no, I’m not mollified by hand-waving reassurances that the Chrome team will figure out some solution for this. Figure out the solution first, then punish the saps like me who want to use
display: browser to allow people to share URLs.
Anyway, the website for HTML5 For Web Designers is now using AppCache and Service Workers. The AppCache part will probably be needed for quite a while yet to provide offline support on iOS. Apple are really dragging their heels on Service Worker support, with at least one WebKit engineer actively looking for reasons not to implement it.
There’s a lot of talk about making apps work offline, but I think it’s just as important that we consider making information work offline. Books are a great example of this. To use the tired transport tropes, the website for a book is something you might genuinely want to access when you’re on a plane, or in the underground, or out at sea.
I really, really like progressive web apps. But I also think it’s important that we don’t fall into the trap of just trying to imitate native apps on the web. I love the idea of taking the best of the web—like information being permanently available at a URL—and marrying that up with the best of native—like offline access. I also like the idea of taking the best of books—a tome of thought—and marrying it up with the best of the web—hypertext.
I’d love to see more experimentation around online/offline hypertext/books. For now, you can visit HTML5 For Web Designers, add it to your home screen, and revisit it whenever and wherever you like.
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