Tags: serviceworkers

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HTTPS + service worker + web app manifest = progressive web app

I gave a quick talk at the Delta V conference in London last week called Any Site can be a Progressive Web App. I had ten minutes, but frankly I only needed enough time to say the title of the talk because, well, that was also the message.

There’s a common misconception that making a Progressive Web App means creating a Single Page App with an app-shell architecture. But the truth is that literally any website can benefit from the performance boost that results from the combination of HTTPS + Service Worker + Web App Manifest.

See how I define a progressive web app as being HTTPS + service worker + web app manifest? I’ve been doing that for a while. Here’s a post from last year called Progressing the web:

Literally any website can be a progressive web app:

That last step can be tricky if you’re new to service workers, but it’s not unsurmountable. It’s certainly a lot easier than completely rearchitecting your existing website to be a JavaScript-driven single page app.

Later I wrote a post called What is a Progressive Web App? where I compared the definition to responsive web design.

Regardless of the specifics of the name, what I like about Progressive Web Apps is that they have a clear definition. It reminds me of Responsive Web Design. Whatever you think of that name, it comes with a clear list of requirements:

  1. A fluid layout,
  2. Fluid images, and
  3. Media queries.

Likewise, Progressive Web Apps consist of:

  1. HTTPS,
  2. A service worker, and
  3. A Web App Manifest.

There’s more you can do in addition to that (just as there’s plenty more you can do on a responsive site), but the core definition is nice and clear.

But here’s the thing. Outside of the confines of my own website, it’s hard to find that definition anywhere.

On Google’s developer site, their definition uses adjectives like “reliable”, “fast”, and “engaging”. Those are all great adjectives, but more useful to a salesperson than a developer.

Over on the Mozilla Developer Network, their section on progressive web apps states:

Progressive web apps use modern web APIs along with traditional progressive enhancement strategy to create cross-platform web applications. These apps work everywhere and provide several features that give them the same user experience advantages as native apps. 

Hmm …I’m not so sure about that comparison to native apps (and I’m a little disturbed that the URL structure is /Apps/Progressive). So let’s click through to the introduction:

PWAs are web apps developed using a number of specific technologies and standard patterns to allow them to take advantage of both web and native app features.

Okay. Specific technologies. That’s good to hear. But instead of then listing those specific technologies, we’re given another list of adjectives (discoverable, installable, linkable, etc.). Again, like Google’s chosen adjectives, they’re very nice and desirable, but not exactly useful to someone who wants to get started making a progressive web app. That’s why I like to cut to the chase and say:

  • You need to be running on HTTPS,
  • Then you can add a service worker,
  • And don’t forget to add a web app manifest file.

If you do that, you’ve got a progressive web app. Now, to be fair, there’a lot that I’m leaving out. Your site should be fast. Your site should be responsive (it is, after all, on the web). There’s not much point mucking about with service workers if you haven’t sorted out the basics first. But those three things—HTTPS + service worker + web app manifest—are specifically what distinguishes a progressive web app. You can—and should—have a reliable, fast, engaging website before turning it into a progressive web app.

Jason has been thinking about progressive web apps a lot lately (he should write a book or something), and he said to me:

I agree with you on the three things that comprise a PWA, but as far as I can tell, you’re the first to declare it as such.

I was quite surprised by that. I always assumed that I was repeating the three ingredients of a progressive web app, not defining them. But looking through all the docs out there, Jason might be right. It’s surprising because I assumed it was obvious why those three things comprise a progressive web app—it’s because they’re testable.

Lighthouse, PWA Builder, Sonarwhal and other tools that evaluate your site will measure its progressive web app score based on the three defining factors (HTTPS, service worker, web app manifest). Then there’s Android’s Add to Home Screen prompt. Here finally we get a concrete description of what your site needs to do to pass muster:

  • Includes a web app manifest…
  • Served over HTTPS (required for service workers)
  • Has registered a service worker with a fetch event handler

(Although, as of this month, Chrome will no longer show the prompt automatically—you also have to write some JavaScript to handle the beforeinstallprompt  event).

Anyway, if you’re looking to turn your website into a progressive web app, here’s what you need to do (assuming it’s already performant and responsive):

  1. Switch over to HTTPS. Certbot can help you here.
  2. Add a web app manifest.
  3. Add a service worker to your site so that it responds even when there’s no network connection.

That last step might sound like an intimidating prospect, but help is at hand: I wrote Going Offline for exactly this situation.

Service worker resources

At the end of my new book, Going Offline, I have a little collection of resources relating to service workers. Here’s how I introduce them:

If this book were a podcast, then this would be the point at which I would be imploring you to rate me on iTunes (or I’d be telling you about a really good mattress). Instead, I’d like to give you some hyperlinks so that you can explore some of the topics in this brief book in more detail.

It always feels a little strange to publish a list of hyperlinks in a physical book, so I figured I’d republish them here for easy access…

Explanations

Guides

Examples

Progressive web apps

Tools

Documentation

Acknowledgements

It feels a little strange to refer to Going Offline as “my” book. I may have written most of the words in it, but it was only thanks to the work of others that they ended up being the right words in the right order in the right format.

I’ve included acknowledgements in the book, but I thought it would be good to reproduce them here in the form of hypertext…

Everyone should experience the joy of working with Katel LeDû and Lisa Maria Martin. From the first discussions right up until the final last-minute tweaks, they were unflaggingly fun to collaborate with. Thank you, Katel, for turning my idea into reality. Thank you, Lisa Maria, for turning my initial mush of words into a far more coherent mush of words.

Jake Archibald and Amber Wilson were the best of technical editors. Jake literally wrote the spec on service workers so I knew I could rely on him to let me know whenever I made any factual missteps. Meanwhile Amber kept me on the straight and narrow, letting me know whenever the writing was becoming unclear. Thank you both for being so generous with your time.

Thanks to my fellow Clearlefty Danielle Huntrods for giving me feedback as the book developed.

Finally, I want to express my heartfelt thanks to everyone who has ever taken the time to write on their website about their experiences with service workers. Lyza Gardner, Ire Aderinokun, Una Kravets, Mariko Kosaka, Jason Grigsby, Ethan Marcotte, Mike Riethmuller, and others inspired me with their generosity. Thank you to everyone who’s making the web better through such kind acts of openness. To quote the original motto of the World Wide Web project, let’s share what we know.

Going Offline, available now!

The day is upon us! The hour is at hand! The book is well and truly apart!

That’s right—Going Offline is no longer available for pre-order …it’s just plain available. ABookApart.com is where you can place your order now.

If you pre-ordered the book, thank you. An email is winging its way to you with download details for the digital edition. If you ordered the paperback, the Elves Apart are shipping your lovingly crafted book to you right now.

If you didn’t pre-order the book, I grudgingly admire your cautiousness, but don’t you think it’s time to throw caution to the wind and treat yourself?

Seriously though, I think you’ll like this book. And I’m not the only one. Here’s what people are saying:

I know you have a pile of professional books to read, but this one should skip the line.

Lívia De Paula Labate

It is so good. So, so good. I cannot recommend it enough.

Sara Soueidan

Super approachable and super easy to follow regardless of your level of knowledge.

—also Sara Soueidan

You’re gonna want to preorder a copy, believe me.

Mat Marquis

Beautifully explained without being patronising.

Chris Smith

I very much look forward to hearing what you think of Going Offline. Get your copy today and let me know what you think of it. Like I said, I think you’ll like this book. Apart.

Timing

Apple Inc. is my accidental marketing department.

On April 29th, 2010, Steve Jobs published his infamous Thoughts on Flash. It thrust the thitherto geek phrase “HTML5” into the mainstream press:

HTML5, the new web standard that has been adopted by Apple, Google and many others, lets web developers create advanced graphics, typography, animations and transitions without relying on third party browser plug-ins (like Flash). HTML5 is completely open and controlled by a standards committee, of which Apple is a member.

Five days later, I announced the first title from A Book Apart: HTML5 For Web Designers. The timing was purely coincidental, but it definitely didn’t hurt that book’s circulation.

Fast forward eight years…

On March 29th, 2018, Apple released the latest version of iOS. Unmentioned in the press release, this update added service worker support to Mobile Safari.

Five days later, I announced the 26th title from A Book Apart: Going Offline.

For a while now, quite a few people have cited Apple’s lack of support as a reason why they weren’t investigating service workers. That excuse no longer holds water.

Once again, the timing is purely coincidental. But it can’t hurt.

Technical balance

Two technical editors worked with me on Going Offline.

Jake was one of the tech editors. He literally (co-)wrote the spec on service workers. There ain’t nuthin’ he don’t know about the code involved. His job was to catch any technical inaccuracies in my writing.

The other tech editor was Amber. She’s relatively new to web development. While I was writing the book, she had a solid grounding in HTML and CSS, but not much experience in JavaScript. That made her the perfect archetypal reader. Her job was to point out whenever I wasn’t explaining something clearly enough.

My job was to satisfy both of them. I needed to explain service workers and all its associated APIs. I also needed to make it approachable and understandable to people who haven’t dived deeply into JavaScript.

I deliberately didn’t wait until I was an expert in this topic before writing Going Offline. I knew that the more familiar I became with the ins-and-outs of getting a service worker up and running, the harder it would be for me to remember what it was like not to know that stuff. I figured the best way to avoid the curse of knowledge would be not to accrue too much of it. But then once I started researching and writing, I inevitably became more au fait with the topic. I had to try to battle against that, trying to keep a beginner’s mind.

My watchword was this great piece of advice from Codebar:

Assume that anyone you’re teaching has no knowledge but infinite intelligence.

It was tricky. I’m still not sure if I managed to pull off the balancing act, although early reports are very, very encouraging. You’ll be able to judge for yourself soon enough. The book is shipping at the start of next week. Get your order in now.

The audience for Going Offline

My new book, Going Offline, starts with no assumption of JavaScript knowledge, but by the end of the book the reader is armed with enough code to make any website work offline.

I didn’t want to overwhelm the reader with lots of code up front, so I’ve tried to dole it out in manageable chunks. The amount of code ramps up a little bit in each chapter until it peaks in chapter five. After that, it ramps down a bit with each subsequent chapter.

This tweet perfectly encapsulates the audience I had in mind for the book:

Some people have received advance copies of the PDF, and I’m very happy with the feedback I’m getting.

Honestly, that is so, so gratifying to hear!

Words cannot express how delighted I am with Sara’s reaction:

She’s walking the walk too:

That gives me a warm fuzzy glow!

If you’ve been nervous about service workers, but you’ve always wanted to turn your site into a progressive web app, you should get a copy of this book.

Table of Contents for Going Offline

A few people on Twitter have asked about the table of contents for my new book about service workers, Going Offline. Fair enough—why not see the menu before placing your order?

  1. Introducing Service Workers Does what is says on the tin. It also talks about switching to HTTPS. This chapter is online at A List Apart so you can try before you buy.
  2. Preparing for Offline This chapter talks about how you register a service worker, and introduces the concept of promises in JavaScript.
  3. Making Fetch Happen Yes, this chapter title is a Mean Girls reference; fight me. The chapter explains fetch events and shows how a service worker can intercept them.
  4. Cache Me if you Can This puntastic chapter is all about caching, and shows you can use caches in your service worker script.
  5. Service Worker Strategies This is the heart of the book, where you get decide what kind of strategy you want to implement—when to go to the network, when to go a cache, and so on. And as a last resort, you can have a custom offline page.
  6. Refining Your Service Worker Building on the previous chapter, this one looks at how you can use different strategies for different kinds of files—images, pages, etc.
  7. Tidying Up This chapter is about good service worker hygiene like deleting old caches. It also introduces some more coding style options.
  8. The Offline Experience By this chapter, the service worker script is done. But there’s still plenty of room for enhancements on that custom offline page, including the use of offline storage.
  9. Progressive Web Apps The book finishes with an explanation of progressive web apps, and a step-by-step guide to creating your own web app manifest.

Sound good? Pre-order your copy of the book now and you’ll have it in your hands ten days from now.

Understandable excitement

An Event Apart Seattle just wrapped. It was a three-day special edition and it was really rather good. Lots of the speakers (myself included) were unveiling brand new talks, so there was a real frisson of excitement.

It was interesting to see repeating, overlapping themes. From a purely technical perspective, three technologies that were front and centre were:

  • CSS grid,
  • variable fonts, and
  • service workers.

From listening to other attendees, the overwhelming message received was “These technologies are here—they’ve arrived.” Now, depending on your mindset, that understanding can be expressed as “Oh shit! These technologies are here!” or “Yay! Finally! These technologies are here!”

My reaction is very firmly the latter. That in itself is an interesting data-point, because (as discussed in my talk) my reaction towards new technological advances isn’t always one of excitement—quite often it’s one of apprehension, even fear.

I’ve been trying to self-analyse to figure out which kinds of technologies trigger which kind of reaction. I don’t have any firm answers yet, but it’s interesting to note that the three technologies mentioned above (CSS grid, variable fonts, and service workers) are all additions to the core languages of the web—the materials we use to build the web. Frameworks, libraries, build tools, and other such technologies are more like tools than materials. I tend to get less excited about advances in those areas. Sometimes advances in those areas not only fail to trigger excitement, they make me feel overwhelmed and worried about falling behind.

Since figuring out this split between materials and tools, it has helped me come to terms with my gut emotional reaction to the latest technological advances on the web. I think it’s okay that I don’t get excited about everything. And given the choice, I think maybe it’s healthier to be more excited about advances in the materials—HTML, CSS, and JavaScript APIs—than advances in tooling …although, it is, of course, perfectly possible to get equally excited about both (that’s just not something I seem to be able to do).

Another split I’ve noticed is between technologies that directly benefit users, and technologies that directly benefit developers. I think there was a bit of a meta-thread running through the talks at An Event Apart about CSS grid, variable fonts, and service workers: all of those advances allow us developers to accomplish more with less. They’re good for performance, in other words. I get much more nervous about CSS frameworks and JavaScript libraries that allow us to accomplish more, but require the user to download the framework or library first. It feels different when something is baked into browsers—support for CSS features, or JavaScript APIs. Then it feels like much more of a win-win situation for users and developers. If anything, the onus is on developers to take the time and do the work and get to grips with these browser-native technologies. I’m okay with that.

Anyway, all of this helps me understand my feelings at the end of An Event Apart Seattle. I’m fired up and eager to make something with CSS grid, variable fonts, and—of course—service workers.

Designing Progressive Web Apps by Jason Grigsby

It’s the afternoon of the second day of An Event Apart Seattle and Jason is talking about Designing Progressive Web Apps. These are my notes…

Jason wants to talk about a situation you might find yourself in. You’re in a room and in walks the boss, who says “We need a progressive web app.” Now everyone is asking themselves “What is a progressive web app?” Or maybe “How does the CEO even know about progressive web apps?”

Well, trade publications are covering progressive web apps. Lots of stats and case studies are being published. When executives see this kind of information, they don’t want to get left out. Jason keeps track of this stuff at PWA Stats.

Answering the question “What is a progressive web app?” is harder than it should be. The phrase was coined by Frances Berriman and Alex Russell. They listed ten characteristics that defined progressive web apps. The “linkable” and “progressive” characteristics are the really interesting and new characteristics. We’ve had technologies before (like Adobe Air) that tried to make app-like experiences, but they weren’t really of the web. Progressive web apps are different.

Despite this list of ten characteristics, even people who are shipping progressive web apps find it hard to define the damn thing. The definition on Google’s developer site keeps changing. They reduced the characteristics from ten to six. Then it became “reliable, fast, and engaging.” What does that mean? Craigslist is reliable, fast, and engaging—does that mean it’s a progressive web app.

The technical definition is useful (kudos to me, says Jason):

  1. HTTPS
  2. service worker
  3. manifest file

If you don’t have those three things, it’s not a progressive web app.

We should definitely use HTTPS if we want make life harder for the NSA. Also browser makers are making APIs available only under HTTPS. By July, Chrome will mark HTTP sites as insecure. Every site should be under HTTPS.

Service workers are where the power is. They act as a proxy. They allow us to say what we want to cache, what we want to go out to the network for; things that native apps have been able to do for a while. With progressive web apps we can cache the app shell and go to the network for content. Service workers can provide a real performance boost.

A manifest file is simply a JSON file. It’s short and clear. It lists information about the app: icons, colours, etc.

Once you provide those three things, you get benefits. Chrome and Opera on Android will prompt to add the app to the home screen.

So that’s what’s required for progressive web apps, but there’s more to them than that (in the same way there’s more to responsive web design than the three requirements in the baseline definition).

The hype around progressive web apps can be a bit of a turn-off. It certainly was for Jason. When he investigated the technologies, he wondered “What’s the big deal?” But then he was on a panel at a marketing conference, and everyone was talking about progressive web apps. People’s expectations of what you could do on the web really hadn’t caught up with what we can do now, and the phrase “progressive web app” gives us a way to encapsulate that. As Frances says, the name isn’t for us; it’s for our boss or marketer.

Jason references my post about using the right language for the right audience.

Should you have a progressive web app? Well, if you have a website, then the answer is almost certainly “Yes!” If you make money from that website, the answer is definitely “Yes!”

But there’s a lot of FUD around progressive web apps. It brings up the tired native vs. web battle. Remember though that not 100% of your users or customers have your app installed. And it’s getting harder to convince people to install apps. The average number of apps installed per month is zero. But your website is often a customer’s first interaction with your company. A better web experience can only benefit you.

Often, people say “The web can’t do…” but a lot of the time that information is out of date. There are articles out there with outdated information. One article said that progressive web apps couldn’t access the camera, location, or the fingerprint sensor. Yet look at Instagram’s progressive web app: it accesses the camera. And just about every website wants access to your location these days. And Jason knows you can use your fingerprint to buy things on the web because he accidentally bought socks when he was trying to take a screenshot of the J.Crew website on his iPhone. So the author of that article was just plain wrong. The web can do much more than we think it can.

Another common objection is “iOS doesn’t support progressive web apps”. Well, as of last week that is no longer true. But even when that was still true, people who had implemented progressive web apps were seeing increased conversion even on iOS. That’s probably because, if you’ve got the mindset for building a progressive web app, you’re thinking deeply about performance. In many ways, progressive web apps are a trojan horse for performance.

These are the things that people think about when it comes to progressive web apps:

  1. Making it feel like a app
  2. Installation and discovery
  3. Offline mode
  4. Push notifications
  5. Beyond progressive web app

Making it feel like a app

What is an app anyway? Nobody can define it. Once again, Jason references my posts on this topic (how “app” is like “obscenity” or “brunch”).

A lot of people think that “app-like” means making it look native. But that’s a trap. Which operating system will you choose to emulate? Also, those design systems change over time. You should define your own design. Make it an exceptional experience regardless of OS.

It makes more sense to talk in terms of goals…

Goal: a more immersive experience.

Possible solution: removing the browser chrome and going fullscreen?

You can define this in the manifest file. But as you remove the browser chrome, you start to lose things that people rely on: the back button, the address bar. Now you have to provide that functionality. If you move to a fullscreen application you need to implement sharing, printing, and the back button (and managing browser history is not simple). Remember that not every customer will add your progressive web app to their home screen. Some will have browser chrome; some won’t.

Goal: a fast fluid experience.

Possible solution: use an app shell model.

You want smooth pages that don’t jump around as the content loads in. The app shell makes things seem faster because something is available instantly—it’s perceived performance. Basically you’re building a single page application. That’s a major transition. But thankfully, you don’t have to do it! Progressive web apps don’t have to be single page apps.

Goal: an app with personality.

Possible solution: Animated transitions and other bits of UI polish.

Really, it’s all about delight.

Installation and discovery

In your manifest file you can declare a background colour for the startup screen. You can also declare a theme colour—it’s like you’re skinning the browser chrome.

You can examine the manifest files for a site in Chrome’s dev tools.

Once you’ve got a progressive web app, some mobile browsers will start prompting users to add it to their home screen. Firefox on Android displays a little explainer the first time you visit a progressive web app. Chrome and Opera have add-to-homescreen banners which are a bit more intrusive. The question of when they show up keeps changing. They use a heuristic to decide this. The heuristic has been changed a few times already. One thing you should consider is suppressing the banner until it’s an optimal time. Flipkart do this: they only allow it on the order confirmation page—the act of buying something makes it really likely that someone will add the progressive web app to their home screen.

What about app stores? We don’t need them for progressive web apps—they’re on the web. But Microsoft is going to start adding progressive web apps to their app store. They’ve built a site called PWA Builder to help you with your progressive web app.

On the Android side, there’s Trusted Web Activity which is kind of like PhoneGap—it allows you to get a progressive web app into the Android app store.

But remember, your progressive web app is your website so all the normal web marketing still applies.

Offline mode

A lot of organisations say they have no need for offline functionality. But everyone has a need for some offline capability. At the very least, you can provide a fallback page, like Trivago’s offline maze game.

You can cache content that has been recently viewed. This is what Jason does on the Cloud Four site. They didn’t want to make any assumptions about what people might want, so they only cache pages as people browse around the site.

If you display cached information, you might want to display how stale the information is e.g. for currency exchange rates.

Another option is to let people choose what they want to keep offline. The Financial Times does this. They also pre-cache the daily edition.

If you have an interactive application, you could queue tasks and then carry them out when there’s a connection.

Or, like Slack does, don’t let people write something if they’re offline. That’s better than letting someone write something and then losing it.

Workbox is a handy library for providing offline functionality.

Push notifications

The JavaScript for push notifications is relatively easy, says Jason. It’s the back-end stuff that’s hard. That’s because successful push notifications are personalised. But to do that means doing a lot more work on the back end. How do you integrate with preferences? Which events trigger notifications?

There are third-party push notification services that take care of a lot of this for you. Jason has used OneSignal.

Remember that people are really annoyed by push notifications. Don’t ask for permission immediately. Don’t ask someone to marry you on a first date. On Cloud Four’s blog, they only prompt after the user has read an article.

Twitter’s progressive web app does this really well. It’s so important that you do this well: if a user says “no” to your push notification permission request, you will never be able to ask them again. There used to be three options on Chrome: allow, block, or close. Now there are just two: allow or block.

Beyond progressive web apps

There are a lot of APIs that aren’t technically part of progressive web apps but get bundled in with them. Like the Credentials Management API or the Payment Request API (which is converging with ApplePay).

So how should you plan your progressive web app launch? Remember it’s progressive. You can keep adding features. Each step along the way, you’re providing value to people.

Start with some planning and definition. Get everyone in a room and get a common definition of what the ideal progressive web app would look like. Remember there’s a continuum of features for all five of the things that Jason has outlined here.

Benchmark your existing site. It will help you later on.

Assess your current website. Is the site reasonably fast? Is it responsive? Fix those usability issues first.

Next, do the baseline. Switch to HTTPS. Add a manifest file. Add a service worker. Apart from the HTTPS switch, this can all be done on the front end. Don’t wait for all three: ship each one when they’re ready.

Then do front-end additions: pre-caching pages, for example.

Finally, there are the larger initiatives (with more complex APIs). This is where your initial benchmarking really pays off. You can demonstrate the value of what you’re proposing.

Every step on the path to a progressive web app makes sense on its own. Figure out where you want to go and start that journey.

See also:

Announcing Going Offline from A Book Apart

I decided that I wanted a new mug.

I already have one very nice mug. It was sent to me by A Book Apart because I wrote the book HTML5 For Web Designers back in 2010. If I wanted another nice mug, it was clear what I had to do. I had to write another book.

So I’ve written a book. It’s called Going Offline and it’s available to pre-order now. It will start shipping a few weeks from now.

I think you will enjoy this book. Here’s why…

You have a website or you make websites for other people. You’re comfortable with HTML and CSS, but maybe you’re a bit apprehensive about JavaScript (like me). You keep hearing lots of talk about service workers and progressive web apps. You’re intrigued. But you’re put off by the resources out there. They all assume a certain level of JavaScript knowledge. What you need is a step-by-step guide to help you make your website work offline …a guide that won’t assume you’re already comfortable with code.

Does that sound like you? Then Going Offline is for you.

Thinking about it, a more accurate title for the book would’ve been Service Workers For Web Designers …although even that would assume too much existing knowledge (like, what the heck a service worker is in the first place).

Pre-order Going Offline today and it will be in your hands in just a few weeks.

Alas, I have no idea when my new mug will be ready.

Minimal viable service worker

I really, really like service workers. They’re one of those technologies that have such clear benefits to users that it seems like a no-brainer to add a service worker to just about any website.

The thing is, every website is different. So the service worker strategy for every website needs to be different too.

Still, I was wondering if it would be possible to create a service worker script that would work for most websites. Here’s the script I came up with.

The logic works like this:

  • If there’s a request for an HTML page, fetch it from the network and store a copy in a cache (but if the network request fails, try looking in the cache instead).
  • For any other files, look for a copy in the cache first but meanwhile fetch a fresh version from the network to update the cache (and if there’s no existing version in the cache, fetch the file from the network and store a copy of it in the cache).

So HTML files are served network-first, while all other files are served cache-first, but in both cases a fresh copy is always put in the cache. The idea is that HTML content will always be fresh (unless there’s a problem with the network), while all other content—images, style sheets, scripts—might be slightly stale, but get refreshed with every request.

My original attempt was riddled with errors. Jake came to my rescue and we revised the script into something that actually worked. In the process, my misunderstanding of how await works led Jake to write a great blog post on await vs return vs return await.

I got there in the end and the script seems solid enough. It’s a fairly simplistic strategy that could work for quite a few sites, but it has some issues…

Service workers don’t perform any automatic cleanup of caches—that’s up to you to do (usually during the activate event). This script doesn’t do any cleanup so the cache might grow and grow and grow. For that reason, I think the script is best suited for fairly small sites.

The strategy also assumes that a file will either be fetched from the network or the cache. There’s no contingency for when both attempts fail. So there’s no fallback offline page, for example.

I decided to test it in the wild, but I expanded it slightly to fix the fallback issue. The version on the Ampersand 2018 website includes a worst-case-scenario option to show a custom offline page that has been pre-cached. (By the way, if you haven’t got a ticket for Ampersand yet, get a ticket now—it’s going to be superb day of web typography nerdery.)

Anyway, this fairly basic script seems to be delivering some good performance improvements. If you’ve got a site that you think would benefit from this network/caching strategy, and it’s served over HTTPS, then:

  1. Feel free to download the script or copy and paste it into a file called serviceworker.js,
  2. Put that file in the root directory of your website,
  3. Add this in a script element at the bottom of your HTML pages:

if (navigator.serviceWorker && !navigator.serviceWorker.controller) { navigator.serviceWorker.register('/serviceworker.js'); }

You can also use the script as a starting point. You might find issues specific to your particular website. That’s okay—you can tweak and adjust the script to suit your needs.

If this minimal service worker script proves in any way useful to you, thank Jake.

Offline itineraries with service workers

The Trivago website is a progressive web app. That means it

  1. is served over HTTPS,
  2. has a web app manifest JSON file, and it
  3. has a service worker script.

The service worker provides an opportunity for a nice bit of fun branding—if you lose your internet connection, the site provides a neat little maze game you can play. Cute!

That’s a fairly simple example of how service workers can enhance the user experience when the dreaded offline situation arises. But it strikes me that the travel industry is the perfect place to imagine other opportunities for offline enhancements.

Travel sites often provide itineraries—think airlines, trains, or hotels. The itineraries consist of places, times, and contact information. This is exactly the kind of information that you might find yourself trying to retrieve in an emergency situation, like maybe in a cab on the way to the airport or train station. Perhaps you’re stuck in traffic, in a tunnel. Or maybe you don’t have a data plan for the country you’re currently in. Either way, wouldn’t it be great if you could hit the website for your airline or hotel and get your itinerary, even if you’re offline.

Alright, let’s think this through…

Let’s assume that an individual itinerary has its own URL. That URL is a web page of information, mostly text, with perhaps an image or two (like a map). Now when you make your booking, let’s have the service worker cache that URL (and its assets) for offline access.

Hmm …but there’s a good chance that the device you make the booking on is not the same device that you’d have with you out and and about. Because caches are local to the browser, that’s a problem.

Okay, but of these kinds of sites have some kind of log-in mechanism. So we could update the log-in flow a bit: when a user logs in, check to see if they have any itineraries assigned to them, and if they do, fire off an event to the service worker (using postMessage) to cache the URLs of the itineraries.

Now that the itineraries are cached, the final step is to create a custom offline page. As well as the usual “Sorry, the internet’s down” message, we can say “Sorry, the internet’s down …but here are your itineraries”. (This is kind of like the pattern you see on blogs like mine, Ethan’s, or Mike’s—a custom offline page that lists cached URLs of articles you’ve previously visited).

That’s just one pattern off the top of my head. It’s fun to imagine the different ways that service workers could be used to enhance the experience of just about any site, but they seem particularly relevant to travel sites—dodgy internet connections and travelling go hand-in-hand. At Clearleft, we’ve been working with quite a few travel-related clients lately so that’s why these scenarios are on my mind: booking holidays, flights, and so on. But, as I’ve said before and I’ll say again, every website can benefit from becoming a progressive web app.

What is a Progressive Web App?

It seems like any new field goes through an inevitable growth spurt that involves “defining the damn thing.” For the first few years of the IA Summit, every second presentation seemed to be about defining what Information Architecture actually is. See also: UX. See also: Content Strategy.

Now it seems to be happening with Progressive Web Apps …which is odd, considering the damn thing is defined damn well.

I’ve written before about the naming of Progressive Web Apps. On the whole, I think it’s a pretty good term, especially if you’re trying to convince the marketing team.

Regardless of the specifics of the name, what I like about Progressive Web Apps is that they have a clear definition. It reminds me of Responsive Web Design. Whatever you think of that name, it comes with a clear list of requirements:

  1. A fluid layout,
  2. Fluid images, and
  3. Media queries.

Likewise, Progressive Web Apps consist of:

  1. HTTPS,
  2. A service worker, and
  3. A Web App Manifest.

There’s more you can do in addition to that (just as there’s plenty more you can do on a responsive site), but the core definition is nice and clear.

Except, for some reason, that clarity is being lost.

Here’s a post by Ben Halpern called What the heck is a “Progressive Web App”? Seriously.

I have a really hard time describing what a progressive web app actually is.

He points to Google’s intro to Progressive Web Apps:

Progressive Web Apps are user experiences that have the reach of the web, and are:

  • Reliable - Load instantly and never show the downasaur, even in uncertain network conditions.
  • Fast - Respond quickly to user interactions with silky smooth animations and no janky scrolling.
  • Engaging - Feel like a natural app on the device, with an immersive user experience.

Those are great descriptions of the benefits of Progressive Web Apps. Perfect material for convincing your clients or your boss. But that appears on developers.google.com …surely it would be more beneficial for that audience to know the technologies that comprise Progressive Web Apps?

Ben Halpern again:

Google’s continued use of the term “quality” in describing things leaves me with a ton of confusion. It really seems like they want PWA to be a general term that doesn’t imply any particular implementation, and have it be focused around the user experience, but all I see over the web is confusion as to what they mean by these things. My website is already “engaging” and “immersive”, does that mean it’s a PWA?

I think it’s important to use the right language for the right audience.

If you’re talking to the business people, tell them about the return on investment you get from Progressive Web Apps.

If you’re talking to the marketing people, tell them about the experiential benefits of Progressive Web Apps.

But if you’re talking to developers, tell them that a Progressive Web App is a website served over HTTPS with a service worker and manifest file.

Installing Progressive Web Apps

When I was testing the dConstruct Audio Archive—which is now a Progressive Web App—I noticed some interesting changes in how Chrome on Android offers the “add to home screen” prompt.

It used to literally say “add to home screen.”

Getting the “add to home screen” prompt for https://huffduffer.com/ on Android Chrome. And there’s the “add to home screen” prompt for https://html5forwebdesigners.com/ HTTPS + manifest.json + Service Worker = “Add to Home Screen” prompt. Add to home screen.

Now it simply says “add.”

The dConstruct Audio Archive is now a Progressive Web App

I vaguely remember there being some talk of changing the labelling, but I could’ve sworn it was going to change to “install”. I’ve got to be honest, just having the word “add” doesn’t seem to provide much context. Based on the quick’n’dirty usability testing I did with some co-workers, it just made things confusing. “Add what?” “What am I adding?”

Additionally, the prompt appeared immediately on the first visit to the site. I thought there was supposed to be an added “engagement” metric in order for the prompt to appear; that the user needs to visit the site more than once.

You’d think I’d be happy that users will be presented with the home-screen prompt immediately, but based on the behaviour I saw, I’m not sure it’s a good thing. Here’s what I observed:

  1. The user types the URL archive.dconstruct.org into the address bar.
  2. The site loads.
  3. The home-screen prompt slides up from the bottom of the screen.
  4. The user immediately moves to dismiss the prompt (cue me interjecting “Don’t close that!”).

This behaviour is entirely unsurprising for three reasons:

  1. We web designers and web developers have trained users to dismiss overlays and pop-ups if they actually want to get to the content. Nobody’s going to bother to actually read the prompt if there’s a 99% chance it’s going to say “Sign up to our newsletter!” or “Take our survey!”.
  2. The prompt appears below the “line of death” so there’s no way to tell it’s a browser or OS-level dialogue rather than a JavaScript-driven pop-up from the site.
  3. Because the prompt now appears on the first visit, no trust has been established between the user and the site. If the prompt only appeared on later visits (or later navigations during the first visit) perhaps it would stand a greater chance of survival.

It’s still possible to add a Progressive Web App to the home screen, but the option to do that is hidden behind the mysterious three-dots-vertically-stacked icon (I propose we call this the shish kebab icon to distinguish it from the equally impenetrable hamburger icon).

I was chatting with Andreas from Mozilla at the View Source conference last week, and he was filling me in on how Firefox on Android does the add-to-homescreen flow. Instead of a one-time prompt, they’ve added a persistent icon above the “line of death” (the icon is a combination of a house and a plus symbol).

When a Firefox 58 user arrives on a website that is served over HTTPS and has a valid manifest, a subtle badge will appear in the address bar: when tapped, an “Add to Home screen” confirmation dialog will slide in, through which the web app can be added to the Android home screen.

This kind of badging also has issues (without the explicit text “add to home screen”, the user doesn’t know what the icon does), but I think a more persistently visible option like this works better than the a one-time prompt.

Firefox is following the lead of the badging approach pioneered by the Samsung Internet browser. It provides a plus symbol that, when pressed, reveals the options to add to home screen or simply bookmark.

What does it mean to be an App?

I don’t think Chrome for Android has any plans for this kind of badging, but they are working on letting the site authors provide their own prompts. I’m not sure this is such a good idea, given our history of abusing pop-ups and overlays.

Sadly, I feel that any solution that relies on an unrequested overlay is doomed. That’s on us. The way we’ve turned browsing the web—especially on mobile—into a frustrating chore of dismissing unwanted overlays is a classic tragedy of the commons. We blew it. Users don’t trust unrequested overlays, and I can’t blame them.

For what it’s worth, my opinion is that ambient badging is a better user experience than one-time prompts. That opinion is informed by a meagre amount of testing though. I’d love to hear from anyone who’s been doing more detailed usability testing of both approaches. I assume that Google, Mozilla, and Samsung are doing this kind of testing, and it would be really great to see the data from that (hint, hint).

But it might well be that ambient badging is just too subtle to even be noticed by the user.

On one end of the scale you’ve got the intrusiveness of an add-to-home-screen prompt, but on the other end of the scale you’ve got the discoverability problem of a subtle badge icon. I wonder if there might be a compromise solution—maybe a badge icon that pulses or glows on the first or second visit?

Of course that would also need to be thoroughly tested.

The dConstruct Audio Archive works offline

The dConstruct conference is as old as Clearleft itself. We put on the first event back in 2005, the year of our founding. The last dConstruct was in 2015. It had a good run.

I’m really proud of the three years I ran the show—2012, 2013, and 2014—and I have great memories from each event. I’m inordinately pleased that the individual websites are still online after all these years. I’m equally pleased with the dConstruct audio archive that we put online in 2012. Now that the event itself is no longer running, it truly is an archive—a treasury of voices from the past.

I think that these kinds of online archives are eminently suitable for some offline design. So I’ve added a service worker script to the dConstruct archive.

Caching

To start with, there’s the no-brainer: as soon as someone hits the website, pre-cache static assets like CSS, JavaScript, the logo, and icon images. Now subsequent page loads will be quicker—those assets are taken straight from the cache.

But what about the individual pages? For something like Resilient Web Design—another site that won’t be updated—I pre-cache everything. I could do that with the dConstruct archive. All of the pages with all of the images add up to less than two megabytes; the entire site weighs less than a single page on Wired.com or The Verge.

In the end, I decided to go with a cache-as-you-go strategy. Every time a page or an image is fetched from the network, it is immediately put in a cache. The next time that page or image is requested, the file is served from that cache instead of the network.

Here’s the logic for fetch requests:

  1. First, look to see if the file is in a cache. If it is, great! Serve that.
  2. If the file isn’t in a cache, make a network request and serve the response …but put a copy of a file in the cache.
  3. The next time that file is requested, go to step one.

Save for offline

That caching strategy works great for pages, images, and other assets. But there’s one kind of file on the dConstruct archive that’s a bit different: the audio files. They can be fairly big, so I don’t want to cache those unless the user specifically requests it.

If you end up on the page for a particular talk, and your browser supports service workers, you’ll get an additional UI element in the list of options: a toggle to “save offline” (under the hood, it’s a checkbox). If you activate that option, then the audio file gets put into a cache.

Now if you lose your network connection while browsing the site, you’ll get a custom offline page with the option to listen to any audio files you saved for offline listening. You’ll also see this collection of talks on the homepage, regardless of whether you’ve got an internet connection or not.

So if you’ve got a long plane journey ahead of you, have a browse around the dConstruct archive and select some talks for your offline listening pleasure.

Or just enjoy the speediness of browsing the site.

Turning another website into a Progressive Web App.

Pattern Libraries, Performance, and Progressive Web Apps

Ever since its founding in 2005, Clearleft has been laser-focused on user experience design.

But we’ve always maintained a strong front-end development arm. The front-end development work at Clearleft is always in service of design. Over the years we’ve built up a wealth of expertise on using HTML, CSS, and JavaScript to make better user experiences.

Recently we’ve been doing a lot of strategic design work—the really in-depth long-term engagements that begin with research and continue through to design consultancy and collaboration. That means we’ve got availability for front-end development work. Whether it’s consultancy or production work you’re looking for, this could be a good opportunity for us to work together.

There are three particular areas of front-end expertise we’re obsessed with…

Pattern Libraries

We caught the design systems bug years ago, way back when Natalie started pioneering pattern libraries as our primary deliverable (or pattern portfolios, as we called them then). This approach has proven effective time and time again. We’ve spent years now refining our workflow and thinking around modular design. Fractal is the natural expression of this obsession. Danielle and Mark have been working flat-out on version 2. They’re very eager to share everything they’ve learned along the way …and help others put together solid pattern libraries.

Danielle Huntrods Mark Perkins

Performance

Thinking about it, it’s no surprise that we’re crazy about performance at Clearleft. Like I said, our focus on user experience, and when it comes to user experience on the web, nothing but nothing is more important than performance. The good news is that the majority of performance fixes can be done on the front end—images, scripts, fonts …it’s remarkable how much a good front-end overhaul can make to the bottom line. That’s what Graham has been obsessing over.

Graham Smith

Progressive Web Apps

Over the years I’ve found myself getting swept up in exciting new technologies on the web. When Clearleft first formed, my head was deep into DOM Scripting and Ajax. Half a decade later it was HTML5. Now it’s service workers. I honestly think it’s a technology that could be as revolutionary as Ajax or HTML5 (maybe I should write a book to that effect).

I’ve been talking about service workers at conferences this year, and I can’t hide my excitement:

There’s endless possibilities of what you can do with this technology. It’s very powerful.

Combine a service worker with a web app manifest and you’ve got yourself a Progressive Web App. It’s not just a great marketing term—it’s an opportunity for the web to truly excel at delivering the kind of user experiences previously only associated with native apps.

Jeremy Keith

I’m very very keen to work with companies and organisations that want to harness the power of service workers and Progressive Web Apps. If that’s you, get in touch.

Whether it’s pattern libraries, performance, or Progressive Web Apps, we’ve got the skills and expertise to share with you.

Progressing the web

Frances has written up some of the history behind her minting of the term “progressive web app”. She points out that accuracy is secondary to marketing:

I keep seeing folks (developers) getting all smart-ass saying they should have been PW “Sites” not “Apps” but I just want to put on the record that it doesn’t matter. The name isn’t for you and worrying about it is distraction from just building things that work better for everyone. The name is for your boss, for your investor, for your marketeer.

Personally, I think “progressive web app” is a pretty good phrase—two out of three words in it are spot on. I really like the word “progressive”, with its echoes of progressive enhancement. I really, really like the word “web”. But, yeah, I’m one of those smart-asses who points out that the “app” part isn’t great.

That’s not just me being a pedant (or, it’s not only me being a pedant). I’ve seen people who were genuinely put off investigating the technologies behind progressive web apps because of the naming.

Here’s an article with the spot-on title Progressive Web Apps — The Next Step In Responsive Web Design:

Late last week, Smashing Magazine, one of the largest and most influential online publications for web design, posted on Facebook that their website was “now running as a Progressive Web App.”

Honestly, I didn’t think much of it. Progressive Web Apps are for the hardcore web application developers creating the next online cloud-based Photoshop (complicated stuff), right? I scrolled on and went about my day.

And here’s someone feeling the cognitive dissonance of turning a website into a progressive web app, even though that’s exactly the right thing to do:

My personal website is a collection of static HTML files and is also a progressive web app. Transforming it into a progressive web app felt a bit weird in the beginning because it’s not an actual application but I wanted to be one of the cool kids, and PWAs still offer a lot of additional improvements.

Still, it could well be that these are the exceptions and that most people are not being discouraged by the “app” phrasing. I certainly hope that there aren’t more people out there thinking “well, progressive web apps aren’t for me because I’m building a content site.”

In short, the name might not be perfect but it’s pretty damn good.

What I find more troubling is the grouping of unrelated technologies under the “progressive web app” banner. If Google devrel events were anything to go by, you’d be forgiven for thinking that progressive web apps have something to do with AMP or Polymer (they don’t). One of the great things about progressive web apps is that they are agnostic to tech stacks. Still, I totally get why Googlers would want to use the opportunity to point to their other projects.

Far more troubling is the entanglement of the term “progressive web app” with the architectural choice of “single page app”. I’m not the only one who’s worried about this.

Here’s the most egregious example: an article on Hacker Noon called Before You Build a PWA You Need a SPA.

No! Not true! Literally any website can be a progressive web app:

That last step can be tricky if you’re new to service workers, but it’s not unsurmountable. It’s certainly a lot easier than completely rearchitecting your existing website to be a JavaScript-driven single page app.

Alas, I think that many of the initial poster-children for progressive web apps gave the impression that you had to make a completely separate app/site at a different URL. It was like a return to the bad old days of m. sites for mobile. The Washington Post’s progressive web app (currently offline) went so far as to turn away traffic from the “wrong” browsers. This is despite the fact that the very first item in the list of criteria for a progressive web app is:

Responsive: to fit any form factor

Now, I absolutely understand that the immediate priority is to demonstrate that a progressive web app can compete with a native mobile app in terms of features (and trounce it in terms of installation friction). But I’m worried that in our rush to match what native apps can do, we may end up ditching the very features that make the web a universally-accessible medium. Killing URLs simply because native apps don’t have URLs is a classic example of throwing the baby out with the bath water:

Up until now I’ve been a big fan of Progressive Web Apps. I understood them to be combining the best of the web (responsiveness, linkability) with the best of native (installable, connectivity independent). Now I see that balance shifting towards the native end of the scale at the expense of the web’s best features. I’d love to see that balance restored with a little less emphasis on the “Apps” and a little more emphasis on the “Web.” Now that would be progressive.

If the goal of the web is just to compete with native, then we’ve set the bar way too low.

So if you’ve been wary of investing the technologies behind progressive web apps because you’re “just” building a website, please try to see past the name. As Frances says:

It’s marketing, just like HTML5 had very little to do with actual HTML. PWAs are just a bunch of technologies with a zingy-new brandname.

Literally any website can—and should—be a progressive web app. Don’t let anyone tell you otherwise.

I was at an event last year where I heard Chris Heilmann say that you shouldn’t make your blog into a progressive web app. I couldn’t believe what I was hearing. He repeats that message in this video chat:

When somebody, for example, turns their blog into a PWA, I don’t see the point. I don’t want to have that icon on my homepage. This doesn’t make any sense to me.

Excuse me!? Just because you don’t want to have someone’s icon on your home screen, that person shouldn’t be using state-of-the-art technologies!? Excuse my French, but Fuck. That. Shit!

Our imaginations have become so limited by what native mobile apps currently do that we can’t see past merely imitating the status quo like a sad cargo cult.

I don’t want the web to equal native; I want the web to surpass it. I, for one, would prefer a reality where my home screen isn’t filled with the icons of startups and companies that have fulfilled the criteria of the gatekeepers. But a home screen filled with the faces of people who didn’t have to ask anyone’s permission to publish? That’s what I want!

Like Frances says:

Remember, this is for everyone.

Going offline at Indie Web Camp Düsseldorf

I’ve just come back from a ten-day trip to Germany. The trip kicked off with Indie Web Camp Düsseldorf over the course of a weekend.

IndieWebCamp Düsseldorf 2017

Once again the wonderful people at Sipgate hosted us in their beautiful building, and once again myself and Aaron helped facilitate the two days.

IndieWebCamp Düsseldorf 2017

Saturday was the BarCamp-like discussion day. Plenty of interesting topics were covered. I led a session on service workers, and that’s also what I decided to work on for the second day—that’s when the talking is done and we get down to making.

IndieWebCamp Düsseldorf 2017 IndieWebCamp Düsseldorf 2017 IndieWebCamp Düsseldorf 2017 IndieWebCamp Düsseldorf 2017

I like what Ethan is doing on his offline page. He shows a list of pages that have been cached, but instead of just listing URLs, he shows a title and description for each page.

I’ve already got a separate cache for pages that gets added to as the user browses around my site. I needed to figure out a way to store the metadata for those pages so that I could then display it on the offline page. I came up with a workable solution, and interestingly, it involved no changes to the service worker script at all.

When you visit any blog post, I put metadata about the page into localStorage (after first checking that there’s an active service worker):

if (navigator.serviceWorker && navigator.serviceWorker.controller) {
  window.addEventListener('load', function() {
    var data = {
      "title": "A minority report on artificial intelligence",
      "description": "Revisiting Spielberg’s films after a decade and a half.",
      "published": "May 7th, 2017",
      "timestamp": "1494171049"
    };
    localStorage.setItem(
      window.location.href,
      JSON.stringify(data)
    );
  });
}

In my case, I’m outputting the metadata from the server, but you could just as easily grab some from the DOM like this:

var data = {
  "title": document.querySelector("title").innerText,
  "description": document.querySelector("meta[name='description']").getAttribute("contents")
}

Meanwhile in my service worker, when you visit that same page, it gets added to a cache called “pages”. Both localStorage and the cache API are using URLs as keys. I take advantage of that on my offline page.

The nice thing about writing JavaScript on my offline page is that I know the page will only be seen by modern browsers that support service workers, so I can use all sorts of fancy from ES6, or whatever we’re calling it now.

I start by looping through the keys of the “pages” cache (that’s right—the cache API isn’t just for service workers; you can access it from any script). Then I check to see if there is a corresponding localStorage key with the same string (a URL). If there is, I pull the metadata out of local storage and add it to an array called browsingHistory:

const browsingHistory = [];
caches.open('pages')
.then( cache => {
  cache.keys()
  .then(keys => {
    keys.forEach( request => {
      let data = JSON.parse(localStorage.getItem(request.url));
        if (data) {
          data['url'] = request.url;
          browsingHistory.push(data);
      }
    });

Then I sort the list of pages in reverse chronological order:

browsingHistory.sort( (a,b) => {
  return b.timestamp - a.timestamp;
});

Now I loop through each page in the browsing history list and construct a link to each URL, complete with title and description:

let markup = '';
browsingHistory.forEach( data => {
  markup += `
<h2><a href="${ data.url }">${ data.title }</a></h2>
<p>${ data.description }</p>
<p class="meta">${ data.published }</p>
`;
});

Finally I dump the constructed markup into a waiting div in the page with an ID of “history”:

let container = document.getElementById('history');
container.insertAdjacentHTML('beforeend', markup);

All those steps need to be wrapped inside the then clause attached to caches.open("pages") because the cache API is asynchronous.

There you have it. Now if you’re browsing adactio.com and your network connection drops (or my server goes offline), you can choose from a list of pages you’ve previously visited.

The current situation isn’t ideal though. I’ve got a clean-up operation in my service worker to limit the number of items stored in my “pages” cache. The cache never gets bigger than 35 items. But there’s no corresponding clean-up of metadata stored in localStorage. So there could be a lot more bits of metadata in local storage than there are pages in the cache. It’s not harmful, but it’s a bit wasteful.

I can’t do a clean-up of localStorage from my service worker because service workers can’t access localStorage. There’s a very good reason for that: the localStorage API is synchronous, and everything that happens in a service worker needs to be asynchronous.

Service workers can access indexedDB: it’s asynchronous. I could use indexedDB instead of localStorage, but I’m not a masochist. My best bet would be to use the localForage library, which wraps indexedDB in the simple syntax of localStorage.

Maybe I’ll do that at the next Homebrew Website Club here in Brighton.

Progressive Web App questions

I got a nice email recently from Colin van Eenige. He wrote:

For my graduation project I’m researching the development of Progressive Web Apps and found your offline book called resilient web design. I was very impressed by the implementation of the website and it really was a nice experience.

I’m very interested in your vision on progressive web apps and what capabilities are waiting for us regarding offline content. Would it be fine if I’d send you some questions?

I said that would be fine, although I couldn’t promise a swift response. He sent me four questions. I finally got ‘round to sending my answers…

1. https://resilientwebdesign.com/ is an offline web book (progressive web app). What was the primary reason make it available like this (besides the other formats)?

Well, given the subject matter, it felt right that the canonical version of the book should be not just online, but made with the building blocks of the web. The other formats are all nice to have, but the HTML version feels (to me) like the “real” book.

Interestingly, it wasn’t too much trouble for people to generate other formats from the HTML (ePub, MOBI, PDF), whereas I think trying to go in the other direction would be trickier.

As for the offline part, that felt like a natural fit. I had already done that with a previous book of mine, HTML5 For Web Designers, which I put online a year or two after its print publication. In that case, I used AppCache for the offline functionality. AppCache is horrible, but this use case might be one of the few where it works well: a static book that’s never going to change. Cache invalidation is one of the worst parts of using AppCache so by not having any kinds of updates at all, I dodged that bullet.

But when it came time for Resilient Web Design, a service worker was definitely the right technology. Still, I’ve got AppCache in there as well for the browsers that don’t yet support service workers.

2. What effect you you think Progressive Web Apps will have on content consuming and do you think these will take over the purpose of some Native Apps?

The biggest effect that service workers could have is to change the expectations that people have about using the web, especially on mobile devices. Right now, people associate the web on mobile with long waits and horrible spammy overlays. Service workers can help solve that first part.

If people then start adding sites to their home screen, that will be a great sign that the web is really holding its own. But I don’t think we should get too optimistic about that: for a user, there’s no difference between a prompt on their screen saying “add to home screen” and a prompt on their screen saying “download our app”—they’re equally likely to be dismissed because we’ve trained people to dismiss anything that covers up the content they actually came for.

It’s entirely possible that websites could start taking over much of the functionality that previously was only possible in a native app. But I think that inertia and habit will keep people using native apps for quite some time.

The big exception is in markets where storage space on devices is in short supply. That’s where the decision to install a native app isn’t taken likely (given the choice between your family photos and an app, most people will reject the app). The web can truly shine here if we build lightweight, performant services.

Even in that situation, I’m still not sure how many people will end up adding those sites to their home screen (it might feel so similar to installing a native app that there may be some residual worry about storage space) but I don’t think that’s too much of a problem: if people get to a site via search or typing, that’s fine.

I worry that the messaging around “progressive web apps” is perhaps over-fetishising the home screen. I don’t think that’s the real battleground. The real battleground is in people’s heads; how they perceive the web and how they perceive native.

After all, if the average number of native apps installed in a month is zero, then that’s not exactly a hard target to match. :-)

3. What is your vision regarding Progressive Web Apps?

For me, progressive web apps don’t feel like a separate thing from making websites. I worry that the marketing of them might inflate expectations or confuse people. I like the idea that they’re simply websites that have taken their vitamins.

So my vision for progressive web apps is the same as my vision for the web: something that people use every day for all sorts of tasks.

I find it really discouraging that progressive web apps are becoming conflated with single page apps and the app shell model. Those architectural decisions have nothing to do with service workers, HTTPS, and manifest files. Yet I keep seeing the concepts used interchangeably. It would be a real shame if people chose not to use these great technologies just because they don’t classify what they’re building as an “app.”

If anything, it’s good ol’ fashioned content sites (newspapers, wikipedia, blogs, and yes, books) that can really benefit from the turbo boost of service worker+HTTPS+manifest.

I was at a conference recently where someone was given a talk encouraging people to build progressive web apps but discouraging people from doing it for their own personal sites. That’s a horrible, elitist attitude. I worry that this attitude is being codified in the term “progressive web app”.

4. What is the biggest learning you’ve had since working on Progressive Web Apps?

Well, like I said, I think that some people are focusing a bit too much on the home screen and not enough on the benefits that service workers can provide to just about any website.

My biggest learning is that these technologies aren’t for a specific subset of services, but can benefit just about anything that’s on the web. I mean, just using a service worker to explicitly cache static assets like CSS, JS, and some images is a no-brainer for almost any project.

So there you go—I’m very excited about the capabilities of these technologies, but very worried about how they’re being “sold”. I’m particularly nervous that in the rush to emulate native apps, we end up losing the very thing that makes the web so powerful: URLs.