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:

• Torre’s notes from this talk.

This was originally posted on my own site.