Tags: performance

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Monday, May 20th, 2019

Web Bloat Score Calculator

Page web bloat score (WebBS for short) is calculated as follows:

WebBS = TotalPageSize / PageImageSize

Yes, this is a tongue-in-cheek somewhat arbitrary measurement, but it’s well worth reading through the rationale for it.

How can the image of a page be smaller than the page itself?

Wednesday, May 8th, 2019

Timing out

Service workers are great for creating a good user experience when someone is offline. Heck, the book I wrote about service workers is literally called Going Offline.

But in some ways, the offline experience is relatively easy to handle. It’s a binary situation; either you’re online or you’re offline. What’s more challenging—and probably more common—is the situation that Jake calls Lie-Fi. That’s when technically you’ve got a network connection …but it’s a shitty connection, like one bar of mobile signal. In that situation, because there’s technically a connection, the user gets a slow frustrating experience. Whatever code you’ve got in your service worker for handling offline situations will never get triggered. When you’re handling fetch events inside a service worker, there’s no automatic time-out.

But you can make one.

That’s what I’ve done recently here on adactio.com. Before showing you what I added to my service worker script to make that happen, let me walk you through my existing strategy for handling offline situations.

Service worker strategies

Alright, so in my service worker script, I’ve got a block of code for handling requests from fetch events:

addEventListener('fetch', fetchEvent => {
        const request = fetchEvent.request;
    // Do something with this request.
});

I’ve got two strategies in my code. One is for dealing with requests for pages:

if (request.headers.get('Accept').includes('text/html')) {
    // Code for handling page requests.
}

By adding an else clause I can have a different strategy for dealing with requests for anything else—images, style sheets, scripts, and so on:

if (request.headers.get('Accept').includes('text/html')) {
    // Code for handling page requests.
} else {
    // Code for handling everthing else.
}

For page requests, I’m going to try to go the network first:

fetchEvent.respondWith(
    fetch(request)
    .then( responseFromFetch => {
        return responseFromFetch;
    })

My logic is:

When someone requests a page, try to fetch it from the network.

If that doesn’t work, we’re in an offline situation. That triggers the catch clause. That’s where I have my offline strategy: show a custom offline page that I’ve previously cached (during the install event):

.catch( fetchError => {
    return caches.match('/offline');
})

Now my logic has been expanded to this:

When someone requests a page, try to fetch it from the network, but if that doesn’t work, show a custom offline page instead.

So my overall code for dealing with requests for pages looks like this:

if (request.headers.get('Accept').includes('text/html')) {
    fetchEvent.respondWith(
        fetch(request)
        .then( responseFromFetch => {
            return responseFromFetch;
        })
        .catch( fetchError => {
            return caches.match('/offline');
        })
    );
}

Now I can fill in the else statement that handles everything else—images, style sheets, scripts, and so on. Here my strategy is different. I’m looking in my caches first, and I only fetch the file from network if the file can’t be found in any cache:

caches.match(request)
.then( responseFromCache => {
    return responseFromCache || fetch(request);
})

Here’s all that fetch-handling code put together:

addEventListener('fetch', fetchEvent => {
    const request = fetchEvent.request;
    if (request.headers.get('Accept').includes('text/html')) {
        fetchEvent.respondWith(
            fetch(request)
            .then( responseFromFetch => {
                return responseFromFetch;
            })
            .catch( fetchError => {
                return caches.match('/offline');
            })
        );
    } else {
        caches.match(request)
        .then( responseFromCache => {
            return responseFromCache || fetch(request);
        })
    }
});

Good.

Cache as you go

Now I want to introduce an extra step in the part of the code where I deal with requests for pages. Whenever I fetch a page from the network, I’m going to take the opportunity to squirrel it away in a cache. I’m calling that cache “pages”. I’m imaginative like that.

fetchEvent.respondWith(
    fetch(request)
    .then( responseFromFetch => {
        const copy = responseFromFetch.clone();
        try {
            fetchEvent.waitUntil(
                caches.open('pages')
                .then( pagesCache => {
                    return pagesCache.put(request, copy);
                })
            )
        } catch(error) {
            console.error(error);
        }
        return responseFromFetch;
    })

You’ll notice that I can’t put the response itself (responseFromCache) into the cache. That’s a stream that I only get to use once. Instead I need to make a copy:

const copy = responseFromFetch.clone();

That’s what gets put in the pages cache:

fetchEvent.waitUntil(
    caches.open('pages')
    .then( pagesCache => {
        return pagesCache.put(request, copy);
    })
)

Now my logic for page requests has an extra piece to it:

When someone requests a page, try to fetch it from the network and store a copy in a cache, but if that doesn’t work, show a custom offline page instead.

Here’s my updated fetch-handling code:

addEventListener('fetch', fetchEvent => {
    const request = fetchEvent.request;
    if (request.headers.get('Accept').includes('text/html')) {
        fetchEvent.respondWith(
            fetch(request)
            .then( responseFromFetch => {
                const copy = responseFromFetch.clone();
                try {
                    fetchEvent.waitUntil(
                        caches.open('pages')
                        .then( pagesCache => {
                            return pagesCache.put(request, copy);
                        })
                    )
                } catch(error) {
                    console.error(error);
                }
                return responseFromFetch;
            })
            .catch( fetchError => {
                return caches.match('/offline');
            })
        );
    } else {
        caches.match(request)
        .then( responseFromCache => {
            return responseFromCache || fetch(request);
        })
    }
});

I call this the cache-as-you-go pattern. The more pages someone views on my site, the more pages they’ll have cached.

Now that there’s an ever-growing cache of previously visited pages, I can update my offline fallback. Currently, I reach straight for the custom offline page:

.catch( fetchError => {
    return caches.match('/offline');
})

But now I can try looking for a cached copy of the requested page first:

.catch( fetchError => {
    caches.match(request)
    .then( responseFromCache => {
        return responseFromCache || caches.match('/offline');
    })
});

Now my offline logic is expanded:

When someone requests a page, try to fetch it from the network and store a copy in a cache, but if that doesn’t work, first look for an existing copy in a cache, and otherwise show a custom offline page instead.

I can also access this ever-growing cache of pages from my custom offline page to show people which pages they can revisit, even if there’s no internet connection.

So far, so good. Everything I’ve outlined so far is a good robust strategy for handling offline situations. Now I’m going to deal with the lie-fi situation, and it’s that cache-as-you-go strategy that sets me up nicely.

Timing out

I want to throw this addition into my logic:

When someone requests a page, try to fetch it from the network and store a copy in a cache, but if that doesn’t work, first look for an existing copy in a cache, and otherwise show a custom offline page instead (but if the request is taking too long, try to show a cached version of the page).

The first thing I’m going to do is rewrite my code a bit. If the fetch event is for a page, I’m going to respond with a promise:

if (request.headers.get('Accept').includes('text/html')) {
    fetchEvent.respondWith(
        new Promise( resolveWithResponse => {
            // Code for handling page requests.
        })
    );
}

Promises are kind of weird things to get your head around. They’re tailor-made for doing things asynchronously. You can set up two parameters; a success condition and a failure condition. If the success condition is executed, then we say the promise has resolved. If the failure condition is executed, then the promise rejects.

In my re-written code, I’m calling the success condition resolveWithResponse (and I haven’t bothered with a failure condition, tsk, tsk). I’m going to use resolveWithResponse in my promise everywhere that I used to have a return statement:

addEventListener('fetch', fetchEvent => {
    const request = fetchEvent.request;
    if (request.headers.get('Accept').includes('text/html')) {
        fetchEvent.respondWith(
            new Promise( resolveWithResponse => {
                fetch(request)
                .then( responseFromFetch => {
                    const copy = responseFromFetch.clone();
                    try {
                        fetchEvent.waitUntil(
                            caches.open('pages')
                            then( pagesCache => {
                                return pagesCache.put(request, copy);
                            })
                        )
                    } catch(error) {
                        console.error(error);
                    }
                    resolveWithResponse(responseFromFetch);
                })
                .catch( fetchError => {
                    caches.match(request)
                    .then( responseFromCache => {
                        resolveWithResponse(
                            responseFromCache || caches.match('/offline')
                        );
                    })
                })
            })
        );
    } else {
        caches.match(request)
        .then( responseFromCache => {
            return responseFromCache || fetch(request);
        })
    }
});

By itself, rewriting my code as a promise doesn’t change anything. Everything’s working the same as it did before. But now I can introduce the time-out logic. I’m going to put this inside my promise:

const timer = setTimeout( () => {
    caches.match(request)
    .then( responseFromCache => {
        if (responseFromCache) {
            resolveWithResponse(responseFromCache);
        }
    })
}, 3000);

If a request takes three seconds (3000 milliseconds), then that code will execute. At that point, the promise attempts to resolve with a response from the cache instead of waiting for the network. If there is a cached response, that’s what the user now gets. If there isn’t, then the wait continues for the network.

The last thing left for me to do is cancel the countdown to timing out if a network response does return within three seconds. So I put this in the then clause that’s triggered by a successful network response:

clearTimeout(timer);

I also add the clearTimeout statement to the catch clause that handles offline situations. Here’s the final code:

addEventListener('fetch', fetchEvent => {
    const request = fetchEvent.request;
    if (request.headers.get('Accept').includes('text/html')) {
        fetchEvent.respondWith(
            new Promise( resolveWithResponse => {
                const timer = setTimeout( () => {
                    caches.match(request)
                    .then( responseFromCache => {
                        if (responseFromCache) {
                            resolveWithResponse(responseFromCache);
                        }
                    })
                }, 3000);
                fetch(request)
                .then( responseFromFetch => {
                    clearTimeout(timer);
                    const copy = responseFromFetch.clone();
                    try {
                        fetchEvent.waitUntil(
                            caches.open('pages')
                            then( pagesCache => {
                                return pagesCache.put(request, copy);
                            })
                        )
                    } catch(error) {
                        console.error(error);
                    }
                    resolveWithResponse(responseFromFetch);
                })
                .catch( fetchError => {
                    clearTimeout(timer);
                    caches.match(request)
                    .then( responseFromCache => {
                        resolveWithResponse(
                            responseFromCache || caches.match('/offline')
                        );
                    })
                })
            })
        );
    } else {
        caches.match(request)
        .then( responseFromCache => {
            return responseFromCache || fetch(request)
        })
    }
});

That’s the JavaScript translation of this logic:

When someone requests a page, try to fetch it from the network and store a copy in a cache, but if that doesn’t work, first look for an existing copy in a cache, and otherwise show a custom offline page instead (but if the request is taking too long, try to show a cached version of the page).

For everything else, try finding a cached version first, otherwise fetch it from the network.

Pros and cons

As with all service worker enhancements to a website, this strategy will do absolutely nothing for first-time visitors. If you’ve never visited my site before, you’ve got nothing cached. But the more you return to the site, the more your cache is primed for speedy retrieval.

I think that serving up a cached copy of a page when the network connection is flaky is a pretty good strategy …most of the time. If we’re talking about a blog post on this site, then sure, there won’t be much that the reader is missing out on—a fixed typo or ten; maybe some additional webmentions at the end of a post. But if we’re talking about the home page, then a reader with a flaky network connection might think there’s nothing new to read when they’re served up a stale version.

What I’d really like is some way to know—on the client side—whether or not the currently-loaded page came from a cache or from a network. Then I could add some kind of interface element that says, “Hey, this page might be stale—click here if you want to check for a fresher version.” I’d also need some way in the service worker to identify any requests originating from that interface element and make sure they always go out to the network.

I think that should be doable somehow. If you can think of a way to do it, please share it. Write a blog post and send me the link.

But even without the option to over-ride the time-out, I’m glad that I’m at least doing something to handle the lie-fi situation. Perhaps I should write a sequel to Going Offline called Still Online But Only In Theory Because The Connection Sucks.

Tuesday, May 7th, 2019

Test the impact of ads and third party scripts

This is a very useful new feature in Calibre, the performance monitoring tool. Now you can get data about just how much third-party scripts are affecting your site’s performance:

The best way of circumventing fear and anxiety around third party script performance is to capture metrics that clearly articulate their performance impact.

Tuesday, April 30th, 2019

Progressive Font Enrichment: reinventing web font performance | Responsive Web Typography

Jason describes the next big thing in web typography: streaming fonts!

…to enable the ability for only the required part of the font be downloaded on any given page, and for subsequent requests for that font to dynamically ‘patch’ the original download with additional sets of glyphs as required on successive page views—even if they occur on separate sites.

Friday, April 26th, 2019

How I failed the <a>

I think the situation that Remy outlines here is quite common (in client-rehydrated server-rendered pages), but what’s less common is Remy’s questioning and iteration.

So I now have a simple rule of thumb: if there’s an onClick, there’s got to be an anchor around the component.

Wednesday, April 24th, 2019

Preload, prefetch and other link tags: what they do and when to use them · PerfPerfPerf

Following on from Harry’s slides, here’s another round-up of thoserel attribute values that begin with pre.

More Than You Ever Wanted to Know About Resource Hints - Speaker Deck

Slides from Harry’s deep dive into rel values: preconnect, prefetch, and preload.

Friday, April 12th, 2019

Google AMP lowered our page speed, and there’s no choice but to use it - unlike kinds

What happens when you’re AMP pages are slower than your regular pages …but you’re forced to use AMP anyway if you want to appear in the top stories carousel.

AMP isn’t about speed. It’s about control.

The elephant in the room here is pre-rendering: that’s why Google aren’t using page speed alone as a determining factor for what goes in the carousel.

Monday, April 8th, 2019

AddyOsmani.com - Native image lazy-loading for the web!

The loading attribute for images and iframes is coming to Chrome. The best part:

You can also use loading as a progressive enhancement. Browsers that support the attribute can get the new lazy-loading behavior with loading=lazy and those that don’t will still have images load.

Thursday, March 28th, 2019

Responsible JavaScript: Part I · An A List Apart Article

As I pick apart yet another bundle not unlike a tangled ball of Christmas tree lights, it’s become clear that the web is drunk on JavaScript. We reach for it for almost everything, even when the occasion doesn’t call for it. Sometimes I wonder how vicious the hangover will be.

I love everything about this article and I can’t wait for part two.

What we tend to forget is that the environment websites and web apps occupy is one and the same. Both are subject to the same environmental pressures that the large gradient of networks and devices impose. Those constraints don’t suddenly vanish when we decide to call what we build “apps”, nor do our users’ phones gain magical new powers when we do so.

Needless to say, I endorse this message:

Whether you think of your site as an “app” or not, adding a service worker to it is perhaps one of the most responsible uses of JavaScript that exists today.

Monday, March 25th, 2019

Stuffing the Front End

53% of mobile visits leave a page that takes longer than 3 seconds to load. That means that a large number of visitors probably abandoned these sites because they were staring at a blank screen for 3 seconds, said “fuck it,” and left approximately half way before the page showed up. The fact that the next page interaction would have been quicker—assuming all the JS files even downloaded correctly in the first attempt—doesn’t amount to much if they didn’t stick around for the first page to load. What was gained by putting the business logic in the front end in this scenario?

Friday, March 22nd, 2019

Who has the fastest website in F1? - JakeArchibald.com

I think I physically winced on more than one occassion as I read through Jake’s report here.

He makes an interesting observation at the end:

However, none of the teams used any of the big modern frameworks. They’re mostly Wordpress & Drupal, with a lot of jQuery. It makes me feel like I’ve been in a bubble in terms of the technologies that make up the bulk of the web.

Yes! This! Contrary to what you might think reading through the latest and greatest tips and tricks from the front-end community, the vast majority of sites out there on the web are not being built with React, Vue, webpack or any other “modern” tools.

Monday, March 18th, 2019

The Lean Web video from Boston CSS | Go Make Things

A good talk from from Chris Ferdinandi, who says:

One of the central themes of my talk on The Lean Web is that we as developers repeatedly take all of the great things the web and browsers give us out-of-the-box, break them, and then re-implement them poorly with JavaScript.

Friday, March 15th, 2019

Wednesday, March 13th, 2019

Chromium Blog: Chrome Lite Pages - For a faster, leaner loading experience

My first reaction to this was nervousness. Of all the companies to trust with intercepting and rerouting page requests, Google aren’t exactly squeeky clean, what with that whole surveillance business model of theirs.

Still, this ultimately seems to be a move to improve the end user experience, and I’m glad to see this clarification:

Lite pages are only triggered for extremely slow sites, so we encourage developers to measure how well their pages are currently performing over slow networks.

Lite pages as a badge of shame (much like AMP in my eyes).

Saturday, March 9th, 2019

Performance Budgets That Stick - TimKadlec.com

I like Tim’s definition here:

A performance budget is a clearly defined limit on one or more performance metrics that the team agrees not to exceed, and that is used to guide design and development.

And I agree about the four attributes required for a performance budget to succeed. It must be:

  1. Concrete
  2. Meaningful
  3. Integrated
  4. Enforceable

The point is not to let the performance budget try to stand on its own, somewhere hidden in company documentation collecting dust. You need to be proactive about making the budget become a part of your everyday work.

Friday, March 8th, 2019

Tuning Performance for New and “Old” Friends | Filament Group, Inc., Boston, MA

This is a really clever technique from Scott that he unveiled at An Event Apart in Seattle. It uses a header sent by a service worker to distinguish between returning and new visitors—much neater than relying on a cookie. I’ve updated my service worker on The Session to use this technique now.

Tuesday, March 5th, 2019

Mobile Planet by Luke Wroblewski

It’s the afternoon of day two of An Event Apart in Seattle. The mighty green one, Luke Wroblewski, is here to deliver a talk called Mobile Planet:

With 3.5 billion active smartphones on Earth, we’re now faced with the challenges and opportunities of designing planet-scale software. Through a data-informed, big-picture walk-through of our mobile planet, Luke will dig into how people use computing devices today and how the design of our products needs to adapt to this reality. He’ll cover key issues like app on-boarding and performance in enough detail to give you clear ways to improve first time and subsequent use of your mobile apps and sites.

Luke has been working on figuring out hardware and software for years. He looks at a lot of data. The more we understand how people use technology in their daily lives, the better we can design for them.

Earth is the third planet from the sun, and the only place that we know of that harbours life. Our population is at about 7.7 billion people. There are about 5.6 billion people in our addressable market (people over 14 years old). There are already 5 billion mobile subscribers in there. That’s interesting, but which of those devices are modern smartphones? There are about 3.6 billion active smartphones. Compare that to about 1.3 billion active personal computers—the vast majority of them Windows devices (about 1.2 billion). Over the next four or five years, we’ll have about 5 billion smartphone users and a global population of 8 billion.

The point is that we can reach a significant proportion of the human species. The diversity of our species makes it challenging to design for everyone.

Let’s take a closer look at these 3.6 billion active smartphones. About 25% of them are iOS devices. 75% of them are Android. Bear in mind that these are active devices—what’s actually being used. That’s different to shipping devices. Apple ships 15% of smartphone, and Android ships 85%, but the iOS devices tend to have longer lifespans (around 2 years for Android; around 4 years for iOS).

The UK has 82% smartphone penetration. Compare that to India, where it’s 27%. There’s room to grow.

Everywhere you look, the growth of these devices has led to a shift of digital things overtaking analogue. Shopping, advertising, music, you name it. We’ve seen enough of these transitions happen, that we should be prepared for it.

So there are lots of smartphones, with basically two major operating systems. But how are people using these devices?

In the US, adults spend about 2.3 - 3.5 hours per day on their mobile devices. Let’s call it an even 3 hours. That’s a lot of time. Where does that time come from? Interestingly, as time spent on mobile devices has surged, time spent on other media has only slowly declined. So mobile is additive. It’s contributing to more time spent on the internet rather than taking it away from existing screen time.

Next question: what the hell are people doing during those 3 hours per day on smartphones? Native apps get about 169 minutes of time compared to only 11 minutes on the web. There are about 2 million native apps on Apple, and about 2 million native apps on Android. But although people have a lot of apps, people only use about half them. Remember folks, downloads does not equal usage. Most apps don’t make it past the first opening. Only a third make it past being opened ten times.

Because people spend so much time and energy on these apps, and given the abysmal abandonment, people start freaking out about “engagement.” So what do they reach for? Push notifications. Either that or onboarding.

Push notifications. The worst. I mean, they do succeed in getting your attention: push notifications do increase the amount of time spent in your app …but there’s a human cost.

Let’s look at app onboarding. Take Flickr, for example. It walks through some of the features and benefits of the service. But it doesn’t actually help you much. It’s a list of marketing slogans. So why do people reach for onboarding?

If you just drop people into an interface and talk to them about it, they’ll say things like “I don’t know what to do. I’m lost.” The Intuit team heard this from people using their app. They reached for onboarding to solve the problem. They created guided tutorials and intro tours. Turns out that nobody would read these screens and everyone would try to skip them. What the hell, people!?

So they try in-context help, with a cute cartoon robot to explain the features. Or they scribble Einstein’s equations over the interface. Test this. People respond with “Please make it stop.”

They decided to try something simpler: one tip that calls out a good first step. That worked.

Vevo used to have an intro tour. Most people were swiping through without reading. They experimented with not running the tour. They got a 10% increase in log-ins and a 6% increase in sign-ups.

Vevo got rid of their tour, but left the sign-in/registration step. You can’t remove that, right?

Well, Hotel Tonight experimented with not doing registration. Signing up was confusing people—it’s Hotels Tonight, not Accounts Today. When they got rid of accounts, they saw a 15% increase in conversions.

Ruthlessly edit.

Google Photos used to have an in-depth on-boarding experience. First they got rid of the animation. Then the start-up screen. Then the animated tutorial. Each time they removed something, conversion went up. All that was left from the original onboarding was a half screen with one option to turn on auto-backup.

Get to your product value as fast as possible. Of course that requires you to know what your core value is. And that’s not easy to figure out.

Google Maps went through a similar reduction, removing intro screens and explanations. Now they just drop you into the map.

It’s not “get rid of everything”. It’s “get rid of everything that gets in the way of the core user action.”

Going back to the Intuit example, that’s exactly what they did in the end. That one initial tip was for the core action.

But it’s worth discussing how to present this kind of thing. If you have to overlay a tooltip for an important UI feature, maybe that UI feature should have a clearer affordance. People treat overlays as annoyances. People ignore or dismiss overlays when they’re focused on a task. It’s like an instinct to get rid of them. So if you put something useful or valuable there, it’s gone.

The core part of your application should feel like the core part of your application. It’s tough because stakeholders want to make things “pop.” We throw contrast, colour, and animation at things. But when something sticks out from the UI, people ignore it. Integrate the core action into the product UI. When elements feel foreign to a product UI, they are at best ignored, or at worst dismissed.

These is why cohesive design matters. It’s not about consistency. It’s about feeling integrated. In many cases, consistency can be counter-productive.

Some principles for successful onboarding:

  1. Get to to the product value as fast as possible. Grubhub needs your address. Pinterest needs your interests.
  2. Get rid of everything that doesn’t lead to that product value. Ruthlessly edit. Remove all friction that distracts the user from experiencing product value.
  3. Don’t be afraid to educate contextually. But do so with integrated UI.

Luke talked a lot about what’s happening in mobile apps, and mentioned that the mobile web only gets 11 minutes to the native’s 169. But let’s dive into this, because people sometimes think that a “mobile strategy” comes down to picking between these two. 50% of those 169 minutes are spent in your most used app (Facebook). 78% of the time is spent in the top 5 apps. Now the mobile web doesn’t look so bad. It turns out you can get people to a mobile web experience much, much faster than to a native one. The audience size is much, much, much higher on the web (although people will do more in a dedicated native app). So strategically both are useful—the web can attract people to native.

Back to our planet, and those 3 hours of usage on smartphones every day. People unlock their phones around 80 times a day. The average time people sleep is about 8 hours. So for every 12 waking minutes, you’re unlocking your phone. Given this frequency, it’s unsurprising that most sessions are very short—most under 30 seconds.

Given that, if things are slow, you’re going to really, really, really hate it. Waiting for slow pages to load is what really pisses people off.

The cognitive load and stress of waiting for slow pages is worse than waiting in line in a store, or watching a horror movie. That’s an industry that’s all about stressing people out by design! But experiencing mobile delays is more stressful! Probably because people aren’t watching horror movies every 12 minutes.

Because mobile delays are such a big deal, many mobile apps reach for loading spinners. But Luke saw that adding a spinner to his product increased complaints of slow loading times. Of course! The spinner is explicitly telling people, “Hey, we’re slow.”

So the switched to skeleton screens. This should feel like something is always happening. Focus on the progress, not the progress indicator. Occupied time feels shorter than unoccupied time.

A lot of people have implemented skeleton screen, but without the progressive loading. Swapping out a skeleton screen to a completely different UI all at once doesn’t help. The skeleton screens should represent the real content.

This is a lot of work; figuring how to prioritise what to load first. Luke isn’t talking about the techical side here, but the user’s experience. Investing in getting this right makes a lot of sense.

Let’s look a little closer at this number: people interacting with their phones 80 times a day. The average user touches the device 2,617 times a day. A power user touches the device over 5,000 times a day. Most touches are within one app.

90% of the touches are dealing with one thumb. Young people tend to operate with one hand. For older people, it’s more like 60%.

This is why your interface targets need to work for the thumb.

On phones, 90% of the time you’re dealing with portrait mode. Things at the top of the screen on larger devices are hard to reach. Core actions gravitate to the bottom of the screen.

Opera Touch is a new browser designed specifically for one-handed use. The Palm Pre’s WebOS was also about one-hand usage. Now that’s how iOS and Android work: swiping up from the bottom.

So mobile usage is:

  • One-handed/thumb.
  • In portrait mode on large screens.
  • Design accordingly.

What’s next? What do we need to be aware of so we don’t get caught with our pants down?

We can use the product lifecycle chart to figure this out. There’s an emergent phase, then a growth phase, then consolidation in a mature market, and then that gets disrupted and becomes a declining market.

  • Mobile devices—hand computers—are in a mature consolidated market.
  • Desktop and laptop computers are in a declining market.
  • Wrist computers and voice computers are in a growth market.

Small screens get used more frequently, but for shorter periods of time than large screens. Wrist and voice computers are figuring out what their core offerings are.

In the emergent category, it’s all about exploration. We have no idea how things will turn out. We just don’t know. But we do know that we are now designing for lots and lots of different devices.

For today, though, focusing on mobile is still a pretty good idea.

To summarise:

  • It’s a mobile planet.
  • Understanding real world usage helps you design.
  • Prep for what’s next

Move Fast and Don’t Break Things by Scott Jehl

Scott Jehl is speaking at An Event Apart in Seattle—yay! His talk is called Move Fast and Don’t Break Things:

Performance is a high priority for any site of scale today, but it can be easier to make a site fast than to keep it that way. As a site’s features and design evolves, its performance is often threatened for a number of reasons, making it hard to ensure fast, resilient access to services. In this session, Scott will draw from real-world examples where business goals and other priorities have conflicted with page performance, and share some strategies and practices that have helped major sites overcome those challenges to defend their speed without compromises.

The title is a riff on the “move fast and break things” motto, which comes from a more naive time on the web. But Scott finds part of it relatable. Things break. We want to move fast without breaking things.

This is a performance talk, which is another kind of moving fast. Scott starts with a brief history of not breaking websites. He’s been chipping away at websites for 20 years now. Remember Positioning Is Everything? How about Quirksmode? That one's still around.

In the early days, building a website that was "not broken" was difficult, but it was difficult for different reasons. We were focused on consistency. We had deal with differences between browsers. There were two ways of dealing with browsers: browser detection and feature detection.

The feature-based approach was more sustainable but harder. It fits nicely with the practice of progressive enhancement. It's a good mindset for dealing with the explosion of devices that kicked off later. Touch screens made us rethink our mouse and hover-centric matters. That made us realise how much keyboard-driven access mattered all along.

Browsers exploded too. And our data networks changed. With this explosion of considerations, it was clear that our early ideas of “not broken” didn’t work. Our notion of what constituted “not broken” was itself broken. Consistency just doesn’t cut it.

But there was a comforting part to this too. It turned out that progressive enhancement was there to help …even though we didn’t know what new devices were going to appear. This is a recurring theme throughout Scott’s career. So given all these benefits of progressive enhancement, it shouldn’t be surprising that it turns out to be really good for performance too. If you practice progressive enhancement, you’re kind of a performance expert already.

People started talking about new performance metrics that we should care about. We’ve got new tools, like Page Speed Insights. It gives tangible advice on how to test things. Web Page Test is another great tool. Once you prove you’re a human, Web Page Test will give you loads of details on how a page loaded. And you get this great visual timeline.

This is where we can start to discuss the metrics we want to focus on. Traditionally, we focused on file size, which still matters. But for goal-setting, we want to focus on user-perceived metrics.

First Meaningful Content. It’s about how soon appears to be useful to a user. Progressive enhancement is a perfect match for this! When you first make request to a website, it’s usually for a web page. But to render that page, it might need to request more files like CSS or JavaScript. All of this adds up. From a user perspective, if the HTML is downloaded, but the browser can’t render it, that’s broken.

The average time for this on the web right now is around six seconds. That’s broken. The render blockers are the problem here.

Consider assets like scripts. Can you get the browser to load them without holding up the rendering of the page? If you can add async or defer to a script element in the head, you should do that. Sometimes that’s not an option though.

For CSS, it’s tricky. We’ve delivered the HTML that we need but we’ve got to wait for the CSS before rendering it. So what can you bundle into that initial payload?

You can user server push. This is a new technology that comes with HTTP2. H2, as it’s called, is very performance-focused. Just turning on H2 will probably make your site faster. Server push allows the server to send files to the browser before the browser has even asked for them. You can do this with directives in Apache, for example. You could push CSS whenever an HTML file is requested. But we need to be careful not to go too far. You don’t want to send too much.

Server push is great in moderation. But it is new, and it may not even be supported by your server.

Another option is to inline CSS (well, actually Scott, this is technically embedding CSS). It’s great for first render, but isn’t it wasteful for caching? Scott has a clever pattern that uses the Cache API to grab the contents of the inlined CSS and put a copy of its contents into the cache. Then it’s ready to be served up by a service worker.

By the way, this isn’t just for CSS. You could grab the contents of inlined SVGs and create cached versions for later use.

So inlining CSS is good, but again, in moderation. You don’t want to embed anything bigger than 15 or 20 kilobytes. You might want separate out the critical CSS and only embed that on first render. You don’t need to go through your CSS by hand to figure out what’s critical—there are tools that to do this that integrate with your build process. Embed that critical CSS into the head of your document, and also start preloading the full CSS. Here’s a clever technique that turns a preload link into a stylesheet link:

<link rel="preload" href="site.css" as="style" onload="this.rel='stylesheet'">

Also include this:

<noscript><link rel="stylesheet" href="site.css"></noscript>

You can also optimise for return visits. It’s all about the cache.

In the past, we might’ve used a cookie to distinguish a returning visitor from a first-time visitor. But cookies kind of suck. Here’s something that Scott has been thinking about: service workers can intercept outgoing requests. A service worker could send a header that matches the current build of CSS. On the server, we can check for this header. If it’s not the latest CSS, we can server push the latest version, or inline it.

The neat thing about service workers is that they have to install before they take over. Scott makes use of this install event to put your important assets into a cache. Only once that is done to we start adding that extra header to requests.

Watch out for an article on the Filament Group blog on this technique!

With performance, more weight doesn’t have to mean more wait. You can have a heavy page that still appears to load quickly by altering the prioritisation of what loads first.

Web pages are very heavy now. There’s a real cost to every byte. Tim’s WhatDoesMySiteCost.com shows that the CNN home page costs almost fifty cents to load for someone in America!

Time to interactive. This is is the time before a user can use what’s on the screen. The issue is almost always with JavaScript. The page looks usable, but you can’t use it yet.

Addy Osmani suggests we should get to interactive in under five seconds on a 3G network on a median mobile device. Your iPhone is not a median mobile device. A typical phone takes six seconds to process a megabyte of JavaScript after it has downloaded. So even if the network is fast, the time to interactive can still be very long.

This all comes down to our industry’s increasing reliance on JavaScript just to render content. There seems to be pendulum shifts between client-side and server-side rendering. It’s been great to see libraries like Vue and Ember embrace server-side rendering.

But even with server-side rendering, there’s still usually a rehydration step where all the JavaScript gets parsed and that really affects time to interaction.

Code splitting can help. Webpack can do this. That helps with first-party JavaScript, but what about third-party JavaScript?

Scott believes easier to make a fast website than to keep a fast website. And that’s down to all the third-party scripts that people throw in: analytics, ads, tracking. They can wreak havoc on all your hard work.

These scripts apparently contribute to the business model, so it can be hard for us to make the case for removing them. Tools like SpeedCurve can help people stay informed on the impact of these scripts. It allows you to set up performance budgets and it shows you when pages go over budget. When that happens, we have leverage to step in and push back.

Assuming you lose that battle, what else can we do?

These days, lots of A/B testing and personalisation happens on the client side. The tooling is easy to use. But they are costly!

A typical problematic pattern is this: the server sends one version of the page, and once the page is loaded, the whole page gets replaced with a different layout targeted at the user. This leads to a terrifying new metric that Scott calls Second Meaningful Content.

Assuming we can’t remove the madness, what can we do? We could at least not do this for first-time visits. We could load the scripts asyncronously. We can preload the scripts at the top of the page. But ideally we want to move these things to the server. Server-side A/B testing and personalisation have existed for a while now.

Scott has been experimenting with a middleware solution. There’s this idea of server workers that Cloudflare is offering. You can manipulate the page that gets sent from the server to the browser—all the things you would do for an A/B test. Scott is doing this by using comments in the HTML to demarcate which portions of the page should be filtered for testing. The server worker then deletes a block for some users, and deletes a different block for other users. Scott has written about this approach.

The point here isn’t about using Cloudflare. The broader point is that it’s much faster to do these things on the server. We need to defend our user’s time.

Another issue, other than third-party scripts, is the page weight on home pages and landing pages. Marketing teams love to fill these things with enticing rich imagery and carousels. They’re really difficult to keep performant because they change all the time. Sometimes we’re not even in control of the source code of these pages.

We can advocate for new best practices like responsive images. The srcset attribute on the img element; the picture element for when you need more control. These are great tools. What’s not so great is writing the markup. It’s confusing! Ideally we’d have a CMS drive this, but a lot of the time, landing pages fall outside of the purview of the CMS.

Scott has been using Vue.js to make a responsive image builder—a form that people can paste their URLs into, which spits out the markup to use. Anything we can do by creating tools like these really helps to defend the performance of a site.

Another thing we can do is lazy loading. Focus on the assets. The BBC homepage uses some lazy loading for images—they blink into view as your scroll down the page. They use LazySizes, which you can find on Github. You use data- attributes to list your image sources. Scott realises that LazySizes is not progressive enhancement. He wouldn’t recommend using it on all images, just some images further down the page.

But thankfully, we won’t need these workarounds soon. Soon we’ll have lazy loading in browsers. There’s a lazyload attribute that we’ll be able to set on img and iframe elements:

<img src=".." alt="..." lazyload="on">

It’s not implemented yet, but it’s coming in Chrome. It might be that this behaviour even becomes the default way of loading images in browsers.

If you dig under the hood of the implementation coming in Chrome, it actually loads all the images, but the ones being lazyloaded are only sent partially with a 206 response header. That gives enough information for the browser to lay out the page without loading the whole image initially.

To wrap up, Scott takes comfort from the fact that there are resilient patterns out there to help us. And remember, it is our job to defend the user’s experience.

Monday, March 4th, 2019

Cache-Control for Civilians – CSS Wizardry

Harry breaks down cache-control headers into steps that even I can understand. I’ll be using this a reference for sure.