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Thursday, August 19th, 2021

Is Safari the new Internet Explorer?

The transcript from the latest episode of the HTTP 203 podcast is well worth perusing.

  • Internet Explorer halted development, no innovation. Would you say Safari is the new IE?
  • There was loads of stuff missing. Is Safari the new IE?
  • My early career was built on knowing the bugs in IE6 and how to solve them. Is Safari the new IE?
  • Internet Explorer 6, it had a really slow JavaScript engine, performance was bad in that browser. Is Safari the new IE?
  • Internet Explorer had a fairly cavalier attitude towards web standards. Is Safari the new IE?
  • Back in the day that we had almost no communication whatsoever. Is Safari the new IE?
  • Slow-release cycle. Is Safari the new IE?

Tuesday, August 17th, 2021

SafarIE

I was moaning about Safari recently. Specifically I was moaning about the ridiculous way that browser updates are tied to operating system updates.

But I felt bad bashing Safari. It felt like a pile-on. That’s because a lot of people have been venting their frustrations with Safari recently:

I think it’s good that people share their frustrations with browsers openly, although I agree with Baldur Bjarnason that’s good to avoid Kremlinology and the motivational fallacy when blogging about Apple.

It’s also not helpful to make claims like “Safari is the new Internet Explorer!” Unless, that is, you can back up the claim.

On a recent episode of the HTTP 203 podcast, Jake and Surma set out to test the claim that Safari is the new IE. They did it by examining Safari according to a number of different measurements and comparing it to the olden days of Internet Explorer. The result is a really fascinating trip down memory lane along with a very nuanced and even-handed critique of Safari.

And the verdict? Well, you’ll just to have to listen to the podcast episode.

If you’d rather read the transcript, tough luck. That’s a real shame because, like I said, it’s an excellent and measured assessment. I’d love to add it to the links section of my site, but I can’t do that in good conscience while it’s inaccessible to the Deaf community.

When I started the Clearleft podcast, it was a no-brainer to have transcripts of every episode. Not only does it make the content more widely available, but it also makes it easier for people to copy and paste choice quotes.

Still, I get it. A small plucky little operation like Google isn’t going to have the deep pockets of a massive corporation like Clearleft. But if Jake and Surma were to open up a tip jar, I’d throw some money in to get HTTP 203 transcribed (I recommend getting Tina Pham to do it—she’s great!).

I apologise for my note of sarcasm there. But I share because I care. It really is an excellent discussion; one that everyone should be able to access.

Update: the bug with that episode of the HTTP 203 podcast has been fixed. Here’s the transcript! And all future episodes will have transcripts too:

Sunday, August 8th, 2021

Browsers

I mentioned recently that there might be quite a difference in tone between my links and my journal here on my website:

’Sfunny, when I look back at older journal entries they’re often written out of frustration, usually when something in the dev world is bugging me. But when I look back at all the links I’ve bookmarked the vibe is much more enthusiastic, like I’m excitedly pointing at something and saying “Check this out!” I feel like sentiment analyses of those two sections of my site would yield two different results.

My journal entries have been even more specifically negative of late. I’ve been bitchin’ and moanin’ about web browsers. But at least I’m an equal-opportunities bitcher and moaner.

I wish my journal weren’t so negative, but my mithering behaviour has been been encouraged. On more than one occasion, someone I know at a browser company has taken me aside to let me know that I should blog about any complaints I might have with their browser. It sounds counterintuitive, I know. But these blog posts can give engineers some ammunition to get those issues prioritised and fixed.

So my message to you is this: if there’s something about a web browser that you’re not happy with (or, indeed, if there’s something you’re really happy with), take the time to write it down and publish it.

Publish it on your website. You could post your gripes on Twitter but whinging on Jack’s website is just pissing in the wind. And I suspect you also might put a bit more thought into a blog post on your own site.

I know it’s a cliché to say that browser makers want to hear from developers—and I’m often cynical about it myself—but they really do want to know what we think. Share your thoughts. I’ll probably end up linking to what you write.

Thursday, August 5th, 2021

Updating Safari

Safari has been subjected to a lot of ire recently. Most of that ire has been aimed at the proposed changes to the navigation bar in Safari on iOS—moving it from a fixed top position to a floaty bottom position right over the content you’re trying to interact with.

Courage.

It remains to be seen whether this change will actually ship. That’s why it’s in beta—to gather all the web’s hot takes first.

But while this very visible change is dominating the discussion, invisible changes can be even more important. Or in the case of Safari, the lack of changes.

Compared to other browsers, Safari lags far behind when it comes to shipping features. I’m not necessarily talking about cutting-edge features either. These are often standards that have been out for years. This creates a gap—albeit an invisible one—between Safari and other browsers.

Jorge Arango has noticed this gap:

I use Safari as my primary browser on all my devices. I like how Safari integrates with the rest of the OS, its speed, and privacy features. But, alas, I increasingly have issues rendering websites and applications on Safari.

That’s the perspective of an end-user. Developers who have to deal with the gap in features are more, um, strident in their opinions. Perry Sun wrote For developers, Apple’s Safari is crap and outdated:

Don’t get me wrong, Safari is very good web browser, delivering fast performance and solid privacy features.

But at the same time, the lack of support for key web technologies and APIs has been both perplexing and annoying at the same time.

Alas, that post also indulges in speculation about Apple’s motives which always feels a bit too much like a conspiracy theory to me. Baldur Bjarnason has more to say on that topic in his post Kremlinology and the motivational fallacy when blogging about Apple. He also points to a good example of critiquing Safari without speculating about motives: Dave’s post One-offs and low-expectations with Safari, which documents all the annoying paper cuts inflicted by Safari’s “quirks.”

Another deep dive that avoids speculating about motives comes from Tim Perry: Safari isn’t protecting the web, it’s killing it. I don’t agree with everything in it. I think that Apple—and Mozilla’s—objections to some device APIs are informed by a real concern about privacy and security. But I agree with his point that it’s not enough to just object; you’ve got to offer an alternative vision too.

That same post has a litany of uncontroversial features that shipped in Safari looong after they shipped in other browsers:

Again: these are not contentious features shipping by only Chrome, they’re features with wide support and no clear objections, but Safari is still not shipping them until years later. They’re also not shiny irrelevant features that “bloat the web” in any sense: each example I’ve included above primarily improving core webpage UX and performance. Safari is slowing that down progress here.

But perhaps most damning of all is how Safari deals with bugs.

A recent release of Safari shipped with a really bad Local Storage bug. The bug was fixed within a day. Yay! But the fix won’t ship until …who knows?

This is because browser updates are tied to operating system updates. Yes, this is just like the 90s when Microsoft claimed that Internet Explorer was intrinsically linked to Windows (a tactic that didn’t work out too well for them in the subsequent court case).

I don’t get it. I’m pretty sure that other Apple products ship updates and fixes independentally of OS releases. I’m sure I’ve received software updates for Keynote, Garage Band, and other pieces of software made by Apple.

And yet, of all the applications that need a speedy update cycle—a user agent for the World Wide Web—Apple’s version is needlessly delayed by the release cycle of the entire operating system.

I don’t want to speculate on why this might be. I don’t know the technical details. But I suspect that the root cause might not be technical in nature. Apple have always tied their browser updates to OS releases. If Google’s cardinal sin is avoiding anything “Not Invented Here”, Apple’s downfall is “We’ve always done it this way.”

Evergreen browsers update in the background, usually at regular intervals. Firefox is an evergreen browser. Chrome is an evergreen browser. Edge is an evergreen browser.

Safari is not an evergreen browser.

That’s frustrating when it comes to new features. It’s unforgivable when it comes to bugs.

At least on Apple’s desktop computers, users have the choice to switch to a different browser. But on Apple’s mobile devices, users have no choice but to use Safari’s rendering engine, bugs and all.

As I wrote when I had to deal with one of Safari’s bugs:

I wish that Apple would allow other rendering engines to be installed on iOS devices. But if that’s a hell-freezing-over prospect, I wish that Safari updates weren’t tied to operating system updates.

Tuesday, March 23rd, 2021

Service worker weirdness in Chrome

I think I’ve found some more strange service worker behaviour in Chrome.

It all started when I was checking out the very nice new redesign of WebPageTest. I figured while I was there, I’d run some of my sites through it. I passed in a URL from The Session. When the test finished, I noticed that the “screenshot” tab said that something was being logged to the console. That’s odd! And the file doing the logging was the service worker script.

I fired up Chrome (which isn’t my usual browser), and started navigating around The Session with dev tools open to see what appeared in the console. Sure enough, there was a failed fetch attempt being logged. The only time my service worker script logs anything is in the catch clause of fetching pages from the network. So Chrome was trying to fetch a web page, failing, and logging this error:

The service worker navigation preload request failed with a network error.

But all my pages were loading just fine. So where was the error coming from?

After a lot of spelunking and debugging, I think I’ve figured out what’s happening…

First of all, I’m making use of navigation preloads in my service worker. That’s all fine.

Secondly, the website is a progressive web app. It has a manifest file that specifies some metadata, including start_url. If someone adds the site to their home screen, this is the URL that will open.

Thirdly, Google recently announced that they’re tightening up the criteria for displaying install prompts for progressive web apps. If there’s no network connection, the site still needs to return a 200 OK response: either a cached copy of the URL or a custom offline page.

So here’s what I think is happening. When I navigate to a page on the site in Chrome, the service worker handles the navigation just fine. It also parses the manifest file I’ve linked to and checks to see if that start URL would load if there were no network connection. And that’s when the error gets logged.

I only noticed this behaviour because I had specified a query string on my start URL in the manifest file. Instead of a start_url value of /, I’ve set a start_url value of /?homescreen. And when the error shows up in the console, the URL being fetched is /?homescreen.

Crucially, I’m not seeing a warning in the console saying “Site cannot be installed: Page does not work offline.” So I think this is all fine. If I were actually offline, there would indeed be an error logged to the console and that start_url request would respond with my custom offline page. It’s just a bit confusing that the error is being logged when I’m online.

I thought I’d share this just in case anyone else is logging errors to the console in the catch clause of fetches and is seeing an error even when everything appears to be working fine. I think there’s nothing to worry about.

Update: Jake confirmed my diagnosis and agreed that the error is a bit confusing. The good news is that it’s changing. In Chrome Canary the error message has already been updated to:

DOMException: The service worker navigation preload request failed due to a network error. This may have been an actual network error, or caused by the browser simulating offline to see if the page works offline: see https://w3c.github.io/manifest/#installability-signals

Much better!

Saturday, December 12th, 2020

Kevin Kelly on Why Technology Has a Will | Palladium Magazine

Technologies are always coming out of networks that require other related ideas to have the next one. The fact that we have simultaneous independent invention as a norm works against the idea of the heroic inventor, that we’re dependent on them for inventions. These things will come when all the other pieces are ready.

Thursday, October 1st, 2020

AddyOsmani.com - Preload late-discovered Hero images faster

Did you know there’s an imagesrcset attribute you can put on link rel="preload" as="image" (along with an imagesizes attribute)?

I didn’t. (Until Amber pointed this out.)

Saturday, July 4th, 2020

The Machines Stop

The Situation feels like it’s changing. It’s not over, not by a long shot. But it feels like it’s entering a different, looser phase.

Throughout the lockdown, there’s been a strange symmetry between the outside world and the inside of our home. As the outside world slowed to a halt, so too did half the machinery in our flat. Our dishwasher broke shortly before the official lockdown began. So did our washing machine.

We had made plans for repairs and replacements, but as events in the world outside escalated, those plans had to be put on hold. Plumbers and engineers weren’t making any house calls, and rightly so.

We even had the gas to our stovetop cut off for a while—you can read Jessica’s account of that whole affair. All the breakdowns just added to the entropic Ballardian mood.

But the gas stovetop was fixed. And so too was the dishwasher, eventually. Just last week, we got our new washing machine installed. Piece by piece, the machinery of our interier world revived in lockstep with the resucitation of the world outside.

As of today, pubs will be open. I won’t be crossing their thresholds just yet. We know so much more about the spread of the virus now, and gatherings of people in indoor spaces are pretty much the worst environments for transmission.

I’m feeling more sanguine about outdoor spaces. Yesterday, Jessica and I went into town for Street Diner. It was the first time since March that we walked in that direction—our other excursions have been in the direction of the countryside.

It was perfectly fine. We wore masks, and while we were certainly in the minority, we were not alone. People were generally behaving responsibly.

Brighton hasn’t done too badly throughout The Situation. But still, like I said, I have no plans to head to the pub on a Saturday night. The British drinking culture is very much concentrated on weekends. Stay in all week and then on the weekend, lassen die Sau raus!, as the Germans would say.

After months of lockdown, reopening pubs on a Saturday seems like a terrible idea. Over in Ireland, pubs have been open since Monday—a sensible day to soft-launch. With plenty of precautions in place, things are going well there.

I’ve been watching The Situation in Ireland throughout. It’s where my mother lives, so I was understandably concerned. But they’ve handled everything really well. It’s not New Zealand, but it’s also not the disaster that is the UK.

It really has been like watching an A/B test run at the country level. Two very similar populations confronted with exactly the same crisis. Ireland took action early, cancelling the St. Patrick’s Day parade(!) while the UK was still merrily letting Cheltenham go ahead. Ireland had clear guidance. The UK had dilly-dallying and waffling. And when the shit really hit the fan, the Irish taoiseach rolled up his sleeves and returned to medical work. Meanwhile the UK had Dominic Cummings making a complete mockery of the sacrifices that everyone was told to endure.

What’s strange is that people here in the UK don’t seem to realise how the rest of the world, especially other European countries, have watched the response here with shock and horror. The narrative here seems to be that we all faced this thing together, and with our collective effort, we averted the worst. But the numbers tell a very different story. Comparing the numbers here with the numbers in Ireland—or pretty much any other country in Europe—is sobering.

So even though the timelines for reopenings here converge with Ireland’s, The Situation is far from over.

Even without any trips to pubs, restaurants, or other indoor spaces, I’m looking forward to making some more excursions into town. Not that it’s been bad staying at home. I’ve really quite enjoyed staying put, playing music, reading books, and watching television.

I was furloughed from work for a while in June. Normally, my work at this time of year would involve plenty of speaking at conferences. Seeing as that wasn’t happening, it made sense to take advantage of the government scheme to go into work hibernation for a bit.

I was worried I might feel at a bit of a loose end, but I actually really enjoyed it. The weather was good so I spent quite a bit of time just sitting in the back garden, reading (I am very, very grateful to have even a small garden). I listened to music. I watched movies. I surfed the web. Yes, properly surfed the web, going from link to link, get lost down rabbit holes. I tell you, this World Wide Web thing is pretty remarkable. Some days I used it to read up on science or philosophy. I spent a week immersed in Napoleonic history. I have no idea how or why. But it was great.

I’m back at work now, and have been for a couple of weeks. But I wouldn’t mind getting furloughed again. It felt kind of like being retired. I’m quite okay with the propsect of retirement now, as long as we have music and sunshine and the World Wide Web.

That’s the future. For now, The Situation continues, albeit in looser form.

I’ve really enjoyed reading other people’s accounts throughout. My RSS reader is getting a good workout. I always look forward to weeknotes from Alice, Nat, and Phil (this piece from Phil has really stuck with me). Jessica has written fifteen installments—and counting—of A Journal of the Plague Week. I know I’m biased, but I think it’s some mighty fine writing. Start here.

Thursday, June 25th, 2020

On dependency | RobWeychert.com V7

I’m very selective about how I depend on other people’s work in my personal projects. Here are the factors I consider when evaluating dependencies.

  • Complexity How complex is it, who absorbs the cost of that complexity, and is that acceptable?
  • Comprehensibility Do I understand how it works, and if not, does that matter?
  • Reliability How consistently and for how long can I expect it to work?

I really like Rob’s approach to choosing a particular kind of dependency when working on the web:

When I’m making things, that’s how I prefer to depend on others and have them depend on me: by sharing strong, simple ideas as a collective, and recombining them in novel ways with rigorous specificity as individuals.

Monday, April 20th, 2020

geoTrad - Google My Maps

Well, this is a rather wonderful mashup made with data from thesession.org:

The distribution of Irish traditional tunes which reference place names in Ireland

Monday, March 30th, 2020

Hobbies for the hell of it | Brad Frost

We should celebrate our hobbies for the joy-giving activities they are, and recognize that they don’t need to become anything bigger than that. And of course that’s not to say they those hobbies can’t turn into something bigger — it’s incredible when your passions and your occupation overlap — but it should be because you want to rather than that you feel pressured to. Not every activity you do needs to become a big official thing.

Monday, March 9th, 2020

41 hours in Galway

It was my birthday recently. I’m a firm believer in the idea that birthday celebrations should last for more than 24 hours. A week is the absolute minimum.

For the day itself, I did indeed indulge in a most luxurious evening out with Jessica at The Little Fish Market in Hove (on the street where we used to live!). The chef, Duncan Ray, is an absolute genius and his love for all things fish-related shines through in his magnificent dishes.

But to keep the celebrations going, we also went on a weekend away to Galway, where I used to live decades ago. It was a quick trip but we packed in a lot. I joked at one point that it felt like one of those travel articles headlined with “36 hours in someplace.” I ran the numbers and it turned out we were in Galway for 41 hours, but I still thought it would be fun to recount events in the imperative style of one of those articles…

A surprisingly sunny day in Galway.

Saturday, February 29th

The 3:30pm train from Dublin will get you into Galway just before 6pm. The train station is right on the doorstep of Loam, the Michelin-starred restaurant where you’ve made your reservation. Enjoy a seven course menu of local and seasonal produce. Despite the quality of the dishes, you may find the overall experience is a little cool, and the service a touch over-rehearsed.

You’ll be released sometime between 8:30pm and 9pm. Stroll through Eyre Square and down Shop Street to the Jury’s Inn, your hotel. It’s nothing luxurious but it’s functional and the location is perfect. It’s close to everything without being in the middle of the noisy weekend action. The only noise you should hear is the rushing of the incredibly fast Corrib river outside your window.

Around 9:30pm, pop ‘round to Dominick Street to enjoy a cocktail in the America Village Apothecary. It’s only open two nights a week, and it’s a showcase of botanicals gathered in Connemara. Have them make you a tasty conconction and then spend time playing guess-that-smell with their specimen jars.

By 10:30pm you should be on your way round the corner to The Crane Bar on Sea Road. Go in the side entrance and head straight upstairs where the music session will be just getting started. Marvel at how chilled out it is for a Saturday night, order a pint, and sit and listen to some lovely jigs’n’reels. Don’t forget to occassionally pester one of the musicians by asking “What was that last tune called? Lovely set!”

Checked in at The Crane Bar. Great tunes! 🎻🎶 — with Jessica

Sunday, March 1st

Skip the hotel breakfast. Instead, get your day started with a coffee from Coffeewerk + Press. Get that coffee to go and walk over to Ard Bia at Nimmos, right at the Spanish Arch. Get there before it opens at 10am. There will already be a line. Once you’re in, order one of the grand brunch options and a nice big pot of tea. The black pudding hash will set you up nicely.

Checked in at Ard Bia at Nimmos. Black pudding hash and a pot of tea — with Jessica

While the weather is far clearer and sunnier than you were expecting, take the opportunity to walk off that hearty brunch with a stroll along the sea front. That’ll blow out the cobwebs.

Galway bay. Galway bay.

When the cold gets too much, head back towards town and duck into Charlie Byrne’s, the independent bookshop. Spend some time in there browsing the shelves and don’t leave without buying something to remember it by.

By 1pm or so, it’s time for some lunch. This is the perfect opportunity to try the sushi at Wa Cafe near the harbour. They have an extensive range of irrestistable nigiri, so just go ahead and get one of everything. The standouts are the local oyster, mackerel, and salmon.

Checked in at wa cafe. Sushi — with Jessica

From there, head to Tigh Cóilí for the 2pm session. Have a Guinness and enjoy the tunes.

Checked in at Tigh Cóilí. Afternoon session — with Jessica

Spend the rest of the afternoon strolling around town. You can walk through the market at St. Nicholas Church, and check out the little Claddagh ring museum at Thomas Dillon’s—the place where you got your wedding rings at the close of the twentieth century.

Return the ring from whence it came!

If you need a pick-me-up, get another coffee from Coffeewerk + Press, but this time grab a spot at the window upstairs so you can watch the world go by outside.

By 6pm, you’ll have a hankering for some more seafood. Head over to Hooked on Henry Street. Order a plate of oysters, and a cup of seafood chowder. If they’ve got ceviche, try that too.

Checked in at Hooked. with Jessica

Walk back along the canal and stop in to The Salt House to sample a flight of beers from Galway Bay Brewery. There’ll probably be some live music.

Checked in at The Salt House. 🍺 — with Jessica

With your appetite suitably whetted, head on over to Cava Bodega for some classic tapas. Be sure to have the scallops with black pudding.

Checked in at Cava Bodega. Scallops with black pudding — with Jessica

The evening session at Tigh Cóilí starts at 8:30pm on a Sunday so you can probably still catch it. You’ll hear some top-class playing from the likes of Mick Conneely and friends.

Checked in at Tigh Cóilí. 🎶🎻 — with Jessica

And when that’s done, there’s still time to catch the session over at The Crane.

Checked in at The Crane Bar. 🎶🎻 — with Jessica

Monday, March 2nd

After a nice lie-in, check out of the hotel and head to McCambridge’s on Shop Street for some breakfast upstairs. A nice bowl of porridge will set you up nicely for the journey back to Dublin.

If you catch the 11am train, you’ll arrive in Dublin by 1:30pm—just enough time to stop off in The Winding Stair for some excellent lunch before heading on to the airport.

Checked in at The Winding Stair. Lunch in Dublin — with Jessica

Getting there

Aer Lingus flies daily from Gatwick to Dublin. Dublin’s Heuston Station has multiple trains per day going to Galway.

Friday, October 4th, 2019

Why Progressive Web Apps Are The Future of Mobile Web [2019 Research]

PWAs just work better than your typical mobile site. Period.

But bear in mind:

Maybe simply because the “A” in PWA stands for “app,” too much discussion around PWAs focuses on comparing and contrasting to native mobile applications. We believe this comparison (and the accompanying discussion) is misguided.

Thursday, August 1st, 2019

Navigation preloads in service workers

There’s a feature in service workers called navigation preloads. It’s relatively recent, so it isn’t supported in every browser, but it’s still well worth using.

Here’s the problem it solves…

If someone makes a return visit to your site, and the service worker you installed on their machine isn’t active yet, the service worker boots up, and then executes its instructions. If those instructions say “fetch the page from the network”, then you’re basically telling the browser to do what it would’ve done anyway if there were no service worker installed. The only difference is that there’s been a slight delay because the service worker had to boot up first.

  1. The service worker activates.
  2. The service worker fetches the file.
  3. The service worker does something with the response.

It’s not a massive performance hit, but it’s still a bit annoying. It would be better if the service worker could boot up and still be requesting the page at the same time, like it would do if no service worker were present. That’s where navigation preloads come in.

  1. The service worker activates while simultaneously requesting the file.
  2. The service worker does something with the response.

Navigation preloads—like the name suggests—are only initiated when someone navigates to a URL on your site, either by following a link, or a bookmark, or by typing a URL directly into a browser. Navigation preloads don’t apply to requests made by a web page for things like images, style sheets, and scripts. By the time a request is made for one of those, the service worker is already up and running.

To enable navigation preloads, call the enable() method on registration.navigationPreload during the activate event in your service worker script. But first do a little feature detection to make sure registration.navigationPreload exists in this browser:

if (registration.navigationPreload) {
  addEventListener('activate', activateEvent => {
    activateEvent.waitUntil(
      registration.navigationPreload.enable()
    );
  });
}

If you’ve already got event listeners on the activate event, that’s absolutely fine: addEventListener isn’t exclusive—you can use it to assign multiple tasks to the same event.

Now you need to make use of navigation preloads when you’re responding to fetch events. So if your strategy is to look in the cache first, there’s probably no point enabling navigation preloads. But if your default strategy is to fetch a page from the network, this will help.

Let’s say your current strategy for handling page requests looks like this:

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

That’s a fairly standard strategy: try the network first; if that doesn’t work, try the cache; as a last resort, show an offline page.

It’s that first step (“try the network first”) that can benefit from navigation preloads. If a preload request is already in flight, you’ll want to use that instead of firing off a new fetch request. Otherwise you’re making two requests for the same file.

To find out if a preload request is underway, you can check for the existence of the preloadResponse promise, which will be made available as a property of the fetch event you’re handling:

fetchEvent.preloadResponse

If that exists, you’ll want to use it instead of fetch(request).

if (fetchEvent.preloadResponse) {
  // do something with fetchEvent.preloadResponse
} else {
  // do something with fetch(request)
}

You could structure your code like this:

addEventListener('fetch', fetchEvent => {
  const request = fetchEvent.request;
  if (request.headers.get('Accept').includes('text/html')) {
    if (fetchEvent.preloadResponse) {
      fetchEvent.respondWith(
        fetchEvent.preloadResponse
        .then( responseFromPreload => {
          // maybe cache this response for later here.
          return responseFromPreload;
        })
        .catch( preloadError => {
          return caches.match(request)
          .then( responseFromCache => {
            return responseFromCache || caches.match('/offline');
          });
        })
      );
    } else {
      fetchEvent.respondWith(
        fetch(request)
        .then( responseFromFetch => {
          // maybe cache this response for later here.
          return responseFromFetch;
        })
        .catch( fetchError => {
          return caches.match(request)
          .then( responseFromCache => {
            return responseFromCache || caches.match('/offline');
          });
        })
      );
    }
  }
});

But that’s not very DRY. Your logic is identical, regardless of whether the response is coming from fetch(request) or from fetchEvent.preloadResponse. It would be better if you could minimise the amount of duplication.

One way of doing that is to abstract away the promise you’re going to use into a variable. Let’s call it retrieve. If a preload is underway, we’ll assign it to that variable:

let retrieve;
if (fetchEvent.preloadResponse) {
  retrieve = fetchEvent.preloadResponse;
}

If there is no preload happening (or this browser doesn’t support it), assign a regular fetch request to the retrieve variable:

let retrieve;
if (fetchEvent.preloadResponse) {
  retrieve = fetchEvent.preloadResponse;
} else {
  retrieve = fetch(request);
}

If you like, you can squash that into a ternary operator:

const retrieve = fetchEvent.preloadResponse ? fetchEvent.preloadResponse : fetch(request);

Use whichever syntax you find more readable.

Now you can apply the same logic, regardless of whether retrieve is a preload navigation or a fetch request:

addEventListener('fetch', fetchEvent => {
  const request = fetchEvent.request;
  if (request.headers.get('Accept').includes('text/html')) {
    const retrieve = fetchEvent.preloadResponse ? fetchEvent.preloadResponse : fetch(request);
    fetchEvent.respondWith(
      retrieve
      .then( responseFromRetrieve => {
        // maybe cache this response for later here.
       return responseFromRetrieve;
      })
      .catch( fetchError => {
        return caches.match(request)
        .then( responseFromCache => {
          return responseFromCache || caches.match('/offline');
        });
      })
    );
  }
});

I think that’s the least invasive way to update your existing service worker script to take advantage of navigation preloads.

Like I said, preload navigations can give a bit of a performance boost if you’re using a network-first strategy. That’s what I’m doing here on adactio.com and on thesession.org so I’ve updated their service workers to take advantage of navigation preloads. But on Resilient Web Design, which uses a cache-first strategy, there wouldn’t be much point enabling navigation preloads.

Jeff Posnick made this point in his write-up of bringing service workers to Google search:

Adding a service worker to your web app means inserting an additional piece of JavaScript that needs to be loaded and executed before your web app gets responses to its requests. If those responses end up coming from a local cache rather than from the network, then the overhead of running the service worker is usually negligible in comparison to the performance win from going cache-first. But if you know that your service worker always has to consult the network when handling navigation requests, using navigation preload is a crucial performance win.

Oh, and those browsers that don’t yet support navigation preloads? No problem. It’s a progressive enhancement. Everything still works just like it did before. And having a service worker on your site in the first place is itself a progressive enhancement. So enabling navigation preloads is like a progressive enhancement within a progressive enhancement. It’s progressive enhancements all the way down!

By the way, if all of this service worker stuff sounds like gibberish, but you wish you understood it, I think my book, Going Offline, will prove quite valuable.

Sunday, July 21st, 2019

The Simplest Way to Load CSS Asynchronously | Filament Group, Inc.

Scott re-examines the browser support for loading everything-but-the-critical-CSS asynchronously and finds that it might now be as straightforward as this one declaration:

<link rel="stylesheet" href="/path/to/my.css" media="print" onload="this.media='all'">

I love the fact the Filament Group are actively looking at how deprecate their loadCSS polyfill—exactly the right attitude for polyfills in general.

Tuesday, July 16th, 2019

Trad time

Fifteen years ago, I went to the Willie Clancy Summer School in Miltown Malbay:

I’m back from the west of Ireland. I was sorry to leave. I had a wonderful, music-filled time.

I’m not sure why it took me a decade and a half to go back, but that’s what I did last week. Myself and Jessica once again immersed ourselves in Irish tradtional music. I’ve written up a trip report over on The Session.

On the face of it, fifteen years is a long time. Last time I made the trip to county Clare, I was taking pictures on a point-and-shoot camera. I had a phone with me, but it had a T9 keyboard that I could use for texting and not much else. Also, my hair wasn’t grey.

But in some ways, fifteen years feels like the blink of an eye.

I spent my mornings at the Willie Clancy Summer School immersed in the history of Irish traditional music, with Paddy Glackin as a guide. We were discussing tradition and change in generational timescales. There was plenty of talk about technology, but we were as likely to discuss the influence of the phonograph as the influence of the internet.

Outside of the classes, there was a real feeling of lengthy timescales too. On any given day, I would find myself listening to pre-teen musicians at one point, and septegenarian masters at another.

Now that I’m back in the Clearleft studio, I’m finding it weird to adjust back in to the shorter timescales of working on the web. Progress is measured in weeks and months. Technologies are deemed outdated after just a year or two.

The one bridging point I have between these two worlds is The Session. It’s been going in one form or another for over twenty years. And while it’s very much on and of the web, it also taps into a longer tradition. Over time it has become an enormous repository of tunes, for which I feel a great sense of responsibility …but in a good way. It’s not something I take lightly. It’s also something that gives me great satisfaction, in a way that’s hard to achieve in the rapidly moving world of the web. It’s somewhat comparable to the feelings I have for my own website, where I’ve been writing for eighteen years. But whereas adactio.com is very much focused on me, thesession.org is much more of a community endeavour.

I question sometimes whether The Session is helping or hindering the Irish music tradition. “It all helps”, Paddy Glackin told me. And I have to admit, it was very gratifying to meet other musicians during Willie Clancy week who told me how much the site benefits them.

I think I benefit from The Session more than anyone though. It keeps me grounded. It gives me a perspective that I don’t think I’d otherwise get. And in a time when it feels entirely to right to question whether the internet is even providing a net gain to our world, I take comfort in being part of a project that I think uses the very best attributes of the World Wide Web.

Monday, July 15th, 2019

Spurious Correlations

Correlation does not imply causation.

Tuesday, May 28th, 2019

How Ireland became Europe’s data watchdog - BBC News

The coming GDPR storm:

Ireland’s Data Protection Commissioner, Helen Dixon, is expected to circulate her decisions on some cases by July or August, with final rulings made by the end of the year.

(That’s my sister-in-law, that is.)

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.