Tags: performance



Minimal viable service worker

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

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

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

The logic works like this:

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

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

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

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

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

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

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

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

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

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

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

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

Needs must

I got a follow-up comment to my follow-up post about the follow-up comment I got on my original post about Google Analytics. Keep up.

I made the point that, from a front-end performance perspective, server logs have no impact whereas a JavaScript-based analytics solution must have some impact on the end user. Paul Anthony says:

Google won the analytics war because dropping one line of JS in the footer and handing a tried and tested interface to customers is an obvious no brainer in comparison to setting up an open source option that needs a cron job to parse the files, a database to store the results and doesn’t provide mobile interface.

Good point. Dropping one snippet of JavaScript into your front-end codebase is certainly an easier solution …easier for you, that is. The cost is passed on to your users. This is a classic example of where user needs and developer needs are in opposition. I’ve said it before and I’ll say it again:

Given the choice between making something my problem, and making something the user’s problem, I’ll choose to make it my problem every time.

It’s true that this often means doing more work. That’s why it’s called work. This is literally what our jobs are supposed to entail: we put in the work to make life easier for users. We’re supposed to be saving them time, not passing it along.

The example of Google Analytics is pretty extreme, I’ll grant you. The cost to the user of adding that snippet of JavaScript—if you’ve configured things reasonably well—is pretty small (again, just from a performance perspective; there’s still the cost of allowing Google to track them across domains), and the cost to you of setting up a comparable analytics system based on server logs can indeed be disproportionately high. But this tension between user needs and developer needs is something I see play out again and again.

I’ve often thought the HTML design principle called the priority of constituencies could be adopted by web developers:

In case of conflict, consider users over authors over implementors over specifiers over theoretical purity. In other words costs or difficulties to the user should be given more weight than costs to authors.

In Resilient Web Design, I documented the three-step approach I take when I’m building anything on the web:

  1. Identify core functionality.
  2. Make that functionality available using the simplest possible technology.
  3. Enhance!

Now I’m wondering if I should’ve clarified that second step further. When I talk about choosing “the simplest possible technology”, what I mean is “the simplest possible technology for the user”, not “the simplest possible technology for the developer.”

For example, suppose I were going to build a news website. The core functionality is fairly easy to identify: providing the news. Next comes the step where I choose the simplest possible technology. Now, if I were a developer who had plenty of experience building JavaScript-driven single page apps, I might conclude that the simplest route for me would be to render the news via JavaScript. But that would be a fragile starting point if I’m trying to reach as many people as possible (I might well end up building a swishy JavaScript-driven single page app in step three, but step two should almost certainly be good ol’ HTML).

Time and time again, I see decisions that favour developer convenience over user needs. Don’t get me wrong—as a developer, I absolutely want developer convenience …but not at the expense of user needs.

I know that “empathy” is an over-used word in the world of user experience and design, but with good reason. I think we should try to remind ourselves of why we make our architectural decisions by invoking who those decisions benefit. For example, “This tech stack is best option for our team”, or “This solution is the best for the widest range of users.” Then, given the choice, favour user needs in the decision-making process.

There will always be situations where, given time and budget constraints, we end up choosing solutions that are easier for us, but not the best for our users. And that’s okay, as long as we acknowledge that compromise and strive to do better next time.

But when the best solutions for us as developers become enshrined as the best possible solutions, then we are failing the people we serve.

That doesn’t mean we must become hairshirt-wearing martyrs; developer convenience is important …but not as important as user needs. Start with user needs.


I wrote about Google Analytics yesterday. As usual, I syndicated the post to Ev’s blog, and I got an interesting response over there. Kelly Burgett set me straight on some of the finer details of how goals work, and finished with this thought:

You mention “delivering a performant, accessible, responsive, scalable website isn’t enough” as if it should be, and I have to disagree. It’s not enough for a business to simply have a great website if you are unable to understand performance of channel marketing, track user demographics and behavior on-site, and optimize your site/brand based on that data. I’ve seen a lot of ugly sites who have done exceptionally well in terms of ROI, simply because they are getting the data they need from the site in order make better business decisions. If your site cannot do that (ie. through data collection, often third party scripts), then your beautifully-designed site can only take you so far.

That makes an excellent case for having analytics. But that’s not necessarily the same as having Google analytics, or even JavaScript-driven analytics at all.

By far the most useful information you get from analytics is around where people have come from, where did they go next, and what kind of device are they using. None of that information requires JavaScript. It’s all available from your server logs.

I don’t want to come across all old-man-yell-at-cloud here, but I’m trying to remember at what point self-hosted software for analysing your log traffic became not good enough.

Here’s the thing: logging on the server has no effect on the user experience. It’s basically free, in terms of performance. Logging via JavaScript, by its very nature, has some cost. Even if its negligible, that’s one more request, and that’s one more bit of processing for the CPU.

All of the data that you can only get via JavaScript (in-page actions, heat maps, etc.) are, in my experience, better handled by dedicated software. To me, that kind of more precise data feels different to analytics in the sense of funnels, conversions, goals and all that stuff.

So in order to get more fine-grained data to analyse, our analytics software has now doubled down on a technology—JavaScript—that has an impact on the end user, where previously the act of observation could be done at a distance.

There are also blind spots that come with JavaScript-based tracking. According to Google Analytics, 0% of your customers don’t have JavaScript. That’s not necessarily true, but there’s literally no way for Google Analytics—which relies on JavaScript—to even do its job in the absence of JavaScript. That can lead to a dangerous situation where you might be led to think that 100% of your potential customers are getting by, when actually a proportion might be struggling, but you’ll never find out about it.

Related: according to Google Analytics, 0% of your customers are using ad-blockers that block requests to Google’s servers. Again, that’s not necessarily a true fact.

So I completely agree than analytics are a good thing to have for your business. But it does not follow that Google Analytics is a good thing for your business. Other options are available.

I feel like the assumption that “analytics = Google Analytics” is like the slippery slope in reverse. If we’re all agreed that analytics are important, then aren’t we also all agreed that JavaScript-based tracking is important?

In a word, no.

This reminds me of the arguments made in favour of intrusive, bloated advertising scripts. All of the arguments focus on the need for advertising—to stay in business, to pay the writers—which are all great reasons for advertising, but have nothing to do with JavaScript, which is at the root of the problem. Everyone I know who uses an ad-blocker—including me—doesn’t use it to stop seeing adverts, but to stop the performance of the page being degraded (and to avoid being tracked across domains).

So let’s not confuse the means with the ends. If you need to have advertising, that doesn’t mean you need to have horribly bloated JavaScript-based advertising. If you need analytics, that doesn’t mean you need an analytics script on your front end.

Analysing analytics

Hell is other people’s JavaScript.

There’s nothing quite so crushing as building a beautifully performant website only to have it infested with a plague of third-party scripts that add to the weight of each page and reduce the responsiveness, making a mockery of your well-considered performance budget.

Trent has been writing about this:

My latest realization is that delivering a performant, accessible, responsive, scalable website isn’t enough: I also need to consider the impact of third-party scripts.

He’s started the process by itemising third-party scripts. Frustratingly though, there’s rarely one single culprit that you can point to—it’s the cumulative effect of “just one more beacon” and “just one more analytics script” and “just one more A/B testing tool” that adds up to a crappy experience that warms your user’s hands by ensuring your site is constantly draining their battery.

Actually, having just said that there’s rarely one single culprit, Adobe Tag Manager is often at the root of third-party problems. That and adverts. It’s like opening the door of your beautifully curated dream home, and inviting a pack of diarrhetic elephants in: “Please, crap wherever you like.”

But even the more well-behaved third-party scripts can get out of hand. Google Analytics is so ubiquitous that it’s hardly even considered in the list of potentially harmful third-party scripts. On the whole, it’s a fairly well-behaved citizen of your site’s population of third-party scripts (y’know, leaving aside the whole surveillance capitalism business model that allows you to use such a useful tool for free in exchange for Google tracking your site’s visitors across the web and selling the insights from that data to advertisers).

The initial analytics script that you—asynchronously—load into your page isn’t very big. But depending on how you’ve configured your Google Analytics account, that might just be the start of a longer chain of downloads and event handlers.

Ed recently gave a lunchtime presentation at Clearleft on using Google Analytics—he professes modesty but he really knows his stuff. He was making sure that everyone knew how to set up goals’n’stuff.

As I understand it, there are two main categories of goals: events and destinations (there are also durations and pages, but they feel similar to destinations). You use events to answer questions like “Did the user click on this button?” or “Did the user click on that search field?”. You use destinations to answer questions like “Did the user arrive at this page?” or “Did the user come from that page?”

You can add as many goals to your site’s analytics as you want. That’s an intoxicating offer. The problem is that there is potentially a cost for each goal you create. It’s an invisible cost. It’s paid by the user in the currency of JavaScript sent down the wire (I wish that the Google Analytics admin interface were more like the old interface for Google Fonts, where each extra file you added literally pushed a needle higher on a dial).

It strikes me that the event-based goals would necessarily require more JavaScript in order to listen out for those clicks and fire off that information. The destination-based goals should be able to get all the information needed from regular page navigations.

So I have a hypothesis. I think that destination-based goals are less harmful to performance than event-based goals. I might well be wrong about that, and if I am, please let me know.

With that hypothesis in mind, and until I learn otherwise, I’ve got two rules of thumb to offer when it comes to using Google Analytics:

  1. Try to keep the number of goals to a minimum.
  2. If you must create a goal, favour destinations over events.

The dConstruct Audio Archive works offline

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

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

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


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

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

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

Here’s the logic for fetch requests:

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

Save for offline

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

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

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

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

Or just enjoy the speediness of browsing the site.

Turning another website into a Progressive Web App.

Pattern Libraries, Performance, and Progressive Web Apps

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

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

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

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

Pattern Libraries

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

Danielle Huntrods Mark Perkins


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

Graham Smith

Progressive Web Apps

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

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

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

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

Jeremy Keith

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

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

In AMP we trust

AMP Conf was one of those deep dive events, with two days dedicated to one single technology: AMP.

Except AMP isn’t really one technology, is it? And therein lies the confusion. This was at the heart of the panel I was on. When we talk about AMP, we could be talking about one of three things:

  1. The AMP format. A bunch of web components. For instance, instead of using an img element on an AMP page, you use an amp-img element instead.
  2. The AMP rules. There’s one JavaScript file, hosted on Google’s servers, that turns those web components from spans into working elements. No other JavaScript is allowed. All your styles must be in a style element instead of an external file, and there’s a limit on what you can do with those styles.
  3. The AMP cache. The source of most confusion—and even downright enmity—this is what’s behind the fact that when you launch an AMP result from Google search, you don’t go to another website. You see Google’s cached copy of the page instead of the original.

The first piece of AMP—the format—is kind of like a collection of marginal gains. Where the img element might have some performance issues, the amp-img element optimises for perceived performance. But if you just used the AMP web components, it wouldn’t be enough to make your site blazingly fast.

The second part of AMP—the rules—is where the speed gains start to really show. You can’t have an external style sheet, and crucially, you can’t have any third-party scripts other than the AMP script itself. This is key to making AMP pages super fast. It’s not so much about what AMP does; it’s more about what it doesn’t allow. If you never used a single AMP component, but stuck to AMP’s rules disallowing external styles and scripts, you could easily make a page that’s even faster than what AMP can do.

At AMP Conf, Natalia pointed out that The Guardian’s non-AMP pages beat out the AMP pages for performance. So why even have AMP pages? Well, that’s down to the third, most contentious, part of the AMP puzzle.

The AMP cache turns the user experience of visiting an AMP page from fast to instant. While you’re still on the search results page, Google will pre-render an AMP page in the background. Not pre-fetch, pre-render. That’s why it opens so damn fast. It’s also what causes the most confusion for end users.

From my unscientific polling, the behaviour of AMP results confuses the hell out of people. The fact that the page opens instantly isn’t the problem—far from it. It’s the fact that you don’t actually go to an another page. Technically, you’re still on Google. An analogous mental model would be an RSS reader, or an email client: you don’t go to an item or an email; you view it in situ.

Well, that mental model would be fine if it were consistent. But in Google search, only some results will behave that way (the AMP pages) and others will behave just like regular links to other websites. No wonder people are confused! Some search results take them away and some search results keep them on Google …even though the page looks like a different website.

The price that we pay for the instantly-opening AMP pages from the Google cache is the URL. Because we’re looking at Google’s pre-rendered copy instead of the original URL, the address bar is not pointing to the site the browser claims to be showing. Everything in the body of the browser looks like an article from The Guardian, but if I look at the URL (which is what security people have been telling us for years is important to avoid being phished), then I’ll see a domain that is not The Guardian’s.

But wait! Couldn’t Google pre-render the page at its original URL?

Yes, they could. But they won’t.

This was a point that Paul kept coming back to: trust. There’s no way that Google can trust that someone else’s URL will play by the AMP rules (no external scripts, only loading embedded content via web components, limited styles, etc.). They can only trust the copies that they themselves are serving up from their cache.

By the way, there was a joint AMP/search panel at AMP Conf with representatives from both teams. As you can imagine, there were many questions for the search team, most of which were Glomar’d. But one thing that the search people said time and again was that Google was not hosting our AMP pages. Now I don’t don’t know if they were trying to make some fine-grained semantic distinction there, but that’s an outright falsehood. If I click on a link, and the URL I get taken to is a Google property, then I am looking at a page hosted by Google. Yes, it might be a copy of a document that started life somewhere else, but if Google are serving something from their cache, they are hosting it.

This is one of the reasons why AMP feels like such a bait’n’switch to me. When it first came along, it felt like a direct competitor to Facebook’s Instant Articles and Apple News. But the big difference, we were told, was that you get to host your own content. That appealed to me much more than having Facebook or Apple host the articles. But now it turns out that Google do host the articles.

This will be the point at which Googlers will say no, no, no, you can totally host your own AMP pages …but you won’t get the benefits of pre-rendering. But without the pre-rendering, what’s the point of even having AMP pages?

Well, there is one non-cache reason to use AMP and it’s a political reason. Beleaguered developers working for publishers of big bloated web pages have a hard time arguing with their boss when they’re told to add another crappy JavaScript tracking script or bloated library to their pages. But when they’re making AMP pages, they can easily refuse, pointing out that the AMP rules don’t allow it. Google plays the bad cop for us, and it’s a very valuable role. Sarah pointed this out on the panel we were on, and she was spot on.

Alright, but what about The Guardian? They’ve already got fast pages, but they still have to create separate AMP pages if they want to get the pre-rendering benefits when they show up in Google search results. Sorry, says Google, but it’s the only way we can trust that the pre-rendered page will be truly fast.

So here’s the impasse we’re at. Google have provided a list of best practices for making fast web pages, but the only way they can truly verify that a page is sticking to those best practices is by hosting their own copy, URLs be damned.

This was the crux of Paul’s argument when he was on the Shop Talk Show podcast (it’s a really good episode—I was genuinely reassured to hear that Paul is not gung-ho about drinking the AMP Kool Aid; he has genuine concerns about the potential downsides for the web).

Initially, I accepted this argument that Google just can’t trust the rest of the web. But the more I talked to people at AMP Conf—and I had some really, really good discussions with people away from the stage—the more I began to question it.

Here’s the thing: the regular Google search can’t guarantee that any web page is actually 100% the right result to return for a search. Instead there’s a lot of fuzziness involved: based on the content, the markup, and the number of trusted sources linking to this, it looks like it should be a good result. In other words, Google search trusts websites to—by and large—do the right thing. Sometimes websites abuse that trust and try to game the system with sneaky tricks. Google responds with penalties when that happens.

Why can’t it be the same for AMP pages? Let me host my own AMP pages (maybe even host my own AMP script) and then when the Googlebot crawls those pages—the same as it crawls any other pages—that’s when it can verify that the AMP page is abiding by the rules. If I do something sneaky and trick Google into flagging a page as fast when it actually isn’t, then take my pre-rendering reward away from me.

To be fair, Google has very, very strict rules about what and how to pre-render the AMP results it’s caching. I can see how allowing even the potential for a false positive would have a negative impact on the user experience of Google search. But c’mon, there are already false positives in regular search results—fake news, spam blogs. Googlers are smart people. They can solve—or at least mitigate—these problems.

Google says it can’t trust our self-hosted AMP pages enough to pre-render them. But they ask for a lot of trust from us. We’re supposed to trust Google to cache and host copies of our pages. We’re supposed to trust Google to provide some mechanism to users to get at the original canonical URL. I’d like to see trust work both ways.

Small steps

The new Clearleft website is live! Huzzah!

Many people have been working very hard on it and it’s all looking rather nice. But, as I said before, the site launch isn’t the end—it’s just the beginning.

There are some obvious next steps: fixing bugs, adding content, tweaking copy, and, oh yeah, that whole “testing with real users” thing. But there’s also an opportunity to have some fun on the front end. Now that the site is out there in the wild, there’s a real incentive to improve its performance.

Off the top of my head, these are some areas where I think we can play around:

  • Font loading. Right now the site is just using @font-face. A smart font-loading strategy—at least for the body copy—could really help improve the perceived performance.
  • Responsive images. A long-term solution will require some wrangling on the back end, but I reckon we can come up with some way of generating different sized images to reference in srcset.
  • Service worker. It’s a no-brainer. Now that the Clearleft site is (finally!) running on HTTPS, having a simple service worker to cache static assets like CSS, JavaScript and some images seems like the obvious next step. The question is: what other offline shenanigans could we get up to?

I’m looking forward to tinkering with some of those technologies. Each one should make an incremental improvement to the site’s performance. There are already some steps on the back-end that are making a big difference: upgrading to PHP7 and using HTTP2.

Now the real fun begins.

Looking beyond launch

It’s all go, go, go at Clearleft while we’re working on a new version of our website …accompanied by a brand new identity. It’s an exciting time in the studio, tinged with the slight stress that comes with any kind of unveiling like this.

I think it’s good to remember that this is the web. I keep telling myself that we’re not unveiling something carved in stone. Even after the launch we can keep making the site better. In fact, if we wait until everything is perfect before we launch, we’ll probably never launch at all.

On the other hand, you only get one chance to make a first impression, right? So it’s got to be good …but it doesn’t have to be done. A website is never done.

I’ve got to get comfortable with that. There’s lots of things that I’d like to be done in time for launch, but realistically it’s fine if those things are completed in the subsequent days or weeks.

Adding a service worker and making a nice offline experience? I really want to do that …but it can wait.

What about other performance tweaks? Yes, we’ll to try have every asset—images, fonts—optimised …but maybe not from day one.

Making sure that each page has good metadata—Open Graph? Twitter Cards? Microformats? Maybe even AMP? Sure …but not just yet.

Having gorgeous animations? Again, I really want to have them but as Val rightly points out, animations are an enhancement—a really, really great enhancement.

If anything, putting the site live before doing all these things acts as an incentive to make sure they get done.

So when you see the new site, if you view source or run it through Web Page Test and spot areas for improvement, rest assured we’re on it.

Making Resilient Web Design work offline

I’ve written before about taking an online book offline, documenting the process behind the web version of HTML5 For Web Designers. A book is quite a static thing so it’s safe to take a fairly aggressive offline-first approach. In fact, a static unchanging book is one of the few situations that AppCache works for. Of course a service worker is better, but until AppCache is removed from browsers (and until service worker is supported across the board), I’m using both. I wouldn’t recommend that for most sites though—for most sites, use a service worker to enhance it, and avoid AppCache like the plague.

For Resilient Web Design, I took a similar approach to HTML5 For Web Designers but I knew that there was a good chance that some of the content would be getting tweaked at least for a while. So while the approach is still cache-first, I decided to keep the cache fairly fresh.

Here’s my service worker. It starts with the usual stuff: when the service worker is installed, there’s a list of static assets to cache. In this case, that list is literally everything; all the HTML, CSS, JavaScript, and images for the whole site. Again, this is a pattern that works well for a book, but wouldn’t be right for other kinds of websites.

The real heavy lifting happens with the fetch event. This is where the logic sits for what the service worker should do everytime there’s a request for a resource. I’ve documented the logic with comments:

// Look in the cache first, fall back to the network
  // CACHE
  // Did we find the file in the cache?
      // If so, fetch a fresh copy from the network in the background
      // NETWORK
          // Stash the fresh copy in the cache
  // If the file wasn't in the cache, make a network request
      // Stash a fresh copy in the cache in the background
  // If the request is for an image, show an offline placeholder
  // If the request is for a page, show an offline message

So my order of preference is:

  1. Try the cache first,
  2. Try the network second,
  3. Fallback to a placeholder as a last resort.

Leaving aside that third part, regardless of whether the response is served straight from the cache or from the network, the cache gets a top-up. If the response is being served from the cache, there’s an additional network request made to get a fresh copy of the resource that was just served. This means that the user might be seeing a slightly stale version of a file, but they’ll get the fresher version next time round.

Again, I think this acceptable for a book where the tweaks and changes should be fairly minor, but I definitely wouldn’t want to do it on a more dynamic site where the freshness matters more.

Here’s what it usually likes like when a file is served up from the cache:

  .then( responseFromCache => {
  // Did we find the file in the cache?
  if (responseFromCache) {
      return responseFromCache;

I’ve introduced an extra step where the fresher version is fetched from the network. This is where the code can look a bit confusing: the network request is happening in the background after the cached file has already been returned, but the code appears before the return statement:

  .then( responseFromCache => {
  // Did we find the file in the cache?
  if (responseFromCache) {
      // If so, fetch a fresh copy from the network in the background
          // NETWORK
          .then( responseFromFetch => {
              // Stash the fresh copy in the cache
              .then( cache => {
                  cache.put(request, responseFromFetch);
      return responseFromCache;

It’s asynchronous, see? So even though all that network code appears before the return statement, it’s pretty much guaranteed to complete after the cache response has been returned. You can verify this by putting in some console.log statements:

.then( responseFromCache => {
  if (responseFromCache) {
          .then( responseFromFetch => {
              console.log('Got a response from the network.');
              .then( cache => {
                  cache.put(request, responseFromFetch);
      console.log('Got a response from the cache.');
      return responseFromCache;

Those log statements will appear in this order:

Got a response from the cache.
Got a response from the network.

That’s the opposite order in which they appear in the code. Everything inside the event.waitUntil part is asynchronous.

Here’s the catch: this kind of asynchronous waitUntil hasn’t landed in all the browsers yet. The code I’ve written will fail.

But never fear! Jake has written a polyfill. All I need to do is include that at the start of my serviceworker.js file and I’m good to go:

// Import Jake's polyfill for async waitUntil

I’m also using it when a file isn’t found in the cache, and is returned from the network instead. Here’s what the usual network code looks like:

  .then( responseFromFetch => {
    return responseFromFetch;

I want to also store that response in the cache, but I want to do it asynchronously—I don’t care how long it takes to put the file in the cache as long as the user gets the response straight away.

Technically, I’m not putting the response in the cache; I’m putting a copy of the response in the cache (it’s a stream, so I need to clone it if I want to do more than one thing with it).

  .then( responseFromFetch => {
    // Stash a fresh copy in the cache in the background
    let responseCopy = responseFromFetch.clone();
      .then( cache => {
          cache.put(request, responseCopy);
    return responseFromFetch;

That all seems to be working well in browsers that support service workers. For legacy browsers, like Mobile Safari, there’s the much blunter caveman logic of an AppCache manifest.

Here’s the JavaScript that decides whether a browser gets the service worker or the AppCache:

if ('serviceWorker' in navigator) {
  // If service workers are supported
} else if ('applicationCache' in window) {
  // Otherwise inject an iframe to use appcache
  var iframe = document.createElement('iframe');
  iframe.setAttribute('src', '/appcache.html');
  iframe.setAttribute('style', 'width: 0; height: 0; border: 0');

Either way, people are making full use of the offline nature of the book and that makes me very happy indeed.

Less JavaScript

Every front-end developer at Clearleft went to FFConf last Friday: me, Mark, Graham, Charlotte, and Danielle. We weren’t about to pass up the opportunity to attend a world-class dev conference right here in our home base of Brighton.

The day was unsurprisingly excellent. All the speakers brought their A-game on a wide range of topics. Of course JavaScript was covered, but there was also plenty of mindfood on CSS, accessibility, progressive enhancement, dev tools, creative coding, and even emoji.

Normally FFConf would be a good opportunity to catch up with some Pauls from the Google devrel team, but because of an unfortunate scheduling clash this year, all the Pauls were at Chrome Dev Summit 2016 on the other side of the Atlantic.

I’ve been catching up on the videos from the event. There’s plenty of tech-related stuff: dev tools, web components, and plenty of talk about progressive web apps. But there was also a very, very heavy focus on performance. I don’t just mean performance at the shallow scale of file size and optimisation, but a genuine questioning of the impact of our developer workflows and tools.

In his talk on service workers (what else?), Jake makes the point that not everything needs to be a single page app, echoing Ada’s talk at FFConf.

He makes the point that if you really want fast rendering, nothing on the client side quite beats a server render.

They’ve written a lot of JavaScript to make this quite slow.

Unfortunately, all too often, I hear people say that a progressive web app must be a single page app. And I am not so sure. You might not need a single page app. A single page app can end up being a lot of work and slower. There’s a lot of cargo-culting around single page apps.

Alex followed up his barnstorming talk from the Polymer Summit with some more uncomfortable truths about how mobile phones work.

Cell networks are basically kryptonite to the protocols and assumptions that the web was built on.

And JavaScript frameworks aren’t helping. Quite the opposite.

But make no mistake: if you’re using one of today’s more popular JavaScript frameworks in the most naive way, you are failing by default. There is no sugarcoating this.

Today’s frameworks are mostly a sign of ignorance, or privilege, or both. The good news is that we can fix the ignorance.


Last year Benedict Evans wrote about the worldwide proliferation and growth of smartphones. Nolan referenced that post when he extrapolated the kind of experience people will be having:

As Benedict Evans has noted, the next billion people who are poised to come online will be using the internet almost exclusively through smartphones. And if Google’s plans with Android One are any indication, then we have a fairly good idea of what kind of devices the “next billion” will be using:

  • They’ll mostly be running Android.
  • They’ll have decent specs (1GB RAM, quad-core processors).
  • They’ll have an evergreen browser and WebView (Android 5+).
  • What they won’t have, however, is a reliable internet connection.

This is the same argument that Tom made in his presentation at Responsive Field Day. The main point is that network conditions are unreliable, and I absolutely agree that we need to be very, very mindful of that. But I’m not so sure about the other conditions either. They smell like assumptions:

Assumptions are the problem. Whether it’s assumptions about screen size, assumptions about being able-bodied, assumptions about network connectivity, or assumptions about browser capabilities, I don’t think any assumptions are a safe bet. Now you might quite reasonably say that we have to make some assumptions when we’re building on the web, and you’d be right. But I think we should still aim to keep them to a minimum.

It’s not necessarily true that all those new web users will be running WebView browser like Chrome—there are millions of Opera Mini users, and I would expect that number to rise, given all the speed and cost benefits that proxy browsing brings.

I also don’t think that just because a device is a smartphone it necessarily means that it’s a pocket supercomputer. It might seem like a reasonable assumption to make, given the specs of even a low-end smartphone, but the specs don’t tell the whole story.

Alex gave a great presentation at the recent Polymer Summit. He dives deep into exactly how smartphones at the lower end of the market deal with websites.

I don’t normally enjoy listening to talk of hardware and specs, but Alex makes the topic very compelling by tying it directly to how we build websites. In short, we’re using waaaaay too much JavaScript. The message here is not “don’t use JavaScript” but rather “use JavaScript wisely.” Alas, many of the current crop of monolithic frameworks aren’t well suited to this.

Alex’s talk prompted Michael Scharnagl to take a look back at past assumptions and lessons learned on the web, from responsive design to progressive web apps.

We are consistently improving and we often have to realize that our assumptions are wrong.

This is particularly true when we’re making assumptions about how people will access the web.

It’s not enough to talk about the “next billion” in abstract, like an opportunity to reach teeming masses of people ripe for monetization. We need to understand their lives and their priorities with the sort of detail that can build empathy for other people living under vastly different circumstances.

That’s from an article Ethan linked to, noting:

Enhance! Conf!

Two weeks from now there will be an event in London. You should go to it. It’s called EnhanceConf:

EnhanceConf is a one day, single track conference covering the state of the art in progressive enhancement. We will look at the tools and techniques that allow you to extend the reach of your website/application without incurring additional costs.

As you can probably guess, this is right up my alley. Wild horses wouldn’t keep me away from it. I’ve been asked to be Master of Ceremonies for the day, which is a great honour. Luckily I have some experience in that department from three years of hosting Responsive Day Out. In fact, EnhanceConf is going to run very much in the mold of Responsive Day Out, as organiser Simon explained in an interview with Aaron.

But the reason to attend is of course the content. Check out that line-up! Now that is going to be a knowledge-packed day: design, development, accessibility, performance …these are a few of my favourite things. Nat Buckley, Jen Simmons, Phil Hawksworth, Anna Debenham, Aaron Gustafson …these are a few of my favourite people.

Tickets are still available. Use the discount code JEREMYK to get a whopping 15% off the ticket price.

There’s also a scholarship:

The scholarships are available to anyone not normally able to attend a conference.

I’m really looking forward to EnhanceConf. See you at RSA House on March 4th!

AMPed up

Apple has Apple News. Facebook has Instant Articles. Now Google has AMP: Accelerated Mobile Pages.

The big players sure are going to a lot of effort to reinvent RSS.

That may sound like a flippant remark, but it’s not too far from the truth. In the case of Apple News, its current incarnation appears to be quite literally an RSS reader, at least until the unveiling of the forthcoming Apple News Format.

Google’s AMP project looks a little bit different to the offerings from Facebook and Apple. Rather than creating a proprietary format from scratch, it mandates a subset of HTML …with some proprietary elements thrown in (or, to use the more diplomatic parlance of the extensible web, custom elements).

The idea is that alongside the regular HTML version of your document, you provide a corresponding AMP HTML version. Because the AMP HTML version will be leaner and meaner, user agents can then grab the AMP HTML version and present that to the end user for a faster browsing experience.

So if an RSS feed is an alternate representation of a homepage or a listing of articles, then an AMP document is an alternate representation of a single article.

Now, my own personal take on providing alternate representations of documents is “Sure. Why not?” Here on adactio.com I provide RSS feeds. On The Session I provide RSS, JSON, and XML. And on Huffduffer I provide RSS, Atom, JSON, and XSPF, adding:

If you would like to see another format supported, share your idea.

Also, each individual item on Huffduffer has a corresponding oEmbed version (and, in theory, an RDF version)—an alternate representation of that item …in principle, not that different from AMP. The big difference with AMP is that it’s using HTML (of sorts) for its format.

All of this sounds pretty reasonable: provide an alternate representation of your canonical HTML pages so that user-agents (Twitter, Google, browsers) can render a faster-loading version …much like an RSS reader.

So should you start providing AMP versions of your pages? My initial reaction is “Sure. Why not?”

The AMP Project website comes with a list of frequently asked questions, which of course, nobody has asked. My own list of invented frequently asked questions might look a little different.

Will this kill advertising?

We live in hope.

Alas, AMP pages will still be able to carry advertising, but in a restricted form. No more scripts that track your movement across the web …unless the script is from an authorised provider, like say, Google.

But it looks like the worst performance offenders won’t be able to get their grubby little scripts into AMP pages. This is a good thing.

Won’t this kill journalism?

Of all the horrid myths currently in circulation, the two that piss me off the most are:

  1. Journalism requires advertising to survive.
  2. Advertising requires invasive JavaScript.

Put the two together and you get the gist of most of the chicken-littling articles currently in circulation: “Journalism requires invasive JavaScript to survive.”

I could argue against the first claim, but let’s leave that for another day. Let’s suppose for now that, sure, journalism requires advertising to survive. Fine.

It’s that second point that is fundamentally wrong. The idea that the current state of advertising is the only way of advertising is incredibly short-sighted and misguided. Invasive JavaScript is not a requirement for showing me an ad. Setting a cookie is not a requirement for showing me an ad. Knowing where I live, who my friends are, what my income level is, and where I’ve been on the web …none of these are requirements for showing me an ad.

It is entirely possible to advertise to me and treat me with respect at the same time. The Deck already does this.

And you know what? Ad networks had their chance. They had their chance to treat us with respect with the Do Not Track initiative. We asked them to respect our wishes. They told us get screwed.

Now those same ad providers are crying because we’re installing ad blockers. They can get screwed.


It is entirely possible to advertise within AMP pages …just not using blocking JavaScript.

For a nicely nuanced take on what AMP could mean for journalism, see Joshua Benton’s article on Nieman Lab—Get AMP’d: Here’s what publishers need to know about Google’s new plan to speed up your website.

Why not just make faster web pages?

Excellent question!

For a site like adactio.com, the difference between the regular HTML version of an article and the corresponding AMP version of the same article is pretty small. It’s a shame that I can’t just say “Hey, the current version of the article is the AMP version”, but that would require that I only use a subset of HTML and that I add some required guff to my page (including an unnecessary JavaScript file).

But for most of the news sites out there, the difference between their regular HTML pages and the corresponding AMP versions will be pretty significant. That’s because the regular HTML versions are bloated with third-party scripts, oversized assets, and cruft around the actual content.

Now it is in theory possible for these news sites to get rid of all those things, and I sincerely hope that they will. But that’s a big political struggle. I am rooting for developers—like the good folks at VOX—who have to battle against bosses who honestly think that journalism requires invasive JavaScript. Best of luck.

Along comes Google saying “If you want to play in our sandbox, you’re going to have to abide by our rules.” Those rules include performance best practices (for the most part—I take issue with some of the requirements, and I’ll go into that in more detail in a moment).

Now when the boss says “Slap a three megabyte JavaScript library on it so we can show a carousel”, the developers can only respond with “Google says No.”

When the boss says “Slap a ton of third-party trackers on it so we can monetise those eyeballs”, the developers can only respond with “Google says No.”

Google have used their influence like this before and it has brought them accusations of monopolistic abuse. Some people got very upset when they began labelling (and later ranking) mobile-friendly pages. Personally, I’ve got no issue with that.

In this particular case, Google aren’t mandating what you can and can’t do on your regular HTML pages; only what you can and can’t do on the corresponding AMP page.

Which brings up another question…

Will the AMP web kill the open web?

If we all start creating AMP versions of our pages, and those pages are faster than our regular HTML versions, won’t everyone just see the AMP versions without ever seeing the “full” versions?

Tim articulates a legitimate concern:

This promise of improved distribution for pages using AMP HTML shifts the incentive. AMP isn’t encouraging better performance on the web; AMP is encouraging the use of their specific tool to build a version of a web page. It doesn’t feel like something helping the open web so much as it feels like something bringing a little bit of the walled garden mentality of native development onto the web.

That troubles me. Using a very specific tool to build a tailored version of my page in order to “reach everyone” doesn’t fit any definition of the “open web” that I’ve ever heard.

Fair point. But I also remember that a lot of people were upset by RSS. They didn’t like that users could go for months at a time without visiting the actual website, and yet they were reading every article. They were reading every article in non-browser user agents in a format that wasn’t HTML. On paper that sounds like the antithesis of the open web, but in practice there was always something very webby about RSS, and RSS feed readers—it put the power back in the hands of the end users.

Some people chose not to play ball. They only put snippets in their RSS feeds, not the full articles. Maybe some publishers will do the same with the AMP versions of their articles: “To read more, click here…”

But I remember what generally tended to happen to the publishers who refused to put the full content in their RSS feeds. We unsubscribed.

Still, I share the concern that any one company—whether it’s Facebook, Apple, or Google—should wield so much power over how we publish on the web. I don’t think you have to be a conspiracy theorist to view the AMP project as an attempt to replace the existing web with an alternate web, more tightly controlled by Google (albeit a faster, more performant, tightly-controlled web).

My hope is that the current will flow in both directions. As well as publishers creating AMP versions of their pages in order to appease Google, perhaps they will start to ask “Why can’t our regular pages be this fast?” By showing that there is life beyond big bloated invasive web pages, perhaps the AMP project will work as a demo of what the whole web could be.

I’ve been playing around with the AMP HTML spec. It has some issues. The good news is that it’s open source and the project owners seem receptive to feedback.


No external JavaScript is allowed in an AMP HTML document. This covers third-party libraries, advertising and tracking scripts. This is A-okay with me.

The reasons given for this ban are related to performance and I agree with them completely. Big bloated JavaScript libraries are one of the biggest performance killers on the web. I’m happy to leave them at the door (although weirdly, web fonts—another big performance killer—are allowed in).

But then there’s a bit of an about-face. In order to have a valid AMP HTML page, you must include a piece of third-party JavaScript. In this case, the third party is Google and the JavaScript file is what handles the loading of assets.

This seems a bit strange to me; on the one hand claiming that third-party JavaScript is bad for performance and on the other, requiring some third-party JavaScript. As Justin says:

For me this is loading one thing too many… the AMP JS library. Surely the document itself is going to be faster than loading a library to try and make it load faster.

On the plus side, this third-party JavaScript is loaded asynchronously. It seems to mostly be there to handle the rendering of embedded content: images, videos, audio, etc.

Embedded content

If you want audio, video, or images on your page, you must use propriet… custom elements like amp-audio, amp-video, and amp-img. In the case of images, I can see how this is a way of getting around the browser’s lookahead pre-parser (although responsive images also solve this problem). In the case of audio and video, the standard audio and video elements already come with a way of specifying preloading behaviour using the preload attribute. Very odd.

Justin again:

I’m not sure if this is solving anything at the moment that we’re not already fixing with something like responsive images.

To use amp-img for images within the flow of a document, you’ll need to specify the dimensions of the image. This makes sense from a rendering point of view—knowing the width and height ahead of time avoids repaints and reflows. Alas, in many of the cases here on adactio.com, I don’t know the dimensions of the images I’m including. So any of my AMP HTML pages that include images will be invalid.

Overall, the way that AMP HTML handles embedded content looks like a whole lot of wheel reinvention. I like the idea of providing custom elements as an option for authors. I hate the idea of making them a requirement.


If you want to provide metadata about your document, AMP HTML currently requires the use of Google’s Schema.org vocabulary. This has a big whiff of vendor lock-in to it. I’ve flagged this up as an issue and Aaron is pushing a change so hopefully this will be resolved soon.


In its initial release, the AMP HTML spec came with some nasty surprises for accessibility. The biggest is probably the requirement to include this in your viewport meta element:


Yowzers! That’s some slap in the face to decent web developers everywhere. Fortunately this has been flagged up and I’m hoping it will be fixed soon.

If it doesn’t get fixed, it’s quite a non-starter. It beggars belief that Google would mandate to authors that they must make their pages inaccessible to pinch/zoom. I would hope that many developers would rebel against such a draconian injunction. If that happens, it’ll be interesting to see what becomes of those theoretically badly-formed AMP HTML documents. Technically, they will fail validation, but for very good reason. Will those accessible documents be rejected?

Please get involved on this issue if this is important to you (hint: this should be important to you).

There are a few smaller issues. Initially the :focus pseudo-class was disallowed in author CSS, but that’s being fixed.

Currently AMP HTML documents must have this line:

<style>body {opacity: 0}</style><noscript><style>body {opacity: 1}</style></noscript>


That’s a horrible conflation of JavaScript availability and CSS. It’s being fixed though, and soon all the opacity jiggery-pokery will only happen via JavaScript, which will be a big improvement: it should either all happen in CSS or all happen in JavaScript, but not the current mixture of the two.


The AMP HTML version of your page is not the canonical version. You can specify where the real HTML version of your document is by using rel="canonical". Great!

But how do you link from your canonical page out to the AMP HTML version? Currently you’re supposed to use rel="amphtml". No, they haven’t checked the registry. Again. I’ll go in and add it.

In the meantime, I’m also requesting that the amphtml value can be combined with the alternate value, seeing as rel values can be space separated:

rel="alternate amphtml" type="text/html"

See? Not that different to RSS:

rel="alterate" type="application/rss+xml"


When I publish something on adactio.com in HTML, it already gets syndicated to different places. This is the Indie Web idea of POSSE: Publish (on your) Own Site, Syndicate Elsewhere. As well as providing RSS feeds, I’ve also got Twitter bots that syndicate to Twitter. An If This, Then That script pushes posts to Facebook. And if I publish a photo, it goes to Flickr. Now that Medium is finally providing a publishing API, I’ll probably start syndicating articles there as well. The more, the merrier.

From that perspective, providing AMP HTML pages feels like just one more syndication option. If it were the only option, and I felt compelled to provide AMP versions of my content, I’d be very concerned. But for now, I’ll give it a whirl and see how it goes.

Here’s a bit of PHP I’m using to convert a regular piece of HTML into AMP HTML—it’s horrible code; it uses regular expressions on HTML which, as we all know, will summon the Elder Gods.

Building the dConstruct 2015 site

I remember when I first saw Paddy’s illustration for this year’s dConstruct site, I thought “Well, that’s a design direction, but there’s no way that Graham will be able to implement all of it.” There was a tight deadline for getting the site out, and let’s face it, there was so much going on in the design that we’d just have to prioritise.

I underestimated Graham’s sheer bloody-mindedness.

At the next front-end pow-wow at Clearleft, Graham showed the dConstruct site in all its glory …in Lynx.

http://2015.dconstruct.org in Lynx.

I love that. Even with the focus on the gorgeous illustration and futuristic atmosphere of the design, Graham took the time to think about the absolute basics: marking up the content in a logical structured way. Everything after that—the imagery, the fonts, the skewed style—all of it was built on a solid foundation.

One site, two browsers.

It would’ve been easy to go crazy with the fonts and images, but Graham made sure to optimise everything to within an inch of its life. The biggest bottleneck comes from a third party provider—the map tiles and associated JavaScript …so that’s loaded in after the initial content is loaded. It turns out that the site build was a matter of prioritisation after all.


There’s plenty of CSS trickery going on: transforms, transitions, and opacity. But for the icing on the cake, Graham reached for canvas and programmed space elevator traffic with randomly seeded velocity and size.

Oh, and of course it’s all responsive.

So, putting that all together…

The dConstruct 2015 site is gorgeous, semantic, responsive, and performant. Conventional wisdom dictates that you have to choose, but this little site—built on a really tight schedule—shows otherwise.

On The Verge

Quite a few people have been linking to an article on The Verge with the inflammatory title The Mobile web sucks. In it, Nilay Patel heaps blame upon mobile browsers, Safari in particular:

But man, the web browsers on phones are terrible. They are an abomination of bad user experience, poor performance, and overall disdain for the open web that kicked off the modern tech revolution.

Les Orchard says what we’re all thinking in his detailed response The Verge’s web sucks:

Calling out browser makers for the performance of sites like his? That’s a bit much.

Nilay does acknowledge that the Verge could do better:

Now, I happen to work at a media company, and I happen to run a website that can be bloated and slow. Some of this is our fault: The Verge is ultra-complicated, we have huge images, and we serve ads from our own direct sales and a variety of programmatic networks.

But still, it sounds like the buck is being passed along. The performance issues are being treated as Somebody Else’s Problem …ad networks, trackers, etc.

The developers at Vox Media take a different, and in my opinion, more correct view. They’re declaring performance bankruptcy:

I mean, let’s cut to the chase here… our sites are friggin’ slow, okay!

But I worry about how they can possibly reconcile their desire for a faster website with a culture that accepts enormously bloated ads and trackers as the inevitable price of doing business on the web:

I’m hearing an awful lot of false dichotomies here: either you can have a performant website or you have a business model based on advertising. Here’s another false dichotomy:

If the message coming down from above is that performance concerns and business concerns are fundamentally at odds, then I just don’t know how the developers are ever going to create a culture of performance (which is a real shame, because they sound like a great bunch). It’s a particularly bizarre false dichotomy to be foisting when you consider that all the evidence points to performance as being a key differentiator when it comes to making moolah.

It’s funny, but I take almost the opposite view that Nilay puts forth in his original article. Instead of thinking “Oh, why won’t these awful browsers improve to be better at delivering our websites?”, I tend to think “Oh, why won’t these awful websites improve to be better at taking advantage of our browsers?” After all, it doesn’t seem like that long ago that web browsers on mobile really were awful; incapable of rendering the “real” web, instead only able to deal with WAP.

As Maciej says in his magnificent presentation Web Design: The First 100 Years:

As soon as a system shows signs of performance, developers will add enough abstraction to make it borderline unusable. Software forever remains at the limits of what people will put up with. Developers and designers together create overweight systems in hopes that the hardware will catch up in time and cover their mistakes.

We complained for years that browsers couldn’t do layout and javascript consistently. As soon as that got fixed, we got busy writing libraries that reimplemented the browser within itself, only slower.

I fear that if Nilay got his wish and mobile browsers made a quantum leap in performance tomorrow, the result would be even more bloated JavaScript for even more ads and trackers on websites like The Verge.

If anything, browser makers might have to take more drastic steps to route around the damage of bloated websites with invasive tracking.

We’ve been here before. When JavaScript first landed in web browsers, it was quickly adopted for three primary use cases:

  1. swapping out images when the user moused over a link,
  2. doing really bad client-side form validation, and
  3. spawning pop-up windows.

The first use case was so popular, it was moved from a procedural language (JavaScript) to a declarative language (CSS). The second use case is still with us today. The third use case was solved by browsers. They added a preference to block unwanted pop-ups.

Tracking and advertising scripts are today’s equivalent of pop-up windows. There are already plenty of tools out there to route around their damage: Ghostery, Adblock Plus, etc., along with tools like Instapaper, Readability, and Pocket.

I’m sure that business owners felt the same way about pop-up ads back in the late ’90s. Just the price of doing business. Shrug shoulders. Just the way things are. Nothing we can do to change that.

For such a young, supposedly-innovative industry, I’m often amazed at what people choose to treat as immovable, unchangeable, carved-in-stone issues. Bloated, invasive ad tracking isn’t a law of nature. It’s a choice. We can choose to change.

Every bloated advertising and tracking script on a website was added by a person. What if that person refused? I guess that person would be fired and another person would be told to add the script. What if that person refused? What if we had a web developer picket line that we collectively refused to cross?

That’s an unrealistic, drastic suggestion. But the way that the web is being destroyed by our collective culpability calls for drastic measures.

By the way, the pop-up ad was first created by Ethan Zuckerman. He has since apologised. What will you be apologising for in decades to come?


When I give talks or workshops, I sometimes get a bit ranty. One of the richest seams of rantiness comes from me complaining about how we web designers and developers are responsible for making the web a hostile place. “Stop getting the web wrong!” I might shout, like an old man yelling at a cloud. I point to services like Instapaper and Readability and describe their existence as a damning indictment of our work.

Don’t get me wrong—I really like Instapaper, Readability, RSS readers, or any other tools that allow people to read what they want when they want it. But think about their fundamental selling point: get to the content you want without having to wade through the cruft. That cruft was put there by us.

So-called modern web design and development is damage that people have to route around.

(Ooh, I can feel myself coming over all ranty and angry again! Calm down, Jeremy, calm down!)

And. Breathe.

Now there’s a new tool to the add to the list: Facebook Instant. Again, I think it’s actually pretty great that this service exists. But once again, it should make us ashamed of the work we’re collectively producing.

In this case, the service is—somewhat ironically—explicitly touting the performance benefits of not going to a website to read an article. Quite right.

PPK points to tools as the source of the problem and Marco Arment agrees:

The entire culture dominant among web developers today is bizarrely framework-heavy, with seemingly no thought given to minimizing dependencies and page weight.

But I think it’s a bit more subtle than that. As John Gruber says:

Business development deals have created problems that no web developer can solve. There’s no way to make a web page with a full-screen content-obscuring ad anything other than a shitty experience.

Now you might be saying to yourself “Well, I’ve never made a bloated web page!” or “I’ve never slapped loads of intrusive crap over the content!” I’d certainly like to think that I can look at my track record and hold my head up reasonably high. But that doesn’t matter. If the overall perception is that going to a URL to read an article is a pain in the ass, it hurts all of us.

Take this article from M.G. Siegler:

Not only is the web not fast enough for apps, it’s not fast enough for text either. …on mobile, the web browser just isn’t cutting it. … Native apps provide a better user experience on mobile than a web browser.

On the face of it, this is kind of a bizarre claim. After all, there’s nothing inherent in web browsers that makes them slow at rendering text—quite the opposite! And native apps still use HTTP (and often HTML) to fetch content; the network doesn’t suddenly get magically faster just because the piece of software requesting a resource doesn’t happen to be a web browser.

But this conflation of slow websites and slow web browsers is perfectly understandable. If it looks like a slow duck, and it quacks like a slow duck, then why not conclude that ducks are slow? Even if we know that there’s nothing inherently slow about making web pages:

My hope is that Facebook Instant will shake things up a bit. M.G. Siegler again:

At the very least, Facebook has put everyone else on notice. Your content better load fast or you’re screwed. Publication websites have become an absolutely bloated mess. They range from beautiful (The Verge) to atrocious (Bloomberg) to unusable (Forbes). The common denominator: they’re all way too slow.

There needs to be a cultural change in how we approach building for the web. Yes, some of the tools we choose are part of the problem, but the bigger problem is that performance still isn’t being recognised as the most important factor in how people feel about websites (and by extension, the web). This isn’t just a developer issue. It’s a design issue. It’s a UX issue. It’s a business issue. Performance is everybody’s collective responsibility.

I’d better stop now before I start getting all ranty again.

I’ll leave you with some other writings on this topic…

Tim Kadlec talks about choosing performance:

It’s not because of any sort of technical limitations. No, if a website is slow it’s because performance was not prioritized. It’s because when push came to shove, time and resources were spent on other features of a site and not on making sure that site loads quickly.

Jim Ray points out that “we learned the wrong lesson from the rise of mobile and the app ecosystem”:

We’ve spent far too long trying to compete with native experiences by making our websites look and behave like apps. This includes not just thousands of lines of JavaScript to mimic native app swipes and scrolling but even the lower overhead aesthetics of fixed position headers and persistent navigation.


Finally, Baldur Bjarnason has written a terrific piece:

The web doesn’t suck. Your websites suck.

All of your websites suck.

You destroy basic usability by hijacking the scrollbar. You take native functionality (scrolling, selection, links, loading) that is fast and efficient and you rewrite it with ‘cutting edge’ javascript toolkits and frameworks so that it is slow and buggy and broken. You balloon your websites with megabytes of cruft. You ignore best practices. You take something that works and is complementary to your business and turn it into a liability.

The lousy performance of your websites becomes a defensive moat around Facebook.

Go read the whole thing—it’s terrific:

This is a long-standing debate. Except it’s only long-standing among web developers. Columnists, managers, pundits, and journalists seem to have no interest in understanding the technical foundation of their livelihoods. Instead they are content with assuming that Facebook can somehow magically render HTML over HTTP faster than anybody else and there is nothing anybody can do to make their crap scroll-jacking websites faster. They buy into the myth that the web is incapable of delivering on its core capabilities: delivering hypertext and images quickly to a diverse and connected readership.

100 words 058

PPK writes of modern web development:

Tools don’t solve problems any more, they have become the problem.

I think he’s mostly correct, but I think there is some clarification required.

Web development tools fall into two broad categories:

  1. Local tools like preprocessors, task managers, and version control systems that help the developer output their own HTML, CSS, and JavaScript.
  2. Tools written in HTML, CSS, and JavaScript that the end user has to download for the developer to gain benefit.

It’s that second category that contain a tax on the end user. Stop solving problems you don’t yet have.

Inlining critical CSS for first-time visits

After listening to Scott rave on about how much of a perceived-performance benefit he got from inlining critical CSS on first load, I thought I’d give it a shot over at The Session. On the chance that this might be useful for others, I figured I’d document what I did.

The idea here is that you can give a massive boost to the perceived performance of the first page load on a site by putting the most important CSS in the head of the page. Then you cache the full stylesheet. For subsequent visits you only ever use the external stylesheet. So if you’re squeamish at the thought of munging your CSS into your HTML (and that’s a perfectly reasonable reaction), don’t worry—this is a temporary workaround just for initial visits.

My particular technology stack here is using Grunt, Apache, and PHP with Twig templates. But I’m sure you can adapt this for other technology stacks: what’s important here isn’t the technology, it’s the thinking behind it. And anyway, the end user never sees any of those technologies: the end user gets HTML, CSS, and JavaScript. As long as that’s what you’re outputting, the specifics of the technology stack really don’t matter.

Generating the critical CSS

Okay. First question: how do you figure out which CSS is critical and which CSS can be deferred?

To help answer that, and automate the task of generating the critical CSS, Filament Group have made a Grunt task called grunt-criticalcss. I added that to my project and updated my Gruntfile accordingly:

    // All my existing Grunt configuration goes here.
    criticalcss: {
        dist: {
            options: {
                url: 'http://thesession.dev',
                width: 1024,
                height: 800,
                filename: '/path/to/main.css',
                outputfile: '/path/to/critical.css'

I’m giving it the name of my locally-hosted version of the site and some parameters to judge which CSS to prioritise. Those parameters are viewport width and height. Now, that’s not a perfect way of judging which CSS matters most, but it’ll do.

Then I add it to the list of Grunt tasks:

// All my existing Grunt tasks go here.

grunt.registerTask('default', ['sass', etc., 'criticalcss']);

The end result is that I’ve got two CSS files: the full stylesheet (called something like main.css) and a stylesheet that only contains the critical styles (called critical.css).

Cache-busting CSS

Okay, this is a bit of a tangent but trust me, it’s going to be relevant…

Most of the time it’s a very good thing that browsers cache external CSS files. But if you’ve made a change to that CSS file, then that feature becomes a bug: you need some way of telling the browser that the CSS file has been updated. The simplest way to do this is to change the name of the file so that the browser sees it as a whole new asset to be cached.

You could use query strings to do this cache-busting but that has some issues. I use a little bit of Apache rewriting to get a similar effect. I point browsers to CSS files like this:

<link rel="stylesheet" href="/css/main.20150310.css">

Now, there isn’t actually a file named main.20150310.css, it’s just called main.css. To tell the server where the actual file is, I use this rewrite rule:

RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+).(d+).(js|css)$ $1.$3 [L]

That tells the server to ignore those numbers in JavaScript and CSS file names, but the browser will still interpret it as a new file whenever I update that number. You can do that in a .htaccess file or directly in the Apache configuration.

Right. With that little detour out of the way, let’s get back to the issue of inlining critical CSS.

Differentiating repeat visits

That number that I’m putting into the filenames of my CSS is something I update in my Twig template, like this (although this is really something that a Grunt task could do, I guess):

{% set cssupdate = '20150310' %}

Then I can use it like this:

<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">

I can also use JavaScript to store that number in a cookie called csscached so I’ll know if the user has a cached version of this revision of the stylesheet:

document.cookie = 'csscached={{ cssupdate }};expires="Tue, 19 Jan 2038 03:14:07 GMT";path=/';

The absence or presence of that cookie is going to be what determines whether the user gets inlined critical CSS (a first-time visitor, or a visitor with an out-of-date cached stylesheet) or whether the user gets a good ol’ fashioned external stylesheet (a repeat visitor with an up-to-date version of the stylesheet in their cache).

Here are the steps I’m going through:

First of all, set the Twig cssupdate variable to the last revision of the CSS:

{% set cssupdate = '20150310' %}

Next, check to see if there’s a cookie called csscached that matches the value of the latest revision. If there is, great! This is a repeat visitor with an up-to-date cache. Give ‘em the external stylesheet:

{% if _cookie.csscached == cssupdate %}
<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">

If not, then dump the critical CSS straight into the head of the document:

{% else %}
{% include '/css/critical.css' %}

Now I still want to load the full stylesheet but I don’t want it to be a blocking request. I can do this using JavaScript. Once again it’s Filament Group to the rescue with their loadCSS script:

    // include loadCSS here...
    loadCSS('/css/main.{{ cssupdate }}.css');

While I’m at it, I store the value of cssupdate in the csscached cookie:

    document.cookie = 'csscached={{ cssupdate }};expires="Tue, 19 Jan 2038 03:14:07 GMT";path=/';

Finally, consider the possibility that JavaScript isn’t available and link to the full CSS file inside a noscript element:

<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">
{% endif %}

And we’re done. Phew!

Here’s how it looks all together in my Twig template:

{% set cssupdate = '20150310' %}
{% if _cookie.csscached == cssupdate %}
<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">
{% else %}
{% include '/css/critical.css' %}
// include loadCSS here...
loadCSS('/css/main.{{ cssupdate }}.css');
document.cookie = 'csscached={{ cssupdate }};expires="Tue, 19 Jan 2038 03:14:07 GMT";path=/';
<link rel="stylesheet" href="/css/main.{{ cssupdate }}.css">
{% endif %}

You can see the production code from The Session in this gist. I’ve tweaked the loadCSS script slightly to match my preferred JavaScript style but otherwise, it’s doing exactly what I’ve outlined here.

The result

According to Google’s PageSpeed Insights, I done good.

Optimising https://thesession.org/

A question of timing

I’ve been updating my collection of design principles lately, adding in some more examples from Android and Windows. Coincidentally, Vasilis unveiled a neat little page that grabs one list of principles at random —just keep refreshing to see more.

I also added this list of seven principles of rich web applications to the collection, although they feel a bit more like engineering principles than design principles per se. That said, they’re really, really good. Every single one is rooted in performance and the user’s experience, not developer convenience.

Don’t get me wrong: developer convenience is very, very important. Nobody wants to feel like they’re doing unnecessary work. But I feel very strongly that the needs of the end user should trump the needs of the developer in almost all instances (you may feel differently and that’s absolutely fine; we’ll agree to differ).

That push and pull between developer convenience and user experience is, I think, most evident in the first principle: server-rendered pages are not optional. Now before you jump to conclusions, the author is not saying that you should never do client-side rendering, but instead points out the very important performance benefits of having the server render the initial page. After that—if the user’s browser cuts the mustard—you can use client-side rendering exclusively.

The issue with that hybrid approach—as I’ve discussed before—is that it’s hard. Isomorphic JavaScript (terrible name) can theoretically help here, but I haven’t seen too many examples of it in action. I suspect that’s because this approach doesn’t yet offer enough developer convenience.

Anyway, I found myself nodding along enthusiastically with that first of seven design principles. Then I got to the second one: act immediately on user input. That sounds eminently sensible, and it’s backed up with sound reasoning. But it finishes with:

Techniques like PJAX or TurboLinks unfortunately largely miss out on the opportunities described in this section.

Ah. See, I’m a big fan of PJAX. It’s essentially the same thing as the Hijax technique I talked about many years ago in Bulletproof Ajax, but with the new addition of HTML5’s History API. It’s a quick’n’dirty way of giving the illusion of a fat client: all the work is actually being done in the server, which sends back chunks of HTML that update the interface. But it’s true that, because of that round-trip to the server, there’s a bit of a delay and so you often end up briefly displaying a loading indicator.

I contend that spinners or “loading indicators” should become a rarity

I agree …but I also like using PJAX/Hijax. Now how do I reconcile what’s best for the user experience with what’s best for my own developer convenience?

I’ve come up with a compromise, and you can see it in action on The Session. There are multiple examples of PJAX in action on that site, like pretty much any page that returns paginated results: new tune settings, the latest events, and so on. The steps for initiating an Ajax request used to be:

  1. Listen for any clicks on the page,
  2. If a “previous” or “next” button is clicked, then:
  3. Display a loading indicator,
  4. Request the new data from the server, and
  5. Update the page with the new data.

In one sense, I am acting immediately to user input, because I always display the loading indicator straight away. But because the loading indicator always appears, no matter how fast or slow the server responds, it sometimes only appears very briefly—just for a flash. In that situation, I wonder if it’s serving any purpose. It might even be doing the opposite to its intended purpose—it draws attention to the fact that there’s a round-trip to the server.

“What if”, I asked myself, “I only showed the loading indicator if the server is taking too long to send a response back?”

The updated flow now looks like this:

  1. Listen for any clicks on the page,
  2. If a “previous” or “next” button is clicked, then:
  3. Start a timer, and
  4. Request the new data from the server.
  5. If the timer reaches an upper limit, show a loading indicator.
  6. When the server sends a response, cancel the timer and
  7. Update the page with the new data.

Even though there are more steps, there’s actually less happening from the user’s perspective. Where previously you would experience this:

  1. I click on a button,
  2. I briefly see a loading indicator,
  3. I see the new data.

Now your experience is:

  1. I click on a button,
  2. I see the new data.

…unless the server or the network is taking too long, in which case the loading indicator appears as an interim step.

The question is: how long is too long? How long do I wait before showing the loading indicator?

The Nielsen Norman group offers this bit of research:

0.1 second is about the limit for having the user feel that the system is reacting instantaneously, meaning that no special feedback is necessary except to display the result.

So I should set my timer to 100 milliseconds. In practice, I found that I can set it to as high as 200 to 250 milliseconds and keep it feeling very close to instantaneous. Anything over that, though, and it’s probably best to display a loading indicator: otherwise the interface starts to feel a little sluggish, and slightly uncanny. (“Did that click do any—? Oh, it did.”)

You can test the response time by looking at some of the simpler pagination examples on The Session: new recordings or new discussions, for example. To see examples of when the server takes a bit longer to send a response, you can try paginating through search results. These take longer because, frankly, I’m not very good at optimising some of those search queries.

There you have it: an interface that—under optimal conditions—reacts to user input instantaneously, but falls back to displaying a loading indicator when conditions are less than ideal. The result is something that feels like a client-side web thang, even though the actual complexity is on the server.

Now to see what else I can learn from the rest of those design principles.