Tags: work



Sunday, January 15th, 2017

Modernizing our Progressive Enhancement Delivery | Filament Group, Inc., Boston, MA

Scott runs through the latest improvements to the Filament Group website. There’s a lot about HTTP2, but also a dab of service workers (using a similar recipe to my site).

Browser Support for evergreen websites

Oh, how I wished everyone approached building for the web the way that Rachel does. Smart, sensible, pragmatic, and exciting!

Wednesday, January 11th, 2017

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.

A Tale of Four Caches · Yoav Weiss

A cute explanation of different browser caches:

  • memory cache,
  • service worker cache,
  • disk cache, and
  • push cache.

Monday, January 9th, 2017

The Futures of Typography

A wonderfully thoughtful piece from Robin, ranging from the printing technologies of the 15th century right up to the latest web technologies. It’s got all my favourite things in there: typography, digital preservation, and service workers. Marvellous!

Friday, January 6th, 2017

From Tape Drives to Memory Orbs, the Data Formats of Star Wars Suck (Spoilers) | Motherboard

As always with sci-fi interfaces, the important part is telling the story, not realism or accuracy. Personally, I liked the way that the World War II trappings of Rogue One extended to communications and networking technologies.

Productivity in Terrible Times

When a solid 67% of your soul is engaged with battles elsewhere, how do you continue on with our ongoing, non-revolutionary work?

Wednesday, December 28th, 2016

What you need to know about using VPN in the UK – By Andy Parker

If you’re prepping your defences against the snooper’s charter (and you/I should be), Andy recommend using NordVPN.

Monday, December 26th, 2016

High Performance Browser Networking (O’Reilly)

Did you know that Ilya’s book was available in its entirety online? I didn’t. But now that I do, I think it’s time I got stuck in and tried to understand the low-level underpinnings of the internet and the web.

Saturday, December 24th, 2016

10 things I learned making the fastest site in the world

Behind the amusing banter there’s some really solid performance advice in here. Good stuff.

Client Side Rendering (CSR), or as I call it “setting money on fire and throwing it in a river” has its uses, but for this site would have been madness.

Thursday, December 8th, 2016

Hey, Hey, Cloud Four is a PWA! - Cloud Four

Jason talks through the service worker strategy for his company website.

Sunday, December 4th, 2016

The world-wide web (PDF) by T.J. Berners-Lee, R. Cailliau and J.-F. Groff

Well, look at these fresh-faced lads presenting their little hypertext system in 1992. A fascinating time capsule.

Service Worker, what are you? - Mariko Kosaka

This is a fun—and accurate—explanation of service workers.

There’s definitely something “alien” about a service worker—it’s kind of like a virus that gets installed on the user’s device. I’ve taken to describing it as “a man-in-the-middle attack on your own website” which makes sound a bit scarier than is necessary.

Monday, November 21st, 2016

My biggest takeaway from the second Offline Camp in Santa Margarita, CA — plus toast!

J. Renée Beach writes on Ev’s blog about three things to consider when planning for offline experiences:

  • Freshness,
  • Reach, and
  • Assurance.

How will you express to your users that the content is up to date, safe and available across their network?

You Are Not Paid to Write Code – Brave New Geek

Gall’s Fundamental Theorem of Systems is that new systems mean new problems. I think the same can safely be said of code—more code, more problems. Do it without a new system if you can

A cautionary tale of the risks involved with embracing new frameworks.

But when you introduce a new system, you introduce new variables, new failure points, and new problems.

almost anything is easier to get into than out of.

Thursday, November 17th, 2016

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.

Thursday, November 3rd, 2016


Tom wrote a post on Ev’s blog a while back called JavaScript Frameworks: Distribution Channels for Good Ideas (I’ve been hoping he’d publish it on his own site so I’d have a more permanent URL to point to, but so far, no joy). It’s well worth a read.

I don’t really have much of an opinion on his central point that browser makers should work more closely with framework makers. I’m not so sure I agree with the central premise that frameworks are going to be around for the long haul. I think good frameworks—like jQuery—should aim to make themselves redundant.

But anyway, along the way, Tom makes this observation:

Google has an institutional tendency to go it alone.

JavaScript not good enough? Let’s create Dart to replace it. HTML not good enough? Let’s create AMP to replace it. I’m just waiting for them to announce Google Style Sheets.

I don’t really mind these inventions. We’re not forced to adopt them, and generally, we don’t. Tom again:

They poured enormous time and money into Dart, even building an entire IDE, without much to show for it. Contrast Dart’s adoption with the adoption of TypeScript and Flow, which layer improvements on top of JavaScript instead of trying to replace it.

See, that’s a really, really good point. It’s so much easier to get people to adjust their behaviour than to change it completely.

Sass is a really good example of this. You can take any .css file, save it as a .scss file, and now you’re using Sass. Then you can start using features (or not) as needed. Very smart.

Incidentally, I’m very curious to know how many people use the scss syntax (which is the same as CSS) compared to how many people use the sass indented syntax (the one with significant whitespace). In his brilliant Sass for Web Designers book, I don’t think Dan even mentioned the indented syntax.

Or compare the adoption of Sass to the adoption of HAML. Now, admittedly, the disparity there might be because Sass adds new features, whereas HAML is a purely stylistic choice. But I think the more fundamental difference is that Sass—with its scss syntax—only requires you to slightly adjust your behaviour, whereas something like HAML requires you to go all in right from the start.

This is something that has been on my mind a lately while I’ve been preparing my new talk on evaluating technology (the talk went down very well at An Event Apart San Francisco, by the way—that’s a relief). In the talk, I made a reference to one of Grace Hopper’s famous quotes:

Humans are allergic to change.

Now, Grace Hopper subsequently says:

I try to fight that.

I contrast that with the approach that Tim Berners-Lee and Robert Cailliau took with their World Wide Web project. The individual pieces were built on what people were already familiar with. URLs use slashes so they’d be feel similar to UNIX file paths. And the first fledging version of HTML took its vocabulary almost wholesale from a version of SGML already in use at CERN. In fact, you could pretty much take an existing CERN SGML file and open it as an HTML file in a web browser.

Oh, and that browser would ignore any tags it didn’t understand—behaviour that, in my opinion, would prove crucial to the growth and success of HTML. Because of its familiarity, its simplicity, and its forgiving error handling, HTML turned to be more successful than Tim Berners-Lee expected, as he wrote in his book Weaving The Web:

I expected HTML to be the basic waft and weft of the Web but documents of all types: video, computer aided design, sound, animation and executable programs to be the colored threads that would contain much of the content. It would turn out that HTML would become amazingly popular for the content as well.

HTML and SGML; Sass and CSS; TypeScript and JavaScript. The new technology builds on top of the existing technology instead of wiping the slate clean and starting from scratch.

Humans are allergic to change. And that’s okay.

Saturday, October 29th, 2016

Mapping the Sneakernet – The New Inquiry

When it seems like all our online activity is being tracked by Google, Facebook, and co., it comforts me to think of all the untracked usage out there, from shared (or fake) Facebook accounts to the good ol’ sneakernet:

Packets of information can be distributed via SMS and mobile 3G but also pieces of paper, USB sticks and Bluetooth.

Connectivity isn’t binary. Long live the papernet!


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:

Friday, October 21st, 2016

Fermat’s Library | Why the Internet only just works annotated/explained version.

A ten-year old paper that looks at the history of the ARAPNET and internet to see how they dealt with necessary changes.

Changing a large network is very difficult. It is much easier to deploy a novel new protocol that fills a void than it is to replace an existing protocol that more or less works.