Journal tags: script

123

sparkline

Accessibility on The Session revisited

Earlier this year, I wrote about an accessibility issue I was having on The Session. Specifically, it was an issue with Ajax and pagination. But I managed to sort it out, and the lesson was very clear:

As is so often the case, the issue was with me trying to be too clever with ARIA, and the solution was to ease up on adding so many ARIA attributes.

Well, fast forward to the past few weeks, when I was contacted by one of the screen-reader users on The Session. There was, once again, a problem with the Ajax pagination, specifically with VoiceOver on iOS. The first page of results were read out just fine, but subsequent pages were not only never announced, the content was completely unavailable. The first page of results would’ve been included in the initial HTML, but the subsequent pages of results are injected with JavaScript (if JavaScript is available—otherwise it’s regular full-page refreshes all the way).

This pagination pattern shows up all over the site: lists of what’s new, search results, and more. I turned on VoiceOver and I was able to reproduce the problem straight away.

I started pulling apart my JavaScript looking for the problem. Was it something to do with how I was handling focus? I just couldn’t figure it out. And other parts of the site that used Ajax didn’t seem to be having the same problem. I was mystified.

Finally, I tracked down the problem, and it wasn’t in the JavaScript at all.

Wherever the pagination pattern appears, there are “previous” and “next” links, marked up with the appropriate rel="prev" and rel="next" attributes. Well, apparently past me thought it would be clever to add some ARIA attributes in there too. My thinking must’ve been something like this:

  • Those links control the area of the page with the search results.
  • That area of the page has an ID of “results”.
  • I should add aria-controls="results" to those links.

That was the problem …which is kind of weird, because VoiceOver isn’t supposed to have any support for aria-controls. Anyway, once I removed that attribute from the links, everything worked just fine.

Just as the solution last time was to remove the aria-atomic attribute on the updated area, the solution this time was to remove the aria-controls attribute on the links that trigger the update. Maybe this time I’ll learn my lesson: don’t mess with ARIA attributes you don’t understand.

Mental models

I’ve found that the older I get, the less I care about looking stupid. This is remarkably freeing. I no longer have any hesitancy about raising my hand in a meeting to ask “What’s that acronym you just mentioned?” This sometimes has the added benefit of clarifying something for others in the room who might have been to shy to ask.

I remember a few years back being really confused about npm. Fortunately, someone who was working at npm at the time came to Brighton for FFConf, so I asked them to explain it to me.

As I understood it, npm was intended to be used for managing packages of code for Node. Wasn’t it actually called “Node Package Manager” at one point, or did I imagine that?

Anyway, the mental model I had of npm was: npm is to Node as PEAR is to PHP. A central repository of open source code projects that you could easily add to your codebase …for your server-side code.

But then I saw people talking about using npm to manage client-side JavaScript. That really confused me. That’s why I was asking for clarification.

It turns out that my confusion was somewhat warranted. The npm project had indeed started life as a repo for server-side code but had since expanded to encompass client-side code too.

I understand how it happened, but it confirmed a worrying trend I had noticed. Developers were writing front-end code as though it were back-end code.

On the one hand, that makes total sense when you consider that the code is literally in the same programming language: JavaScript.

On the other hand, it makes no sense at all! If your code’s run-time is on the server, then the size of the codebase doesn’t matter that much. Whether it’s hundreds or thousands of lines of code, the execution happens more or less independentally of the network. But that’s not how front-end development works. Every byte matters. The more code you write that needs to be executed on the user’s device, the worse the experience is for that user. You need to limit how much you’re using the network. That means leaning on what the browser gives you by default (that’s your run-time environment) and keeping your code as lean as possible.

Dave echoes my concerns in his end-of-the-year piece called The Kind of Development I Like:

I now think about npm and wonder if it’s somewhat responsible for some of the pain points of modern web development today. Fact is, npm is a server-side technology that we’ve co-opted on the client and I think we’re feeling those repercussions in the browser.

Writing back-end and writing front-end code require very different approaches, in my opinion. But those differences have been erased in “modern” JavaScript.

The Unix Philosophy encourages us to write small micro libraries that do one thing and do it well. The Node.js Ecosystem did this in spades. This works great on the server where importing a small file has a very small cost. On the client, however, this has enormous costs.

In a funny way, this situation reminds me of something I saw happening over twenty years ago. Print designers were starting to do web design. They had a wealth of experience and knowledge around colour theory, typography, hierarchy and contrast. That was all very valuable to bring to the world of the web. But the web also has fundamental differences to print design. In print, you can use as many typefaces as you want, whereas on the web, to this day, you need to be judicious in the range of fonts you use. But in print, you might have to limit your colour palette for cost reasons (depending on the printing process), whereas on the web, colours are basically free. And then there’s the biggest difference of all: working within known dimensions of a fixed page in print compared to working within the unknowable dimensions of flexible viewports on the web.

Fast forward to today and we’ve got a lot of Computer Science graduates moving into front-end development. They’re bringing with them a treasure trove of experience in writing robust scalable code. But web browsers aren’t like web servers. If your back-end code is getting so big that it’s starting to run noticably slowly, you can throw more computing power at it by scaling up your server. That’s not an option on the front-end where you don’t really have one run-time environment—your end users have their own run-time environment with its own constraints around computing power and network connectivity.

That’s a very, very challenging world to get your head around. The safer option is to stick to the mental model you’re familiar with, whether you’re a print designer or a Computer Science graduate. But that does a disservice to end users who are relying on you to deliver a good experience on the World Wide Web.

Third party

The web turned 30 this year. When I was back at CERN to mark this anniversary, there was a lot of introspection and questioning the direction that the web has taken. Everyone I know that uses the web is in agreement that tracking and surveillance are out of control. It seems only right to question whether the web has lost its way.

But here’s the thing: the technologies that enable tracking and surveillance didn’t exist in the early years of the web—JavaScript and cookies.

Without cookies, the web was stateless. This was by design. Now, I totally understand why cookies—or something like cookies—were needed. Without some way of keeping track of state, there’s no good way for a website to “remember” what’s in your shopping cart, or whether you’ve authenticated yourself.

But why would cookies ever need to work across domains? Authentication, shopping carts and all that good stuff can happen on the same domain. Third-party cookies, on the other hand, seem custom made for tracking and frankly, not much else.

Browsers allow you to disable third-party cookies, though it’s not yet the default. If enough people do it—and complain about the sites that stop working when third-party cookies are disabled—then maybe it can become the default.

Firefox is taking steps in this direction, automatically disabling some third-party cookies—the ones that known trackers. Safari is also taking steps to prevent cross-site tracking. It’s not too late to change the tide of third-party cookies.

Then there’s third-party JavaScript.

In retrospect, it seems unbelievable that third-party JavaScript is even possible. I mean, putting arbitrary code—that can then inject even more arbitrary code—onto your website? That seems like a security nightmare!

I imagine if JavaScript were being specced today, it would almost certainly be restricted to the same origin by default. But I guess the precedent had been set with images and style sheets: they could be embedded regardless of whether their domain names matched yours. Still, this is executable code we’re talking about here: that’s quite a footgun that the web has given site owners. And boy, oh boy, has it been used by the worst people to do the most damage.

Again, as with cookies, if we were to imagine what the web would be like if JavaScript was restricted by a same-domain policy, there are certainly things that would be trickier to do.

  • Embedding video, audio, and maps would get a lot finickier.
  • Analytics would need to be self-hosted. I don’t think that would bother any site owners. An analytics platform like Google Analytics that tracks people across domains is doing it for its own benefit rather than that of site owners.
  • Advertising wouldn’t be creepy and annoying. Instead of what’s so euphemistically called “personalisation”, advertisers would have to rely on serving relevant ads based on the content of the site rather than an invasive psychological profile of the user. (I honestly think that advertisers would benefit from this kind of targetting.)

It’s harder to imagine putting the genie back in the bottle when it comes to third-party JavaScript than it is with third-party cookies. All the same, I wish that browsers made it easier to experiment with it. Just as I can choose to accept all cookies, reject all cookies, or only accept same-origin cookies, I wish I could accept all JavaScript, reject all JavaScript, or only accept same-origin JavaScript.

As it is, browsers are making it harder and harder to exercise any control over JavaScript at all. So we reach for third-party tools. We don’t call them JavaScript managers though. We call them ad blockers. But honestly, most of the ad-blocker users I know—myself included—are not bothered by the advertising; we’re bothered by the tracking. We should really call them surveillance blockers.

If third-party JavaScript weren’t the norm, not only would it make the web more secure, it would make it way more performant. Read the chapter on third parties in this year’s newly-released Web Almanac. The figures are staggering.

93% of pages include at least one third-party resource, 76% of pages issue a request to an analytics domain, the median page requests content from at least 9 unique third-party domains that represent 35% of their total network activity, and the most active 10% of pages issue a whopping 175 third-party requests or more.

I don’t think all the web’s performance ills are due to third-party scripts; developers are doing a bang-up job of making their sites big and bloated with their own self-hosted frameworks and code. But as long as third-party JavaScript is allowed onto a site, there’s a limit to how much good developers can do to improve the performance of their sites.

I go to performance-related conferences and you know who I’ve never seen at those events? The people who write the JavaScript for third-party tracking scripts. Those developers are wielding an outsized influence on the health of the web.

I’m very happy to see the work being done by Mozilla and Apple to normalise the idea of rejecting third-party cookies. I’d love to see the rejection of third-party JavaScript normalised in the same way. I know that it would make my life as a developer harder. But that’s of lesser importance. It would be better for the web.

Indy maps

Remember when I wrote about adding travel maps to my site at the recent Indie Web Camp Brighton? I must confess that the last line I wrote was an attempt to catch a fish from the river of the lazy web:

It’s a shame that I can’t use the lovely Stamen watercolour tiles for these static maps though.

In the spirit of Cunningham’s Law, I was hoping that somebody was going to respond with “It’s totally possible to use Stamen’s watercolour tiles for static maps, dumbass—look!” (to which my response would have been “thank you very much!”).

Alas, no such response was forthcoming. The hoped-for schooling never forthcame.

Still, I couldn’t quite let go of the idea of using those lovely watercolour maps somewhere on my site. But I had decided that dynamic maps would have been overkill for my archive pages:

Sure, it looked good, but displaying the map required requests for a script, a style sheet, and multiple map tiles.

Then I had a thought. What if I keep the static maps on my archive pages, but make them clickable? Then, on the other end of that link, I can have the dynamic version. In other words, what if I had a separate URL just for the dynamic maps?

These seemed like a good plan to me, so while I was travelling by Eurostar—the only way to travel—back from the lovely city of Antwerp where I had been speaking at Full Stack Europe, I started hacking away on making the dynamic maps even more dynamic. After all, now that they were going to have their own pages, I could go all out with any fancy features I wanted.

I kept coming back to my original goal:

I was looking for something more like the maps in Indiana Jones films—a line drawn from place to place to show the movement over time.

I found a plug-in for Leaflet.js that animates polylines—thanks, Iván! With a bit of wrangling, I was able to get it to animate between the lat/lon points of whichever archive section the map was in. Rather than have it play out automatically, I also added a control so that you can start and stop the animation. While I was at it, I decided to make that “play/pause” button do something else too. Ahem.

If you’d like to see the maps in action, click the “play” button on any of these maps:

You get the idea. It’s all very silly really. It’s right up there with the time I made my sparklines playable. But that’s kind of the point. It’s my website so I can do whatever I want with it, no matter how silly.

First of all, the research department for adactio.com (that’s me) came up with the idea. Then that had to be sold in to upper management (that’s me too). A team was spun up to handle design and development (consisting of me and me). Finally, the finished result went live thanks to the tireless efforts of the adactio.com ops group (that would be me). Any feedback should be directed at the marketing department (no idea who that is).

Indy web

It was Indie Web Camp Brighton on the weekend. After a day of thought-provoking discussions, I thoroughly enjoyed spending the second day tinkering on my website.

For a while now, I’ve wanted to add maps to my monthly archive pages (to accompany the calendar heatmaps I added at a previous Indie Web Camp). Whenever I post anything to my site—a blog post, a note, a link—it’s timestamped and geotagged. I thought it would be fun to expose that in a glanceable way. A map seems like the right medium for that, but I wanted to avoid the obvious route of dropping a load of pins on a map. Instead I was looking for something more like the maps in Indiana Jones films—a line drawn from place to place to show the movement over time.

I talked to Aaron about this and his advice was that a client-side JavaScript embedded map would be the easiest option. But that seemed like overkill to me. This map didn’t need to be pannable or zoomable; just glanceable. So I decided to see if how far I could get with a static map. I timeboxed two hours for it.

After two hours, I admitted defeat.

I was able to find the kind of static maps I wanted from Mapbox—I’m already using them for my check-ins. I could even add a polyline, which is exactly what I wanted. But instead of passing latitude and longitude co-ordinates for the points on the polyline, the docs explain that I needed to provide …cur ominous thunder and lightning… The Encoded Polyline Algorithm Format.

Go to that link. I’ll wait.

Did you read through the eleven steps of instructions? Did you also think it was a piss take?

  1. Take the initial signed value.
  2. Multiply it by 1e5.
  3. Convert that decimal value to binary.
  4. Left-shift the binary value one bit.
  5. If the original decimal value is negative, invert this encoding.
  6. Break the binary value out into 5-bit chunks.
  7. Place the 5-bit chunks into reverse order.
  8. OR each value with 0x20 if another bit chunk follows.
  9. Convert each value to decimal.
  10. Add 63 to each value.
  11. Convert each value to its ASCII equivalent.

This was way beyond my brain’s pay grade. But surely someone else had written the code I needed? I did some Duck Duck Going and found a piece of PHP code to do the encoding. It didn’t work. I Ducked Ducked and Went some more. I found a different piece of PHP code. That didn’t work either.

At this point, my allotted time was up. If I wanted to have something to demo by the end of the day, I needed to switch gears. So I did.

I used Leaflet.js to create the maps I wanted using client-side JavaScript. Here’s the JavaScript code I wrote.

It waits until the page has finished loading, then it searches for any instances of the h-geo microformat (a way of encoding latitude and longitude coordinates in HTML). If there are three or more, it generates a script element to pull in the Leaflet library, and a corresponding style element. Then it draws the map with the polyline on it. I ended up using Stamen’s beautiful watercolour map tiles.

Had some fun at Indie Web Camp Brighton on the weekend messing around with @Stamen’s lovely watercolour map tiles. (I was trying to create Indiana Jones style travel maps for my site …a different kind of Indy web.)

That’s what I demoed at the end of the day.

But I wasn’t happy with it.

Sure, it looked good, but displaying the map required requests for a script, a style sheet, and multiple map tiles. I made sure that it didn’t hold up the loading of the rest of the page, but it still felt wasteful.

So after Indie Web Camp, I went back to investigate static maps again. This time I did finally manage to find some PHP code for encoding lat/lon coordinates into a polyline that worked. Finally I was able to construct URLs for a static map image that displays a line connecting multiple points with a line.

I’ve put this maps on any of the archive pages that also have calendar heat maps. Some examples:

If you go back much further than that, the maps start to trail off. That’s because I wasn’t geotagging everything from the start.

I’m pretty happy with the final results. It’s certainly far more responsible from a performance point of view. Oh, and I’ve also got the maps inside a picture element so that I can swap out the tiles if you switch to dark mode.

It’s a shame that I can’t use the lovely Stamen watercolour tiles for these static maps though.

Going offline with microformats

For the offline page on my website, I’ve been using a mixture of the Cache API and the localStorage API. My service worker script uses the Cache API to store copies of pages for offline retrieval. But I used the localStorage API to store metadata about the page—title, description, and so on. Then, my offline page would rifle through the pages stored in a cache, and retreive the corresponding metadata from localStorage.

It all worked fine, but as soon as I read Remy’s post about the forehead-slappingly brilliant technique he’s using, I knew I’d be switching my code over. Instead of using localStorage—or any other browser API—to store and retrieve metadata, he uses the pages themselves! Using the Cache API, you can examine the contents of the pages you’ve stored, and get at whatever information you need:

I realised I didn’t need to store anything. HTML is the API.

Refactoring the code for my offline page felt good for a couple of reasons. First of all, I was able to remove a dependency—localStorage—and simplify the JavaScript. That always feels good. But the other reason for the warm fuzzies is that I was able to use data instead of metadata.

Many years ago, Cory Doctorow wrote a piece called Metacrap. In it, he enumerates the many issues with metadata—data about data. The source of many problems is when the metadata is stored separately from the data it describes. The data may get updated, without a corresponding update happening to the metadata. Metadata tends to rot because it’s invisible—out of sight and out of mind.

In fact, that’s always been at the heart of one of the core principles behind microformats. Instead of duplicating information—once as data and again as metadata—repurpose the visible data; mark it up so its meta-information is directly attached to the information itself.

So if you have a person’s contact details on a web page, rather than repeating that information somewhere else—in the head of the document, say—you could instead attach some kind of marker to indicate which bits of the visible information are contact details. In the case of microformats, that’s done with class attributes. You can mark up a page that already has your contact information with classes from the h-card microformat.

Here on my website, I’ve marked up my blog posts, articles, and links using the h-entry microformat. These classes explicitly mark up the content to say “this is the title”, “this is the content”, and so on. This makes it easier for other people to repurpose my content. If, for example, I reply to a post on someone else’s website, and ping them with a webmention, they can retrieve my post and know which bit is the title, which bit is the content, and so on.

When I read Remy’s post about using the Cache API to retrieve information directly from cached pages, I knew I wouldn’t have to do much work. Because all of my posts are already marked up with h-entry classes, I could use those hooks to create a nice offline page.

The markup for my offline page looks like this:

<h1>Offline</h1>
<p>Sorry. It looks like the network connection isn’t working right now.</p>
<div id="history">
</div>

I’ll populate that “history” div with information from a cache called “pages” that I’ve created using the Cache API in my service worker.

I’m going to use async/await to do this because there are lots of steps that rely on the completion of the step before. “Open this cache, then get the keys of that cache, then loop through the pages, then…” All of those thens would lead to some serious indentation without async/await.

All async functions have to have a name—no anonymous async functions allowed. I’m calling this one listPages, just like Remy is doing. I’m making the listPages function execute immediately:

(async function listPages() {
...
})();

Now for the code to go inside that immediately-invoked function.

I create an array called browsingHistory that I’ll populate with the data I’ll use for that “history” div.

const browsingHistory = [];

I’m going to be parsing web pages later on, so I’m going to need a DOM parser. I give it the imaginative name of …parser.

const parser = new DOMParser();

Time to open up my “pages” cache. This is the first await statement. When the cache is opened, this promise will resolve and I’ll have access to this cache using the variable …cache (again with the imaginative naming).

const cache = await caches.open('pages');

Now I get the keys of the cache—that’s a list of all the page requests in there. This is the second await. Once the keys have been retrieved, I’ll have a variable that’s got a list of all those pages. You’ll never guess what I’m calling the variable that stores the keys of the cache. That’s right …keys!

const keys = await cache.keys();

Time to get looping. I’m getting each request in the list of keys using a for/of loop:

for (const request of keys) {
...
}

Inside the loop, I pull the page out of the cache using the match() method of the Cache API. I’ll store what I get back in a variable called response. As with everything involving the Cache API, this is asynchronous so I need to use the await keyword here.

const response = await cache.match(request);

I’m not interested in the headers of the response. I’m specifically looking for the HTML itself. I can get at that using the text() method. Again, it’s asynchronous and I want this promise to resolve before doing anything else, so I use the await keyword. When the promise resolves, I’ll have a variable called html that contains the body of the response.

const html = await response.text();

Now I can use that DOM parser I created earlier. I’ve got a string of text in the html variable. I can generate a Document Object Model from that string using the parseFromString() method. This isn’t asynchronous so there’s no need for the await keyword.

const dom = parser.parseFromString(html, 'text/html');

Now I’ve got a DOM, which I have creatively stored in a variable called …dom.

I can poke at it using DOM methods like querySelector. I can test to see if this particular page has an h-entry on it by looking for an element with a class attribute containing the value “h-entry”:

if (dom.querySelector('.h-entry h1.p-name') {
...
}

In this particular case, I’m also checking to see if the h1 element of the page is the title of the h-entry. That’s so that index pages (like my home page) won’t get past this if statement.

Inside the if statement, I’m going to store the data I retrieve from the DOM. I’ll save the data into an object called …data!

const data = new Object;

Well, the first piece of data isn’t actually in the markup: it’s the URL of the page. I can get that from the request variable in my for loop.

data.url = request.url;

I’m going to store the timestamp for this h-entry. I can get that from the datetime attribute of the time element marked up with a class of dt-published.

data.timestamp = new Date(dom.querySelector('.h-entry .dt-published').getAttribute('datetime'));

While I’m at it, I’m going to grab the human-readable date from the innerText property of that same time.dt-published element.

data.published = dom.querySelector('.h-entry .dt-published').innerText;

The title of the h-entry is in the innerText of the element with a class of p-name.

data.title = dom.querySelector('.h-entry .p-name').innerText;

At this point, I am actually going to use some metacrap instead of the visible h-entry content. I don’t output a description of the post anywhere in the body of the page, but I do put it in the head in a meta element. I’ll grab that now.

data.description = dom.querySelector('meta[name="description"]').getAttribute('content');

Alright. I’ve got a URL, a timestamp, a publication date, a title, and a description, all retrieved from the HTML. I’ll stick all of that data into my browsingHistory array.

browsingHistory.push(data);

My if statement and my for/in loop are finished at this point. Here’s how the whole loop looks:

for (const request of keys) {
  const response = await cache.match(request);
  const html = await response.text();
  const dom = parser.parseFromString(html, 'text/html');
  if (dom.querySelector('.h-entry h1.p-name')) {
    const data = new Object;
    data.url = request.url;
    data.timestamp = new Date(dom.querySelector('.h-entry .dt-published').getAttribute('datetime'));
    data.published = dom.querySelector('.h-entry .dt-published').innerText;
    data.title = dom.querySelector('.h-entry .p-name').innerText;
    data.description = dom.querySelector('meta[name="description"]').getAttribute('content');
    browsingHistory.push(data);
  }
}

That’s the data collection part of the code. Now I’m going to take all that yummy information an output it onto the page.

First of all, I want to make sure that the browsingHistory array isn’t empty. There’s no point going any further if it is.

if (browsingHistory.length) {
...
}

Within this if statement, I can do what I want with the data I’ve put into the browsingHistory array.

I’m going to arrange the data by date published. I’m not sure if this is the right thing to do. Maybe it makes more sense to show the pages in the order in which you last visited them. I may end up removing this at some point, but for now, here’s how I sort the browsingHistory array according to the timestamp property of each item within it:

browsingHistory.sort( (a,b) => {
  return b.timestamp - a.timestamp;
});

Now I’m going to concatenate some strings. This is the string of HTML text that will eventually be put into the “history” div. I’m storing the markup in a string called …markup (my imagination knows no bounds).

let markup = '<p>But you still have something to read:</p>';

I’m going to add a chunk of markup for each item of data.

browsingHistory.forEach( data => {
  markup += `
<h2><a href="${ data.url }">${ data.title }</a></h2>
<p>${ data.description }</p>
<p class="meta">${ data.published }</p>
`;
});

With my markup assembled, I can now insert it into the “history” part of my offline page. I’m using the handy insertAdjacentHTML() method to do this.

document.getElementById('history').insertAdjacentHTML('beforeend', markup);

Here’s what my finished JavaScript looks like:

<script>
(async function listPages() {
  const browsingHistory = [];
  const parser = new DOMParser();
  const cache = await caches.open('pages');
  const keys = await cache.keys();
  for (const request of keys) {
    const response = await cache.match(request);
    const html = await response.text();
    const dom = parser.parseFromString(html, 'text/html');
    if (dom.querySelector('.h-entry h1.p-name')) {
      const data = new Object;
      data.url = request.url;
      data.timestamp = new Date(dom.querySelector('.h-entry .dt-published').getAttribute('datetime'));
      data.published = dom.querySelector('.h-entry .dt-published').innerText;
      data.title = dom.querySelector('.h-entry .p-name').innerText;
      data.description = dom.querySelector('meta[name="description"]').getAttribute('content');
      browsingHistory.push(data);
    }
  }
  if (browsingHistory.length) {
    browsingHistory.sort( (a,b) => {
      return b.timestamp - a.timestamp;
    });
    let markup = '<p>But you still have something to read:</p>';
    browsingHistory.forEach( data => {
      markup += `
<h2><a href="${ data.url }">${ data.title }</a></h2>
<p>${ data.description }</p>
<p class="meta">${ data.published }</p>
`;
    });
    document.getElementById('history').insertAdjacentHTML('beforeend', markup);
  }
})();
</script>

I’m pretty happy with that. It’s not too long but it’s still quite readable (I hope). It shows that the Cache API and the h-entry microformat are a match made in heaven.

If you’ve got an offline strategy for your website, and you’re using h-entry to mark up your content, feel free to use that code.

If you don’t have an offline strategy for your website, there’s a book for that.

Request mapping

The Request Map Generator is a terrific tool. It’s made by Simon Hearne and uses the WebPageTest API.

You pop in a URL, it fetches the page and maps out all the subsequent requests in a nifty interactive diagram of circles, showing how many requests third-party scripts are themselves generating. I’ve found it to be a very effective way of showing the impact of third-party scripts to people who aren’t interested in looking at waterfall diagrams.

I was wondering… Wouldn’t it be great if this were built into browsers?

We already have a “Network” tab in our developer tools. The purpose of this tab is to show requests coming in. The browser already has all the information it needs to make a diagram of requests in the same that the request map generator does.

In Firefox, there’s a little clock icon in the bottom left corner of the “Network” tab. Clicking that shows a pie-chart view of requests. That’s useful, but I’d love it if there were the option to also see the connected circles that the request map generator shows.

Just a thought.

Navigation preloads in service workers

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

Here’s the problem it solves…

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

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

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

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

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

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

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

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

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

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

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

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

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

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

fetchEvent.preloadResponse

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

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

You could structure your code like this:

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

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

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

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

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

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

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

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

Use whichever syntax you find more readable.

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

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

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

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

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

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

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

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

Principle

I like good design principles. I collect design principles—of varying quality—at principles.adactio.com. Ben Brignell also has a (much larger) collection at principles.design.

You can spot the less useful design principles after a while. They tend to be wishy-washy; more like empty aspirational exhortations than genuinely useful guidelines for alignment. I’ve written about what makes for good design principles before. Matthew Ström also asked—and answered—What makes a good design principle?

  • Good design principles are memorable.
  • Good design principles help you say no.
  • Good design principles aren’t truisms.
  • Good design principles are applicable.

I like those. They’re like design principles for design principles.

One set of design principles that I’ve included in my collection is from gov.uk: government design principles . I think they’re very well thought-through (although I’m always suspicious when I see a nice even number like 10 for the amount of items in the list). There’s a great line in design principle number two—Do less:

Government should only do what only government can do.

This wasn’t a theoretical issue. The multiple departmental websites that preceded gov.uk were notorious for having too much irrelevant content—content that was readily available elsewhere. It was downright wasteful to duplicate that content on a government site. It wasn’t appropriate.

Appropriateness is something I keep coming back to when it comes to evaluating web technologies. I don’t think there are good tools and bad tools; just tools that are appropriate or inapropriate for the task at hand. Whether it’s task runners or JavaScript frameworks, appropriateness feels like it should be the deciding factor.

I think that the design principle from GDS could be abstracted into a general technology principle:

Any particular technology should only do what only that particular technology can do.

Take JavaScript, for example. It feels “wrong” when a powerful client-side JavaScript framework is applied to something that could be accomplished using HTML. Making a blog that’s a single page app is over-engineering. It violates this principle:

JavaScript should only do what only JavaScript can do.

Need to manage state or immediately update the interface in response to user action? Only JavaScript can do that. But if you need to present the user with some static content, JavaScript can do that …but it’s not the only technology that can do that. HTML would be more appropriate.

I realise that this is basically a reformulation of one of my favourite design principles, the rule of least power:

Choose the least powerful language suitable for a given purpose.

Or, as Derek put it:

In the web front-end stack — HTML, CSS, JS, and ARIA — if you can solve a problem with a simpler solution lower in the stack, you should. It’s less fragile, more foolproof, and just works.

ARIA should only do what only ARIA can do.

JavaScript should only do what only JavaScript can do.

CSS should only do what only CSS can do.

HTML should only do what only HTML can do.

The trimCache function in Going Offline …again

It seems that some code that I wrote in Going Offline is haunted. It’s the trimCache function.

First, there was the issue of a typo. Or maybe it’s more of a brainfart than a typo, but either way, there’s a mistake in the syntax that was published in the book.

Now it turns out that there’s also a problem with my logic.

To recap, this is a function that takes two arguments: the name of a cache, and the maximum number of items that cache should hold.

function trimCache(cacheName, maxItems) {

First, we open up the cache:

caches.open(cacheName)
.then( cache => {

Then, we get the items (keys) in that cache:

cache.keys()
.then(keys => {

Now we compare the number of items (keys.length) to the maximum number of items allowed:

if (keys.length > maxItems) {

If there are too many items, delete the first item in the cache—that should be the oldest item:

cache.delete(keys[0])

And then run the function again:

.then(
    trimCache(cacheName, maxItems)
);

A-ha! See the problem?

Neither did I.

It turns out that, even though I’m using then, the function will be invoked immediately, instead of waiting until the first item has been deleted.

Trys helped me understand what was going on by making a useful analogy. You know when you use setTimeout, you can’t put a function—complete with parentheses—as the first argument?

window.setTimeout(doSomething(someValue), 1000);

In that example, doSomething(someValue) will be invoked immediately—not after 1000 milliseconds. Instead, you need to create an anonymous function like this:

window.setTimeout( function() {
    doSomething(someValue)
}, 1000);

Well, it’s the same in my trimCache function. Instead of this:

cache.delete(keys[0])
.then(
    trimCache(cacheName, maxItems)
);

I need to do this:

cache.delete(keys[0])
.then( function() {
    trimCache(cacheName, maxItems)
});

Or, if you prefer the more modern arrow function syntax:

cache.delete(keys[0])
.then( () => {
    trimCache(cacheName, maxItems)
});

Either way, I have to wrap the recursive function call in an anonymous function.

Here’s a gist with the updated trimCache function.

What’s annoying is that this mistake wasn’t throwing an error. Instead, it was causing a performance problem. I’m using this pattern right here on my own site, and whenever my cache of pages or images gets too big, the trimCaches function would get called …and then wouldn’t stop running.

I’m very glad that—witht the help of Trys at last week’s Homebrew Website Club Brighton—I was finally able to get to the bottom of this. If you’re using the trimCache function in your service worker, please update the code accordingly.

Management regrets the error.

Am I cached or not?

When I was writing about the lie-fi strategy I’ve added to adactio.com, I finished with this thought:

What I’d really like is some way to know—on the client side—whether or not the currently-loaded page came from a cache or from a network. Then I could add some kind of interface element that says, “Hey, this page might be stale—click here if you want to check for a fresher version.”

Trys heard my plea, and came up with a very clever technique to alter the HTML of a page when it’s put into a cache.

It’s a function that reads the response body stream in, returning a new stream. Whilst reading the stream, it searches for the character codes that make up: <html. If it finds them, it tacks on a data-cached attribute.

Nice!

But then I was discussing this issue with Tantek and Aaron late one night after Indie Web Camp Düsseldorf. I realised that I might have another potential solution that doesn’t involve the service worker at all.

Caveat: this will only work for pages that have some kind of server-side generation. This won’t work for static sites.

In my case, pages are generated by PHP. I’m not doing a database lookup every time you request a page—I’ve got a server-side cache of posts, for example—but there is a little bit of assembly done for every request: get the header from here; get the main content from over there; get the footer; put them all together into a single page and serve that up.

This means I can add a timestamp to the page (using PHP). I can mark the moment that it was served up. Then I can use JavaScript on the client side to compare that timestamp to the current time.

I’ve published the code as a gist.

In a script element on each page, I have this bit of coducken:

var serverTimestamp = <?php echo time(); ?>;

Now the JavaScript variable serverTimestamp holds the timestamp that the page was generated. When the page is put in the cache, this won’t change. This number should be the number of seconds since January 1st, 1970 in the UTC timezone (that’s what my server’s timezone is set to).

Starting with JavaScript’s Date object, I use a caravan of methods like toUTCString() and getTime() to end up with a variable called clientTimestamp. This will give the current number of seconds since January 1st, 1970, regardless of whether the page is coming from the server or from the cache.

var localDate = new Date();
var localUTCString = localDate.toUTCString();
var UTCDate = new Date(localUTCString);
var clientTimestamp = UTCDate.getTime() / 1000;

Then I compare the two and see if there’s a discrepency greater than five minutes:

if (clientTimestamp - serverTimestamp > (60 * 5))

If there is, then I inject some markup into the page, telling the reader that this page might be stale:

document.querySelector('main').insertAdjacentHTML('afterbegin',`
  <p class="feedback">
    <button onclick="this.parentNode.remove()">dismiss</button>
    This page might be out of date. You can try <a href="javascript:window.location=window.location.href">refreshing</a>.
  </p>
`);

The reader has the option to refresh the page or dismiss the message.

This page might be out of date. You can try refreshing.

It’s not foolproof by any means. If the visitor’s computer has their clock set weirdly, then the comparison might return a false positive every time. Still, I thought that using UTC might be a safer bet.

All in all, I think this is a pretty good method for detecting if a page is being served from a cache. Remember, the goal here is not to determine if the user is offline—for that, there’s navigator.onLine.

The upshot is this: if you visit my site with a crappy internet connection (lie-fi), then after three seconds you may be served with a cached version of the page you’re requesting (if you visited that page previously). If that happens, you’ll now also be presented with a little message telling you that the page isn’t fresh. Then it’s up to you whether you want to have another go.

I like the way that this puts control back into the hands of the user.

Timing out

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

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

But you can make one.

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

Service worker strategies

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

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

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

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

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

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

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

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

My logic is:

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

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

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

Now my logic has been expanded to this:

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

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

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

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

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

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

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

Good.

Cache as you go

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

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

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

const copy = responseFromFetch.clone();

That’s what gets put in the pages cache:

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

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

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

Here’s my updated fetch-handling code:

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

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

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

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

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

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

Now my offline logic is expanded:

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

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

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

Timing out

I want to throw this addition into my logic:

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

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

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

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

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

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

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

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

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

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

clearTimeout(timer);

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

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

That’s the JavaScript translation of this logic:

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

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

Pros and cons

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

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

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

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

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

Frameworking

There are many reasons to use a JavaScript framework like Vue, Angular, or React. Last year, Nicole asked for some of those reasons. Her question received many, many answers from people pointing out the benefits of using a framework. Interesingly, though, not a single one of those benefits was for end users.

(Mind you, if the framework is being used on the server to pre-render pages, then it’s a moot point—in that situation, it makes no difference to the end user whether you use a framework or not.)

Hidde recently tried using a client-side JavaScript framework for the first time and documented the process:

In the last few months I built my very first framework-based front-end, in Vue.js. I complemented it with a router, a store and a GraphQL library, in order to have, respectively, multiple (virtual) pages, globally shared data and a smart way to load new data in my templates.

It’s a very even-handed write-up. I highly recommend reading it. He describes the pros and cons of using a framework and using vanilla JavaScript:

I am glad I tried a framework and found its features were extremely helpful in creating a consistent interface for my users. My hope is though, that I won’t forget about vanilla. It’s perfectly valid to build a website with no or few dependencies.

Speaking of vanilla JavaScript… the blogging machine that is Chris Ferdinandi also wrote a comparison post recently, asking Why do people choose frameworks over vanilla JS? Again, it’s very even-handed and well worth a read. He readily concedes that if you’re working at scale, a framework is almost certainly a good idea:

If you’re building a large scale application (literally Facebook, Twitter, QuickBooks scale), the performance wins of a framework make the overhead worth it.

Alas, I’ve seen many, many framework-driven sites that are most definitely not that operating at that scale. Trys speaks the honest truth here:

We kid ourselves into thinking we’re building groundbreakingly complex systems that require bleeding-edge tools, but in reality, much of what we build is a way to render two things: a list, and a single item. Here are some users, here is a user. Here are your contacts, here are your messages with that contact. There ain’t much more to it than that.

Just the other day, I saw a new site launch that was mostly a marketing site—the home page weighed over five megabytes, two megabytes of which were taken up with JavaScript, and the whole thing required JavaScript to render text to the screen (I’m not going to link to it because I don’t want to engage in any kind of public shaming and finger-wagging).

I worry that all the perfectly valid (developer experience) reasons for using a framwork are outweighing the more important (user experience) reasons for avoiding shipping your dependencies to end users. Like Alex says:

If your conception of “DX” doesn’t include it, or isn’t subservient to the user experience, rethink.

And yes, I am going to take this opportunity to link once again to Alex’s article The “Developer Experience” Bait-and-Switch. Please read it if you haven’t already. Please re-read it if you have.

Anyway, my main reason for writing this is to point you to thoughtful posts like Hidde’s and Chris’s. I think it’s great to see people thoughtfully weighing up the pros and cons of choosing any particular technology—I’m a bit obsessed with the topic of evaluating technology.

If you’re weighing up the pros and cons of using, say, a particular JavaScript library or framework, that’s wonderful. My worry is that there are people working in front-end development who aren’t putting that level of thought into their technology choices, but are instead using a particular framework because it’s what they’re used to.

To quote Grace Hopper:

The most dangerous phrase in the language is, ‘We’ve always done it this way.’

Split

When I talk about evaluating technology for front-end development, I like to draw a distinction between two categories of technology.

On the one hand, you’ve got the raw materials of the web: HTML, CSS, and JavaScript. This is what users will ultimately interact with.

On the other hand, you’ve got all the tools and technologies that help you produce the HTML, CSS, and JavaScript: pre-processors, post-processors, transpilers, bundlers, and other build tools.

Personally, I’m much more interested and excited by the materials than I am by the tools. But I think it’s right and proper that other developers are excited by the tools. A good balance of both is probably the healthiest mix.

I’m never sure what to call these two categories. Maybe the materials are the “external” technologies, because they’re what users will interact with. Whereas all the other technologies—that mosty live on a developer’s machine—are the “internal” technologies.

Another nice phrase is something I heard during Chris’s talk at An Event Apart in Seattle, when he quoted Brad, who talked about the front of the front end and the back of the front end.

I’m definitely more of a front-of-the-front-end kind of developer. I have opinions on the quality of the materials that get served up to users; the output should be accessible and performant. But I don’t particularly care about the tools that produced those materials on the back of the front end. Use whatever works for you (or whatever works for your team).

As a user-centred developer, my priority is doing what’s best for end users. That’s not to say I don’t value developer convenience. I do. But I prioritise user needs over developer needs. And in any case, those two needs don’t even come into conflict most of the time. Like I said, from a user’s point of view, it’s irrelevant what text editor or version control system you use.

Now, you could make the argument that anything that is good for developer convenience is automatically good for user experience because faster, more efficient development should result in better output. While that’s true in theory, I highly recommend Alex’s post, The “Developer Experience” Bait-and-Switch.

Where it gets interesting is when a technology that’s designed for developer convenience is made out of the very materials being delivered to users. For example, a CSS framework like Bootstrap is made of CSS. That’s different to a tool like Sass which outputs CSS. Whether or not a developer chooses to use Sass is irrelevant to the user—the final output will be CSS either way. But if a developer chooses to use a CSS framework, that decision has a direct impact on the user experience. The user must download the framework in order for the developer to get the benefit.

So whereas Sass sits at the back of the front end—where I don’t care what you use—Bootstrap sits at the front of the front end. For tools like that, I don’t think saying “use whatever works for you” is good enough. It’s got to be weighed against the cost to the user.

Historically, it’s been a similar story with JavaScript libraries. They’re written in JavaScript, and so they’re going to be executed in the browser. If a developer wanted to use jQuery to make their life easier, the user paid the price in downloading the jQuery library.

But I’ve noticed a welcome change with some of the bigger JavaScript frameworks. Whereas the initial messaging around frameworks like React touted the benefits of state management and the virtual DOM, I feel like that’s not as prevalent now. You’re much more likely to hear people—quite rightly—talk about the benefits of modularity and componentisation. If you combine that with the rise of Node—which means that JavaScript is no longer confined to the browser—then these frameworks can move from the front of the front end to the back of the front end.

We’ve certainly seen that at Clearleft. We’ve worked on multiple React projects, but in every case, the output was server-rendered. Developers get the benefit of working with a tool that helps them. Users don’t pay the price.

For me, this question of whether a framework will be used on the client side or the server side is crucial.

Let me tell you about a Clearleft project that sticks in my mind. We were working with a big international client on a product that was going to be rolled out to students and teachers in developing countries. This was right up my alley! We did plenty of research into network conditions and typical device usage. That then informed a tight performance budget. Every design decision—from web fonts to images—was informed by that performance budget. We were producing lean, mean markup, CSS, and JavaScript. But we weren’t the ones implementing the final site. That was being done by the client’s offshore software team, and they insisted on using React. “That’s okay”, I thought. “React can be used server-side so we can still output just what’s needed, right?” Alas, no. These developers did everything client side. When the final site launched, the log-in screen alone required megabytes of JavaScript just to render a form. It was, in my opinion, entirely unfit for purpose. It still pains me when I think about it.

That was a few years ago. I think that these days it has become a lot easier to make the decision to use a framework on the back of the front end. Like I said, that’s certainly been the case on recent Clearleft projects that involved React or Vue.

It surprises me, then, when I see the question of server rendering or client rendering treated almost like an implementation detail. It might be an implementation detail from a developer’s perspective, but it’s a key decision for the user experience. The performance cost of putting your entire tech stack into the browser can be enormous.

Alex Sanders from the development team at The Guardian published a post recently called Revisiting the rendering tier . In it, he describes how they’re moving to React. Now, if this were a move to client-rendered React, that would make a big impact on the user experience. The thing is, I couldn’t tell from the article whether React was going to be used in the browser or on the server. The article talks about “rendering”—which is something that browsers do—and “the DOM”—which is something that only exists in browsers.

So I asked. It turns out that this plan is very much about generating HTML and CSS on the server before sending it to the browser. Excellent!

With that question answered, I’m cool with whatever they choose to use. In this case, they’re choosing to use CSS-in-JS (although, to be pedantic, there’s no C anymore so technically it’s SS-in-JS). As long as the “JS” part is JavaScript on a server, then it makes no difference to the end user, and therefore no difference to me. Not my circus, not my monkeys. For users, the end result is the same whether styling is applied via a selector in an external stylesheet or, for example, via an inline style declaration (and in some situations, a server-rendered CSS-in-JS solution might be better for performance). And so, as a user-centred developer, this is something that I don’t need to care about.

Except…

I have misgivings. But just to be clear, these misgivings have nothing to do with users. My misgivings are entirely to do with another group of people: the people who make websites.

There’s a second-order effect. By making React—or even JavaScript in general—a requirement for styling something on a web page, the barrier to entry is raised.

At least, I think that the barrier to entry is raised. I completely acknowledge that this is a subjective judgement. In fact, the reason why a team might decide to make JavaScript a requirement for participation might well be because they believe it makes it easier for people to participate. Let me explain…

It wasn’t that long ago that devs coming from a Computer Science background were deriding CSS for its simplicity, complaining that “it’s broken” and turning their noses up at it. That rhetoric, thankfully, is waning. Nowadays they’re far more likely to acknowledge that CSS might be simple, but it isn’t easy. Concepts like the cascade and specificity are real head-scratchers, and any prior knowledge from imperative programming languages won’t help you in this declarative world—all your hard-won experience and know-how isn’t fungible. Instead, it seems as though all this cascading and specificity is butchering the modularity of your nicely isolated components.

It’s no surprise that programmers with this kind of background would treat CSS as damage and find ways to route around it. The many flavours of CSS-in-JS are testament to this. From a programmer’s point of view, this solution has made things easier. Best of all, as long as it’s being done on the server, there’s no penalty for end users. But now the price is paid in the diversity of your team. In order to participate, a Computer Science programming mindset is now pretty much a requirement. For someone coming from a more declarative background—with really good HTML and CSS skills—everything suddenly seems needlessly complex. And as Tantek observed:

Complexity reinforces privilege.

The result is a form of gatekeeping. I don’t think it’s intentional. I don’t think it’s malicious. It’s being done with the best of intentions, in pursuit of efficiency and productivity. But these code decisions are reflected in hiring practices that exclude people with different but equally valuable skills and perspectives.

Rachel describes HTML, CSS and our vanishing industry entry points:

If we make it so that you have to understand programming to even start, then we take something open and enabling, and place it back in the hands of those who are already privileged.

I think there’s a comparison here with toxic masculinity. Toxic masculinity is obviously terrible for women, but it’s also really shitty for men in the way it stigmatises any male behaviour that doesn’t fit its worldview. Likewise, if the only people your team is interested in hiring are traditional programmers, then those programmers are going to resent having to spend their time dealing with semantic markup, accessibility, styling, and other disciplines that they never trained in. Heydon correctly identifies this as reluctant gatekeeping:

By assuming the role of the Full Stack Developer (which is, in practice, a computer scientist who also writes HTML and CSS), one takes responsibility for all the code, in spite of its radical variance in syntax and purpose, and becomes the gatekeeper of at least some kinds of code one simply doesn’t care about writing well.

This hurts everyone. It’s bad for your team. It’s even worse for the wider development community.

Last year, I was asked “Is there a fear or professional challenge that keeps you up at night?” I responded:

My greatest fear for the web is that it becomes the domain of an elite priesthood of developers. I firmly believe that, as Tim Berners-Lee put it, “this is for everyone.” And I don’t just mean it’s for everyone to use—I believe it’s for everyone to make as well. That’s why I get very worried by anything that raises the barrier to entry to web design and web development.

I’ve described a number of dichotomies here:

  • Materials vs. tools,
  • Front of the front end vs. back of the front end,
  • User experience vs. developer experience,
  • Client-side rendering vs. server-side rendering,
  • Declarative languages vs. imperative languages.

But the split that worries the most is this:

  • The people who make the web vs. the people who are excluded from making the web.

Updating email addresses with Mailchimp’s API

I’ve been using Mailchimp for years now to send out a weekly newsletter from The Session. But I never visit the Mailchimp website. Instead, I use the API to create a campaign each week, and then send it out. I also use the API whenever a member of The Session updates their email preferences (or changes their details).

I got an email from Mailchimp that their old API was being deprecated and I’d need to update to their more recent one. The code I was using had been happily running for about seven years, but now I’d have to change it.

Luckily, Drew has written a really handy Mailchimp API wrapper for PHP, the language that The Session’s codebase is in. Thanks, Drew! I downloaded that wrapper and updated my code accordingly.

Everything went pretty smoothly. I was able to create campaigns, send campaigns, add new subscribers, and delete subscribers. But I ran into an issue when I wanted to update someone’s email address (on The Session, you can edit your details at any time, including your email address).

Here’s the set up:

use \DrewM\MailChimp\MailChimp;
$MailChimp = new MailChimp('abc123abc123abc123abc123abc123-us1');
$list_id = 'b1234346';
$subscriber_hash = $MailChimp -> subscriberHash('currentemail@example.com');
$endpoint = 'lists/'.$listID.'/members/'.$subscriber_hash;

Now to update details, according to the API, I can use the patch method on that endpoint:

$MailChimp -> patch($endpoint, [
    'email_address' => 'newemail@example.com'
]);

But that doesn’t work. Mailchimp effectively treats email addresses as unique IDs for subscribers. So the only way to change someone’s email address appears to be to delete them, and then subscribe them fresh with the new email address:

$MailChimp -> delete($endpoint);
$newendpoint = 'lists/'.$listID.'/members';
$MailChimp -> post($newendpoint, [
    'email_address' => 'newemail@example.com',
    'status' => 'subscribed'
]);

That’s somewhat annoying, as the previous version of the API allowed email addresses to be updated, but this workaround isn’t too arduous.

Anyway, I figured it share this just in case it was useful for anyone else migrating to the newer API.

Update: Belay that. Turns out that you can update email addresses, but you have to be sure to include the status value:

$MailChimp -> patch($endpoint, [
    'email_address' => 'newemail@example.com',
    'status' => 'subscribed'
]);

Okay, that’s a lot more straightforward. Ignore everything I said.

Going Offline—the talk of the book

I gave a new talk at An Event Apart in Seattle yesterday morning. The talk was called Going Offline, which the eagle-eyed amongst you will recognise as the title of my most recent book, all about service workers.

I was quite nervous about this talk. It’s very different from my usual fare. Usually I have some big sweeping arc of history, and lots of pretentious ideas joined together into some kind of narrative arc. But this talk needed to be more straightforward and practical. I wasn’t sure how well I would manage that brief.

I knew from pretty early on that I was going to show—and explain—some code examples. Those were the parts I sweated over the most. I knew I’d be presenting to a mixed audience of designers, developers, and other web professionals. I couldn’t assume too much existing knowledge. At the same time, I didn’t want to teach anyone to such eggs.

In the end, there was an overarching meta-theme to talk, which was this: logic is more important than code. In other words, figuring out what you’re trying to accomplish (and describing it clearly) is more important than typing curly braces and semi-colons. Programming is an act of translation. Before you can translate something, you need to be able to articulate it clearly in your own language first. By emphasising that point, I hoped to make the code less overwhelming to people unfamilar with it.

I had tested the talk with some of my Clearleft colleagues, and they gave me great feedback. But I never know until I’ve actually given a talk in front of a real conference audience whether the talk is any good or not. Now that I’ve given the talk, and received more feedback, I think I can confidentally say that it’s pretty damn good.

My goal was to explain some fairly gnarly concepts—let’s face it: service workers are downright weird, and not the easiest thing to get your head around—and to leave the audience with two feelings:

  1. This is exciting, and
  2. This is something I can do today.

I deliberately left time for questions, bribing people with free copies of my book. I got some great questions, and I may incorporate some of them into future versions of this talk (conference organisers, if this sounds like the kind of talk you’d like at your event, please get in touch). Some of the points brought up in the questions were:

  • Is there some kind of wizard for creating a typical service worker script for any site? I didn’t have a direct answer to this, but I have attempted to make a minimal viable service worker that could be used for just about any site. Mostly I encouraged the questioner to roll their sleeves up and try writing a bespoke script. I also mentioned the Workbox library, but I gave my opinion that if you’re going to spend the time to learn the library, you may as well spend the time to learn the underlying language.
  • What are some state-of-the-art progressive web apps for offline user experiences? Ooh, this one kind of stumped me. I mean, the obvious poster children for progressive webs apps are things like Twitter, Instagram, and Pinterest. They’re all great but the offline experience is somewhat limited. To be honest, I think there’s more potential for great offline experiences by publishers. I especially love the pattern on personal sites like Una’s and Sara’s where people can choose to save articles offline to read later—like a bespoke Instapaper or Pocket. I’d love so see that pattern adopted by some big publications. I particularly like that gives so much more control directly to the end user. Instead of trying to guess what kind of offline experience they want, we give them the tools to craft their own.
  • Do caches get cleaned up automatically? Great question! And the answer is mostly no—although browsers do have their own heuristics about how much space you get to play with. There’s a whole chapter in my book about being a good citizen and cleaning up your caches, but I didn’t include that in the talk because it isn’t exactly exciting: “Hey everyone! Now we’re going to do some housekeeping—yay!”
  • Isn’t there potential for abuse here? This is related to the previous question, and it’s another great question to ask of any technology. In short, yes. Bad actors could use service workers to fill up caches uneccesarily. I’ve written about back door service workers too, although the real problem there is with iframes rather than service workers—iframes and cookies are technologies that are already being abused by bad actors, and we’re going to see more and more interventions by ethical browser makers (like Mozilla) to clamp down on those technologies …just as browsers had to clamp down on the abuse of pop-up windows in the early days of JavaScript. The cache API could become a tragedy of the commons. I liken the situation to regulation: we should self-regulate, but if we prove ourselves incapable of that, then outside regulation (by browsers) will be imposed upon us.
  • What kind of things are in the future for service workers? Excellent question! If you think about it, a service worker is kind of a conduit that gives you access to different APIs: the Cache API and the Fetch API being the main ones now. A service worker is like an airport and the APIs are like the airlines. There are other APIs that you can access through service workers. Notifications are available now on desktop and on Android, and they’ll be coming to iOS soon. Background Sync is another powerful API accessed through service workers that will get more and more browser support over time. The great thing is that you can start using these APIs today even if they aren’t universally supported. Then, over time, more and more of your users will benefit from those enhancements.

If you attended the talk and want to learn more about about service workers, there’s my book (obvs), but I’ve also written lots of blog posts about service workers and I’ve linked to lots of resources too.

Finally, here’s a list of links to all the books, sites, and articles I referenced in my talk…

Books

Sites

Progressive Web Apps

Move Fast and Don’t Break Things by Scott Jehl

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Also include this:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

How to Think Like a Front-End Developer by Chris Coyier

Alright! It’s day two of An Event Apart in Seattle. The first speaker of the day is Chris Coyier. His talk is called How to Think Like a Front-End Developer. From the website:

The job title “front-end developer” is very real: job boards around the world confirm that. But what is that job, exactly? What do you need to know to do it? You might think those answers are pretty cut and dried, but they’re anything but; front-end development is going through something of an identity crisis. In this engaging talk, Chris will explore this identity through the lens of someone who has self-identified as a front-end developer for a few decades, but more interestingly, through many conversations he’s had with other successful front-end developers. You’ll see just how differently this job can be done and how differently people and companies can think of this role—not just for the sake of doing so, but because you’ll learn to be better at your own jobs by understanding how other people are good at theirs.

I’m going to see if I can keep up with Chris’s frenetic pace…

Chris has his own thoughts about what front-end dev is but he wants to share other ideas too. First of all, some grammar:

I work as a front-end developer.

I work on the front end.

Those are correct. These are not:

I work as a front end developer.

I work on the front-end.

And this is just not a word:

Frontend.

Lots of people are hiring front-end developers. So it’s definitely a job and a common job title. But what does it mean. Chris and Dave talked to eight different people on their Shop Talk Show podcast. Some highlights:

Eric feels that the term “front-end developer” is newer than the CSS Zen Garden. Everyone was a webmaster, or as we’d say now, a full-stack developer. But if someone back then used the term “front-end developer”, he’d know what it meant.

Mina says it deals with things you can see. If it’s a user-facing interface, that’s front-end development.

Trent says that he thinks of himself as a web designer and web builder. He doesn’t feel he has the deep expertise of a developer, and yet he spends all of his time in the browser.

So our job is in the browser. You deal with the browser (moreso than other roles). And by the way, there are a lot of browsers out there.

Maybe the user is what differentiates front-end work. Monica says that a back-end developer is allowed not to care about the user if their job is putting a database together. It’s totally fine not to call yourself a front-end developer, but if you do, you need to care about the user.

There are tons of different devices and browsers. It’s overwhelming. So we just gave up.

So, a front-end developer:

  • Is a job and a job title.
  • It deals with browsers, devices, and users.
  • But what skills does it involve?

It’s taken for granted that you can use a computer. There’s also the soft skills of interacting with co-workers. Then there are the language-specific core skills. Finally, there are the bonus skills—all the stuff that makes you you.

Core skills

The languages you need to strongly understand to read, write and maintain them.

HTML and CSS. Definitely. You don’t come across front-end developers who don’t do those languages. But what about JavaScript?

Eric says it’s fine if you know lots of JavaScript but it’s also fine if you don’t write everything from scratch. But you can’t be oblivious to it. You need to understand what it can do.

So let’s put JavaScript into the bucket of core skills too.

Peggy believes that as a front-end developer you need to have a basic proficiency in accessibility too. This is, after all, about user-facing interfaces.

Bonus skills

The Figma team have a somewhat over-engineered graphic of all the skillsets that people might have, between “baseline” and “supplementary”.

Perhaps we all share a common trunk of skills, and then we branch in different directions.

Right now though, it feels like front-end development is having an identity crisis. It’s all about JavaScript, which is eating the planet.

JavaScript

JavaScript is crazy popular now. It’s unignorable. Yes, it’s the language in the browser, but now it’s also the language in loads of other places too.

Steven Davis says maybe we need to fork the term front-end development. Maybe we need to have UX engineers and JavaScript engineers. Can one person be great at both? Maybe the trunk of skills forks in two very different directions.

Vernon Joyce called this an identity crisis. The concepts in JavaScript frameworks are very alien to people with a background in HTML, CSS, and basic interactive JavaScript.

You could imagine two people called front-end developers meeting, and having nothing in common to talk about. Maybe sports.

Brad says he doesn’t want to be configuring build tools. He thinks of himself as being at the front of front-end development, whereas other people are at the back of front-end development.

This divide is super frustrating to people right now.

Hiring

Michael Schnarnagl brings up the point about how it’s affecting hiring. Back-end developers are being replaced with JavaScript engineers. Lots of things that used to be back-end tasks are now happening on the client side. Component-driven design, site-level architecture, routing, getting data from the back end, mutating data, talking to APIs, and managing state—all of those things are now largely a front-end concern.

Let’s look at CodePen. There’s a little heart icon on each pen. It’s an icon component. And the combination of the heart and the overall count is also a component. And the bar of items altogether—that’s also a component. And the pen it sits under is a component. And the page it’s in is a component. And the URL for that page is a component. Now the whole site is a front-end developer’s concern.

In the past, a front-end developer would ask a back-end developer for an API endpoint. Now with GraphQL, the front-end developer can craft a query to get exactly what they need. Sure, the GraphQL stuff had to be set up in the first place, but that’s one-time task. Once it’s set up, the front-end developer has everything they need.

All the old work hasn’t gone away either. Semantics, accessibility, styling—that’s still the work of a front-end developer as well as all of the new stuff listed above.

Hiring is a big part of this. Lara Schenk talks about going for an interview where she met 90% of the skills listed. Then in an interview, she was asked to do a fizzbuzz test. That’s not the way that Lara thinks. She would’ve been great for that job, but this single task derailed her. She wrote about it, and got snarky comments from people who thought she should’ve been able to do the task. But Lara’s main point was the mismatch between what was advertised and what was actually being hired for.

You see a job posting for front-end developer. Who is that for? Is it for someone into React, webpack, and GraphQL? Or is it for someone into SVG, interaction design, and accessibility? They’re both front-end developers. And remember, they can learn one another’s skills, but when it comes to hiring, it has to be about the skills people have right now.

Peggy talks about how specialised your work can be. You can specialise in SVG. You can specialise in APIs and data.

We’re probably not going to solve this right now. The hiring part is definitely the worst part right now. One solution is to use plain language in job posts. Make it clear what you’re looking for right now and explain what background you’re coming from. Use words instead of a laundry list of requirements.

Heydon Pickering talks about full-stack developers. Their core skills are hardcore computer science skills.

Brad Frost concurs. It tends not to be the other way around. The output tends to be the badly-sketched front of the horse.

Even if there is a divide, that doesn’t absolve any of us from doing a good job. That’s true whether it’s computer science tasks or markup and CSS.

Despite the divide, performance, accessibility, and user experience are all our jobs.

Maybe this term “front-end developer” needs rethinking.

The brain game

Let’s peak into the minds of very different front-end developers. Chris and Dave went to Dribbble, pulled up a bunch of designs and put them in front of their guests on the Shop Talk Show.

Here’s a design of a page.

  • Brad looks at the design and sees a lot of components of different sizes and complexity.
  • Mina sees a bunch of media objects.
  • Eric sees HTML structures. That’s a heading. That’s a list. Over there is an unordered list.
  • Sam sees a lot of typography. She sees a type system.
  • Trent immediately starts thinking about how the design is supposed to work in different screen sizes.

Here’s a different, more image-heavy design.

  • Mina would love to tackle the animations.
  • Trent sees interesting textures and noise. He wonders how he could achieve those effects without exporting giant image files.
  • Brad, unsurprisingly, sees components, even in a seemingly bespoke layout.
  • Eric immediately sees a lot of SVG.
  • Sam needs to know what the HTML is.

Here’s a more geometric design.

  • Sam is drawn to the typography.
  • Mina sees an opportunity to use writing modes.
  • Trent sees a design that would reflow and reshape itself well.
  • Eric sees something with writing mode, grid, and custom fonts.

Here’s a financial mobile UI.

  • Trent wants to run it through a colour-contrast analyser, and he wants to know if the font size is too small.

Here’s a crazy festival website.

  • Mina wonders if it needs a background video, but worries about the performance.

Here’s an on-trend mobile design.

  • Monica sees something that looks like every other website.
  • Ben wonders whether it will work in other parts of the world. How will the interactions work? Separate pages or transitions? How will it feel?

Here’s an image-heavy design.

  • Monica wonders about the priority of which images to load first.

Here’s an extreme navigation with big images.

  • Ben worries about the performance on slow connections.
  • Monica gets stressed out about how much happens when you just click on a link.
  • Peggy sees something static and imagines using Gatsby for it.

Here’s a design that’s map-based.

  • Ben worries about the size of the touch targets.
  • Monica sees an opportunity to use SVGs.

Here’s a card UI.

  • Ben wonders what the browser support is. Can we use CSS grid or do we have to use something older?
  • Monica worries that this needs drag’n’drop. Now you’ve got a nightmare scenario.

Chris has been thinking about and writing about this topic of what makes someone a front-end developer, and what makes someone a good front-end developer. The debate will continue…

Accessibility on The Session

I spent some time this weekend working on an accessibility issue over on The Session. Someone using VoiceOver on iOS was having a hard time with some multi-step forms.

These forms have been enhanced with some Ajax to add some motion design: instead of refreshing the whole page, the next form is grabbed from the server while the previous one swooshes off the screen.

You can see similar functionality—without the animation—wherever there’s pagination on the site.

The pagination is using Ajax to enhance regular prev/next links—here’s the code.

The multi-step forms are using Ajax to enhance regular form submissions—here’s the code for that.

Both of those are using a wrapper I wrote for XMLHttpRequest.

That wrapper also adds some ARIA attributes. The region of the page that will be updated gets an aria-live value of polite. Then, whenever new content is being injected, the same region gets an aria-busy value of true. Once the update is done, the aria-busy value gets changed back to false.

That all seems to work fine, but I was also giving the same region of the page an aria-atomic value of true. My thinking was that, because the whole region was going to be updated with new content from the server, it was safe to treat it as one self-contained unit. But it looks like this is what was causing the problem, especially when I was also adding and removing class values on the region in order to trigger animations. VoiceOver seemed to be getting a bit confused and overly verbose.

I’ve removed the aria-atomic attribute now. True to its name, I’m guessing it’s better suited to small areas of a document rather than big chunks. (If anyone has a good primer on when to use and when to avoid aria-atomic, I’m all ears).

I was glad I was able to find a fix—hopefully one that doesn’t negatively impact the experience in other screen readers. As is so often the case, the issue was with me trying to be too clever with ARIA, and the solution was to ease up on adding so many ARIA attributes.

It also led to a nice discussion with some of the screen-reader users on The Session.

For me, all of this really highlights the beauty of the web, when everyone is able to contribute to a community like The Session, regardless of what kind of software they may be using. In the tunes section, that’s really helped by the use of ABC notation, as I wrote five years ago:

One of those screen-reader users got in touch with me shortly after joining to ask me to explain what ABC was all about. I pointed them at some explanatory links. Once the format “clicked” with them, they got quite enthused. They pointed out that if the sheet music were only available as an image, it would mean very little to them. But by providing the ABC notation alongside the sheet music, they could read the music note-for-note.

That’s when it struck me that ABC notation is effectively alt text for sheet music!

Then, for those of use who can read sheet music, the text of the ABC notation is automatically turned into an SVG image using the brilliant abcjs. It’s like an enhancement that’s applied, I dunno, what’s the word …progressively.

A tiny lesson in query selection

We have a saying at Clearleft:

Everything is a tiny lesson.

I bet you learn something new every day, even if it’s something small. These small tips and techniques can easily get lost. They seem almost not worth sharing. But it’s the small stuff that takes the least effort to share, and often provides the most reward for someone else out there. Take for example, this great tip for getting assets out of Sketch that Cassie shared with me.

Cassie was working on a piece of JavaScript yesterday when we spotted a tiny lesson that tripped up both of us. The script was a fairly straightforward piece of DOM scripting. As a general rule, we do a sort of feature detection near the start of the script. Let’s say you’re using querySelector to get a reference to an element in the DOM:

var someElement = document.querySelector('.someClass');

Before going any further, check to make sure that the reference isn’t falsey (in other words, make sure that DOM node actually exists):

if (!someElement) return;

That will exit the script if there’s no element with a class of someClass on the page.

The situation that tripped us up was like this:

var myLinks = document.querySelectorAll('a.someClass');

if (!myLinks) return;

That should exit the script if there are no A elements with a class of someClass, right?

As it turns out, querySelectorAll is subtly different to querySelector. If you give querySelector a reference to non-existent element, it will return a value of null (I think). But querySelectorAll always returns an array (well, technically it’s a NodeList but same difference mostly). So if the selector you pass to querySelectorAll doesn’t match anything, it still returns an array, but the array is empty. That means instead of just testing for its existence, you need to test that it’s not empty by checking its length property:

if (!myLinks.length) return;

That’s a tiny lesson.