Journal

2622 sparkline

Tuesday, October 29th, 2019

Periodic background sync

Yesterday I wrote about how much I’d like to see silent push for the web:

I’d really like silent push for the web—the ability to update a cache with fresh content as soon as it’s published; that would be nifty! At the same time, I understand the concerns. It feels more powerful than other permission-based APIs like notifications.

Today, John Holt Ripley responded on Twitter:

hi there, just read your blog post about Silent Push for acthe web, and wondering if Periodic Background Sync would cover a few of those use cases?

Periodic background sync looks very interesting indeed!

It’s not the same as silent push. As the name suggests, this is about your service worker waking up periodically and potentially fetching (and caching) fresh content from the network. So the service worker is polling rather than receiving a push. But I’ll take it! It’s definitely close enough for the kind of use-cases I’ve been thinking about.

Interestingly, periodic background sync also ties into the other part of what I was writing about: permissions. I mentioned that adding a site the home screen could be interpreted as a signal to potentially allow more permissions (or at least allow prompts for more permissions).

Well, Chromium has a document outlining metrics for attempting to gauge site engagement. There’s some good thinking in there.

Monday, October 28th, 2019

Silent push for the web

After Indie Web Camp in Berlin last year, I wrote about Seb’s nifty demo of push without notifications:

While I’m very unwilling to grant permission to be interrupted by intrusive notifications, I’d be more than willing to grant permission to allow a website to silently cache timely content in the background. It would be a more calm technology.

Phil Nash left a comment on the Medium copy of my post explaining that Seb’s demo of using the Push API without showing a notification wouldn’t work for long:

The browsers allow a certain number of mistakes(?) before they start to show a generic notification to say that your site sent a push notification without showing a notification. I believe that after ~10 or so notifications, and that’s different between browsers, they run out of patience.

He also provided me with the name to describe what I’m after:

You’re looking for “silent push” as are many others.

Silent push is something that is possible in native apps. It isn’t (yet?) available on the web, presumably because of security concerns.

It’s an API that would ripe for abuse. I mean, just look at the mess we’ve made with APIs like notifications and geolocation. Sure, they require explicit user opt-in, but these opt-ins are seen so often that users are sick of seeing them. Silent push would be one more permission-based API to add to the stack of annoyances.

Still, I’d really like silent push for the web—the ability to update a cache with fresh content as soon as it’s published; that would be nifty! At the same time, I understand the concerns. It feels more powerful than other permission-based APIs like notifications.

Maybe there could be another layer of permissions. What if adding a site to your home screen was the first step? If a site is running on HTTPS, has a service worker, has a web app manifest, and has been added to the homescreen, maybe then and only then should it be allowed to prompt for permission to do silent push.

In other words, what if certain very powerful APIs were only available to progressive web apps that have successfully been added to the home screen?

Frankly, I’d be happy if the same permissions model applied to web notifications too, but I guess that ship has sailed.

Anyway, all this is pure conjecture on my part. As far as I know, silent push isn’t on the roadmap for any of the browser vendors right now. That’s fair enough. Although it does annoy me that native apps have this capability that web sites don’t.

It used to be that there was a long list of features that only native apps could do, but that list has grown shorter and shorter. The web’s hare is catching up to native’s tortoise.

Monday, October 21st, 2019

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.

Friday, October 18th, 2019

Web talk

At the start of this month I was in Amsterdam for a series of back-to-back events: Indie Web Camp Amsterdam, View Source, and Fronteers. That last one was where Remy and I debuted talk we’d been working on.

The Fronteers folk have been quick off the mark so the video is already available. I’ve also published the text of the talk here:

How We Built The World Wide Web In Five Days

This was a fun talk to put together. The first challenge was figuring out the right format for a two-person talk. It quickly became clear that Remy’s focus would be on the events of the five days we spent at CERN, whereas my focus would be on the history of computing, hypertext, and networks leading up to the creation of the web.

Now, we could’ve just done everything chronologically, but that would mean I’d do the first half of the talk and Remy would do the second half. That didn’t appeal. And it sounded kind of boring. So then we come up with the idea of interweaving the two timelines.

That worked remarkably well. The talk starts with me describing the creation of CERN in the 1950s. Then Remy talks about the first day of the hack week. I then talk about events in the 1960s. Remy talks about the second day at CERN. This continues until we join up about half way through the talk: I’ve arrived at the moment that Tim Berners-Lee first published the proposal for the World Wide Web, and Remy has arrived at the point of having running code.

At this point, the presentation switches gears and turns into a demo. I do not have the fortitude to do a live demo, so this was all down to Remy. He did it flawlessly. I have so much respect for people brave enough to do live demos, and do them well.

But the talk doesn’t finish there. There’s a coda about our return to CERN a month after the initial hack week. This was an opportunity for both of us to close out the talk with our hopes and dreams for the World Wide Web.

I know I’m biased, but I thought the structure of the presentation worked really well: two interweaving timelines culminating in a demo and finishing with the big picture.

There was a forcing function on preparing this presentation: Remy was moving house, and I was already going to be away speaking at some other events. That limited the amount of time we could be in the same place to practice the talk. In the end, I think that might have helped us make the most of that time.

We were both feeling the pressure to tell this story well—it means so much to us. Personally, I found that presenting with Remy made me up my game. Like I said:

It’s been a real treat working with Remy on this. Don’t tell him I said this, but he’s kind of a web hero of mine, so this was a real honour and a privilege for me.

This talk could have easily turned into a boring slideshow of “what we did on our holidays”, but I think we managed to successfully avoid that trap. We’re both proud of this talk and we’d love to give it again some time. If you’d like it at your event, get in touch.

In the meantime, you can read the text, watch the video, or look at the slides (but the slides really don’t make much sense in isolation).

Wednesday, October 16th, 2019

The Web Share API in Safari on iOS

I implemented the Web Share API over on The Session back when it was first available in Chrome in Android. It’s a nifty and quite straightforward API that allows websites to make use of the “sharing drawer” that mobile operating systems provide from within a web browser.

I already had sharing buttons that popped open links to Twitter, Facebook, and email. You can see these sharing buttons on individual pages for tunes, recordings, sessions, and so on.

I was already intercepting clicks on those buttons. I didn’t have to add too much to also check for support for the Web Share API and trigger that instead:

if (navigator.share) {
  navigator.share(
    {
      title: document.querySelector('title').textContent,
      text: document.querySelector('meta[name="description"]').getAttribute('content'),
      url: document.querySelector('link[rel="canonical"]').getAttribute('href')
    }
  );
}

That worked a treat. As you can see, there are three fields you can pass to the share() method: title, text, and url. You don’t have to provide all three.

Earlier this year, Safari on iOS shipped support for the Web Share API. I didn’t need to do anything. ‘Cause that’s how standards work. You can make use of APIs before every browser supports them, and then your website gets better and better as more and more browsers add support.

But I recently discovered something interesting about the iOS implementation.

When the share() method is triggered, iOS provides multiple ways of sharing: Messages, Airdrop, email, and so on. But the simplest option is the one labelled “copy”, which copies to the clipboard.

Here’s the thing: if you’ve provided a text parameter to the share() method then that’s what’s going to get copied to the clipboard—not the URL.

That’s a shame. Personally, I think the url field should take precedence. But I don’t think this is a bug, per se. There’s nothing in the spec to say how operating systems should handle the data sent via the Web Share API. Still, I think it’s a bit counterintuitive. If I’m looking at a web page, and I opt to share it, then surely the URL is the most important piece of data?

I’m not even sure where to direct this feedback. I guess it’s under the purview of the Safari team, but it also touches on OS-level interactions. Either way, I hope that somebody at Apple will consider changing the current behaviour for copying Web Share data to the clipboard.

In the meantime, I’ve decided to update my code to remove the text parameter:

if (navigator.share) {
  navigator.share(
    {
      title: document.querySelector('title').textContent,
      url: document.querySelector('link[rel="canonical"]').getAttribute('href')
    }
  );
}

If the behaviour of Safari on iOS changes, I’ll reinstate the missing field.

By the way, if you’re making progressive web apps that have display: standalone in the web app manifest, please consider using the Web Share API. When you remove the browser chrome, you’re removing the ability for users to easily share URLs. The Web Share API gives you a way to reinstate that functionality.

Monday, October 14th, 2019

Something for the weekend

Your weekends are valuable. Spend them wisely. I have some suggestion on how you might spend next weekend, October 19th and 20th, depending on where you are in the world.

If you’re in the bay area, or anywhere near San Francisco, I highly recommend that you go to Science Hack Day—two days of science, hacking, and fun. This will be the last one in San Francisco so don’t miss your chance.

If you’re in the south of England, or anywhere near Brighton, come along to Indie Web Camp. Saturday will feature discussions on owning your data. Sunday will be a day of doing. I’ve written about previous Indie Web Camps before, and I really can’t recommend it highly enough!

Do me a favour and register for a spot—it’s free—so I’ve got some idea of numbers. Looking forward to seeing you there!

Sunday, October 6th, 2019

Dark mode

I had a very productive time at Indie Web Camp Amsterdam. The format really lends itself to getting the most of a weekend—one day of discussions followed by one day of hands-on making and doing. You should definitely come along to Indie Web Camp Brighton on October 19th and 20th to experience it for yourself.

By the end of the “doing” day, I had something fun to demo—a dark mode for my website.

Y’know, when I first heard about Apple adding dark mode to their OS—and also to CSS—I thought, “Oh, great, Apple are making shit up again!” But then I realised that, like user style sheets, this is one more reminder to designers and developers that they don’t get the last word—users do.

Applying the dark mode styles is pretty straightforward in theory. You put the styles inside this media query:

@media (prefers-color-scheme: dark) {
...
}

Rather than over-riding every instance of a colour in my style sheet, I decided I’d do a little bit of refactoring first and switch to using CSS custom properties (or variables, if you will).

:root {
  --background-color: #fff;
  --text-color: #333;
  --link-color: #b52;
}
body {
  background-color: var(--background-color);
  color: var(--text-color);
}
a {
  color: var(--link-color);
}

Then I can over-ride the custom properties without having to touch the already-declared styles:

@media (prefers-color-scheme: dark) {
  :root {
    --background-color: #111416
    --text-color: #ccc;
    --link-color: #f96;
  }
}

All in all, I have about a dozen custom properties for colours—variations for text, backgrounds, and interface elements like links and buttons.

By using custom properties and the prefers-color-scheme media query, I was 90% of the way there. But the devil is in the details.

I have SVGs of sparklines on my homepage. The SVG has a hard-coded colour value in the stroke attribute of the path element that draws the sparkline. Fortunately, this can be over-ridden in the style sheet:

svg.activity-sparkline path {
  stroke: var(--text-color);
}

The real challenge came with the images I use in the headers of my pages. They’re JPEGs with white corners on one side and white gradients on the other.

header images

I could make them PNGs to get transparency, but the file size would shoot up—they’re photographic images (with a little bit of scan-line treatment) so JPEGs (or WEBPs) are the better format. Then I realised I could use CSS to recreate the two effects:

  1. For the cut-out triangle in the top corner, there’s clip-path.
  2. For the gradient, there’s …gradients!
background-image: linear-gradient(
  to right,
  transparent 50%,
  var(—background-color) 100%
);

Oh, and I noticed that when I applied the clip-path for the corners, it had no effect in Safari. It turns out that after half a decade of support, it still only exists with -webkit prefix. That’s just ridiculous. At this point we should be burning vendor prefixes with fire. I can’t believe that Apple still ships standardised CSS properties that only work with a prefix.

In order to apply the CSS clip-path and gradient, I needed to save out the images again, this time without the effects baked in. I found the original Photoshop file I used to export the images. But I don’t have a copy of Photoshop any more. I haven’t had a copy of Photoshop since Adobe switched to their Mafia model of pricing. A quick bit of searching turned up Photopea, which is pretty much an entire recreation of Photoshop in the browser. I was able to open my old PSD file and re-export my images.

LEGO clone trooper Brighton bandstand Scaffolding Tokyo Florence

Let’s just take a moment here to pause and reflect on the fact that we can now use CSS to create all sorts of effects that previously required a graphic design tool like Photoshop. I could probably do those raster scan lines with CSS if I were smart enough.

dark mode

This is what I demo’d at the end of Indie Web Camp Amsterdam, and I was pleased with the results. But fate had an extra bit of good timing in store for me.

The very next day at the View Source conference, Melanie Richards gave a fantastic talk called The Tailored Web: Effectively Honoring Visual Preferences (seriously, conference organisers, you want this talk on your line-up). It was packed with great insights and advice on impementing dark mode, like this little gem for adjusting images:

@media (prefers-color-scheme: dark) {
  img {
    filter: brightness(.8) contrast(1.2);
  }
}

Melanie also pointed out that you can indicate the presence of dark mode styles to browsers, although the mechanism is yet to shake out. You can do it in CSS:

:root {
  color-scheme: light dark;
}

But you can also do it in HTML:

That allows browsers to swap out replaced content; interface elements like form fields and dropdowns.

Oh, and one other addition I added after the fact was swapping out map imagery by using the picture element to point to darker map tiles:

<picture>
<source media="(prefers-color-scheme: dark)" srcset="https://api.mapbox.com/styles/v1/mapbox/dark-v10/static...">
<img src="https://api.mapbox.com/styles/v1/mapbox/outdoors-v10/static..." alt="map">
</picture>

light map dark map

So now I’ve got a dark mode for my website. Admittedly, it’s for just one of the eight style sheets. I’ve decided that, while I’ll update my default styles at every opportunity, I’m going to preservethe other skins as they are, like the historical museum pieces they are.

If you’re on the latest version of iOS, go ahead and toggle the light and dark options in your system preferences to flip between this site’s colour schemes.

Thursday, October 3rd, 2019

Travel talk

It’s been a busy two weeks of travelling and speaking. Last week I spoke at Finch Conf in Edinburgh, Code Motion in Madrid, and Generate CSS in London. This week I was at Indie Web Camp, View Source, and Fronteers, all in Amsterdam.

The Edinburgh-Madrid-London whirlwind wasn’t ideal. I gave the opening talk at Finch Conf, then immediately jumped in a taxi to get to the airport to fly to Madrid, so I missed all the excellent talks. I had FOMO for a conference I actually spoke at.

I did get to spend some time at Code Motion in Madrid, but that was a waste of time. It was one of those multi-track events where the trade show floor is prioritised over the talks (and the speakers don’t get paid). I gave my talk to a mostly empty room—the classic multi-track experience. On the plus side, I had a wonderful time with Jessica exploring Madrid’s many tapas delights. The food and drink made up for the sub-par conference.

I flew back from Madrid to the UK, and immediately went straight to London to deliver the closing talk of Generate CSS. So once again, I didn’t get to see any of the other talks. That’s a real shame—it sounds like they were all excellent.

The day after Generate though, I took the Eurostar to Amsterdam. That’s where I’ve been ever since. There were just as many events as in the previous week, but because they were all in Amsterdam, I could savour them properly, instead of spending half my time travelling.

Indie Web Camp Amsterdam was excellent, although I missed out on the afternoon discussions on the first day because I popped over to the Mozilla Tech Speakers event happening at the same time. I was there to offer feedback on lightning talks. I really, really enjoyed it.

I’d really like to do more of this kind of thing. There aren’t many activities I feel qualified to give advice on, but public speaking is an exception. I’ve got plenty of experience that I’m eager to share with up-and-coming speakers. Also, I got to see some really great lightning talks!

Then it was time for View Source. There was a mix of talks, panels, and breakout conversation corners. I saw some fantastic talks by people I hadn’t seen speak before: Melanie Richards, Ali Spittal, Sharell Bryant, and Tejas Kumar. I gave the closing keynote, which was warmly received—that’s always very gratifying.

After one day of rest, it was time for Fronteers. This was where myself and Remy gave the joint talk we’ve been working on:

Neither of us is under any illusions about the nature of a joint talk. It’s not half as much work; it’s more like twice the work. We’ve both seen enough uneven joint presentations to know what we want to avoid.

I’m happy to say that it went off without a hitch. Remy definitely had the tougher task—he did a live demo. Needless to say, he did it flawlessly. It’s been a real treat working with Remy on this. Don’t tell him I said this, but he’s kind of a web hero of mine, so this was a real honour and a privilege for me.

I’ve got some more speaking engagements ahead of me. Most of them are in Europe so I’m going to do my utmost to travel to them by train. Flying is usually more convenient but it’s terrible for my carbon footprint. I’m feeling pretty guilty about that Madrid trip; I need to make ammends.

I’ll be travelling to France next week for Paris Web. Taking the Eurostar is a no-brainer for that one. Straight after that Jessica and I will be going to Frankfurt for the book fair. Taking the train from Paris to Frankfurt will be nice and straightforward.

I’ll be back in Brighton for Indie Web Camp on the weekend of October 19th and 20th—you should come!—and then I’ll be heading off to Antwerp for Full Stack Fest. Anywhere in Belgium is easily reachable by train so that’ll be another Eurostar journey.

After that, it gets a little trickier. I’ll be going to Berlin for Beyond Tellerrand but I’m not sure I can make it work by train. Same goes for Web Clerks in Vienna. Cities that far east are tough to get to by train in a reasonable amount of time (although I realise that, compared to many others, I have the luxury of spending time travelling by train).

Then there are the places that I can only get to by plane. There’s the United States. I’ll be speaking at An Event Apart in San Francisco in December. A flight is unavoidable. Last time we went to the States, Jessica and I travelled by ocean liner. But that isn’t any better for the environment, given the low-grade fuel burned by ships.

And then there’s Ireland. I make trips back there to see my mother, but there’s no alternative to flying or taking a ferry—neither are ideal for the environment. At least I can offset the carbon from my flights; the travel equivalent to putting coins in the swear jar.

Don’t get me wrong—I’m not moaning about the amount of travel involved in going to conferences and workshops. It’s fantastic that I get to go to new and interesting places. That’s something I hope I never take for granted. But I can’t ignore the environmental damage I’m doing. I’ll be making more of an effort to travel by train to Europe’s many excellent web events. While I’m at it, I can ask Paul for his trainspotter expertise.

Saturday, September 21st, 2019

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.

Tuesday, September 17th, 2019

Geneva Copenhagen Amsterdam

Back in the late 2000s, I used to go to Copenhagen every for an event called Reboot. It was a fun, eclectic mix of talks and discussions, but alas, the last one was over a decade ago.

It was organised by Thomas Madsen-Mygdal. I hadn’t seen Thomas in years, but then, earlier this year, our paths crossed when I was back at CERN for the 30th anniversary of the web. He got a real kick out of the browser recreation project I was part of.

I few months ago, I got an email from Thomas about the new event he’s running in Copenhagen called Techfestival. He was wondering if there was some way of making the WorldWideWeb project part of the event. We ended up settling on having a stand—a modern computer running a modern web browser running a recreation of the first ever web browser from almost three decades ago.

So I showed up at Techfestival and found that the computer had been set up in a Shoreditchian shipping container. I wasn’t exactly sure what I was supposed to do, so I just hung around nearby until someone wandering by would pause and start tentatively approaching the stand.

If you’re at Techfestival.co in Copenhagen, drop in to this shipping container where I’ll be demoing WorldWideWeb.cern.ch

“Would you like to try the time machine?” I asked. Nobody refused the offer. I explained that they were looking at a recreation of the world’s first web browser, and then showed them how they could enter a URL to see how the oldest web browser would render a modern website.

Lots of people entered facebook.com or google.com, but some people had their own websites, either personal or for their business. They enjoyed seeing how well (or not) their pages held up. They’d take photos of the screen.

People asked lots of questions, which I really enjoyed answering. After a while, I was able to spot the themes that came up frequently. Some people were confusing the origin story of the internet with the origin story of the web, so I was more than happy to go into detail on either or both.

The experience helped me clarify in my own mind what was exciting and interesting about the birth of the web—how much has changed, and how much and stayed the same.

All of this very useful fodder for a conference talk I’m putting together. This will be a joint talk with Remy at the Fronteers conference in Amsterdam in a couple of weeks. We’re calling the talk How We Built the World Wide Web in Five Days:

The World Wide Web turned 30 years old this year. To mark the occasion, a motley group of web nerds gathered at CERN, the birthplace of the web, to build a time machine. The first ever web browser was, confusingly, called WorldWideWeb. What if we could recreate the experience of using it …but within a modern browser! Join (Je)Remy on a journey through time and space and code as they excavate the foundations of Tim Berners-Lee’s gloriously ambitious and hacky hypertext system that went on to conquer the world.

Neither of us is under any illusions about the nature of a joint talk. It’s not half as much work; it’s more like twice the work. We’ve both seen enough uneven joint presentations to know what we want to avoid.

We’ve been honing the material and doing some run-throughs at the Clearleft HQ at 68 Middle Street this week. The talk has a somewhat unusual structure with two converging timelines. I think it’s going to work really well, but I won’t know until we actually deliver the talk in Amsterdam. I’m excited—and a bit nervous—about it.

Whether it’s in a shipping container in Copenhagen or on a stage in Amsterdam, I’m starting to realise just how much I enjoy talking about web history.