Tags: code

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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.

Wednesday, October 16th, 2019

IndieWeb Link Sharing | Max Böck - Frontend Web Developer

Max describes how he does bookmarking on his own site—he’s got a bookmarklet for sharing links, like I do. But he goes further with a smart use of the “share target” section in his web app manifest, as described by Aaron.

By the way, Max’s upcoming talk at the Web Clerks conference in Vienna sounds like it’s going to be unmissable!

The lines of code that changed everything.

We construct top-10 lists for movies, games, TV—pieces of work that shape our souls. But we don’t sit around compiling lists of the world’s most consequential bits of code, even though they arguably inform the zeitgeist just as much.

This is a fascinating way to look at the history of computing, by focusing in on culturally significant pieces of code. The whole list is excellent, but if I had to pick a favourite …well, see if you can guess what it is.

Tuesday, October 15th, 2019

GitSheet

A handy translation of git commands into English.

Sunday, October 6th, 2019

How to be a more productive developer | Go Make Things

Like Michael Pollan’s food rules, but for JavaScript:

  1. Plan your scripts out on paper.
  2. Stop obsessing over tools.
  3. Focus on solving problems.
  4. Maintain a library of snippets that you can reuse.

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.

Blog service workers and the chicken and the egg

This is a great little technique from Remy: when a service worker is being installed, you make sure that the page(s) the user is first visiting get added to a cache.

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 10th, 2019

Simplicity (II)

When you ever had to fix just a few lines of CSS and it took two hours to get an ancient version of Gulp up and running, you know what I’m talking about.

I feel seen.

When everything works, it feels like magic. When something breaks, it’s hell.

I concur with Bastian’s advice:

I have a simple rule of thumb when it comes to programming:

less code === less potential issues

And this observation rings very true:

This dependency hell is also the reason why old projects are almost like sealed capsules. You can hardly let a project lie around for more than a year, because afterwards it’s probably broken.

Friday, September 6th, 2019

Enigma machine / Tom MacWright / Observable

See how an Enigma machine works …and interact with it.

Letters to be encrypted enter at the boundary, move through the wire matrix, and exit.

Offline listings

This is brilliant technique by Remy!

If you’ve got a custom offline page that lists previously-visited pages (like I do on my site), you don’t have to choose between localStorage or IndexedDB—you can read the metadata straight from the HTML of the cached pages instead!

This seems forehead-smackingly obvious in hindsight. I’m totally stealing this.

Thursday, August 22nd, 2019

AccentDesign/Fractal-Atomic: An awesome starter point for your Fractal UI component library

If you want to use Brad’s Atomic Design naming convention—atoms, molecules, etc.—and you like using Fractal for making your components, this starter kit is just for you:

Keep what you need, delete what you don’t and add whatever you like on top of whats already there.

Friday, August 9th, 2019

Building an extensible app or library with vanilla JS | Go Make Things

This looks like a sensible approach to creating a modular architecture for a complex client-side JavaScript codebase.

I know a lot of people swear by ES6 imports, but this systems worked really well for us. It gave us a simple, modular, extensible framework we can easily build on in the future.

Thursday, August 1st, 2019

The web without the web - DEV Community 👩‍💻👨‍💻

I love React. I love how server side rendering React apps is trivial because it all compiles down to vanilla HTML rather than web components, effectively turning it into a kickass template engine that can come alive. I love the way you can very effectively still do progressive enhancement by using completely semantic markup and then letting hydration do more to it.

I also hate React. I hate React because these behaviours are not defaults. React is not gonna warn you if you make a form using divs and unlabelled textboxes and send the whole thing to a server. I hate React because CSS-in-JS approaches by default encourage you to write completely self contained one off components rather than trying to build a website UI up as a whole. I hate the way server side rendering and progressive enhancement are not defaults, but rather things you have to go out of your way to do.

An absolutely brilliant post by Laura on how the priorites baked into JavaScript tools like React are really out of whack. They’ll make sure your behind-the-scenes code is super clean, but not give a rat’s ass for the quality of the output that users have to interact with.

And if you want to adjust the front-end code, you’ve got to set up all this tooling just to change a div to a button. That’s quite a barrier to entry.

In elevating frontend to the land of Serious Code we have not just made things incredibly over-engineered but we have also set fire to all the ladders that we used to get up here in the first place.

AMEN!

I love React because it lets me do my best work faster and more easily. I hate React because the culture around it more than the library itself actively prevents other people from doing their best work.

Tuesday, July 30th, 2019

Creating my logo animation - cassie.codes

What a wonderfully in-depth and clear tutorial from Cassie on how she created the animation for her nifty SVG logo!

Also: Cassie is on the indie web now, writing on her own website—yay!

Tuesday, July 23rd, 2019

Pseudo Code | CSS-Tricks

I find myself doing pseudo code before I write real code, sure, but I also leave it in place sometimes in code comments.

Same!

Friday, July 19th, 2019

Micro Frontends

Chris succinctly describes the multiple-iframes-with-multiple-codebases approach to web development, AKA “micro frontends”:

The idea really is that you might build a React app and I build a Vue app and we’ll slap ‘em together on the same page. I definitely come from an era where we laughed-then-winced when we found sites that used multiple versions of jQuery on the same page, plus one thing that loaded all of MooTools and Prototype thrown on there seemingly by accident. We winced because that was a bucket full of JavaScript, mostly duplicated for no reason, causing bugs and slowing down the page. This doesn’t seem all that much different.

Tuesday, July 2nd, 2019

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.

Monday, July 1st, 2019

Why Did I Have Difficulty Learning React? - Snook.ca

When people talk about learning React, I think that React, in and of itself, is relatively easy to understand. At least, I felt it was. I have components. I have JSX. I hit some hiccups with required keys or making sure I was wrapping child elements properly. But overall, I felt like I grasped it well enough.

Throw in everything else at the same time, though, and things get confusing because it’s hard at first to recognize what belongs to what. “Oh, this is Redux. That is React. That other thing is lodash. Got it.”

This resonates a lot with Dave’s post:

React is an ecosystem. I feel like it’s a disservice to anyone trying to learn to diminish all that React entails. React shows up on the scene with Babel, Webpack, and JSX (which each have their own learning curve) then quickly branches out into technologies like Redux, React-Router, Immutable.js, Axios, Jest, Next.js, Create-React-App, GraphQL, and whatever weird plugin you need for your app.

Monday, June 24th, 2019

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.