Tags: optimisation

38

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Wednesday, September 11th, 2019

The Ugly Truth about Design Systems

The video of a talk in which Mark discusses pace layers, dogs, and design systems. He concludes:

  1. Current design systems thinking limits free, playful expression.
  2. Design systems uncover organisational disfunction.
  3. Continual design improvement and delivery is a lie.
  4. Component-focussed design is siloed thinking.

It’s true many design systems are the blueprints for manufacturing and large scale application. But in almost every instance I can think of, once you move from design to manufacturing the horse has bolted. It’s very difficult to move back into design because the results of the system are in the wild. The more strict the system, the less able you are to change it. That’s why broad principles, just enough governance, and directional examples are far superior to locked-down cookie cutters.

Thursday, August 1st, 2019

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.

Wednesday, June 12th, 2019

Breaking the physical limits of fonts

This broke my brain.

The challenge: in the fewest resources possible, render meaningful text.

  • How small can a font really go?
  • How many bytes of memory would you need (to store it and run it?)
  • How much code would it take to express it?

Lets see just how far we can take this!

Sunday, August 12th, 2018

Let’s serve everyone good-looking content

A terrific piece by Hidde, about CSS grid, but also about a much bigger question:

I don’t think we owe it to any users to make it all exactly the same. Therefore we can get away with keeping fallbacks very simple. My hypothesis: users don’t mind, they’ve come for the content.

If users don’t mind, that leaves us with team members, bosses and clients. In my ideal world we should convince each other, and with that I mean visual designers, product owners, brand people, developers, that it is ok for our lay-out not to look the same everywhere. Because serving good-looking content everywhere is more important than same grids everywhere.

Tuesday, July 31st, 2018

Prioritizing the Long-Tail of Performance - TimKadlec.com

Focusing on the median or average is the equivalent of walking around with a pair of blinders on. We’re limiting our perspective and, in the process, missing out on so much crucial detail. By definition, when we make improving the median or average our goal, we are focusing on optimizing for only about half of our sessions.

Tim does the numbers…

By honing in on the 90th—or 95th or similar—we ensure those weaknesses don’t get ignored. Our goal is to optimize the performance of our site for the majority of our users—not just a small subset of them.

Saturday, June 23rd, 2018

The Critical Request - Speaker Deck

There are some handy performance tips from Ben in this slide deck.

In this talk we’ll study how browsers determine which requests should be made, in what order, and what prevents the browser from rendering content quickly.

Thursday, June 7th, 2018

Fostering a Web Performance Culture - José M. Pérez

Six steps to kickstart a web performance culture:

  1. Your dev environment is not your user’s environment
  2. It’s better to learn the fundamentals than the library
  3. Get the time to experiment and validate
  4. Educate your colleagues
  5. Share and celebrate success (and failure) stories
  6. Make performance part of your workflow

Saturday, March 10th, 2018

It’s Dangerous to Go Stallone. Take Glyphhanger | Filament Group, Inc., Boston, MA

You’ll need to be comfortable with using the command line, but this is a very useful font subsetting tool from those clever folks at Filament Group.

Thursday, January 18th, 2018

Finding Dead CSS – CSS Wizardry

Here’s a clever idea from Harry if you’re willing to play the long game in tracking down redundant CSS—add a transparent background image to the rule block and then sit back and watch your server logs for any sign of that sleeper agent ever getting activated.

If you do find entries for that particular image, you know that, somehow, the legacy feature is potentially still accessible—the number of entries should give you a clue as to how severe the problem might be.

Thursday, November 9th, 2017

The Contrast Swap Technique: Improved Image Performance with CSS Filters | CSS-Tricks

A clever performance trick for images:

  1. Reduce image contrast using a linear transform function (Photoshop can do this)
  2. Apply a contrast filter in CSS to the image to make up for the contrast removal

Wednesday, November 1st, 2017

Rebuilding slack.com – Several People Are Coding

A really great case study of a code refactor by Mina, with particular emphasis on the benefits of CSS Grid, fluid typography, and accessibility.

Monday, October 2nd, 2017

Essential Image Optimization

Following on from Amber’s introduction, here’s a really in-depth look at image formats, compression and optimisation techniques from Addy.

This is a really nicely put together little web book released under a Creative Commons licence.

When Should You Use Which Image Format? JPG? PNG? SVG?

Amber has been investigating which image formats make sense for which situations.

Choosing image format is only one step towards optimising images on the web. There are many, many other steps to consider, and so, so much to learn!

Sunday, March 12th, 2017

WebPonize - webponize.github.io

A Mac app for converting PNGs and JPEGs to WebP.

Thursday, February 9th, 2017

Performance Under Pressure - performance, responsive web design - Bocoup

The transcript of a really great—and entertaining—talk on performance by Wilto. I may have laughed out loud at points.

Most of the web really sucks if you have a slow connection

Just like many people develop with an average connection speed in mind, many people have a fixed view of who a user is. Maybe they think there are customers with a lot of money with fast connections and customers who won’t spend money on slow connections. That is, very roughly speaking, perhaps true on average, but sites don’t operate on average, they operate in particular domains.

Tuesday, March 15th, 2016

Managing Mobile Performance Optimization – Smashing Magazine

Some solid sensible advice on optimising performance.

Sunday, February 28th, 2016

Preload: What Is It Good For? – Smashing Magazine

A comprehensive overview of rel="preload" which looks very useful indeed …I just wish it wasn’t (like “nofollow”) a nonsensical value for the rel attribute: a resource can’t have a relationship of “preload” to the linking document.

Tuesday, December 8th, 2015

briangonzalez/fontprep

The missing font generator for Mac OS X.

Very handy for subsetting fonts for the web. It doesn’t (yet) export WOFF2 unfortunately.

Thursday, November 19th, 2015

Tips for Creating and Exporting Better SVGs for the Web

Sara enumerates some handy tips aimed squarely at designers exporting SVGs. It focuses on Illustrator in particular but I’m sure a lot of this could equally apply to Sketch.