These snippets are my attempt to save and organize various bits of code, best practices, and resources relating to web development and design. They also function as a to do list of sorts, for things I want to implement in my own code, but haven't yet. The concept is inspired by Jeremy Keith's links, among other things. Enjoy.

The problems with feature detection

The principle of feature detection is really simple. Before you use a particular API you test if it is actually available. If it is not, you can provide an alternative or fail gracefully. Why is this necessary? Well, unlike HTML and CSS, JavaScript can be very unforgiving. If you would use an API without actually testing for its existence and assume it just works you risk that your script will simply throw an error and die when it tries to call the API.

Take the following example:


if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(function(pos) {
        alert('You are at: ' + pos.coords.latitude + ', ' + pos.coords.longitude);

Before we call the getCurrentPosition() function, we actually check if the Geolocation API is available. This is a pattern we see again and again with feature detection.

If you look carefully you will notice that we don’t actually test if the getCurrentPosition() function is available. We assume it is, because navigator.geolocation exists. But is there actually a guarantee? No.


Permalink to this heading.Cutting the mustard

There is another principle that has gotten very popular lately. By using some very specific feature tests you can make a distinction between old legacy browsers and modern browsers.


if ('querySelector' in document
    && 'localStorage' in window
    && 'addEventListener' in window) 
    // bootstrap the javascript application

In itself it is a perfectly valid way make sure the browser has a certain level of standards support. But at the same time also dangerous, because supporting querySelector, localStorage and addEventListener doesn’t say anything about supporting other standards.

Even if the browser passes the test, you really still need to do proper feature detection for each and every API you are depending on.


There are features where the whole premise of feature detection just fails horribly. Some browsers ship features that are so broken that they do not work at all. Sometimes it is a bug, and sometimes it is just pure laziness or incompetence. That may sound harsh, but I’m sure you agree with me at the end of this article.

The most benign variants are simply bugs. Everybody ships bugs. And the good browsers quickly fix them. Take for example Opera 18 which did have the API for Web Notifications, but crashed when you tried to use it. Blink, the rendering engine, actually supported the API, but Opera did not have a proper back-end implementation. And unfortunately this feature got enabled by mistake. I reported it and it was fixed in Opera 19. These things happen.


Introducing Resilient Web Design

I wrote a thing. The thing is a book. But the book is not published on paper. This book is on the web. It’s a web book. Or “wook” if you prefer …please don’t prefer. Here it is:

Resilient Web Design.

It’s yours for free.

Much of the subject matter will be familiar if you’ve seen my conference talks from the past couple of years, particularly Enhance! and Resilience. But the book ended up taking some twists and turns that surprised me. It turned out to be a bit of a history book: the history of design, the history of the web.

Resilient Web Design is a short book. It’s between sixteen and seventeen megawords long. You could read the whole thing in a couple of hours. Or—because the book has seven chapters—you could take fifteen to twenty minutes out of a day to read one chapter and you’d have read the whole thing done in a week.

If you make websites in any capacity, I hope that this book will resonate with you. Even if you don’t make websites, I still hope there’s an interesting story in there for you.

You can read the whole book on the web, but if you’d rather have a single file to carry around, I’ve made some PDFs as well: one in portrait, one in landscape.

I’ve licensed the book quite liberally. It’s released under a Creative Commons attribution share-alike licence. That means you can re-use the material in any way you want (even commercial usage) as long as you provide some attribution and use the same licence. So if you’d like to release the book in some other format like ePub or anything, go for it.

I’m currently making an audio version of Resilient Web Design. I’ll be releasing it one chapter at a time as a podcast. Here’s the RSS feed if you want to subscribe to it. Or you can subscribe directly from iTunes.

I took my sweet time writing this book. I wrote the first chapter in March 2015. I wrote the last chapter in May 2016. Then I sat on it for a while, figuring out what to do with it. Eventually I decided to just put the whole thing up on the web—it seems fitting.

Whereas the writing took over a year of solid procrastination, making the website went surprisingly quickly. After one weekend of marking up and styling, I had most of it ready to go. Then I spent a while tweaking. The source files are on Github.

I’m pretty happy with the end result. I’ll write a bit more about some of the details over the next while—the typography, the offline functionality, print styles, and stuff like that. In the meantime, I hope you’ll peruse this little book at your leisure…

Resilient Web Design.

If you like it, please spread the word.


More Proof We Don’t Control Our Web Pages

I’ve talked about this before: As web designers, we can’t trust the network. Sure, we have to contend with mobile data “dead zones” and dropped connections as our users move about throughout the day, but there’s a lot more to the network that’s beyond our control.

Here’s a roundup of some of my “favorite” network issue related headlines from the last few years:

Some of these issues can be avoided by serving content over HTTPS, but that still won’t enable you to bypass things like firewall blacklists (which led to the jQuery outage on Sky). Your best bet is to design defensively and make sure your users can still accomplish their goals on your site when some resources are missing or markup is altered.

We can’t control what happens to us in this world, we can only control our reaction to it.


You Can't Detect A Touchscreen

Whatever you may think, it currently isn't possible to reliably detect whether or not the current device has a touchscreen, from within the browser.

And it may be a long time before you can.

Let me explain why...

Permalink to this heading.Boxed in

The browser environment is a sandbox. Your app's code can only get at things the browser wants you to, in order to limit the damage a malicious website can cause.

This means that the only information about the system you can get is what the browser exposes to you, in the form of HTML, CSS and JavaScript APIs. To determine if a system supports a certain feature, we can a) see if a certain API is present, or b) see if it actually does the right thing.

Historically, two browser features have been used for "touchscreen detection": media queries and touch APIs. But these are far from foolproof.

Walk with me.

Permalink to this heading.Device width media queries

Mobiles have small screens and mobiles have touchscreens, so small screen equals touchscreen, right?


So, so very wrong. Large tablets and touchscreen laptops/desktops have clearly proven this wrong. Plus thousands of older mobile handset models had small non-touch screens. Unfortunately, sites applying the mantra "If it’s a small screen, it’s touch; if it’s a big screen, it’s mouse-driven" are now everywhere, leaving tablet and hybrid users with a rubbish experience.

Permalink to this heading.Touch APIs


If the browser supports events like touchstart (or other events in the Touch Events API spec) it must be a touchscreen device, right?


Well, maybe. The problem is, no one ever said that a non-touch device can't implement touch APIs, or at least have the event handlers in the DOM.

Chrome 24.0 shipped with these APIs always-on, so that they could start supporting touchscreens without having separate "touch" and "non-touch" builds. But loads of developers had already used detects like the example above, so it broke a lot of sites. The Chrome team "fixed" this with an update, which only enables touch APIs if a touch-capable input device is detected on start-up.

So we're all good, right?

Not quite.

Permalink to this heading.An API for an API

The browser is still quite a long way from the device itself. It only has access to the devices via the operating system, which has it's own APIs for letting the browser know what devices are connected.

While these APIs appear to be fairly reliable for the most part, we recently came across cases whereby they'd give incorrect results in Chrome on Windows 8... they were reporting presence of a touchscreen ("digitizer"), when no touchscreen was connected.

Firefox also does some kind of similar switching and it appears to fail in the same cases as Chrome, so it looks like it might use the same cues – although I can't profess to know for sure.

It appears certain settings and services can mess with the results these APIs give. I've only seen this in Windows 8 so far, but theoretically it could happen on any operating system.

Some versions of BlackBerry OS have also been known to leave the touch APIs permanently enabled on non-touch devices too.

So it looks like the browser doesn't know with 100% confidence either. If the browser doesn't know, how can our app know?

Permalink to this heading.Drawing a blank

Assuming the presence of one of these touch APIs did mean the device had a touchscreen... does that mean that if such a touch API isn't present then there definitely isn't a touchscreen?

Of course not. The original iPhone (released in 2007) was the first device to support Touch Events, but touchscreens have been around in one form or another since the 1970s. Even recently, Nokia's Symbian browser didn't support touch events until version 8.2 was released last year.

IE 10 offers the (arguably superior) Pointer Events API on touch devices instead of the Touch Events spec, so would return false for the ontouchstart test.


Neither Safari nor Opera has implemented either touch API in their desktop browsers yet, so they'll draw a blank on touch devices too.

Without dedicated touch APIs, browsers just emulate mouse events... so there are loads of devices kicking about with touchscreens which you simply can't detect using this kind of detection.


Permalink to this heading.You're doing it wrong

In my opinion, if you're trying to "detect a touchscreen" in the first place, you're probably making some dangerous assumptions.


Permalink to this heading.So what should I do?

For layouts, assume everyone has a touchscreen. Mouse users can use large UI controls much more easily than touch users can use small ones. The same goes for hover states.

For events and interactions, assume anyone may have a touchscreen. Implement keyboard, mouse and touch interactions alongside each other, ensuring none block each other.


Front-End Performance Checklist 2017

This is an incredibly exhaustive list of performance tweaks, improvements, and best practices. Some may be outside the scope of smaller websites, but there are plenty of things for everyone.

Back in the day, performance was often a mere afterthought. Often deferred till the very end of the project, it would boil down to minification, concatenation, asset optimization and potentially a few fine adjustments on the server’s config file. Looking back now, things seem to have changed quite significantly.

Performance isn’t just a technical concern: It matters, and when baking it into the workflow, design decisions have to be informed by their performance implications. Performance has to be measured, monitored and refined continually, and the growing complexity of the web poses new challenges that make it hard to keep track of metrics, because metrics will vary significantly depending on the device, browser, protocol, network type and latency (CDNs, ISPs, caches, proxies, firewalls, load balancers and servers all play a role in performance).

So, if we created an overview of all the things we have to keep in mind when improving performance — from the very start of the process until the final release of the website — what would that list look like? Below you’ll find a (hopefully unbiased and objective) front-end performance checklist for 2017 — an overview of the issues you might need to consider to ensure that your response times are fast and your website smooth.


Don't go single-page-app too soon, or how GitHub reimplementing navigation in JavaScript loses streaming capability

A few weeks ago I was at Heathrow airport getting a bit of work done before a flight, and I noticed something odd about the performance of GitHub: It was quicker to open links in a new window than simply click them.


When you load a page, the browser takes a network stream and pipes it to the HTML parser, and the HTML parser is piped to the document. This means the page can render progressively as it's downloading. The page may be 100k, but it can render useful content after only 20k is received.

This is a great, ancient browser feature, but as developers we often engineer it away. Most load-time performance advice boils down to "show them what you got" - don't hold back, don't wait until you have everything before showing the user anything.

GitHub cares about performance so they server-render their pages. However, when navigating within the same tab navigation is entirely reimplemented using JavaScript. Something like…


// …lots of code to reimplement browser navigation…
const response = await fetch('');
const html = await response.text();
document.querySelector('.content').innerHTML = html;
// …loads more code to reimplement browser navigation…

This breaks the rule, as all of is downloaded before anything is done with it. The server-rendered version doesn't hoard content this way, it streams, making it faster. For GitHub's client-side render, a lot of JavaScript was written to make this slow.

I'm just using GitHub as an example here - this anti-pattern is used by almost every single-page-app.

Switching content in the page can have some benefits, especially if you have some heavy scripts, as you can update content without re-evaluating all that JS. But can we do that without losing streaming?


Permalink to this heading.Newline-delimited JSON

A lot of sites deliver their dynamic updates as JSON. Unfortunately JSON isn't a streaming-friendly format. There are streaming JSON parsers out there, but they aren't easy to use.

So instead of delivering a chunk of JSON:


  "Comments": [
    {"author": "Alex", "body": "…"},
    {"author": "Jake", "body": "…"}

…deliver each JSON object on a new line:


{"author": "Alex", "body": "…"}
{"author": "Jake", "body": "…"}

This is called "newline-delimited JSON" and there's a sort-of standard for it. Writing a parser for the above is much simpler. In 2017 we'll be able to express this as a series of composable transform streams:


const response = await fetch('comments.ndjson');
const comments = response.body
  // From bytes to text:
  .pipeThrough(new TextDecoder())
  // Buffer until newlines:
  // Parse chunks as JSON:
for await (const comment of comments) {
  // Process each comment and add it to the page:
  // (via whatever template or VDOM you're using)

…where splitStream and parseJSON are reusable transform streams. But in the meantime, for maximum browser compatibility we can hack it on top of XHR.

Again, I've built a little demo where you can compare the two, here are the 3g results:

A table of initial load times for the various methods tried: XHR + innerHTML at 2s, Streaming iframe hack at 0.5s, XHR + JSON at 2.1s, and XHR + ND-JSON at 0.6s.

Versus normal JSON, ND-JSON gets content on screen 1.5 seconds sooner, although it isn't quite as fast as the iframe solution. It has to wait for a complete JSON object before it can create elements, you may run into a lack-of-streaming if your JSON objects are huge.

Permalink to this heading.Don't go single-page-app too soon

As I mentioned above, GitHub wrote a lot of code to create this performance problem. Reimplementing navigations on the client is hard, and if you're changing large parts of the page it might not be worth it.


[A] simple no-JavaScript browser navigation to a server rendered page is roughly as fast. The test page is really simple aside from the comments list, your mileage may vary if you have a lot of complex content repeated between pages (basically, I mean horrible ad scripts), but always test! You might be writing a lot of code for very little benefit, or even making it slower.


An Intro to Monkey Testing with Gremlins.js

A common idiom in our industry is, "You never can predict how the user will use your product once they get it in their hands." If you've ever watched a stakeholder use a website or web application for the first time, you may know this firsthand. I can't count the number of times I've seen a user seemingly forget how to use websites on a mobile device, or try to use it in a way that makes you think, "But no one would actually do that in real life!"

The thing is, you never really do know what a user may do in the moment. They might be in a frantic state of mind, trying to accomplish something too quickly, and don't tap or type the way a calm, focused user might. This fits right into the all-too-common scenario of designing and developing for the best case scenario, and not thinking about edge cases or "what happens if things don't happen perfectly in this order?" As developers, we tend to build things thinking that everything will be understood, that the user is rational and should just know that tapping around too quickly might cause something weird to happen. It can even affect those who might make accidental taps or clicks when not giving an app full attention - how many times have you accidentally tapped on a mobile device when you were walking and talking while also trying to reply to a tweet or email.

Building out tools to help us test the unpredictable aren't entirely new. In 2012, Netflix had open-sourced their internal service Chaos Monkey, which "terminates virtual machine instances and containers that run inside of your production environment." In plain language, it's a service that tears down servers at random to ensure an entire system doesn't violently collapse during a failure. Our development communities also remind us to not just design for "the happy path", but how can we actually detect for unpredicted points of failure in our interfaces the way we can with our server architectures?

If a hundred monkeys at typewriters can write the works of Shakespeare, then one monkey should surely be able to find bugs and problems in our interfaces.

Permalink to this heading.Bring in the monkeys

Monkey testing is a method of testing that generates random user input - clicks, swipes, entering input - with the sole purpose of finding issues with, or entirely breaking, your application. Unlike unit and acceptance testing, where you are writing test cases that occur in a specific order or set of conditions, which ultimately creates bias in how your interface is tested. Developers have less control over how a monkey test will execute, and since they are random every time they are run, you'll never be testing for just one scenario, but rather an infinite combination of interactions.

Although this type of testing is available for most technology stacks, things built for the web haven't necessarily got there yet. For example, the Android SDK has a UI Exerciser Monkey that handles most interface-level and system-level events. As web developers have begun to think more critically about performance and stress testing, some of these ideas have finally made it over to the world of the web in the form of Gremlins.js, a JavaScript-based monkey testing library written by the team at Marmelab.


How Medium does progressive image loading

A screenshot of a Medium article, with the header image still loading, shown as a very blurry placeholder.

Recently, I was browsing a post on Medium and I spotted a nice image loading effect. First, load a small blurry image, and then transition to the large image. I found it pretty neat and wanted to dissect how it was done.


I have performed a WebPageTest test against this page on Medium where you can see how it loads too. And if you want to see it by yourself, open Medium’s post in your browser, disable the cache and throttle the response so it takes longer to fetch the images and you can see the effect.

Here is what is going on:

  1. Render a div where the image will be displayed. Medium uses a <div/> with a padding-bottom set to a percentage, which corresponds to the aspect ratio of the image. Thus, they prevent reflows while the images are loaded since everything is rendered in its final position. This has also been referred to as intrinsic placeholders.

  2. Load a tiny version of the image. At the moment, they seem to be requesting small JPEG thumbnails with a very low quality (e.g. 20%). The markup for this small image is returned in the initial HTML as an <img/>, so the browser starts fetching them right away.

  3. Once the image is loaded, it is drawn in a <canvas/>. Then, the image data is taken and passed through a custom blur() function You can see it, a bit scrambled, in the main-base.bundle JS file. This function is similar, though not identical, to StackBlur‘s blur function. At the same time, the main image is requested.

  4. Once the main image is loaded, it is shown and the canvas is hidden.

All the transitions are quite smooth, thanks to the CSS animations applied.