Monthly Archives: June 2013

Browsers – Broken By Design

I set out a few hours ago to write about a problem I had experienced in Safari, Chrome, Firefox, and Internet Explorer. Opera worked as I expected, which had me convinced the other vendors merely dropped the ball, and shipped partial implementations for the :visited and :link pseudo-classes.

My CSS was very simple:

:link {
    color: white;
    background: red;

:link::before {
    content: "Pseudo: ";

A color set for unvisited links, followed by some content in the ::before pseudo element on all unvisited links. So when I dropped in two links (one visited, one not) I expected to see the following:

image00 copy

Instead, what I saw was a litter of inconsistent results between Chrome, Safari, Internet Explorer, Firefox, and Opera. The above image came from Opera. It performed exactly as I suspected. The others, not so much.

Chrome and Firefox gave similar results; both set “Pseudo” as a virtual first-child of both anchors (though I only asked to have it on unvisited links), and leaked the background color from :link into :visited.

Internet Explorer did better than Chrome and Firefox; it preserved the “pseudo” text, but left the background of the visited link untouched. I was still very perplexed as to why it was spilling values from :link over into :visited.

You can observe something interesting in Internet Explorer – :visited links start visually identical to :link links, but are transitioned into their :visited state immediately thereafter. Setting a transition on all links reveals the change when the document loads:

a {
    transition: background 10s;

You’ll see the :link links remain unchanged but :visited links slowly adopt their end style. This is not the case for Chrome, Firefox, Opera, or Safari.

Safari appeared to be the most broken of them all. It duplicated everything. Further, I attempted to set additional styles to :visited, and it completely ignored them.

Discovering History

I found it incredible that all of these browsers, with the exception of Opera, would get this so wrong. So like any good developer I took to the web to see who else might be complaining about this, which is when I came across a Stack Overflow post suggesting this was somehow related to security concerns.

This offered another search vector; security issues. That was the needed catalyst for opening up a fascinating story about yet another creative attempt by developers to put their nose where it may not belong – in the client browser’s history.

Browsers typically style links with a default color to indicate whether it is a visited link or not. We’ve all seen those blue and purple links before – they’ve become quite at home on the web. Somebody got the (seriously) brilliant idea to create anchors ad hoc, and use getComputedStyle to see if the links represented visited or unvisited locations.

Mozilla reports that you could test more than 200,000 urls every minute with this approach. As such, you could – with a great deal of accuracy – fingerprint the user visiting your site based on the other urls they have visited; and browser history runs deep.

Scorched Earth Solution

The solution implemented by Firefox (and apparently others) was to greatly reduce the presence of visited links. They started by instructing functions like getComputedStyle and querySelectorAll to lie (their words, not mine) about their results. Sure enough, a simple check confirms that though my :visited links have a different font color than :link links, getComputedStyle says they’re the same rgb value.

Mozilla’s Christopher Blizzard continues with a very key point (emphasis added):

You will still be able to visually style visited links, but you’re severely limited in what you can use. We’re limiting the CSS properties that can be used to style visited links to color, background-color, border-*-color, and outline-color and the color parts of the fill and stroke properties. For any other parts of the style for visited links, the style for unvisited links is used instead. In addition, for the list of properties you can change above, you won’t be able to set rgba() or hsla() colors or transparent on them.

And there it was, the explanation that tied all of the seemingly broken pieces together. The browser would instruct :visited to share property values with :link. The browsers aren’t broken; they were designed to fail.

Test Confirmations

I wanted to explore the now-understood implementation a bit further, so I tried a few things. Querying the DOM for :visited links (expecting 1 of 2) was my first decision. I also queried the DOM for :link as well – expecting 2 due to the new security:

Browser Number of :visited Number of :link
Chrome 0 2
Firefox 0 2
Internet Explorer 0 2
Safari 0 2
Opera 1 2

Nearly all of the browsers report no :visited link, with the exception of Opera. All browsers report a total of 2 links when querying :link.

So it seems like you can still get a list of visited sites in Opera. Internet Explorer, Firefox, Chrome, and Safari all prevented the exploit from being carried out. But one thing about Internet Explorer intrigued me; remember the transitioning I spoke of earlier?

Internet Explorer Still Vulnerable?

I noticed that if I set transition: background 10s on anchors in Internet Explorer you would slowly see all visited links slowly tween into their end state. Transitions fire the transitionend event when they complete, so could we still get the user’s visited links in Internet Explorer?

The CSS to test this is very simple:

a { transition: background .01s }
:link { background: red }

And the following JavaScript:

/* Anchor var, fragment, and array of guesses */
var anchor;
var fragment = document.createDocumentFragment();
var websites = [

/* Listen for completed transitions */
document.addEventListener("transitionend", function (event){
}, false);

/* Create a link for each url */
    anchor = document.createElement("a");
    anchor.setAttribute("href", url);
    anchor.innerHTML = url;
    fragment.appendChild( anchor );

/* Add our document fragment to our DOM */

Immediately upon being added to the DOM our :visited anchors will start to transition away from looking like a :link anchor. Once that transition is complete, we learn what the URL is, and confirm that the user has visited that site.

Closing Thoughts

I was reminded today just how exciting our industry is. People are constantly experimenting, learning new things, and sharing that knowledge. Industry experts, developers, designers, and browser vendors are always working to shift and adjust in light of the ever-evolving web.

Although the CSS2.1 Specification says something, that doesn’t make it so – even if the feature is 15 years old. If the ends justify the means, browser vendors will (and did) fire-bomb their own code-base to protect the end user.

Finally, we’re all in this together; we ought to work together. Microsoft launched the @IEDevChat twitter account not too long ago to assist developer’s who are attempting to follow web-standards. Then even organized a group of developers who wanted to volunteer and help build a better web; you can find (and join) it online at

I’m sure there’s more history here that I’ve yet to discover, but what I have seen is enough to pique my interest. If you have anything else to share, or can contribute to the vulnerability test approach above, please leave a comment below. I may swing back around and check out the other browsers later on.

Designing with Pseudo Elements in IE10

Pseudo Elements in IE10

When Internet Explorer 10 came onto the scene as one of the first desktop browsers engineered for touch, it brought with it a few upgrades to many form elements. Input fields began, overnight, to render with their own clear buttons, causing some anguish among designers who had already provided similar functionality on their own.


It wasn’t long until Stack Overflow, and other communities, began hearing the groans of web designers wanting to know how they can turn off these new progressive enhancements. But what initially appeared to be a nuisance is actually a great opportunity. These new pseudo elements give us more control than ever before.

Quick Brushup

Pseudo elements are parts of the document that are not declared in our markup, but are provided by the browser when rendering certain elements. For instance, pseudo-elements exist that represent the ::first-line of text in a paragraph. This requires no additional markup to function, but gives us great control over how things look.


I would like to cover nearly 20 pseudo elements in the remainder of this article, demonstrating with each what type of effect(s) we can achieve in our presentation.

Here’s a list of what we’re going to cover:

::after ::before
::first-letter ::first-line
::-ms-browse ::-ms-value
::-ms-check ::-ms-clear
::-ms-expand ::-ms-fill
::-ms-fill-lower ::-ms-fill-upper
::-ms-reveal ::-ms-thumb
::-ms-ticks-after ::-ms-ticks-before
::-ms-tooltip ::-ms-track

Before and After Pseudo Elements

The ::before and ::after pseudo elements create virtual children within the container (like an invisible <span> element). These appear before all other children, and after all other children, respectively. You can use these to achieve many great effects, such as fading an image out and adding text over the top of it.


The HTML for the above is very simple. It’s nothing more than an image within a figure element.

    <img src=”jonathan-sampson.jpg">

In the CSS we’re using ::after (::before is used the same way) to add a positioned element over the top of our image, give it a gradient background, and some text content.

figure {
    position: relative;

figure::after {
    /* Text and Color */
    color: white;
    font: 1em "Segoe UI";
    content: "@jonathansampson";
    text-shadow: 0 .1em .2em #004D71;
    /* Size and Placement */
    left: 0; bottom: 0;
    width: 100%; padding: 2em 0;
    display: block; position: absolute; 
    /* Background */
    background: linear-gradient(to top, white 1em, transparent);

First Line and Letter Pseudo Elements

By using the ::first-line and ::first-letter pseudo elements we can target the first line of text in a text block, as well as the first letter in that line, and modify their styles independently of their surroundings. By combining both of these, we can achieve an effect like the following:


The above consists of nothing more than a simple paragraph, as far as markup is concerned.

<p>When Internet Explorer 10 came onto the scene...</p>

The styles too are very concise and easy to understand.

p {
    font: 1em "Segoe UI";

p::first-line {
    font-weight: bold;

p::first-letter {
    font: 5em "Script";
    float: left;
    line-height: .5em;
    padding: .15em .15em 0;

Browse and Value Pseudo Elements

File uploads have always been a pain to style; in the past we didn’t have much access to the button itself. Today with the ::-ms-browse and ::-ms-value pseudo elements we can target individual parts of the file upload control and create a far better presentation than was ever possible before.


The markup here is familiar and short; it’s just a single file input.

<input type="file">

The CSS, on the other hand, is slightly more verbose since we’re targeting the input element, the browse and value pseudo elements collectively, as well as individually.

input {
    background: transparent;

::-ms-browse, ::-ms-value {
    border: 0;
    padding: 1em;
    color: rgb(71,194,254);
    background-color: rgb(1,132,195);
        linear-gradient(to bottom, transparent 1px, rgb(71, 194, 254) 1px, transparent 1em),
        linear-gradient(to top, transparent 1px, rgba(0,0,0,.2) 1px, transparent 2em);

::-ms-browse {
    font-weight: bold;
    background-color: rgb(1, 107, 157);
    border-radius: 0 .5em .5em 0;

::-ms-value {
    border-radius: .5em 0 0 .5em;

Check Pseudo Element

With ::-ms-check we now have access to the inner-part of a radio or checkbox. This means we can now modify its presentation just as easily as we could the rest of the element itself. In the example below we’ve increased padding, changed the background color of the checked-portion, updated the foreground color, and even added a subtle inner glow.


The CSS is very straightforward.

::-ms-check {
    border: 0;
    color: white;
    padding: .25em;
    background-color: rgb(1,132,195);
    box-shadow: inset 0 0 .5em rgb(71, 194, 254),

Clear and Reveal Pseudo Elements

This article opened with an example of the new ::-ms-clear pseudo element, and a short description of the frustration it has caused many designers who have already had long-standing functionality in place to clear fields. Often times designers just want it to go away.

::-ms-clear {
    display: none;

Easy enough.

Similar to the ::-ms-clear pseudo element is the ::-ms-reveal pseudo element. This is represented as a button in password fields. When pressed, and held, it reveals the password in the text box to which it is associated.

You can also set its display to none if you wish to get rid of it.

Expand Pseudo Element

The ::-ms-expand pseudo element grants you power over the button typically displayed with select menus. By leveraging this pseudo element we can round corners, set gradient backgrounds, and so much more.


I cheated here just a bit and added styles to both the select element, and the ::-ms-expand pseudo element.

select {
    color: #333;
    padding: .25em;
    border-radius: .5em;
    background-color: #f1f1f1;
        linear-gradient(to bottom, white, transparent);
    border: 1px solid rgb(71, 194, 254);

::-ms-expand {
    padding: .25em;
    margin-left: .25em;
    border-radius: 50%;
    color: rgba(0, 0, 0, .25);
    background-color: rgb(71, 194, 254);
        linear-gradient(to bottom, rgba(255, 255, 255, .8), transparent 1em);
    border: 1px solid rgba(71, 194, 254, .5);

Fill Pseudo Element

The ::-ms-fill pseudo element works with the <progress> element, which shows an advancement in a set of sequences or length of time. The “filled” portion of the progress bar is exposed to us for additional styling on top of those styles applied directly to the main element itself.

While this element, visually, isn’t as complex as others we can still have some fun with it.


progress {
    border: 0;
    height: 1.5em;
    border-radius: .25em;
    background-color: #f1f1f1;

::-ms-fill {
    border: 0;
        linear-gradient(to top, transparent 1px, rgba(255,255,255,.5) 1px, transparent 1em),
        linear-gradient(to left, rgba(0,0,0,.3) 3px, transparent 3px),
        linear-gradient(to right, rgba(0, 0, 0, .3), transparent);

Fill Upper/Lower, Ticks Before/After, Thumb, Tooltip, and Track Pseudo Elements

The range control is full of pseudo elements. The right side of the range, the left, the (optionally visible) ticks above or beside the control, the track itself, the popup tooltip, and the handle to change the value. In the following image you can see nearly every pseudo element adjusted in some way, shape, or form (tooltip not visible).


The upper fill was given a slight glimmer while the lower fill was left solid. The ticks before (above the slider) and after (below) were made lighter. The thumb was rounded, given a slight gradient for depth, and a hollow-looking center. Lastly the track pseudo element was given white, semi-opaque, markers.

::-ms-tooltip {
    display: none;

::-ms-ticks-before, ::-ms-ticks-after {
    color: #999;
    display: block;

::-ms-ticks-before {
    background: linear-gradient(to top, #CCC, transparent 30%);

::-ms-ticks-after {
    background: linear-gradient(to top, transparent 70%, #CCC);

::-ms-fill-upper {
    background-color: rgb(1, 107, 157);
        linear-gradient(to bottom, transparent 1px, rgba(255,255,255,.25) 1px, transparent 70%);

::-ms-fill-lower {
    background-color: rgb(1,132,195);

::-ms-thumb {
    background-color: white;
        radial-gradient(circle, rgb(1, 107, 157) 20%, transparent 20%),
        linear-gradient(to top, #CCC, white);
    border-radius: 50%;
    border: 0;

::-ms-track {
    color: rgba(255, 255, 255, .5);

Selection Pseudo Element

The last pseudo element we’re going to look at is the ::selection pseudo element. This represents any selection of text in the document. The control you have over this is extended to the foreground color, and background color of the selection.


By default selected text is white with a blue background. In the example above we have changed the text to black, and the background to hot pink (in true Irish fashion).

::selection {
    color: black;
    background: pink;


We’ve looked at nearly every pseudo element available in Internet Explorer 10, as well as a few types of modifications we can make to the UI by leveraging their presence in the document. It’s important to note that different browsers may have different pseudo elements you’ll have to target in order to modify the same (or similar) document elements. This post was merely an exploration of those that presently exist in Internet Explorer.

If you have any questions about the above examples, please feel free to reach out to myself, or any of my fellow IE User Agents. You can do so by leaving a comment below on this post, or tagging your tweet with the #IEUserAgents hashtag (we’re listening). If you have questions about general development and Internet Explorer, follow and interact with @IEDevChat on twitter.

If you would like access to Internet Explorer from your Mac to test these features, you can use BrowserStack, or download a free Virtual Machine from I use both methods regularly – I would encourage the virtual machine route if you have the space/memory.

That’s it. Go change the web.

Display: Grid – The Future of Responsive Grid Layouts

Brief History

The history of front-end design strategies is a wild thing to study. We started with linear page-outlines, largely consisting of a wall of text and hyperlinks. We later got clever and began co-opting <table> to give us more control over page layouts. We should have all been smacked for doing it, but it was the convention at the time.

When tables began to be more of a nuisance than a solution the community started leveraging floats, and working to define their design requirements in terms of laterally-shifted elements that sat next to one another. Of course that too presented a new set of problems – we had to perform an embarrassing amount of CSS acrobatics to clear our floats, or achieve something as simple as the Holy Grail of layouts (which was trivial with <table>).

Things got better; tried and true conventions and approaches were packaged up into wildly popular frameworks like Nathan Smith’s 960 Grid System, and appeared to have solved all of our problems for a short while. But the fact remained that while we had comfort, it came at the cost of meaningless additional markup, and cryptic classnames. The DOM was getting noisy.

Introducing Grid Layouts

Browser vendors and standards bodies took it upon themselves to start working on alternative, more reliable solutions. With the release of Internet Explorer 10 we saw the first major browser implement a CSS-based Grid System.

For the first time, we are able to author our content as it ought to be, without nesting it in arbitrary ad-hoc divs to give ourselves a little advantage in CSS. We can now turn simple markup into easily-manipulated sophisticated layouts.

No more absolutely positioned elements, pointless margins or padding, etc. CSS Grids completely liberate you – the designer – from having to wrestle with the layout engine to get the effect you want without forcing you to compromise on your markup or CSS.

Defining Columns and Rows

The CSS is remarkably very simple to grok; and if you’ve ever spent any time in the past wiggling through tables, you’ll find much of the code very familiar-sounding. We start by setting an element up as our grid container. In the code above, I used the body element:

body {
  display: -ms-grid;

Because this technology is still experimental, you can only access it by using the -ms- prefix. Once we have set our display mode to -ms-grid, we have to define our columns and rows. This too is very straightforward:

body {
  display: -ms-grid;
  -ms-grid-rows: 100px 200px 1fr;
  -ms-grid-columns: 1fr 150px;

This results in a grid that has three rows, and two columns. Think of a table that has three table rows, and two table cells in each row. Our first row is 100px tall. Our second is 200px tall. Lastly, our third row is the full remaining fractional value; so whatever is left over after 300px is taken away, that will be the height of our third row.

We took a similar approach for our columns. Our first column takes the remainder of the horizontal space left over after 150 pixels have been given to our second column. At this point, your design will be mangled beyond recognition. Until you specify where each element ought to reside, they will all be tossed into row one, column one – do you even grid, bro?

Placing and Sizing Grid Items

Once you have your rows and columns defined, it’s trivial to move your elements around from any column or row to another. For instance, suppose we wanted to move our <h1> element into the first row, and have it span both columns:

h1 {
  -ms-grid-row: 1;
  -ms-grid-column: 1;
  -ms-grid-column-span: 2;

It’s so straightforward that it requires no explanation.

Not only can we specify which column and row our element resides in, we can also instruct our element to span additional columns and rows to better align our grid contents as we see fit.

Your main bag of tools consists of the following properties:

Property Description
-ms-grid-row target row
-ms-grid-row-align horizontal alignment
-ms-grid-row-span number of rows to span
-ms-grid-column Target column
-ms-grid-column-align Vertical alignment
-ms-grid-column-span Number of columns to span

The alignment properties accept values such as start, end, center, and stretch. In a left-to-right layout, start will align the element to the left while end will align it to the right. Stretch will cause the element to consume all available space in the grid location. By default grid items are stretch, so don’t freak out if an image initially looks wonky.

Responsive Grids

With this much control over the layout in our CSS, you can imagine the amount of flexibility we have when we add media queries into the mix. All of a sudden, we can rearrange everything when in portrait mode as opposed to landscape, or desktop as opposed to mobile.

Below I created a simple example that shifts the layout around above and below the 400 pixel mark. In the left image we have more of a “mobile” experience, and in the right we’ve rearranged the elements (without touching the markup, woot) to present a wider experience.


Here are the two media queries. Note the small amount of changes needed to completely restructure things.

body {
  -ms-grid-columns: 50% 50%;
  -ms-grid-rows: auto auto 1fr;

@media screen and (max-width: 400px) {
  nav  {
    -ms-grid-row: 2;
    -ms-grid-column: 1;
    -ms-grid-row-align: center;
    -ms-grid-column-align: center;
  h1 {
    -ms-grid-row: 1;
    -ms-grid-column: 1;
    -ms-grid-column-span: 2;
    -ms-grid-row-align: center;
    -ms-grid-column-align: center;
  img {
    -ms-grid-row: 2;
    -ms-grid-column: 2;
  article {
    -ms-grid-row: 3;
    -ms-grid-column: 1;
    -ms-grid-column-span: 2;

@media screen and (min-width: 400px) {
  nav  {
    -ms-grid-row: 3;
    -ms-grid-column: 2;
  h1 {
    -ms-grid-row: 2;
    -ms-grid-column: 2;
  img {
    -ms-grid-row: 1;
    -ms-grid-column: 2;
  article {
    -ms-grid-row: 1;
    -ms-grid-column: 1;
    -ms-grid-row-span: 3;

I have purposefully kept the examples here relatively simple, but only because I don’t feel this requires a great deal of explanation to get my point across – grids are freaking amazing.

In this short introduction we’ve seen how to create a grid container, assign arbitrary numbers of columns and rows with various dimensions. We placed elements, moved them around, and dynamically updated their properties to completely reconfigure our layout.
In the midst of all this excitement, there is a bit of bad news (isn’t there always?).

The Caveat

As of writing this the only browser to currently support CSS Grids is Internet Explorer 10. This means all of the code from above will have no effect in Chrome, Firefox, Opera, or any of the other major browsers. Check for most recent changes.

If you are interested in developing Windows Store Applications with HTML, CSS, and JavaScript, you can definitely put this feature into your bag of tricks to ensure your app looks and feels the way you expect.

Although you can’t put it to much use on the open web, it is still good to begin developing a familiarity with the technology as the W3C Grid Layout spec is in the works and will hopefully find its way to Candidate Recommendation in the future.

Need More Direction?

If you’re looking for some assistance with any of the above content, or even with IE’s implementation of CSS Grids, you have a few places you can go to get assistance. Stack Overflow is almost always my first suggestion, though it currently doesn’t have much content around IE’s CSS Grids implementation (likely to change in the near future).

Another great place to look would be the @IEDevChat account on twitter. Additionally, if you want to get the attention of the User Agents (of you can tag your tweet with #IEUserAgents. This notifies a developer experienced in Internet Explorer to come and assist you. Sweet deal, right?

On a Mac? Don’t have Internet Explorer 10? You’re not out of luck – you can test all of these features using Additionally, you can download a free virtual machine with IE10 from I happen to be working on this demo in a virtual machine, and the performance is stellar on my MacBook Air in Parallels.

That’s it. Go be awesome.

Taming the Lawless Web with Feature Detection

The Lawless Web

Over the past 15 years or so that I’ve been developing websites, I’ve seen various conventions come and go. Common practices arise, thrive for a while, and die. I, myself, spent a great portion of my past hammering out lines of tabular markup (and teaching classrooms to do the same) when working on my layout.

When I wasn’t building complicated table-based layouts littered with colspans, I was double-wrapping elements to iron out the differences between browser-interpretations of the box-model.

Fortunately, these practices have died, and others like them continue to die every day.

The Web Hasn’t Been Completely Tamed

While atrocities like table-based layouts are quickly becoming a thing of the past, other old habits have chosen not to go as peacefully. One that has managed to stick around for some time is user-agent sniffing; the practice of inferring a browser’s abilities by reading an identification token.

var browser = {
     vendor: navigator.userAgent.match(/Chrome|Mozilla|Opera|MSIE/),
    version: navigator.userAgent.match(/\d+/)

if ( browser.vendor == “Mozilla” && browser.version == 5 ) {
    // This matched Chrome, Internet Explorer, and a Playstation!
    // Nailed it.

Since shortly after the dawn of the epoch, developers have been scanning the browser’s navigator.userAgent string for bits and pieces of data. They then couple this with a knowledge of which browsers support which features, and in conclusion make judgements against the user’s browser and machine. Sometimes their conclusions are correct, but the ends don’t justify the means.

Don’t Gamble With Bad Practices

Sniffing a browser’s user agent string is a bit like playing Russian Roulette. Sure, you may have avoided the loaded chamber this time, but if you keep playing the game you will inevitably increase your chances of making a rather nasty mistake.

The navigator.userAgent string is not, and has never been, immutable. It changes. It gets modified. As browsers are released, as new versions are distributed, as browsers are installed on different operating systems, as software is installed in parallel to the browser, and as add-ons are installed within the browser, this string gets modified. So what you sniff today, is not what you will sniff tomorrow.

Have a quick look at a handful of examples for Chrome, Firefox, Opera, and Internet Explorer. Bottom line is that you can’t be sure what you’ll get when you approach the user agent string buffet. As is immediately clear, the above approach would not even match version 12 of Opera consistently with its variations.

So, have I thoroughly convinced you that sniffing is bad? And have you sworn it off as long as you shall live? Let me give you something to replace it; something reliable that will nearly never let you down – feature detection.

Go With What’s Reliable

Feature detection is the practice of giving the browser a test, directly related to the feature you need, and seeing whether it passes or fails. For instance, we can see if the browser supports the <video> tag by quizzing it on whether it places the correct properties on a freshly-created instance of the element. If the browser fails to add the .canPlayType method to the element, we can assume support isn’t there, or isn’t sufficient to be relied upon.

This approach doesn’t require us to make any assumptions. We don’t couple poorly-scavenged data with naive assumptions about which browsers support which feature. Rather, we invite the browser out onto our stage, and we demand it do tricks. If it succeeds, we reward it. If it fails, we ditch it and take another approach.

What Does “Reliable” Look Like?

So how exactly do we quiz the browser? Feature-detections come in all shapes and sizes; some very small and concise, while others can be somewhat lengthy and verbose – it all depends on what feature you’re trying to test for. Working off of our example of checking for <video> support, we could do the following:

if ( document.createElement(“video”).canPlayType ) {
    // Your browser supports the video element
} else {
    // Aw, man. Gotta load Flash.

This approach creates a brand new video element for testing. We then check for the presence of the .canPlayType method. If this property exists, and points to a function, the expression will be truthy and our test will pass. If the browser doesn’t understand what a video element is, there won’t be a .canPlayType method, and this property will instead be undefined – which is falsy.

The Work Has Been Done For You

You could be rightly freaked out about now, thinking about all of the tests you would have to write. You might want to see if localStorage is supported, gradients, video, audio, or geolocation. Who on Earth has time to write all of those tests? Let alone learn the various technologies intimately enough to do so? This is where the community has saved the day.

Modernizr is an open-source library packed full of feature-detection tests authored by dozens of talented developers, and all bundled up in an easy to use solution that you can drop into any new project. You build your custom download of Modernizr, drop it into your project, and then conditionally deliver the best possible experience to all visitors.

Modernizr exposes a global Modernizr object with various properties. You can test for the support of certain features simply by calling properties on the Modernizr object.

if ( ) {
    // Browser supports the video element

Additionally, it can optionally add classes to your <html> element so your CSS can get in on the action too! This allows you to make conditional adjustments to your document based upon feature support. {
    /* Woot! Video support. */
} #custom-video-controls {
    /* Bummer. No video support. */
    display: none;

Building A Better Web

By using feature-detection, and forever turning your back on user agent sniffing, you create a more reliable web that more people on more devices and browsers can enjoy. No longer are you bound to hundreds upon hundreds of user agent strings, or naive assumptions that will come back and bite you in the end. Feature-detection liberates you so that no babysitting of the browser landscape is necessary.

Code for features and APIs. Don’t code for specific browsers. Don’t get caught writing “Best viewed in WebKit” code – build something for everybody. When you focus on features, rather than ever-changing strings that don’t give you much insight, you help make the Internet better for us all. Do it for the children ;)

You’re Not Alone

When you set out to do things the right way, you will undoubtedly run into obstacles and complications. Let’s face it, quality work often times requires more of an investment than the slop that is so often slung out onto the web. The great news though is that you’re not alone – the web is more open than ever before, full of those willing to help you along the way.

Drop in to Stack Overflow to catch up on the various feature detection questions being asked there. Or if you’re trying to get Chrome and Internet Explorer to play nice with one another, post a question on Twitter using the #IEUserAgents hashtag. This notifies an “agent” to come to your aid.

Just be sure to pay it forward. As you learn, and grow, help others to do so as well. Maybe even write a few feature-tests and contribute them back into Modernizr along the way.