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Last week you had a chance to ask Guido van Rossum, Python's BDFL (Benevolent Dictator For Life), about all things Python and his move to Dropbox. Guido wasted no time answering your questions and you'll find his responses below.

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Wilson Page

  

When the mockups for the new Financial Times application hit our desks in mid-2012, we knew we had a real challenge on our hands. Many of us on the team (including me) swore that parts of interface would not be possible in HTML5. Given the product team’s passion for the new UI, we rolled up our sleeves and gave it our best shot.

We were tasked with implementing a far more challenging product, without compromising the reliable, performant experience that made the first app so successful.

promo-500-compr

We didn’t just want to build a product that fulfilled its current requirements; we wanted to build a foundation that we could innovate on in the future. This meant building with a maintenance-first mentality, writing clean, well-commented code and, at the same time, ensuring that our code could accommodate the demands of an ever-changing feature set.

In this article, I’ll discuss some of the changes we made in the latest release and the decision-making behind them. I hope you will come away with some ideas and learn from our solutions as well as our mistakes.

Supported Devices

The first Financial Times Web app ran on iPad and iPhone in the browser, and it shipped in a native (PhoneGap-esque) application wrapper for Android and Windows 8 Metro devices. The latest Web app is currently being served to iPad devices only; but as support is built in and tested, it will be rolled out to all existing supported platforms. HTML5 gives developers the advantage of occupying almost any mobile platform. With 2013 promising the launch of several new Web application marketplaces (eg. Chrome Web Store and Mozilla Marketplace), we are excited by the possibilities that lie ahead for the mobile Web.

Fixed-Height Layouts

The first shock that came from the new mockups was that they were all fixed height. By “fixed height,” I mean that, unlike a conventional website, the height of the page is restricted to the height of the device’s viewport. If there is more content than there is screen space, overflow must be dealt with at a component level, as opposed to the page level. We wanted to use JavaScript only as a last resort, so the first tool that sprang to mind was flexbox. Flexbox gives developers the ability to declare flexible elements that can fill the available horizontal or vertical space, something that has been very tricky to do with CSS. Chris Coyier has a great introduction to flexbox.

Using Flexbox in Production

Flexbox has been around since 2009 and has great support on all the popular smartphones and tablets. We jumped at the chance to use flexbox when we found out how easily it could solve some of our complex layouts, and we started throwing it at every layout problem we faced. As the app began to grow, we found performance was getting worse and worse.

We spent a good few hours in Chrome Developers Tools’ timeline and found the culprit: Shock, horror! — it was our new best friend, flexbox. The timeline showed that some layouts were taking close to 100 milliseconds; reworking our layouts without flexbox reduced this to 10 milliseconds! This may not seem like a lot, but when swiping between sections, 90 milliseconds of unresponsiveness is very noticeable.

Back to the Old School

We had no other choice but to tear out flexbox wherever we could. We used 100% height, floats, negative margins, border-box sizing and padding to achieve the same layouts with much greater performance (albeit with more complex CSS). Flexbox is still used in some parts of the app. We found that its impact on performance was less expensive when used for small UI components.

layout-time-with-flexbox-500_comp
Page layout time with flexbox

layout-time-without-flexbox-500_comp
Page layout time without flexbox

Truncation

The content of a fixed-height layout will rarely fit its container; eventually it has to overflow. Traditionally in print, designers have used ellipses (three dots) to solve this problem; however, on the Web, this isn’t the simplest technique to implement.

Ellipsis

You might be familiar with the text-overflow: ellipsis declaration in CSS. It works great, has awesome browser support, but has one shortfall: it can’t be used for text that spans multiple lines. We needed a solution that would insert an ellipsis at the point where the paragraph overflows its container. JavaScript had to step in.

ellipsis-500_mini
Ellipsis truncation is used throughout.

After an in-depth research and exploration of several different approaches, we created our FTEllipsis library. In essence, it measures the available height of the container, then measures the height of each child element. When it finds the child element that overflows the container, it caps its height to a sensible number of lines. For WebKit-based browsers, we use the little-known -webkit-line-clamp property to truncate an element’s text by a set number of lines. For non-WebKit browsers, the library allows the developer to style the overflowing container however they wish using regular CSS.

Modularization

Having tackled some of the low-level visual challenges, we needed to step back and decide on the best way to manage our application’s views. We wanted to be able to reuse small parts of our views in different contexts and find a way to architect rock-solid styling that wouldn’t leak between components.

One of the best decisions we made in implementing the new application was to modularize the views. This started when we were first looking over the designs. We scribbled over printouts, breaking the page down into chunks (or modules). Our plan was to identify all of the possible layouts and modules, and define each view (or page) as a combination of modules sitting inside the slots of a single layout.

Each module needed to be named, but we found it very hard to describe a module, especially when some modules could have multiple appearances depending on screen size or context. As a result, we abandoned semantic naming and decided to name each component after a type of fruit — no more time wasted thinking up sensible, unambiguous names!

An example of a module’s markup:


<div class="apple">
  <h2 class="apple_headline">{{headline}}</h2>
  <h3 class="apple_sub-head">{{subhead}}</h3>
  <div class="apple_body">{{body}}</div>
</div>

An example of a module’s styling:


.apple {}

.apple_headline {
  font-size: 40px;
}

.apple_sub-head {
  font-size: 20px;
}

.apple_body {
  font-size: 14px;
  column-count: 2;
  color: #333;
}

Notice how each class is prefixed with the module’s name. This ensures that the styling for one component will never affect another; every module’s styling is encapsulated. Also, notice how we use just one class in our CSS selectors; this makes our component transportable. Ridding selectors of any ancestral context means that modules may be dropped anywhere in our application and will look the same. This is all imperative if we want to be able to reuse components throughout the application (and even across applications).

What If a Module Needs Interactions?

Each module (or fruit) has its own markup and style, which we wrote in such a way that it can be reused. But what if we need a module to respond to interactions or events? We need a way to bring the component to life, but still ensure that it is unbound from context so that it can be reused in different places. This is a little trickier that just writing smart markup and styling. To solve this problem, we wrote FruitMachine.

Reusable Components

FruitMachine is a lightweight library that assembles our layout’s components and enables us to declare interactions on a per-module basis. It was inspired by the simplicity of Backbone views, but with a little more structure to keep “boilerplate” code to a minimum. FruitMachine gives our team a consistent way to work with views, while at the same time remaining relatively unopinionated so that it can be used in almost any view.

The Component Mentality

Thinking about your application as a collection of standalone components changes the way you approach problems. Components need to be dumb; they can’t know anything of their context or of the consequences of any interactions that may occur within them. They can have a public API and should emit events when they are interacted with. An application-specific controller assembles each layout and is the brain behind everything. Its job is to create, control and listen to each component in the view.

For example, to show a popover when a component named “button” is clicked, we would not hardcode this logic into the button component. Instead “button” would emit a buttonclicked event on itself every time its button is clicked; the view controller would listen for this event and then show the popover. By working like this, we can create a large collection of components that can be reused in many different contexts. A view component may not have any application-specific dependencies if it is to be used across projects.

Working like this has simplified our architecture considerably. Breaking down our views into components and decoupling them from our application focuses our decision-making and moves us away from baking complex, heavily dependent modules into our application.

The Future of FruitMachine

FruitMachine was our solution to achieve fully transportable view components. It enables us to quickly define and assemble views with minimal effort. We are currently using FruitMachine only on the client, but server-side (NodeJS) usage has been considered throughout development. In the coming months, we hope to move towards producing server-side-rendered websites that progressively enhance into a rich app experience.

You can find out more about FruitMachine and check out some more examples in the public GitHub repository.

Retina Support

The Financial Times’ first Web app was released before the age of “Retina” screens. We retrofitted some high-resolution solutions, but never went the whole hog. For our designers, 100% Retina support was a must-have in the new application. We developers were sick of maintaining multiple sizes and resolutions of each tiny image within the UI, so a single vector-based solution seemed like the best approach. We ended up choosing icon fonts to replace our old PNGs, and because they are implemented just like any other custom font, they are really well supported. SVG graphics were considered, but after finding a lack of support in Android 2.3 and below, this option was ruled out. Plus, there is something nice about having all of your icons bundled up in a single file, whilst not sacrificing the individuality of each graphic (like sprites).

Our first move was to replace the Financial Times’ logo image with a single glyph in our own custom icon font. A font glyph may be any color and size, and it always looks super-sharp and is usually lighter in weight than the original image. Once we had proved it could work, we began replacing every UI image and icon with an icon font alternative. Now, the only pixel-based image in our CSS is the full-color logo on the splash screen. We used the powerful but rather archaic-looking FontForge to achieve this.

Once past the installation phase, you can open any font file in FontForge and individually change the vector shape of any character. We imported SVG vector shapes (created in Adobe Illustrator) into suitable character slots of our font and exported as WOFF and TTF font types. A combination of WOFF and TTF file formats are required to support iOS, Android and Windows devices, although we hope to rely only on WOFFs once Android gains support (plus, WOFFs are around 25% smaller in file size than TTFs).

icon-font-500-compr
The Financial Times’ icon font in Font Forge

Images

Article images are crucial for user engagement. Our images are delivered as double-resolution JPEGs so that they look sharp on Retina screens. Our image service (running ImageMagick) outputs JPEGs at the lowest possible quality level without causing noticeable degradation (we use 35 for Retina devices and 70 for non-Retina). Scaling down retina size images in the browser enables us to reduce JPEG quality to a lower level than would otherwise be possible without compression artifacts becoming noticeable. This article explains this technique in more detail.

It’s worth noting that this technique does require the browser to work a little harder. In old browsers, the work of scaling down many large images could have a noticeable impact on performance, but we haven’t encountered any serious problems.

Native-Like Scrolling

Like almost any application, we require full-page and subcomponent scrolling in order to manage all of the content we want to show our users. On desktop, we can make use of the well-established overflow CSS property. When dealing with the mobile Web, this isn’t so straightforward. We require a single solution that provides a “momentum” scrolling experience across all of the devices we support.

overflow: scroll

The overflow: scroll declaration is becoming usable on the mobile Web. Android and iOS now support it, but only since Android 3.0 and iOS 5. IOS 5 came with the exciting new -webkit-overflow-scrolling: touch property, which allows for native momentum-like scrolling in the browser. Both of these options have their limitations.

Standard overflow: scroll and overflow: auto don’t display scroll bars as users might expect, and they don’t have the momentum touch-scrolling feel that users have become accustomed to from their native apps. The -webkit-overflow-scrolling: touch declaration does add momentum scrolling and scroll bars, but it doesn’t allow developers to style the scroll bars in any way, and has limited support (iOS 5+ and Chrome on Android).

A Consistent Experience

Fragmented support and an inconsistent feel forced us to turn to JavaScript. Our first implementation used the TouchScroll library. This solution met our needs, but as our list of supported devices grew and as more complex scrolling interactions were required, working with it became trickier. TouchScroll lacks IE 10 support, and its API interface is difficult to work with. We also tried Scrollability and Zynga Scroller, neither of which have the features, performance or cross-browser capability we were looking for. Out of this problem, FTScroller was developed: a high-performance, momentum-scrolling library with support for iOS, Android, Playbook and IE 10.

FTScroller

FTScroller’s scrolling implementation is similar to TouchScroll’s, with a flexible API much like Zynga Scroller. We added some enhancements, such as CSS bezier curves for bouncing, requestAnimationFrame for smoother frame rates, and support for IE 10. The advantage of writing our own solution is that we could develop a product that exactly meets our requirements. When you know the code base inside out, fixing bugs and adding features is a lot simpler.

FTScroller is dead simple to use. Just pass in the element that will wrap the overflowing content, and FTScroller will implement horizontal or vertical scrolling as and when needed. Many other options may be declared in an object as the second argument, for more custom requirements. We use FTScroller throughout the Financial Times’ Web app for a consistent cross-platform scrolling experience.

A simple example:


var container = document.getElementById('scrollcontainer');
var scroller = new FTScroller(container);

The Gallery

The part of our application that holds and animates the page views is known as the “gallery.” It consists of three divisions: left, center and right. The page that is currently in view is located in the center pane. The previous page is positioned off screen in the left-hand pane, and the next page is positioned off screen in the right-hand pane. When the user swipes to the next page, we use CSS transitions to animate the three panes to the left, revealing the hidden right pane. When the transition has finished, the right pane becomes the center pane, and the far-left pane skips over to become the right pane. By using only three page containers, we keep the DOM light, while still creating the illusion of infinite pages.

Web
Infinite scrolling made possible with a three-pane gallery

Making It All Work Offline

Not many Web apps currently offer an offline experience, and there’s a good reason for that: implementing it is a bloody pain! The application cache (AppCache) at first glance appears to be the answer to all offline problems, but dig a little deeper and stuff gets nasty. Talks by Andrew Betts and Jake Archibald explain really well the problems you will encounter. Unfortunately, AppCache is currently the only way to achieve offline support, so we have to work around its many deficiencies.

Our approach to offline is to store as little in the AppCache as possible. We use it for fonts, the favicon and one or two UI images — things that we know will rarely or never need updating. Our JavaScript, CSS and templates live in LocalStorage. This approach gives us complete control over serving and updating the most crucial parts of our application. When the application starts, the bare minimum required to get the app up and running is sent down the wire, embedded in a single HTML page; we call this the preload.

We show a splash screen, and behind the scenes we make a request for the application’s full resources. This request returns a big JSON object containing our JavaScript, CSS and Mustache templates. We eval the JavaScript and inject the CSS into the DOM, and then the application launches. This “bootstrap” JSON is then stored in LocalStorage, ready to be used when the app is next started up.

On subsequent startups, we always use the JSON from LocalStorage and then check for resource updates in the background. If an update is found, we download the latest JSON object and replace the existing one in LocalStorage. Then, the next time the app starts, it launches with the new assets. If the app is launched offline, the startup process is the same, except that we cannot make the request for resource updates.

Images

Managing offline images is currently not as easy as it should be. Our image requests are run through a custom image loader and cached in the local database (IndexedDB or WebSQL) so that the images can be loaded when a network connection is not present. We never load images in the conventional way, otherwise they would break when users are offline.

Our image-loading process:

  1. The loader scans the page for image placeholders declared by a particular class.
  2. It takes the src attribute of each image placeholder found and requests the source from our JavaScript image-loader library.
  3. The local database is checked for each image. Failing that, a single HTTP request is made listing all missing images.
  4. A JSON array of Base64-encoded images is returned from the HTTP response and stored separately in the local database.
  5. A callback is fired for each image request, passing the Base64 string as an argument.
  6. An <img> element is created, and its src attribute is set to the Base64 data-URI string.
  7. The image is faded in.

I should also mention that we compress our Base64-encoded image strings in order to fit as many images in the database as possible. My colleague Andrew Betts goes into detail on how this can be achieved.

In some cases, we use this cool trick to handle images that fail to load:


<img src="image.jpg" onerror="this.style.display='none';" />

Ever-Evolving Applications

In order to stay competitive, a digital product needs to evolve, and as developers, we need to be prepared for this. When the request for a redesign landed at the Financial Times, we already had a fast, popular, feature-rich application, but it wasn’t built for change. At the time, we were able to implement small changes to features, but implementing anything big became a slow process and often introduced a lot of unrelated regressions.

Our application was drastically reworked to make the new requirements possible, and this took a lot of time. Having made this investment, we hope the new application not only meets (and even exceeds) the standard of the first product, but gives us a platform on which we can develop faster and more flexibly in the future.

(al)

© Wilson Page for Smashing Magazine, 2013.

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Original author: 
Peter Bright

Aurich Lawson / Thinkstock

In a bid to make JavaScript run ever faster, Mozilla has developed asm.js. It's a limited, stripped down subset of JavaScript that the company claims will offer performance that's within a factor of two of native—good enough to use the browser for almost any application. Can JavaScript really start to rival native code performance? We've been taking a closer look.

The quest for faster JavaScript

JavaScript performance became a big deal in 2008. Prior to this, the JavaScript engines found in common Web browsers tended to be pretty slow. These were good enough for the basic scripting that the Web used at the time, but it was largely inadequate for those wanting to use the Web as a rich application platform.

In 2008, however, Google released Chrome with its V8 JavaScript engine. Around the same time, Apple brought out Safari 4 with its Nitro (née Squirrelfish Extreme) engine. These engines brought something new to the world of JavaScript: high performance achieved through just-in-time (JIT) compilation. V8 and Nitro would convert JavaScript into pieces of executable code that the CPU could run directly, improving performance by a factor of three or more.

Read 94 remaining paragraphs | Comments

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Original author: 
David Storey

  

Flexible box layout (or flexbox) is a new box model optimized for UI layout. As one of the first CSS modules designed for actual layout (floats were really meant mostly for things such as wrapping text around images), it makes a lot of tasks much easier, or even possible at all. Flexbox’s repertoire includes the simple centering of elements (both horizontally and vertically), the expansion and contraction of elements to fill available space, and source-code independent layout, among others abilities.

Flexbox has lived a storied existence. It started as a feature of Mozilla’s XUL, where it was used to lay out application UI, such as the toolbars in Firefox, and it has since been rewritten multiple times. The specification has only recently reached stability, and we have fairly complete support across the latest versions of the leading browsers.

There are, however, some caveats. The specification changed between the implementation in Internet Explorer (IE) and the release of IE 10, so you will need to use a slightly different syntax. Chrome currently still requires the -webkit- prefix, and Firefox and Safari are still on the much older syntax. Firefox has updated to the latest specification, but that implementation is currently behind a runtime flag until it is considered stable and bug-free enough to be turned on by default. Until then, Firefox still requires the old syntax.

When you specify that an element will use the flexbox model, its children are laid out along either the horizontal or vertical axis, depending on the direction specified. The widths of these children expand or contract to fill the available space, based on the flexible length they are assigned.

Example: Horizontal And Vertical Centering (Or The Holy Grail Of Web Design)

Being able to center an element on the page is perhaps the number one wish among Web designers — yes, probably even higher than gaining the highly prized parent selector or putting IE 6 out of its misery (OK, maybe a close second then). With flexbox, this is trivially easy. Let’s start with a basic HTML template, with a heading that we want to center. Eventually, once we’ve added all the styling, it will end up looking like this vertically and horizontally centered demo.


<!DOCTYPE html>
<html lang="en">
<head>
   <meta charset="utf-8"/>
   <title>Centering an Element on the Page</title>
</head>
<body>
   <h1>OMG, I’m centered</h1>
</body>
</html>

Nothing special here, not even a wrapper div. The magic all happens in the CSS:


html {
   height: 100%;
} 

body {
   display: -webkit-box;   /* OLD: Safari,  iOS, Android browser, older WebKit browsers.  */
   display: -moz-box;   /* OLD: Firefox (buggy) */ 
   display: -ms-flexbox;   /* MID: IE 10 */
   display: -webkit-flex;    /* NEW, Chrome 21+ */
   display: flex;       /* NEW: Opera 12.1, Firefox 22+ */

   -webkit-box-align: center; -moz-box-align: center; /* OLD… */
   -ms-flex-align: center; /* You know the drill now… */
   -webkit-align-items: center;
   align-items: center;

    -webkit-box-pack: center; -moz-box-pack: center; 
   -ms-flex-pack: center; 
   -webkit-justify-content: center;
   justify-content: center;

   margin: 0;
   height: 100%;
   width: 100% /* needed for Firefox */
} 

h1 {
   display: -webkit-box; display: -moz-box;
   display: -ms-flexbox;
   display: -webkit-flex;
   display: flex;
 
   -webkit-box-align: center; -moz-box-align: center;
   -ms-flex-align: center;
   -webkit-align-items: center;
   align-items: center;

   height: 10rem;
}

I’ve included all of the different prefixed versions in the CSS above, from the very oldest, which is still needed, to the modern and hopefully final syntax. This might look confusing, but the different syntaxes map fairly well to each other, and I’ve included tables at the end of this article to show the exact mappings.

This is not exactly all of the CSS needed for our example, because I’ve stripped out the extra styling that you probably already know how to use in order to save space.

Let’s look at the CSS that is needed to center the heading on the page. First, we set the html and body elements to have 100% height and remove any margins. This will make the container of our h1 take up the full height of the browser’s window. Firefox also needs a width specified on the body to force it to behave. Now, we just need to center everything.

Enabling Flexbox

Because the body element contains the heading that we want to center, we will set its display value to flex:


body {
   display: flex;
}

This switches the body element to use the flexbox layout, rather than the regular block layout. All of its children in the flow of the document (i.e. not absolutely positioned elements) will now become flex items.

The syntax used by IE 10 is display: -ms-flexbox, while older Firefox and WebKit browsers use display: -prefix-box (where prefix is either moz or webkit). You can see the tables at the end of this article to see the mappings of the various versions.

What do we gain now that our elements have been to yoga class and become all flexible? They gain untold powers: they can flex their size and position relative to the available space; they can be laid out either horizontally or vertically; and they can even achieve source-order independence. (Two holy grails in one specification? We’re doing well.)

Centering Horizontally

Next, we want to horizontally center our h1 element. No big deal, you might say; but it is somewhat easier than playing around with auto margins. We just need to tell the flexbox to center its flex items. By default, flex items are laid out horizontally, so setting the justify-content property will align the items along the main axis:


body {
   display: flex;
   justify-content: center;
}

For IE 10, the property is called flex-pack, while for older browsers it is box-pack (again, with the appropriate prefixes). The other possible values are flex-start, flex-end, space-between and space-around. These are start, end, justify and distribute, respectively, in IE 10 and the old specification (distribute is, however, not supported in the old specification). The flex-start value aligns to the left (or to the right with right-to-left text), flex-end aligns to the right, space-between evenly distributes the elements along the axis, and space-around evenly distributes along the axis, with half-sized spaces at the start and end of the line.

To explicitly set the axis that the element is aligned along, you can do this with the flex-flow property. The default is row, which will give us the same result that we’ve just achieved. To align along the vertical axis, we can use flex-flow: column. If we add this to our example, you will notice that the element is vertically centered but loses the horizontal centering. Reversing the order by appending -reverse to the row or column values is also possible (flex-flow: row-reverse or flex-flow: column-reverse), but that won’t do much in our example because we have only one item.

There are some differences here in the various versions of the specification, which are highlighted at the end of this article. Another caveat to bear in mind is that flex-flow directions are writing-mode sensitive. That is, when using writing-mode: vertical-rl to switch to vertical text layout (as used traditionally in China, Japan and Korea), flex-flow: row will align the items vertically, and column will align them horizontally.

Centering Vertically

Centering vertically is as easy as centering horizontally. We just need to use the appropriate property to align along the “cross-axis.” The what? The cross-axis is basically the axis perpendicular to the main one. So, if flex items are aligned horizontally, then the cross-axis would be vertical, and vice versa. We set this with the align-items property (flex-align in IE 10, and box-align for older browsers):


body {
   /* Remember to use the other versions for IE 10 and older browsers! */
   display: flex;
   justify-content: center;
   align-items: center;
}

This is all there is to centering elements with flexbox! We can also use the flex-start (start) and flex-end (end) values, as well as baseline and stretch. Let’s have another look at the finished example:

figure1.1_mini
Simple horizontal and vertical centering using flexbox. Larger view.

You might notice that the text is also center-aligned vertically inside the h1 element. This could have been done with margins or a line height, but we used flexbox again to show that it works with anonymous boxes (in this case, the line of text inside the h1 element). No matter how high the h1 element gets, the text will always be in the center:


h1 {
   /* Remember to use the other versions for IE 10 and older browsers! */
   display: flex;
   align-items: center;
   height: 10rem;
}

Flexible Sizes

If centering elements was all flexbox could do, it’d be pretty darn cool. But there is more. Let’s see how flex items can expand and contract to fit the available space within a flexbox element. Point your browser to this next example.

figure1.2_mini
An interactive slideshow built using flexbox. Larger view.

The HTML and CSS for this example are similar to the previous one’s. We’re enabling flexbox and centering the elements on the page in the same way. In addition, we want to make the title (inside the header element) remain consistent in size, while the five boxes (the section elements) adjust in size to fill the width of the window. To do this, we use the new flex property:


section {
   /* removed other styles to save space */
   -prefix-box-flex: 1; /* old spec webkit, moz */
   flex: 1;
   height: 250px;
}

What we’ve just done here is to make each section element take up 1 flex unit. Because we haven’t set any explicit width, each of the five boxes will be the same width. The header element will take up a set width (277 pixels) because it is not flexible. We divide the remaining width inside the body element by 5 to calculate the width of each of the section elements. Now, if we resize the browser window, the section elements will grow or shrink.

In this example, we’ve set a consistent height, but this could be set to be flexible, too, in exactly the same way. We probably wouldn’t always want all elements to be the same size, so let’s make one bigger. On hover, we’ve set the element to take up 2 flex units:


section:hover {
   -prefix-box-flex: 2;
   flex: 2;
   cursor: pointer;
}

Now the available space is divided by 6 rather than 5, and the hovered element gets twice the base amount. Note that an element with 2 flex units does not necessarily become twice as wide as one with 1 unit. It just gets twice the share of the available space added to its “preferred width.” In our examples, the “preferred width” is 0 (the default).

Source-Order Independence

For our last party trick, we’ll study how to achieve source-order independence in our layouts. When clicking on a box, we will tell that element to move to the left of all the other boxes, directly after the title. All we have to do is set the order with the order property. By default, all flex items are in the 0 position. Because they’re in the same position, they follow the source order. Click on your favorite person in the updated example to see their order change.

figure1.3_mini
An interactive slideshow with flex-order. Larger view.

To make our chosen element move to the first position, we just have to set a lower number. I chose -1. We also need to set the header to -1 so that the selected section element doesn’t get moved before it:


header {
   -prefix-box-ordinal-group: 1; /* old spec; must be positive */
   -ms-flex-order: -1; /* IE 10 syntax */
   order: -1; /* new syntax */
} 

section[aria-pressed="true"] {
   /* Set order lower than 0 so it moves before other section elements,
      except old spec, where it must be positive.
 */
   -prefix-box-ordinal-group: 1;
   -ms-flex-order: -1;
   order: -1;

   -prefix-box-flex: 3;
   flex: 3;
   max-width: 370px; /* Stops it from getting too wide. */
}

In the old specification, the property for setting the order (box-ordinal-group) accepts only a positive integer. Therefore, I’ve set the order to 2 for each section element (code not shown) and updated it to 1 for the active element. If you are wondering what aria-pressed="true" means in the example above, it is a WAI-ARIA attribute/value that I add via JavaScript when the user clicks on one of the sections.

This relays accessibility hints to the underlying system and to assistive technology to tell the user that that element is pressed and, thus, active. If you’d like more information on WAI-ARIA, check out “Introduction to WAI-ARIA” by Gez Lemon. Because I’m adding the attribute after the user clicks, this example requires a simple JavaScript file in order to work, but flexbox itself doesn’t require it; it’s just there to handle the user interaction.

Hopefully, this has given you some inspiration and enough introductory knowledge of flexbox to enable you to experiment with your own designs.

Syntax Changes

As you will have noticed throughout this article, the syntax has changed a number of times since it was first implemented. To aid backward- and forward-porting between the different versions, we’ve included tables below, which map the changes between the specifications.

Specification versions

Specification
IE
Opera
Firefox
Chrome
Safari

Standard
11?
12.10+ *
Behind flag
21+ (-webkit-)

Mid
10 (-ms-)

Old

3+ (-moz-)
<21 (-webkit-)
3+ (-webkit-)

* Opera will soon switch to WebKit. It will then require the -webkit- prefix if it has not been dropped by that time.

Enabling flexbox: setting an element to be a flex container

Specification
Property name
Block-level flex
Inline-level flex

Standard
display
flex
inline-flex

Mid
display
flexbox
inline-flexbox

Old
display
box
inline-box

Axis alignment: specifying alignment of items along the main flexbox axis

Specification
Property name
start
center
end
justify
distribute

Standard
justify-content
flex-start
center
flex-end
space-between
space-around

Mid
flex-pack
start
center
end
justify
distribute

Old
box-pack
start
center
end
justify
N/A

Cross-axis alignment: specifying alignment of items along the cross-axis

Specification
Property name
start
center
end
baseline
stretch

Standard
align-items
flex-start
center
flex-end
baseline
stretch

Mid
flex-align
start
center
end
baseline
stretch

Old
box-align
start
center
end
baseline
stretch

Individual cross-axis alignment: override to align individual items along the cross-axis

Specification
Property name
auto
start
center
end
baseline
stretch

Standard
align-self
auto
flex-start
center
flex-end
baseline
stretch

Mid
flex-item-align
auto
start
center
end
baseline
stretch

Old
N/A

Flex line alignment: specifying alignment of flex lines along the cross-axis

Specification
Property name
start
center
end
justify
distribute
stretch

Standard
align-content
flex-start
center
flex-end
space-between
space-around
stretch

Mid
flex-line-pack
start
center
end
justify
distribute
stretch

Old
N/A

This takes effect only when there are multiple flex lines, which is the case when flex items are allowed to wrap using the flex-wrap property and there isn’t enough space for all flex items to display on one line. This will align each line, rather than each item.

Display order: specifying the order of flex items

Specification
Property name
Value

Standard
order

Mid
flex-order
<number>

Old
box-ordinal-group
<integer>

Flexibility: specifying how the size of items flex

Specification
Property name
Value

Standard
flex
none | [ <flex-grow> <flex-shrink>? || <flex-basis>]

Mid
flex
none | [ [ <pos-flex> <neg-flex>? ] || <preferred-size> ]

Old
box-flex
<number>

The flex property is more or less unchanged between the new standard and the draft supported by Microsoft. The main difference is that it has been converted to a shorthand in the new version, with separate properties: flex-grow, flex-shrink and flex-basis. The values may be used in the same way in the shorthand. However, the default value for flex-shrink (previously called negative flex) is now 1. This means that items do not shrink by default. Previously, negative free space would be distributed using the flex-shrink ratio, but now it is distributed in proportion to flex-basis multiplied by the flex-shrink ratio.

Direction: specifying the direction of the main flexbox axis

Specification
Property name
Horizontal
Reversed horizontal
Vertical
Reversed vertical

Standard
flex-direction
row
row-reverse
column
column-reverse

Mid
flex-direction
row
row-reverse
column
column-reverse

Old
box-orient

box-direction
horizontal

normal
horizontal

reverse
vertical

normal
vertical

reverse

In the old version of the specification, the box-direction property needs to be set to reverse to get the same behavior as row-reverse or column-reverse in the later version of the specification. This can be omitted if you want the same behavior as row or column because normal is the initial value.

When setting the direction to reverse, the main flexbox axis is flipped. This means that when using a left-to-right writing system, the items will display from right to left when row-reverse is specified. Similarly, column-reverse will lay out flex items from bottom to top, instead of top to bottom.

The old version of the specification also has writing mode-independent values for box-orient. When using a left-to-write writing system, horizontal may be substituted for inline-axis, and vertical may be substituted for block-axis. If you are using a top-to-bottom writing system, such as those traditional in East Asia, then these values would be flipped.

Wrapping: specifying whether and how flex items wrap along the cross-axis

Specification
Property name
No wrapping
Wrapping
Reversed wrap

Standard
flex-wrap
nowrap
wrap
wrap-reverse

Mid
flex-wrap
nowrap
wrap
wrap-reverse

Old
box-lines
single
multiple
N/A

The wrap-reverse value flips the start and end of the cross-axis, so that if flex items are laid out horizontally, instead of items wrapping onto a new line below, they will wrap onto a new line above.

At the time of writing, Firefox does not support the flex-wrap or older box-lines property. It also doesn’t support the shorthand.

The current specification has a flex-flow shorthand, which controls both wrapping and direction. The behavior is the same as the one in the version of the specification implemented by IE 10. It is also currently not supported by Firefox, so I would recommend to avoid using it when specifying only the flex-direction value.

Conclusion

Well, that’s a (flex-)wrap. In this article, I’ve introduced some of the myriad of possibilities afforded by flexbox. Be it source-order independence, flexible sizing or just the humble centering of elements, I’m sure you can find ways to employ flexbox in your websites and applications. The syntax has settled down (finally!), and implementations are here. All major browsers now support flexbox in at least their latest versions.

While some browsers use an older syntax, Firefox looks like it is close to updating, and IE 11 uses the latest version in leaked Windows Blue builds. There is currently no word on Safari, but it is a no-brainer considering that Chrome had the latest syntax before the Blink-WebKit split. For the time being, use the tables above to map the various syntaxes, and get your flex on.

Layout in CSS is only getting more powerful, and flexbox is one of the first steps out of the quagmire we’ve found ourselves in over the years, first with table-based layouts, then float-based layouts. IE 10 already supports an early draft of the Grid layout specification, which is great for page layout, and Regions and Exclusions will revolutionize how we handle content flow and layout.

Flexbox can be used today if you only need to support relatively modern browsers or can provide a fallback, and in the not too distant future, all sorts of options will be available, so that we can use the best tool for the job. Flexbox is shaping up to be a mighty fine tool.

Further Reading

(al)

© David Storey for Smashing Magazine, 2013.

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We’ve all been there: that bit of JavaScript functionality that started out as just a handful of lines grows to a dozen, then two dozen, then more. Along the way, a function picks up a few more arguments; a conditional picks up a few more conditions. And then one day, the bug report comes in: something’s broken, and it’s up to us to untangle the mess.

As we ask our client-side code to take on more and more responsibilities—indeed, whole applications are living largely in the browser these days—two things are becoming clear. One, we can’t just point and click our way through testing that things are working as we expect; automated tests are key to having confidence in our code. Two, we’re probably going to have to change how we write our code in order to make it possible to write tests.

Really, we need to change how we code? Yes—because even if we know that automated tests are a good thing, most of us are probably only able to write integration tests right now. Integration tests are valuable because they focus on how the pieces of an application work together, but what they don’t do is tell us whether individual units of functionality are behaving as expected.

That’s where unit testing comes in. And we’ll have a very hard time writing unit tests until we start writing testable JavaScript.

Unit vs. integration: what’s the difference?

Writing integration tests is usually fairly straightforward: we simply write code that describes how a user interacts with our app, and what the user should expect to see as she does. Selenium is a popular tool for automating browsers. Capybara for Ruby makes it easy to talk to Selenium, and there are plenty of tools for other languages, too.

Here’s an integration test for a portion of a search app:

def test_search
  fill_in('q', :with => 'cat')
  find('.btn').click
  assert( find('#results li').has_content?('cat'), 'Search results are shown' )
  assert( page.has_no_selector?('#results li.no-results'), 'No results is not shown' )
end

Whereas an integration test is interested in a user’s interaction with an app, a unit test is narrowly focused on a small piece of code:

When I call a function with a certain input, do I receive the expected output?

Apps that are written in a traditional procedural style can be very difficult to unit test—and difficult to maintain, debug, and extend, too. But if we write our code with our future unit testing needs in mind, we will not only find that writing the tests becomes more straightforward than we might have expected, but also that we’ll simply write better code, too.

To see what I’m talking about, let’s take a look at a simple search app:

Srchr

When a user enters a search term, the app sends an XHR to the server for the corresponding data. When the server responds with the data, formatted as JSON, the app takes that data and displays it on the page, using client-side templating. A user can click on a search result to indicate that he “likes” it; when this happens, the name of the person he liked is added to the “Liked” list on the right-hand side.

A “traditional” JavaScript implementation of this app might look like this:

var tmplCache = {};

function loadTemplate (name) {
  if (!tmplCache[name]) {
    tmplCache[name] = $.get('/templates/' + name);
  }
  return tmplCache[name];
}

$(function () {

  var resultsList = $('#results');
  var liked = $('#liked');
  var pending = false;

  $('#searchForm').on('submit', function (e) {
    e.preventDefault();

    if (pending) { return; }

    var form = $(this);
    var query = $.trim( form.find('input[name="q"]').val() );

    if (!query) { return; }

    pending = true;

    $.ajax('/data/search.json', {
      data : { q: query },
      dataType : 'json',
      success : function (data) {
        loadTemplate('people-detailed.tmpl').then(function (t) {
          var tmpl = _.template(t);
          resultsList.html( tmpl({ people : data.results }) );
          pending = false;
        });
      }
    });

    $('<li>', {
      'class' : 'pending',
      html : 'Searching &hellip;'
    }).appendTo( resultsList.empty() );
  });

  resultsList.on('click', '.like', function (e) {
    e.preventDefault();
    var name = $(this).closest('li').find('h2').text();
    liked.find('.no-results').remove();
    $('<li>', { text: name }).appendTo(liked);
  });

});

My friend Adam Sontag calls this Choose Your Own Adventure code—on any given line, we might be dealing with presentation, or data, or user interaction, or application state. Who knows! It’s easy enough to write integration tests for this kind of code, but it’s hard to test individual units of functionality.

What makes it hard? Four things:

  • A general lack of structure; almost everything happens in a $(document).ready() callback, and then in anonymous functions that can’t be tested because they aren’t exposed.
  • Complex functions; if a function is more than 10 lines, like the submit handler, it’s highly likely that it’s doing too much.
  • Hidden or shared state; for example, since pending is in a closure, there’s no way to test whether the pending state is set correctly.
  • Tight coupling; for example, a $.ajax success handler shouldn’t need direct access to the DOM.

Organizing our code

The first step toward solving this is to take a less tangled approach to our code, breaking it up into a few different areas of responsibility:

  • Presentation and interaction
  • Data management and persistence
  • Overall application state
  • Setup and glue code to make the pieces work together

In the “traditional” implementation shown above, these four categories are intermingled—on one line we’re dealing with presentation, and two lines later we might be communicating with the server.

Code Lines

While we can absolutely write integration tests for this code—and we should!—writing unit tests for it is pretty difficult. In our functional tests, we can make assertions such as “when a user searches for something, she should see the appropriate results,” but we can’t get much more specific. If something goes wrong, we’ll have to track down exactly where it went wrong, and our functional tests won’t help much with that.

If we rethink how we write our code, though, we can write unit tests that will give us better insight into where things went wrong, and also help us end up with code that’s easier to reuse, maintain, and extend.

Our new code will follow a few guiding principles:

  • Represent each distinct piece of behavior as a separate object that falls into one of the four areas of responsibility and doesn’t need to know about other objects. This will help us avoid creating tangled code.
  • Support configurability, rather than hard-coding things. This will prevent us from replicating our entire HTML environment in order to write our tests.
  • Keep our objects’ methods simple and brief. This will help us keep our tests simple and our code easy to read.
  • Use constructor functions to create instances of objects. This will make it possible to create “clean” copies of each piece of code for the sake of testing.

To start with, we need to figure out how we’ll break our application into different pieces. We’ll have three pieces dedicated to presentation and interaction: the Search Form, the Search Results, and the Likes Box.

Application Views

We’ll also have a piece dedicated to fetching data from the server and a piece dedicated to gluing everything together.

Let’s start by looking at one of the simplest pieces of our application: the Likes Box. In the original version of the app, this code was responsible for updating the Likes Box:

var liked = $('#liked');

var resultsList = $('#results');


// ...


resultsList.on('click', '.like', function (e) {
  e.preventDefault();

  var name = $(this).closest('li').find('h2').text();

  liked.find( '.no-results' ).remove();

  $('<li>', { text: name }).appendTo(liked);

});

The Search Results piece is completely intertwined with the Likes Box piece and needs to know a lot about its markup. A much better and more testable approach would be to create a Likes Box object that’s responsible for manipulating the DOM related to the Likes Box:

var Likes = function (el) {
  this.el = $(el);
  return this;
};

Likes.prototype.add = function (name) {
  this.el.find('.no-results').remove();
  $('<li>', { text: name }).appendTo(this.el);
};

This code provides a constructor function that creates a new instance of a Likes Box. The instance that’s created has an .add() method, which we can use to add new results. We can write a couple of tests to prove that it works:

var ul;

setup(function(){
  ul = $('<ul><li class="no-results"></li></ul>');
});

test('constructor', function () {
  var l = new Likes(ul);
  assert(l);
});

test('adding a name', function () {
  var l = new Likes(ul);
  l.add('Brendan Eich');

  assert.equal(ul.find('li').length, 1);
  assert.equal(ul.find('li').first().html(), 'Brendan Eich');
  assert.equal(ul.find('li.no-results').length, 0);
});

Not so hard, is it? Here we’re using Mocha as the test framework, and Chai as the assertion library. Mocha provides the test and setup functions; Chai provides assert. There are plenty of other test frameworks and assertion libraries to choose from, but for the sake of an introduction, I find these two work well. You should find the one that works best for you and your project—aside from Mocha, QUnit is popular, and Intern is a new framework that shows a lot of promise.

Our test code starts out by creating an element that we’ll use as the container for our Likes Box. Then, it runs two tests: one is a sanity check to make sure we can make a Likes Box; the other is a test to ensure that our .add() method has the desired effect. With these tests in place, we can safely refactor the code for our Likes Box, and be confident that we’ll know if we break anything.

Our new application code can now look like this:

var liked = new Likes('#liked');
var resultsList = $('#results');



// ...



resultsList.on('click', '.like', function (e) {
  e.preventDefault();

  var name = $(this).closest('li').find('h2').text();

  liked.add(name);
});

The Search Results piece is more complex than the Likes Box, but let’s take a stab at refactoring that, too. Just as we created an .add() method on the Likes Box, we also want to create methods for interacting with the Search Results. We’ll want a way to add new results, as well as a way to “broadcast” to the rest of the app when things happen within the Search Results—for example, when someone likes a result.

var SearchResults = function (el) {
  this.el = $(el);
  this.el.on( 'click', '.btn.like', _.bind(this._handleClick, this) );
};

SearchResults.prototype.setResults = function (results) {
  var templateRequest = $.get('people-detailed.tmpl');
  templateRequest.then( _.bind(this._populate, this, results) );
};

SearchResults.prototype._handleClick = function (evt) {
  var name = $(evt.target).closest('li.result').attr('data-name');
  $(document).trigger('like', [ name ]);
};

SearchResults.prototype._populate = function (results, tmpl) {
  var html = _.template(tmpl, { people: results });
  this.el.html(html);
};

Now, our old app code for managing the interaction between Search Results and the Likes Box could look like this:

var liked = new Likes('#liked');
var resultsList = new SearchResults('#results');


// ...


$(document).on('like', function (evt, name) {
  liked.add(name);
})

It’s much simpler and less entangled, because we’re using the document as a global message bus, and passing messages through it so individual components don’t need to know about each other. (Note that in a real app, we’d use something like Backbone or the RSVP library to manage events. We’re just triggering on document to keep things simple here.) We’re also hiding all the dirty work—such as finding the name of the person who was liked—inside the Search Results object, rather than having it muddy up our application code. The best part: we can now write tests to prove that our Search Results object works as we expect:

var ul;
var data = [ /* fake data here */ ];

setup(function () {
  ul = $('<ul><li class="no-results"></li></ul>');
});

test('constructor', function () {
  var sr = new SearchResults(ul);
  assert(sr);
});

test('display received results', function () {
  var sr = new SearchResults(ul);
  sr.setResults(data);

  assert.equal(ul.find('.no-results').length, 0);
  assert.equal(ul.find('li.result').length, data.length);
  assert.equal(
    ul.find('li.result').first().attr('data-name'),
    data[0].name
  );
});

test('announce likes', function() {
  var sr = new SearchResults(ul);
  var flag;
  var spy = function () {
    flag = [].slice.call(arguments);
  };

  sr.setResults(data);
  $(document).on('like', spy);

  ul.find('li').first().find('.like.btn').click();

  assert(flag, 'event handler called');
  assert.equal(flag[1], data[0].name, 'event handler receives data' );
});

The interaction with the server is another interesting piece to consider. The original code included a direct $.ajax() request, and the callback interacted directly with the DOM:

$.ajax('/data/search.json', {
  data : { q: query },
  dataType : 'json',
  success : function( data ) {
    loadTemplate('people-detailed.tmpl').then(function(t) {
      var tmpl = _.template( t );
      resultsList.html( tmpl({ people : data.results }) );
      pending = false;
    });
  }
});

Again, this is difficult to write a unit test for, because so many different things are happening in just a few lines of code. We can restructure the data portion of our application as an object of its own:

var SearchData = function () { };

SearchData.prototype.fetch = function (query) {
  var dfd;

  if (!query) {
    dfd = $.Deferred();
    dfd.resolve([]);
    return dfd.promise();
  }

  return $.ajax( '/data/search.json', {
    data : { q: query },
    dataType : 'json'
  }).pipe(function( resp ) {
    return resp.results;
  });
};

Now, we can change our code for getting the results onto the page:

var resultsList = new SearchResults('#results');

var searchData = new SearchData();

// ...

searchData.fetch(query).then(resultsList.setResults);

Again, we’ve dramatically simplified our application code, and isolated the complexity within the Search Data object, rather than having it live in our main application code. We’ve also made our search interface testable, though there are a couple caveats to bear in mind when testing code that interacts with the server.

The first is that we don’t want to actually interact with the server—to do so would be to reenter the world of integration tests, and because we’re responsible developers, we already have tests that ensure the server does the right thing, right? Instead, we want to “mock” the interaction with the server, which we can do using the Sinon library. The second caveat is that we should also test non-ideal paths, such as an empty query.

test('constructor', function () {
  var sd = new SearchData();
  assert(sd);
});

suite('fetch', function () {
  var xhr, requests;

  setup(function () {
    requests = [];
    xhr = sinon.useFakeXMLHttpRequest();
    xhr.onCreate = function (req) {
      requests.push(req);
    };
  });

  teardown(function () {
    xhr.restore();
  });

  test('fetches from correct URL', function () {
    var sd = new SearchData();
    sd.fetch('cat');

    assert.equal(requests[0].url, '/data/search.json?q=cat');
  });

  test('returns a promise', function () {
    var sd = new SearchData();
    var req = sd.fetch('cat');

    assert.isFunction(req.then);
  });

  test('no request if no query', function () {
    var sd = new SearchData();
    var req = sd.fetch();
    assert.equal(requests.length, 0);
  });

  test('return a promise even if no query', function () {
    var sd = new SearchData();
    var req = sd.fetch();

    assert.isFunction( req.then );
  });

  test('no query promise resolves with empty array', function () {
    var sd = new SearchData();
    var req = sd.fetch();
    var spy = sinon.spy();

    req.then(spy);

    assert.deepEqual(spy.args[0][0], []);
  });

  test('returns contents of results property of the response', function () {
    var sd = new SearchData();
    var req = sd.fetch('cat');
    var spy = sinon.spy();

    requests[0].respond(
      200, { 'Content-type': 'text/json' },
      JSON.stringify({ results: [ 1, 2, 3 ] })
    );

    req.then(spy);

    assert.deepEqual(spy.args[0][0], [ 1, 2, 3 ]);
  });
});

For the sake of brevity, I’ve left out the refactoring of the Search Form, and also simplified some of the other refactorings and tests, but you can see a finished version of the app here if you’re interested.

When we’re done rewriting our application using testable JavaScript patterns, we end up with something much cleaner than what we started with:

$(function() {
  var pending = false;

  var searchForm = new SearchForm('#searchForm');
  var searchResults = new SearchResults('#results');
  var likes = new Likes('#liked');
  var searchData = new SearchData();

  $(document).on('search', function (event, query) {
    if (pending) { return; }

    pending = true;

    searchData.fetch(query).then(function (results) {
      searchResults.setResults(results);
      pending = false;
    });

    searchResults.pending();
  });

  $(document).on('like', function (evt, name) {
    likes.add(name);
  });
});

Even more important than our much cleaner application code, though, is the fact that we end up with a codebase that is thoroughly tested. That means we can safely refactor it and add to it without the fear of breaking things. We can even write new tests as we find new issues, and then write the code that makes those tests pass.

Testing makes life easier in the long run

It’s easy to look at all of this and say, “Wait, you want me to write more code to do the same job?”

The thing is, there are a few inescapable facts of life about Making Things On The Internet. You will spend time designing an approach to a problem. You will test your solution, whether by clicking around in a browser, writing automated tests, or—shudder—letting your users do your testing for you in production. You will make changes to your code, and other people will use your code. Finally: there will be bugs, no matter how many tests you write.

The thing about testing is that while it might require a bit more time at the outset, it really does save time in the long run. You’ll be patting yourself on the back the first time a test you wrote catches a bug before it finds its way into production. You’ll be grateful, too, when you have a system in place that can prove that your bug fix really does fix a bug that slips through.

Additional resources

This article just scratches the surface of JavaScript testing, but if you’d like to learn more, check out:

  • My presentation from the 2012 Full Frontal conference in Brighton, UK.
  • Grunt, a tool that helps automate the testing process and lots of other things.
  • Test-Driven JavaScript Development by Christian Johansen, the creator of the Sinon library. It is a dense but informative examination of the practice of testing JavaScript.
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I know you’ve been asked this plenty of times already, but: no new vendor prefixes, right? Right?

Nope, none! They’re great in theory but turns out they fail in practice, so we’re joining Mozilla and the W3C CSS WG and moving away them. There’s a few parts to this.

Firstly, we won’t be migrating the existing -webkit- prefixed properties to a -chrome- or -blink- prefix, that’d just make extra work for everyone. Secondly, we inherited some existing properties that are prefixed. Some, like -webkit-transform, are standards track and we work with the CSS WG to move ahead those standards while we fix any remaining issues in our implementation and we’ll unprefix them when they’re ready. Others, like -webkit-box-reflect are not standards track and we’ll bring them to standards bodies or responsibly deprecate these on a case-by-case basis. Lastly, we’re not introducing any new CSS properties behind a prefix.

Pinky swear?

Totes. New stuff will be available to experiment with behind a flag you can turn on in about:flags called “Experimental Web Platform Features”. When the feature is ready, it’ll graduate to Canary, and then follow its ~12 week path down through Dev Channel, Beta to all users at Stable.

The Blink prefix policy is documented and, in fact, WebKit just nailed down their prefix policy going forward. If you’re really into prefix drama (and who isn’t!) Chris Wilson and I discussed this a lot more on the Web Ahead podcast [37:20].

How long before we can try Blink out in Chrome?

Blink’s been in Chrome Canary as of the day we announced it. The codebase was 99.9% the same when Blink launched, so no need to rush out and check everything. All your sites should be pretty much the same.

Chrome 27 has the Blink engine, and that’s available on the beta channel for
Win, Mac, Linux, ChromeOS and Android. (See the full beta/stable/dev/canary
view
).

While the internals are apt to be fairly different, will there be any radical changes to the rendering side of things in the near future?

Nothing too alarming, layout and CSS stuff is all staying the same. Grid layout is still in development, though, and our Windows text rendering has been getting a new backend that we can hook up soon, greatly boosting the quality of webfont rendering there.

We’re also interested in better taking advantage of multiple cores on machines, so the more we can move painting, layout (aka reflow), and style recalculation to a separate thread, but the faster everyone’s sites will render. We’re already doing multi-threaded painting on ChromeOS and Android, and looking into doing it on Mac & Windows. If you’re interested in these experimental efforts or watching new feature proposals, take a look at the blink-dev mailing list. A recent proposed experiment is called Oilpan, where we’ll look into the advantages of moving the implementation of Chrome’s DOM into JavaScript.

Will features added to Blink be contributed back to the WebKit project? Short term; long term?

Since Blink launched there’s been a few patches that have been landed in both Blink and WebKit, though this is expected to decline in the long-term, as the code bases will diverge.

When are we likely to start seeing Blink-powered versions of Chrome on Android? Is it even possible on iOS, or is iOS Chrome still stuck with a Safari webview due to Apple’s policies?

Blink is now in the Chrome Beta for Android. Chrome for iOS, due to platform limitations, is based on the WebKit-based WebView that’s provided by iOS.

Part of this move seems to be giving Google the freedom to remove old or disused features that have been collecting dust in WebKit for ages. There must be a few things high on that list—what are some of those things, and how can we be certain their removal won’t lead to the occasional broken website?

A few old ’n crusty things that we’re looking at removing: the isindex attribute, RangeException, and XMLHttpRequestException. Old things that have little use in the wild and just haven’t gotten a spring cleaning from the web platform for ages.

Now, we don’t want to break the web, and that’s something that web browser engineers have always been kept very aware of. We carefully gauge real-world usage of things like CSS and DOM features before deprecating anything. At Google we have a copy of the web that we run queries against, so we have a pretty OK idea of what CSS and JavaScript out there is using.

Blink also has over 32,000 tests in its test suite, and manual confirmation that over 100 sites work great before every release ships. And we’re working closely with the W3C and Adobe to share tests and testing infrastructure across browsers, with the goals of reducing maintenance burden, improving interoperability, and increasing test coverage. Eventually we’d like all new features to ship with shared conformance tests, ensuring interoperability even as we add cutting-edge stuff.

Still, any deprecation has to be done responsibly. There’s now a draft Blink process for deprecating features which includes:

  • Anonymous metrics to understand how much any specific feature is used “in the wild”
  • ”Intent to deprecate” emails that hit blink-dev months before anything is
    removed
  • Warnings that you’ll find in your DevTools console if you’re using anything
    deprecated
  • Mentions on the Chromium blog like this Chrome 27
    wrap-up
    .

Did part of the decision to branch away from WebKit involve resistance to adding a Dart VM? WebKit’s goals explicitly mention JavaScript, and Apple representatives have been fairly vocal about not seeing a need.

Nope, not at all. The decision was made by the core web platform engineers. Introducing a new VM to a browser introduces considerable maintenance cost (we saw this with V8 and JavaScriptCore both in WebKit) and right now Dart isn’t yet ready to be considered for an integration with Blink. (more on that in a sec). Blink’s got strong principles around compatibility risk and this guides a lot of the decisions around our commitments to potential features as they are proposed. You can hear a more complete answer here from Darin Fisher, one of the Chrome web platform leads.

Have any non-WebKit browsers recently expressed an interest in Dart? A
scripting language that only stands to work in one browser sounds a little
VBScript-y.

Not yet, but since Dart compiles to JavaScript and runs across the modern web, it’s not gated by other browsers integrating the VM. But it’s still early days, Dart has not yet reached a stable 1.0 milestone and that there are still technical challenges with the Dart VM around performance and memory management. Still, It’s important to point out that Dart is an open source project, with a bunch of external contributors and committers.

Let me take a moment to provide my own perspective on Dart. :) Now, as you know, I’m a JavaScript guy, so early on, I took a side and and considered Dart an enemy. JavaScript should win; Dart is bad! But then I came to realize the Dart guys aren’t just setting out to improve the authoring and scalability of web application development. They also really want the web to win.  Now I’ve recently spoke about how The Mobile Web Is In Trouble, and clarified that my priorities are seeing it provide a fantastic user experience to everyone. For me, seeing the mobile web be successful trumps language wars and certainly quibbling over syntax. So I’m happy to see developers embrace the authoring advantages of Coffeescript, the smart subset of JavaScript strict mode, the legendary Emscripten & asm.js combo, the compiler feedback of TypeScript and the performance ambitions of Dart. It’s worth trying out technologies that can leapfrog the current expectations of the user experience that we can deliver. Our web is worth it.

Will Opera be using the Chromium version of Blink wholesale, as far as you know? Are we likely to see some divergence between Opera and Chrome?

As I understand it, Opera Mobile, Opera Desktop, and Opera Mini will all be based on Chromium. This means that they’ll not only share the exact version of Blink that Chrome uses, but also the same graphics stack, JavaScript engine, and networking stack. Already, Opera has contributed some great things to Blink and we’re excited about what’s next.

Why the name “Blink,” anyway?

Haha. Well… it’s a two parter. First, Blink evokes a certain feeling of speed and simplicity—two core principles of Chrome. Then, Chrome has a little tradition of slightly ironic names. Chrome itself is all about minimizing the browser chrome, and the Chromebook Pixel is all about not seeing any pixels at all. So naturally, it fits that Blink will never support the infamous <blink> tag. ;)

<3z

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