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Starting with templates, Android features can be added quickly with a single line of DSL code.

In the first installment of this two-part series on developing Android Apps with Scala and Scaloid, I explained how Scaloid simplifies and reduces the required Android code as much as possible while leveraging type safety. In this article, I explain how to utilize asynchronous task processing, the execution of methods from system services, and specific Scaloid classes and traits.

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Addy Osmani


Today we’ll discuss how to improve the paint performance of your websites and Web apps. This is an area that we Web developers have only recently started looking at more closely, and it’s important because it could have an impact on your user engagement and user experience.

Frame Rate Applies To The Web, Too

Frame rate is the rate at which a device produces consecutive images to the screen. A low frames per second (FPS) means that individual frames can be made out by the eye. A high FPS gives users a more responsive feel. You’re probably used to this concept from the world of gaming, but it applies to the Web, too.

Long image decoding, unnecessary image resizing, heavy animation and data processing can all lead to dropped frames, which reduces the frame rate, resulting in janky pages. We’ll explain what exactly we mean by “jank” shortly.

Why Care About Frame Rate?

Smooth, high frame rates drive user engagement and can affect how much users interact with your website or app.

At EdgeConf earlier this year, Facebook confirmed this when it mentioned that in an A/B test, it slowed down scrolling from 60 FPS to 30 FPS, causing engagement to collapse. That said, if you can’t do high frame rates and 60 FPS is out of reach, then you’d at least want something smooth. If you’re doing your own animation, this is one benefit of using requestAnimationFrame: the browser can dynamically adjust to keep the frame rate normal.

In cases where you’re concerned about scrolling, the browser can manage the frame rate for you. But if you introduce a large amount of jank, then it won’t be able to do as good a job. So, try to avoid big hitches, such as long paints, long JavaScript execution times, long anything.

Don’t Guess It, Test It!

Before getting started, we need to step back and look at our approach. We all want our websites and apps to run more quickly. In fact, we’re arguably paid to write code that runs not only correctly, but quickly. As busy developers with deadlines, we find it very easy to rely on snippets of advice that we’ve read or heard. Problems arise when we do that, though, because the internals of browsers change very rapidly, and something that’s slow today could be quick tomorrow.

Another point to remember is that your app or website is unique, and, therefore, the performance issues you face will depend heavily on what you’re building. Optimizing a game is a very different beast to optimizing an app that users will have open for 200+ hours. If it’s a game, then you’ll likely need to focus your attention on the main loop and heavily optimize the chunk of code that is going to run every frame. With a DOM-heavy application, the memory usage might be the biggest performance bottleneck.

Your best option is to learn how to measure your application and understand what the code is doing. That way, when browsers change, you will still be clear about what matters to you and your team and will be able to make informed decisions. So, no matter what, don’t guess it, test it!

We’re going to discuss how to measure frame rate and paint performance shortly, so hold onto your seats!

Note: Some of the tools mentioned in this article require Chrome Canary, with the “Developer Tools experiments” enabled in about:flags. (We — Addy Osmani and Paul Lewis — are engineers on the Developer Relations team at Chrome.)

Case Study: Pinterest

The other day we were on Pinterest, trying to find some ponies to add to our pony board (Addy loves ponies!). So, we went over to the Pinterest feed and started scrolling through, looking for some ponies to add.

Screen Shot 2013-03-25 at 14.30.57-500
Addy adding some ponies to his Pinterest board, as one does. Larger view.

Jank Affects User Experience

The first thing we noticed as we scrolled was that scrolling on this page doesn’t perform very well — scrolling up and down takes effort, and the experience just feels sluggish. When they come up against this, users get frustrated, which means they’re more likely to leave. Of course, this is the last thing we want them to do!

Screen Shot 2013-03-25 at 14.31.27-500
Pinterest showing a performance bottleneck when a user scrolls. Larger view.

This break in consistent frame rate is something the Chrome team calls “jank,” and we’re not sure what’s causing it here. You can actually notice some of the frames being drawn as we scroll. But let’s visualize it! We’re going to open up Frames mode and show what slow looks like there in just a moment.

Note: What we’re really looking for is a consistently high FPS, ideally matching the refresh rate of the screen. In many cases, this will be 60 FPS, but it’s not guaranteed, so check the devices you’re targeting.

Now, as JavaScript developers, our first instinct is to suspect a memory leak as being the cause. Perhaps some objects are being held around after a round of garbage collection. The reality, however, is that very often these days JavaScript is not a bottleneck. Our major performance problems come down to slow painting and rendering times. The DOM needs to be turned into pixels on the screen, and a lot of paint work when the user scrolls could result in a lot of slowing down.

Note: HTML5 Rocks specifically discusses some of the causes of slow scrolling. If you think you’re running into this problem, it’s worth a read.

Measuring Paint Performance

Frame Rate

We suspect that something on this page is affecting the frame rate. So, let’s go open up Chrome’s Developer Tools and head to the “Timeline” and “Frames” mode to record a new session. We’ll click the record button and start scrolling the page the way a normal user would. Now, to simulate a few minutes of usage, we’re going to scroll just a little faster.

Screen Shot 2013-05-15 at 17.57.48-500
Using Chrome’s Developer Tools to profile scrolling interactions. Larger view.

Up, down, up, down. What you’ll notice now in the summary view up at the top is a lot of purple and green, corresponding to painting and rendering times. Let’s stop recording for now. As we flip through these various frames, we see some pretty hefty “Recalculate Styles” and a lot of “Layout.”

If you look at the legend to the very right, you’ll see that we’ve actually blown our budget of 60 FPS, and we’re not even hitting 30 FPS either in many cases. It’s just performing quite poorly. Now, each of these bars in the summary view correspond to one frame — i.e. all of the work that Chrome has to do in order to be able to draw an app to the screen.

Chrome’s Developer Tools showing a long paint time. Larger view.

Frame Budget

If you’re targeting 60 FPS, which is generally the optimal number of frames to target these days, then to match the refresh rate of the devices we commonly use, you’ll have a 16.7-millisecond budget in which to complete everything — JavaScript, layout, image decoding and resizing, painting, compositing — everything.

Note: A constant frame rate is our ideal here. If you can’t hit 60 FPS for whatever reason, then you’re likely better off targeting 30 FPS, rather than allowing a variable frame rate between 30 and 60 FPS. In practice, this can be challenging to code because when the JavaScript finishes executing, all of the layout, paint and compositing work still has to be done, and predicting that ahead of time is very difficult. In any case, whatever your frame rate, ensure that it is consistent and doesn’t fluctuate (which would appear as stuttering).

If you’re aiming for low-end devices, such as mobile phones, then that frame budget of 16 milliseconds is really more like 8 to 10 milliseconds. This could be true on desktop as well, where your frame budget might be lowered as a result of miscellaneous browser processes. If you blow this budget, you will miss frames and see jank on the page. So, you likely have somewhere nearer 8 to 10 milliseconds, but be sure to test the devices you’re supporting to get a realistic idea of your budget.

Screen Shot 2013-03-25 at 14.34.26-500
An extremely costly layout operation of over 500 milliseconds. Larger view.

Note: We’ve also got an article on how to use the Chrome Developer Tools to find and fix rendering performance issues that focuses more on the timeline.

Going back to scrolling, we have a sneaking suspicion that a number of unnecessary repaints are occurring on this page with onscroll.

One common mistake is to stuff just way too much JavaScript into the onscroll handlers of a page — making it difficult to meet the frame budget at all. Aligning the work to the rendering pipeline (for example, by placing it in requestAnimationFrame) gives you a little more headroom, but you still have only those few milliseconds in which to get everything done.

The best thing you can do is just capture values such as scrollTop in your scroll handlers, and then use the most recent value inside a requestAnimationFrame callback.

Paint Rectangles

Let’s go back to Developer Tools → Settings and enable “Show paint rectangles.” This visualizes the areas of the screen that are being painted with a nice red highlight. Now look at what happens as we scroll through Pinterest.

Screen Shot 2013-03-25 at 14.35.17-500
Enabling Chrome Developer Tools’ “Paint Rectangles” feature. Larger view.

Every few milliseconds, we experience a big bright flash of red across the entire screen. There seems to be a paint of the whole screen every time we scroll, which is potentially very expensive. What we want to see is the browser just painting what is new to the page — so, typically just the bottom or top of the page as it gets scrolled into view. The cause of this issue seems to be the little “scroll to top” button in the lower-right corner. As the user scrolls, the fixed header at the top needs to be repainted, but so does the button. The way that Chrome deals with this is to create a union of the two areas that need to be repainted.

Screen Shot 2013-05-15 at 19.00.12-500
Chrome shows freshly painted areas with a red box. Larger view.

In this case, there is a rectangle from the top left to top right, but not very tall, plus a rectangle in the lower-right corner. This leaves us with a rectangle from the top left to bottom right, which is essentially the whole screen! If you inspect the button element in Developer Tools and either hide it (using the H key) or delete it and then scroll again, you will see that only the header area is repainted. The way to solve this particular problem is to move the scroll button to its own layer so that it doesn’t get unioned with the header. This essentially isolates the button so that it can be composited on top of the rest of the page. But we’ll talk about layers and compositing in more detail in a little bit.

The next thing we notice has to do with hovering. When we hover over a pin, Pinterest paints an action bar containing “Repin, comment and like” buttons — let’s call this the action bar. When we hover over a single pin, it paints not just the bar but also the elements underlying it. Painting should happen only on those elements that you expect to change visually.

Screen Shot 2013-03-25 at 14.35.46-500
A cause for concern: full-screen flashes of red indicate a lot of painting. Larger view.

There’s another interesting thing about scrolling here. Let’s keep our cursor hovered over this pin and start scrolling the page again.

Every time we scroll through a new row of images, this action bar gets painted on yet another pin, even though we don’t mean to hover over it. This comes down more to UX than anything else, but scrolling performance in this case might be more important than the hover effect during scrolling. Hovering amplifies jank during scrolling because the browser essentially pauses to go off and paint the effect (the same is true when we roll out of the element!). One option here is to use a setTimeout with a delay to ensure that the bar is painted only when the user really intends to use it, an approach we covered in “Avoiding Unnecessary Paints.” A more aggressive approach would be to measure the mouseenter or the mouse’s trajectory before enabling hover behaviors. While this measure might seem rather extreme, remember that we are trying to avoid unnecessary paints at all costs, especially when the user is scrolling.

Overall Paint Cost

We now have a really great workflow for looking at the overall cost of painting on a page; go back into Developer Tools and “Enable continuous page repainting.” This feature will constantly paint to your screen so that you can find out what elements have costly paint times. You’ll get this really nice black box in the top corner that summarizes paint times, with the minimum and maximum also displayed.

Chrome’s “Continuous Page Repainting” mode helps you to assess the overall cost of a page. Larger view.

Let’s head back to the “Elements” panel. Here, we can select a node and just use the keyboard to walk the DOM tree. If we suspect that an element has an expensive paint, we can use the H shortcut key (something recently added to Chrome) to toggle visibility on that element. Using the continuous paint box, we can instantly see whether this has a positive effect on our pages’ paint times. We should expect it to in many cases, because if we hide an element, we should expect a corresponding reduction in paint times. But by doing this, we might see one element that is especially expensive, which would bear further scrutiny!

Screen Shot 2013-06-10 at 09.46.31_500_mini
The “Continuous Page Repainting” chart showing the time taken to paint the page.

For Pinterest’s website, we can do it to the categories bar or to the header, and, as you’d expect, because we don’t have to paint these elements at all, we see a drop in the time it takes to paint to the screen. If we want even more detailed insight, we can go right back to the timeline and record a new session to measure the impact. Isn’t that great? Now, while this workflow should work great for most pages, there might be times when it isn’t as useful. In Pinterest’s case, the pins are actually quite deeply nested in the page, making it hard for us to measure paint times in this workflow.

Luckily, we can still get some good mileage by selecting an element (such as a pin here), going to the “Styles” panel and looking at what CSS styles are being used. We can toggle properties on and off to see how they effect the paint times. This gives us much finer-grained insight into the paint profile of the page.

Here, we see that Pinterest is using box-shadow on these pins. We’ve optimized the performance of box-shadow in Chrome over the past two years, but in combination with other styles and when heavily used, it could cause a bottleneck, so it’s worth looking at.

Pinterest has reduced continuous paint mode times by 40% by moving box-shadow to a separate element that doesn’t have border-radius. The side effect is slightly fuzzy-looking corners; however, it is barely noticeable due to the color scheme and the low border-radius values.

Note: You can read more about this topic in “CSS Paint Times and Page Render Weight.”

Screen Shot 2013-03-25 at 15.47.40-500
Toggling styles to measure their effect on page-rendering weight. Larger view.

Let’s disable box-shadow to see whether it makes a difference. As you can see, it’s no longer visible on any of the pins. So, let’s go back to the timeline and record a new session in which we scroll the same way as we did before (up and down, up and down, up and down). We’re getting closer to 60 FPS now, and that’s just from one change.

Public service announcement: We’re absolutely not saying don’t use box-shadow — by all means, do! Just make sure that if you have a performance problem, measure correctly to find out what your own bottlenecks are. Always measure! Your website or application is unique, as will any performance bottleneck be. Browser internals change almost daily, so measuring is the smartest way to stay up to date on the changes, and Chrome’s Developer Tools makes this really easy to do.

Screen Shot 2013-03-25 at 15.50.25-500
Using Chrome Developer Tools to profile is the best way to track browser performance changes. Larger view.

Note: Eberhard Grather recently wrote a detailed post on “Profiling Long Paint Times With DevTools’ Continuous Painting Mode,” which you should spend some quality time with.

Another thing we noticed is that if you click on the “Repin” button, do you see the animated effect and the lightbox being painted? There’s a big red flash of repaint in the background. It’s not clear from the tooling if the paint is the white cover or some other affected being area. Be sure to double check that the paint rectangles correspond to the element or elements that you think are being repainted, and not just what it looks like. In this case, it looks like the whole screen is being repainted, but it could well be just the white cover, which might not be all that expensive. It’s nuanced; the important thing is to understand what you’re seeing and why.

Hardware Compositing (GPU Acceleration)

The last thing we’re going to look at on Pinterest is GPU acceleration. In the past, Web browsers have relied pretty heavily on the CPU to render pages. This involved two things: firstly, painting elements into a bunch of textures, called layers; and secondly, compositing all of those layers together to the final picture seen on screen.

Over the past few years, however, we’ve found that getting the GPU involved in the compositing process can lead to some significant speeding up. The premise is that, while the textures are still painted on the CPU, they can be uploaded to the GPU for compositing. Assuming that all we do on future frames is move elements around (using CSS transitions or animations) or change their opacity, we simply provide these changes to the GPU and it takes care of the rest. We essentially avoid having to give the GPU any new graphics; rather, we just ask it to move existing ones around. This is something that the GPU is exceptionally quick at doing, thus improving performance overall.

There is no guarantee that this hardware compositing will be available and enabled on a given platform, but if it is available the first time you use, say, a 3D transform on an element, then it will be enabled in Chrome. Many developers use the translateZ hack to do just that. The other side effect of using this hack is that the element in question will get its own layer, which may or may not be what you want. It can be very useful to effectively isolate an element so that it doesn’t affect others as and when it gets repainted. It’s worth remembering that the uploading of these textures from system memory to the video memory is not necessarily very quick. The more layers you have, the more textures need to be uploaded and the more layers that will need to be managed, so it’s best not to overdo it.

Note: Tom Wiltzius has written about the layer model in Chrome, which is a relevant read if you are interested in understanding how compositing works behind the scenes. Paul has also written a post about the translateZ hack and how to make sure you’re using it in the right ways.

Another great setting in Developer Tools that can help here is “Show composited layer borders.” This feature will give you insight into those DOM elements that are being manipulated at the GPU level.

Switching on composited layer borders will indicate Chrome’s rendering layers. Larger view.

If an element is taking advantage of the GPU acceleration, you’ll see an orange border around it with this on. Now as we scroll through, we don’t really see any use of composited layers on this page — not when we click “Scroll to top” or otherwise.

Chrome is getting better at automatically handling layer promotion in the background; but, as mentioned, developers sometimes use the translateZ hack to create a composited layer. Below is Pinterest’s feed with translateZ(0) applied to all pins. It’s not hitting 60 FPS, but it is getting closer to a consistent 30 FPS on desktop, which is actually not bad.

Screen Shot 2013-05-15 at 19.03.13-500
Using the translateZ(0) hack on all Pinterest pins. Note the orange borders. Larger view.

Remember to test on both desktop and mobile, though; their performance characteristics vary wildly. Use the timeline in both, and watch your paint time chart in Continuous Paint mode to evaluate how fast you’re busting your budget.

Again, don’t use this hack on every element on the page — it might pass muster on desktop, but it won’t on mobile. The reason is that there is increased video memory usage and an increased layer management cost, both of which could have a negative impact on performance. Instead, use hardware compositing only to isolate elements where the paint cost is measurably high.

Note: In the WebKit nightlies, the Web Inspector now also gives you the reasons for layers being composited. To enable this, switch off the “Use WebKit Web Inspector” option and you’ll get the front end with this feature in there. Switch it on using the “Layers” button.

A Find-and-Fix Workflow

Now that we’ve concluded our Pinterest case study, what about the workflow for diagnosing and addressing your own paint problems?

Finding the Problem

  • Make sure you’re in “Incognito” mode. Extensions and apps can skew the figures that are reported when profiling performance.
  • Open the page and the Developer Tools.
  • In the timeline, record and interact with your page.
  • Check for frames that go over budget (i.e. over 60 FPS).
  • If you’re close to budget, then you’re likely way over the budget on mobile.
  • Check the cause of the jank. Long paint? CSS layout? JavaScript?

Screen Shot 2013-05-15 at 19.36.22-500
Spend some quality time with Frame mode in Chrome Developer Tools to understand your website’s runtime profile. Larger view.

Fixing the Problem

  • Go to “Settings” and enable “Continuous Page Repainting.”
  • In the “Elements” panel, hide anything non-essential using the hide (H) shortcut.
  • Walk through the DOM tree, hiding elements and checking the FPS in the timeline.
  • See which element(s) are causing long paints.
  • Uncheck styles that could affect paint time, and track the FPS.
  • Continue until you’ve located the elements and styles responsible for the slow-down.

Switch on extra Developer Tools features for more insight. Larger view.

What About Other Browsers?

Although at the time of writing, Chrome has the best tools to profile paint performance, we strongly recommend testing and measuring your pages in other browsers to get a feel for what your own users might experience (where feasible). Performance can vary massively between them, and a performance smell in one browser might not be present in another.

As we said earlier, don’t guess it, test it! Measure for yourself, understand the abstractions, know your browser’s internals. In time, we hope that the cross- browser tooling for this area improves so that developers can get an accurate picture of rendering performance, regardless of the browser being used.


Performance is important. Not all machines are created equal, and the fast machines that developers work on might not have the performance problems encountered on the devices of real users. Frame rate in particular can have a big impact on engagement and, consequently, on a project’s success. Luckily, a lot of great tools out there can help with that.

Be sure to measure paint performance on both desktop and mobile. If all goes well, your users will end up with snappier, more silky-smooth experiences, regardless of the device they’re using.

Further Reading

About the Authors

Addy Osmani and Paul Lewis are engineers on the Developer Relations team at Chrome, with a focus on tooling and rendering performance, respectively. When they’re not causing trouble, they have a passion for helping developers build snappy, fluid experiences on the Web.


© Addy Osmani for Smashing Magazine, 2013.

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(author unknown)

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')
  assert( find('#results li').has_content?('cat'), 'Search results are shown' )
  assert( page.has_no_selector?('#results'), 'No results is not shown' )

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:


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) {

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

  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) {
  $('<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;

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

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

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('').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) {

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


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', '', _.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 = $('li.result').attr('data-name');
  $(document).trigger('like', [ name ]);

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

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) {

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);

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

  assert.equal(ul.find('.no-results').length, 0);
  assert.equal(ul.find('li.result').length, data.length);

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

  $(document).on('like', spy);


  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();
    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();

// ...


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();

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

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

  teardown(function () {

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

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

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


  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();


    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();

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


    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) {
      pending = false;


  $(document).on('like', function (evt, 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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Imagine you’re at an intersection waiting for your turn to walk across the street. You push the button to call the walk signal, and you take out your phone. You want to accomplish one thing: maybe check your e-mail, add an item to your to-do list, or check Twitter. You have a limited amount of time to accomplish that one thing.

That amount of time is how long users have to finish what they want to do on your site. And it matters.

Adding half a second to a search results page can decrease traffic and ad revenues by 20 percent, according to a Google study. The same article reports Amazon found that every additional 100 milliseconds of load time decreased sales by 1 percent. Users expect pages to load in two seconds—and after three seconds, up to 40 percent will simply leave.

Can you keep up? If you’re designing sites with rich content, lots of dynamic elements, larger JavaScript files, and complex graphics—like so many of us are—the answer might be “no.”

It’s time we make performance optimization a fundamental part of how we design, build, and test every single site we create—for every single device.

Designing for performance

Website performance starts with design. Weigh a design choice’s impact on page speed against its impact on your site’s conversion rate. Do you really need eight different shades of blue? What value does this 1,000px-wide background image add? Will replacing a sprite with an icon font actually add more page weight and slow rendering, or will it be faster than the original image?

Not every design decision will favor performance. I’ve found that a button style that slightly slows page speed can still increase conversions, and it’s worth the small web performance sacrifice.

But sometimes, performance will win. I once had a landing page redesign that added a significant amount of images to a page, and I wasn’t sure whether the performance hit would have a negative impact on conversions, so I rolled the redesign out to a small subset of users in an A/B test to see what the impact would be. The new design took twice as long to load, and I immediately saw a high exit rate and lower conversion rate, so we kept the original lightweight design. Being wrong is okay—it’s what gives you a benchmark.

In another experiment, the homepage featured a thumbnail image section with 26 images that rotated in and out of 10 slots. homepage.

My teammate at the time put all 26 images into a sprite, which:

  • Increased the total homepage size by 60K with the increased CSS, JavaScript, and image size needed to recreate this effect with the sprite
  • Decreased the number of requests by 21 percent
  • Cut the total homepage load time by a whopping 35 percent

This proves that it’s worth experimenting: We weren’t sure whether or not this would be a page speed success, but we felt it was worth it to learn from the experiment.

Coding for performance

Clean your HTML, and everything else will follow.

Start by renaming non-semantic elements in your HTML. This is probably the toughest, but once you start thinking about theming in terms of semantics like “nav” or “article” and less with design or grid names, you’ll make significant headway. Often we get to elements with non-semantic names by way of needing more weight in CSS selectors, and instead of cleaning our CSS and adding specificity the right way, we add unnecessary IDs and elements to our HTML.

Then, clean up your CSS. Remove inefficient selectors first. In a study I performed for, I found that adding inefficient selectors to a CSS file actually increased page load time by 5.5 percent. More efficient CSS selectors will actually be easier to redesign and customize the styles of in the future since they are easier to read in your stylesheet and have semantic meaning. Repurposable, editable code often goes hand-in-hand with good performance. In that case study, I saved 39 percent of the CSS file size by cleaning my CSS files.

Next, focus on curing your HTML of div-itis. Typically the cleaner your markup ends up, the smaller your CSS will be, and the easier redesigning and editing will be in the future. It saves you not just page load time, but development time too.

Last, focus on creating repurposable code, which saves time and results in smaller CSS and HTML files. Less HTML and CSS will be significantly easier to maintain and redesign later, and the smaller page sizes will have a positive impact on page speed.

Optimizing requests

Requests are when your browser has to go fetch something like a file or a DNS record. The cleaner your markup, the fewer requests the browser has to make—and the less time users will spend waiting for their browser to make those round trips.

In addition to clean markup, minimize JavaScript requests by only loading it when absolutely necessary. Don’t call a file on every page if you don’t need it on every page. Don’t load a JavaScript file on a responsive design that is only needed for larger screens; for example, replace social scripts with simple links instead. You can also load JavaScript asynchronously so that the JavaScript won’t block any content from rendering.

Though a responsive design typically means more CSS and images (larger page weight), you can still get faster load times from larger page sizes if you cut requests.

Optimizing images

Save as many image requests as you can, too. First, focus on creating sprites. In my study, I found that a sprite for the icons in the example cut page load time by 16.6 percent. I like to start cleaning up images by creating one sprite for repeating backgrounds. You may need to create one for vertical repeats and one for horizontal repeats.

Next, create one transparent sprite for no-repeat backgrounds. This will include things like your logo and icons. As you get more advanced, you can also use tools like Grunticon, which takes SVG icon and background images and figures out how best to serve them based on the user’s browser’s capabilities.

After you regenerate your images, run them through an optimizer like ImageOptim. Similarly, retina-sized images can still be made smaller with extensive compression that isn’t noticeable in the end result.

Now see which images you can replace with CSS3 gradients. This will not only make a dent in page load time, but it will also make it infinitely easier to edit the site later, as developers won’t have to find original image files to edit, regenerate, or re-optimize in the future.

Last, look at using Base64 encode, which allows you to embed an image into your CSS file instead of calling it using a separate URL. It ends up looking like this:

#nav li:after { content:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAA

The random letters and numbers add up to a small circle that’s used in many places within Embedding the image allows you to save an image request each time you want to use it in your design. Embedding images using this method will make your CSS file larger, so it’s worth testing the page load time before and after to ensure you’re making improvements.

Measuring performance

Now for the fun part: determining whether your efforts are paying off.

Both Google’s PageSpeed and Yahoo!’s YSlow offer suggestions on how you can improve page load time, including identifying which elements block page rendering and the size of your page’s different components like CSS or HTML.

I also recommend the YSlow extension 3PO, which checks your site for integration with popular third-party scripts like Twitter, Facebook, and Google+. The plugin can give you recommendations on how to further optimize the social scripts on your page to improve page load time. has been my go-to benchmarking tool ever since I first started making improvements based on PageSpeed and YSlow’s suggestions. It gives very detailed information about requests, file size, and timing, and it offers multiple locations and browsers to test in.

Benchmarking can help you troubleshoot as you design. Measuring performance and analyzing the results will help you make both your large- and small-screen designs faster. You can also test and benchmark techniques like conditional loading of images as you get more comfortable developing for performance.

The impact of web performance

Web performance affects your users—and that means its everyone’s job to understand it, measure it, and improve it. All of these techniques will lead to better page load time, which creates a significant improvement to your site’s user experience.

Happier users mean better conversion rates, whether you’re measuring in revenue, signups, returning visits, or downloads. With a fast page load time, people can use your site and accomplish what they want in a short amount of time—even if it’s just while they’re waiting for a walk signal.

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Soupe du jour: tags. Image: clogozm/Flickr

Somewhere far in the web’s primordial past it was decided that the best way to mark up a menu in HTML was to use the unordered list element: <ul>. The vast majority of tutorials – if not all – you’ll ever see for creating navigation menus use the familiar list element structure, nesting links inside <li> tags. Menu plugins for WordPress and other popular publishing systems use lists for menus as well. Even the HTML5 spec uses an unordered list in its <nav> element examples.

There is, as CSS-Tricks’ Chris Coyier writes, “no debate” about how menus should be marked up. But HTML5 adds the <nav> element and there’s also a navigation role in WAI-ARIA so should we still be using lists to mark up menus?

Coyier says no. He’s dropped lists from his <nav> elements and instead uses just links and span tags. Coyier cites a talk by Reinhard Stebner, who is blind, and suggests that with most screen readers the far better solution for menus is to use divs and spans for menus.

Be sure to read through Coyier’s post for some more data on why ditching the list might be a good idea and check out Jim Doran’s write up on Stebner’s original talk, which makes a distinction between accessible and usable. That is, a technically “accessible” site might still be a usability nightmare for some users.

However, as Mozilla’s Chris Heilmann points out in the comments of Coyier’s post, the problems lists cause in some screen readers are really a result of the sorry state of screen readers. “Screen readers are damn slow to update and vary immensely between different versions… I gave up a long time ago calling something accessible or not when it works in Jaws.”

Lists for menus have advantages over the div and span route, like some extra elements for styling and the fact that they render as, well, lists even in the absence of CSS.

What do you think? Are lists for menus a legacy workaround we no longer need in the day and age of <nav> and role="navigation"? Or do they still offer enough advantages to keep using for menus?

For his part Coyier says he’s going to keep building list-free menus. “Until I see some solid research that suggests that’s dumb, I’m sticking to it,” he writes. “As always, the best would be to get more information from real screen reader users like Reinhard.”

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Many of us care deeply about developing our craft. But staying up to date can be a true challenge, because the quantity of fresh information we’re regularly exposed to can be a lot to take in. 2012 has been no exception, with a wealth of evolution and refinement going on in the front end.

Great strides have been made in how we approach workflow, use abstractions, appreciate code quality and tackle the measurement and betterment of performance. If you’ve been busy and haven’t had time to catch up on the latest developments in these areas, don’t worry.

With the holiday season upon us and a little more time on our hands, I thought it would be useful to share a carefully curated list of the most relevant front-end talks I’ve found helpful this year. You certainly don’t have to read through them all, but the advice shared in them will equip you with the knowledge needed to go into the new year as a better front-end engineer.

Image credit: Jacob Bøtter


Have a Strategy for Staying Up to Date

How to Stay Up to Date on Web Stuff, Chris Coyier

Part of continually developing your craft is staying up to date. Doing this is important for all professionals, and in this talk you’ll learn strategies for staying updated even when the ideas that surround the technologies we use are constantly evolving.


Make Sure Your Baseline for Development Is Current

A New Baseline for Front-End Developers, Rebecca Murphey

There was a time when editing files, testing them locally and simply FTP’ing them was the common workflow for a front-end developer. We would measure our abilities based on how well we could harass IE 6 into rendering pages correctly, and we generally lacked strong skills in HTML, CSS and JavaScript.

This has greatly changed over the past few years, with improvements in workflow and tooling. Front-end development is now taken more seriously, and this talk sheds light on the new baseline process for developing on the front end.


Understand How Browsers Work Behind the Scenes

So, You Want to Be a Front-End Engineer, David Mosher (Video)

Some would say that the browser is the most volatile development platform the world has ever known. If you’re a client-side developer, understanding how browser internals work can help you both make better decisions and appreciate the justifications behind many development best practices. In one of the best talks this year, David Mosher takes you through how browsers parse and render your pages.


Know What the Web Platform Now Has to Offer

The Web Can Do That!?, Eric Bidelman (Video)

The Web is constantly evolving, and keeping up with what’s new on the platform can be hard. HTML5’s new capabilities enable us to build an entirely new suite of applications with features that were simply impossible to achieve before (at least, not without the use of plugins) but are now a reality.

In this talk, my teammate Eric guides you through the bleeding edge of HTML5, focusing on solving many real-world problems. You’ll learn about media streaming, device input, modern CSS design, media capture, file I/O and more.



For Web App Developers

Tooling for the Modern Web App Developer, Addy Osmani

Whether you’re using JavaScript or CoffeeScript, LESS or Sass, building an awesome Web application these days usually requires a plethora of boilerplates, frameworks and tools and a lot of glue to get them to work together. In short, you need a kick-ass utility belt.

In this talk, you’ll get an overview of the current tooling eco-system for the front-end and learn about a new tool that tries to bring together all of the pieces of this eco-system for you, called Yeoman.


An extended version of this talk is also available.

For Web Designers

A Modern Web Designer’s Workflow, Chris Coyier (Video)

A lot is expected from today’s Web designers. If this role defines what you do, then it’s now not just about visual design, but increasingly about building interactions. Designs need to work across different devices of varying shapes, sizes and connections, and they also need to be accessible.

As a designer, you often need to communicate and share code across teams and be familiar with many different technologies. In this talk, Chris Coyier discusses many of the amazing tools that can help things along, discussing what does what and giving a high-level view of a modern workflow.


For Mobile Web Developers

Mobile Web Developers Toolbelt, Pete Le Page (Video)

Building for the mobile Web requires a different mindset to the one we use when developing for desktop, and a different set of tools. Thankfully, a number of great options are available. From remote debugging to emulation, mobile browsers are offering more and more tools to make our lives easier.

In this talk, Pete Le Page takes you through a couple of tools that you can use today to make cross-platform mobile Web development easier, and then he peers into the crystal ball to see what tools the future may bring.


For Debugging

Secrets of the Chrome DevTools, Patrick Dubroy (Video)

Google Chrome Developer Tools provide powerful ways to understand, debug and profile Web applications. Most developers are familiar with Chrome’s basic inspection and debugging tools, but some of its most valuable features, like the Timeline and memory analysis tools, are less known.

In his demo-based walkthrough, Patrick Dubroy provides an overview of Chrome Developer Tools and an in-depth demonstration of some lesser-known features.


The Future


The CSS of Tomorrow, Peter Gasston

In this talk, Peter looks briefly at the state of CSS3: what you can do right now, and what you’ll be able to do in the very near future. He then looks into the long-term future, to a time when CSS3 will make possible page layouts far richer and more dynamic than we’d thought possible, and when CSS3 has taken on aspects of programming languages. This is effectively what CSS developers will be learning years from now.



The Future of JavaScript, Dave Herman

The Web platform is growing, and JavaScript is growing along with it. EcmaScript 6, the next edition of the JavaScript standard, is gearing up to be a huge step forward for Web programming. In this talk, Dave Herman discusses the exciting new features being worked on for EcmaScript 6 and how they can be used.


Web Applications

Web Components and the Future of Web App Development, Eric Bidelman

Web components are going to fundamentally change the way we think, build and consume Web apps. ShadowDOM, Mutation Observers, custom elements, MDV, Object.observe(), CSS — how do they all fit together?

This talk prepares you for the future of the Web platform by discussing the fundamentals of Web components and how we can use them today with frameworks such as AngularJS.



State of the Art

All the New CSS Hawtness, Darcy Clarke

This talk dives into some of the latest CSS implementations and specifications floating around. You’ll learn what’s here and what’s around the corner, and you’ll gain insight into why these new features will change our development workflow.

Darcy Clarke touches on modules such as paged-media, multi-columns, flex-box, filters, regions, box-sizing, masking and 3D.



Your CSS Is a Mess, Jonathan Snook

We all think that CSS is easy. Take some selectors, add some properties, maybe a dash of media queries, and — presto! — you have a beautiful website. And yet, as the project changes and the team grows, we see the frustration build, with increasingly complex selectors and overuse of !important.

In this talk, Jonathan looks at common problems and solutions that will make your CSS (and your projects) easier to manage and easier to scale.



CSS Pre-Processors, Bermon Painter

If you haven’t jumped on the pre-processor train this year, you’re missing out. In this helpful overview of (current) popular pre-processors, Bermon Painter takes you through Stylus, LESS and Sass, with features subdivided into easy-to-learn sections of beginner, intermediate and advanced. I’ve been using mixins quite heavily this year, and I simply wouldn’t have been able to if it weren’t for projects like Sass.



A Better Future With KSS, Kyle Neath

Writing maintainable CSS within a team is one of those problems that a lot of people think can be solved by writing CSS in a particular style. But in Kyle’s experience, that never works out.

In this talk, he introduces you to his latest creation, KSS. It’s a documentation and style guide format. He’ll show you why he built KSS and how it’s been helping him at GitHub to refactor its four-and-a-half year old CSS, and he’ll give you a glimpse into the future of KSS.



The Importance of Code Style

Maintainable JavaScript, Nicholas Zakas

Some say that good code is its own documentation, and the fact is that the more readable our code is, the easier it is to maintain.

Writing JavaScript for fun and writing it professionally are two different things, and in this talk by Zakas, you’ll learn practices to make JavaScript maintainable over the long run, to reduce errors and to make your code easily adaptable to future changes. It’s highly recommended reading.


A Modern Large-Scale App Stack

SoundCloud’s Stack, Nick Fisher

I’ve talked a lot about large-scale development in the past. It’s a non-trivial problem that’s difficult to get right, and so it’s exciting when someone working on such challenges shares their experience.

In this talk, Nick Fisher of SoundCloud discusses the company’s story of developing large-scale applications with JavaScript, not only at runtime, but also its steps to make development and deployment easier. In particular, he looks at RequireJS and Backbone, talking about how SoundCloud has used and abused each to suit its needs, sometimes in uncommon ways.


Rethinking Application Structure

Re-Imagining the Browser With AngularJS, Igor Minar

What if you could a write modern Web app with dramatically fewer lines of code and improve its readability and expressiveness at the same time? In case you’re wondering: no, there’s no new language to learn, just familiar old HTML and JavaScript. As a matter of fact, there are concepts for you to unlearn.

AngularJS is a client-side JavaScript Web development framework whose authors believe they’ve done something special. Instead of asking what kind of functions they could provide to make writing apps smoother, they asked, “What if the browser worked differently in a way that eliminates code and gives structure to apps?”

In this talk, you’ll get a tour of how to get the power of tomorrow’s Web platform in today’s Web applications.


Internationalization and i18n

Entschuldigen you, parlez vouz JavaScript, Sebastian Golasch (Video)

While JavaScript applications grow in size and complexity, there are still some white spots on the big map of Web applications: internationalization and globalization! If you´re still thinking that switching strings in and out is the way to go, you are definitely headed in the wrong direction.

In this talk, Sebastian takes you through how to spot real-world internationalization problems and how to solve them in the most elegant way.


I couldn’t cover internationalization without mentioning Alex Sexton, who has also spoken a great deal on this topic. His JSConf talk on client-side internationalization is available in video form if you’re interested in checking it out.

Patterns and Principles

The Plight of Pinocchio, Brandon Keepers

JavaScript is no longer a toy language, and many of our Web applications can’t function without it. Brandon states that if we are going to use JavaScript to do real things, then we need to treat it like a real language, adopting the same practices that we use with real languages. I completely agree with him.

This framework-agnostic talk takes a serious look at how we develop JavaScript applications in the real world. Despite their prototypical nature, good object-oriented programming principles are still relevant. The design patterns that we’ve grown to know and love work just as well in JavaScript as they do in any other language.


When to Lazy Load Scripts

How Late Is Later?, Massimiliano Marcon

Reducing the loading time of a Web application is a well-known challenge. Developers need to make sure that the browser downloads only the code that is strictly necessary to bootstrap the application, and leave the rest for later. This is what we commonly call “lazy loading.”

But when is “later”? When is the right time to lazy load? This talk shows how JavaScript code — functions and objects — can be delivered to the browser on demand, thus reducing the perceived loading time of a Web application.



Building Touch-Based Interfaces

Creating Responsive HTML5 Touch Interfaces, Stephen Woods (Video | Audio)

Flickr front-end engineer Stephen Woods shares some hard-learned lessons about building responsive touch-based interfaces using HTML5 and CSS. Because our users are demanding better instant feedback from touch-based UIs, understanding how to approach this problem and avoid the pitfalls will be critical for many application developers in the future.


The Challenge With Scrolling

Embracing Touch: Cross-Platform Scrolling, Mark Dalgleish (Video)

Scrolling effects are a popular way to add personality to the simple act of moving down the page. Unfortunately, these effects don’t work natively on mobile devices, where the touch interaction would make these techniques more effective. In this talk, Mark looks at some ways to implement these effects within the limitations of mobile browsers.


Native, HTML5 and Hybrid Apps

Native, HTML5 and Hybrid Mobile Development, Eran Zinman

One of the toughest decisions every mobile developer faces is choosing a development strategy: “Should I develop a native, HTML5 or hybrid mobile app?” Over the past two years, Eran has led Conduit’s mobile client development efforts, experimenting with cross-platform development in various flavors: from complete HTML5 solutions (using PhoneGap and other technologies) to hybrid solutions to semi-hybrid solutions to fully native solutions.

In this talk, Eran shares some real-life experiences in cross-platform development, describing changes that Conduit has implemented along the way, and sharing what some of the “big players” (such as Facebook, LinkedIn and Twitter) are doing in their mobile app development.


Performance, Distribution and Facebook on HTML5

On the Future of Mobile Web Apps, Simon Cross

Simon looks at Facebook’s experience with and investment in the mobile Web, the issues affecting mobile Web developers and what Facebook and the industry are doing to push the mobile Web forward. Mark Zuckerberg’s comments on HTML5 were undoubtedly one of the most discussed topics in mobile this year, and I personally found these slides a good summary of Facebook’s current take on what works and what still requires improvement.


Tools for Mobile Debugging

Mobile Debugging, Remy Sharp

Debugging Web apps on mobile devices can be a genuine pain. Luckily, a number of tools are available today to ease the process. From remote debuggers to cross-device consoles, this talk summarizes the current state of debugging for mobile, going into more depth on debugging than Pete’s talk from earlier in the post.


Responsive Design Techniques

Responsive Web Design: Clever Tips and Techniques, Vitaly Friedman

Responsive Web design challenges designers to apply a new mindset to their design processes and to the techniques they use in design and coding. This talk (by Smashing Magazine’s own Vitaly Friedman) provides an overview of various practical techniques, tips and tricks that you might want to be aware of when working on a new responsive design project.


Web Apps

Offline Web Apps

Offline Rules, Andrew Betts (Video)

In the last couple of years, a deluge of new offline storage technologies have appeared. In this talk, Andrew looks at why they are all excellent and rubbish at the same time and why you need to use all of them, and he walks through techniques to consider when building a Web application that can load and function with no network connectivity.

But making use of client-side storage is necessary not only in order to make an app that works offline, but it can also hugely improve the experience of your website when the user actually does have connectivity.


State of the Art

Building Web Apps of the Future: Tomorrow, Today and Yesterday, Paul Kinlan (Audio)

The browser is an amazing runtime that can already deliver amazing apps. Paul dives into the technologies that will help you deliver Web apps that will blow your users’ socks off now and in the future.


Client-Side Storage

Storage in the Browser, Andrew Betts

Installed native applications can use all the space they want, but in the browser we’re much more limited. This talk explores how to make the best use of the storage technologies available to Web apps, comparing the virtues of different packaging and encoding techniques, and covering simple forms of in-browser compression that can yield surprising results.

As more apps are developed to surf over network turbulence, and to work even when completely disconnected from the network, local storage becomes ever more important.


Application Cache

Application Cache: Douchebag, Jake Archibald (Video)

The Application Cache is one of the cool bits of HTML5. It allows websites to work without a network connection, and it brings us much closer to native app-like behavior. However, from roundup articles and talks about HTML5, you might be left with the impression that it’s a magic bullet. Unfortunately, it isn’t; the Application Cache is, as Jake famously puts it, a douchebag.

In this talk, he looks at how to use the features of Application Cache without the horrible side effects, comparing techniques that you’d use for both a simple client-side app and a large content-driven website. He explores the many gotchas left out of most articles about Application Cache and discusses how to build your website to survive them.




High-Performance CSS, Paul Irish

Paul dives into the tools available in and outside of the browser to assess the performance of your CSS. Find out what’s slow (is box-shadow causing paints to be 70 milliseconds longer?) and how to fix it. Learn about about:tracing, CSS profiling and speed tracer, and get a better understanding of the browser’s internals in the process.


There’s also Jon Rohan’s talk about some problems related to CSS performance that were solved at GitHub. Recommended reading.

GitHub’s CSS Performance, Jon Rohan


Avoiding Jank

Jank-Free: In Pursuit of Smooth Web Apps, Tom Wiltzius

Building beautiful experiences on the mobile Web takes more than a good designer and fancy CSS: performance is critical for a Web app to feel fluid. Smooth animation that never drops a frame can give your app a native feel. But when animations stutter, effects lag or pages scroll slowly, we call that “jank.” This talk is about identifying jank and getting rid of it.



Building Faster Websites, Ilya Grigorik

In this comprehensive crash course, Ilya Grigorik shares some really juicy tips on how to make the Web faster, including Google’s findings on what slows down people’s Web experience and how Chrome and other services have improved it. If you’re an engineer looking to improve the performance of your websites or apps, this talk comes highly recommended.



Breaking the JavaScript Speed Limit With V8, Daniel Clifford

Are you interested in making JavaScript run blazingly fast? If so, this talk looks at V8 under the hood to help you identify how to optimize your JavaScript. Daniel shows you how to leverage V8’s sampling profiler to eliminate performance bottlenecks and optimize JavaScript programs. He also exposes how V8 uses hidden classes and runtime-type feedback to generate efficient JIT code. A very interesting talk for performance junkies.


Note: Some of the optimizations mentioned in this talk are specific to V8 and may not apply to other JavaScript engines. I wrote about how to write memory-efficient JavaScript on Smashing Magazine recently, in case you’re interested in exploring the topic further.


Understanding Code Smells

Why Our Code Smells, Brandon Keepers (Video)

Odors exist for a reason, and they are usually trying to tell us something. If our code smells, it might be trying to tell us what is wrong.

Does a test case require an abundance of setting up? Maybe the code being tested is doing too much, or it is not isolated enough for the test? Does an object have an abundance of instance variables? Maybe it should be split into multiple objects? Is a view brittle? Maybe it is too tightly coupled to a model, or maybe the logic needs to be abstracted into an object that can be tested?

In this talk, Brandon walks through code from projects that he works on every day, looking for smells that indicate problems, understanding why the smells are there, what the smells are trying to tell us, and how to refactor them.


Current State of the Art

JavaScript Testing: The Holy Grail, Adam Hawkins (Video)

Adam talks about this Holy Grail for JavaScript developers: getting a test suite up and running fast and having multiple browsers execute the tests. Getting the Holy Grail is difficult, though, even though several tools have been created in the past in attempts to solve this problem.

Barriers to entries are everywhere. How easy is it to get going testing small parts of JavaScript functionality? What happens as your become bigger and more complex? What about headless testing? Does this process scale up to CI? Can you even do this stuff locally?

A myriad of testing tools and solutions are available, and Adam shows what’s out there and what we as a community need to do next to get the Holy Grail, to ensure a better Web experience for everyone.


Tip: One tool for testing that I’m loving at the moment is Testling-CI, which runs browser tests on every push.

Improving the Testability of Your Code

Writing Testable JavaScript, Rebecca Murphey (Audio)

It’s one thing to write the code that you need to write to get something working; quite another to write the code that you need to write to prove that it works — and to prove that it will continue to work as you refactor and add new features.

In her talk, Rebecca looks at what it means to write testable JavaScript code.



Time spent thinking about (and developing) your craft is time well spent. The more honed your skills are, the more opportunity you will have to become an efficient engineer.

While this list doesn’t cover every excellent talk presented this year, it hopefully offers some direction for you to accentuate your skills. Do consider reading through a few of them. Focused reading in this way will add to your value as a craftsperson and hopefully improve your daily development workflow.

With that, do enjoy the holiday season and have a fantastic new year.


© Addy Osmani for Smashing Magazine, 2012.

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