Alex MacCaw

JavaScript programmer, O'Reilly author.

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Dynamic pagination

Pagination over a constantly changing list is hard. Really hard. In fact it should be one of those computer science problems up there with naming and cache invalidation.

The issue especially surfaces in news sites, like Hacker News. The hierarchy of posts is constantly changing. By the time you click ‘next page’, page two has an entirely different set of posts. So how do you ensure that the next page contains what the user expects to see?

Paginating on offset is out, since the valid offset is constantly changing. Paginating on a post’s date is also out, since HN’s sort order is not determined by date, but rather by a dynamic score.

Well one one method is to store every possible sort order in memory. In fact, this is exactly what Hacker News does. When you click ‘next page’, HN knows what you’re expecting to see, because it has the particular sort order you’re looking at stored in a...

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SEO in JS Web Apps

JavaScript and search engines have always had a tricky relationship, and SEO is often used as an argument against single page applications. I’m aiming to put some of those misconceptions to rest in this article and show you that it’s perfectly possible to create a pure JavaScript web application and still have good SEO.

To demonstrate, take a look at the search results for Monocle, a single page web app. You can see that even though the application relies on JavaScript, articles are still getting fetched and indexed correctly.

While there are indications that Google’s spiders can index some urls they find in JavaScript, in my experience they haven’t been able to render and index complex JS web apps without a little help. The key to spidering JS apps lies in Google’s Ajax crawling specification.

The Ajax crawling specification was originally intended for JS apps that use the hash...

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How yield will transform Node.js

Node v0.11.2 was released recently, and with it support for v8 generators. Generators can be hard to grasp, but essentially they’re decorated functions that you can execute multiple times and resume execution at different points inside the function.

What this means in practice is that we can get rid of the callback hell that has plagued node applications, and write code in a synchronous style, while it’s executed asynchronously behind the scenes.

 Using yield

A code example is worth a thousand words, so let’s dive right in. We’re going to need Node v0.11.2, which you can easily install with nvm.

nvm install 0.11.2

We’re going to use a promise based server called Mach, and a promise library called Q. Install both of those with npm if you haven’t already.

Since we’re using bleeding edge v8 features, you’ll need to pass the --harmony flag through to Node whenever you invoke it.


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Time to first tweet

At Twitter, one of our key metrics for success was ‘time to first tweet’, the time taken between someone navigating to, and seeing the first Tweet in the page. I’ve always thought it a useful metric, as initial interaction speed is vitally important; take too long, and users lose focus and leave.

There seems to be a lot of fear, uncertainty and doubt (FUD) in the programming community around the speed of JS web apps, especially with the initial page load. Server-side generated HTML is making a come-back, indeed Twitter eventually moved back to that away from a stateful client. It seems the single-page-app approach has many vocal opponents.

I’m here to put some of that FUD to rest, and show you that it’s perfectly possible to make JS web apps that load extremely fast. I’m going to show you some of the techniques I used to make so fast.

First, a little...

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Regulation and Innovation

Paradoxically, regulation can sometimes result in innovation. Within highly regulated industries, you often get entrenched businesses and monopolies ripe for disruption. While regulation and red tape may strangle fledgling startups, if they can struggle through and overcome it they have a distinct advantage – less competition.

What’s more, regulation is often ‘hackable’. Look hard, and you’ll see lots of startups out there flirting with grey areas and testing the boundaries. Often it requires a startup environment to think outside the box when it comes to interpreting and applying regulations. Most don’t like to talk about it for obvious reasons.

The are three industries that are great examples of this phenomena at work: drones, bio-tech and payments.


Commercial drones and quadcopters are an exciting area, and the use cases for them are endless. I went round a startup called...

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Memory Management in JS Web Apps

Memory management is a fairly crucial part to building JavaScript web applications, and just because the language has a garbage collector it doesn’t absolve you from all duties.

Take your classic controller (or view in Backbone land). In its constructor it may bind to some model events, perhaps re-rendering itself when a record changes. You’ll need to clean up these events listeners at some stage, especially if you’re constantly instantiating and removing the controller.

Backbone and Spine have a ‘remove’ method which, behind the scenes, will remove the controller from the DOM via jQuery. Backbone will even cleanup any event handlers using it’s Event.fn.listenTo feature. However, calling this manually whenever we want to remove a controller is a bit onerous, and means we can’t use features like jQuery.fn.html() to remove controllers. We somehow need to detect when the controller’s...

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Queuing Ajax Requests in JS Web Apps

Queueing Ajax requests in JavaScript Web Apps can be important, especially if the interface doesn’t always represent database state.

In both Backbone and Spine, the default behavior is to update the user-interface before sending requests to the server, i.e. an asynchronous user-interface. However, this can cause race conditions. For example:

  1. User creates a record, say a page
  2. Interface is updated and an POST request is sent
  3. User immediately deletes page
  4. DELETE request is sent to the server
  5. The server responds to the DELETE request before the POST request to create the page has finished.
  6. Server 404s because it can’t find the referenced page by ID

The solution to this race condition is to queue Ajax requests, particularly destructive ones (POST, PUT, DELETE). I’ve written a very simple jQuery 1.9 plugin to do just this. All you need to do is pass a queue flag when creating Ajax...

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Speed up Heroku deploys

While building Monocle, I noticed that deploys to Heroku were taking absolutely ages; specifically the asset pre-compilation stage. I tried a variety of things, including removing a bunch of CoffeeScript files, but deploys were still taking in the order of several minutes.

After talking to Josh, it seems the solution is a simple one. Simply enable Memcache caching for sprockets during the pre-compilation stage. By doing this, I’ve reduced asset compilation from 100 seconds to between 4-9 seconds.

By default, each Heroku deploy is in a isolated environment. This means that Sprockets can’t take advantage of previous asset compilations, and has to compile everything from scratch. The solution is to have a shared cache between deploys.

If you’re using Heroku, the first step is enabling a Memcache addon. I’ve gone with the memcachier service, as they’ve got a generous free plan (which is...

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I’ve been working on a project called Monocle these past few weeks, and it’s time to show it to the world.

Monocle is an experiment in creating a friendly and intelligent community around sharing quality content with a focus on technology, startups and frankly anything that appeals to the inquisitive mind.

Screen Shot 2013-07-03 at 12.05.36 PM.png


Over the next few weeks I’m going to be writing about the more interesting aspects to Monocle, but for now I want to talk about the motivations behind it.

The motivation for developing Monocle was to create a friendly and safe place for ideas and feedback. Criticism is kept to the constructive variety, and social accountability is provided by linking your Twitter or GitHub accounts.

There can be too much negativity in the tech community. It seems the average response to someone out on a limb, showcasing their latest idea or startup, is one of snark and derision...

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How to travel around the world for a year

While my last post covered my previous year traveling, writing and programming, this article will go into the specifics of planning your own round the world trip, including flights, costs, activities and accommodation. I’ll show you how affordable traveling actually is, and how to plan your own adventure.

“Travel is fatal to prejudice, bigotry, and narrow-mindedness.” - Mark Twain

I think it’s especially important for people to get out of the Silicon Valley echo chamber, to travel and get some perspective. Traveling opens your eyes to some of the real problems people face, and gives you the opportunity to come up with solutions to tackle those, rather than some of the more trivial ideas closer to home. You can’t fail to come away from traveling inspired with a fresh perspective and new ideas.

Stuck in Customs

 Choosing where to go

Choosing where to go can be overwhelming at first, especially when...

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