One of the nice things about nodejs is that since the majority of its libraries are asynchronous it boasts strong support for concurrently performing IO heavy workloads. Even though node is single threaded the event loop is able to concurrently progress separate operations because of the asynchronous style of its libraries. A canonical example would something like fetching 10 web pages and extracting all the links from the fetched HTML. This fits into node’s computational model nicely since the most time consuming part of an HTTP request is waiting around for the network during which node can use the CPU for something else. For the sake of discussion, let’s consider this sample implementation:
Request debugging is enabled so you’ll see that node starts fetching all the URLs at the same time and then the various events fire at different times for each URL:
So we’ve demonstrated that node will concurrently “do” several things at the same time but what happens if computationally intensive code is tying up the event loop? As a concrete example, imagine doing something like compressing the results of the HTTP request. For our purposes we’ll just throw in a while(1) so it’s easier to see what’s going on:
If you run the script you’ll notice it takes much longer to finish since we’ve now introduced a while() loop that causes each URL to take at least 5 seconds to be processed:
And now back to the original problem, how can we fetch the URLs in parallel so that our script completes in around 5 seconds? It turns out it’s possible to do this with node with the child_process module. Child_process basically lets you fire up a second nodejs instance and use IPC to pass messages between the parent and it’s child. We’ll need to move a couple of things around to get this to work and the implementation ends up looking like:
What’s happening now is that we’re launching a child process for each URL we want to process, passing a message with the target URL, and then passing the links back to the parent. And then running along with a timer results in:
It isn’t exactly 5 seconds since there’s a non-trivial amount of time required to start each of the child processes but it’s around what you’d expect. So there you have it, we’ve successfully demonstrated how you can achieve parallelism with nodejs.
Here at Setfive, when not helping our clients with their technology woes, we love experimenting with fun new technology and continuously growing our professional tool kit. As of late we have been throwing around some potential ideas for a Setfive iPhone app (get Chicken Pad Thai delivered no matter where you are in the world) and have been looking at a couple of tools to turn this lofty dream into a reality.
In the past we have taken our chances with other cross-platform native apps (PhoneGap in particular) that allow you to wrap a web app into a web view however, these methods fall short; if the looks of your app don’t bother you then the serious performance hit that comes from interfacing directly with native objects will.
In order to test React a little bit farther than the simple hello world example we decided to build a simple application on top of our preexisting Rotorobot API. This app allows users to see the available players for a daily fantasy sports contest on that night.
To get started, we needed an index page that would show up when the app was loaded. Just to keep things simple we incorporated a minimalist layout with a UIButton that responds when pressed.
Upon pressing the button a new scene is added to the storyboard of our application. This scene is a ListView Component that has a row for every available slate of games that will be played that night. In addition, each one of these rows is also wrapped in a TouchableHighlight Component, which allows them to respond to touches.
Any row that you touch results in an AJAX request being made to the Rotorobot API and the available players in that slate are displayed, sorted in descending order based on salary.
Getting something up and running with React Native was definitely a lot easier than expected. It was honestly as simple as using npm to install react-native-cli and then creating a new react native project using react-native init. The init function provides everything that you need to run a React Native application.
After your project has been setup it’s time for all of you Xcode naysayers to either bite the bullet and download Xcode or look for guidance in the form of another SaaS solution.
In order to help you out we’ve provided links to a couple:
If you’re old fashioned like us, and opted for the traditional route then you installed X-Code. The react-native init function creates an Xcode project file inside the ios folder in your new project’s directory. Simply open this up using Xcode and you are off to the races and ready to build/run your project at will.
There was only one minor gotcha that reared it ugly head while trying to get our application up and running. The React Native Packager runs underneath node and requires a port for its functionality. The default port that it runs on is 8081, and there is a chance that you could have a process already running on that port so your application will not be able to run. So before you try and run your Xcode project for the first time it is worth doing a quick check to make sure that port 8081 is free using:
sudo lsof -i :8081
Other than this minor inconvenience you should be all set for development!
After an hour or two of playing with React Native and building a pretty simple app, the power and simplicity of this framework became clear to us. First and foremost it was very refreshing to only have to run one or two npm commands and then be writing code in minutes afterwards. Setup was quick and painless which is always appreciated. During development we immediately noticed that developing our app felt just like developing for the web. Laying out the application was done using the CSS flex box, and was both quick and intuitive. Additionally, and probably more importantly, the framework just works. The UI components are native UIViews so naturally they look, feel, and behave the same as normal native components. We would definitely consider using React in the future and look forward to seeing how it improves and progresses from here.
This lack of an inherent language structure, though initially causing a few headaches and even more than a few fist shaking bugs has, over time, helped ingrain both strong development skills as well an inherent need to intuitively structure code. Both of these skills are at the forefront of programming with AngualrJs.
My experience with Angularjs has definitely been an incredibly positive one, although the beginning was quite rough. Actually, the beginning was fairly easy however, the step after the “hello (insert name bound from text box)” step was actually the rough one. With Angular, easy things are very easy but can become difficult very quickly as soon as you are trying to develop something that is not so rudimentary.
My first experience with Angular came in the form of writing unit tests for a project that was under development here during the Summer. I spent a couple of weeks delving through a large Angular application written by one of our head engineers. After my introduction to the framework I was given the chance to use it for some development while working on some frontend modules for the Rotorobot site. These are the main challenges that I ran into while trying to learn Angular Js.
The first challenge that I had to overcome was understanding the structure of the Angular framework. Being very inexperienced with the design pattern of Model View Controller (MVC) made this aspect the hardest part of learning Angular. Angular implements MVC by having the developer split their application into MVC components and then acts as a pipeline connecting them together. It is a robust MVC framework that promotes complicated integration of different components into whole applications. If you don’t have a sense of how the pieces fit together then the “Set it and forget it” or 2-way data-binding nature of the framework can easily turn into one of your biggest headaches.
Posted In: AngularJS
One of the more opaque concepts about AngularJS is the process that converts a chunk of HTML from a template into “Angularized” HTML which is then inserted into the DOM. During this conversions, custom directives are replaced with their corresponding HTML content, Angular directives like ng-repeat are processed, and any event handlers of interest are wired up. As it turns out, Angular’s $compile service is what’s responsible for making the magic happen. OK great, but why is this interesting or important? Because leveraging the $compile service directly lets you take dynamic content and process it to enable Angular directives and behaviors.
Since examples are always helpful, here’s an admittedly contrived one that we’ll walkthrough. Imagine that we’re building a WordPress slideshow plugin and we want to support custom themes for individual slides. So in our plugin, a user would be able to modify the HTML that displays a slide, we’d save it to the database, and then retrieve that template when we render the slides. For arguments sake, let’s assume the “default” template for the slideshow looks something like this:
As you can see, we’ve got a few directives and by default we’re displaying some description. Generally, we could set this up by creating a “slide” directive that looks something like:
Great, nothing to crazy but with this setup there’s no way to supply dynamic HTML from our database to use in the template. In order to allow a custom template you’d just need to modify the directive to look something like:
And then you’d be able to use it with:
The key difference is that in the modified directive the template is inserted into the directive’s element using “angular.element(el).html(scope[“slide”].template);” and then finally the $compile service is invoked to process the regular HTML to get Angular magic.
Anyway, as always questions or comments welcome!
A couple of days ago in my journey down the AngularJS rabbit hole I ran into an interesting issue. If you have a directive that’s dynamically adding an iframe tag how can you set an onLoad handler on the iframe with access to the directive’s $scope?
Interestingly, the top StackOverflow answer on Google recommends adding a function to the window object and then setting the onLoad attribute to that function. Although it works, this approach is decidedly not “the Angular way” and would definitely become unwieldy with more than one iframe on the page. I poked around a bit and turns out there’s a better way to do this. The “trick” is that it’s possible to access a directive’s $scope from inside its link function so you can set onLoad on the iframe element from there. This post provides an overview but it’s a bit light on details so here’s a concrete example.