I recently wrote a post about node.js and this time I’m going to talk about one of it’s most common uses; a web server.

Thanks to the libraries that come packed by default with node, creating a very simple server is very easy. Create a file named server.js and add this content to it:

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var http = require('http');

http.createServer(function(req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('I\'m a server');
}).listen('9000', '127.0.0.1');

Save the file and open a terminal in the folder where that file is stored. Then run node server.js and visit http://127.0.0.1:9000. You will see something like this:

Might not be very exciting but this is were everything starts.

Node.js is a relatively new technology (born on 2009) that allows us run JavaScript code from outside a browser. This had already been done in the past by Mozilla Rhino, but node.js gained a lot of popularity for it’s ease of use. Node code runs inside Google’s V8 JavaScript Engine which is exactly the same engine that is used for Google Chrome. Because node code runs on this engine, when you write node code you don’t have to worry about browser compatibility issues. Node also gets rid of some restrictions that are given to JS when running on a browser, so with node you have access to things like the file system and hardware.

Node can be used for a lot of tasks like most other programming languages, but one of it’s most common uses is as a server side scripting language. Probably The main benefit of using JavaScript in the server is that if you are a web developer you will be using a syntax that you are already familiar with, so it will be easy to get up to speed.

Routers are a common way for web frameworks to translate a URL to an action. On backbone they are used when creating single page applications to refresh the content of the page without actually refreshing the page.

Lets see an example of how they work:

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var MyAppRouter = Backbone.Router.extend({
  // Define the routes we want to listen to
  routes: {
    '': 'indexAction',
    'main': 'mainAction',
    'listing/:page': 'listingAction',
    'profile/:id(/:username)': 'profileAction',
    'anything/*all': 'anythingAction'
  },

  // Acts as a constructor
  initialize: function() {
    console.log('Router started');
  },

  indexAction: function() {
    console.log('Index action');
  },

  // Now we list our router actions
  mainAction: function() {
    console.log('Main page');
  },

  listingAction: function(page) {
    console.log('Show page ' + page);
  },

  profileAction: function(id, username) {
    console.log('You passed id: ' + id + ' and username: ' + username);
  },

  anythingAction: function(all) {
    console.log(all);
  }
});

// We need to instantiate it
var router = new MyAppRouter();

// This tells backbone to start listening for URL changes
Backbone.history.start();

Collections are a convenient way to group models together. An example usage of them is when you want to show a list of elements in your page. You can create a simple collection using Backbone.Collection (I am using the models I defined on Introduction to Backbone.js):

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// Create some people
var juan = new Person({'weight': 80});
var carlos = new Person({'weight': 70});
var alicia = new Person({'weight': 75});

var persons = new Backbone.Collection([
  juan,
  carlos,
  alicia
]);

Git submodules is a way to organize your code so you can include libraries or other projects into your project. You want to treat these libraries as a separate repository so they are by themselves versioned by git in another repository.

Lets start with a very simple, but not very practical example:

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# Create a git repository
mkdir somedir
cd somedir
touch file
git add file
git commit -m 'Added file'

# Create another repository inside the current repository
mkdir submodule
cd submodule
touch submodule_file
git add submodule_file
git commit -m 'Added file'

# Add the child repository to the parent repository as a submodule
cd ..
git submodule add ./submodule/
git commit -m 'Added submodule'

For this post I am assuming you have already a Django environment setup.

Django apps

Once you have your environment set up, you will want to create apps for your project. Here is what Django documentations has to say about apps:

What’s the difference between a project and an app? An app is a Web application that does something — e.g., a Weblog system, a database of public records or a simple poll app. A project is a collection of configuration and apps for a particular Web site. A project can contain multiple apps. An app can be in multiple projects.

We can use manage.py to help us create our apps. Just go to your project folder and type this command in a terminal:

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python manage.py startapp crud

I chose crud as the name of my app because I am just going to show a simple CRUD(Create, Read, Update, Delete) interface to a DB table.

PHP 5.4 introduced a technique called traits. This technique aims to provide code re-usability functionality similar to mixins in other programming languages. The most common use case is to reuse methods among different classes.

Here is an example of the syntax;

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trait someMath
{
    function add($a, $b)
    {
        return $a + $b;
    }

    function multiply($a, $b)
    {
        return $a * $b;
    }
}

class Calculator
{
    use someMath;
}

$cal = new Calculator();
echo $cal->add(4, 6); // echoes 10

As you can see traits syntax is very similar to the syntax to create a class. We just need to change the keyword class for trait. Then we can apply the trait inside a class using the use keyword.

Android doesn’t support ant anymore. Take a look at: Building an Android project from scratch using Gradle to learn how to create a project with gradle.

Getting the environment set up

There are two packages needed for developing android applications. One is the Java Development Kit and the other is the Android SDK. You can install JDK with this command:

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sudo apt-get install default-jdk

You can get Android SDK from this site: http://developer.android.com/sdk/index.html. The site will give you two options, to download ADT (Android Development Tookit), which is the SDK + Eclipse or just the SDK. Choose to download only the SDK.

After downloading the package you need to unzip it, open a terminal, navigate to the folder where you downloaded it, go the the tools folder and run the android script:

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cd /android-sdk/tools
./android

In reality you probably don’t want to host you websites on your local computer unless you have a very good computer, a very good internet connection and you are an expert system administrator, but this is very useful to learn how the internet works.

In this case I am doing this because I want to be able to develop on my computer no matter where I am. So I want to be able to SSH to my machine, modify my files and view my changes from a web browser. Here are the things that need to be done:

• Setup a local HTTP server
• Allow inbound traffic on port 80
• Setup a free DNS service
• Setup an SSH server
• Forward requests to port 22 on your router to your computer

Backbone.js is a JavaScript framework that facilitates the separation between models and views. It’s lack of controllers make me think of it as being similar to Django framework, so familiarity with Django may make it easier to understand backbone.

Backbone comes packaged in a js file that you can download from backbonejs.org. If you are not planning to hack backbone you should probably download the production version. Backbone can be used with any templating system but it comes with underscore.js support by default. For this reason to use backbone you will also need to download it from underscorejs.org. jQuery is another dependency of backbone, so you also need to include it in your bundle.

In all the examples I show I assume that you have already included jQuery, underscore.js and backbone.js with something similar to:

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<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" src="underscore.js"></script>
<script type="text/javascript" src="backbone.js"></script>