Promises, REST API’s & Angular JS

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Before breaking it down, to all those who don’t know what REST API’s are :

“REST is acronym for REpresentational State Transfer. It is architectural style for distributed hypermedia systems ans was first presented by Roy Fielding in 2000 in his famous dissertation.”

Source : “restfulapi.net”

So what is a Promise ?

Generally promises are representation of a value that which might not be available to us as of now but at some point eventually it will be available. Observe the below image to understand how promises work.

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So how is this better than callbacks ?

Generally if you are using callbacks in your codebase then at some point of time either for i/o’s or file buffers or something might come in your way and makes you write nested callbacks. Writing nested callbacks is difficult and an alternative to that is promise.

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REST API’s, promises what are you about to explain ?

Angular has this beautiful service called $q which is helpful for creating promises and using them in your angular applications. Generally many people have concerns over $q but $q is tightly integrated with the scope life cycle. So be it any task it contains all the necessary features needed by most of the heavy duty asynchronous tasks.

Now to start off angular can be really powerfull with the $http Service provided the fact that it has immense potential in allowing us to create heavy duty REST ful API’s, CRUD operation based web applications etc. So let us understand the $http service first before using promises for creating a REST ful API.

$http
|_____ .success()
For a success(), callback is called asynchronously when the request completes and the response arrives from the server
|_____ .error()
For an error(), the error callback is fired

Callbacks which are accpeted by above methods are :

  • data: It is a response obtained from server.
  • status: HTTP status codes 100x, 200x, 300x, 400x, etc which returned from server.
  • config: Object used for generating the request.
  • headers: Headers sent by the server.
  • statusText: HTTP status text of the status code.

Promise Chaining

Chaining is one of the most important aspects of promises. Here the basic idea is that promises can be composed through chaining. This means you can trigger a specified task only after previous promise has been resolved.

Handling errors by designing a promise that always rejects

No API is complete without writing a handler or a middleware that takes care of all the requests which are generally errored. Designing this will be useful if we want to tell a user about the occurrence of an error in terms of a promise rather than a simple value.

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NOTE : Generally while using $http Service there are somethings which one should have knowledge of, If we happen to send a JS object as POST data in a POST/PUT request, it’s serialized to JSON before getting sent. Similarly, if the server responds with a JSON string it’s parsed into a JavaScript object and passed to the success callback attached to the promise.

Thats it folks,
Happy Hacking !!

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Factories, Services and Controllers

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So before I start the blog post, it is better if you know more about what sTeam web interface is and what are the capabilites of sTeam. Click here.

So what is a Controller ?

It is simply a a constructor function which is instantiated by AngularJS when it encounters ng-controller directive in HTML.

So what is a Factory ?

In Angular Js a factory is an injectable type which helps us in encapsulating repetitive logic.

How are they helpful for sTeam web interface ?

So as my first week of work started of for GSOC, the core concentration has been on primarily working with the controllers of the workarea and integrating them with the respective views. In an attempt i started of with adding a :

commentsCtrl

: Used for adding comments to the web interface

workspaceeditorCtrl

: Used for integrating textAngular to the web interface

Things apart, in a broader aspect here what should be understood is about how things should be implemented using controllers, factories and services. Let me illustrate how it should be properly done in angular js.

To start off

How are controllers really helpful in Angular and how should they be used ?

Generally we should understand that controllers responsible for augmenting the scope which is done by attaching models and functions to it that are subsequently accessed in the view. There are some things which are to be understood while writing controllers. Lets go one by one,

  • A Straight “No” for all the DOM manipulation. This must be achieved only with directives
  • If you are having a situation where you are about to write repeatable code, then don’t do it with controllers, instead encapsulate them in services.
  • If you are trying to expose the whole controller instance then it isn’t a good idea. In fact the scope object exists in order to clear separation of concern between controller and view .

So what about Factories ?

“Services, factories, and providers are all injectable types. We must understand that Factories in angular Js are just another example for an injectable type. It looks almost the same as Service but when it comes to implementation you can decide and determine what to instantiate and return from the factory”

scribes by hector | Akhil Pandey

Let me give you a small example before i wrap up, Have a look at the below image,

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Observe broadcastItem, prepForBroadcast. If you look keenly essentially what i am doing there is creating an injectable type which enables me to change the message that which has to be printed depending on the broadcast item.

One more key thing about factories is that a factory can also depend on other services or factories. Also there is one more point to grab which is we are returning an object from the factory function, so we absolutely have the freedom to determine what should be the object which is to be returned, going further we can base it on certain parameters as well.

Thats it folks,
Happy Hacking !!

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KnitWeb Localization

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  • Post category:FOSSASIA

Why Localization important

Localization is the process of adapting, translating and customizing a product for a specific locale or cultural conventions. Localization distinguishes a good web front end from a truly successful one. Today English is a priority language to be learning to use computers. Having Localization we can gain benefits such as, no need to local users to learn English first, Reduce amount of training and localization brings additional value. Localization To improve localization community of volunteers needs to get together and first establish a guiding set of terms to guarantee accurate and consistent translation. Community is the strongest part for an Open Source project. Translation process can be improved by making sure that efforts in translations are consistent and structured. So the lots of local users can enjoy KnitWeb and hopefully become a part of the community.

How Localization work on KnitWeb

KnitWeb construct elements of the interface using JavaScript dynamically. Retrieve the correct localized string in JavaScript is the most important part for localize an app like KnitWeb. For the Localization I used 3 types of files i.e. languge.properties, locles.ini and l10.js.

.properties files (en.properties, ge.properties): These files contain the translations of strings used in the KnitWeb. Each line is the translation of a single string in “name=value” format; name is an identifier for this string, It is used to map the string; value is the translation of the string in particular language.

Inside ge.properties

#Inputs
input_port=Port
input_machine=Maschine:

Inside si.properties

#Inputs
input_port=කවුළුව
input_machine=යන්ත්‍රය:

locales.ini : locales.ini includes which is the default language in case app does not support current language, what type of other locales KnitWeb supports and the location of the each translated file.

l10n.js: JavaScript library. Automatic localization of strings appearing in your app’s HTML. Provides a JavaScript API your app can use to retrieve localized strings( get, getLanguage, setLanguage, getDirection)

global_translate_german
Localization – German
global_tranlate_sinhala
Localization – Sinhala
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