AngularJS Concepts

                                                     AngularJS Concepts


Dear reader ,

I am going to light on some AngularJS concepts and features .
So please  read and provide your suggestions  if required.

What is AngularJS?

Ø AngularJS is an awesome Javascript framework that can be used to create powerful and dynamic web apps. It also covers the building of complex client-side applications. Since its release in 2009, AngularJS has been widely used by many developers for its convenient extending of custom HTML tags and attributes, known as ‘directives’.

Ø   AngularJS is an open source web application framework. It was originally developed in 2009 by Misko Hevery and Adam Abrons. It is now maintained by Google. Its latest version is 1.3.14.

Features

·        AngularJS is a powerful JavaScript based development framework to create RICH Internet Application(RIA).

·        AngulajJS provides developers options to write client side application (using JavaScript) in a clean MVC(Model View Controller) way.

·        Application written in AngularJS is cross-browser compliant. AngularJS automatically handles javascript code suitable for each browser.

·        AngularJS is open source, completely free, and used by thousands of developers around the world. It is licensed under the Apache License version 2.0.

·        It supports two way binding.

Overall, AngularJS is a framework to build large scale and high performance web appliation while keeping them as easy-to-maintain.

AngularJS is a MVC based framework. In the coming chapters, we will see how AngularJS uses MVC methodology.

 

 Core Features

Following are most important core features of AngularJS:

·        Data-binding: It is the automatic synchronization of data between model and view components. Supports Two way binding.

·        Scope: These are objects that refer to the model. They act as a glue between controller and view.

·        Controller: These are Javascript functions that are bound to a particular scope.

·        Services: AngularJS come with several built-in services for example $http to make a XMLHttpRequests. These are singleton objects which are instantiated only once in app.

·        Filters: These select a subset of items from an array and returns a new array.

·        Directives: Directives are markers on DOM elements (such as elements, attributes, css, and more). These can be used to create custom HTML tags that serve as new, custom widgets. AngularJS has built-in directives (ngBind, ngModel...)

·        Templates:These are the rendered view with information from the controller and model. These can be a single file (like index.html) or multiple views in one page using "partials".

·        Routing: It is concept of switching views.

·        Model View Whatever: MVC is a design pattern for dividing an application into different parts (called Model, View and Controller), each with distinct responsibilities. AngularJS does not implement MVC in the traditional sense, but rather something closer to MVVM (Model-View-ViewModel). The Angular JS team refers it humorously as Model View Whatever.

·        Deep Linking: Deep linking allows you to encode the state of application in the URL so that it can be bookmarked. The application can then be restored from the URL to the same state.

·        Dependency Injection: AngularJS has a built-in dependency injection subsystem that helps the developer by making the application easier to develop, understand, and test.

Concepts

Following diagram depicts some important parts of AngularJS which we will discuss in detail in the subsequent chapters.

Advantages of AngularJS

·        AngularJS provides capability to create Single Page Application in a very clean and maintainable way.

·        AngularJS provides data binding capability to HTML thus giving user a rich and responsive experience

·        AngularJS code is unit testable.

·        AngularJS uses dependency injection and make use of separation of concerns.

·        AngularJS provides reusable components.

·        With AngularJS, developer write less code and get more functionality.

·        In AngularJS, views are pure html pages, and controllers written in javascript do the business processing.

On top of everything, AngularJS applications can run on all major browsers and smart phones including Android and iOS based phones/tablets.

Disadvantages of AngulaJS

Though AngularJS comes with lots of plus points but same time we should consider the following points:

·        Not Secure : Being JavaScript only framework, application written in AngularJS are not safe. Server side authentication and authorization is must to keep an application secure.

·        Not degradable: If your application user disables Javascript then user will just see the basic page and nothing more.

 The AngularJS Components

The AngularJS framework can be divided into following three major parts:

·        ng-app : This directive defines and links an AngularJS application to HTML.

·        ng-model : This directive binds the values of AngularJS application data to HTML input controls.

·        ng-bind : This directive binds the AngularJS Application data to HTML tags.

Example

Now let us write a simple example using AngularJS library. Let us create an HTML filemyfirstexample.html as below:

<!doctype html>

<html>

   <head>

      <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.0-beta.17/angular.min.js"></script>

   </head>

   <body ng-app="myapp">

      <div ng-controller="HelloController" >

         <h2>Welcome {{helloTo.title}} to the world of Tutorialspoint!</h2>

      </div>

      <script>

         angular.module("myapp", [])

         .controller("HelloController", function($scope) {

            $scope.helloTo = {};

            $scope.helloTo.title = "AngularJS";

         });

      </script>

   </body></html>

Following sections describe the above code in detail:

Include AngularJS

We have included the AngularJS JavaScript file in the HTML page so we can use AngularJS:

<head>

   <script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>

</head>

Check the latest version of AngularJS on their official website.

Point to AngularJS app

Next we tell what part of the HTML contains the AngularJS app. This done by adding the ng-app attribute to the root HTML element of the AngularJS app. You can either add it to htmlelement or body element as shown below:

<body ng-app="myapp">

</body>

View

The view is this part:

<div ng-controller="HelloController" >

   <h2>Welcome {{helloTo.title}} to the world of Tutorialspoint!</h2>

</div>

ng-controller tells AngularJS what controller to use with this view. helloTo.title tells AngularJS to write the "model" value named helloTo.title to the HTML at this location.

 Controller

The controller part is:

<script>

   angular.module("myapp", [])

   .controller("HelloController", function($scope) {

      $scope.helloTo = {};

      $scope.helloTo.title = "AngularJS";

    });

</script>

This code registers a controller function named HelloController in the angular module named myapp. We will study more about modules and controllers in their respective chapters. The controller function is registered in angular via the angular.module(...).controller(...) function call.

The $scope parameter passed to the controller function is the model. The controller function adds a helloTo JavaScript object, and in that object it adds a title field.

Execution

Save the above code as myfirstexample.html and open it in any browser. You will see an output as below:

When the page is loaded in the browser, following things happen:

·        HTML document is loaded into the browser, and evaluated by the browser. AngularJS JavaScript file is loaded, the angular global object is created. Next, JavaScript which registers controller functions is executed.

·        Next AngularJS scans through the HTML to look for AngularJS apps and views. Once view is located, it connects that view to the corresponding controller function.

·        Next, AngularJS executes the controller functions. It then renders the views with data from the model populated by the controller. The page is now ready.

AngularJS First Application

Before we start with creating actual HelloWorld application using AngularJS, let us see what are the actual parts of a AngularJS application. An AngularJS application consists of following three important parts

·        ng-app : This directive defines and links an AngularJS application to HTML.

·        ng-model : This directive binds the values of AngularJS application data to HTML input controls.

·        ng-bind : This directive bidns the AngularJS Application data to HTML tags.

Steps to create AngularJS Application

Step 1: Load framework

Being a pure JavaScript framework, It can be added using <Script> tag.

<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js">

</script>

Step 2: Define AngularJS Application using ng-app directive

<div ng-app="">

...

</div>

Step 3: Define a model name using ng-model directive

<p>Enter your Name: <input type="text" ng-model="name"></p>

Step 3: Bind the value of above model defined using ng-bind directive.

<p>Hello <span ng-bind="name"></span>!</p>

Steps to run AngularJS Application

Use above mentioned three stpes in an HTML page.

testAngularJS.htm

<html>

<title>AngularJS First Application</title>

<body>

<h1>Sample Application</h1>

<div ng-app="">

   <p>Enter your Name: <input type="text" ng-model="name"></p>

   <p>Hello <span ng-bind="name"></span>!</p> or  <h1>Hello {{name}}!</h1>

</div>

<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>

</body>

</html>

Output

Open textAngularJS.htm in a web browser. Enter your name and see the result.

How AngularJS integrates with HTML

·        ng-app directive indicates the start of AngularJS application.

·        ng-model directive then creates a model variable named "name" which can be used with the html page and within the div having ng-app directive.

·        ng-bind then uses the name model to be displayed in the html span tag whenever user input something in the text box.

·        Closing</div> tag indicates the end of AngularJS application.

AngularJS directives are used to extend HTML. These are special attributes starting with ng- prefix. We're going to discuss following directives:

·        ng-app - This directive starts an AngularJS Application.

·        ng-init - This directive initializes application data.

·        ng-model - This directive defines the model that is variable to be used in AngularJS.

·        ng-repeat - This directive repeats html elements for each item in a collection.

·                   ng-app directive

·         ng-app directive starts an AngularJS Application. It defines the root element. It automatically initializes or bootstraps the application when web page containing AngularJS Application is loaded. It is also used to load various AngularJS modules in AngularJS Application. In following example, we've defined a default AngularJS application using ng-app attribute of a div element.

·         <div ng-app="">

·         ...

·         </div>

·                   ng-init directive

·         ng-init directive initializes an AngularJS Application data. It is used to put values to the variables to be used in the application. In following example, we'll initialize an array of countries. We're using JSON syntax to define array of countries.

·         <div ng-app="" ng-init="countries=[{locale:'en-US',name:'United States'},

·                                             {locale:'en-GB',name:'United Kingdom'},

·                                             {locale:'en-FR',name:'France'}]">

·                                                                                

·         ...

·         </div>

·                   ng-model directive

·         ng-model directive defines the model/variable to be used in AngularJS Application. In following example, we've defined a model named "name".

·         <div ng-app="">

·         ...

·         <p>Enter your Name: <input type="text" ng-model="name"></p>

·         </div>

·                   ng-repeat directive

·         ng-repeat directive repeats html elements for each item in a collection.. In following example, we've iterated over array of countries.

·         <div ng-app="">

·         ...

·            <p>List of Countries with locale:</p>

·            <ol>

·               <li ng-repeat="country in countries">

·                  {{ 'Country: ' + country.name + ', Locale: ' + country.locale }}

·               </li>

·            </ol>

·         </div>

·                   Example

·         Following example will showcase all the above mentioned directives.

·         testAngularJS.htm

·         <html>

·         <title>AngularJS Directives</title>

·         <body>

·         <h1>Sample Application</h1>

·         <div ng-app="" ng-init="countries=[{locale:'en-US',name:'United States'},

·                                             {locale:'en-GB',name:'United Kingdom'},

·                                             {locale:'en-FR',name:'France'}]">

·            <p>Enter your Name: <input type="text" ng-model="name"></p>

·            <p>Hello <span ng-bind="name"></span>!</p>

·            <p>List of Countries with locale:</p>

·            <ol>

·               <li ng-repeat="country in countries">

·                  {{ 'Country: ' + country.name + ', Locale: ' + country.locale }}

·               </li>

·            </ol>

·         </div>

·         <script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>

·         </body>

·         </html>

Output

Open textAngularJS.htm in a web browser. Enter your name and see the result.

Reference from :

http://www.tutorialspoint.com/angularjs/angularjs_overview.htm