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What is AngularJS?
AngularJS is a framework to build large scale and high performance web application while keeping them as easy-to-maintain. Following are the features of AngularJS framework.
AngularJS is a powerful JavaScript based development framework to create RICH Internet Application (RIA).
AngularJS 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.
What is data binding in AngularJS? Data binding is the automatic synchronization of data between model and view components. ng-model directive is used in data binding. Scopes are objects that refer to the model. They act as glue between controller and view. Controllers are JavaScript functions that are bound to a particular scope. They are the prime actors in AngularJS framework and carry functions to operate on data and decide which view is to be updated to show the updated model based data. AngularJS come with several built-in services. For example $http service is used to make XMLHttpRequests (Ajax calls). Services are singleton objects which are instantiated only once in app. Filters select a subset of items from an array and return a new array. Filters are used to show filtered items from a list of items based on defined criteria. 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 (ng-bind, ng-model, etc) to perform most of the task that developers have to do. Templates 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". It is concept of switching views. AngularJS based controller decides which view to render based on the business logic. 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. Following are the 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 writes less code and gets more functionality.
In AngularJS, views are pure html pages, and controllers written in JavaScript do the business processing.
AngularJS applications can run on all major browsers and smart phones including Android and iOS based phones/tablets.
Following are the disadvantages of AngularJS.
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.
Following are the three core directives of AngularJS.
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.
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 gets ready.
M V C
Model − It is the lowest level of the pattern responsible for maintaining data.
View − It is responsible for displaying all or a portion of the data to the user.
Controller − It is a software Code that controls the interactions between the Model and View.
ng-app directive defines and links an AngularJS application to HTML. It also indicate the start of the application. ng-model directive binds the values of AngularJS application data to HTML input controls. It creates a model variable which can be used with the html page and within the container control( for example, div) having ng-app directive. ng-bind directive binds the AngularJS Application data to HTML tags. ng-bind updates the model created by ng-model directive to be displayed in the html tag whenever user input something in the control or updates the html control's data when model data is updated by controller. ng-controller directive tells AngularJS what controller to use with this view. AngularJS application mainly relies on controllers to control the flow of data in the application. A controller is a JavaScript object containing attributes/properties and functions. Each controller accepts $scope as a parameter which refers to the application/module that controller is to control.
AngularJS being a pure javaScript based library integrates easily with HTML.
Step 1 − Include angularjs javascript libray in the html page
<head>
<script src = "http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js" ></script>
</head>
Step 2 − 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 html element or body element as shown below:
<body ng-app = "myapp" >
</body> ng-init directive initializes an AngularJS Application data. It is used to put values to the variables to be used in the application. ng-repeat directive repeats html elements for each item in a collection. Expressions are used to bind application data to html. Expressions are written inside double braces like {{ expression}}. Expressions behave in same way as ng-bind directives. AngularJS application expressions are pure JavaScript expressions and outputs the data where they are used.
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