Basic Concepts in AngularJs

Pradeep Sahoo
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AngularJS is an open-source platform for building web applications and is maintained by Google. Its purpose is to develop Single Page Applications. It supports Test Driven Development (TDD).

Let us get started with AngularJS.

For starting with AngularJs we need to have a basic understanding of HTML and JavaScript but that is not mandatory. We need an editor like Visual Studio 2012, 2013, 2015 or higher or Sublime Text. AngularJs works in the browser like Safari, Chrome, Firefox, Opera 15+, IE9+ and mobile browsers (Android, Chrome Mobile, iOS Safari and Opera Mobile). For IE8 it is not supported.

Download the Sublime text editor at http://www.sublimetext.com/.

Download the AngularJs script from https://angularjs.org/ and refer to the angular.min.js script in your HTML.

Open the Sublime editor and enter the following code, refer to angular.min.js from your downloaded path and open in the Chrome browser.

Example-1 Running a Sample AngularJs

<html ng-app="">
<head>
<script src="angular.min.js"></script>
</head>
<body>
<div>Sum of 10 and 20 is : {{10+20}}
<div>
<div>
Write some text in textbox:
<input type="text" ng-model="sometext">
<h1>Welcome {{ sometext }}</h1>
<h4>Uppercase: {{ sometext | uppercase }}</h4>
<h4>Lowercase: {{ sometext | lowercase }}</h4>
</div>
</body>
</html>

The output is shown as in the following in Chrome. The left side shows the Sublime text editor.

Now we understand the example in AngularJs. Let's go deeper and understand what the various features of AngularJs are.

Features

The following are the features of AngularJs:

Modules.
Directives.
Expressions.
Controller.
Scope.
Data Binding.
Validations.
Filters.
Services.
Routing.
Dependency Injection.
Testing.

The following is an explanation of the preceding features listed.

1. Modules

An Angular module defines an application. A module is a container for the various parts of an application. All application controllers should belong to a module.
An Angular module is simply a collection of functions defined in a JavaScript file.
A module divides an Angular app into small, reusable and functional components that can be integrated with other Angular apps.
Each module is identified by a unique name and can be dependent on other modules. In AngularJS, every web page (view) can have a single module assigned to it via ng-app directive.

Example-2 Showing a module

<! DOCTYPE html>
<html>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>
<body>
<div ng-app="myApp" ng-controller="myCtrl"> //Referring module name myApp
{{ firstName + " " + lastName }}
</div>
<script src="myApp.js"></script>
<script src="myCtrl.js"></script>
</body>
</html>

MyApp.js

var app = angular.module("myApp", []); //defining the module name “myApp”

myCtrl.js

app.controller("myCtrl", function($scope) {
$scope.firstName = "Pradeep";
$scope.lastName= "K";
});

2. Directives

Directives are markers on a DOM element (such as an attribute, element name, comment or CSS class) that tells the AngularJS HTML compiler ($compile) to attach a specified behaviour to that DOM element or even transform the DOM element and its children. The angular directives start with “ng-”. Some of the directives is listed here with their purpose.

ng-app: To bootstrap the application
ng-controller: To set a controller on a view
ng-view: Indicates the portion of the page to be updated when route changes
ng-show / ng-hide: Shows/hides the content within the directive based on the boolean equivalent of value assigned
ng-if: Places or removes the DOM elements under this directive based on the boolean equivalent of value assigned
ng-model: Enables two-way data binding on any input controls and sends the validity of data in the input control to the enclosing form
ng-class: Provides an option to assign a value of a model to CSS, conditionally apply styles and use multiple models for CSS declaratively
ng-repeat: Loops through a list of items and copies the HTML for every record in the collection
ng-options: Used with HTML select element to render options based on data in a collection
ng-href: Assigns a model as hyperlink to an anchor element
ng-src: Assigns a model to source of an image element
ng-click: To handle the click event on an element
ng-change: Requires ng-model to be present along with it. Calls the event handler or evaluates the assigned expression when there is a change to the value of the model
ng-form: Works the same as a HTML form and allows the nesting of forms
ng-non-bindable: Prevents AngularJS from compiling or binding the contents of the current DOM element
ng-repeat-start and ng-repeat-end: Repeats top-level attributes
ng-include: Loads a partial view
ng-init: Used to evaluate an expression in the current scope
ng-switch conditionally displays elements
ng-cloak to prevent Angular HTML to load before bindings are applied

Note: In the project while working the build in directive doesn't fulfil our requirements and in that case we need to go for creating custom directives. The best example for creating a custom directive is DOM Manipulation in the page. The ng-app is an important directive that designates the root element of the application and is typically placed near the root element of the page, for example on the <body> or <html> tags.

Some sample codes for directive

Example-3 ng-Repeat directive

<!DOCTYPE html>
<html>
<script src= "http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>
<body>
<div ng-app="" ng-init="names=['Pradeep','John','Kai']">
<p>Looping with ng-repeat:</p>
<ul>
<li ng-repeat="x in names">
{{ x }}
</li>
</ul>
</div>
</body>
</html>

Example-4 ng-options directive

<html
xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Binding both value and text in select dropdown in Angular.js</title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.9/angular.min.js"></script>
<script type="text/javascript">
var app = angular.module('sampleapp', [])
app.controller('samplecontrol', function ($scope) {
$scope.sample = [{id: '1',
name: 'Bangalore'
}, {id: '2',
name: 'Chennai'
}, {id: '3',
name: 'Kolkata'
}, {id: '4',
name: 'Mumbai'
}, {id: '5',
name: 'Delhi'
}, {id: '6',
name: 'Pune'
}];
});
</script>
</head>
<body data-ng-app="sampleapp" ng-controller="samplecontrol">
<form id="form1">
Select Name:
<select ng-model="selectedItem" ng-options="s.id as s.name for s in sample" ng-model="col">
<option value="">--Select--</option>
</select>
<p>selected item is: {{selectedItem}}</p>
</form>
</body>
</html>

Output

3. Expressions

The {{ }} are a declarative way of specifying a data binding location in HTML. AngularJS will automatically update this text.
Using an expression we can do data binding, as in {{ }}.
Angular expressions can be added inside the HTML templates.
Angular expressions doesn't support control flow statements (conditionals, loops, or exceptions).
Angular expressions support filters to format data before displaying it.

Example-5 Showing Expressions

<!DOCTYPE html>
<html>
<script src= "http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>
<body>
<div ng-app="" ng-init="firstName='John'">
<p>Input something in the input box:</p>
<p>Name:
<input type="text" ng-model="firstName">
</p>
<p>You wrote: {{ firstName }}</p>
</div>
</body>
</html>

{{ firstName}} is the expression here.

4. Controller

AngularJS applications are controlled by controllers.
The ng-controller directive defines the application controller.
A controller is a JavaScript Object, created by a standard JavaScript object constructor.
In Angular, a Controller is a JavaScript constructor function that augments the Angular Scope.

Example-6 Showing controller

<!DOCTYPE html>
<html>
<script src= "http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>
<body>
<div ng-app="myApp" ng-controller="myCtrl">
First Name:
<input type="text" ng-model="firstName">
<br>
Last Name:
<input type="text" ng-model="lastName">
<br>
<br>
Full Name: {{firstName + " " + lastName}}
</div>
<script>
var app = angular.module('myApp', []);
app.controller('myCtrl', function ($scope) {
$scope.firstName = "Pradeep";
$scope.lastName = "K";
});
</script>
</body>
</html>

5. Scope

A $scope is a JavaScript object that is used for communication between the controller and view. Basically, $scope binds a view (DOM element) to the viewmodel and functions defined in a controller.

Scope is the bridge between the Controller and the View.
Scope is the data source for angular js
scope is considered as model and ViewModel in MV-Whatever design pattern
scope provides two-way binding when the model data changes scope data changes by notification in Angular js
We can add and remove a property when required.
When calling a database or any service to do a CRUD operation, all the data manipulation and assignment of data happens through a scope object.

6. Data Binding

Two-way data binding synchronizes data between a model and a view. In other words, any change in model will update the view and vice versa. The ng-model directive is used for two-way data binding. In the first example we saw that when the user types into the text box the changed value shows in upper and lower case in the label. This is two-way binding.

AngularJS handles the data-binding mechanism using the three powerful functions: $watch(), $digest() and $apply (). Most of the time AngularJS will call the $watch() and $digest() functions on the scope object for you, but in some cases you may need to call these functions yourself to update new values.

7. Validations

AngularJS forms and controls can validate input data.

AngularJS forms and controls can provide validation services and notify users of invalid data.

Example-7 Showing Validations

<!DOCTYPE html>
<html>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>
<body>
<h2>Validation Example</h2>
<form ng-app="myApp" ng-controller="validateCtrl"
name="myForm" novalidate>
<table style="border: 1px solid gray; width: 500px;">
<tr>
<td colspan="2">
<span style="color: red; padding-left:100px; border: 3px;">Log In </span>
</td>
</tr>
<br />
<tr>
<td>Username:
</td>
<td>
<input type="text" name="user" ng-model="user" required>*
<span style="color: red" ng-show="myForm.user.$dirty && myForm.user.$invalid">
<span ng-show="myForm.user.$error.required">Username is required.</span>
</span>
</td>
</tr>
<tr>
<td>Email:
</td>
<td>
<input type="email" name="email" ng-model="email" required>*
<span style="color: red" ng-show="myForm.email.$dirty && myForm.email.$invalid">
<span ng-show="myForm.email.$error.required">Email is required.</span>
<span ng-show="myForm.email.$error.email">Invalid email address.</span>
</span>
</td>
</tr>
<tr>
<td colspan="2">
<p>
<input type="submit"
ng-disabled="myForm.user.$dirty && myForm.user.$invalid ||
myForm.email.$dirty && myForm.email.$invalid">
</p>
</td>
</tr>
</table>
</form>
<script>
var app = angular.module('myApp', []);
app.controller('validateCtrl', function ($scope) {
$scope.user = 'Pradeep K';
$scope.email = '[email protected]';
});
</script>
</body>
</html>

Output

8. Filters

Filters are used to extend the behaviour of binding expressions and directives.
Filters allow formatting the data to be displayed on the DOM.
Filters are invoked in the HTML with the | (pipe) character inside expressions {{ }}.
They are used to format values or to apply certain conditions. They are executed whenever the value bound in the binding expression is updated.

Example-7 Showing Filter example

<html>
<head>
<script src= "http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>
<script>
var app = angular.module('myApp', []);
app.controller("namesCtrl", function ($scope) {
$scope.friends = [
{ name: "Karl", age: 27, city: "Bangalore" },
{ name: "Lewis", age: 55, city: "Newyork" },
{ name: "Adarsh", age: 20, city: "London" },
{ name: "John", age: 21, city: "Newyork" },
{ name: "David", age: 20, city: "Chenai" },
{ name: "Miller", age: 32, city: "Paris" }
];
});
</script>
</head>
<div ng-app="myApp" ng-controller="namesCtrl">
<p>Filtering input:</p>
<p>
<input type="text" ng-model="test">
</p>
<ul>
<li ng-repeat="x in friends | filter:test | orderBy:'name'">
{{ (x.name | uppercase) + ', ' + x.age +','+x.city }}
</li>
</ul>
</div>
</html>

Output

9. Services

If you need to share state across your application, or need a solution for data storage or cache, think of Services. Services are singletons and can be used by other components such as directives, controllers, filters and even other services. Services do not have a scope of their own, so it is permissible to add eventlisteners in Services using $rootScope.

There are the following few services that we use frequently:

$http – Used for Ajax calls for server communications
$window-Provide a reference to a DOM object.
$Location- Provides reference to the browser location
$timeout –Provides a reference to window.settimeout function
$Log- Used for logging
$sanitize- used to avoid script injections and display raw html in page
$Rootscope –Used for scope hierarchy manipulation
$Route –used to display browser based path in browser URL.
$Filter –Used for providing filter access.
$resource- used to work with Restful API
$document – used to access window. Document object
$exceptionHandler- used for handling exceptions.
$q- provides a promise object

10. Routing

AngularJS Routing helps you to divide your app into multiple views and bind multiple views to Controllers. The magic of Routing is taken care by an AngularJS service $routeProvider. The $routeProvider service provides the methods when() and otherwise() to define the routes for your app. Routing has dependency on the ngRoute module.

It helps us to divide a Single Page Application (SPA) into multiple views. Dividing a SPA into multiple views helps to logically divide the app and make it more manageable. Routing in an Angular application is taken care of by a service provider known as “$routeProvider”. The $routeProvider is configured in app the module's config() function. $routeProvider provides the following two methods:

when(): that matches a pattern
otherwise(): otherwise() method to define a
default route.
App.config(['$routeProvider',
function($routeProvider)
{
$routeProvider.
when('/List',
{
templateUrl: 'Views/list.html',
controller: 'ListController'
}).
when('/Add',
{
templateUrl: 'Views/add.html',
controller: 'AddController'
}).
otherwise({
redirectTo: '/List'
});
}]);

11. Dependency Injection

Dependency Injection (DI) is a software design pattern that deals with how components get hold of their dependencies. Dependency injection helps us to create a loosely-coupled architecture. Dependency Injection is designed on the following two principles.

A. High-level modules should not depend on low-level modules. Both should depend on abstractions.

B. Abstractions should not depend on details. Details should depend on abstractions.

The Angular injector subsystem is in charge of creating components, resolving their dependencies and providing them to other components when needed. Components such as services, directives, filters and animations are defined by an injectable factory method or constructor function. These components can be injected with "service" and "value" components as dependencies. AngularJS has a built-in dependency injector that keeps track of all components (services, values and so on) and returns instances of needed components using dependency injection. The Dependency injector of AngularJS works based on names of the components.

A simple case of dependency injection in Angular js:

AppModule.controller("AppController", function($scope, $window, $log,$http)
{
});

Here, $scope, $window and $log, $http are passed into the controller using dependency injection.

12. Testing

As said before, Angular components supports dependency injections. This dependency injections allows Angular codes to be testable. Use any kind of component in Angular, it can't be written without getting some of the external components injected in. The testing framework like Jasmine and Karma are the most widely used testing framework with Angular. These two frameworks support mocking and are highly configurable using a JSON file and the use of various plug-ins.

In the next article I will return with each concept in details. I hope you now have a basic understanding of AngularJS contents. Thanks for reading!

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