Dependency Injection is a software design pattern in which components are given their dependencies instead of hard coding them within the component. This relieves a component from locating the dependency and makes dependencies configurable. This helps in making components reusable, maintainable and testable.

AngularJS provides a supreme Dependency Injection mechanism. It provides following core components which can be injected into each other as dependencies.

value
factory
service
provider
constant

value

value is simple javascript object and it is used to pass values to controller during config phase.

//define a module

var mainApp = angular.module(“mainApp”, []);

//create a value object as “defaultInput” and pass it a data.

mainApp.value(“defaultInput”, 5);

…

//inject the value in the controller using its name “defaultInput”

mainApp.controller(‘CalcController’, function($scope, CalcService, defaultInput) {

$scope.number = defaultInput;

$scope.result = CalcService.square($scope.number);

$scope.square = function() {

$scope.result = CalcService.square($scope.number);

}

});

factory

factory is a function which is used to return value. It creates value on demand whenever a service or controller requires. It normally uses a factory function to calculate and return the value.

//define a module

var mainApp = angular.module(“mainApp”, []);

//create a factory “MathService” which provides a method multiply to return multiplication of two numbers

mainApp.factory(‘MathService’, function() {

var factory = {};

factory.multiply = function(a, b) {

return a * b

}

return factory;

});

//inject the factory “MathService” in a service to utilize the multiply method of factory.

mainApp.service(‘CalcService’, function(MathService) {

this.square = function(a) {

return MathService.multiply(a,a);

}

});

…

service

service is a singleton javascript object containing a set of functions to perform certain tasks. Services are defined using service() functions and then injected into controllers.

//define a module

var mainApp = angular.module(“mainApp”, []);

…

//create a service which defines a method square to return square of a number.

mainApp.service(‘CalcService’, function(MathService) {

this.square = function(a) {

return MathService.multiply(a,a);

}

});

//inject the service “CalcService” into the controller

mainApp.controller(‘CalcController’, function($scope, CalcService, defaultInput) {

$scope.number = defaultInput;

$scope.result = CalcService.square($scope.number);

$scope.square = function() {

$scope.result = CalcService.square($scope.number);

}

});

provider

provider is used by AngularJS internally to create services, factory etc. during config phase(phase during which AngularJS bootstraps itself). Below mention script can be used to create MathService that we’ve created earlier. Provider is a special factory method with a method get() which is used to return the value/service/factory.

//define a module

var mainApp = angular.module(“mainApp”, []);

…

//create a service using provider which defines a method square to return square of a number.

mainApp.config(function($provide) {

$provide.provider(‘MathService’, function() {

this.$get = function() {

var factory = {};

factory.multiply = function(a, b) {

return a * b;

}

return factory;

};

});

constant

constants are used to pass values at config phase considering the fact that value can not be used to be passed during config phase.

mainApp.constant(“configParam”, “constant value”);

Example

Following example will showcase all the above mentioned directives.

testAngularJS.htm

<html>

<head>

<title>AngularJS Dependency Injection</title>

</head>

<body>

<h2>AngularJS Sample Application</h2>

<p>Enter a number: <input type = “number” ng-model = “number” /></p>

<p>Result: {{result}}</p>

</div>

</script>

var mainApp = angular.module(“mainApp”, []);

mainApp.config(function($provide) {

$provide.provider(‘MathService’, function() {

this.$get = function() {

var factory = {};

factory.multiply = function(a, b) {

return a * b;

}

return factory;

};

});

mainApp.value(“defaultInput”, 5);

mainApp.factory(‘MathService’, function() {

var factory = {};

factory.multiply = function(a, b) {

return a * b;

}

return factory;

});

mainApp.service(‘CalcService’, function(MathService) {

this.square = function(a) {

return MathService.multiply(a,a);

}

});

mainApp.controller(‘CalcController’, function($scope, CalcService, defaultInput) {

$scope.number = defaultInput;

$scope.result = CalcService.square($scope.number);

$scope.square = function() {

$scope.result = CalcService.square($scope.number);

}

});

</script>

</body>

</html>

Result

Open textAngularJS.htm in a web browser. See the result.

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Comparison between front-end tools
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Angular CLI
Angular CLI commands
Angular Modules

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Working of Angular Applications
Angular App Bootstrapping
Angular Components
Creating A Component Through Angular CLI
Ways to specify selectors
Template and styles
Installing bootstrap to design application
Data Binding
Types of Data Binding
Component Interaction using @Input and @Output decorator
Angular Animations

TypeScript

What is TypeScript
Need of TypeScript
How to install TypeScript
Nodemon for monitoring changes
Interfaces in Class, String Templates, Maps,
Sets and Object Restructuring

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Angular Directives
@Component Directive
Structural Directives
Attribute Directives
Custom Directives
Pipes
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Chaining pipes
Custom pipes
Pipe Transform Interface & Transform Function
Pure and Impure pipes

Angular Services and Dependency Injection

Angular service
Need for a service
Dependency Injection
Creating a service
Hierarchical Injector
Injecting A Service into Another Service
Observables
RxJS Library
Angular’s Interaction with Backend
Parts of an Http Request
HttpClient

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Forms in Angular
What are their functions
Advantages of Forms
Various Types of Forms
What is Angular Validation and Model driven approach

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Angular Routing
Angular Routing benefits and features
Building a single page application and updating it dynamically with Angular Routing
What is Parameter Routing
Router Lifecycle Hooks and Child Routes

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What is Authentication?
Authentication and authorization
Types of Authentication
Where to store tokens?
JSON Web Tokens (JWT)
Authentication in Angular application
Security threats in web application

Testing Angular applications

Testing of Angular applications
Deployment of Angular Test Bed for testing on Angular framework
Setup of various tools for testing
Testing services in Angular Framework
E2E and Document Object Model testing

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