Web Front-endJS TutorialDetailed explanation of dependency injection mechanism in AngularJS_AngularJSDetailed explanation of dependency injection mechanism in AngularJS_AngularJS
Dependency injection is a software design pattern that replaces hard coding of their dependencies within components by giving them in components. This relieves one component, from locating dependencies, to dependency configuration. This helps make components reusable, maintainable and testable.
AngularJS provides a supreme dependency injection mechanism. It provides the following core components that can inject dependencies on each other.
- Value
- Factory
- Service
- Provider
- Constant value
Value
Values are simple JavaScript objects that are used to pass values during configuration phase controllers.
//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 used to return the value of the function. It creates value on demand, whenever a service or controller requires it. It usually uses a factory function to calculate and return the corresponding 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
A service is a single JavaScript object that contains a set of functions to perform certain tasks. Services are defined using the service() function, which is then injected into the controller.
//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 services, factories, etc. used during the configuration phase of the AngularJS internal creation process (corresponding to when AngularJS bootstraps itself). The script mentioned below can be used to create the MathService we have already created earlier. The provider is a special factory method and get() method that returns a 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 account for the fact that values cannot be passed during the configuration phase by configuring them, and values cannot be passed during the configuration phase.
mainApp.constant("configParam", "constant value");
Example
The following example will demonstrate all the above commands.
testAngularJS.html
<html>
<head>
<title>AngularJS Dependency Injection</title>
</head>
<body>
<h2 id="AngularJS-Sample-Application">AngularJS Sample Application</h2>
<div ng-app="mainApp" ng-controller="CalcController">
<p>Enter a number: <input type="number" ng-model="number" />
<button ng-click="square()">X<sup>2</sup></button>
<p>Result: {{result}}</p>
</div>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.2.15/angular.min.js"></script>
<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>
Results
Open textAngularJS.html in your web browser. See the results below.
From Websites to Apps: The Diverse Applications of JavaScriptApr 22, 2025 am 12:02 AMJavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.
Python vs. JavaScript: Use Cases and Applications ComparedApr 21, 2025 am 12:01 AMPython is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.
The Role of C/C in JavaScript Interpreters and CompilersApr 20, 2025 am 12:01 AMC and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.
JavaScript in Action: Real-World Examples and ProjectsApr 19, 2025 am 12:13 AMJavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.
JavaScript and the Web: Core Functionality and Use CasesApr 18, 2025 am 12:19 AMThe main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.
Understanding the JavaScript Engine: Implementation DetailsApr 17, 2025 am 12:05 AMUnderstanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.
Python vs. JavaScript: The Learning Curve and Ease of UseApr 16, 2025 am 12:12 AMPython is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.
Python vs. JavaScript: Community, Libraries, and ResourcesApr 15, 2025 am 12:16 AMPython and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.
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