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AngularJS is an open-source front-end web framework maintained by Google and a vast community. It is specifically designed to overcome challenges in Single-Page Applications (SPAs) development.
AngularJS structures applications into distinct modules, facilitating modular development and easy maintenance.
Data changes in the Model (back-end) or the View (front-end) automatically update the other.
This design pattern makes components independent by injecting dependencies from external sources rather than hard-coding them.
They are markers in the DOM that tell AngularJS's HTML compiler to attach a specific behavior to the DOM element or to transform the DOM element and its children.
AngularJS leverages templates that combine HTML with AngularJS directives and expressions for dynamic content. The framework offers sophisticated data binding to keep the UI and app data in sync.
AngularJS simplifies communication with RESTful APIs, making it easy to work with server-side data.
AngularJS embraces the Model-View-Controller (MVC) design pattern, which helps in organizing code into modular, testable, and maintainable units.
The framework supports advanced routing capabilities, enabling a multi-view layout by defining the route for each view.
AngularJS facilitates the creation of reusable business logic units using services. These units encapsulate specific tasks and can be injected where needed.
Built-in support for unit testing allows components to be tested in isolation, aiding in bug detection and rapid iteration.
AngularJS readily integrates with third-party libraries such as Bootstrap and jQuery.
The framework, adhering to web standards, offers consistent behavior across platforms and browsers.
AngularJS simplifies the process of form validation through its built-in directives and services.
As the framework progresses from AngularJS to Angular, later versions offer enhancements in performance, developer experience, and security.
AngularJS maintains a unidirectional flow of data and has mechanisms in place to manage state, ensuring data accuracy and minimizing unexpected behaviors.
Components in AngularJS go through a consistent lifecycle: creation, rendering, updates, and eventual destruction. This lifecycle management allows for targeted operations at various stages.
Developers can enhance AngularJS applications using tools like Ahead-of-Time (AOT) compilation, which optimizes performance by moving logic and templates to offline, pre-compiled files.
Two-way data binding in AngularJS ensures that model changes automatically reflect in the view, and vice versa.
When a model or the input field value in UI gets updated, AngularJS instantly reflects the changes both ways. It essentially acts as a bridge, allowing seamless synchronization between the model and view in near real-time.
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Initial Data: The data originates from the model and populates the view, providing users with initial values or content.
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View Modification: When a user interacts with the UI, such as modifying an input field or selecting an option, AngularJS instantly updates the associated model.
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Model Changes: These model adjustments, occurring in real-time, are then immediately updated in both model and view, aligning the two components.
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Validation and Coercion: Inputs are also validated and optionally coerced.
- When a user input contradicts data type expectations or fails validation rules, AngularJS can correct or validate it, ensuring data integrity.
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View Update: The now-validated or coerced data returns to the view, empowering users with visual feedback on any adjustments or corrections.
The entire two-way data binding cycle ensures an instantaneous, synchronized relationship between the model and the UI. This feature significantly lowers the need for manual DOM manipulation or event handling.
Directives in AngularJS are markers in the DOM that AngularJS library can reinterpret to inject extra behavior or allow data-binding. They encompass JS functions, DOM elements, and even comment elements.
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ngApp: Defines the root element of the AngularJS application.
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ngController: Associates the controller with a section of the view.
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ngModel: Links an HTML element such as an input, select or textarea to a property on the scope.
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ngBind: Binds the innerHTML of the element to the expression.
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ngBindHtml: For DOM-based XSS protection, binds innerHTML to the expression after sanitizing it.
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ngBindTemplate: Used for inline templates.
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ngClick: Executes custom behavior on a click event.
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Validation Directives: AngularJS offers two types of field validation attributes:
-
Regular HTML5 Validation Attributes
AngularJS sets up the appropriate validation properties on the model using the following HTML5 attributes:
- required
- min
- max
- minlength
- maxlength
- pattern
-
Custom Validation Directives
You can build these custom directives to suit specific requirements. Common examples are:
- match
- unique-email
These directives react to particular DOM events:
-
ngBlur and ngFocus: Used to detect element focus or blur.
-
ngChange: Triggers when the associated model is changed.
The library supports more specific ones like ngCut, ngCopy, ngPaste.
These directives dynamically alter CSS classes and inline styles:
- ngClass : switches classes based on object states.
- ngStyle : dynamically applies inline styles.
AngularJS aligns with other libraries through integration directives:
- ngIf : conditionally includes an element.
- ngSwitch : operates like a switch statement.
- ngRepeat : loops over arrays and objects.
AngularJS extends form behavior with:
-
ngForm : groups form controls.
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ngSubmit : binds to the submit method of a form.
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ngOptions : dynamically populates select elements.
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ngInclude : fetches, compiles and includes an external HTML fragment into the directive element.
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ngView : sets up a consistent mechanism for multiple views in a Single Page Application (SPA).
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ngClassEven and ngClassOdd : Simplify zebra striping.
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ngCsp : Essential in Content Security Policy protection.
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ngPluralize : Optimizes pluralization for different languages.
The AngularJS Digest Cycle is responsible for managing two-way data binding, keeping the View and Model synchronized. The cycle usually runs automatically but can be triggered manually in certain cases.
- Watchers: These are functions that observe changes in the model, ensuring the View is updated accordingly.
- Dirty-Checking: Angular performs this by comparing the current state of data (the "new" state) with the previous state (the "old" state). If there's a discrepancy, the system flags the data as "dirty", indicating a change requiring action.
- $watch: This directive is used to track changes in model properties, although it should be used judiciously as excessive
$watchercreation can negatively impact app performance.
Even though Angular aptly manages the Digest Cycle, developers can manually initiate it as well. This can be useful in cases where the Cycle does not trigger automatically.
To do this, you can use:
-
$scope.$apply(): This tells Angular that a part of the code (a function or code block) was executed outside of its context and changes might have occurred. Consequently, it forces a two-way data binding sync. However, this typically triggers the complete Digest Cycle, which might lead to performance issues if used in high-frequency contexts. -
$scope.$digest(): Instead of initiating a complete Digest Cycle, you can specify to sync only certain portions. This method runs the Digest Cycle on the current scope and its children, stopping if no changes are detected.
Angular initiates the Digest Cycle in response to various events, like user actions or asynchronous activities. The process essentially involves two steps: change detection and view updating.
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Change Detection: Identify alterations in the data. Angular does this by continuously comparing the current state with the previous state, flagging any discrepancies.
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View Update: If changes are detected, update the View to reflect the new state. Angular ensures these updates are efficient and minimized to only the affected portions, optimizing application performance.
The Digest Cycle continues iteratively until:
- It encounters a stable state where no further changes are detected.
- It reaches maximum iteration counts, after which it throws an error, indicating a possible problem in the code.
Below is the AngularJS code that demonstrates the Digest Cycle with ng-click and manual control using $digest:
<!DOCTYPE html>
<html>
<head>
<title>Digest Cycle</title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js"></script>
</head>
<body ng-app="digestApp" ng-controller="digestCtrl">
<h1>{{ title }}</h1>
<p>Click count: {{ clickCount }}</p>
<button ng-click="incrementCount()">Click me</button>
</body>
<script type="text/javascript">
var app = angular.module('digestApp', []);
app.controller('digestCtrl', function($scope) {
$scope.title = 'Digest Cycle Example';
$scope.clickCount = 0;
$scope.incrementCount = function() {
$scope.clickCount++;
// Manually trigger the Digest Cycle after incrementing the click count
$scope.$digest();
};
});
</script>
</html>In this example, with each button click, we trigger $scope.incrementCount() to increment the click count and force a manual Digest Cycle with $scope.$digest(). Be aware that the manual initiation might not always be appropriate and can potentially lead to performance issues if not handled carefully.
Scope in AngularJS and JavaScript serve analogous purposes but differ in several aspects.
| Distinction | AngularJS Scope | JavaScript Scope |
|---|---|---|
| Scope Creation | Automatically established for each controller | Manually created with each function |
| Initiation Control | Programmatic declaration in a controller | Unpredictable scope setup can sometimes lead to issues |
| Hierarchical Structure | Forms parent-child relationship in views | Unidirectional from inner to outer functions |
| Scope Prototyping | Inherits method childScope.prototype = parentScope; |
Does not inherit prototype chains |
| Definition Isolation | Local to the controller and its views | Global by default; local when using functions |
| Scope Destruction Control | Automatic disposal on controller exit | Garbage collection for variables with no references |
Here is the JavaScript code:
// Controller 1
angular.module('myApp').controller('Ctrl1', function($scope) {
$scope.message = "Hello from Ctrl1!";
});
// Controller 2
angular.module('myApp').controller('Ctrl2', function($scope) {
console.log($scope.message); // This will output "Hello from Ctrl1!"
$scope.message = "Hello from Ctrl2!";
});Here is the AngularJS code:
// Controller 1
angular.module('myApp').controller('Ctrl1', function($scope) {
$scope.message = "Hello from Ctrl1!";
});
// Controller 2
angular.module('myApp').controller('Ctrl2', function($scope) {
console.log($scope.message); // This will output "Hello from Ctrl1!"
$scope.message = "Hello from Ctrl2!";
});In AngularJS, the controller is a core component that manages data interaction and mediates between the view and the model.
It's responsible for initializing the state of the $scope, binding model to the view, and handling any user interactions.
The controller's primary role is to initialize the $scope object, which acts as the glue between the controller and the view HTML.
-
Managing Scope: The controller defines what part of the model should be exposed to the view by attaching properties and functions to the
$scopeobject. -
Data Handling: It mediates data operations, such as fetching initial data, processing input, and updating the model.
-
Event Handling: The controller handles both view-specific DOM events and custom events $using
$emitand$broadcastto communicate upwards or downwards through the scope hierarchy, respectively$. -
Code Encapsulation: Encloses data and behavior, limiting the exposure to the global state where other components can also access it.
-
Lifecycle Management: Conducts cleanup tasks during specific stages of the component's lifecycle, such as removing event listeners or unsubscribing from observables.
-
Service Integration: It collaborates with various AngularJS services such as
$httpfor making HTTP requests or$qfor asynchronous operations.
Every controller in AngularJS is associated with an HTML element via the ng-controller directive, specifying the controller's name.
For instance, in the code snippet below, the MyController is the registered controller, and its functionality is available within the div element it's associated with:
<div ng-controller="MyController">
<p>{{ myProperty }}</p>
</div>Here is the AngularJS code:
// Define a controller named 'MyController'
app.controller('MyController', function($scope) {
// Initialize a property on the $scope object
$scope.myProperty = 'Hello, world!';
});In this example, app is the reference to the AngularJS module. By invoking the controller method on app and providing a name $here, 'MyController'$ and a controller function, a new controller is created. The controller function typically takes $scope as an argument, through which it configures the scope object for the given view.
Lastly, the ng-controller directive is used. When the AngularJS framework encounters this directive, it connects the div element and its children with the controller, enabling $scope-based properties and methods within that "scope".
Services in AngularJS are singletons and facilitate sharing of functions, objects, or values among different parts of an application. They cover various aspects such as data management, communication with servers, and more.
-
$animate: Offers methods for animation, helping UI elements transition in a controlled manner. -
$cacheFactory: Serves as a key-value store for temporary data, enhancing application performance by reducing excessive data requests. -
$compile: Transforms AngularJS directives, templates, and scopes into corresponding HTML, ready for rendering. -
$controller: Primarily responsible for constructing the application’s controllers. -
$document: Acts as a wrapper around the browser's globaldocumentobject. -
$exceptionHandler: Centralizes error handling, easing the process of debugging and monitoring errors in an AngularJS application. -
$http: Facilitates synchronous and asynchronous communication with remote servers. It provides support for traditional RESTful APIs as well as AJAX requests. -
$injector: Serves as the dependency injection module, managing dependencies across different components of the application. -
$interval: Offers recurring task scheduling based on a specific time interval. -
$location: Encapsulates and abstracts the URL of the browser. -
$log: A centralized logging tool for error and debugging messages. -
$parse: Responsible for parsing AngularJS expressions and converting them into functions. -
$q: Provides mechanisms for asynchronous task management, such as promises and deferred objects. -
$rootElement: Represents the root element of the entire AngularJS application. -
$rootScope: Acts as the parent scope of all other scopes within the application. Modifications to$rootScopeare often discouraged. -
$templateCache: Stores AngularJS templates, enabling their retrieval without a server request. -
$timeout: Offers a way to schedule specific tasks to execute after a certain time delay. -
$window: Acts as a wrapper, encapsulating the globalwindowobject.
Developers can create their own custom AngularJS services using any of three primary methods: factory, service, and provider.
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Factory: Delivers objects or primitives. A factory function returns whatever type of object you want to provide. This gives you more freedom and can be particularly useful when there are dependencies that need to be injected into the factory function.
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Service: Utilizes constructor functions. The service method takes a constructor function, or the name of a constructor function. When AngularJS injects your service into another component, it calls your constructor function with the "new" keyword to create an instance of the service.
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Provider: The provider method is the most flexible and powerful of the three. It allows you to configure your service before your application starts by defining a provider recipe.
While AngularJS promotes a modular architecture where components are typically self-contained, you may need to share data between controllers. To facilitate this, AngularJS offers a few primary methods.
Identify that a hierarchal relationship already exists with one controller as the parent of the other. Here it is not mandatory to use the vm.
When to Use: Parent-child relationships are useful when one view must contain the other and when you are building composite widgets.
// Parent Controller
angular.module('myApp').controller('ParentCtrl', function($scope) {
$scope.sharedData = 'Hello from parent';
});
// Child Controller
angular.module('myApp').controller('ChildCtrl', function($scope) {
// Access the shared data from the parent
$scope.childSharedData = $scope.sharedData;
});Create a service that acts as a data mediator between controllers. Use the this context to make the service's data accessible.
When to Use: Services are an ideal choice when multiple controllers across the application need access to the same data.
// Shared Data Service
angular.module('myApp').service('sharedDataService', function() {
this.sharedData = 'Hello from shared service';
});
// Controller 1
angular.module('myApp').controller('Ctrl1', function(sharedDataService) {
this.dataFromService = sharedDataService.sharedData;
});
// Controller 2
angular.module('myApp').controller('Ctrl2', function(sharedDataService) {
this.dataFromService = sharedDataService.sharedData;
});Utilize $emit and $broadcast to trigger and capture events throughout the application. $rootScope is essential for broadcasting.
$emit: Triggers events upwards through the $scope hierarchy.$broadcast: Triggers events downwards through the $scope hierarchy.
When to Use: Events are useful when one controller needs to notify other controllers in the application about an update or a change in the data.
// Controller 1
angular.module('myApp').controller('Ctrl1', function($rootScope) {
this.sendMessage = function(data) {
$rootScope.$emit('customEvent', data);
};
});
// Controller 2
angular.module('myApp').controller('Ctrl2', function($rootScope) {
var unregister = $rootScope.$on('customEvent', function(event, data) {
console.log(data); // Process the received data
unregister(); // Unsubscribe from the custom event
});
});The ng-app directive in AngularJS acts as the application's starting point. It designates the root element of an Angular application and initializes the relevant application module.
- Bootstrapping: The directive is primarily responsible for kickstarting the Angular application.
- Module Specification: By specifying the ng-app directive, you connect it explicitly to an Angular module. Without this connection, the HTML for individual modules could become difficult to manage in larger applications.
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Load Angular: At the outset, the browser loads the Angular framework.
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Identify Root Element: Upon document loading, Angular locates the HTML element hosting the ng-app directive. This step is central to the bootstrapping process, signaling the commencement of Angular operations.
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Bootstrapping and Initialization: Angular boots up the application, linking the identified root element to a specific module. The framework thematically organizes application components into modules.
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Compilation and Binding: Angular carries out two major operations: Template Compilation - translating HTML into a set of instructions for the browser, and Data Binding - setting up the data binding context. This process associates the view with the logic managed inside the application modules.
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Rendering and Interaction: The framework renders the prepared, efficient template and establishes interactivity.
The ng-app directive points out the root element of an AngularJS application. Once the directive is used on any element, AngularJS assumes control of that part.
Here is an example:
<!DOCTYPE html>
<html lang="en" ng-app="myApp">
<head>
<!-- Head content -->
</head>
<body>
<div ng-controller="myCtrl">
{{ greeting }} World! <!-- The controller provides the value of 'greeting' -->
</div>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js"></script>
<!-- The app module and main controller are defined and connected here -->
<script>
angular.module('myApp', []).controller('myCtrl', function($scope) {
$scope.greeting = 'Hello';
});
</script>
</body>
</html>AngularJS's two-way data binding feature is powered by directives like ng-model. This mechanism synchronizes the Model and View layers, ensuring real-time updates.
- Registers User Input:
ng-modelbinds form elements to model data, using their value/input as a source. - Keeps Model Updated: When the form element changes, the associated model updates automatically. This action is observable through
$watchfunctions. - Syncs with the Backend: When the model changes,
ng-modeltriggers necessary operations, like form validity checks and web service updates, ensuring the backend remains in sync with the UI.
Here is the HTML:
<div ng-app="myApp" ng-controller="myCtrl">
<p>Name: <input type="text" ng-model="name"></p>
<p>Your name is: {{name}}</p>
</div>The JavaScript:
var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope) {
$scope.name = "John Doe";
});The $scope in AngularJS represents the context within which model, view, and controller interact. This two-way bridge enables real-time data synchronization and is fundamental to AngularJS 1.x applications.
-
Data Share:
$scopestores both model data and references to functions or objects, making them available across controllers, directives, and views. -
Watchers: These special agents, maintained by the
$digestcycle, monitor$scopeproperties for changes. When a change is detected, the associated actions are executed, ensuring dynamic view updates.
Here is the JavaScript code:
// Define a controller
app.controller('MyController', function($scope) {
// Initialize a property on scope
$scope.username = 'John Doe';
// Define a function to change the username
$scope.changeUsername = function() {
$scope.username = 'Jane Doe';
};
});And here's the HTML:
<div ng-controller="MyController">
<input type="text" ng-model="username">
<button ng-click="changeUsername()">Change Name</button>
<h2>Welcome, {{ username }}!</h2>
</div>In this example, the ng-model directive establishes a data-binding between the text input and the $scope.username. As a result, any changes to the username property in the MyController reflect in real-time in the associated view.
While using AngularJS, you may benefit from the $rootScope in specific scenarios. However, its use should generally be avoided as it could lead to poorer code readability and harder debugging.
- Directives
- Cross-Component Communication
- Bootstrap Scope (Rare)
- Scope Level switches in Angular: $rootScope
Medium: This answer can be delivered in 60-90 seconds.
- Scope Level switches in Angular: $rootScope
<div ng-app="myApp" ng-controller="myCtrl">
<button ng-click="incrementCounter()">Increment</button>
<my-custom-component></my-custom-component>
</div>var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope, $rootScope) {
$scope.counter = 0;
$scope.incrementCounter = function () {
$scope.counter++;
$rootScope.$broadcast('counterUpdated', $scope.counter);
};
});
app.directive('myCustomComponent', function() {
return {
restrict: 'E',
template: '<p>Counter from RootScope: {{rootCounter}}</p>',
link: function(scope) {
var counterListener = $rootScope.$on('counterUpdated', function(event, counter) {
scope.rootCounter = counter;
});
scope.$on('$destroy', counterListener); // cleanup to prevent memory leaks
}
};
});Scope hierarchy refers to the nesting of scopes in an AngularJS application, resembling a tree structure. Each scope is responsible for a section of the DOM, and its lifecycle is closely linked with this DOM segment.
AngularJS has a global scope represented by $rootScope. It's primarily used to share data or trigger events across the application.
Each AngularJS controller instantiates its own scope. This local scope is a child of the $rootScope and serves as a foundation for batching related to its assigned view.
- Segregation: Controllers define specific boundaries within the DOM by creating new child scopes.
- Inheritance: Scopes inherit elements from their parent scopes, establishing a flow of data from the top to the bottom of the tree.
- (Parent -> Child): A change in a parent scope can affect all its child scopes, but the reverse is not true. This unidirectional data flow solidifies encapsulation and enhances control.
- Parent elements assign objects or function references to their scopes. Child scopes that don't redefine these elements retain references to the parent's objects. However, when a child scope modifies a prototypically-linked object, it does create a new reference, leading to potential side effects.
In AngularJS, a controller binds the view, typically an HTML page, with the model data. It plays a pivotal role in defining and initializing the data and business logic of a section of your application.
-
Data Modeling: The controller depicts defined data models using Scope objects. AngularJS uses two-way data binding, automatically keeping the model and view in sync.
-
Business Logic: The controller implements business logic, often in the form of functions, that governs the behavior of the model and its interaction with the view.
-
Event Handling: Controllers can respond to user-initiated events like clicks or form submissions. They also emit and handle custom events within the application for inter-component communication.
-
Isolation: AngularJS controllers offer varying degrees of scope isolation, ensuring modularity and preventing data or action overlaps in nested or sibling components.
-
Initialization: Controllers set up an initial state, execute start-up tasks, and prepare the contextual environment for the rest of the application.
A controller in AngularJS is defined using the app.controller() method, where app is your module:
-
JavaScript:
// Define the module var app = angular.module('myApp', []); // Create the controller app.controller('MyController', function($scope) { $scope.greeting = 'Hello, World!'; });
The controller is attached to a module using the
app.controller()method, which takes the controller name and a function, called the controller's constructor. -
HTML:
<div ng-app="myApp" ng-controller="MyController"> {{ greeting }} </div>
In this example,
ng-controller="MyController"attaches the defined controller to the section of HTML enclosed within the element.
AngularJS uses two-way data binding. Any changes in the model, like variables defined in the $scope object, automatically reflect in the view, and vice versa.
-
JavaScript:
app.controller('MyController', function($scope) { $scope.greeting = 'Hello, World!'; $scope.updateGreeting = function(newGreeting) { $scope.greeting = newGreeting; }; });
-
HTML:
<div ng-app="myApp" ng-controller="MyController"> <input type="text" ng-model="greeting"> <button ng-click="updateGreeting('Goodbye!')">Update Greeting</button> </div>
As seen in both the HTML and JavaScript snippets, any changes in the text input or via the button immediately update the
greetingdisplayed.
AngularJS controllers are constructed using the Dependency Injection design pattern. The $scope object is the nexus for data-binding and a medium through which the controller interacts with the view.
The definition of the controller function receives dependencies like $scope, and AngularJS maintains a registry of these dependencies, resolving them whenever the controller is initialized.
AngularJS uses the MVC architectural pattern. In this context, a controller contains methods that manipulate the model. In AngularJS, you can define and handle Controller methods through several techniques, including $scope.
- Define Method on
$scopein the Controller:
app.controller("myController", function($scope) {
$scope.greet = function(name) {
alert("Hello, " + name + "!");
};
});Here, $scope.greet is the method.
- Invoke in the View with a suitable directive such as
ng-click. You can then pass arguments, such as anng-modeldirectly.
<!DOCTYPE html>
<html ng-app="myApp">
<head>
<title>AngularJS Application</title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js"></script>
</head>
<body>
<div ng-controller="myController">
<input type="text" ng-model="user.name" placeholder="Enter your name" />
<button ng-click="greet(user.name)">Greet</button>
</div>
<script>
var app = angular.module('myApp', []);
app.controller('myController', function($scope) {
$scope.greet = function(name) {
alert("Hello, " + name + "!");
};
});
</script>
</body>
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