Angular.js Controllers

Controllers in Angular.js are JavaScript functions that are responsible for defining the behavior of a part of the application's UI. They interact with the HTML view and model data using scopes.

1. Overview

Angular.js controllers play a crucial role in separating the concerns of an application by providing a place to define UI behavior and interact with data. They are used to:

Define Behavior: Controllers define the behavior of a specific part of the UI, such as a section of a web page or a component.
Interact with Data: Controllers interact with model data and update the view accordingly. They manipulate data through scopes, which act as glue between the controller and the view.
Manage Scope: Controllers create and manage scopes, which are used to share data between the controller and the view. They provide a context for data binding and event handling.

2. Usage

To create a controller in Angular.js, you define a JavaScript function and attach it to a specific part of the HTML using the ng-controller directive:

// Define a controller function
function MyController($scope) {
    // Controller logic
    $scope.message = 'Hello, Angular!';
}

// Attach the controller to a specific HTML element
<div ng-controller="MyController">
    {{ message }}
</div>

In this example, the MyController function is defined with a $scope parameter, which is used to interact with the view. Inside the controller, a message property is assigned to the scope, which can be accessed and displayed in the HTML view.

3. Scope Management

Controllers create a new scope for each instance, which inherits from its parent scope. This allows for hierarchical scope management and prevents scope pollution. However, it's important to avoid excessive nesting of scopes to maintain performance.

4. Conclusion

Angular.js controllers are essential for defining the behavior of UI components and interacting with model data. By encapsulating UI logic within controllers and managing scope effectively, you can build modular and maintainable Angular.js applications.

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