AngularJS encourages the use of Directives to isolate DOM manipulations in event handlers for better testability and modularity. Directives are a powerful feature in AngularJS that allows developers to create reusable components with encapsulated behavior. By leveraging directives, developers can achieve cleaner and more maintainable code by separating DOM manipulations from controller logic.

In AngularJS, expressions can directly call functions defined in the Controller scope. The Controller scope holds the application data and functions, and expressions can access and invoke these functions directly. This feature enhances the flexibility of AngularJS applications by allowing seamless integration of logic defined in the Controller with the HTML templates.

Data Binding is the feature of AngularJS that helps in binding the view to the model. With data binding, changes in the model are automatically reflected in the view, and vice versa. This bidirectional synchronization simplifies the development process, reduces boilerplate code, and enhances the responsiveness of AngularJS applications. Understanding data binding is crucial for effective development in AngularJS.

The primary purpose of data binding in AngularJS controllers is to establish a connection between the model and the view. Data binding allows automatic synchronization of data between these two layers, ensuring that changes in the model are reflected in the view and vice versa. This simplifies the process of keeping the user interface up-to-date with the underlying data and enhances the responsiveness of AngularJS applications. Understanding data binding is fundamental to building dynamic and interactive user interfaces.

In AngularJS, handling global events in controllers can be achieved using $rootScope. While $rootScope provides a way to broadcast events globally, developers should be cautious about its impact on application performance. Broadcasting global events can lead to increased coupling between components and potential performance bottlenecks. Understanding the trade-offs is essential for maintaining a well-performing AngularJS application.

In AngularJS, you apply a controller to a specific part of the view using the ng-controller directive. This directive associates a controller with a portion of the HTML, defining the scope of that controller's influence. By understanding how to use ng-controller, developers can create modular and organized AngularJS applications, where controllers are responsible for specific sections of the UI.

To optimize performance in AngularJS, caching can be implemented when retrieving data from an external API. Caching involves storing previously fetched data locally so that subsequent requests for the same data can be served quickly without making additional network calls. Implementing caching strategies is an advanced technique to enhance the responsiveness and efficiency of AngularJS applications.

A controller in AngularJS is defined using the ngController directive. This directive is used to attach a controller to the HTML element it is declared on. The ngController directive takes the name of the controller as its attribute value, allowing the developer to specify which controller should be associated with a particular section of the view. Understanding how to define controllers is fundamental for organizing and managing application logic in AngularJS.

The "$digest" cycle in AngularJS is crucial for tracking changes and updating bindings in a controlled manner. During the digest cycle, AngularJS checks for changes in the model and updates the view accordingly. This automatic synchronization ensures that the UI reflects the latest changes in the underlying data model. Understanding the $digest cycle is fundamental to managing data binding effectively in AngularJS applications.

Using nested controllers in AngularJS can lead to increased complexity. While it allows for a more modular structure, it can make the code harder to understand and maintain. Developers need to carefully consider the trade-offs and use nested controllers judiciously to strike a balance between modularity and code clarity.