A use case for a custom directive in AngularJS that manipulates DOM elements based on specific conditions could be "Implementing Lazy Loading with a Directive." In this scenario, you can create a custom directive to load content dynamically as the user scrolls, improving the performance of the web page. Custom directives in AngularJS provide a powerful mechanism for extending the functionality of the framework to meet specific requirements. Understanding how to create and use custom directives is crucial for advanced AngularJS development.

In AngularJS, you define a new module using the angular.module() method. This method allows you to create a module or retrieve an existing one. Modules play a crucial role in structuring AngularJS applications, and knowing how to define them is essential for organizing and managing the components of your application effectively.

The ng-switch directive in AngularJS enhances decision-making capabilities in the view by dynamically switching between different views based on the provided conditions. It acts as a more expressive and efficient alternative to using multiple if-else conditions in the view. With ng-switch, the view can adapt and display different content based on the evaluated expressions, providing a cleaner and more readable way to handle complex conditional rendering in AngularJS applications.

In AngularJS's two-way data binding mechanism, the Scope plays the role of synchronizing data between the model and the view. Any changes made in the model or the view are automatically reflected in the other, ensuring real-time updates. This bidirectional data flow simplifies development and enhances the responsiveness of AngularJS applications.

The ng-class directive in AngularJS allows you to dynamically manipulate CSS classes on an HTML element based on the data in the scope. It is commonly used for conditional styling, where the presence or absence of a class depends on certain conditions. Understanding how to use ng-class is crucial for creating dynamic and responsive user interfaces in AngularJS applications.

The ng-repeat directive is essential for rendering lists or tables dynamically in AngularJS. It iterates over a collection of items and generates HTML elements for each item. This powerful directive is commonly used to display data from arrays or objects, making it a key feature for building dynamic and responsive user interfaces in AngularJS applications.

Modules are a key AngularJS concept that helps in preventing scope conflicts in large applications. Modules provide a way to organize and structure an AngularJS application by encapsulating related components. They help in managing dependencies, defining reusable code, and enhancing modularity. Understanding how to use modules is fundamental for building scalable and maintainable AngularJS applications.

In AngularJS, errors while making HTTP requests to an external API can be handled using error callback functions. When working with promises, developers can attach an error callback to handle any errors that occur during the HTTP request. This ensures a graceful handling of errors and provides an opportunity to notify users or take appropriate actions based on the error type. Understanding how to handle errors in asynchronous operations is a critical skill for AngularJS developers working with external APIs.

AngularJS optimizes DOM manipulation using directives like ng-show and ng-if by employing Virtual DOM manipulation. Instead of directly manipulating the actual DOM, AngularJS creates a virtual representation of the DOM in memory. Changes are made to this virtual DOM, and then AngularJS efficiently updates the actual DOM based on the differences. This minimizes the number of DOM manipulations, leading to better performance in AngularJS applications.

When integrating with an external API in AngularJS, the typical format used for data exchange is JSON (JavaScript Object Notation). JSON is a lightweight and readable data interchange format that is easy to work with in JavaScript applications. AngularJS developers often parse JSON responses from APIs and format data as JSON when making requests, ensuring compatibility and efficient data transfer.