Introduction

In Angular, which is a TypeScript-based open-source web application framework, developers often leverage various design patterns to build scalable, maintainable, and efficient applications.

Some of the commonly used design patterns in Angular development include:

1. Component Pattern: Angular applications are built around components. Each component encapsulates a part of the user interface and its behavior. This follows the Component-based architecture pattern.

2. Module Pattern: Angular applications are modular, organized into separate modules to encapsulate functionality. Modules help in organizing the application into cohesive units and facilitate lazy loading for better performance.

3. Service Pattern: Services are singleton objects used to encapsulate and share logic across components. They facilitate code reuse and help in maintaining separation of concerns by keeping business logic separate from presentation logic.

4. Dependency Injection (DI) Pattern: Angular leverages dependency injection to provide components with the services or dependencies they need. This pattern helps in making components more modular, testable, and decoupled.

5. Observable Pattern: Angular extensively uses observables from the RxJS library to handle asynchronous operations such as HTTP requests, event handling, and data streaming. Observables facilitate handling of asynchronous data streams and provide powerful operators for data manipulation.

6. Decorator Pattern: Decorators in Angular are used to annotate and modify classes, methods, or properties. They are extensively used for metadata configuration, dependency injection, and creating custom decorators for various purposes.

7. Facade Pattern: Facades in Angular provide a simplified interface to a complex subsystem of services or functionality. They help in abstracting away the complexities of underlying systems and provide a unified interface for clients to interact with.

8. Singleton Pattern: While Angular's dependency injection system handles singleton services by default, developers sometimes implement singleton patterns explicitly for certain services or objects to ensure a single instance throughout the application.

9. State Management Patterns: Angular applications often use various state management patterns such as Redux, NgRx, or Angular's built-in mechanisms like BehaviorSubjects and ngRx Store for managing application state, especially in larger or more complex applications.

10. Template Method Pattern: Angular's component lifecycle hooks such as ngOnInit, ngOnDestroy, etc., follow the template method pattern, allowing developers to hook into certain points of a component's lifecycle and execute custom logic.

These patterns help Angular developers in building scalable, maintainable, and well-structured applications by providing best practices for organizing code, managing state, handling dependencies, and structuring components.