decorator questions

To create a custom Angular directive, you define a class and decorate it with the `@Directive` decorator. Within this class, you can specify the directive's behavior by implementing methods such as `ngOnInit`, `ngOnChanges`, or using lifecycle hooks. You also define the directive's selector, which determines how it is applied in the template. Custom directives can be used to manipulate the DOM, add custom behavior to elements, or create reusable components. For example, you might create a directive to change the background color of an element based on certain conditions.

The `@Injectable` decorator in Angular is used to mark a class as a service that can participate in Angular's dependency injection system. When applied to a class, it indicates that the class can be injected into other classes via the constructor, allowing it to be used as a service. This decorator ensures that Angular can create and manage instances of the class and handle its dependencies, enabling efficient and modular code. `@Injectable` is essential for services, as it facilitates their registration and injection into components, other services, or modules.

The `NgModule` decorator in Angular is used to define an Angular module, which groups together related components, directives, pipes, and services into a cohesive unit. An `NgModule` class includes metadata such as declarations (components, directives, pipes), imports (other modules), providers (services), and bootstrap (root component). This modular approach helps in organizing code, improving maintainability, and facilitating lazy loading. Modules can be imported into other modules, enabling a structured and scalable application architecture.

The `@login_required` decorator is used to restrict access to a view so that only authenticated users can access it. When applied to a view function, it redirects unauthenticated users to the login page. It ensures that certain views are only accessible to users who have logged in.