NgModule

NgModule is a decorator in Angular that defines a module, a cohesive block of code dedicated to a workload or feature. An NgModule is a class decorated with @NgModule, and the class itself typically contains no logic. The module aggregates related components, directives, pipes, and services and provides a context for compilation and runtime.

The NgModule metadata includes several properties. Declarations list the components, directives, and pipes that belong to the module. Imports specify other modules whose exported declarations are required in the templates of this module. Exports make a subset of declarations (and optionally imported modules) available to templates in other modules. Providers register services with the module's injector, controlling their scope and lifetime. Bootstrap identifies the root component(s) to initialize when the module is bootstrapped as the application root. Historically there was an entryComponents property for components loaded dynamically, but with the Ivy compiler this is generally unnecessary.

NgModules influence the Angular dependency injection system and the compiler. The root module bootstraps the application, while feature modules encapsulate functionality and can be lazy-loaded via the router. A common practice is to create shared modules that re-export commonly used directives and components, and feature modules that declare and export their own UI pieces. Use of CommonModule in feature modules provides common directives such as ngIf and ngFor. Since Angular 9, the Ivy compiler minimizes the need for certain boilerplate, but the core concepts of declarations, imports, exports, and providers remain central to module organization.