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NgModules (NgModule decorator (declarations (A list of the module's…

- - - - e.g. declarations, entryComponents
      - Compiler configuration
    - - Injector configuration
      - e.g. providers
    - - Grouping
      - e.g. imports, exports
- - - - Using the Injectable decorator's providedIn property is preferred
      - Using NgModule decorator's providers array if the module is not known when defining the service
      - Each lazy-loaded module creates a child injector
      - Child injector's service instances are shadow the root injector's service instances
      - Not all services can be lazy-loaded (e.g. Router)
    - - Controlled by the root application injector
      - Available throughout the app
      - Providers added to the
    - - Using Component decorator's providers array
      - Limited to the component and its hierarchy
  - - - Provide the service in the app root (preferred)
      - Include the service in the AppModule or a module only imported by AppModule
    - - Service providers would be duplicated if the module is also loaded by a child injector
      - Providers should be placed in a static method (conventionally forRoot) of the module class
      - Root module should import forRoot() while feature modules should import the module itself
      - forRoot() takes a configuration object and returns a ModuleWithProviders
    - - Add a check to the constructor of the service class
- - - - A module that provides singleton services
      - Imported by the root module only
    - - A module that declares shared declarables
      - Imported by feature modules
- - - - Feature modules that are only accessed through lazy-loading
      - Shouldn't be imported by other modules
    - - Separates routing concerns from another module
      - Imported by the companion module
    - - Defines providers for utility services
      - Imported by the root module
    - - Defines declarables for exporting
      - Imported by any consumer module
    - - Imported by larger feature modules or the root module
      - Feature module with a component hierarchy
  - - - Contains routes to feature modules
      - Imports Router.forRoot() which also configures the Router
    - - Contains child routes specific to the feature module context
      - Imports Router.forChild()
    - - App's routing module imports feature modules
      - Feature modules in turn import their companion routing modules
      - Feature chunks are downloaded only when the route is activated for the first time