I wonder how NgModule actually affects Angular 2 injector hierarchy.
What does the hierarchy look like in an app with nested modules? Does it create a new injector instance per each module or gets access to top-level injector (similarly to Angular 1.x modules)?
It can be somewhat confusing to figure out the tree in a big app.
Is there a way to print out, inspect or explore visually the hierarchy of injectors (like it could be done for scope hierarchy in Angular 1.x)?
According to the Modules documentation: https://angular.io/docs/ts/latest/guide/ngmodule.html
Angular registers these providers with the root injector of the module's execution context. That's the application's root injector for all modules loaded when the application starts.
Angular can inject one of these provider services into any component in the application. If this module provides the HeroService, or any module loaded at launch provides the HeroService, Angular can inject the same HeroService intance into any app component.
A lazy loaded module has its own sub-root injector which typically is a direct child of the application root injector.
Lazy loaded services are scoped to the lazy module's injector. If a lazy loaded module also provides the HeroService, any component created within that module's context (e.g., by router navigation) gets the local instance of the service, not the instance in the root application injector.
Components in external modules continue to receive the instance created for the application root.
So, you have one injector that is shared between all the modules. However, lazy-loaded components will have a child injector
You should be able to investigate providers using ng.probe($0) in the browser console. See also https://stackoverflow.com/a/35233711/217408.
You can load modules with MyModule.forRoot() (see also https://angular.io/docs/ts/latest/guide/ngmodule.html#!#providers) to get providers added at the root level.
If you provide it in a module, then it's available to the components in this module. I haven't seen it mentioned that a module introduces a child injector explicitly but to me this looks like it has to be the case.
