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Confusion on 'providedIn' for a specific NgModule

See original GitHub issue

I’m submitting a…


[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Performance issue
[ ] Feature request
[ X  ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

This is from the doc

The @Injectable() decorator has the providedIn metadata option, where you can specify the provider of the decorated service class with the root injector, or with the injector for a specific NgModule.

Providing a service with the app's root injector is a typical case, and the CLI sets up this kind of a provider automatically for you when generating a new service. However, you might not always want to provide your service at the root level. You might, for instance, want users to explicitly opt-in to using the service.

Instead of specifying the root injector, you can set providedIn to a specific NgModule.

For example, in the following excerpt, the @Injectable() decorator configures a provider that is available in any injector that includes the HeroModule.

What I understand from the doc, when you use providedIn: 'root' in your service, you don’t have to configure this service at the app module level. And the service is available anywhere the class is imported.

But if I use providedIn: HeroModule, I thought I didn’t have to configure this service at the HeroModule level and I could use this service in HeroComponent (HeroComponent declared in HeroModule). This is not the case. And I still need to configure that service in HeroModule.

So What is this providedIn: SpecificModule for?

here is the demo

Expected behavior

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

Environment


Angular version: 6.*.*


Browser:
- [ ] Chrome (desktop) version XX
- [ ] Chrome (Android) version XX
- [ ] Chrome (iOS) version XX
- [ ] Firefox version XX
- [ ] Safari (desktop) version XX
- [ ] Safari (iOS) version XX
- [ ] IE version XX
- [ ] Edge version XX
 
For Tooling issues:
- Node version: XX  
- Platform:  

Others: