Do inject new instance Angular

Question

I have a simple factory and an injection token which I use in Angular dependency injection like this:

const TOKEN = new InjectionToken<EventEmitter<MyType>>("Create p");

and the factory:

const createEventEmitter = () => new EventEmitter<MyType>();

Now I provide it in my module like so:

providers: [
 {provide: TOKEN, useFactory: createEventEmitter}]

And I inject it in some constructor:

constructor(@Inject(TOKEN) emitter: EventEmitter<MyType>)

This works. However, I do get a singleton instance.

What if I want to do this like the factory pattern, so that I get a new instance whenever I inject a reference? Is this possible? Kinda like Spring's @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE).

Bonus question: Is it possible to create an injector token that injects a new instance of a class with a generic type parameter? So one injector token that injects all EventEmitter.

Abel Valdez · Accepted Answer · 2018-08-28 14:42:33Z

2

The key there is the module where you are providing if you provide on app.module it is going to be a singleton but if you provide in a custom component you will have same number of instances of components and injection class.

@Component({
  selector: 'custom',
  templateUrl: './custom.component.html',
  styleUrls: ['./custom.component.scss'],
  provider:[{provide: TOKEN, useFactory: createEventEmitter}]
})

If you have a child module you can do it too.

answered Aug 28, 2018 at 14:42

Abel Valdez

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5 Comments

Christian S. Over a year ago

I do this now. It works, but it is a bit cumbersome, because I need to repeat the same lines over and over again. Is this recommended? Or is it recommended to build a service that has factory methods which I then can call in my components?

Abel Valdez Over a year ago

Yes I use it as a service.

Abel Valdez Over a year ago

Did you get a solution for your problem?

Christian S. Over a year ago

I do it on component level now. However, I am still trying to figure out a better way though. While a factory service provides a lot of flexibility, it is not really an ideal solution either.

Dan R. Over a year ago

Is there some update regarding this? looking for something similar too.

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