@angular/core

InjectionToken

Class

Creates a token that can be used in a DI Provider.

  
    class InjectionToken<T> {}

Creates a token that can be used in a DI Provider.

Use an InjectionToken whenever the type you are injecting is not reified (does not have a runtime representation) such as when injecting an interface, callable type, array or parameterized type.

InjectionToken is parameterized on T which is the type of object which will be returned by the Injector. This provides an additional level of type safety.

Important Note: Ensure that you use the same instance of the InjectionToken in both the provider and the injection call. Creating a new instance of InjectionToken in different places, even with the same description, will be treated as different tokens by Angular's DI system, leading to a NullInjectorError.

{@example injection-token/src/main.ts region='InjectionToken'}

When creating an InjectionToken, you can optionally specify a factory function which returns (possibly by creating) a default value of the parameterized type T. This sets up the InjectionToken using this factory as a provider as if it was defined explicitly in the application's root injector. If the factory function, which takes zero arguments, needs to inject dependencies, it can do so using the inject function. As you can see in the Tree-shakable InjectionToken example below.

Additionally, if a factory is specified you can also specify the providedIn option, which overrides the above behavior and marks the token as belonging to a particular @NgModule (note: this option is now deprecated). As mentioned above, 'root' is the default value for providedIn.

The providedIn: NgModule and providedIn: 'any' options are deprecated.

Basic Examples

Plain InjectionToken

          const BASE_URL = new InjectionToken<string>('BaseUrl');      const injector = Injector.create({        providers: [{provide: BASE_URL, useValue: 'http://localhost'}],      });      const url = injector.get(BASE_URL);      // Note: since `BASE_URL` is `InjectionToken<string>`      // `url` is correctly inferred to be `string`      expect(url).toBe('http://localhost');

Tree-shakable InjectionToken

          class MyService {        constructor(readonly myDep: MyDep) {}      }      const MY_SERVICE_TOKEN = new InjectionToken<MyService>('Manually constructed MyService', {        providedIn: 'root',        factory: () => new MyService(inject(MyDep)),      });      const instance = injector.get(MY_SERVICE_TOKEN);      expect(instance instanceof MyService).toBeTruthy();      expect(instance.myDep instanceof MyDep).toBeTruthy();

toString

string

@returnsstring