Injects a token from the currently active injector. inject is only supported during instantiation of a dependency by the DI system. It can be used during:

• Construction (via the constructor) of a class being instantiated by the DI system, such as an @Injectable or @Component.
• In the initializer for fields of such classes.
• In the factory function specified for useFactory of a Provider or an @Injectable.
• In the factory function specified for an InjectionToken.

Overloads

Usage notes

In practice the inject() calls are allowed in a constructor, a constructor parameter and a field initializer:

@Injectable({providedIn: 'root'})
export class Car {
  radio: Radio|undefined;
  // OK: field initializer
  spareTyre = inject(Tyre);

  constructor() {
    // OK: constructor body
    this.radio = inject(Radio);
  }
}

It is also legal to call inject from a provider's factory:

providers: [
  {provide: Car, useFactory: () => {
    // OK: a class factory
    const engine = inject(Engine);
    return new Car(engine);
  }}
]

Calls to the inject() function outside of the class creation context will result in error. Most notably, calls to inject() are disallowed after a class instance was created, in methods (including lifecycle hooks):

@Component({ ... })
export class CarComponent {
  ngOnInit() {
    // ERROR: too late, the component instance was already created
    const engine = inject(Engine);
    engine.start();
  }
}