Angular: NG0200: Circular dependency in DI detected for X

Meaning

The injector builds a service by first building its dependencies. If A needs B and B needs A, it loops. Break the cycle by extracting shared logic into a third service, injecting lazily with Injector.get, or using events instead of direct references.

Common causes

• Service A and service B inject each other
• A longer cycle through three or more services
• A token provided in a component that also injects the parent
• Barrel file import order hiding a cycle
• An HTTP_INTERCEPTOR injecting a service that uses HttpClient

Detailed fix by platform

Code examples

@Injectable({ providedIn: 'root' })
export class AuthInterceptorService {
  private injector = inject(Injector);
  token() { return this.injector.get(AuthService).token; }   // resolved when called, not at construction
}

How to diagnose

1. Chain — Which services are named in the message?
2. Cycle — Does A need B and B need A?
3. Interceptor — Does an interceptor inject something using HttpClient?

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