Compilation error occurs when importing Angular4 service that includes only event handler methods

Trying to implement an Angular service to monitor route changed events has led to a compilation error at the AppModule level. The error message indicates "Service is declared but its value is never read", which I understand and acknowledge. The challenge lies in not needing to call any of the service functions externally. Below is a snippet resembling my Service implementation:

@Injectable()
export class MyService {
  constructor(
    private router: Router,
    private route: ActivatedRoute
  ) {
    this.router.events
      .filter(e => e instanceof NavigationEnd)
      .forEach(e => this.onRouteChanged(this.route.root.firstChild.snapshot.data.analytics.pageName));
  }
  onRouteChanged(pageName: string) {
    // perform operations with the page name
  }
}

In my app.module.ts, including the ngOnInit function that simply logs my service prevents compilation errors like so:

export class AppModule {
  constructor(
    private myService: MyService // necessary for service to load and track route changes
  ) { }

  ngOnInit() {
    console.log(this.myService);
  }
}

The console.log confirms the firing of route changed events, ensuring that the service is loaded successfully. Is there a way to include the MyService reference without relying on the console.log statement?

Answer №1

You mentioned that the solution works, but I'm having trouble understanding how it does. It seems like you're missing out on subscribing to the route events. Consider using this approach instead:

this.router.events
  .filter(event => event instanceof NavigationEnd)
  .map(event => this.route.root.firstChild.snapshot.data.analytics.pageName)
  .subscribe(this.onRouteChanged)

Additionally, this snippet of code is essential for Angular to instantiate your service:

constructor(
    private myService: MyService
  ) { }

In a recent test, I found that I didn't need to include console.log(this.myService) in order for the functionality to work as expected. Providing more details could help us troubleshoot further.

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