Dynamically change header string in angular 2

You can create a service dedicated for updating the title in your header component. Simply inject the service in your header component and subscribe to a dedicated BehaviorSubject. Then you can inject this service in any component you have and use the setTitle method from that component which will update the title in the header component. Check out the following code

//headerTitle.service.ts
@Injectable()
export class headerTitleService {
  title = new BehaviorSubject('Initial Title');

  setTitle(title: string) {
    this.title.next(title);
  }
}

//header.component.ts
title = '';

constructor(private headerTitleService: HeaderTitleService) {}

ngOnInit() {
  this.headerTitleService.title.subscribe(updatedTitle => {
    this.title = updatedTitle;
  });
}

//header.component.html
<h1>{{title}}</h1>

//about.component.ts
constructor(private headerTitleService: HeaderTitleService) {}

ngOnInit() {
  this.headerTitleService.setTitle('About');
}

Working demo

Use the title service in @angular/platform-browser and add router component with data property.

const appRoutes: Routes = [
  { path: 'home',component:HomeComponent , data:{title:'Home'}}

  ];

Call this function in the root component

ngOnInit() {
    this.router.events
      .filter((event) => event instanceof NavigationEnd)
      .map(() => this.activatedRoute)
      .map((route) => {
        while (route.firstChild) route = route.firstChild;
        return route;
      })
      .filter((route) => route.outlet === 'primary')
      .mergeMap((route) => route.data)
      .subscribe((event) => this.titleService.setTitle(event['title']));
  }
}