get previous url angular

1//Update angular 6+
2//The events.filter gives error because filter is not part of events, so change the code to
3
4import { filter, pairwise } from 'rxjs/operators';
5
6this.router.events
7.pipe(filter((evt: any) => evt instanceof RoutesRecognized), pairwise())
8.subscribe((events: RoutesRecognized[]) => {
9  console.log('previous url', events[0].urlAfterRedirects);
10  console.log('current url', events[1].urlAfterRedirects);
11});

1  // private router: Router//inject
2    this.router.events
3    .pipe( filter(        (evt:any)=>evt instanceof RoutesRecognized),pairwise())
4    .subscribe((events: RoutesRecognized[]) =>{        
5        console.log('previous',events[0].urlAfterRedirects);//previous url
6        console.log('current url',events[1].urlAfterRedirects);//current url
7      }    );