Angular5 - role guard

RoleGuard.ts

import { Injectable } from '@angular/core';
import {CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot, Router} from '@angular/router';
import { Observable } from 'rxjs/Observable';
import {tap} from 'rxjs/operators/tap';
import {UsersDsService} from '../data-source/users-ds.service';

@Injectable()
export class RoleGuard implements CanActivate {
  constructor( private router: Router, private userDS: UsersDsService) {}
  canActivate(
    next: ActivatedRouteSnapshot,
    state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
    return this.userDS.getRole().map(resp => {
      return (resp === 'admin');
    }).pipe(
        tap(isAdmin => {
          if (!isAdmin) {
            this.router.navigate(['auth/login']);
          }
        }),
      );
  }
}