-import { Route, PreloadingStrategy } from '@angular/router';
-import { Observable } from 'rxjs/Observable';
-import 'rxjs/add/observable/timer';
-import 'rxjs/add/operator/switchMap';
+import { Observable, of as ofObservable, timer as observableTimer } from 'rxjs'
+import { switchMap } from 'rxjs/operators'
+import { PreloadingStrategy, Route } from '@angular/router'
+import { Injectable } from '@angular/core'