app_preloading_strategy.ts

export class AppPreloadingStrategy implements PreloadingStrategy {
    preload(route: Route, load: Function): Observable<any> {
        const loadRoute = (delay) => delay
            ? timer(150).pipe(flatMap(_ => load()))
            : load();
        return route.data && route.data.preload 
            ? loadRoute(route.data.delay)
            : of(null);
      }
}

Where do I gettimer, flatMap, and of from? I've not worked with these before and I see no import statement.

rxjs? lodash?

May I recommend when making example code, please use universally understood code without extra implicit code

Where do I gettimer, flatMap, and of from? I've not worked with these before and I see no import statement.

rxjs? lodash?

May I recommend when making example code, please use universally understood code without extra implicit code

This example describes an advanced Angular strategy and assumes that the reader knows at least rxJS

Where do I gettimer, flatMap, and of from? I've not worked with these before and I see no import statement.

rxjs? lodash?

May I recommend when making example code, please use universally understood code without extra implicit code

import {PreloadingStrategy, Route} from '@angular/router';
import {Observable, of, timer} from 'rxjs';
import {flatMap} from 'rxjs/operators';