OnDemandPreloadService that will be using within our CustomPreloadService

on-demand-preload.service.ts

import { Injectable } from '@angular/core';
import { Subject } from 'rxjs';

export class OnDemandPreloadOptions {
  constructor(public routePath: string, public preload = true) {}
}

@Injectable({
  providedIn: 'root'
})
export class OnDemandPreloadService {
  private subject = new Subject<OnDemandPreloadOptions>();
  state = this.subject.asObservable();

  startPreload(routePath: string) {
    const message = new OnDemandPreloadOptions(routePath, true);
    this.subject.next(message);
  }
}