Discussion on: Predictive Preloading Strategy for Your Angular Bundles

[John Papa]

Just a name I chose. You could certainly name it the same.

[Charlie Greenman]

I think my question wasn't clear enough. My question is different. The service is being included as the preloading strategy. The interface for preloading strategy(angular.io/api/router/PreloadingSt...) specifies that the method to be overridden is preload. However, here you are including the service as the preloading strategy, which uses startPreload. So I'm just trying to figure out how the preloadingStrategy knows to use the service for preloading? Sort of confused how this all working

[John Papa]

I'm not sure I understand, but let me try to see if I follow your question. Angular has the interface PreloadingStrategy which we can implement in a class. This code implements it with export class OnDemandPreloadStrategy implements PreloadingStrategy. So the OnDemandPreloadStrategy must implement the preload method in that interface, which it does with

  preload(route: Route, load: () => Observable<any>): Observable<any> {
    return this.preloadOnDemand$.pipe(
      mergeMap(preloadOptions => {
        const shouldPreload = this.preloadCheck(route, preloadOptions);
        return shouldPreload ? load() : EMPTY;
      })
    );
  }

Then to use this strategy we must specify a class that implements the strategy, so in the router module we specify

RouterModule.forRoot(routes, {
      preloadingStrategy: OnDemandPreloadStrategy
    })

Ah - I think I see your point ... that last line of code in the article had a typo that didn't match my code. I just fixed it to point to the strategy. Thanks!

[Charlie Greenman]

There we go, that would be it. Thank you.