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What are preloading strategies?

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01

Understand the problem

Explain route preloading.

routingpreloading
02

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03

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After the initial load, Angular can preload lazy modules in the background: PreloadAllModules loads everything, NoPreloading (default) loads on demand, and custom strategies preload selectively (e.g. only routes flagged for it) to balance speed and bandwidth.

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04

Read the code

Enable preloading + a custom strategy
import { PreloadAllModules, PreloadingStrategy, Route } from '@angular/router';
import { Observable, of } from 'rxjs';

// option A: preload everything when idle
//   provideRouter(routes, withPreloading(PreloadAllModules))

// option B: custom — only routes flagged data:{ preload: true }
export class SelectivePreload implements PreloadingStrategy {
  preload(route: Route, load: () => Observable<any>): Observable<any> {
    return route.data?.['preload'] ? load() : of(null);
  }
}
//   { path: 'admin', loadComponent: ..., data: { preload: true } }
05

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