Angular multiple optional bootstrap (entry) components

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AppModule.ts

import { Inject, Type, ApplicationRef, ComponentFactoryResolver } from '@angular/core';
import { DOCUMENT } from '@angular/common';

@NgModule({
  imports: [BrowserModule],
  declarations: [App, Bpp],
  entryComponents: [App, Bpp]
})
export class AppModule {
  static bootstrapComponents: Type[] = [App, Bpp];

  constructor(
    @Inject(DOCUMENT) private _document: any,
    private _componentFactoryResolver: ComponentFactoryResolver
  ) {}
  
  ngDoBootstrap(applicationRef: ApplicationRef) {
    for (const component of AppModule.bootstrapComponents) {
      const { selector } = this._componentFactoryResolver.resolveComponentFactory(component);
      
      if (this._document.querySelector(selector)) {
        applicationRef.bootstrap(component);
      } 
    }
  }
}

This was very useful but things have changed a little in Angular 8 - I got it working as described in the answer to this SO question.