Customizing module loader

The built-in application module loader uses SystemJS. But we can provide our own implementation of the loader as follows:

@NgModule({
  //...
  bootstrap: [MailAppCmp],
  imports: [RouterModule.forRoot(ROUTES)],
  providers: [{provide: NgModuleFactoryLoader, useClass: MyCustomLoader}]
})
class MailModule {}

platformBrowserDynamic().bootstrapModule(MailModule);

You can look at SystemJsNgModuleLoader to see an example of a module loader. Finally, you don't have to use the loader at all. Instead, you can provide a callback the route will use to fetch the module.

{
  path: 'contacts',
  loadChildren: () => System.import('somePath'),
}