How to use provideAppInitializer instead of APP_INITIALIZER

I have a library that should run when the app boots.

I see that Angular 19 now use provideAppInitializer. I did use the automatic angular ng update migration cli and it changed the code.

// From
{
provide: APP_INITIALIZER,
useFactory: (service: NgxBackButtonService) => () => service,
deps: [NgxBackButtonService],
multi: true,
},


// To
provideAppInitializer(() => {
const initializerFn = ((service: NgxBackButtonService) => () => service)(inject(NgxBackButtonService))
return initializerFn()
}


But this doesn't work and throw me the following error

Argument of type '() => NgxBackButtonService' is not assignable to parameter of type '() => void | Observable<unknown> | Promise<unknown>'.
Type 'NgxBackButtonService' is not assignable to type 'void | Observable<unknown> | Promise<unknown>'.ts(2345)


Does someone knows how I should adapt it ?

Here the Stackblitz code

Continue reading...