Angular (v5) service is getting constructed before APP_INITIALIZER promise resolves

I had also a simmilar issue what solved the issue for me was to use Observable methods and operators to do everything. Then in the end just use the toPromise method of the Observable to return a Promise. This is also simpler because you don’t need to create a promise yourself.

The AppConfig service will then look something like that:

import { Injectable, Injector } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import { tap } from 'rxjs/operators/tap';

@Injectable()
export class AppConfig {

    config: any = null;

    constructor(
        private injector: Injector
    ){
    }

    public loadConfig() {
        const http = this.injector.get(HttpClient);

        return http.get('https://jsonplaceholder.typicode.com/posts/1').pipe(
          tap((returnedConfig) => this.config = returnedConfig)
        ).toPromise();
        //return from([1]).toPromise();
    }
}

I’m using the new pipeable operators in rxjs which is recommended by Google for Angular 5. The tap operator is equivalent to the old do operator.

I have also created a working sample on stackblitz.com so you can se it working. Sample link