How to inject different service based on certain build environment in Angular2?

Question

I have HeroMockService that will return mocked data and HeroService that will call back end service to retrieve heroes from database.

Assum

Answer 1

This worked for me in Angular 6. Leverages @void's Interface approach (where both the true service and the mock service implement the service interface). The accepted answer neglects to mention that the purpose of a factory is to return an implementation of an interface.

heroservice/heroservice.module.ts

import { NgModule, ModuleWithProviders } from '@angular/core';
import { CommonModule } from '@angular/common';
import { IHeroService } from './ihero.service';
import { HeroService } from './hero.service';
import { MockHeroService } from './mock-hero.service';


@NgModule({
  imports: [
    CommonModule
  ],
})
export class HeroServiceModule {
  static forRoot(mock: boolean): ModuleWithProviders {
    return {
      ngModule: HeroServiceModule ,
      providers: [
        {
          provide: IHeroService,
          useClass: mock ? MockHeroService : HeroService,
        },
      ],
    };
  }
}

app.module.ts

import { NgModule, isDevMode } from '@angular/core';
import { HeroServiceModule } from './heroservice/heroservice.module';

// ...

  imports: [
    BrowserModule,
    HttpClientModule,
    // ...
    HeroServiceModule.forRoot(
      isDevMode() // use mock service in dev mode
    ),
  ],

// ...

some/some.component.ts

Import and use the interface as you would the actual service (the implementation will be "provided" at runtime).

import { IHeroService } from '../heroservice/iheroservice.service';

// ...