import { NgModule, ModuleWithProviders, SkipSelf, Optional } from '@angular/core'; import { Configuration } from './configuration'; import { HttpClient } from '@angular/common/http'; import { AccountService } from './api/account.service'; import { LoginService } from './api/login.service'; import { PropertiesService } from './api/properties.service'; import { UsersService } from './api/users.service'; @NgModule({ imports: [], declarations: [], exports: [], providers: [] }) export class ApiModule { public static forRoot(configurationFactory: () => Configuration): ModuleWithProviders { return { ngModule: ApiModule, providers: [ { provide: Configuration, useFactory: configurationFactory } ] }; } constructor( @Optional() @SkipSelf() parentModule: ApiModule, @Optional() http: HttpClient) { if (parentModule) { throw new Error('ApiModule is already loaded. Import in your base AppModule only.'); } if (!http) { throw new Error('You need to import the HttpClientModule in your AppModule! \n' + 'See also https://github.com/angular/angular/issues/20575'); } } }