service

1-1 生成服务

ng g service services/common

1-2 在根模块中配置

//app.module.ts
import {CommonService} from './services/common.service';
@NgModule({
  providers: [CommonService]
})
export class AppModule { }

1-3 组件使用服务

export class CommonService {
  public defaultCity:string = "武汉"
  constructor() { }
}

//1.导入服务
import {CommonService} from '../../services/common.service'
export class HomeComponent implements OnInit {
    //2.构造函数中配置
  constructor(public common:CommonService) { }
  ngOnInit() {
      //3.使用
    console.log(this.common.defaultCity);
  }
}