[Angular 依赖注入详谈] Angular Module Providers几种类型的实现源代码具体位置

onst MessageServiceFactory = () => {

 if (environment.production) {

   return new MessageService();

 } else {

   return new NewMessageService();

 }

};

{

 // ...

 providers: [

   {

     provide: MessageService,

     useFactory: MessageServiceFactory

   }

 ]

 // ...

}