In this lesson, we discuss how and when to use factory providers, to enable dependencies that shouldn’t be available to Angular’s DI.

If you have this service:

export class LoggerProvider {

    constructor(enabled: boolean){

        if(enabled){

            console.log("Logger is enabled")

        }

    }

}

Which requires you provide param in constructor function.

If you just use it like normal provider:

@Component({

   selector: 'todos',

   providers: [TodoService, LoggerProvider],

   template: `...`

})

It will NOT work, because when init the LoggerProvider instance, we need to pass a boolean value as a param.

But you can use factory provider for this:

 providers: [

    TodoService

   ,{

        provide: LoggerProvider, useFactory: () => {

             return new LoggerProvider(true)

        }

    }

],