Angular 2 - Model changes listener / Observable (best practices)

Question

I have a component which needs to listen to a property changes (timeRemaining) available in a model. When this variable reaches 0, the component triggers an action (for instance, router.navigate(['/my/path']) )

For this purpose, my component subscribes to a Subject, which is notified whenever the value of the property changes. This is working perfectly.

My question is quite simple : where should this Subject be declared? In my model or in the service handling my model?

Example :

In my service :

 onTimeExpired(model, callback){
     model.getTimeExpiredSubject().subscribe(
     () => { 
         // some logic here 
         callback();
     }
 }

OR

In my model

 onTimeExpired(callback){
     this.getTimeExpiredSubject().subscribe(
     () => { 
         // some logic here 
         callback();
     }
 }

Which one is better and why? Thank you.

Answer 1

why you are passing a callback :

 //service
 onTimeExpired(){
     return model.getTimeExpiredSubject();
 }

subscription must not be in the service, because the service may be consumed in many components so you have to return an observable.

you have to subscribe in a consumer like a component

// in the component
this.service.subsucribe(data =>{
 // do something
})