import { ISubscription } from "rxjs/Subscription";
....
export class MyComponent implements OnDestroy, OnInit {
    private showModalStreamSubscription: ISubscription;
...
    ngOnInit() {
        this.mySubscription = this.myService.doSomething.subscribe(() => {
            this.thingToDo();
        });
    }
...
    ngOnDestroy() {
        this.mySubscription.unsubscribe();
    }
...
}