Please see How I Learned To Stop Worrying About Lifecycle Events. In your case, you’ve already done much of the work, because TemperatureService is already present and available to provide Observables. I’m not sure from what you’ve posted whether currentPlace is something that can or should also be tracked in the service, but assuming it isn’t:
type TemperatureScale = "c" | "f";
private scale$ = new BehaviorSubject<TemperatureScale>();
private scalify(temp: number, scale: TemperatureScale): string {
/* TODO */
}
displayTemperature(place: Place): Observable<string> {
return this.scale$.pipe(
map(scale => this.scalify(place.currTemp, scale));
}
Naturally, if there is a logical way to encapsulate the concept of “current place” into the service, then displayTemperature can do all its work with no arguments, and the component no longer needs to track currentPlace at all.