RX JS Subject keep tracks of objects based on keys New Subscriber will get snapshot of accumulated messages and then updates
In Financial Market data applications e.g. we want to display market data based on some key
const sub = new SnapShotReplaySubject<any>((value) => {return value.key});
sub.next({key:'IBM', bid:100, ask:101});
sub.next({key:'IBM', bid:102, ask:104});
sub.subscribe((val) => { console.log(value); } ); }
will display only
{key:'IBM', bid:102, ask:104}