timestamp method
Wraps each item emitted by the source Observable in a Timestamped object that includes the emitted item and the time when the item was emitted.
Example
new Observable.just(1)
.timestamp()
.listen((i) => print(i)); // prints 'TimeStamp{timestamp: XXX, value: 1}';
Implementation
Observable<Timestamped<T>> timestamp() {
return transform(TimestampStreamTransformer<T>());
}