Is it possible to model if/else control structures via RxJS operators. As far as I understood we could use Observable.filter() to simulate an IF branch, but I am not sure if we simulate an ELSE branch via any of the Observable operator.
1 Answer
There are a couple operators that you could use to emulate this:
In order from most likely what you are asking for
//Returns an array containing two Observables
//One whose elements pass the filter, and another whose elements don't
var items = observableSource.partition((x) => x % 2 == 0);
var evens = items[0];
var odds = items[1];
//Only even numbers
evens.subscribe();
//Only odd numbers
odds.subscribe();
// Using RxJS >= 6
const [evens, odds] = partition(observableSource, x => x % 2 == 0);
//Only even numbers
evens.subscribe();
//Only odd numbers
odds.subscribe();
//Uses a key selector and equality comparer to generate an Observable of GroupedObservables
observableSource.groupBy((value) => value % 2, (value) => value)
.subscribe(groupedObservable => {
groupedObservable.subscribe(groupedObservable.key ? oddObserver : evenObserver);
});
//Propagates one of the sources based on a particular condition
//!!Only one Observable will be subscribed to!!
Rx.Observable.if(() => value > 5, Rx.Observable.just(5), Rx.Observable.from([1,2, 3]))
// Using RxJS >= 6
iif(() => value > 5, of(5), from([1, 2, 3]))
case (Only available in RxJS 4)
//Similar to `if` but it takes an object and only propagates based on key matching
//It takes an optional argument if none of the items match
//!!Only one Observable will be subscribed to!!
Rx.Observable.case(() => "blah",
{
blah : //..Observable,
foo : //..Another Observable,
bar : //..Yet another
}, Rx.Observable.throw("Should have matched!"))
6 Comments
Artur Ciocanu
thanks for providing this comprehensive list of operators. I guess depending on use case I can use one of these operators to simulate
if/else. For my particular example Rx.Observable.if() did the trick.
Jacob McKay
Tons more operators/details at the rxjs docs: github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/…
Artur Ciocanu
Thanks for all the details.
Rx.Observable.if() with elseSource did the trick.
ggranum
Despite it being nowhere to be found in the docs, Observable.if is in fact available in RxJs 5.
John
@paulpdaniels how does the groupby works if we're using hot observable ?
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elseSourceparameter from theifoperator. Thanks a lot theRx.Observable.if()worked like a charm.