CODEWITHSUNDEEP
rxjs
Artur Ciocanu
Artur Ciocanu

Reputation: 335

RxJS modeling if else control structures with Observables operators

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.

Upvotes: 30

Views: 19684

Answers (1)

paulpdaniels
paulpdaniels

Reputation: 18663

There are a couple operators that you could use to emulate this:

In order from most likely what you are asking for

partition

//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();

groupBy

//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);
  });

if edit renamed to iif in v6

//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!"))

Upvotes: 50

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