Conditionally choose observable in RxJS

Question

I would like to know how to create a new observable that will return one of two other observables based on if the first observable is empty (without calling the second observable by default). Eg:

 // scenario 1 let obs1 = Observable.empty(); let obs2 = Observable.of([1,2,3]); // This line doesn't work, but is essentially what I'm attempting to do let obs3 = (obs1.isEmpty()) ? obs2 : obs1; obs3.subscribe( i => console.log('Next: ', i)); // Next: 1 // Next: 2 // Next: 3 // Complete // scenario 2 let obs1 = Observable.of([6,7,8]); let obs2 = Observable.of([1,2,3]); // This line doesn't work, but is essentially what I'm attempting to do let obs3 = (obs1.isEmpty()) ? obs2 : obs1; obs3.subscribe( i => console.log('Next: ', i)); // Next: 6 // Next: 7 // Next: 8 // Complete 

Answer 1

You could try :

let obs3 = obs1.isEmpty().map(x => x? obs2 : obs1;)

Will check quickly now if that would work.

Yep, according to the doc , it should be fine, as isEmpty emits a boolean which is true if the observable is empty, so you can use that to pick up the observable you want.