Rxjs - How can I extract multiple values inside an array and feed them back to the observable stream synchronously

Question

I have created a Rx.Observable from a stream of events:

Rx.Observable.fromEvent(recognizeStream, \'data\')

In which every data

Answer 1

The family of xxxMap() operators all deal with higher-order Observables. Which means they allow you to create Observables inside the main Observable and inline the resulting values into the primary stream. So you could read the type signature as Observable> => Observable

Given a stream which every emission x is an Observable containing 4 value emissions:

input:  --x----------x 
flatMap   a-a-a-a-|  b-b-b-b-|
result: --a-a-a-a----b-b-b-b-|

Typecasting xxxMap(myFnc) return values

The xxxMap() operators all work with results of type Observable, Promise or Array. Depending on what you put into it will get converted to Observable if needed.

Rx.Observable.of('')
  .flatMap(() => [1,2,3,4])
  .subscribe(val => console.log('array value: ' + val));

Rx.Observable.of('')
  .flatMap(() => Promise.resolve(1))
  .subscribe(val => console.log('promise value: ' + val));

Rx.Observable.of('')
  .flatMap(() => Promise.resolve([1,2,3,4]))
  .subscribe(val => console.log('promise array value: ' + val));

Rx.Observable.of('')
  .flatMap(() => Rx.Observable.from([1,2,3,4]))
  .subscribe(val => console.log('Observable value: ' + val));

In your case you can easily flatMap the objects and return the arrays:

Rx.Observable.of({ error: null, alternatives: ['result1', 'result2', 'result3'] })
  .flatMap(val => val.alternatives)
  .subscribe(console.log);

Difference between all xxxMap operators

What does mergeMap do

flatMap, better known as mergeMap will merge all emissions whenever they come into the main stream.

concatMap

concatMap will wait for all emissions to complete before concat the next stream:

switchMap

but switchMap will abandon the previous stream when a new emission is available and switch to emit values from the new stream: