RxJs 6 : Manage array iteration and delay - rxjs

Question

i need help on managing delay on an array iteration.
Regarding my https://jsfiddle.net/mlefree/vrL813j2/93/, two questions :
How to add delay on each iteration action ?
How to reduce all iteration computed values ?
```
...
const arrayAsObservable = of(null).pipe(
delay(500),
switchMap(_ => getObjectWithArrayInPromise()),
map(val => {
log('array', val);
return (val.myArray);
}),
switchMap(val => from(val))
);
const eachElementAsObservable = arrayAsObservable.pipe(
delay(500), // Not working : we want to wait 500ms more for each value
map(val => {
log('value', val);
return val ;
}),
switchMap(val => getNewValueInPromise(val)),
map(val => {
// Not working : why not all new values ?
log('value after computing (KO)', val);
return (val);
})
);
const summarizeAsObservable = eachElementAsObservable.pipe(
// Not working : we want to sum all new values
map(val => {
log('value before reduce (KO)', val);
return val ;
}),
reduce((a,b) => a + b)
);
summarizeAsObservable.subscribe(msg => {
log('We did a total of (KO)', msg);
});
```

Answer 1

Overall the code is a bit too complex, there's a few lines become the root problem of your code.
The reason that you only receive one value after computing (KO) is you used switchMap which will unsubscribe the inner observable once the source emit, so you always get the last emitted value. I also change delay to timer and mapTo the emitted value
const eachElementAsObservable = arrayAsObservable.pipe(
concatMap(value => timer(1500).pipe(mapTo(value))), // Not working : we want to wait 500ms for each value
map(val => {
log('value', val);
return val;
}),
mergeMap(val => from(getNewValueInPromise(val))),
map(val => {
// Not working : why not all new values ?
console.log('value after computing (KO)', val);
return (val);
})
);
this is a updated fiddle https://jsfiddle.net/fancheung/vrL813j2/109/
The code is not fully working because you throw an error by reject in promise that will cause the observable to stop emitting, you will need to put a catchError somewhere in the stream