source$: Source observable that the hook will subscribe to.
unsubscribeGraceTime: Amount of time in ms that the hook should wait before unsubscribing from the source observable after it unmounts (default = 200).

Important: This hook doesn't trigger any updates.

A React Component that creates a subscription to the provided observable once the component mounts and it unsubscribes from it when the component unmounts.

Properties:

source$: Source observable that the Component will subscribe to.
graceTime: an optional property that describes the amount of time in ms that the Component should wait before unsubscribing from the source observable after it unmounts (default = 200).

Important: This Component doesn't trigger any updates.

groupInMap

A RxJS pipeable operator which groups all values by key and emits a Map that holds the latest value for each key

Arguments:

keyGetter: A function that extracts the key for each item.
projection: Projection function for each group.

const votesByKey$ = new Subject<{key: string}>()
const counters$ = votesByKey$.pipe(
  groupInMap(
    vote => vote.key,
    votes$ => votes$.pipe(
      mapTo(1),
      scan(count => count + 1),
      takeWhile(count => count < 3)
    )
  )
)

counters$.subscribe(counters => {
  console.log('counters$:')
  counters.forEach((value, key) => {
    console.log(`${key}: ${value}`);
  })
})

votesByKey$.next({key: 'foo'})
// > counters$:
// > foo: 1

votesByKey$.next({key: 'foo'})
// > counters$:
// > foo: 2

votesByKey$.next({key: 'bar'})
// > counters$:
// > foo: 2
// > bar: 1

votesByKey$.next({key: 'foo'})
// > counters$:
// > bar: 1

votesByKey$.next({key: 'bar'})
// > counters$:
// > bar: 2
//
votesByKey$.next({key: 'bar'})
// > counters$:

mergeWithKey

Emits the values from all the streams of the provided object, in a result which provides the key of the stream of that emission.

Arguments:

inputObject: Object of streams

const inc$ = new Subject()
const dec$ = new Subject()
const resetTo$ = new Subject<number>()

const counter$ = mergeWithKey({
  inc$,
  dec$,
  resetTo$,
}).pipe(
  scan((acc, current) => {
    switch (current.type) {
      case "inc$":
        return acc + 1
      case "dec$":
        return acc - 1
      case "resetTo$":
        return current.payload
      default:
        return acc
    }
  }, 0),
  startWith(0),
)