How can I chain RxJS observable in a redux-observable epic?

Question

I've just started learning redux-observables and RxJS for work recently. We have alerts globally set in Redux. I want to be able to set an alert, then after a set period, close that same alert. There can also be multiple alerts at any time, and the user could manually close one alert before it automatically closes itself. I have added to id here, so I can close the correct alert. I have attempted to use delay after the initial map than another map to achieve this so far. However, this skips the first map.

export const addAlertEpic: Epic<Action, Action, RootState> = (
  action$,
  state$
) =>
  action$.pipe(
    ofType(slice.actions.addAlert),
    map((values: any) =>
      slice.actions.addAlertSuccess({ id: uuid(), ...values.payload })
    )
  );

Thank you for help!

Answer 1

Add another epic for addAlertSucess, include a delay to dispatch the remove action.

export const addAlertSuccessEpic: Epic<Action, Action, RootState> = (
  action$,
  state$
) =>
  action$.pipe(
    ofType(slice.actions.addAlertSuccess),
    delay(myTimeToWait),
    map(foo =>
      slice.actions.removeAlert({ id: foo.id })
    )
  );

Answer 2

set an alert, then after a set period, close that same alert [...] he user could manually close one alert before it automatically closes itself

With that in mind, here would be my approach:

actions$.pipe(
  ofType(slice.actions.addAlert),

  // `There can also be multiple alerts at any time`
  mergeMap(action => {
    const id = uuid();

    // using `NEVER` is important, it's essentially the same as new Observable(() => {})
    // it is needed because we don't want the inner observable to complete unless `takeUntil` decides to
    return NEVER
      .pipe(

        // start with opening the alert
        startWith(slice.actions.addAlertSuccess({ id, ...action.payload }))
        
        // close the alert either
        takeUntil(merge(
          
          // when `TIME` expires
          timer(TIME),
          
          // or when the user decides to
          userClosedActions.pipe(
            filter(action => action.id === id)
          )
        )),

        // at the end(when the stream completed due to `takeUntil`), close the alert
        endWith(slice.actions.closeAlertSuccess(...))
      )
  })
)

userClosedActions can be a Subject that sends next notifications as a result of user action. For example:

onClick (closedId) {
 userClosedActions.next({ id: closedId })
}