How to update progress of long request with redux-observable

Problem

I want to send a couple of requests an update a progress after each one is successful. In the end, I want to dispatch success action.

Solution

constepic=action$=>
  action$.filter(action.fetchRequestStart).switchMap(action=>
    Observable.range(1, repeatTimes).mergeMap(()=>
        Observable.from(fetchRequest).mergeMapTo(
          Observable.of(action.increaseProgress()))).concat(Observable.of(action.fetchRequestSuccess())).catch(action=> Observable.of(action.fetchRequestError())))

This is a simple epic implementing this logic. How does it work? After I filter out the action that is interesting for me from a stream, I map through it using switchMap so if user action dispatches the same action one more time during Observable.range the pending operation will be canceled.

Operator range works like intended - it will emit as many observables as I provide in repeatTimes. Right after that, I’m using mergeMap so I can add multiple observables - in my case, I only add one to dispatch action of increasingProgress. In the end, I use concat to emit action of success at the end of range. If anything goes wrong I catch errors in catch.

This is it for today! I was a quick blog post but you can email me with your feedback.