typescript-fsa-reducers | Fluent syntax for defining typesafe reducers | State Container library

I can reproduce the problem if I do the default npm install typescript-fsa typescript-fsa-reducers, which gives me typescript-fsa@3.0.0-beta-2 and typescript-fsa-reducers@0.4.5, with the latter having its own copy of typescript-fsa@2.5.0. The inference is failing because typescript-fsa@3.0.0-beta-2 and typescript-fsa@2.5.0 have different definitions of ActionCreator. (It's embarrassing how long it took me to realize that!) The new definition has a conditional type that tests Payload extends void; when Payload is a concrete type that is known not to be assignable to void, the new definition simplifies to be sufficiently similar to the old that your code happened to work, but when Payload is the type variable TStartPayload, no simplification is possible.

You shouldn't try to use two incompatible versions of typescript-fsa together; the compile error may only be the beginning of trouble. If you want to use typescript-fsa-reducers, you should switch your project to a version of typescript-fsa that is compatible with it.

In React without the typescript-fsa abstraction, you'd make async API callsat the action creator level, since actions are just dispatched POJOs and reducers are supposed to not have any side effects.

There are two projects that make it easy to do this, redux-thunk and redux-saga. I prefer redux-thunk because it is easier to wrap your head around. Basically your action creators get passed the dispatch function, and then they can be responsible for dispatching more than one thing... like so: