combineEpics using TypeScript gives type error

Question

I am getting this error when combining my epics:

TS2345: Argument of type 'Epic<SessionAction, GlobalState, any>' is not assignable to parameter of type 'Epic<EmployeeAction, GlobalState, any>'.
Type 'SessionAction' is not assignable to type 'EmployeeAction'.
Types of property 'type' are incompatible.
  Type 'SessionActionTypes' is not assignable to type 'EmployeeActionTypes'.

The following is the code:

import { combineEpics } from 'redux-observable';
import { fetchUserSession } from './sessionEpics';
import { fetchEmployee } from './employeeEpics';

export default combineEpics(
  fetchEmployee,
  fetchUserSession
);

Did you manage to solve this? – Roy Art Feb 21 '18 at 12:23 — Roy Art, Feb 21 '18 at 12:23

score 3 · Accepted Answer · answered Feb 21 '18 at 12:31

I have pretty much the same problem. It seems like typescript grabs the first epic, infers it's type and expect all the rest to be the same.

What I did was cast the first one.

Using your code as example:

import { Observable } from 'rxjs/Observable';
import { AnyAction } from 'redux';
import { combineEpics } from 'redux-observable';
import { fetchUserSession } from './sessionEpics';
import { fetchEmployee } from './employeeEpics';

export default combineEpics(
  fetchEmployee as Observable<AnyAction>,
  fetchUserSession
);

score 3 · Answer 2 · edited May 06 '18 at 08:56

3

Or use combineEpics<any>:

export default combineEpics<any>(
  fetchEmployee,
  fetchUserSession
);

edited May 06 '18 at 08:56

Syscall

19,327
10
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answered May 06 '18 at 08:49

Axel186

541
5
17

score 1 · Answer 3 · answered Jun 14 '18 at 15:38

1

A better solution might be using the correct types: AnyAction and Observable:

import { AnyAction } from "redux"
import { combineEpics, createEpicMiddleware } from "redux-observable"
import { Observable } from "rxjs"

export const clientMiddleware = createEpicMiddleware(
  combineEpics<AnyAction, Observable<AnyAction>>(
    authenticateEpic(request),
    registerEpic(request)
  ))

answered Jun 14 '18 at 15:38

squidfunk

391
3
17

1

Can you kindly explain why these are the correct types? what's the logic behind this? – Elyasaf755 Apr 05 '22 at 15:09

combineEpics using TypeScript gives type error

3 Answers3