[SOLVED] redux-observable epic typescript warning: 'store' is declared but its value is never read

redux-observable epic typescript warning: 'store' is declared but its value is never read

I have a redux observable epic as below

export const fetchUserEpic:Epic<Action, RootState, any> = 
    (action$: ActionsObservable<Action>, store: MiddlewareAPI<RootState> , { getJSON } ): Observable<Action> => 
        action$.filter((action: Action) => action.type === actionTypes.FETCH_USER)
            .mergeMap(  (action: Action) =>
                getJSON(`/api/user/${action.payload}`)
                .map((response: any) => Actions.fetchUserSuccess(response))
            )

Everything works fine and the tests are great, but on compiling the typescript code, I get the following warning

semantic error TS6133 'store' is declared but its value is never read.

How do I resolve this issue

Solution

It's a linting error from TypeScript noUnusedParameters aka no-unused-variable setting. It means that your function has the store parameter defined but does not actually use it. To fix you can prefix the store parameter with an underscore _store and it will ignore it, or you can remove the linting option from either your tsconfig or your compiler flags.

(action$: ActionsObservable<Action>, _store: MiddlewareAPI<RootState> , { getJSON } ): Observable<Action>

This works because the TypeScript compiler explicitly added this convention as an exception to the linting rule. It was done for exactly these sorts of cases.