Return type of a `yield call`

Question

I've noticed that the result of a yield call effect is typed as any when used as

const data = yield call(f);

while f is a () => Promise<number> function.

Am I missing something or is it a redux-saga typings limitation?

Answer 1

Check this ongoing thread, tldr; it's a typescript limitation

Answer 2

In the meantime, you can use this package instead: typed-redux-saga

Before

import { call, all } from "redux-saga/effects";
...
// Api.fetchUser return User
// but user has type any
const user = yield call(Api.fetchUser, action.payload.userId);

After

import { call, all } from "typed-redux-saga";
...
// user now has the correct type User
// NOTE: it's yield*, not yield
const user = yield* call(Api.fetchUser, action.payload.userId);

Answer 3

define this types

export type PromiseFn = (...args: any) => Promise<any>;
export type GetT<T> = T extends Promise<infer N> ? N : any;
export type GetFnResult<T extends PromiseFn> = GetT<ReturnType<T>>;

then

const data: GetFnResult<typeof f> = yield call(f);

Answer 4

You can use

const data = (yield call(f)) as number