This is something I'd be willing to open a PR for if wanted.

PRs are welcome. I would like to see how you implement the typecheck for takeEvery. It is complex since takeEvery has several overloading.

@BenLorantfy will you be able to prepare a PR for this? if not we might close this issue because we are not actively working on typings, this is a community effort, not ours.

@aikoven is it possible to type check this?

I took a quick look but it looks pretty complicated and I’m not sure where to start. In theory it’s possible (using generics) but I’m not sure how to fit it into the existing typings. I think this would be a useful type check though, so I don’t think this should be closed.

This indeed looks pretty complicated, since you can use many different things as pattern: predicates, action creators, action types and arrays of those.

This is how ActionPattern type is defined:

export type ActionType = string | number | symbol;

export type StringableActionCreator<A extends Action = Action> = {
  (...args: any[]): A;
  toString(): string;
};

export type ActionSubPattern<Guard extends Action = Action> =
  | GuardPredicate<Guard, Action>
  | StringableActionCreator<Guard>
  | Predicate<Action>
  | ActionType

export type ActionPattern<Guard extends Action = Action> =
  | ActionSubPattern<Guard>
  | ActionSubPattern<Guard>[];

The path we're interested in is ActionPattern<T> -> ActionSubPattern<T> -> ActionType, and ActionType is not parametric.

We could parametrize it like this:

type ActionType<A extends Action = Action> = A['type'];

But unfortunately in Redux typings the type of Action.type is any, so this would effectively cast ActionPattern to any when used without a type parameter.

if takeLatest is invoked with type argument which extends Action (any object, which has type property), Guard type argument of ActionSubPattern will be properly typed.

So if change ActionSubPattern to something like

export type ActionSubPattern<Guard extends Action = Action> =
  | GuardPredicate<Guard, Action>
  | StringableActionCreator<Guard>
  | Predicate<Action>
  | Guard['type']

The result will be as expected. Below code will produce type error

type LoadDataAction = { type: 'LOAD_DATA' }
yield takeLatest<LoadDataAction>('blablabla', loadData);

The only this which confuse me is form of takeEvery<P extends ActionPattern>. I'll look at why there are two different forms of takeEvery exists and then propose change of typing.

Closing due to inactivity. If this is still something worth discussing please reply and I will reopen to help. Thanks!