Fix MiddlewareAPI in .ts

[gorshkov-leonid]

MiddlewareAPI should have 2 params in type same as flow-typed/redux.js:

https://github.com/reactjs/redux/blob/master/index.d.ts#L256-L259

[aikoven]

Should it? Dispatch is able to accept any action, not just a specific subtype of {type: string}.

[gorshkov-leonid]

generic type of state vs generic type of action. it is differen things...

[gorshkov-leonid]

click on links please...

[aikoven]

I did.

State type is generic because it depends on your state shape.

Actions are not restricted to any subtype of {type: string}: dispatch accepts any object with type property, even if actions in your codebase are all of the specific shape e.g. {type: string, payload: object}. Imagine a third-party library that has its own action shapes.

Also, there might be a misconception with the generic parameter of Dispatch: the S in Dispatch<S> is not the action type, but the state type. You may notice that Dispatch signature doesn't even use this parameter:

interface Dispatch<S> {
    <A extends Action>(action: A): A;
}

The reason for this is to allow middlewares to augment this interface with custom signatures, i.e. redux-thunk. See #1537

[timdorr]

@aikoven is correct here. Because you can enhance the store with middleware to accept any type of input as an "action", it needs to be generic.

[gorshkov-leonid]

OK. I understood. Yes it is logical. But it is not clear at first sight. Flow js - 2 type parameters. Ts - 1 type parameter. Think you need to leave a comment in code for the descendants