The old code was returning a fn because TypeScript could not figure out
generic type parameters when params was an object like:
interface Params<State> {
a: Reducer<State>
b: Partial<State>
}
function test<State>(params: Params<State>) {
// ...
}
Since TypeScript can infer types based on string types, it has became
easier to define a single constant of an action that returns a promise,
and then dispatch actions with different statuses: pending, resolved,
and/or rejected. This seems like more typing at first, but in the long
run it will become easier to write generic reducer methods, and the
names of reduced types will not have to be repeated every time.
For example, previously we had to write:
type MyActionTypes =
IAsyncAction<IUser, 'LOGIN_PENDING', 'LOGIN_RESOLVED', 'LOGIN_REJECTED'>
| ...
And now we can write:
type MyActionTypes =
IAsyncAction<IUser, 'LOGIN'>
| ...
