Optional `payload` in `ActionCreator`?

Hello, thanks for the library!

I’ve got a question regarding async action creator. What if my action should receive no params?

export const FETCH_TEAMS = 'FETCH_TEAMS';
const fetchTeams = actionCreator.async<
	{}, // <- here, how can we specify to be optional?
	Array<Team>,
	AxiosError
>(FETCH_TEAMS);

// how i can handle it how
fetchTeams.started({});
fetchTeams.done({
  result: teams,
  params: {}
});

// how it would be nice to handle, but now i see errors in this case
fetchTeams.started();
fetchTeams.done({
  result: teams
});

Thanks in advance!

[rclmenezes]

Similarly, empty actions return undefined payloads:

import actionCreatorFactory from 'typescript-fsa';
const actionCreator = actionCreatorFactory();

const action = actionCreator('ACTION');
console.log(action())  // {type: 'ACTION', payload: undefined}

It’s possible for us to fix both by adopting the following syntax:

const emptyAction = actionCreator.empty('ACTION');
console.log(emptyAction())  // {type: 'ACTION'}

type Success = string;
type Error = string;
const asyncAction = actionCreator.emptyAsync<Success, Error>('ACTION');
console.log(asyncAction.started())  // {type: 'ACTION_STARTED'}
console.log(asyncAction.done('success'))  // {type: 'ACTION_DONE', payload: {results: 'success'}}
console.log(asyncAction.done('failure'))  // {type: 'ACTION_FAILED', payload: {results: 'failure'}}

Benefits of doing it this way:

• Empty actions will be a little cleaner.
• Doesn’t affect the existing API.
• Pretty easy to implement.
• No need to do asyncAction.started({})
• If https://github.com/Microsoft/TypeScript/issues/14400 ever gets released, it’ll be easy to deprecate.

Cons:

• This would expand our supported API surface area
• Async actions without parameters are pretty rare
• Most people never notice that action.payload is undefined anyway 🤷‍♂️

If you decide that you like this, I’d be happy to make the PR 😃

[aikoven]

I would rather not expand the API because of TS shortcomings.

The undefined payload can be easily fixed at runtime, not the typing side.

I’m thinking about just making a payload parameter optional This would make it a bit less type-safe, but at least it would get easier to express things. For instance, the built-in typings for Promise do the same:

// in PromiseConstructor interface

new <T>(executor: (
  resolve: (value?: T | PromiseLike<T>) => void, 
  reject: (reason?: any) => void
) => void): Promise<T>;