isOfType could accept an array of actions instead of one

[paszkowskiDamian]

Is your feature request related to a problem?

Sometimes we have epics that listen for more than one action. It would be really cool if could preserve type-safety of isOfType while being able to filter more than one action.

Describe a solution you'd like

return action$.pipe(
    filter(isOfTypes(RELOAD_ORDERS , ORDERS_FETCH_REQUEST)),
    mergeMap(async action =>  ordersheetRepository.loadOrders(action.payload)) // action is union of RELOAD_ORDERS , ORDERS_FETCH_REQUEST actions
    ...

Who does this impact? Who is this for?

It is for TypeScript users who would like to handle multiple actions using one epic.

Describe alternatives you've considered

We could use ofType operator from redux-observable but it doesn't return proper types.

Additional context

This is my local implementaion:

export function isOfTypes<T extends string[]>(...actions: T):
  <Action extends {type: string}>(action: Action) => action is Action extends {type: Unboxed<T>} ? Action : never {
    return <Action extends {type: string}>(action: Action):
    action is Action extends {type: Unboxed<T>}
      ? Action
      : never => actions.includes(action.type);
}

This could be integrated to already existing ifOsType.

[Carl-Foster]

Any reason you don't use isActionOf?

[piotrwitek]

Hey @paszkowskiDamian, thanks for the proposal.
Currently isActionOf supports an array as parameter to handle a parallel scenario.
So IMO it would be just to extend isOfType API to also support an array as alternative parameter and API will stay consistent.

I agree and will integrate this change into the API.

Our test suite will also need to be extended with new API cases.

[paszkowskiDamian]

I've opened a new PR #86 implementing new API

[paszkowskiDamian]

@Carl-Foster actaully, I didn't try with isActionOf but it seems as it is not narrowing action types properly but I didn't researched it why.

action$.pipe(
    filter(isActionOf([fetchMoreAccountsFailed, fetchAccountsListFailed])),
    mergeMap(async action /*inferes as RootAction*/ => accountsRepository.doSth(action.paylod)),

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[piotrwitek]

Resolved by #86