Update TypeScript declarations to work with Redux 3 & 4

[xuoe]

For more details, see PR #6.

[KagamiChan]

The main reason to update the TS declaration is that Redux has been rewritten with TypeScript, so the @types/redux is no longer required and we see some incompat in both declarations

(Off topic, are you interested in doing similar rewrite?)

The suggestions from @ankon are excellent. As Dispatcher is an internal typing that user will not touch, redux 3/4 users won't notice any difference.

But for those who use pre-TS redux, if we drop @types/redux dependency, their code would break because they have to upgrade redux, for this reason it is going to be a breaking change.

So we need to drop the @types/redux dep, add a redux@4 peer dep, and bump a major version

Besides, in TS Redux definition, Dispatch accepts an Action generics, we could consider adding an extra argument for that, so the additional reload could be:

import { Action } from 'redux'

type Dispatcher<MS, A> = (dispatch: Dispatch<A>, currentState: MS, previousState: MS) => unknown;
// or no reload, just type Dispatcher<MS, A extends Action = AnyAction> = (dispatch: Dispatch<A>, currentState: MS, previousState: MS) => unknown;

export function observer<S, MS, A extends Action>(mapper: Mapper<S, MS>, dispatcher: Dispatcher<MS, A>, options?: Options): Observer<S, MS>;

Please correct me in case of any error @ankon

[KagamiChan]

and also, we need to add some TypeScript type checking to make sure the declaration works with some concrete example

[xuoe]

Thanks a lot for your input, @KagamiChan.

I created a pull request with some changes to the TypeScript declarations (#8) and added some comments there. Please take a look, if you have the time.

I should mention upfront that I haven't written any TypeScript before today and I haven't used this package (or Redux) in years, so I'm learning as we're going.

Regarding @types/redux: removing it from package.json and reinstalling all development dependencies and then issuing tsc --strict --noImplicitAny --noEmit ./index.d.ts does not generate any errors with either version of Redux (3.7.2 or 4.0.4). With 3.7.2, there's even a deprecation warning issued at install time, which states that @types/redux is unnecessary since redux comes with its own declaration file. I tried this even against older versions that didn't have a declaration file and it still worked, which is confusing (I don't have @types/redux installed globally). It seems that 3.4.0 is the first version that supports type declarations, and it's been released almost 4 years ago. TypeScript users that use older versions of Redux could fix the problem by tagging @types/redux as their own dependency, which they probably already have done, but that's a lot of assumptions.

Regarding a rewrite: do you mean a rewrite in TypeScript? No, I don't think it's necessary. Getting the declarations to work correctly would be more than enough, in my opinion.

Regarding your code suggestions: I did include something similar in #8 (f13a2a4). What do you make of it?

[KagamiChan]

Thanks for your quick response

The type checking I mentioned is write some TS code to consume the package in various way and see if there's no conplaints from tsc, Maybe you could take some examples from tests, or I prepare some later when I have bandwidth (my project consuming the package is not in TS so I don't have any example at hand).

Sorry, I forgot that they have shipped with typings before TS rewrite. They should have picked the dts file from definitivelyTyped repo, and I see that currently @types/redux depends on redux and exports the typings from redux. Then it seems simpler, things making difference is just the typing change between version 3 and 4

[xuoe]

Yes, I'm writing some tests to ensure that the type declarations work with >3.4.x (as described on the dtslint README). The typing issue appears to be solved by using Dispatch<AnyAction> instead of Dispatch<MS> (with AnyAction being the type exported by redux).

I'll take a look at your comments from #8 a bit later. Thanks!