Wrong typing using combine middleware

[simon-milleto]

Bug Description

I'm encountering an issue with the combine middleware. I'm not sure if it's a mistake about my usage or if it's a typing issue.

import { createStore } from "zustand/vanilla";
import { combine } from "zustand/middleware/combine";

const exampleStore = createStore(
  combine({ count: 0 }, (set, get) => ({
    setCount: (count: number) => set({ count }),
    sideEffectFunc: () => {
      get().setCount(10);
    }
  }))
);


exampleStore.getState().sideEffectFunc();

In this example get().setCount() is not valid for typescript as setCount doesn't exist in get() but as shown by @dai-shi here #307 (comment) it works and it's valid

Is it an issue with the typing or is it better to change the pattern and do not call action within another action of the same store ?
Thanks !

Reproduction Link

https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBAbzgYygUwIYzQZRtNOAXzgDMoIQ4AiALwFcBnGDAOwBMB6ANzeABt+GagG4AUKEixEKSgCNgrQiXKUaDZmy4hg7dvzQB3DOk7J5itKLFjzrZnDQAPDOAN4CcALwp0WXPjoABRicLIgCkpBSOb0rDAAXHAADMQANHBBjGgwGQDmOQCU3gB8mQihYXDZMADCEHGJmbHxSaz0EWhQxV5lNdGyjcSFaZVhjLpoAKKkpGjIMABicchJQT1lFVVVBTDrAHQ19Y1BAIzJheLbRJVEhYVilzZizq5g7oFo+7t4-gcT7Gms3mSxW63EQA

[dai-shi]

That's how combine works. We can't recursively define types, so get() type is only to return the first part.

By the way, you could do this: https://tsplay.dev/WKJqzm

import { createStore } from "zustand/vanilla";
import { combine } from "zustand/middleware/combine";

const exampleStore = createStore(
  combine({ count: 0 }, (set, get) => {
    const setCount = (count: number) => set({ count });
    return {
      setCount,
      sideEffectFunc: () => {
        setCount(10);
      },
    };
  }),
);

exampleStore.getState().sideEffectFunc();

[simon-milleto]

Thanks for the answer ! Would you consider it a good pattern or is it worth looking for another way to achieve this?

[dai-shi]

combine is the simplest solution for type inference. It's good.
Check out some alternatives: #2672
I personally hope to push zustand-slices more.