zustand-redux-extends-type

To be used with zustand's redux middleware. To install:

npm add zustand-redux-extends-type -D # or yarn add zustand-redux-extends-type -D

Leveraging typings (ReduxExtends and FeatureEventActions) as below eliminates the need to use any type assertions in reducers. It also enforces only valid values for properties when dispatch is being typed out.

import type { ReduxExtends } from "zustand-redux-extends-type";

type FeatureEventActions = {
  grumpiness: {
    increase: number;
    decrease: number;
    reset: undefined;
  };
  happiness: {
    "show all": User[];
    level: "low" | "sort of" | "high";
  };
};

const useGrumpyStore = create(
  redux(
    (
      state: { count: number; level: "low" | "sort of" | "high" },
      { type, payload }: ReduxExtends<FeatureEventActions>
    ) => {
      switch (type) {
        case "grumpiness/increase":
          return { ...state, count: state.count + payload };
        case "grumpiness/decrease":
          return { ...state, count: state.count - payload };
        case "grumpiness/reset":
          return { ...state, count: 0 };
        //removed happiness cases for brevity
        default:
          return state;
      }
    },
    { count: 0, level: "high" }
  )
);

const dispatch = useGrumpyStore((state) => state.dispatch);
dispatch({ type: "grumpiness/decrease", payload: 1 });

The structure of this map type, FeatureEventActions, is premised on Redux's recommendation for actions:

"The type field should be a readable string, and is usually written as 'feature/eventName'"

For this example, 'grumpiness' and 'happiness' are features with event names of 'increase' and 'show all' respectively. Each event name is typed for what will be its payload type. Any action object of ReduxExtends<FeatureEventActions>, either as a parameter of reducer or dispatch, has its type property constrained to what will be parsed by TypeScript. This will also dictate the payload type.