TypeScript Type For useReducer() action

The TypeScript type of the action parameter in the useReducer hook depends on the type of the reducer function that you are using.

In general, the action parameter can have any type that is compatible with the action types that the reducer function expects. For example, if your reducer function expects actions of type { type: string, payload: any }, then the action parameter in useReducer should have that same type or a subtype of it.

Here's an example of how you could define a Reducer type that takes a specific action type:

type MyActionType = { type: string; payload: any };

type MyStateType = {
  /* ... */
};

type MyReducerType = (state: MyStateType, action: MyActionType) => MyStateType;

In this example, MyActionType represents the shape of the actions that your reducer expects, MyStateType represents the shape of your state, and MyReducerType is the type of the reducer function that you will pass to useReducer.