actions-old.ts

import { Reducer, Action } from 'redux';

interface CounterState { count: number }
const initialState: CounterState = { count: 0 };


const ADD = 'ADD';
interface AddAction extends Action<typeof ADD> {
  payload: { amt: number };
}
export const addAction = (payload: AddAction['payload']): AddAction => ({
  type: ADD, payload,
});

const SUBTRACT = 'SUBTRACT';
interface SubtractAction extends Action<typeof SUBTRACT> {
  payload: { howMany: number };
}
export const subtractAction = (payload: SubtractAction['payload']): SubtractAction => ({
  type: SUBTRACT, payload,
});

type CounterAction =
  | AddAction
  | SubtractAction

export const counterReducer: Reducer<CounterState, CounterAction> = (s = initialState, action) => {
  switch (action.type) {
    case ADD: return { ...s, count: s.count + action.payload.amt };
    case SUBTRACT: return { ...s, count: s.count - action.payload.howMany };
  }
};