Function reducer

videos/long/learn-react-hooks-useReducer/index.tsx:12–37

(state: State, action: Action)

}

function reducer(state: State, action: Action) {
  const { type } = action;

  switch (type) {
    case 'increment': {
      const newCount = state.count + 1;
      const hasError = newCount > 5;
      return {
        ...state,
        count: hasError ? state.count : newCount,
        error: hasError ? 'Maximum reached' : null,
      };
    }
    case 'decrement': {
      const newCount = state.count - 1;
      const hasError = newCount < 0;
      return {
        ...state,
        count: hasError ? state.count : newCount,
        error: hasError ? 'Minimum reached' : null,
      };
    }
    default:
      return state;
  }
}

export default function Demo() {
  const [state, dispatch] = useReducer(reducer, {