Asterisk Medium Article: reducer

todo.ts

// Reducer
const reducer = (state: TodoState = defaultState, action: TodoAction): TodoState => {
  switch (action.type) {

    ...

    case "TODO_UNCOMPLETED_STARTED": {
      return { ...state, isUncompletingTodo: true }
    }
    case "TODO_UNCOMPLETED": {
      return {
        ...state,
        isCompletingTodo: false,
        todos: state.todos.reduce((todos, nextTodo) => {
          if (nextTodo._id === action.payload.todo._id) {
            return [...todos, action.payload.todo]
          }
          return [...todos, nextTodo]
        }, [] as TodoItem[]),
      }
    }
    default: {
      return state
    }
  }
}