Typescript Redux todo feature

addTodo.ts

// store/todo/addTodo.ts

import {Reducer} from 'redux'
import {Action} from 'store/redux' // our fancy new generic type!

interface Todo {
  id: number
  text: string
}

const ADD = 'todo/ADD'
interface AddTodoActionPayload extends Todo {}
interface AddTodoAction extends Action<typeof ADD, AddTodoActionPayload> {}

let nextTodoId = 0
const addTodo = (text: string): AddTodoAction => ({
  type: ADD,
  payload: {
    id: nextTodoId++,
    text,
  },
})

export const actions = {
  addTodo,
}

export type State = Todo[]
const initialState: State = []

export const reducer: Reducer<State> = (state: State = initialState, action: AddTodoAction): State => {
  switch (action.type) {
    case ADD:
      return [
        ...state,
        action.payload,
      ]
    default:
      return state
  }
}