reactjs - useReducer 的 initialState 类型为 never？

Question

initialState 有错误:Argument of type '{ email: string;密码:字符串；有效: bool 值； }' 不可分配给 'never' 类型的参数。ts(2345)

function reducer(state: IState, action: IFluxAction) {
  const Users = UsersFetch()
  switch (action.type) {
    case 'email':
      const email = action.value
      const valid = Users.find(e => e === email) ? true : false

      return {
        email,
        valid,
      }
    case 'password':
      const password = action.value
      return {
        password,
      }
    default:
      throw new Error()
  }
}

  const initialState = {
    email: '',
    password: '',
    valid: false,
  }
  const [state, dispatch] = React.useReducer(reducer, initialState)

输入此内容以满足错误的正确方法是什么？

react 16.8.1 typescript 3.3.1

应该(由...修复)将 ...state 添加到返回值中，例如

  switch (action.type) {
    case 'email':
      const email = action.value
      const valid = Users.find(e => e === email) ? true : false

      return {
        ...state,
        email,
        valid,
      }
    case 'password':
      const password = action.value
      return {
        ...state,
        password,
      }
    default:
      throw new Error()
  }

另外 - 正如@madflanderz 所建议的，将 IState 设置为 reducer 的预期返回值有助于捕获此类问题。

Answer 1

我也遇到过这个问题。在我看来，防止错误的最佳方法是将状态接口(interface)添加为 reducer 的返回类型。然后你会在 useReducer 行看到 reducer 内部的类型错误。

像这样:

function reducer(state: IState, action: IFluxAction): IState {
   // reducer code
   // type errors are visible here 
}