帮忙看下这个函数参数是怎么传的，这是啥写法。

Question

const helloReducer = (state: Immut = initialState, action: { type: string, payload: any }) => {
  switch (action.type) {
    case SAY_HELLO:
      return state.set('message', action.payload)
    default:
      return state
  }
}

(state: Immut = initialState, action: { type: string, payload: any }) 这个参数是什么写法？解构也不长这个样子啊？
跪求答案？

Answer 1

这是typescript或者flow的语法
写成js的话就是这样

const helloReducer = (state = initialState, action) => {
    /*...*/
}

冒号后面指定的类型是用于编译期检查参数类型的

Answer 2

应该是React Redux

Answer 3

对象解构。

helloReducer(1, { type: '1', payload:2 });