React 手动实现一个简易useReducer

const useReducer = (reducer, initState) => {
  const [state, setState] = useState(initState)
  const dispatch = (action) => {
    setState(reducer(state, action))
  }
 return [state, dispatch]
}
// 使用
const someReducer = (state, action) => {
 switch(action.type) {
  case 'add': {
    return [...state, {a:  1, id: 1}]
  }
  case 'delete': {
    if (action.id) {
      state.splice(state.findIndex(item=> item.id === action.id), 1) 
      return [...state]
    }
  }
 }
}

const [state, dispatch] = useReducer(somoReducer, {a: 1, b: 2})