无法将 undefined 或 null 转换为对象 redux答案

【问题标题】：Cannot convert undefined or null to object redux无法将 undefined 或 null 转换为对象 redux
【发布时间】：2017-05-29 22:50:40
【问题描述】：

我正在使用 Redux 制作一个简单的商店，不幸的是它抛出了这个错误：

 Cannot convert undefined or null to object

浏览器指向导入Redux的那一行

import * as redux from "redux"

我也尝试过以这种方式导入它，但它给出了同样的错误从“redux”导入 { createStore }

这是代码：

import * as redux from "redux"

let reducer = (state ={}, action) =>{
    switch(action.type) {
        case "ADD_POLL":
            return {
                polls: [
                    ...state.polls,
                    action.poll
                ]
            }
        default:
            return state
    }
}

let store = redux.createStore(reducer)

store.subscribe(()=>{
    let currentState = store.getState()
    console.log(currentState)
})

store.dispatch({
    type: "ADD_POLL",
    poll: {
        id: 1,
        title: "What's  your fav Color",
        votes: 230
    }
})

【问题讨论】：

标签： javascript reactjs redux react-redux

【解决方案1】：

该错误被抛出，因为在你的减速器中你试图在状态对象上传播一个不存在的属性

...state.polls,

为此，您必须将初始状态的形状定义为

const initialState = {
    polls: [],
};

您的示例的完整工作代码

import * as redux from "redux"

const initialState = {
    polls: [],
};

const reducer = (state = initialState, action) =>{
    switch(action.type) {
        case "ADD_POLL":
            return {
                polls: [
                    ...state.polls,
                    action.poll
                ]
            }
        default:
            return state
    }
}

const store = redux.createStore(reducer)

store.subscribe(()=>{
    let currentState = store.getState()
    console.log(currentState)
})

store.dispatch({
    type: "ADD_POLL",
    poll: {
        id: 1,
        title: "What's  your fav Color",
        votes: 230
    }
})

【讨论】：