已回答Uncaught TypeError：state.concat不是函数错误

Question

我正在关注React和redux的教程，但是在视频结尾处我得到了一个错误，即使我有相同的代码。

未捕获的TypeError：state.concat不是函数

任何帮助都会受到赞赏！

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//action is a parameter and the reducer is the function
//We will make change to the state based on the action (function)

//Function will be reducers
const cards = (state, action) => {
    switch (action.type){
        case 'ADD_CARD':
            let newCard = Object.assign({}, action.data, {
                score: 1,
                id: +new Date
            });
//error is here
            return state.concat([newCard]);
        default:
            return state || {};
    }


};

//Redux helper function to pass reducer functions
const store = Redux.createStore(Redux.combineReducers({
    cards: cards
}));

//Keep an eye on the store for changes
store.subscribe(() => {
    console.log(store.getState());
});

//activate store action
store.dispatch({
    type: 'ADD_CARD',
    data: {
        front: 'front',
        back: 'back'
    }
});

//Another action
store.dispatch({
    type: 'ADD_CARD',
    data: {}
});

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Answer 1

State应该是一个对象，而不是一个数组，所以.concat不会对它起作用。您必须执行state.cards.concat（foobar）之类的操作。如果我在这里错了，请纠正我，但要看看状态并验证其类型。

Answer 2

我在卡片的默认级别返回了一个对象{}而不是一个数组[]。

//action is a parameter and the reducer is the function
//We will make change to the state based on the action (function)

//Function will be reducers
const cards = (state, action) => {
    switch (action.type){
        case 'ADD_CARD':
            let newCard = Object.assign({}, action.data, {
                score: 1,
                id: +new Date
            });
        //splitting the state object into individual properties
            return state.concat([newCard]);
        default:
            return state || [];
    }


};

//Redux helper function to pass reducer functions
const store = Redux.createStore(Redux.combineReducers({
    cards: cards
}));

//Keep an eye on the store for changes
store.subscribe(() => {
    console.log(store.getState());
});

//activate store action
store.dispatch({
    type: 'ADD_CARD',
    data: {
        front: 'front',
        back: 'back'
    }
});
I wasn't reutning an array at the default in cards instead I had {}. I guest I was returning an object ?


//Another action
store.dispatch({
    type: 'ADD_CARD',
    data: {}
});

Answer 3

试试这段代码

const cards = (state = [], action) => {
    switch (action.type){
        case 'ADD_CARD':
            let newCard = Object.assign({}, action.data, {
                score: 1,
                id: +new Date
            });
            //error is here
            return state.concat(newCard);
        default:
            return state || {};
    }
};

Answer 4

State.Cards.Concat（newCard）; 您的阵列是Cards not state。