无法读取未定义的javaScript属性'length'

Question

我正在尝试构建一个预算应用程序，但出现错误

无法读取未定义的属性'length'

在Object.addItem（app.js：36）

在HTMLButtonElement.ctrlAddItem（app.js：128）

这是我的代码：

// DATA Module
var budgetController = (function() {

var Expense = function(id, description, value) {
    this.id = id;
    this.description = description;
    this.value = value;
};

var Income = function (id, description, value) {
    this.id = id;
    this.description = description;
    this.value = value;
};



var data = {
    allItems: {
        exp: [],
        inc: []
    },
    totals: {
        exp: 0,
        inc: 0
    }
};

return {
    addItem: function(type, des, val) {
        var newItem, ID;

        // create new ID
        if (data.allItems[type].length > 0) {
            ID = data.allItems[type][data.allItems[type].length - 1].id + 1;
        } else {
            ID = 0;
        }


        //create new item based on 'inc' or 'exp' type
        if(type === 'exp') {
            newItem = new Expense(ID, des, val);
        } else if (type === 'inc') {
            newItem = new Income(ID, des, val);
        }

        // push it into our data structure
        data.allItems[type].push(newItem);

        // return the new element
        return newItem;
    },

    testing: function() {
        console.log(data)
    }
};

})();

var data = {
allItems: {
    exp: [1,2,3],
    inc: []
},
totals: {
    exp: 0,
    inc: 0
}
};

// UI module
var UIController = (function() {

var DOMstrings = {
    inputType: '.add__type',
    inputDescription: '.add__description',
    inputValue: '.add__value',
    inputBtn: '.add__btn'
};

return {
    getInput: function() {
        return {
            type: document.querySelector(DOMstrings.inputType).value , // will be either inc or exp
            description: document.querySelector(DOMstrings.inputDescription).value ,
            value: document.querySelector(DOMstrings.inputValue).value
        };
    },

    getDOMstrings: function() {
        return DOMstrings;
    }

};

})();

// GLOPAL APP CONTROLLER 
var controller = (function(budgetCtrl, UICtrl) {

var setupEvenetListeners = function() {

    var DOM = UICtrl.getDOMstrings();

    document.querySelector(DOM.inputBtn).addEventListener("click", ctrlAddItem);

    document.addEventListener('keypress', function (event) {
        if (event.keyCode === 13 || event.which === 13) {
            ctrlAddItem();
        }
    });
};



var ctrlAddItem = function() {

    var input, newItem;

    // 1. get the field input data
    input = UICtrl.getInput();

    // 2. add the item to the budget controller
    newItem = budgetCtrl.addItem(input.type, input.description, input.value);

    // 3. add the new item to the UI 

    // 4. calculate the budget

    // 5. display the budget on the UI

}

return {
    init: function() {
        setupEvenetListeners();
    }
};

})(budgetController, UIController);

controller.init();

我确定那里的错误，但过去两个小时来了，我在这里找不到它：

 if (data.allItems[type].length > 0) {
            ID = data.allItems[type][data.allItems[type].length - 1].id + 1;
        } else {
            ID = 0;
        }

这应该从输入字段中获取数据，然后为每个输入数据创建唯一的ID，然后将其推送到data.allItems ['exp'或'inc']