带有函数的 AJAX 发送对象会在函数处抛出错误

我有以下Ajax：

    $.ajax({
        type: 'POST',
        url: '/Jeopardy/saveCategoryData',
        dataType: 'json',
        data: {
            name: this.name,
            questions: this.question_array,
            sort_number: this.sort_number,
            game_id: game_id
        },
        success: function (data)
        {
            this.id = data;
        }
    });

更新 这是 ajax 所属的完整类：

function Category(name, sort_number)
{
    this.name = name;
    this.sort_number = sort_number;
    this.question_array = [];
    this.id = 0;
    /*
        Functions
     */
}
Category.prototype.saveCategory = function()
{
    $.ajax({
        type: 'POST',
        url: '/Jeopardy/createCategory',
        dataType: 'json',
        data: {
            request: 'ajax',
            name: this.name,
            sort_number: this.sort_number,
            game_id: game_id
        },
        success: function (data)
        {
            this.id = data;
        }
    });
    $('.category_'+this.sort_number).each(function()
    {
        $(this).css('opacity', '1');
        $(this).addClass('question');
    })
}
Category.prototype.submitCategory = function()
{
        $.ajax({
            type: 'POST',
            url: '/Jeopardy/saveCategoryData',
            dataType: 'json',
            data: {
                request: 'ajax',
                name: this.name,
                questions: this.question_array,
                sort_number: this.sort_number,
                game_id: game_id
            },
            success: function (data)
            {
                this.id = data;
            }
        });
}
Category.prototype.addQuestion = function(question,index)
{
    this.question_array[index] = question
}

其中this.question_array是question对象的数组：

function Question(question, score)
{
    this.question = question;
    this.score = score;
    this.answer = [];
}
Question.prototype.getScore = function()
{
    return this.score;
}
Question.prototype.addAnswer = function(answer)
{
   this.answer.push(answer)
}

我的回答对象：

    function Answer(answer, is_correct)
{
    this.answer = answer;
    this.is_correct = is_correct;
}

当我的Ajax提交时，我在函数addAnswer出现错误，说：Cannot read property 'push' of undefined

谁能告诉我为什么会发生这种情况（我对 JavaScript 中的 OOP 相当陌生）

更新创建.js（控制对象的脚本）

保存问题功能：

function saveQuestion() {
    var question = new Question($('#txt_question').val(), current_money);
    var array_index = (current_money / 100) - 1;
    $('.txt_answer').each(function ()
    {
        var answer = new Answer($(this).val(), $(this).prev().find('input').is(':checked'));
        question.addAnswer(answer); // <-- Add answer
    })
    if(current_element.find('.badge').length == 0)
    {
        current_element.prepend('<span class="badge badge-sm up bg-success m-l-n-sm count pull-right" style="top: 0.5px;"><i class="fa fa-check"></i></span>');
    }
    addQuestionToCategory(question, array_index);
    questionObject.fadeOutAnimation();
}
function addQuestionToCategory(question, index) {
switch (current_category_id) {
    case "1":
        category_1.addQuestion(question, index);
        break;
    case "2":
        category_2.addQuestion(question, index);
        break;
    case "3":
        category_3.addQuestion(question, index);
        break;
    case "4":
        category_4.addQuestion(question, index);
        break;
}

}

以及在每个类别对象上调用 ajax 的函数：

    function saveGame()
{
    category_1.submitCategory();
    category_2.submitCategory();
    category_3.submitCategory();
    category_4.submitCategory();
}

调试调用堆栈：

Question.addAnswer (question.js:25)
n.param.e (jquery-1.11.0.min.js:4)
Wc (jquery-1.11.0.min.js:4)
Wc (jquery-1.11.0.min.js:4)
(anonymous function) (jquery-1.11.0.min.js:4)
n.extend.each (jquery-1.11.0.min.js:2)
Wc (jquery-1.11.0.min.js:4)
n.param (jquery-1.11.0.min.js:4)
n.extend.ajax (jquery-1.11.0.min.js:4)
Category.submitCategory (category.js:47)
saveGame (create.js:116)
onclick (create?game_id=1:182)

*更新

好吧，如果我将 addAnswer 函数更改为以下内容，就会发生一些奇怪的事情：

    Question.prototype.addAnswer = function(answer)
{
   if(this.answers != undefined)
   {
       this.answers.push(answer)
   }
}

它工作正常吗？