Javascript 未捕获类型错误：未定义不是在for循环中创建的函数、对象

我正在构建一个小测验应用程序，用户可以在其中构建自己的测验，但在for循环中创建对象时遇到了问题

以下是问题对象的构造函数：

var question = function(questionNumber, question, choices, correctAnswer) {
    this.questionNumber = questionNumber;
    this.question = question;
    this.choices = choices;
    this.correctAnswer = correctAnswer; //The number stored here must be the location of the answer in the array

    this.populateQuestions = function populateQuestions() {
        var h2 = $('<h2>').append(this.question);
        $('#quizSpace').append(h2);
        for (var i = 0; i < choices.length; i++) {
            //Create the input element
            var radio = $('<input type="radio">').attr({value: choices[i], name: 'answer'});

            //Insert the radio into the DOM
            $('#quizSpace').append(radio);
            radio.after('<br>');
            radio.after(choices[i]);
        }
    };
    allQuestions.push(this);
};

在这一行：

var question = new question(i, questionTitle, inputChoices, correctAnswer);

---

这是因为行

var question=新问题（i，问题标题，输入选项，正确答案）

在其范围内，即在click事件处理程序中创建另一个变量

question

。由于可变提升，它被移动到范围（功能）的顶部，最终成为：

   $('#buildQuiz').click(function() {
     var question; //undefined
      ...
      ...
      //here question is not the one (constructor) in the outer scope but it is undefined in the inner scope.
     question = new question(i, questionTitle, inputChoices, correctAnswer);

只需将变量名更改为其他名称，然后重试

     var qn = new question(i, questionTitle, inputChoices, correctAnswer);

或者为了避免这些问题，您可以用Pascalcase命名构造函数函数，即

 var Question = function(questionNumber, question, choices, correctAnswer) {
 .....

---

您正在用

未定义

覆盖全局

问题

变量。以下内容相当于您所拥有的内容：

$('#buildQuiz').click(function() {
    var question; // this is why `question` is undefined

    var questionLength = $('.question').length;
    for ( var i = 1; i <= questionLength; i++ ) {
        var questionTitle = $('#question' + i + ' .questionTitle').val();
        var correctAnswer = $('#question' + i + ' .correctAnswer').val() - 1;
        var inputChoices = [];
        $('#question' + i + ' .choice').each(function(){
            inputChoices.push($(this).val()); 
        });

        question = new question(i, questionTitle, inputChoices, correctAnswer);

    }
    allQuestions[0].populateQuestions();
    $('#questionBuilder').hide();
    $('#quizWrapper').show();
});

$（'#buildquick'）。单击（函数（）{
var question；//这就是为什么'question'没有定义
var questionLength=$（'.question'）.length；
对于（var i=1；i），一个好的经验法则是使用构造函数的大写字母。将
var-question=function（…）
更改为
var-question=function（…）
。
 var Question = function(questionNumber, question, choices, correctAnswer) {
 .....

$('#buildQuiz').click(function() {
    var question; // this is why `question` is undefined

    var questionLength = $('.question').length;
    for ( var i = 1; i <= questionLength; i++ ) {
        var questionTitle = $('#question' + i + ' .questionTitle').val();
        var correctAnswer = $('#question' + i + ' .correctAnswer').val() - 1;
        var inputChoices = [];
        $('#question' + i + ' .choice').each(function(){
            inputChoices.push($(this).val()); 
        });

        question = new question(i, questionTitle, inputChoices, correctAnswer);

    }
    allQuestions[0].populateQuestions();
    $('#questionBuilder').hide();
    $('#quizWrapper').show();
});