javascript - 未捕获的 TypeError : undefined is not a function, 在 for 循环中创建的对象

Question

我正在构建一个小型测验应用程序，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。

这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);
};

我有一堆动态生成的 HTML，然后我从中提取值并将它们放在一个新对象中，如下所示:

$('#buildQuiz').click(function() {
    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()); 
        });

        var question = new question(i, questionTitle, inputChoices, correctAnswer);
        }
    allQuestions[0].populateQuestions();
    $('#questionBuilder').hide();
    $('#quizWrapper').show();
});

但是，当我单击 #buildQuiz 按钮时，我收到错误消息:

Uncaught TypeError: undefined is not a function 

在这一行:

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

Answer 1

这是因为 var question = new question(i, questionTitle, inputChoices, correctAnswer); 这行在它的范围内创建了另一个变量 question 即在点击事件处理程序。由于变量提升，它被移动到范围(函数)的顶部，最终变成:

   $('#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并尝试。

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

或者为了避免此类问题，您可以使用 Pascalcase 命名您的构造函数，即

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