未捕获的TypeError：undefined不是函数，在for循环中创建的对象

Question

我正在构建一个小的测验应用程序，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Question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：

Uncaught TypeError: undefined is not a function 

在这一行：

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

Answer 1

那是因为行var question = new question(i, questionTitle, inputChoices, correctAnswer); 这会在其范围内创建另一个变量question ，即在click事件处理程序中。 由于可变的提升，它被移动到范围（功能）的顶部，最终变为：

   $('#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);

只需将变量名称更改为其他名称即可尝试。

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

或者为了避免这些问题，您可以在Pascalcase中命名构造函数，即

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

Answer 2

你用undefined来覆盖全局question var。 以下相当于你拥有的：

$('#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();
});

您需要使用不同的变量名称，或者将您的类重命名为大写第一个字母（这是非常标准的）