TypeError：无法读取未定义的属性…

Question

在过去的一个小时里，我一直在努力寻找线索。 当我将其放在IDE中时，intellisense不会出现任何错误，因此我认为没有任何错别字，但是当我在chrome或node中运行js文件时，会收到以下错误：

“ TypeError：无法读取未定义的属性displayQuestion”

这是下面的代码，我要做的就是让它选择随机问题之一，提示用户进行输入，然后在控制台中询问该问题。 然后，它将输入与之比较的正确答案。

(function() {

function Question(question, answers, correct){
        this.question = question;
        this.answers = answers;
        this.correct = correct;
    }

Question.prototype.displayQuestion = function(){
    console.log(this.question);

    for(i in this.answers){
        console.log(this.answers[i]);
    }
}

Question.prototype.checkAnswer = function(answer){
    if(answer === correct){
        console.log("Great job! Correct.");
    }
    else{
        console.log("Incorrect. Please try again.");
    }

}

let q1 = Question("Will I eat dinner?", ["Yes", "No"], 0);
let q2 = Question("What is my name?", ["John", "James", "Charles"], 2);
let q3 = Question("Will I go to sleep?", ["Yes", "No"], 1);

let questions = [q1, q2, q3]

let n = Math.floor(Math.random() * questions.length);
questions[n].displayQuestion();
var answer = prompt('Please select the correct answer.');
questions[n].checkAnswer(answer);
})();

Answer 1

使用new关键字创建新实例

 (function() { function Question(question, answers, correct){ this.question = question; this.answers = answers; this.correct = correct; } Question.prototype.displayQuestion = function(){ console.log(this.question); for(i in this.answers){ console.log(this.answers[i]); } } Question.prototype.checkAnswer = function(answer){ if(answer === correct){ console.log("Great job! Correct."); } else{ console.log("Incorrect. Please try again."); } } let q1 = new Question("Will I eat dinner?", ["Yes", "No"], 0); let q2 = new Question("What is my name?", ["John", "James", "Charles"], 2); let q3 = Question("Will I go to sleep?", ["Yes", "No"], 1); let questions = [q1, q2, q3] let n = Math.floor(Math.random() * questions.length); questions[n].displayQuestion(); var answer = prompt('Please select the correct answer.'); questions[n].checkAnswer(answer); })(); 

Answer 2

对于function Question ，您正在尝试构造一个类。 您需要在Question调用上调用new ，以返回Question对象。

let q1 = Question("Will I eat dinner?", ["Yes", "No"], 0);
typeof q1 // 'undefined'
let q2 = new Question("What is my name?", ["John", "James", "Charles"], 2);
typeof q2 // 'object'

对于背景，请看一下调用一个函数与对该函数调用new之间的区别： https : //developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new

Answer 3

您错过了构造函数。 尝试添加新

令q1 =新问题（“我要吃晚餐吗？”，[“是”，“否”]，0）；