javascript - 类型错误 : Cannot read property . ... 未定义

Question

在过去的一个小时里我一直在努力寻找。当我将其放入 IDE 中时，智能感知不会出现任何错误，因此我认为没有任何拼写错误，但是当我在 chrome 或 Node 中运行 js 文件时，我收到以下错误:

"TypeError: Cannot read property displayQuestion of undefined"

下面是我的代码，我想做的就是让它选择一个随机问题，提示用户要求输入，然后在控制台中询问问题。然后它将输入与正确答案进行比较。

(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);
})();