Uncaught TypeError: Cannot read property 'quest' of undefined

问题

I know that this question may have been asked before but I believe that this awesome community can forgive me for this :) I am developing (Quiz time) app but there's a bug that's is killing me :( When I run this application every and press the lock button it acts as wanted but after a random number of clicks (may be 4 or 2) It stops and gives me this error :

         Uncaught TypeError: Cannot read property 'quest' of undefined
at QuestionReset 

Here's the code

        $(document).ready(function () {
var overwallScore = 0;
//prototype
function Question(quest, option1, option2, option3, correct) {
    this.quest = quest;
    this.option1 = option1;
    this.option2 = option2;
    this.option3 = option3;
    this.correct = correct;

}
//creating questions
var question1 = new Question("1 + 1", 2, 3, 3, 1);
var question2 = new Question("2 + 2", 4, 3, 3, 2);
var question3 = new Question("3 + 3", 6, 3, 3, 3);
var question4 = new Question("4 + 4", 8, 3, 3, 1);
var question5 = new Question("5 + 5", 10, 3, 3, 2);
var question6 = new Question("6 + 6", 12, 3, 3, 3);
//the questions array
var questions = [];
//pushing questions to array
questions.push(question1);
questions.push(question2);
questions.push(question3);
questions.push(question4);
questions.push(question5);
questions.push(question6);
var randomQuestionIndex = Math.floor(Math.random() * 6 + 1);

function QuestionPre() {
    randomQuestionIndex = Math.floor(Math.random() * 6 + 1);
    document.querySelector("#question").innerHTML = questions[randomQuestionIndex].quest;
    document.querySelector(".option-1").innerHTML = questions[randomQuestionIndex].option1;
    document.querySelector(".option-2").innerHTML = questions[randomQuestionIndex].option2;
    document.querySelector(".option-3").innerHTML = questions[randomQuestionIndex].option3;

}
QuestionPre();

function QuestionReset() {
    randomQuestionIndex = Math.floor(Math.random() * 6 + 1);
    document.querySelector("#question").innerHTML = questions[randomQuestionIndex].quest;
    document.querySelector(".option-1").innerHTML = questions[randomQuestionIndex].option1;
    document.querySelector(".option-2").innerHTML = questions[randomQuestionIndex].option2;
    document.querySelector(".option-3").innerHTML = questions[randomQuestionIndex].option3;
}
document.querySelector(".lock-btn").addEventListener("click", function () {
    if (document.querySelector(".option-" + questions[randomQuestionIndex].correct + "-check").checked === true) {
        alert("Correct, such a Genius !");
        overwallScore = overwallScore + 1;
        QuestionReset();
    } else {
        alert("Wrong mate, such a bad luck !");
        randomQuestionIndex = Math.floor(Math.random() * 6 + 1);
        QuestionReset();


    }
}); });

Thanks in advance.

回答1:

The problem lies in the line

var randomQuestionIndex = Math.floor(Math.random() * 6 + 1);

The value of randomQuestionIndex might go out of range. Just remove the +1 part and it should work.

来源：https://stackoverflow.com/questions/46529698/uncaught-typeerror-cannot-read-property-quest-of-undefined