onclick工作，但addEventListener不？

Question

好的，我正在创建一个我在另一个网站上看到的练习项目

我习惯于addEventListeners作为默认事件处理函数，但是，在下面的代码中;我创建的测验应用程序会解决问题，但即使答案是正确的，也不要更新分数。我保持调试和控制台日志记录将近2个小时，直到我发现“非常奇怪”的问题只是我将addEventListener处理程序添加到用户单击以选择答案而不是{{1函数..我想知道究竟是什么问题......

请打开代码面板查看代码。

问题恰好在代码中onclick。

更令我困惑的是，当我在on line 73方法中移动if语句中的this.currentQuestionIndex++ on line 17时，它与Quiz.prototype.checkAnswer一起工作正常。

需要你的帮助才能理解这背后的奥秘。

addEventListener

//Creating the Quiz object
function Quiz(questions) {
  this.questions = questions;
  this.score = 0;
  this.currentQuestionIndex = 0;
}

Quiz.prototype.grabQuestion = function() {
  return this.questions[this.currentQuestionIndex];
}

Quiz.prototype.checkAnswer = function(answer) {
  if(this.grabQuestion().isCorrectAnswer(answer)) {
    this.score++;
    console.log(this.score);
  }
  this.currentQuestionIndex++;
}

Quiz.prototype.hasEnded = function() {
  return this.currentQuestionIndex >= this.questions.length;
}

//creating the Question object.
function Question(title,choices,answer) {
  this.title = title;
  this.choices = choices;
  this.answer = answer;
}

Question.prototype.isCorrectAnswer = function(choice) {
  return this.answer === choice;
}

//Creating the Quiz Interface(Rendering into HTML)

var quizInterface = {
  displayNext: function() {
    if(quiz.hasEnded()) {
      this.displayScore();
    }
    else {
    this.displayQuestion();
    this.displayChoices();
    this.displayProgress();
    }
  },

  displayScore: function() {
    var scoreDisplay = 'your score is ' + quiz.score;
    this.populateIdWithHTML("quiz",scoreDisplay)
  },
  displayQuestion: function() {
    this.populateIdWithHTML("question",quiz.grabQuestion().title);
  },

  displayChoices: function() {
    var choices = quiz.grabQuestion().choices;
    for (var i = 0; i < choices.length; i++) {
      this.populateIdWithHTML("choice" + i, choices[i]);
      this.checkingHandler("guess" + i, choices[i]);
    }
  },

  displayProgress: function() {
    var currentQuestionNum = quiz.currentQuestionIndex + 1;
    this.populateIdWithHTML("progress","Question " + currentQuestionNum + " of " + quiz.questions.length)
  },

  checkingHandler: function(id,checking) {
    var btn = document.getElementById(id);

    /* The addEventListener function throws an error for some reason */

      btn.addEventListener('click',function(e){
      e.preventDefault();
      quiz.checkAnswer(checking);
      quizInterface.displayNext();
      },false)

    //The onclick function works though normally though...
    /*  btn.onclick = function() {
        quiz.checkAnswer(checking);
        quizInterface.displayNext();
      }
     */
  },

  populateIdWithHTML: function(id,theHTML) {
    var elem = document.getElementById(id);
    elem.innerHTML = theHTML;
  }
}

var questionOne = new Question('What is the whole area of Egypt?',['1MKM','2MKM'],'1MKM');
var questionTwo = new Question('What is the currency of Egypt?',['EGP','USD'],'EGP');
var questionThree = new Question('What is the capital of Egypt?',['cairo','baghdad'],'cairo');
var questionFour = new Question('What is the latest Battlefield game?',['BF4','BF1'],'BF1');
var questionFive = new Question('What is the OS of Mac laptops?',['Mac IOS','Mac OS'],'Mac OS');

var questions = [questionOne,questionTwo,questionThree,questionFour,questionFive];

var quiz = new Quiz(questions);
quizInterface.displayNext();

.grid:after {
  content: "";
  display: table;
  clear: both; }

.srt, .form__label--hidden {
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[class^="progbar__"]:after, .icn--nav-toggle:before {
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canvas,
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audio:not([controls]) {
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[hidden],
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a {
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a:active,
a:hover {
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strong {
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dfn {
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mark {
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sup {
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sup {
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sub {
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img {
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svg:not(:root) {
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figure {
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hr {
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pre {
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kbd,
pre,
samp {
  font-family: monospace, monospace;
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button,
input,
optgroup,
select,
textarea {
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  margin: 0; }

button {
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button,
select {
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button,
html input[type="button"],
input[type="reset"],
input[type="submit"] {
  -webkit-appearance: button;
  cursor: pointer; }

button[disabled],
html input[disabled] {
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button::-moz-focus-inner,
input::-moz-focus-inner {
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input {
  line-height: normal; }

*
input[type="checkbox"],
input[type="radio"] {
  box-sizing: border-box;
  padding: 0; }

input[type="number"]::-webkit-inner-spin-button,
input[type="number"]::-webkit-outer-spin-button {
  height: auto; }

input[type="search"] {
  -webkit-appearance: textfield;
  -moz-box-sizing: content-box;
  -webkit-box-sizing: content-box;
  box-sizing: content-box; }

input[type="search"]::-webkit-search-cancel-button,
input[type="search"]::-webkit-search-decoration {
  -webkit-appearance: none; }

fieldset {
  border: 1px solid #c0c0c0;
  margin: 0 2px;
  padding: 0.35em 0.625em 0.75em; }

legend {
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textarea {
  overflow: auto; }

optgroup {
  font-weight: bold; }

table {
  border-collapse: collapse;
  border-spacing: 0; }

td,
th {
  padding: 0; }

* {
  -moz-box-sizing: border-box;
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body {
  color: #797e83;
  font-size: 16px;
  font-family: "Lato", "Helvetica Neue", Helvetica, Arial, sans-serif;
  line-height: 1.5; }

h3 {
  font-size: 1.125em; }

h4 {
  margin-top: 1.375em;
  margin-bottom: 2.57143em;
  color: #d6d7d9;
  text-transform: uppercase;
  letter-spacing: 1px;
  font-weight: 400;
  font-size: 0.875em; }
  @media (min-width: 769px) {
    h4 {
      margin-top: 2.625em; } }

a {
  color: #656a6e;
  text-decoration: none;
  font-weight: 400; }

p {
  margin: .8em 0;
  font-weight: 300;
  font-size: 1.125em;
  line-height: 1.5; }

blockquote {
  font-weight: 300;
  font-style: italic;
  font-size: 1.25em; }
  @media (min-width: 769px) {
    blockquote {
      margin: 1.33333em 0;
      padding: 0 0 0 5%;
      border-left: 0.33333em solid #ebecec;
      font-size: 1.5em; } }

ul,
li {
  margin: 0;
  padding: 0;
  list-style-type: none; }

img {
  margin-bottom: 1.5em;
  max-width: 100%;
  height: auto; }

input,
textarea {
  display: block;
  padding: 15px;
  width: 100%;
  outline: 0;
  border: 0; }

input:focus,
textarea:focus {
  transition: 0.3s; }

button {
  outline: 0; }

footer {
  border-top: 1px solid #ebecec;
  margin-top: 1.375em; }
  footer p {
    font-size: 1em;
    margin-top: 1.375em; }

.panel, .panel--centered {
  padding-top: 1.875em; }
  @media (min-width: 769px) {
    .panel, .panel--centered {
      padding-bottom: 1.25em; } }

.panel--padded, .panel--padded--centered {
  padding-top: 2.125em; }
  @media (min-width: 769px) {
    .panel--padded, .panel--padded--centered {
      padding-top: 5em;
      padding-bottom: 2.125em; } }

.grid {
  width: 90%; }
  [class*="grid__col--"] > .grid {
    width: 100%; }
  @media (min-width: 1100px) {
    .grid {
      max-width: 1050px; } }

@media (min-width: 769px) {
  .grid__col--1 {
    width: 6.5%; }
  .grid__col--2 {
    width: 15%; }
  .grid__col--3 {
    width: 23.5%; }
  .grid__col--4 {
    width: 32%; }
  .grid__col--5 {
    width: 40.5%; }
  .grid__col--6 {
    width: 49%; }
  .grid__col--7 {
    width: 57.5%; }
  .grid__col--8 {
    width: 66%; }
  .grid__col--9 {
    width: 74.5%; }
  .grid__col--10 {
    width: 83%; }
  .grid__col--11 {
    width: 91.5%; }
  .grid__col--12 {
    width: 100%; } }

@media (min-width: 1px) and (max-width: 768px) {
  [class^="grid__col--"] {
    margin-top: 0.75em;
    margin-bottom: 0.75em; } }
@media (min-width: 769px) {
  [class^="grid__col--"] {
    float: left;
    min-height: 1px;
    padding-left: 10px;
    padding-right: 10px; }
    [class^="grid__col--"] + [class^="grid__col--"] {
      margin-left: 2%; }
    [class^="grid__col--"]:last-of-type {
      float: right; } }

.theme__poly .grid [class*="grid__col"] {
  font-weight: 100;
  margin-bottom: 1em;
  padding: 1.75%; }

@media (min-width: 769px) {
  .nav__item, .nav__item--current {
    display: inline-block;
    margin: 0 0.625em; } }

.nav__item--current a, .nav__item a {
  font-weight: 300;
  text-align: center;
  font-size: 1.125em;
  display: block;
  padding: 0.4em;
  border-bottom: 1px solid transparent; }
  @media (min-width: 1px) and (max-width: 768px) {
    .nav__item--current a, .nav__item a {
      border-bottom-color: #ebecec;
      padding-top: 0.77778em;
      padding-bottom: 0.77778em; } }

.nav__item--current a, .nav__item a:hover {
  color: #0b0b0b;
  border-color: #52bab3; }

h1, .headline-primary, .headline-primary--grouped {
  color: #525559;
  font-weight: 300;
  font-size: 2.625em;
  line-height: 1.09524;
  margin-top: 0; }

h2, .headline-secondary, .headline-secondary--grouped {
  color: #999da1;
  letter-spacing: 1px;
  font-weight: 300;
  font-size: 1.5em;
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; }

.form__btn, [class^="btn--"] {
  padding: 10px 20px;
  border: 0;
  border-radius: 0.4em;
  color: #fff;
  text-transform: uppercase;
  font-size: 0.875em;
  font-weight: 400;
  transition: opacity 0.3s;
  display: block; }
  .form__btn:hover, [class^="btn--"]:hover {
    opacity: .75; }
  .form__btn:active, [class^="btn--"]:active {
    opacity: initial; }

.menu__link, .menu__link--end {
  display: block;
  padding-top: 1em;
  padding-bottom: 1em;
  color: #fff;
  text-align: center;
  text-shadow: 0 1px rgba(11, 11, 11, 0.2);
  font-size: 1.125em; }

.icn--nav-toggle, .icn--close {
  line-height: 0;
  cursor: pointer; }

.img--wrap {
  border: 1px solid #d6d7d9;
  padding: 0.75em; }
.img--avatar {
  display: block;
  margin-left: auto;
  margin-right: auto;
  border-radius: 50%; }
  @media (min-width: 769px) {
    .img--avatar {
      margin-top: 1.5em; } }
@media (min-width: 769px) {
  .img--hero {
    margin-bottom: 2.625em; } }

.headline-primary {
  margin-bottom: 1.66667em; }
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    margin-bottom: 2.25em; }

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  margin-bottom: 1.11111em;
  border-bottom: 6px solid #d6d7d9;
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  color: black;
  font-weight: 300; }
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    border-color: #52bab3; }
.form__btn {
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.btn--default {
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.btn--error {
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.btn--warning {
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.btn--info {
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[class^="btn--"] {
  margin-bottom: 1.42857em; }
  @media (min-width: 1px) and (max-width: 768px) {
    [class^="btn--"] {
      width: 100%; } }
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    [class^="btn--"] {
      width: auto;
      display: inline-block; }
      [class^="btn--"] + [class^="btn--"] {
        margin-left: 20px; } }

.navbar {
  position: relative; }
  @media (min-width: 769px) {
    .navbar {
      margin-top: 3.375em;
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.nav {
  margin-top: 1.25em;
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.offcanvas {
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  background: #39add1;
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.menu {
  margin-top: 1.25em; }
  .menu__link {
    border-bottom: solid 1px rgba(255, 255, 255, 0.3); }

.progbar {
  height: 4px;
  border-radius: 2px;
  background: #d6d7d9;
  position: relative;
  margin-bottom: 2.875em; }
  .progbar__status--default {
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    .progbar__status--default:after {
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    background-color: #5ece7f; }
    .progbar__status--success:after {
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    .progbar__status--error:after {
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    .progbar__status--warning:after {
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    .progbar__status--info:after {
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[class^="progbar__"] {
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    right: -10px;
    top: -8px; }

.site-logo {
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  background-repeat: no-repeat;
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.icn--nav-toggle {
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  height: 17px;
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  border-bottom: solid 3px #797e83;
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    height: 3px;
    background: #999da1;
    top: 4px; }
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  background-repeat: no-repeat;
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  height: 20px;
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  position: absolute;
  right: 4%;
  top: 4%; }

@media (min-width: 1px) and (max-width: 768px) {
  .is-displayed-mobile {
    display: block; }
    .is-hidden-mobile {
      display: none; } }
@media (min-width: 769px) {
  .is-displayed-mobile {
    display: none; } }

@media (min-width: 1px) and (max-width: 768px) {
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    padding: 0;
    height: 0;
    margin: 0;
    line-height: 0; } }

.theme__poly .grid__col--12 {
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.theme__poly .grid__col--8 {
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.theme__poly .grid__col--7 {
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.theme__poly .grid__col--6 {
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.theme__poly .grid__col--4 {
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.theme__poly .grid__col--5 {
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.theme__poly .grid__col--2 {
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.theme__poly .grid__col--3 {
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