需要帮助循环一些报价

我正在尝试循环一些引号，以便它们一遍又一遍地展示，但我遇到了麻烦，我已经在Google和这里查看了其他一些帖子，但不能弄清楚如何更改帖子上的代码以与我的代码一起使用。我已经使用了一个名为Edit Fiddle -jsfiddle的网站来测试代码，目前它只是在上一个报价中停止。任何帮助将不胜感激。

var slideIndex = 0;
showSlides();
function showSlides() {
  var i;
  var slides = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("dot");
  for (i = 0; i < slides.length; i++) {
    slides[i].style.display = "none";
  }
  slideIndex++;
  if (slideIndex > slides.length) {
    slideIndex = 1
  }
  for (i = 0; i < dots.length; i++) {
    dots[i].className = dots[i].className.replace(" active", "");
  }
  slides[slideIndex - 1].style.display = "block";
  dots[slideIndex - 1].className += " active";
  setTimeout(showSlides, 8000); // Change image every 10 seconds
}

* {
  box-sizing: border-box
}
body {
  font-family: Verdana, sans-serif;
  margin: 0
}
/* Slideshow container */
.slideshow-container {
  position: relative;
}
/* Slides */
.mySlides {
  display: none;
  padding: 80px;
  text-align: center;
}
/* Add an italic font style to all quotes */
q {
  font-style: italic;
}
/* Add a blue color to the author */
.author {
  color: cornflowerblue;
}

<!DOCTYPE html>
<html>
<head>
  <meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
  <div class="slideshow-container">
    <div class="mySlides">
      <q>I HATE EVERY MINUTE OF TRAINING. BUT I SAID, DON’T QUIT. SUFFER NOW 
    AND LIVE THE REST OF YOUR LIFE AS A CHAMPION.</q>
      <p class="author">- MOHAMMAD ALI</p>
    </div>
    <div class="mySlides">
      <q>YOU’RE THE ONLY ONE WHO CAN MAKE THE DIFFERENCE. WHATEVER YOUR DREAM 
    IS, GO FOR IT. </q>
      <p class="author">– MAGIC JOHNSON.</p>
    </div>
    <div class="mySlides">
      <q>IF YOU TURN UP WORRYING ABOUT HOW YOU’RE GOING TO PERFORM, YOU’VE 
    ALREADY LOST. TRAIN HARD, TURN UP, RUN YOUR BEST AND THE REST WILL TAKE 
    CARE OF ITSELF. </q>
      <p class="author">– USAIN BOLT.</p>
    </div>
    <div class="mySlides">
      <q>I have not failed. I've just found 10,000 ways that won't work.</q>
      <p class="author">- Thomas A. Edison</p>
    </div>
    <div style="text-align:center">
      <span class="dot"></span>
      <span class="dot"></span>
      <span class="dot"></span>
    </div>
</body>
</html>

它没有循环，因为脚本中的错误是崩溃的：

slideIndex++;
if (slideIndex > slides.length) {slideIndex = 1}

这将超过数组内部的元素数量。

您可以通过在增量之前对其进行检查：

  if (slideIndex+1 > slides.length) {
    slideIndex = 1;
  }else
  {
    slideIndex++;
  }

附加的您缺少跨度元素类=" dot"，以匹配引号。

var slideIndex = 0;
showSlides();
function showSlides() {
  var i;
  var slides = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("dot");
  for (i = 0; i < slides.length; i++) {
    slides[i].style.display = "none";
  }
  if (slideIndex+1 > slides.length) {
    slideIndex = 1;
  }else
  {
    slideIndex++;
  }
  for (i = 0; i < dots.length; i++) {
    dots[i].className = dots[i].className.replace(" active", "");
  }
  slides[slideIndex - 1].style.display = "block";
  dots[slideIndex - 1].className += " active";
  setTimeout(showSlides, 2000); // Change image every 10 seconds
}

* {
  box-sizing: border-box
}
body {
  font-family: Verdana, sans-serif;
  margin: 0
}
/* Slideshow container */
.slideshow-container {
  position: relative;
}
/* Slides */
.mySlides {
  display: none;
  padding: 80px;
  text-align: center;
}
/* Add an italic font style to all quotes */
q {
  font-style: italic;
}
/* Add a blue color to the author */
.author {
  color: cornflowerblue;
}

<div class="slideshow-container">
  <div class="mySlides">
    <q>I HATE EVERY MINUTE OF TRAINING. BUT I SAID, DON’T QUIT. SUFFER NOW 
AND LIVE THE REST OF YOUR LIFE AS A CHAMPION.</q>
    <p class="author">- MOHAMMAD ALI</p>
  </div>
  <div class="mySlides">
    <q>YOU’RE THE ONLY ONE WHO CAN MAKE THE DIFFERENCE. WHATEVER YOUR DREAM 
IS, GO FOR IT. </q>
    <p class="author">– MAGIC JOHNSON.</p>
  </div>
  <div class="mySlides">
    <q>IF YOU TURN UP WORRYING ABOUT HOW YOU’RE GOING TO PERFORM, YOU’VE 
ALREADY LOST. TRAIN HARD, TURN UP, RUN YOUR BEST AND THE REST WILL TAKE 
CARE OF ITSELF. </q>
    <p class="author">– USAIN BOLT.</p>
  </div>
  <div class="mySlides">
    <q>I have not failed. I've just found 10,000 ways that won't work.</q>
    <p class="author">- Thomas A. Edison</p>
  </div>
  <div style="text-align:center">
    <span class="dot"></span>
    <span class="dot"></span>
    <span class="dot"></span>
    <span class="dot"></span>
  </div>

您可以在showSlides()函数if (slideIndex > slides.length) {slideIndex = 1}中将此条件更改为：

if (slideIndex > slides.length - 1) {
  slideIndex = 1;
}

将幻灯片索引重置为1，以便幻灯片可以继续更改。

您有4个幻灯片，但只有3个"点"。当第四幻灯片显示时，它试图显示不存在的第四点。

var slideIndex = 0;
showSlides();
function showSlides() {
  var i;
  var slides = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("dot");
  // Hide all slides
  for (i = 0; i < slides.length; i++) {
    slides[i].style.display = "none";
  }
  // Hide all dots
  for (i = 0; i < dots.length; i++) {
    dots[i].className = dots[i].className.replace(" active", "");
  }
  // Show current slide
  slides[slideIndex].style.display = "block";
  dots[slideIndex].className += " active";
  // Increase slide index
  slideIndex++;
  if (slideIndex == slides.length) {
    slideIndex = 0;
  }
  // Wait, then show next slide
  setTimeout(showSlides, 1000);
}

* {
  box-sizing: border-box
}
body {
  font-family: Verdana, sans-serif;
  margin: 0
}
/* Slideshow container */
.slideshow-container {
  position: relative;
}
/* Slides */
.mySlides {
  display: none;
  padding: 80px;
  text-align: center;
}
/* Add an italic font style to all quotes */
q {
  font-style: italic;
}
/* Add a blue color to the author */
.author {
  color: cornflowerblue;
}

<div class="slideshow-container">
  <div class="mySlides">
    <q>I HATE EVERY MINUTE OF TRAINING. BUT I SAID, DON’T QUIT. SUFFER NOW AND LIVE THE REST OF YOUR LIFE AS A CHAMPION.</q>
    <p class="author">- MOHAMMAD ALI</p>
  </div>
  <div class="mySlides">
    <q>YOU’RE THE ONLY ONE WHO CAN MAKE THE DIFFERENCE. WHATEVER YOUR DREAM IS, GO FOR IT. </q>
    <p class="author">– MAGIC JOHNSON.</p>
  </div>
  <div class="mySlides">
    <q>IF YOU TURN UP WORRYING ABOUT HOW YOU’RE GOING TO PERFORM, YOU’VE ALREADY LOST. TRAIN HARD, TURN UP, RUN YOUR BEST AND THE REST WILL TAKE CARE OF ITSELF. </q>
    <p class="author">– USAIN BOLT.</p>
  </div>
  <div class="mySlides">
    <q>I have not failed. I've just found 10,000 ways that won't work.</q>
    <p class="author">- Thomas A. Edison</p>
  </div>
  <div style="text-align:center">
    <span class="dot"></span>
    <span class="dot"></span>
    <span class="dot"></span>
    <span class="dot"></span>
  </div>

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