如何防止幻灯片循环回到开头？

Question

我目前正在尝试根据 W3Schools.com 上提供的示例代码在 JavaScript 中制作幻灯片。但是，对于此示例幻灯片，当在最后一页上按下下一个按钮时，它会返回到第一页。同样，当在第一页上按下上一个按钮时，它会转到最后一页。我想让幻灯片放映不在任一方向循环播放，因此上一个按钮不起作用或在第一页上不存在，下一个按钮不起作用或在第一页上不存在。我该怎么做？

（代码只是 W3Schools.com 提供的示例代码，因为这是我正在处理的。）

<body>

<div class="slideshow-container">

<div class="mySlides fade">
  <div class="numbertext">1 / 3</div>
  <img src="img_nature_wide.jpg" style="width:100%">
  <div class="text">Caption Text</div>
</div>

<div class="mySlides fade">
  <div class="numbertext">2 / 3</div>
  <img src="img_fjords_wide.jpg" style="width:100%">
  <div class="text">Caption Two</div>
</div>

<div class="mySlides fade">
  <div class="numbertext">3 / 3</div>
  <img src="img_mountains_wide.jpg" style="width:100%">
  <div class="text">Caption Three</div>
</div>

<a class="prev" onclick="plusSlides(-1)">&#10094;</a>
<a class="next" onclick="plusSlides(1)">&#10095;</a>

</div>
<br>

<div style="text-align:center">
  <span class="dot" onclick="currentSlide(1)"></span> 
  <span class="dot" onclick="currentSlide(2)"></span> 
  <span class="dot" onclick="currentSlide(3)"></span> 
</div>

<script>
var slideIndex = 1;
showSlides(slideIndex);

function plusSlides(n) {
  showSlides(slideIndex += n);
}

function currentSlide(n) {
  showSlides(slideIndex = n);
}

function showSlides(n) {
  var i;
  var slides = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("dot");
  if (n > slides.length) {slideIndex = 1}    
  if (n < 1) {slideIndex = slides.length}
  for (i = 0; i < slides.length; i++) {
      slides[i].style.display = "none";  
  }
  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";
}
</script>

</body>

Answer 1

如果 n < 1 或 > 则删除重置代码并离开幻灯片

//  if (n > slides.length) {slideIndex = 1} // code to check end    
//  if (n < 1) {slideIndex = slides.length} // code to check beginning

if (n>slides.length || n<1) return; // my addition to not execute if either

var slideIndex = 1;
showSlides(slideIndex);

function plusSlides(n) {
  showSlides(slideIndex += n);
}

function currentSlide(n) {
  showSlides(slideIndex = n);
}

function showSlides(n) {
  var i, slides = document.getElementsByClassName("mySlides");

  if (n > slides.length || n < 1) return;
  var dots = document.getElementsByClassName("dot");
  //  if (n > slides.length) {slideIndex = 1}    
  //  if (n < 1) {slideIndex = slides.length}
  for (i = 0; i < slides.length; i++) {
    slides[i].style.display = "none";
  }
  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";
}

<body>

  <div class="slideshow-container">

    <div class="mySlides fade">
      <div class="numbertext">1 / 3</div>
      <img src="img_nature_wide.jpg" style="width:100%">
      <div class="text">Caption Text</div>
    </div>

    <div class="mySlides fade">
      <div class="numbertext">2 / 3</div>
      <img src="img_fjords_wide.jpg" style="width:100%">
      <div class="text">Caption Two</div>
    </div>

    <div class="mySlides fade">
      <div class="numbertext">3 / 3</div>
      <img src="img_mountains_wide.jpg" style="width:100%">
      <div class="text">Caption Three</div>
    </div>

    <a class="prev" onclick="plusSlides(-1)">&#10094;</a>
    <a class="next" onclick="plusSlides(1)">&#10095;</a>

  </div>
  <br>

  <div style="text-align:center">
    <span class="dot" onclick="currentSlide(1)"></span>
    <span class="dot" onclick="currentSlide(2)"></span>
    <span class="dot" onclick="currentSlide(3)"></span>
  </div>

如何防止幻灯片循环回到开头？

How do I keep a slideshow from looping back to the beginning?

html

javascript

slideshow