javascript - Multiple slideshows on one page makes the first one not work anymore

Question

First of all I know this question's been asked before the answer wasn't solving my problem so I'd like to ask it again : I used a Slideshow code from "W3school" wich provides a nice animated Jquery slideshow. unfortunately, I need more than one on my page and the second one stops the first one from working. Even before finding this solution here, I tried changing the CSS and HTML names of the objects of the different slideshows, wich successfully sovled part of the problem (the second one was not showing) but as mentioned earlier, stopped the first one from working. The slideshow is here but clicking the arrows won't do anything. I slightly understand what the problem is but can't fix it. Here is how I modified the code for the second one :

var slideIndex = 7;
showSlides(slideIndex);

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

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

function showSlides(n) {
    var i;
    var slides = document.getElementsByClassName("mySlides2");
    var dots = document.getElementsByClassName("dot2");
    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(" active2", "");
    }
    slides[slideIndex-1].style.display = "block";  
    dots[slideIndex-1].className += " active2";
}

As you see I just added '2' for every type of objects in both Jquery and CSS. I guess I have to give different names to commands that multiply but how to do it ?

EDIT:https://jsfiddle.net/mgb7k239/ Here is a an exemple in Jsfiddle but I dont understand why here the first one isnt even a slideshow and the second one doesn't work either :/ It does on my computer however ! And I forgot to say on my computer, clicking arrows on the first slideshow changes pictures on the second one ! I replaced the pictures with random ones found on the internet.

Answer 1

Main problem in their code is that it is made, well... for one slideshow, and when you try to apply it to multiple slideshows, some serious problems arise, as you have experienced. They used global vars (index, n), which is not problem when you have one slideshow, but with more slideshows - hard to handle stuff, and it is hard to get reference to current slideshow div with existing concept.

And, yes, this is plain javascript slideshow, NO jQuery here. I've changed slightly your HTML and CSS (dots div is INSIDE slideshow div, just for easier targetting), also, i've removed inline event handlers, just to make things little easier and cleaner.

This could be solved on many ways, i've choosed this one:

(function() {

  init(); //on page load - show first slide, hidethe rest

  function init() {

    parents = document.getElementsByClassName('slideshow-container');

    for (j = 0; j < parents.length; j++) {
      var slides = parents[j].getElementsByClassName("mySlides");
      var dots = parents[j].getElementsByClassName("dot");
      slides[0].classList.add('active-slide');
      dots[0].classList.add('active');
    }
  }

  dots = document.getElementsByClassName('dot'); //dots functionality

  for (i = 0; i < dots.length; i++) {

    dots[i].onclick = function() {

      slides = this.parentNode.parentNode.getElementsByClassName("mySlides");

      for (j = 0; j < this.parentNode.children.length; j++) {
        this.parentNode.children[j].classList.remove('active');
        slides[j].classList.remove('active-slide');
        if (this.parentNode.children[j] == this) {
          index = j;
        }
      }
      this.classList.add('active');
      slides[index].classList.add('active-slide');

    }
  }
//prev/next functionality
  links = document.querySelectorAll('.slideshow-container a');

  for (i = 0; i < links.length; i++) {
    links[i].onclick = function() {
      current = this.parentNode;

      var slides = current.getElementsByClassName("mySlides");
      var dots = current.getElementsByClassName("dot");
      curr_slide = current.getElementsByClassName('active-slide')[0];
      curr_dot = current.getElementsByClassName('active')[0];
      curr_slide.classList.remove('active-slide');
      curr_dot.classList.remove('active');
      if (this.className == 'next') {

        if (curr_slide.nextElementSibling.classList.contains('mySlides')) {
          curr_slide.nextElementSibling.classList.add('active-slide');
          curr_dot.nextElementSibling.classList.add('active');
        } else {
          slides[0].classList.add('active-slide');
          dots[0].classList.add('active');
        }

      }

      if (this.className == 'prev') {

        if (curr_slide.previousElementSibling) {
          curr_slide.previousElementSibling.classList.add('active-slide');
          curr_dot.previousElementSibling.classList.add('active');
        } else {
          slides[slides.length - 1].classList.add('active-slide');
          dots[slides.length - 1].classList.add('active');
        }

      }

    }

  }
})();

 /* Slideshow container */
 
 
.slideshow-container {
  max-width: 1000px;
  position: relative;
  margin: auto;
}

/* Next & previous buttons */
.prev, .next {
  cursor: pointer;
  position: absolute;
  top: 50%;
  width: auto;
  margin-top: -22px;
  padding: 16px;
  color: white;
  font-weight: bold;
  font-size: 18px;
  transition: 0.6s ease;
  border-radius: 0 3px 3px 0;
}

/* Position the "next button" to the right */
.next {
  right: 0;
  border-radius: 3px 0 0 3px;
}

/* On hover, add a black background color with a little bit see-through */
.prev:hover, .next:hover {
  background-color: rgba(0,0,0,0.8);
}

/* Caption text */
.text {
  color: #f2f2f2;
  font-size: 15px;
  padding: 8px 12px;
  position: absolute;
  bottom:20px;
  width: 100%;
  text-align: center;
}
.mySlides {
  display:none;
}
.active-slide {
  display:block;
}
/* Number text (1/3 etc) */
.numbertext {
  color: #f2f2f2;
  font-size: 12px;
  padding: 8px 12px;
  position: absolute;
  top: 0;
}

/* The dots/bullets/indicators */
.dot {
  cursor:pointer;
  height: 13px;
  width: 13px;
  margin: 0 2px;
  background-color: #bbb;
  border-radius: 50%;
  display: inline-block;
  transition: background-color 0.6s ease;
}

.active, .dot:hover {
  background-color: #717171;
}

/* Fading animation */
.fade {
  -webkit-animation-name: fade;
  -webkit-animation-duration: 1.5s;
  animation-name: fade;
  animation-duration: 1.5s;
}

@-webkit-keyframes fade {
  from {opacity: .4}
  to {opacity: 1}
}

@keyframes fade {
  from {opacity: .4}
  to {opacity: 1}
}

<div class="slideshow-container">
  <div class="mySlides fade">
    <div class="numbertext">1 / 4</div>
    <img src="http://www.w3schools.com/howto/img_mountains_wide.jpg" style="width:100%">
    <div class="text">Caption Text</div>
  </div>

  <div class="mySlides fade">
    <div class="numbertext">2 / 4</div>
    <img src="http://www.w3schools.com/howto/img_fjords_wide.jpg" style="width:100%">
    <div class="text">Caption Two</div>
  </div>

  <div class="mySlides fade">
    <div class="numbertext">3 / 4</div>
    <img src="http://www.w3schools.com/howto/img_nature_wide.jpg" style="width:100%">
    <div class="text">Caption Three</div>
  </div>
  
    <div class="mySlides fade">
    <div class="numbertext">4 / 4</div>
    <img src="http://placehold.it/1000x350" style="width:100%">
    <div class="text">Caption Four</div>
  </div>

  <a class="prev">&#10094;</a>
  <a class="next">&#10095;</a>

<div style="text-align:center">
  <span class="dot"></span>
  <span class="dot" ></span>
  <span class="dot" ></span>
   <span class="dot"></span>
</div>
</div>
<br>








<div class="slideshow-container">
  <div class="mySlides fade">
    <div class="numbertext">1 / 3</div>
    <img src="http://www.w3schools.com/howto/img_mountains_wide.jpg" style="width:100%">
    <div class="text">Caption Text</div>
  </div>

  <div class="mySlides fade">
    <div class="numbertext">2 / 3</div>
    <img src="http://www.w3schools.com/howto/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="http://www.w3schools.com/howto/img_nature_wide.jpg" style="width:100%">
    <div class="text">Caption Three</div>
  </div>

  <a class="prev" >&#10094;</a>
  <a class="next">&#10095;</a>
<div style="text-align:center">
  <span class="dot"></span>
  <span class="dot"></span>
  <span class="dot"></span>
</div>  
</div>


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