How to randomize an image within a slidershow gallery with html, css, and javascript?

Question

Currently the image slideshow gallery allows for the browsing of the image by clicking arrow buttons to view previous or the next picture.

Is there a way to make it so that a random image loads everytime the website is visit? Instead of always starting from page 1, the website will start from page 2 or 3 for example.

Here is the HTML, CSS, and javascript.

HTML

        <div class="slideshow-container">
          <!-- Full-width images with number and caption text -->
          <div class="mySlides fade">
            <div class="numbertext">1 / 3</div>
            <img src="images/art/38.jpg" style="width: 75%" />
            <div class="text">1</div>
          </div>

          <div class="mySlides fade">
            <div class="numbertext">2 / 3</div>
            <img src="images/art/43.jpg" style="width: 75%" />
            <div class="text">2</div>
          </div>

          <div class="mySlides fade">
            <div class="numbertext">3 / 3</div>
            <img src="images/art/39.jpg" style="width: 75%" />
            <div class="text">3</div>
          </div>

          <!-- Next and previous buttons -->
          <a class="prev" onclick="plusSlides(-1)">&#10094;</a>
          <a class="next" onclick="plusSlides(1)">&#10095;</a>
        </div>

Javascript

      var slideIndex = 1;
      showSlides(slideIndex);

      // Next/previous controls
      function plusSlides(n) {
        showSlides((slideIndex += n));
      }

      // Thumbnail image controls
      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";
      }

CSS

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

.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;
  user-select: none;
}

.prev {
  left: 0;
  border-radius: 3px 0 0 3px;
}

.next {
  right: 0;
  border-radius: 3px 0 0 3px;
}

Answer 1

You can use

var slideIndex = Math.floor(Math.random() * slides.length) + 1;

This assigns the variable slideIndex to a random integer between 1 and the number of slides. Note that you will have to put

var slides = document.getElementsByClassName("mySlides");

before this in order for it to work.

Or you could just replace slides.length with the number of elements you have, but you will have to update this every time you add or remove an element.