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Why do I keep getting 4 slides when there are only 3 div elements?

I created a slideshow with 3 slides but for some reason, it keeps adding an additional slide
const slideshow = document.getElementById("slideshow");
const slides = slideshow.children;
let currentSlide = 0;
function goToSlide(n) {
slides[currentSlide].classList.remove("active");
currentSlide = (n + slides.length) % slides.length;
slides[currentSlide].classList.add("active");
updateSlideshowCounter();
}
function nextSlide() {
goToSlide(currentSlide + 1);
}
function prevSlide() {
goToSlide(currentSlide - 1);
}
function updateSlideshowCounter() {
const slideshowCounter = document.getElementById("slideshow-counter");
slideshowCounter.textContent = `${currentSlide + 1} / ${slides.length}`;
}
const prevButton = document.getElementById("prev-button");
prevButton.addEventListener("click", prevSlide);
const nextButton = document.getElementById("next-button");
nextButton.addEventListener("click", nextSlide);
updateSlideshowCounter();
#slideshow {
position: relative;
text-align: center;
width: 400px;
height: 300px;
border: 1px black solid;
}
.slide {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
opacity: 0;
transition: opacity 1s;
}
.slide.active {
opacity: 1;
}
#slideshow-controls {
position: absolute;
bottom: 20px;
left: 50%;
transform: translateX(-50%);
display: flex;
align-items: center;
}
#prev-button,
#next-button {
padding: 10px 20px;
border: none;
background-color: #333;
color: #fff;
cursor: pointer;
}
#prev-button {
margin-right: 20px;
}
#next-button {
margin-left: 20px;
}
#slideshow-counter {
margin: 0 20px;
}
<div id="slideshow">
<div class="slide">Slide 1</div>
<div class="slide">Slide 2</div>
<div class="slide">Slide 3</div>
<div id="slideshow-controls">
<button id="prev-button">Prev</button>
<span id="slideshow-counter"></span>
<button id="next-button">Next</button>
</div>
</div>
Can someone tell me what my mistake is and how I can get 3 slides in the output instead of 4.

You're defining your slides with the statement const slides = slideshow.children;. Your slideshow has a total of 4 direct children, so the counter is technically correct (see slide 1, slide 2, slide 3, and slideshow-controls).
One approach to get just the slides you want is to use const slides = document.getElementsByClassName("slide"). I hope this helps!

The problem is your slides variable is not assigned to the correct list of elements, as the previous answer said, you should replace slideshow.children with either document.getElementsByClassName('slide') or document.querySelectorAll('.slide'), use any of the two.
By using slideshow.children, you're not getting .slide classes, you're getting all children of #slideshow.
So, your variable in line 67, should be as the following:
const slides = document.querySelectorAll('.slide');
or
const slides = document.getElementsByClassName('.slide');

You should keep slideshow controls out of your slideshow div. I am attaching Code Below. Run it and check.
const slideshow = document.getElementById("slideshow");
const slides = slideshow.children;
let currentSlide = 0;
function goToSlide(n) {
slides[currentSlide].classList.remove("active");
currentSlide = (n + slides.length) % slides.length;
slides[currentSlide].classList.add("active");
updateSlideshowCounter();
}
function nextSlide() {
goToSlide(currentSlide + 1);
}
function prevSlide() {
goToSlide(currentSlide - 1);
}
function updateSlideshowCounter() {
const slideshowCounter = document.getElementById("slideshow-counter");
slideshowCounter.textContent = `${currentSlide + 1} / ${slides.length}`;
}
const prevButton = document.getElementById("prev-button");
prevButton.addEventListener("click", prevSlide);
const nextButton = document.getElementById("next-button");
nextButton.addEventListener("click", nextSlide);
updateSlideshowCounter();
#slideshowbox {
position: relative;
width: 400px;
height: 300px;
}
#slideshow {
position: relative;
text-align: center;
width: 400px;
height: 300px;
border: 1px black solid;
}
.slide {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
opacity: 0;
transition: opacity 1s;
}
.slide.active {
opacity: 1;
}
#slideshow-controls {
position: absolute;
bottom: 20px;
left: 50%;
transform: translateX(-50%);
display: flex;
align-items: center;
}
#prev-button,
#next-button {
padding: 10px 20px;
border: none;
background-color: #333;
color: #fff;
cursor: pointer;
}
#prev-button {
margin-right: 20px;
}
#next-button {
margin-left: 20px;
}
#slideshow-counter {
margin: 0 20px;
}
<div id="slideshowbox">
<div id="slideshow">
<div class="slide">Slide 1</div>
<div class="slide">Slide 2</div>
<div class="slide">Slide 3</div>
</div>
<div id="slideshow-controls">
<button id="prev-button">Prev</button>
<span id="slideshow-counter"></span>
<button id="next-button">Next</button>
</div>
</div>

Your slideshow div childs is throwing 4 because your 4th div is slideshow-controls. You may want to add -1 to the counter or redifine the way you make your div. Best of luck!

Carousel prev and next button logic does not work

I am trying to a make carousel using pure Javascript. I successfully manage to slide the carousel and have created left and right buttons.
I took my slide functions and added them to the button on-click event-listener, but I have problems when I implement the function on my buttons. It does not behave as expected. My code is below, how can I fix this?
const images = document.getElementById('imgs'); //here
const allImages = document.querySelectorAll('#imgs img');
const leftBtn = document.getElementById('left');
const rightBtn = document.getElementById('right');
let index = 0;
function changeSliderPage() {
const dot = [...document.getElementsByClassName('star')];
index++;
if (index > allImages.length - 1) {
index = 0
}
imgs.style.transform = `translateX(${-index * 500}px)`;
dot.forEach((dot, i) => {
if (i === index) {
dot.classList.add('active')
} else {
dot.classList.remove('active')
}
});
};
allImages.forEach(i => {
const elem = document.createElement('div');
elem.classList.add('star');
document.body.appendChild(elem)
});
rightBtn.onclick = () => {
changeSliderPage(index + 1);
}
leftBtn.onclick = () => {
changeSliderPage(index - 1);
}
let x = setInterval(changeSliderPage, 100000);
images.onmouseover = () => {
clearInterval(x)
}
images.onmouseout = () => {
x = setInterval(changeSliderPage, 2000);
}
*{
box-sizing: border-box;
}
body {
margin: 0;
display: flex;
justify-content: center;
align-items: center;
min-height: 100vh;
}
.carousel {
overflow: hidden;
width: 500px;
height: 500px;
box-shadow: 2px 2px 5px rgba(0, 0, 0, .3);
border-radius: 5px;
}
.image-container {
display: flex;
transition: transform 300ms linear;
transform: translateX(0);
}
img {
width:500px;
height: 500px;
object-fit: cover;
}
.star{
cursor: pointer;
height: 15px;
width: 15px;
margin: 0 10px;
border-radius: 50%;
display: inline-block;
transition: background-color 0.6s ease;
background-color: #eeeeee;
}
.star.active{
background-color: red;
}
button{
cursor: pointer;
position: relative;
font-size: 18px;
transition: 0.6s ease;
user-select: none;
height: 50px;
width: 40px;
display: flex;
justify-content: center;
align-items: center;
align-content: center;
top: calc(50% - 25px);
}
button:hover {
background-color: rgba(0,0,0,0.8);
};
button.left {
border-radius: 3px 0 0 3px;
right: 0;
}
button.left {
border-radius: 3px 0 0 3px;
left: 0;
}
<button id="left">❮</button>
<button id="right">❯</button>
<div class="carousel">
<div class="image-container" id="imgs" >
<img src="https://images.unsplash.com/photo-1599736375341-51b0a848f3c7?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=800&q=60" alt="">
<img src="https://images.unsplash.com/photo-1516026672322-bc52d61a55d5?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=800&q=60" alt="">
<img src="https://images.unsplash.com/photo-1573081586928-127ecc7948b0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=800&q=60" alt="">
<img src="https://images.unsplash.com/flagged/photo-1572850005109-f4ac7529bf9f?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=800&q=60" alt="">
</div>
</div>

Logic that I use with carousels:
for example you have 4 images:
[1][2][3][4]
I have an animation for sliding every image, I add 5th image which is same as image no 1:
[1][2][3][4][1]
Imagine cursor which shows what image is currently displayed, Ill mark cursor as ! !
So at begin:
[!1!][2][3][4][1]
Now the slider moves on...
[1][!2!][3][4][1]
etc...
It moves to last image:
[1][2][3][4][!1!]
And now it has to move under the hood from last image to first image, but without any animation so the whole change is not visible by user:
[!1!][2][3][4][5]
This way you can get inifinite carousel, just need to check in javascript if current image is last one and you want to slide right -> no animation. Same if you are on 1st image and want to slide left.

Position an invisible div element over a photo(onclick)(repl.it)

Visual of element placement
I am trying to make a little “pet the dog game” and I would like to put a div over his head and when you click the DIV it will trigger a JS function to change the photo to a .gif then back again here is my code
JS:
function pet_head(){
var image = getElementById("image");
image.src="DogPet.gif";
setTimeout(function(){
image.src="dog.jpeg";
}, 1000//length of gif
);
};
HTML:
<div class="main">
<img id="image" src="dog.jpeg">
<div class="click></div>
</div>
CSS:
img{
height:100%;
width100%;
position:absolute;
}

If you use absolute in the image it will always be on top of everything else.
Take a look below and see if that is what you looking for.
function pet_head(event) {
/*var image = getElementById("image");
image.src = "DogPet.gif";
setTimeout(function() {
image.src = "dog.jpeg";
}, 1000 //length of gif
);*/
alert('changed');
};
document.getElementById('click').addEventListener('click', pet_head);
img {
height: 100%;
width: 100%;
}
div {
/* This will center the image horizontally */
display: flex;
justify-content: center;
position: absolute;
}
div#click {
color: green;
border: 2px solid red;
top: 14%;
height: 45%;
width: 300px;
position: absolute;
}
<div class="main">
<div id="click"></div>
<img id="image" src="https://i.insider.com/5df126b679d7570ad2044f3e?width=1100&format=jpeg&auto=webp" />
</div>

Here is a working version of your code. Also note that (besides removing code typos) I added object-fit: cover to your img, so that it preserves aspect ratio as the viewport size changes.
function pet_head() {
// var image = document.getElementById("image");
alert("petting the dog");
/* image.src = "DogPet.gif";
setTimeout(function() {
image.src = "dog.jpeg";
}, 1000 //length of gif
); */
};
document.querySelector(".click").addEventListener("click", pet_head);
img {
height: 100%;
width: 100%;
position: absolute;
object-fit: cover;
}
.click {
position: absolute;
left: 49%;
top: 22px;
height: 13vh;
width: 17vw;
cursor: pointer;
}
/* Presentational styles */
.click {
background: yellow;
opacity: .1;
}
html, body {
margin: 0;
}
*, *::before, &::after {
box-sizing: border-box;
}
<div class="main">
<img id="image" src="https://i.stack.imgur.com/FthXz.jpg">
<div class="click"></div>
</div>
jsFiddle

CSS - Absolute and Relative Position with image fader

I'm working with an image fader program, but I'm not understanding absolute positioning. I have the images fading nicely and resizing the way I want if the screen resizes. but I have 2 problems. Div#2 gets covered up by the images. I want div2 to always appear below the image div. Also, I have control buttons on the images. I want them in the middle. I thought using top:50% would do that, but it's not. Here's an example...
var slides = document.querySelectorAll('#slides .slide');
var currentSlide = 0;
var slideInterval = setInterval(nextSlide,5000);
function nextSlide(){goToSlide(currentSlide+1);}
function previousSlide(){goToSlide(currentSlide-1);}
function goToSlide(n){
slides[currentSlide].className = 'slide';
currentSlide = (n+slides.length)%slides.length;
slides[currentSlide].className = 'slide showing';}
var next = document.getElementById('next');
var previous = document.getElementById('previous');
next.onclick = function(){nextSlide();};
previous.onclick = function(){previousSlide();};
#slides {position: relative}
.slide{
position: absolute;
left: 0px;
top: 0px;
width:100%;
height:auto;
min-height:300px;
object-fit:cover;
opacity: 0;
box-sizing:border-box;
transition: opacity 2s;}
.showing{opacity: 1;}
.controls{
background: transparent;
color: #fff;
font-size: 30px;
cursor: pointer;
border: 1px solid #555;
width: 30px;
position: absolute;
}
.controls:hover{ opacity:.5}
.fadenext{right: 10px; top: 50%;}
.fadeprev{left: 10px; top: 50%;}
<br><br>
<div id="slides">
<img src='https://www.panotools.org/dersch/Monp.JPG' class="slide showing">
<img src='https://www.panotools.org/dersch/StBp.JPG' class="slide">
<button class="controls fadeprev" id="previous"><</button>
<button class="controls fadenext" id="next">></button>
</div>
<div style='margin-top:40px;border:1px solid red;width:200px;height:100px'>
This is Div # 2</div>

I've amended your snippet to fix your issues.
Adding margin-top instead of top will fix your issue with the
controls.
Div 2 will now always remain below your slider.
P.S. I moved your div2 inline styles to keep it neat.
var slides = document.querySelectorAll('#slides .slide');
var currentSlide = 0;
var slideInterval = setInterval(nextSlide, 5000);
function nextSlide() {
goToSlide(currentSlide + 1);
}
function previousSlide() {
goToSlide(currentSlide - 1);
}
function goToSlide(n) {
slides[currentSlide].className = 'slide';
currentSlide = (n + slides.length) % slides.length;
slides[currentSlide].className = 'slide showing';
}
var next = document.getElementById('next');
var previous = document.getElementById('previous');
next.onclick = function() {
nextSlide();
};
previous.onclick = function() {
previousSlide();
};
* {
margin: 0;
padding: 0;
}
#slides {
position: relative
}
.slide {
position: absolute;
left: 0px;
top: 0px;
width: 100%;
height: auto;
min-height: 300px;
object-fit: cover;
opacity: 0;
box-sizing: border-box;
transition: opacity 2s;
}
.showing {
opacity: 1;
}
.controls {
background: transparent;
color: #fff;
font-size: 30px;
cursor: pointer;
border: 1px solid #555;
width: 30px;
position: absolute;
}
.controls:hover {
opacity: .5
}
.fadenext {
right: 10px;
margin-top: 25%;
}
.fadeprev {
left: 10px;
margin-top: 25%;
}
.div2 {
margin-top: 50%;
border: 1px solid red;
width: 200px;
height: 100px;
}
<br><br>
<div id="slides">
<img src='https://www.panotools.org/dersch/Monp.JPG' class="slide showing">
<img src='https://www.panotools.org/dersch/StBp.JPG' class="slide">
<button class="controls fadeprev" id="previous"><</button>
<button class="controls fadenext" id="next">></button>
</div>
<div class="div2">This is Div # 2</div>

It's not feasible to use % based positions when you use "top" style. So to achieve what you want to do, use margin-top instead. As shown below:
.fadenext{right: 10px; margin-top: 25%;}
.fadeprev{left: 10px; margin-top: 25%;}
And for your div2, just change it's style to:
margin-top: 50%

How to make a background change its position based on the position on the cursor

I am wanting to make a website that uses a background that moves based on the position that the curser is on the website. I have found this website that gives a visual representation of what I want to do. http://www.alexandrerochet.com/I just need to know how to make the letters move. I will replace them with images later.

You can achieve that using css properties.
Based on Lea Verou's talk
const root = document.documentElement;
document.addEventListener("mousemove", evt => {
let x = evt.clientX / innerWidth;
let y = evt.clientY / innerHeight;
root.style.setProperty("--mouse-x", x);
root.style.setProperty("--mouse-y", y);
});
html {
height: 100%
}
:root {
--mouse-x: .5;
--mouse-y: .5;
}
body {
height: 100%;
background-image: radial-gradient( at calc(var(--mouse-x) * 100%) calc(var(--mouse-y) * 100%), transparent, black);
}

You may want to try using parallax.js to achieve the desired effect.
Demo site.
Quick jsfiddle.
var scene = document.getElementById('scene');
var parallaxInstance = new Parallax(scene);
parallaxInstance.friction(0.2, 0.2);
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
.container {
background-color: #F9F871;
width: 100vw;
height: 100vh;
}
.scene {
top: 30%;
}
.layer {
width: 100%;
height: 200px;
}
.item {
width: 50px;
height: 50px;
border-radius: 200px;
background-color: red;
position: relative;
}
.item-1 {
background-color: #FF9671;
left: 30%;
}
.item-2 {
background-color: #D65DB1;
left: 60%;
}
.item-3 {
background-color: #FF6F91;
left: 40%;
}
.item-4 {
background-color: #FFC75F;
left: 70%;
}
<div class="container">
<div id="scene" class="scene">
<div data-depth="0.2" class="layer layer-1">
<div class="item item-1"></div>
<div class="item item-2"></div>
</div>
<div data-depth="0.6" class="layer layer-2">
<div class="item item-3"></div>
<div class="item item-4"></div>
</div>
</div>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/parallax/3.1.0/parallax.min.js"></script>