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Opacity reduction script does not working

I have a problem with a script that until recently worked, but now seems not to want to work.
I want to reduce the opacity of the green spheres when scrolling down, it seems to be working until recently, but now I can't figure out what the problem is.
The website is this: https://attiliosantomo.com/PROVA/
The script is this:
$(document).ready(function() {
$(window).scroll(function(event) {
let scroll = $(this).scrollTop();
let opacity = 1 - (scroll / 1300);
if (opacity > 0.2) {
$('.bg-bubble').css('opacity', opacity);
}
});
});
</script>
Thank you so much for you help

The issue is that it's not the window that is scrolling. It's the .main-desktop element that is being scrolled. Targeting the scroll event of the .main-desktop as per below should solve the issue.
$(document).ready(function() {
// \/ Changed \/ selector from window to '.main-desktop'
$('.main-desktop').scroll(function(event) {
let scroll = $(this).scrollTop();
let opacity = 1 - (scroll / 1300);
if (opacity > 0.2) {
$('.bg-bubble').css('opacity', opacity);
}
});
});
html,
body {
height: 100%;
margin: 0;
}
.main-desktop {
overflow: scroll;
height: 100%;
}
.inner {
height: 3000px;
}
.bg-bubble {
height: 100px;
width: 100px;
background-color: blue;
position: absolute;
top: 0;
left: 0;
border-radius: 50%;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="bg-bubble"></div>
<div class="main-desktop">
<div class="inner"></div>
</div>

Is there any way to change a div size on scroll using intersectionObserver?

I'm trying to change the size (or scale) of a div while scrolling.
This div has a .8 scale attached to it css. I'd like to reach a scale of 1 progressively while scrolling.
IntersectionObserver seems to be a good choice to work with instead of scroll event but i don't know if i can change the state of an element using it.

You can change the scale of a div using.
document.getElementById("scaledDiv").style.transform = "scale(1)";
The scroll event should do what you want it to do. You can continue to add more if statements and check how many pixels they are scrolling to change it gradually to 1 or even back to 0.8 when they scroll back up. The 50 below represents 50 pixels from the top of the page.
window.onscroll = function() {
if (document.body.scrollTop > 50 || document.documentElement.scrollTop > 50) {
// They are scrolling past a certain position
document.getElementById("scaledDiv").style.transform = "scale(1)";
} else {
// They are scrolling back
}
};

I hope this will help you:
const container = document.querySelector('.container');
const containerHeight = container.scrollHeight;
const iWillExpand = document.querySelector('.iWillExpand');
container.onscroll = function(e) {
iWillExpand.style.transform = `scale(${0.8 + 0.2 * container.scrollTop / (containerHeight - 300)})`;
};
.container {
height: 300px;
width: 100%;
overflow-y: scroll;
}
.scrollMe {
height: 1500px;
width: 100%;
}
.iWillExpand {
position: fixed;
width: 200px;
height: 200px;
top: 10px;
left: 10px;
background-color: aqua;
transform: scale(0.8);
}
<div class='container'>
<div class='scrollMe' />
<div class='iWillExpand' />
</div>

Javascript mousemove function to show element not working as expected

I am trying to to get a mousemove function to display a custom cursor element i created when the mouse is moved inside the specific div. The custom cursor is an absolute positioned div within the div i want it to appear in. The wierd thing i am seeing is i can see from the developer tools that it is infact working but the custom cursor doesnt actually show. If i however move the custom cursor div outside of the div i want it in and into the main body it displays fine.
I know this must be a simple error on my part but i cant see it! Appreciate any advice.
let customCursor = document.querySelector('.custom-cursor');
const section2 = document.querySelector('.section2');
section2.addEventListener('mousemove', function(e) {
customCursor.classList.add('active');
customCursor.setAttribute("style", "top:" + (e.pageY) + "px; left: " + e.pageX + "px;");
});
section2.addEventListener('mouseleave', function() {
customCursor.classList.remove('active');
});
.section {
position: relative;
}
.section1 {
height: 500px;
}
.section2 {
height: 500px;
}
.custom-cursor {
width: 50px;
height: 50px;
background: black;
border-radius: 50%;
display: none;
position: absolute;
}
.custom-cursor.active {
display: block;
}
<body>
<section class="section1 section">Section 1</section>
<section class="section2 section">Section 2
<div class="custom-cursor"></div>
</section>
</body>

Like #Titus comment, you can use CSS with cursor.
But if you implemeting it with JS that need to track position of your mouse relative to section2, you will need to subtract the section2 element offset left and top, then subtract half of the cursor width and height to center the cursor:
let customCursor = document.querySelector('.custom-cursor');
const section2 = document.querySelector('.section2');
section2.addEventListener('mousemove', function(e) {
customCursor.classList.add('active');
customCursor.setAttribute("style", "top:" + (e.pageY - section2.offsetTop - (customCursor.offsetWidth/2) ) + "px; left: " + (e.pageX - section2.offsetLeft - (customCursor.offsetHeight/2)) + "px;");
});
section2.addEventListener('mouseleave', function() {
customCursor.classList.remove('active');
});
.section {
position: relative;
}
.section1 {
height: 500px;
}
.section2 {
height: 500px;
}
.custom-cursor {
width: 50px;
height: 50px;
background: black;
border-radius: 50%;
display: none;
position: absolute;
}
.custom-cursor.active {
display: block;
}
<body>
<section class="section1 section">Section 1</section>
<section class="section2 section">Section 2
<div class="custom-cursor"></div>
</section>
</body>

position: absolute
is relative to the parent if the parent has
position:relative
so in order to have the correct position within your section2, you need to use e.layerY and e.layerX instead of e.pageY and e.pageX since those are based on the top left corner of your screen. e.layerY and e.layerX is relative to the container that the mouseevent is attached to.
Try this: https://jsfiddle.net/42kq1w8m/9/

Absolute position after zooming

I have divs with class="myDiv". I need to do this logic: on mouse over, I want to show a popup in the middle of the div.
For that I have the following:
$(".myDiv").mouseover(function () {
positionDiv($(this).position().left + $(this).width() / 2, $(this).position().top + $(this).height() / 2);
});
function positionDiv(xPosition ,yPosition ) {
$("#popupWindow").css("left", xPosition + "px");
$("#popupWindow").css("top", yPosition + "px");
$("#popupWindow").show();
}
The CSS:
.popupWindow{
position:absolute;
width:313px;
height:383px;
display:none;
}
This will position the popup window in the middle of the div on mouse over. Everything works great at this point.
However, if the website is zoomed in (using the browser zoom functionality), tHe position will get messed up. The popup window no longer appears in the middle of myDiv.
Any idea what might be the problem?
Edit:
For more info, if it is created and I zoom it, it is fine. But when I move my mouse to another myDiv and the new popup appears in a weird position. The left and top attribute of the Div are messing up.

You don't need JS for this:
http://jsfiddle.net/coma/6VUpS/1/
The key is to play with CSS and avoid JS calculations. The container div (myDiv) should be position: relative, the popup must be inside and position: absolute, top and left to 50% and using negative margins to center it (http://www.css-101.org/negative-margin/06.php).
Try avoiding JS for visual fanciness, only CSS ensures the correct position even on zoom since it's rendered by the browser.
HTML
<div class="myDiv">
Hi!
<div class="popupWindow">you are welcome!</div>
</div>
CSS
div.myDiv {
padding: 10px;
background-color: #eee;
margin: 50px 0;
position: relative;
}
div.popupWindow {
position: absolute;
top: 50%;
left: 50%;
margin: -50px 0 0 -100px;
width: 200px;
line-height: 100px;
background-color: #111;
color: #fff;
text-align: center;
display: none;
pointer-events: none;
}
div.myDiv:hover > div.popupWindow {
display: block;
}
Bonus track using a checkbox to click/tap/toggle popup and some fade in:
http://jsfiddle.net/coma/6VUpS/3/
More hacky:
http://jsfiddle.net/coma/6VUpS/
More complex example:
http://jsfiddle.net/coma/dHTHG/

I understand your problem and my solution is to put every object containing a pop up in pos relative and then set your pop up with those CSS :
.myPopUp{
position:absolute;
display : none;
width:400px;
height : 100px;
margin-top : -50px;
margin-left:-200px;
background-color: red;
top : 50%;
left: 50%;
}
It will alway be centered.
Now i understand you have only 1 pop up for all your hoverable div. My trick is to save the pop up in a var and remove it from its parent container to append it in the hovered div like this :
var popUp = $('.myPopUp');
$('.myDiv').mouseover(appendPopUp);
$('.myDiv').mouseout(function(){popUp.css('display', 'none')});
function appendPopUp(){
console.log(popUp.parent(), $(this))
if(popUp.parent()[0] != $(this)[0]){
popUp.remove();
$(this).append(popUp);
}
popUp.css('display', 'block')
}
That should work, here's my fiddle : http://jsfiddle.net/7EEZT/

$(window).on('resize', function(){
var $md = $('.myDiv');
positionDiv($md.position().left + $md.width() / 2, $md.position().top + $(this).height() / 2);
});

I have a simple css solution if you have a div with known height and width you can do same task with help of css only
.popupWindow {
position:absolute;
width:313px;
height:383px;
left:50%;
top:50%;
margin-left:-156px;/*half of width*/
margin-top:-191px;/*half of height*/
display:none;
}

Go with position:relative and try this. It will solved your problem relate to position.
$(".myDiv").mouseover(function () {
positionDiv( $(this).width() / 2, $(this).height() / 2);
});
function positionDiv(xPosition ,yPosition ) {
$("#popupWindow").css("left","-" + xPosition + "px");
$("#popupWindow").css("top", "-" + yPosition + "px");
$("#popupWindow").show();
}
The CSS:
.popupWindow{
position:relative;
width:313px;
height:383px;
display:none;
}
http://jsfiddle.net/kishan6446/PdNkg/13/

Move Box/Div up or down when scrolling

When I scroll up or down, I want a box/div to move up or down too.
For example:
See categories box

in your css write
#my-box {
position: fixed;
}
it will probably move it from the center so you will have to do some math if it is a fixed width and height box like
#my-box-fixed {
position: fixed;
width:200px;
height: 150px;
top: 50%;
left: 50%;
margin-left: -100px; // half of the width
margin-top: -75px; // half of the height
}

This is all you need: http://blog.yjl.im/2010/01/stick-div-at-top-after-scrolling.html

Also, in javascript you can do:
document.getElementById("my-box-fixed").style.position = "fixed";

you can do it whit jquery:
$().ready(function () {
var $scrollingDiv = $("#YouDivID");
$(window).scroll(function () {
$scrollingDiv
.stop()
.animate({ "marginTop": ($(window).scrollTop() + 5) + "px" }, "1000");
});
});