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Strange flickering after manipulating html with JS

I am stuck with a problem and I cannot figure out what the cause is, I have created a small js script that modifies a table element, but every time it does I see flickering of the elements, I checked the HTML elements and there is no white space or whatsoever.
Short video: https://i.imgur.com/86RODJL.mp4
Is it possible an css property that causes this behavior ?
Tried to troubleshoot by inspecting the html elements for white space or similar.
JS function:
function correctOrderQtyMinus(element) {
var elementTR = element.parentNode.parentNode.parentNode;
var totalExBTW = document.getElementById('totalExBTW');
var totalBtw = document.getElementById('totalBtw');
var btwAmount = document.getElementById('btwAmount');
if(document.getElementById('checkoutForm')) {
if(element.parentNode.querySelector('#productQty').value > 1) {
var newAmount =+ parseFloat(elementTR.querySelector('#productPriceTotalBtw').innerText) - parseFloat(elementTR.querySelector('#productPriceWithBtw').innerText);
elementTR.querySelector('#productPriceTotalBtw').innerText =+ newAmount.toFixed(2);
totalExBTW.innerText =+ (parseFloat(totalExBTW.innerText)- parseFloat(elementTR.querySelector('#productPriceExBtw').innerText)).toFixed(2);
totalBtw.innerText =+ (parseFloat(totalBtw.innerText) - parseFloat(elementTR.querySelector('#productPriceWithBtw').innerText)).toFixed(2);
btwAmount.innerText = parseFloat(totalBtw.innerText - totalExBTW.innerText).toFixed(2);
totalBtw.innerText = parseFloat(totalBtw.innerText).toFixed(2);
totalExBTW.innerText = parseFloat(totalExBTW.innerText).toFixed(2);
elementTR.querySelector('#productPriceTotalBtw').innerText = parseFloat(elementTR.querySelector('#productPriceTotalBtw').innerText).toFixed(2);
} else {
console.log('Cannot go less than 1');
}
}
event.preventDefault();
}

Fix header after scrolling Angular 4

I am having issue fixing the header after scrolling, I tried a lot of stuff but can't get it to work. I checked this thread but it doesnt work for me: Angular 4 #HostListener Window scroll event strangely does not work in Firefox . This is my component structure:
Layout
Steps
Routes
Inside steps is my header which I want to fix, after scrolling for 50px. Inside Layout is some other content like a div with logo background (above the content of steps).
This is what I tried inside Steps.ts
#HostListener('window:scroll', [])
onWindowScroll() {
const number = window.scrollY;
if (number > 40) {
this.fixed = true;
} else if (this.fixed && number < 10) {
this.fixed = false;
}
}
but the problem is that scroll is not triggering at all. I found examples
where scroll logs the event, but for me it doesn't work (I tried with $event as well). Anyone has a solution?

Found a solution. On my layout component I put a function
(scroll)="onWindowScroll($event)"
and in layout component i used:
#HostListener('window:scroll', ['$event'])
onWindowScroll($event) {
const number = $event.target.scrollTop;
if (number > 40) {
this.fixed = true;
} else if (this.fixed && number < 10) {
this.fixed = false;
}
}
I removed Steps component since I didnt need it anymore, all the content is inside layout now.

In Angular 5+ it works a little differently:
const number = $event.target.scrollingElement.scrollTop || $event.target.documentElement.scrollTop;

Since some people come via Google to this question:
I'm quite a fan of moving logic like this into something re-useable. For Angular this would mean a directive. Therefore as I run into this issue myself I created a library from my code that at least has some tests and support across many browsers. So feel free to use this tested piece of code instead of polluting your components with more code.
https://w11k.github.io/angular-sticky-things/
With the code I see in the answer I did run into some issues. In another SO I found this solution. It is crucial to determine the offsetY of the header element correctly.
// Thanks to https://stanko.github.io/javascript-get-element-offset/
function getPosition(el) {
let top = 0;
let left = 0;
let element = el;
// Loop through the DOM tree
// and add it's parent's offset to get page offset
do {
top += element.offsetTop || 0;
left += element.offsetLeft || 0;
element = element.offsetParent;
} while (element);
return {
y: top,
x: left,
};

Replacing Bootstrap Dropdown with Dropup (Different activity on two near identical implementations)

I'm working on a project over at github pages, which I replace a bootstrap .dropdown with .dropup if the div's overflow-y: scroll will cause the dropdown menu to be cutoff / overflow. You can see the function working properly at this jsfiddle. Notice if you click on the ellipsis icon to the right on the top rows, it will drop down, if you click on the icon on the bottom rows, it will drop up.
Now, my actual implementation (github page), the code is exactly the same (below), but it wants to replace all .dropdown classes with .dropup when opened, including the top-most row which gets cut off, seen in the photo below.
I've been struggling with this for a week and can't quite figure it out. I've tried a few different things that I thought fixed it but ended up just being a hack and didn't work on mobile, or replaced some but not all etc.
Here is the Javascript / jQuery I'm using, which can be seen in the jsfiddle and my github source here.
$(document).on("shown.bs.dropdown", ".dropdown", function () {
// calculate the required sizes, spaces
var $ul = $(this).children(".dropdown-menu");
var $button = $(this).children(".song-menu");
var ulOffset = $ul.offset();
// how much space would be left on the top if the dropdown opened that direction
var spaceUp = (ulOffset.top - $button.height() - $ul.height()) - $('#playlist').scrollTop();
// how much space is left at the bottom
var spaceDown = $('#playlist').scrollTop() + $('#playlist').height() - ((ulOffset.top + 10) + $ul.height());
// switch to dropup only if there is no space at the bottom AND there is space at the top, or there isn't either but it would be still better fit
if (spaceDown < 0 && (spaceUp >= 0 || spaceUp > spaceDown))
$(this).addClass("dropup");
}).on("hidden.bs.dropdown", ".dropdown", function() {
// always reset after close
$(this).removeClass("dropup");
});
Edit:
To clear up any confusion, here's an example of the behavior without my added .dropup function. jsfiddle Notice when you click the last menu item, it opens the menu but requires scrolling. I specifically want to remove the .dropdown class and add .dropup in this case, so no scrolling is required.

It took some basic math, but I managed to figure out what you desired to do. This code changes the bootstrap classes between dropup and dropdown depending on the room available for a normal dropdown.
I calculated this by detracting the height of the button, dropdownmenu and how far the button was scrolled down in the scrollContainer from the height of the scrollContainer. I got the value how much the div was scrolled down by using the buttons offset and detracting the offset from the scrollContainer.
Here is my jQuery (I selected the .playlist class because this was attached to your scrollContainer, but you should replace it by an id or select it by other means):
$(".dropdown, .dropup").click(function(){
var dropdownClassCheck = $(this).hasClass('dropdown');
var buttonOffset = $(this).offset().top;
var scrollboxOffset = $('.playlist').offset().top;
var buttonHeight = $(this).height();
var scrollBoxHeight = $('.playlist').height();
var dropDownButtonHeight = $(this).children('ul').height();
dropdownSpaceCheck = scrollBoxHeight>buttonOffset-scrollboxOffset+buttonHeight+dropDownButtonHeight;
if(dropdownClassCheck && !dropdownSpaceCheck){
$(this).removeClass('dropdown').addClass('dropup');
}
else if(!dropdownClassCheck && dropdownSpaceCheck){
$(this).removeClass('dropup').addClass('dropdown');
}
});
A working JSFiddle
Let me know if there are parts of the code that could be improved/done easier or if there are any problems with my solution.

I have not thoroughly checked, but .scrollTop() is probably why the code fails when combined with other elements in the DOM, so here is a solution without it:
function checkHeights(){
// LOOP through each dropdown
$('.dropdown,.dropup').each(function(index,element){
var $dropDown = $(element),
$dropDownMenu = $dropDown.find('.dropdown-menu'),
dropDownTop = $dropDown.offset().top,
visibleHeight = $dropDown.height(),
hiddenHeight = $dropDownMenu.height(),
ddTop = dropDownTop - hiddenHeight,
ddBottom = dropDownTop + visibleHeight + hiddenHeight;
// LOOP through all parents
$dropDown.parents().each(function(ix,el){
var $el = $(el);
// CHECK if any of them have overflow property set
if( $el.css('overflow') !== 'visible' ){
var limitTop = $el.offset().top,
limitBottom = limitTop + $el.height();
// CHECK if parent is better fit when dropped upside
if( limitBottom < ddBottom && ( ddTop - limitTop ) > ( limitBottom - ddBottom ) )
$dropDown.removeClass('dropdown').addClass('dropup');
else
$dropDown.removeClass('dropup').addClass('dropdown');
// BREAK LOOP
return false;
}
});
});
}
$(document).ready(function() {
checkHeights();
$('.playlist').scroll(checkHeights);
});
JS Fiddle here.
This one does not require any class or id given to it except for dropdown,dropdown-menu, and dropup (all of which are Bootstrap defaults) and would work fine even if there are multiple playlists on page.
UPDATE
The code is modified and wrapped in a function in order to allow being called when scroll event fires.

I think that the problem it's that you have a big header, and the jsFiddle don't. So ulOffset.top it's always big, and spaceDown is always negative

Replace parent div.dropdown with div.dropup.

Adding and removing classes at different heights on page using jQuery

I want to remove/add classes when the user is at different distances from the top by using jQuery.
I have successfully done it, and it works fine, but I think I'm doing it wrong, and I would like your help to optimize the code.
The html is simple, basically the sections(including the header), have 100% width. and different colors. I want to make the header change color when its over the first section(for aesthetical purposes).
And I also want it to have a shadow when the page has been scrolled more than 1 pixel.
I'm doing it by adding/removing classes.
When I use one big else if statement it doesn't work well because whenever any any condition is matched js stops checking for other matches, so it doesn't apply all the classes needed.
The next code works, however as I said, I think that it's not optimal/bad written.
Here is the HTML markup:
<header class="dark no-shadow">
Header
</header>
<section class="blue">
Please Scroll Down to see the header changes...
</section>
<section>
The header color Should change when you pass through me.
</section>
And here is the jQuery code:
var header = $('header'),
blueSection = $('section.blue'),
// Calculate when to change the color.
offset = blueSection.offset().top + blueSection.height() - header.height();
$(window).scroll(function(){
var scroll = $(window).scrollTop();
// Remove Class "dark" after scrolling over the dark section
if (scroll >= offset) {
header.removeClass('dark');
} else {
header.addClass('dark');
}
// Remove Class "no-shadows" whenever not on the top of the page.
if (scroll >= 1) {
header.removeClass('no-shadow');
} else {
header.addClass('no-shadow');
}
});
And for those of you who like to use jsfiddle(like me!):
https://jsfiddle.net/shock/wztdt077/6/
Thanks ahead guys!

Here is what I've come up with:
var header = $('header'),
blueSection = $('section.blue'),
// Calculate when to change the color.
offset = blueSection.offset().top + blueSection.height() - header.height();
var add = function(obj, cls) {obj.addClass(cls);}
var remove = function(obj, cls) {obj.removeClass(cls);}
var stylePoints = [offset, 1, 100, 200];
var styleTo = ['dark', 'no-shadow', 'blue', 'tall'];
var styleType = [add, add, remove, remove];
$(window).scroll(function() {
var scroll = $(window).scrollTop();
for (i = 0; i < stylePoints.length; i++) {
var func = styleType[i];
if (scroll >= stylePoints[i])
(styleType[i] == add) ? remove(header, styleTo[i]) : add(header, styleTo[i]);
else func(header, styleTo[i]);
}
});
It's not that much longer than your current jQuery, and allows for (theoretically) an infinite number of style changes without having to add a million long if/else statements. To add a new style change, you have to add a value to the end of each of the three arrays. stylePoints specifies the scrollTop() value at which a style should either be added or removed. styleTo specifies the class to be added or removed. styleType specifies whether this class should be added or removed when the user is scrolled above the corresponding stylePoints value. The opposite will occur when the user is scrolled below or at the corresponding stylePoints value. For instance, you can see from the code that the tall class will be removed from the header when the user is scrolled above 200, and added when the user is scrolled below or at 200.

JavaScript transition between images on top of others by Z-index

I have 30 images whose file names are the same, but ending with a number in a range of 1 to 30. Each image has a z-index from the same range, placing them on top of each other in the same div. Now, I want the image on top to go to the bottom, while I increment the other images' z-index by 1, consecutively, until the image with the id="image30" reaches a certain position, for the loop to stop. When I execute this code in Firefox I get a pop-up window requesting me to stop the script, but when I check the console for errors there are none.
function placeImage(x) {
var div = document.getElementById("div_picture_right");
div.innerHTML = ""; // clear images
for (counter=1;counter<=x;counter++) {
var image=document.createElement("img");
image.src="borboleta/Borboleta"+counter+".png";
image.width="195";
image.height="390";
image.alt="borboleta"+counter;
image.id="imagem"+counter;
image.style.position="absolute";
image.style.zIndex=counter;
div.appendChild(image);
}
};
var animaRight = function(x) {
var imageArray = [];
for (counter=0;counter<x-1;counter++) {
imageArray[counter] = document.getElementById("imagem"+counter+1);
}
setTimeout(function() {
for (var number in imageArray) {
if (imageArray[number].style.zIndex==number+1) {
imageArray[number].style.zIndex=imageArray.length-counter;
}
}
}, 1000/x);
};
window.onload = function() {
placeImage(30);
document.getElementById("div_picture_right").onclick=function() {animaRight(30)}
};
If you need more code to help analyze my problem, I'll gladly edit this. I'd appreciate examples where I can peek at the code for analysis, more than a solution I can copy paste. Directions are most welcome! Thanks in advance!

Your loop is checking on ultimateImagem. Maybe instead you mean to check on image? For example:
while (image.style.zIndex != x-1) {
...
}
Your while loop doesn't modify ultimaImagem, so checking on ultimaImagem.style.zIndex creates an infinite loop.
Also, as I said in the comments, you could just move the top image, no need to re-index the others. For example give imagem1 a z-index of 1001, imagem2 a z-index of 1002, etc. Then your code just becomes:
var ultimaImagem = document.getElementById("imagem"+x);
ultimateImagem.style.zIndex -= x;