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Scrolling link text on hover - endless marquee effect

I'm looking for a performant and also smooth solution for links that scroll their text inside of their inline-block box like a marquee effect.
$(document).ready(function() {
function scroll(ele){
var s = $(ele).text().substr(1)+$(ele).text().substr(0,1);
$(ele).text(s);
}
scrollInterval = null;
function startScrolling(e) {
if (!scrollInterval) {
scrollInterval = setInterval(function(){
scroll(e)
},100);
}
}
function stopScrolling(e) {
clearInterval(scrollInterval);
scrollInterval = null;
}
$(".mali").hover(function(){
startScrolling($(this));
});
$(".mali").mouseout(function(){
stopScrolling($(this));
});
$(".mali").mousedown(function(){
stopScrolling($(this));
});
});
.mali {
display: inline-block;
background: black;
color: white;
padding: 10px;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
Something something darkside, Something something complete.
My solution so far is something I actually found here on stackoverlow in another thread and tried to work with it.
Two problems though.
1.) As this is basically using an interval to loop through the single letters this effect is not very smooth. The effect is stuttering.
Has anyone an Idea on how to make this more smooth? Maybe in that case don't use this method at all and maybe use a CSS transition to animate the text?
2.) Does anyone have a clever solution on how to return to the initial state once I hover off? I want the effect on hover but when moving the mouse off the link it should animate back to the initial text state.
Thanks,
Matt

2) You can save initial state and then just revert it:
$(document).ready(function() {
function scroll(ele){
var s = $(ele).text().substr(1)+$(ele).text().substr(0,1);
$(ele).text(s);
}
scrollInterval = null;
function startScrolling(e) {
if (!scrollInterval) {
$(e).data("text", $(e).text());
scrollInterval = setInterval(function(){
scroll(e)
},100);
}
}
function stopScrolling(e) {
clearInterval(scrollInterval);
scrollInterval = null;
$(e).text($(e).data("text"));
}
$(".mali").hover(function(){
startScrolling($(this));
});
$(".mali").mouseout(function(){
stopScrolling($(this));
});
$(".mali").mousedown(function(){
stopScrolling($(this));
});
});
.mali {
display: inline-block;
background: black;
color: white;
padding: 10px;
transition: all .2s;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
Something something darkside, Something something complete.
1) As a smooth animation, i thought of this as a PoC. Maybe it will help you with further ideas.
$(document).ready(function() {
// Those global data could be stored in element's data.
var indent = 0,
width = 0,
padding = 10;
function scroll(ele){
// Every iteration decrease indent by value
indent -= 1;
// If is indent greater than or equal than real width
// (width with padding) reset indent.
if(-indent >= width+padding)
indent = 0;
// Aplly property
$(ele).css("text-indent", indent);
}
var scrollInterval = null;
function startScrolling(e) {
if (!scrollInterval) {
// Get text and real width
let text = $(e).text();
width = $(e).width()
$(e)
// Set real width & height, so that container stays
.width($(e).width())
.height($(e).height())
// Save text to data for reset
.data("text", text)
// Add 2 spans with text:
// <span>text</span><span>text</span>
// Where second span has defined padding on the left
.html($("<span>").text(text))
.append($("<span>").text(text).css("padding-left", padding+"px"));
resumeScrolling(e);
}
}
function stopScrolling(e) {
pauseScrolling(e);
// Reset
$(e)
// Revert real text and reset indent
.text($(e).data("text"))
.css("text-indent", indent = 0);
}
function pauseScrolling(e) {
clearInterval(scrollInterval);
scrollInterval = null;
}
function resumeScrolling(e) {
if (!scrollInterval) {
// Every 30ms repeat animation. It must be at least 25x per second
// so it runs smoothly. (So 1 - 40).
scrollInterval = setInterval(function(){
scroll(e)
},30);
}
}
$(".mali").hover(function(){
startScrolling($(this));
});
$(".mali").mouseout(function(){
stopScrolling($(this));
});
$(".mali").mousedown(function(){
stopScrolling($(this));
});
$("#start").click(function(){
startScrolling($(".mali"));
});
$("#stop").click(function(){
stopScrolling($(".mali"));
});
$("#pause").click(function(){
pauseScrolling($(".mali"));
});
$("#resume").click(function(){
resumeScrolling($(".mali"));
});
});
.mali {
display: inline-block;
background: black;
color: white;
padding: 10px;
/*
This could help, but you can't reset text-indent without animation.
transition: all .1s;
*/
overflow: hidden;
vertical-align: middle;
}
/* When you hover element, new span elements
can't take pointer events, so your elements
stays hovered. */
.mali span {
pointer-events: none;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
Something something darkside, Something something complete.
<br><br>
<button id="start">Start</button>
<button id="stop">Stop</button>
<button id="pause">Pause</button>
<button id="resume">Resume</button>
Idea behind this is:
make element overflow:hidden; so no text will overflow
set fix dimension
duplicate text inside
change text indent every x miliseconds (x < 40 so it is smooth, must be at least 25fps)
when it overflows, reset it so it can be in infinite loop

Change style header/nav with Intersection Observer (IO)

Fiddle latest
I started this question with the scroll event approach, but due to the suggestion of using IntersectionObserver which seems much better approach i'm trying to get it to work in that way.
What is the goal:
I would like to change the style (color+background-color) of the header depending on what current div/section is observed by looking for (i'm thinking of?) its class or data that will override the default header style (black on white).
Header styling:
font-color:
Depending on the content (div/section) the default header should be able to change the font-color into only two possible colors:
black
white
background-color:
Depending on the content the background-color could have unlimited colors or be transparent, so would be better to address that separate, these are the probably the most used background-colors:
white (default)
black
no color (transparent)
CSS:
header {
position: fixed;
width: 100%;
top: 0;
line-height: 32px;
padding: 0 15px;
z-index: 5;
color: black; /* default */
background-color: white; /* default */
}
Div/section example with default header no change on content:
<div class="grid-30-span g-100vh">
<img
src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1.414 1'%3E%3C/svg%3E"
data-src="/images/example_default_header.jpg"
class="lazyload"
alt="">
</div>
Div/section example change header on content:
<div class="grid-30-span g-100vh" data-color="white" data-background="darkblue">
<img
src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1.414 1'%3E%3C/svg%3E"
data-src="/images/example_darkblue.jpg"
class="lazyload"
alt="">
</div>
<div class="grid-30-span g-100vh" data-color="white" data-background="black">
<img
src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1.414 1'%3E%3C/svg%3E"
data-src="/images/example_black.jpg"
class="lazyload"
alt="">
</div>
Intersection Observer approach:
var mq = window.matchMedia( "(min-width: 568px)" );
if (mq.matches) {
// Add for mobile reset
document.addEventListener("DOMContentLoaded", function(event) {
// Add document load callback for leaving script in head
const header = document.querySelector('header');
const sections = document.querySelectorAll('div');
const config = {
rootMargin: '0px',
threshold: [0.00, 0.95]
};
const observer = new IntersectionObserver(function (entries, self) {
entries.forEach(entry => {
if (entry.isIntersecting) {
if (entry.intersectionRatio > 0.95) {
header.style.color = entry.target.dataset.color !== undefined ? entry.target.dataset.color : "black";
header.style.background = entry.target.dataset.background !== undefined ? entry.target.dataset.background : "white";
} else {
if (entry.target.getBoundingClientRect().top < 0 ) {
header.style.color = entry.target.dataset.color !== undefined ? entry.target.dataset.color : "black";
header.style.background = entry.target.dataset.background !== undefined ? entry.target.dataset.background : "white";
}
}
}
});
}, config);
sections.forEach(section => {
observer.observe(section);
});
});
}

Instead of listening to scroll event you should have a look at Intersection Observer (IO).
This was designed to solve problems like yours. And it is much more performant than listening to scroll events and then calculating the position yourself.
First, here is a codepen which shows a solution for your problem.
I am not the author of this codepen and I would maybe do some things a bit different but it definitely shows you the basic approach on how to solve your problem.
Things I would change: You can see in the example that if you scoll 99% to a new section, the heading changes even tough the new section is not fully visible.
Now with that out of the way, some explaining on how this works (note, I will not blindly copy-paste from codepen, I will also change const to let, but use whatever is more appropriate for your project.
First, you have to specify the options for IO:
let options = {
rootMargin: '-50px 0px -55%'
}
let observer = new IntersectionObserver(callback, options);
In the example the IO is executing the callback once an element is 50px away from getting into view. I can't recommend some better values from the top of my head but if I would have the time I would try to tweak these parameters to see if I could get better results.
In the codepen they define the callback function inline, I just wrote it that way to make it clearer on what's happening where.
Next step for IO is to define some elements to watch. In your case you should add some class to your divs, like <div class="section">
let entries = document.querySelectorAll('div.section');
entries.forEach(entry => {observer.observe(entry);})
Finally you have to define the callback function:
entries.forEach(entry => {
if (entry.isIntersecting) {
//specify what should happen if an element is coming into view, like defined in the options.
}
});
Edit: As I said this is just an example on how to get you started, it's NOT a finished solution for you to copy paste. In the example based on the ID of the section that get's visible the current element is getting highlighted. You have to change this part so that instead of setting the active class to, for example, third element you set the color and background-color depending on some attribute you set on the Element. I would recommend using data attributes for that.
Edit 2: Of course you can continue using just scroll events, the official Polyfill from W3C uses scroll events to emulate IO for older browsers.it's just that listening for scroll event and calculating position is not performant, especially if there are multiple elements. So if you care about user experience I really recommend using IO. Just wanted to add this answer to show what the modern solution for such a problem would be.
Edit 3: I took my time to create an example based on IO, this should get you started.
Basically I defined two thresholds: One for 20 and one for 90%. If the element is 90% in the viewport then it's save to assume it will cover the header. So I set the class for the header to the element that is 90% in view.
Second threshold is for 20%, here we have to check if the element comes from the top or from the bottom into view. If it's visible 20% from the top then it will overlap with the header.
Adjust these values and adapt the logic as you see.
const sections = document.querySelectorAll('div');
const config = {
rootMargin: '0px',
threshold: [.2, .9]
};
const observer = new IntersectionObserver(function (entries, self) {
entries.forEach(entry => {
if (entry.isIntersecting) {
var headerEl = document.querySelector('header');
if (entry.intersectionRatio > 0.9) {
//intersection ratio bigger than 90%
//-> set header according to target
headerEl.className=entry.target.dataset.header;
} else {
//-> check if element is coming from top or from bottom into view
if (entry.target.getBoundingClientRect().top < 0 ) {
headerEl.className=entry.target.dataset.header;
}
}
}
});
}, config);
sections.forEach(section => {
observer.observe(section);
});
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
.g-100vh {
height: 100vh
}
header {
min-height: 50px;
position: fixed;
background-color: green;
width: 100%;
}
header.white-menu {
color: white;
background-color: black;
}
header.black-menu {
color: black;
background-color: white;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<header>
<p>Header Content </p>
</header>
<div class="grid-30-span g-100vh white-menu" style="background-color:darkblue;" data-header="white-menu">
<img
src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1.414 1'%3E%3C/svg%3E"
data-src="/images/example_darkblue.jpg"
class="lazyload"
alt="<?php echo $title; ?>">
</div>
<div class="grid-30-span g-100vh black-menu" style="background-color:lightgrey;" data-header="black-menu">
<img
src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1.414 1'%3E%3C/svg%3E"
data-src="/images/example_lightgrey.jpg"
class="lazyload"
alt="<?php echo $title; ?>">
</div>

I might not understand the question completely, but as for your example - you can solve it by using the mix-blend-mode css property without using javascript at all.
Example:
header {background: white; position: relative; height: 20vh;}
header h1 {
position: fixed;
color: white;
mix-blend-mode: difference;
}
div {height: 100vh; }
<header>
<h1>StudioX, Project Title, Category...</h1>
</header>
<div style="background-color:darkblue;"></div>
<div style="background-color:lightgrey;"></div>

I've encountered the same situation and the solution I implemented is very precise because it doesn't rely on percentages but on real elements' bounding boxes:
class Header {
constructor() {
this.header = document.querySelector("header");
this.span = this.header.querySelector('span');
this.invertedSections = document.querySelectorAll(".invertedSection");
window.addEventListener('resize', () => this.resetObserver());
this.resetObserver();
}
resetObserver() {
if (this.observer) this.observer.disconnect();
const {
top,
height
} = this.span.getBoundingClientRect();
this.observer = new IntersectionObserver(entries => this.observerCallback(entries), {
root: document,
rootMargin: `-${top}px 0px -${window.innerHeight - top - height}px 0px`,
});
this.invertedSections.forEach((el) => this.observer.observe(el));
};
observerCallback(entries) {
let inverted = false;
entries.forEach((entry) => {
if (entry.isIntersecting) inverted = true;
});
if (inverted) this.header.classList.add('inverted');
else this.header.classList.remove('inverted');
};
}
new Header();
header {
position: fixed;
top: 0;
left: 0;
right: 0;
padding: 20px 0;
text-transform: uppercase;
text-align: center;
font-weight: 700;
}
header.inverted {
color: #fff;
}
section {
height: 500px;
}
section.invertedSection {
background-color: #000;
}
<body>
<header>
<span>header</span>
</header>
<main>
<section></section>
<section class="invertedSection"></section>
<section></section>
<section class="invertedSection"></section>
</main>
</body>
What it does is actually quite simple: we can't use IntersectionObserver to know when the header and other elements are crossing (because the root must be a parent of the observed elements), but we can calculate the position and size of the header to add rootMargin to the observer.
Sometimes, the header is taller than its content (because of padding and other stuff) so I calculate the bounding-box of the span in the header (I want it to become white only when this element overlaps a black section).
Because the height of the window can change, I have to reset the IntersectionObserver on window resize.
The root property is set to document here because of iframe restrictions of the snippet (otherwise you can leave this field undefined).
With the rootMargin, I specify in which area I want the observer to look for intersections.
Then I observe every black section. In the callback function, I define if at least one section is overlapping, and if this is true, I add an inverted className to the header.
If we could use values like calc(100vh - 50px) in the rootMargin property, we may not need to use the resize listener.
We could even improve this system by adding side rootMargin, for instance if I have black sections that are only half of the window width and may or may not intersect with the span in the header depending on its horizontal position.

#Quentin D
I searched the internet for something like this, and I found this code to be the best solution for my needs.
Therefore I decided to build on it and create a universal "Observer" class, that can be used in many cases where IntesectionObserver is required, including changing the header styles.
I haven't tested it much, only in a few basic cases, and it worked for me. I haven't tested it on a page that has a horizontal scroll.
Having it this way makes it easy to use it, just save it as a .js file and include/import it in your code, something like a plugin. :)
I hope someone will find it useful.
If someone finds better ideas (especially for "horizontal" sites), it would be nice to see them here.
Edit: I hadn't made the correct "unobserve", so I fixed it.
/* The Intersection Observer API provides a way to asynchronously observe changes in the intersection of a target element with an ancestor element or with a top-level document's viewport.
ROOT:
It is not necessary for the root to be the ancestor element of the target. The root is allways the document, and the so-called root element is used only to get its size and position, to create an area in the document, with options.rootMargin.
Leave it false to have the viewport as root.
TARGET:
IntersectionObserver triggers when the target is entering at the specified ratio(s), and when it exits at the same ratio(s).
For more on IntersectionObserverEntry object, see:
https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API#targeting_an_element_to_be_observed
IntersectionObserverEntry.time // Timestamp when the change occurred
IntersectionObserverEntry.rootBounds // Unclipped area of root
IntersectionObserverEntry.intersectionRatio // Ratio of intersectionRect area to boundingClientRect area
IntersectionObserverEntry.target // the Element target
IntersectionObserverEntry.boundingClientRect // target.boundingClientRect()
IntersectionObserverEntry.intersectionRect // boundingClientRect, clipped by its containing block ancestors, and intersected with rootBounds
THRESHOLD:
Intersection ratio/threshold can be an array, and then it will trigger on each value, when in and when out.
If root element's size, for example, is only 10% of the target element's size, then intersection ratio/threshold can't be set to more than 10% (that is 0.1).
CALLBACKS:
There can be created two functions; when the target is entering and when it's exiting. These functions can do what's required for each event (visible/invisible).
Each function is passed three arguments, the root (html) element, IntersectionObserverEntry object, and intersectionObserver options used for that observer.
Set only root and targets to only have some info in the browser's console.
For more info on IntersectionObserver see: https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API
Polyfill: <script src="https://polyfill.io/v3/polyfill.js?features=IntersectionObserver"></script>
or:
https://github.com/w3c/IntersectionObserver/tree/main/polyfill
Based on answer by Quentin D, answered Oct 27 '20 at 12:12
https://stackoverflow.com/questions/57834100/change-style-header-nav-with-intersection-observer-io
root - (any selector) - root element, intersection parent (only the first element is selected).
targets - (any selector) - observed elements that trigger function when visible/invisible.
inCb - (function name) - custom callback function to trigger when the target is intersecting.
outCb - (function name) - custom callback function to trigger when the target is not intersecting.
thres - (number 0-1) - threshold to trigger the observer (e.g. 0.1 will trigger when 10% is visible).
unobserve- (bolean) - if true, the target is unobserved after triggering the callback.
EXAMPLE:
(place in 'load' event listener, to have the correct dimensions)
var invertedHeader = new Observer({
root: '.header--main', // don't set to have the viewport as root
targets: '[data-bgd-dark]',
thres: [0, .16],
inCb: someCustomFunction,
});
*/
class Observer {
constructor({
root = false,
targets = false,
inCb = this.isIn,
outCb = this.isOut,
thres = 0,
unobserve = false,
} = {}) {
// this element's position creates with rootMargin the area in the document
// which is used as intersection observer's root area.
// the real root is allways the document.
this.area = document.querySelector(root); // intersection area
this.targets = document.querySelectorAll(targets); // intersection targets
this.inCallback = inCb; // callback when intersecting
this.outCallback = outCb; // callback when not intersecting
this.unobserve = unobserve; // unobserve after intersection
this.margins; // rootMargin for observer
this.windowW = document.documentElement.clientWidth;
this.windowH = document.documentElement.clientHeight;
// intersection is being checked like:
// if (entry.isIntersecting || entry.intersectionRatio >= this.ratio),
// and if ratio is 0, "entry.intersectionRatio >= this.ratio" will be true,
// even for non-intersecting elements, therefore:
this.ratio = thres;
if (Array.isArray(thres)) {
for (var i = 0; i < thres.length; i++) {
if (thres[i] == 0) {
this.ratio[i] = 0.0001;
}
}
} else {
if (thres == 0) {
this.ratio = 0.0001;
}
}
// if root selected use its position to create margins, else no margins (viewport as root)
if (this.area) {
this.iArea = this.area.getBoundingClientRect(); // intersection area
this.margins = `-${this.iArea.top}px -${(this.windowW - this.iArea.right)}px -${(this.windowH - this.iArea.bottom)}px -${this.iArea.left}px`;
} else {
this.margins = '0px';
}
// Keep this last (this.ratio has to be defined before).
// targets are required to create an observer.
if (this.targets) {
window.addEventListener('resize', () => this.resetObserver());
this.resetObserver();
}
}
resetObserver() {
if (this.observer) this.observer.disconnect();
const options = {
root: null, // null for the viewport
rootMargin: this.margins,
threshold: this.ratio,
}
this.observer = new IntersectionObserver(
entries => this.observerCallback(entries, options),
options,
);
this.targets.forEach((target) => this.observer.observe(target));
};
observerCallback(entries, options) {
entries.forEach(entry => {
// "entry.intersectionRatio >= this.ratio" for older browsers
if (entry.isIntersecting || entry.intersectionRatio >= this.ratio) {
// callback when visible
this.inCallback(this.area, entry, options);
// unobserve
if (this.unobserve) {
this.observer.unobserve(entry.target);
}
} else {
// callback when hidden
this.outCallback(this.area, entry, options);
// No unobserve, because all invisible targets will be unobserved automatically
}
});
};
isIn(rootElmnt, targetElmt, options) {
if (!rootElmnt) {
console.log(`IO Root: VIEWPORT`);
} else {
console.log(`IO Root: ${rootElmnt.tagName} class="${rootElmnt.classList}"`);
}
console.log(`IO Target: ${targetElmt.target.tagName} class="${targetElmt.target.classList}" IS IN (${targetElmt.intersectionRatio * 100}%)`);
console.log(`IO Threshold: ${options.threshold}`);
//console.log(targetElmt.rootBounds);
console.log(`============================================`);
}
isOut(rootElmnt, targetElmt, options) {
if (!rootElmnt) {
console.log(`IO Root: VIEWPORT`);
} else {
console.log(`IO Root: ${rootElmnt.tagName} class="${rootElmnt.classList}"`);
}
console.log(`IO Target: ${targetElmt.target.tagName} class="${targetElmt.target.classList}" IS OUT `);
console.log(`============================================`);
}
}

This still needs adjustment, but you could try the following:
const header = document.getElementsByTagName('header')[0];
const observer = new IntersectionObserver((entries) => {
entries.forEach((entry) => {
if (entry.isIntersecting) {
header.style.color = entry.target.dataset.color || '';
header.style.backgroundColor = entry.target.dataset.background;
}
});
}, { threshold: 0.51 });
[...document.getElementsByClassName('observed')].forEach((t) => {
t.dataset.background = t.dataset.background || window.getComputedStyle(t).backgroundColor;
observer.observe(t);
});
body {
font-family: arial;
margin: 0;
}
header {
border-bottom: 1px solid red;
margin: 0 auto;
width: 100vw;
display: flex;
justify-content: center;
position: fixed;
background: transparent;
transition: all 0.5s ease-out;
}
header div {
padding: 0.5rem 1rem;
border: 1px solid red;
margin: -1px -1px -1px 0;
}
.observed {
height: 100vh;
border: 1px solid black;
}
.observed:nth-of-type(2) {
background-color: grey;
}
.observed:nth-of-type(3) {
background-color: white;
}
<header>
<div>One</div>
<div>Two</div>
<div>Three</div>
</header>
<div class="observed">
<img src="http://placekitten.com/g/200/300">
<img src="http://placekitten.com/g/400/300">
</div>
<div class="observed" data-color="white" data-background="black">
<img src="http://placekitten.com/g/600/300">
</div>
<div class="observed" data-color="black" data-background="white">
<img src="http://placekitten.com/g/600/250">
</div>
The CSS ensures each observed section takes up 100vw and the observer does its thing when anyone of those comes into view by at least 51% percent.
In the callback the headers background-color is then set to the background-color of the intersecting element.

Trigger a function at a specific transition value

I want to trigger a function at a specific transitionY Value.
I found this:
document.getElementById("main").addEventListener("webkitTransitionEnd", myFunction);
document.getElementById("main").addEventListener("transitionend", myFunction);
function myFunction() {
alert('huuh');
}
But it's only a trigger after a transition End. When I scroll down on my Page, a div box change the style value by (transform: translateY(-100%)).
I tried:
if (document.getElementsByClassName('scroll-container').style.transform == "translateY(-100%)")
.......
but it doesn't work.

You can use jQuery's $.animate function. Using progress attribute, you will be getting current status of the animation. e.g.
setTimeout(function() {
var transitionPointReached = false;
$('#some-id').animate({
opacity: 0.1
}, {
duration: 1000,
progress: function(animation, progress, remaining){
console.log('progress called', progress, remaining);
if(!transitionPointReached && progress >= 0.7) {
transitionPointReached = true;
// call the required callback once.
}
}
});
}, 1000);
#some-id {
width: 200px;
height: 200px;
background-color: yellow;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="some-id"></div>
Hope it helps.

or is it possible to trigger a function if the page reaches a new section? Like #0 (<a id="button" href="#0"></a> ) and went to #1 ?
greetings
Here u can see what i mean :
http://salon-lifestyle.de.w0192ceb.kasserver.com/#0

or is it possible to trigger a function if the page reaches a new
section? Like #0 ( ) and went to #1 ?
The Intersection Observer API was designed for such usecases, it allows to triggers callback when the viewport reaches/crosses/has reached a set of children.
Regarding your transition question, you can do something like this but I would not recommend using it. You can fetch the exact value of the transition property using element.cssText
const dummyDiv = document.getElementById('dummy')
// Assuming the transition is linear and lasts 2secs,
// mid-transiton happens after 1000ms
dummyDiv.addEventListener('transitionstart', () => {
window.setTimeout(() => {
dummyDiv.innerHTML = 'mid transition'
}, 1000)
})
dummyDiv.addEventListener('transitionend', () => {
dummyDiv.innerHTML = 'end transition'
})
#dummy{
padding: 50px 100px;
font-size: 35px;
background: #000;
color: #FFF;
transition: 2s linear;
}
#dummy:hover{
background:red
}
<div id="dummy">Hover me</div>

Vue.js - improving performance of infinite list loop

I need a list of users to vertically loop infinitely.
I know that I should use 'translateY' rather than 'top' for that kind of stuff - but I don't know how.
I've done the 'top' version and it works. Any ideas how to improve that?
Thanks guys!
Example in Codepen
<div id="app">
<div id="rows">
<div class="row" v-for="row in rows" v-bind:style="{ top: row.top + 'px' }">
{{row.id}}
</div>
</div>
</div>
<script>
const app = new Vue({
el: '#app',
data() {
return {
rows: []
}
},
created() {
for (let i = 0; i < 30; i++) {
this.rows.push({
id: i,
top: i * 40
})
}
setInterval(() => {
window.requestAnimationFrame(this.update);
}, 16);
},
methods: {
update() {
this.rows.forEach(row => {
row.top -= 0.5
});
if (this.rows[0].top <= -40) {
this.rows.push({
id: this.rows[0].id,
top: (this.rows.length - 1) * 40
})
this.rows.shift();
}
}
}
})
</script>
<style>
#rows {
position: relative;
}
.row {
position: absolute;
width: 100%;
height: 40px;
border: 1px solid black;
}
</style>

Here's my attempt:
new Vue({
el: '#app',
data() {
const rows = []
for (let i = 0; i < 30; i++) {
rows.push({
id: i
})
}
return {
offset: 0,
rows
}
},
mounted () {
this.frameTime = Date.now()
const animate = () => {
this.animationId = requestAnimationFrame(() => {
this.update()
animate()
})
}
animate()
},
beforeDestroy () {
cancelAnimationFrame(this.animationId)
},
methods: {
update() {
const now = Date.now()
const elapsed = now - this.frameTime
this.offset -= elapsed / 16
this.frameTime = now
if (this.offset < -400) {
while (this.offset < -40) {
this.rows.push(this.rows.shift())
this.offset += 40
}
}
}
}
})
* {
box-sizing: border-box;
}
#rows {
border: 1px solid #f00;
height: 200px;
overflow: hidden;
}
.row {
width: 100%;
height: 40px;
border: 2px solid black;
}
<script src="https://unpkg.com/vue#2.6.10/dist/vue.js"></script>
<div id="app">
<div id="rows">
<div :style="{ transform: `translateY(${Math.round(offset)}px)` }">
<div
v-for="row in rows"
:key="row.id"
class="row"
>
{{row.id}}
</div>
</div>
</div>
</div>
You don't necessarily have to make all the changes I've made, most can be made selectively if you prefer. The major changes are:
Putting a key on the list items so Vue moves the DOM nodes rather than updating all of them when the shuffle occurs.
Using a wrapper <div> so that only one element is actually moving (I got rid of the absolute positioning as part of this).
Using translateY, as requested.
Getting rid of setInterval, you should only need requestAnimationFrame for this. The animation speed is kept in check by keeping track of how much time has elapsed.
When a row jumps I just move the object to the end of the array rather than making a copy.
The animation is cancelled when the component is destroyed.
Update:
Three further changes:
I've added box-sizing: border-box to fix the 2px inaccuracy in the calculations.
The DOM node reordering is now batched to only happen every 400px. No idea if this is actually a good idea, for such a simple example it doesn't really make any difference.
I've rounded the translateY to use whole pixels. For me this looked slightly better but on screens with higher pixel ratios I could imagine it might look worse.
There are further optimisations that might be applicable depending on the circumstances.
Rows that aren't visible could be omitted.
Reordering could be avoided altogether by applying the translateY to each row, though for large numbers of rows that may not be practical.
Animating this using transitions or CSS animations would be tricky due to the requirement for rows to jump back down to the bottom. If each row were animated independently I'm not sure how easy it would be to keep all the animations synchronised.

Check if scrolled past div with JavaScript (no jQuery)

I am currently learning JavaScript and all the solutions that I've come across use the jQuery library. Is there a way to do it, just using pure JavaScript?
The idea is to have something like:
function passed(element) {if passed: do something}

Listen for the scroll event. To find the current scroll position, you can call the scollY method.
To get the Y coordinate of the top of an element, you can use the element's offsetTop. Because the element has a height, we want to add the height to our calculation.
That's it.
window.addEventListener("scroll", function() {
var elementTarget = document.getElementById("section-2");
if (window.scrollY > (elementTarget.offsetTop + elementTarget.offsetHeight)) {
alert("You've scrolled past the second div");
}
});
.section-1 {
height: 400px;
width: 100%;
background: green;
}
.section-3 {
height: 400px;
width: 100%;
background: orange;
}
<div class="section-1"></div>
<div id="section-2">Scroll past this div</div>
<div class="section-3"></div>

You should be able to use the following:
if(window.scrollY >(element.offsetHeight + element.offsetTop)){
// do something
}

With https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/offsetTop you can get the Y coordinate of an element.
With https://developer.mozilla.org/en-US/docs/Web/API/Window/scrollY you can get the current Y coordinate of the scroll.
With https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/offsetHeight you get the height of an element.
So the only thing that remains to do is to check if scrollY > (offsetHeight + offsetTop). If this is true, you passed the element with the scroll.
I leave to you the implementation, as a practice to learn Javascript ;)

if (element.getBoundingClientRect().y < 0) {
// do something
}

This can be achieved with the IntersectionObserver API without having to rely on scroll events at all.
const elementTarget = document.getElementById("section-2");
// skip first callback when first observing
let firstCallback = true;
const observer = new IntersectionObserver(entries => {
if (!entries[0].isIntersecting) {
if (firstCallback) {
firstCallback = false;
} else {
alert("You've scrolled past the second div");
}
}
});
observer.observe(elementTarget);
// remember to unobserve when done
.section-1 {
height: 1000px;
width: 100%;
background: green;
}
.section-3 {
height: 1000px;
width: 100%;
background: orange;
}
<div class="section-1"></div>
<div id="section-2">Scroll past this div</div>
<div class="section-3"></div>