Develop Reference

I want to create a zoom-in-down effect of a background which triggers only on scroll down and goes back on scroll up but does not do viceversa

I want to create my background circle so that it will cover my whole width of container but the problems that I am facing are:
I am using wheel method which I want to change with scroll method but won't able to give a exact scroll position to start scrolling scrollTop is using start of my website but I want to start my scroll after 3rd container div.
In wheel function my background zooms-in with wheel up as well as well down I only want it to work on scroll down.
I want my zoom to zoom out once it reached width of whole screen.
my code:
const zoomElement = document.querySelector(".zoom");
let zoom = 1;
const ZOOM_SPEED = 1;
document.addEventListener("wheel", function(e) {
if (e.deltaY > 0) {
zoomElement.style.transform = `scale(${zoom += ZOOM_SPEED})`;
} else {
zoomElement.style.transform = `scale(${zoom -= ZOOM_SPEED})`;
}
});
* {
margin: 0;
padding: 0;
box-sizing: border-box;
overflow-x: hidden;
}
.downarrow {
position: relative;
left: 50%;
font-size: 2rem;
color: #f0f0f0;
}
.zoom {
background: #282828;
width: 100px;
height: 100px;
border-radius: 50%;
position: relative;
left: 47.80%;
}
.container {
width: 100%;
height: 100vh;
}
<div class="container">
<div class="zoom"></div>
<p class="downarrow">↓</p>
</div>
I want to mimic this site downarrow effect:
https://lione.axiomthemes.com/

How to put an element in hover state when scrolled down using javascript

I am trying to make a div element which when scrolled down will change properties drastically. Here is the codepen example of how I want it to work.
Instead of hover I want it so that when scrolled down, the page wide div will turn into that little circle div which when clicked will function as a back to the top button. It doesn't matter if more classes are added or anything of that sort. I am very new to js and I tried a few things and also googled about it, I got the scroll code from w3school's how to make a back to top button guide which specifies that when scrolled down by 20px the code would react, but I don't know how to turn the JavaScript to JS when scrolled down along with the transformation of the div.
Thanks in advance

I think you want to implement scroll to top functionality, very common these days in most of the web app.
You need to keep below things and design that feature.
There is one header, that should have a reference ID with hash to scroll back to top
Create a button that will always static position (JS) button, will show up when user scroll the window
Bind click event on the button that scroll back to top
Here is the you can see this implementation and use it.
.html
<h1 class="intro-copy">
Scroll down to use this simple back-to-top button made with modern vanilla javascript.
</h1>
<a class="top-link hide" href="" id="js-top">
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 12 6"><path d="M12 6H0l6-6z"/></svg>
<span class="screen-reader-text">Back to top</span>
</a>
.css
body {
height: 2000px;
position: relative;
}
.intro-copy {
padding: 1em;
margin: 50vh auto;
max-width: 15em;
font-family: Helvetica;
font-weight: lighter;
font-size: 2em;
line-height: 1.2;
text-align: center;
}
.top-link {
transition: all .25s ease-in-out;
position: fixed;
bottom: 0;
right: 0;
display: inline-flex;
cursor: pointer;
align-items: center;
justify-content: center;
margin: 0 3em 3em 0;
border-radius: 50%;
padding: .25em;
width: 80px;
height: 80px;
background-color: #F8F8F8;
&.show {
visibility: visible;
opacity: 1;
}
&.hide {
visibility: hidden;
opacity: 0;
}
svg {
fill: #000;
width: 24px;
height: 12px;
}
&:hover {
background-color: #E8E8E8;
svg {
fill: #000000;
}
}
}
// Text meant only for screen readers.
.screen-reader-text {
position: absolute;
clip-path: inset(50%);
margin: -1px;
border: 0;
padding: 0;
width: 1px;
height: 1px;
overflow: hidden;
word-wrap: normal !important;
clip: rect(1px, 1px, 1px, 1px);
&:focus {
display: block;
top: 5px;
left: 5px;
z-index: 100000; // Above WP toolbar
clip-path: none;
background-color: #eee;
padding: 15px 23px 14px;
width: auto;
height: auto;
text-decoration: none;
line-height: normal;
color: #444;
font-size: 1em;
clip: auto !important;
}
}
JS:
// Set a variable for our button element.
const scrollToTopButton = document.getElementById('js-top');
// Let's set up a function that shows our scroll-to-top button if we scroll beyond the height of the initial window.
const scrollFunc = () => {
// Get the current scroll value
let y = window.scrollY;
// If the scroll value is greater than the window height, let's add a class to the scroll-to-top button to show it!
if (y > 0) {
scrollToTopButton.className = "top-link show";
} else {
scrollToTopButton.className = "top-link hide";
}
};
window.addEventListener("scroll", scrollFunc);
const scrollToTop = () => {
// Let's set a variable for the number of pixels we are from the top of the document.
const c = document.documentElement.scrollTop || document.body.scrollTop;
// If that number is greater than 0, we'll scroll back to 0, or the top of the document.
// We'll also animate that scroll with requestAnimationFrame:
// https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame
if (c > 0) {
window.requestAnimationFrame(scrollToTop);
// ScrollTo takes an x and a y coordinate.
// Increase the '10' value to get a smoother/slower scroll!
window.scrollTo(0, c - c / 10);
}
};
// When the button is clicked, run our ScrolltoTop function above!
scrollToTopButton.onclick = function(e) {
e.preventDefault();
scrollToTop();
}

Detect When Mouse Enters Specific Area of Document (Not a Div Element)

I'm trying to figure out how Medium made their bottom action / menu bar slide up when your mouse enters the bottom of the document. The slide up effect is not triggered by moving the mouse over the invisible div (it slides up & down via transform translateY).
Besides, the menu bar is only 44px in height, but its is-visible class gets triggered way before your mouse is near it — but by what? When using Inspect Element, I can't see any hidden divs that could be triggering it..
I've searched for countless of ways, e.g. "show element when mouse enters specific part of document" but all search results involve when the mouse enters or moves over a div element, which is not the solution I'm looking for.
Obviously, you can solve this problem by putting the slide up menu inside a hidden container like I've done here, and then you get the desired result:
(function() {
var actionBar = document.querySelector('.action-bar');
var actionBarWrapper = document.querySelector('.action-bar-detection');
function showDiv() {
actionBar.classList.add('js-is-visible')
}
function hideDiv() {
actionBar.classList.remove('js-is-visible')
}
actionBarWrapper.onmouseover = showDiv;
actionBarWrapper.onmouseout = hideDiv;
})();
* {
margin: 0;
padding: 0;
box-sizing: border-box;
line-height: 1.5;
}
body {
height: 100%;
}
.wrapper {
width: 90%;
max-width: 600px;
margin: 5% auto;
}
.action-bar {
position: absolute;
left: 0;
bottom: 0;
border: 1px solid #252321;
background: #fff;
padding: 16px;
width: 100%;
min-height: 50px;
opacity: 0;
transform: translateY(100%);
transition: all .5s;
z-index: 99;
}
.action-bar-detection {
height: 150px;
width: 100%;
opacity: 1;
position: fixed;
bottom: 0;
left: 0;
z-index: 1;
}
.js-is-visible {
opacity: 1;
transform: translateY(0%);
}
<html>
<head>
<meta charset="UTF-8" />
<title>Document</title>
</head>
<body>
<div class="wrapper">
<p>When mouse enters the hidden action bar element, slides up.</p>
<p>But it's only happening because the action-bar is inside an invisible detection layer class (action-bar-detection) with a height of 150px.</p>
</div>
<div class="action-bar-detection">
<div class="action-bar">
Bottom Menu
</div>
</div>
</body>
</html>
However, this doesn't seem to be what Medium have done, and if this can be done without adding more HTML & CSS, I want to learn how! :-)
I think I'm not phrasing the problem correctly, since I can't find any solutions even remotely close (I've searched A LOT).
Any advice? What should I read up on? :-)

Get height of viewport, track onmousemove, and compare clientY from the mouse event to the viewport height:
(function() {
var actionBar = document.querySelector('.action-bar');
var viewHeight = window.innerHeight - 150;
function toggleDiv(e) {
if (e.clientY >= viewHeight) {
actionBar.classList.add('js-is-visible');
} else {
actionBar.classList.remove('js-is-visible');
}
}
window.onmousemove = toggleDiv;
})();
* {
margin: 0;
padding: 0;
box-sizing: border-box;
line-height: 1.5;
}
body {
height: 100%;
}
.wrapper {
width: 90%;
max-width: 600px;
margin: 5% auto;
}
.action-bar {
position: absolute;
left: 0;
bottom: 0;
border: 1px solid #252321;
background: #fff;
padding: 16px;
width: 100%;
min-height: 50px;
opacity: 0;
transform: translateY(100%);
transition: all .5s;
z-index: 99;
}
.action-bar-detection {
height: 150px;
width: 100%;
opacity: 1;
position: fixed;
bottom: 0;
left: 0;
z-index: 1;
}
.js-is-visible {
opacity: 1;
transform: translateY(0%);
}
<div class="wrapper">
<p>When mouse comes within 150px of the bottom part of the screen, the bar slides up.</p>
<p>When the mouse leaves this defined area of the screen, the bar slides down.</p>
</div>
<div class="action-bar-detection">
<div class="action-bar">
Bottom Menu
</div>
</div>

You could do this by listening to the mousemove event on the document, you will want to invest effort into making this performant as it will be triggered frequently. The most common way to regulate events like this is through throttling.
Once you are hooked into the mousemove event you will need to get the Y coordinate of the cursor and compare that to the height of the window, if it is within a threshold then you can reveal your panel, once it moves out you can proceed to hide it again.
Here is an example showing a basic implementation jsFiddle
// Using underscore for the throttle function though you can implement your own if you wish
document.addEventListener('mousemove', _.throttle(mouseMoveEventAction, 200));
function mouseMoveEventAction(e) {
doPanelStuff(isInsideThreshold(e.clientY));
}
function doPanelStuff(isActive) {
var panelElement = document.querySelector('.panel');
if (isActive) {
panelElement.style.background = 'red';
} else {
panelElement.style.removeProperty('background');
}
}
function isInsideThreshold(cursorY) {
var threshold = 200;
var clientHeight = document.documentElement.clientHeight;
return cursorY > (clientHeight - threshold);
}
html, body {
height: 100%;
}
.container, .content {
height: 100%;
width: 100%;
}
.panel {
height: 50px;
position: absolute;
bottom: 0;
width: 100%;
background: green;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>
<div class="container">
<div class="content"></div>
<div class="panel"></div>
</div>

Dynamic float menu issue

I want to make the menu fixed on top when window scroll down over 160 pixel, but if the body content is too short, it will become an infinite loop, because if I scroll down over 160 pixel, menu will become fixed which means scroll height will turn to under 160 pixel, so script will make the menu relative back, how to solve this.
Demo
HTML
<div id="header">header</div>
<div id="content">content</div>
JavaScript
$(window).on('scroll', function() {
var scroll = $(window).scrollTop();
if (scroll > 160) {
$('#header').css('position', 'fixed');
} else {
$('#header').css('position', 'relative');
}
});
CSS
body {
margin: 0;
padding: 0;
}
#header {
width: 100%;
height: 60px;
background: black;
color: yellow;
position: relative;
padding: 6px;
}
#content {
width: 100%;
height: 780px;
background: gray;
}

when adding position fixed to menu, add also paddin-top for content (padding-top value equals header height + header top and bottom padding)
JS:
$(window).on('scroll', function() {
var scroll = $(window).scrollTop();
if (scroll > 160) {
$('#content').css('padding-top', '72px');
$('#header').css('position', 'fixed');
} else {
$('#content').css('padding-top', '0');
$('#header').css('position', 'relative');
}
});
fiddle

you do not need any javascript here...so remove all js... and edit your css:
#header {
width: 100%;
height: 60px;
background: black;
color: yellow;
position: fixed; /* make menu header always fixed */
padding: 6px;
top:0px;
}
#content {
width: 100%;
height: 780px;
margin-top:72px; /* margin top 72px because of header height is 60px + pedding 6px*2 */
background: gray;
}

Moving divs with javascript

This is my problem, I have a div and inside 2 divs, one is centered and the other one is fixed on the left, the problem is when I resize the screen the centered div overlaps the fixed one, what I wanted to do is detect when the centered div overlaps the other div and change its left value with javascript, but is not working, any ideas?
This is my design:
<div id="content-wrap">
<div id="content">
</div>
<div id="leftbar">
</div>
</div>
and the CSS:
#content-wrap
{
clear: both;
float: left;
width: 100%;
}
#content
{
text-align: left;
padding: 0;
margin: 0 auto;
height: 470px;
width: 760px;
overflow: auto;
}
#leftbar
{
background-color: transparent;
width: 200px;
height: 470px;
position: absolute;
top: 185px;
left: 50px;
}
and this is the javascript code:
window.onload = function Centrar() {
var leftBar = $get("leftbar");
if (leftBar != null) {
var content = $get("content");
var size = leftBar.offsetLeft + leftBar.offsetWidth;
if (content.offsetLeft < size) {
content.style.left = size + 20 + 'px';
}
}
}
Thanks in advance for any help.

The easiest fix would be to apply a min-width to your #content-wrap container that prevented the overlap from occurring:
#content-wrap {
clear: both;
float: left;
width: 100%;
/* #leftbar width x 2 + #content width */
min-width: 1160px;
}
However, if you want to use Javascript, you'll need to attach the code to the window load and resize events:
$(window).bind('load resize', function() {
var content = $('#content');
var leftbar = $('#leftbar');
// get the right edge of the #leftbar
var leftbarEdge = leftbar.width() + leftbar.offset().left;
// check if an overlap has occured and adjust #content left position if yes
if (leftbarEdge > content.offset().left) {
content.css({
left: leftbarEdge - content.offset().left
});
}
});
The last change you'll need to apply to get this working is to set #content to position: relative in the CSS so it respects the left property you're setting with Javascript:
#content {
position: relative;
/* remaining css */
}
You can see it in action here.