Develop Reference

Pinning Elements with Debounced Scroll Event for Performance

What is the right way to smoothly pin an element according to scroll position?
I tried debouncing a scroll listener for performance but the pinning is not accurate. Even with debouncing set to 10ms it's not smooth and the element doesn't snap cleanly to its initial position.
var scrolling = false;
var stickPosY = 100;
var heights = [];
$(".element").each( function(index) {
heights[index] = $(".element[data-trigger=" + index + "]").offset().top;
});
function pin() {
if ( !$("#aside").hasClass("fixed") ) {
var stickyLeft = $("#aside").offset().left;
var stickyWidth = $("#aside").outerWidth();
var stickyTop = $("#aside").offset().top - stickPosY;
$("#aside").addClass("fixed");
$("#aside").css({"left": stickyLeft, "top": stickyTop, "width": stickyWidth});
}
}
function unpin() {
$("#aside").css({"left": "", "top": "", "width": ""});
$("#aside").removeClass("fixed")
}
$( window ).scroll( function() {
scrolling = true;
});
setInterval( function() {
if ( scrolling ) {
scrolling = false;
var y = window.scrollY;
console.log(y);
// PIN SIDEBAR
y > stickPosY ? pin() : unpin();
//TRIGGERS
for (var i=0; i < heights.length; i++) {
if (y >= heights[i]) {
$('.element[data-trigger="' + i + '"]').addClass("blue");
}
else {
$('.element[data-trigger="' + i + '"]').removeClass("blue");
}
}
}
}, 250 );
Here's my Pen
I tried to use scrollMagic for the project on a scene with a pin and additional triggers but the scrolling wasn't very smooth. So I'm trying to rebuild it with a stripped-down version and debounced listeners. Is this approach possible, or should I rather try to optimize my scrollMagic scene?

As James points out, you can just use position: sticky as one option, but that doesn't work in older browsers and its uses are limited to simpler situations in newer browsers, so I'll continue with the JS solution assuming you want to go that route.
There is a lot going on in your JS, and I think you are probably overcomplicating things, so I will give you a few basics to consider.
When you are toggling things based on scroll, either toggle inline styles or a class, but not both. I would recommend toggling a class because it allows you to have one function that can work on multiple screen sizes (i.e., you can use media queries to change the behavior of your toggled class based on screen size). Also it keeps all your styles in one place instead of having them split between your JS and your stylesheet.
Try to keep the work you're doing while scrolling as minimal as possible. For example, cache references to elements in variables outside your scroll function so you're not continually looking them up every time you scroll a pixel. Avoid loops inside scroll functions.
Using setInterval is not generally the recommended approach for increasing performance on scroll functions. All that is going to do is run a function every X amount of time, all the time, whether you're scrolling or not. What you really want to do is rate-limit your scroll function directly. That way, if you scroll a long ways real fast your function will only be called a fraction of the total times it would otherwise be called, but if you scroll a short distance slowly it will still be called a minimum number of times to keep things looking smooth, and if you don't scroll at all then you're not calling your function at all. Also, you probably want to throttle your function in this case, not debounce it.
Consider using the throttle function from Underscore.js or Lodash.js instead of inventing your own because those ones are highly performant and guaranteed to work across a wide variety of browsers.
Here is a simple example of sticking an element to the top of the screen on scroll, throttled with Lodash. I'm using a 25ms throttle, which is about the maximum amount I'd recommend for keeping things looking smooth where you won't really notice the delay in the element sticking/unsticking as you scroll past your threshold. You could go down to as little as 10ms.
$(function() {
$(window).on('scroll', _.throttle(toggleClass, 25));
const myThing = $('#my-thing');
const threshold = $('#dummy-1').height();
function toggleClass() {
const y = window.scrollY;
if (y > threshold) {
myThing.addClass('stuck')
} else {
myThing.removeClass('stuck');
}
}
});
#dummy-1 {
height: 150px;
background-color: steelblue;
}
#dummy-2 {
height: 150px;
background-color: gold;
}
#my-thing {
width: 300px;
height: 75px;
background-color: firebrick;
position: absolute;
top: 150px;
left: 0;
}
#my-thing.stuck {
position: fixed;
top: 0;
}
body {
margin: 0;
height: 2000px;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.0.0/lodash.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="dummy-1"></div>
<div id="dummy-2"></div>
<div id="my-thing"></div>

You could try fixed or sticky CSS positioning:
#element {
position: fixed;
top: 80px;
left: 10px;
}
Position: fixed would keep the element always at 80px from the top and 10px from the left edge regardless of scroll position.
#element{
position: sticky;
top: 0;
right: 0;
left: 0;
}
This is from a project of mine. The element is a nav bar. It sits below a header bar, so when you are at the top of the page, you see the header then the nav below it, and as you scroll down, the header moves off screen but the nav sticks at the top and is always visible.

Changing an HTML element's style in JavaScript with its CSS transition temporarily disabled isn't reliably functioning [duplicate]

This question already has answers here:
How can I force WebKit to redraw/repaint to propagate style changes?
(33 answers)
Closed 4 years ago.
Currently I am working on an animation for a website which involves two elements having their position changed over a period of time and usually reset to their initial position. Only one element will be visible at a time and everything ought to run as smoothly as possible.
Before you ask, a CSS-only solution is not possible as it is dynamically generated and must be synchronised. For the sake of this question, I will be using a very simplified version which simply consists of a box moving to the right. I shall be referring only to this latter example unless explicitly stated for the remainder of this question to keep things simple.
Anyway, the movement is handled by the CSS transition property being set so that the browser can do the heavy lifting for that. This transition must then be done away with in order to reset the element's position in an instant. The obvious way of doing so would be to do just that then reapply transition when it needs to get moving again, which is also right away. However, this isn't working. Not quite. I'll explain.
Take a look at the JavaScript at the end of this question or in the linked JSFiddle and you can see that is what I'm doing, but setTimeout is adding a delay of 25ms in between. The reason for this is (and it's probably best you try this yourself) if there is either no delay (which is what I want) or a very short delay, the element will either intermittently or continually stay in place, which isn't the desired effect. The higher the delay, the more likely it is to work, although in my actual animation this causes a minor jitter because the animation works in two parts and is not designed to have a delay.
This does seem like the sort of thing that could be a browser bug but I've tested this on Chrome, Firefox 52 and the current version of Firefox, all with similar results. I'm not sure where to go from here as I have been unable to find this issue reported anywhere or any solutions/workarounds. It would be much appreciated if someone could find a way to get this reliably working as intended. :)
Here is the JSFiddle page with an example of what I mean.
The markup and code is also pasted here:
var box = document.getElementById("box");
//Reduce this value or set it to 0 (I
//want rid of the timeout altogether)
//and it will only function correctly
//intermittently.
var delay = 25;
setInterval(function() {
box.style.transition = "none";
box.style.left = "1em";
setTimeout(function() {
box.style.transition = "1s linear";
box.style.left = "11em";
}, delay);
}, 1000);
#box {
width: 5em;
height: 5em;
background-color: cyan;
position: absolute;
top: 1em;
left: 1em;
}
<div id="box"></div>

Force the DOM to recalculate itself before setting a new transition after reset. This can be achieved for example by reading the offset of the box, something like this:
var box = document.getElementById("box");
setInterval(function(){
box.style.transition = "none";
box.style.left = "1em";
let x = box.offsetLeft; // Reading a positioning value forces DOM to recalculate all the positions after changes
box.style.transition = "1s linear";
box.style.left = "11em";
}, 1000);
body {
background-color: rgba(0,0,0,0);
}
#box {
width: 5em;
height: 5em;
background-color: cyan;
position: absolute;
top: 1em;
left: 1em;
}
<div id="box"></div>
See also a working demo at jsFiddle.
Normally the DOM is not updated when you set its properties until the script will be finished. Then the DOM is recalculated and rendered. However, if you read a DOM property after changing it, it forces a recalculation immediately.
What happens without the timeout (and property reading) is, that the style.left value is first changed to 1em, and then immediately to 11em. Transition takes place after the script will be fihished, and sees the last set value (11em). But if you read a position value between the changes, transition has a fresh value to go with.

Instead of making the transition behave as an animation, use animation, it will do a much better job, most importantly performance-wise and one don't need a timer to watch it.
With the animation events one can synchronize the animation any way suited, including fire of a timer to restart or alter it.
Either with some parts being setup with CSS
var box = document.getElementById("box");
box.style.left = "11em"; // start
box.addEventListener("animationend", animation_ended, false);
function animation_ended (e) {
if (e.type == 'animationend') {
this.style.left = "1em";
}
}
#box {
width: 5em;
height: 5em;
background-color: cyan;
position: absolute;
top: 1em;
left: 1em;
animation: move_me 1s linear 4;
}
#keyframes move_me {
0% { left: 1em; }
}
<div id="box"></div>
Or completely script based
var prop = 'left', value1 = '1em', value2 = '11em';
var s = document.createElement('style');
s.type = 'text/css';
s.innerHTML = '#keyframes move_me {0% { ' + prop + ':' + value1 +' }}';
document.getElementsByTagName('head')[0].appendChild(s);
var box = document.getElementById("box");
box.style.animation = 'move_me 1s linear 4';
box.style.left = value2; // start
box.addEventListener("animationend", animation_ended, false);
function animation_ended (e) {
if (e.type == 'animationend') {
this.style.left = value1;
}
}
#box {
width: 5em;
height: 5em;
background-color: cyan;
position: absolute;
top: 1em;
left: 1em;
}
<div id="box"></div>

Display some element user scrolling

I would like to display some element (div for example) when the user scrolling.
I seeing that a scrollTop, but isn't work. Because for sure I use badly.
I can't find some help without JQuery. I don't want to use JQuery.
I try this :
var scroll = document.body.scrollTop;
var divLis = document.querySelectorAll("div");
for(let i = 0; i < divLis.length; i++) {
if(scroll === divLis[i]) {
divLis[i].style.transform = "translateX(0)";
divLis[i].style.transition = "2s";
}
}

I honestly can't really tell what you're trying to do, but given your response to #uom-pgregorio's answer, I'm guessing you might just want a pure JS scroll listener:
window.addEventListener('scroll', function() {});

Edit: Sorry I just noticed that you didn't want jQuery but I'll just leave this here in case you change your mind.
$(window).scroll(function() {
// show the div(s)
});
That's an event handler where the function runs or fires up whenever the window or viewport scrolls.

Ok... I understand.
I wanted to try this :
* {
margin: 0;
padding: 0;
border: 0;
}
body {
height: 200vh;
}
.left {
width: 300px;
height: 300px;
background-color: red;
position: absolute;
top: 150%;
transform: translateX(-300px);
transition: 5s;
}
// HTML :
<div class="left"></div>
// JS
var divLis = document.querySelector(".left");
window.addEventListener("scroll", function (e) {
if(window.pageYOffset > 500) {
console.log(window.pageYOffset)
divLis.style.transform = "translateX(0)";
}
})
So, it's very simple and I took my head for nothing.
So thanks so much for answering me !
Enjoy your Weekend

Temporarily disable all onclick events and bind them back

How to disable all onclick events on a page, bind my custom function, and after the execution enable all the previous events?
I'm building a bookmarklet, which should work on any already loaded page and I'm using jQuery to handle my custom logic (the page is jquerified after it is loaded). Note, that I don't have any control which events and when are being bound.
Currently the best stable solution i found is to unbind the events, bind by custom function preventing the default action and then, reload the page. This works, however I want to avoid the reload. A partial workaround would be to reload the page and scroll to the previous position (how to achieve this effect?). Some possible solution would use iframes, but I'd prefer to avoid this.

it's easier to lay a div-element over all... something like
CSS
.noclick {
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
z-index: 9999; /* or maybe higher */
background-color: transparent;
}
jQuery
jQuery(document).ready(function() {
jQuery('body').append('<div class="noclick" />');
});

A nice way I've seen it done, and done it myself is to use a modal 'mask' overlay.
The grayed out transparent mask that covers the entire page, except for the element you're interacting with, eg. modal popup window.
One more way is to use the jQuery BlockUI plugin.

You can reassign the onclick to another property and than override it.
Example with one element
var btn = document.getElementById("button");
btn._onclick = btn.onclick;
btn.onclick = function(){ return false; };
and when you want to transfer it back to the original event
var btn = document.getElementById("button");
if (btn._onclick) {
btn.onclick = btn._onclick;
btn._onclick = null;
}

It depends on whether your onclick event is dependent on the element being clicked (i.e. whether it needs to know which element was clicked):
If it's independent, then you can just add an event handler to the body element or other parent (because the parent event gets called first, then the child, which is what you want):
$('body').click(function() { /* your code here */});
It it is dependent on the the element, then you can access the previous onclick event code that has been registered in the 'click' property of element which is being clicked, so something like this (probably being a little more specific with the selectors):
$('body *').each(function() {
var previousClick = this.click;
this.click = null; // remove previous
$(this).click(function() { /* your code here */});
$(this).click(function() { previousClick();}); // run the code that was already there.
})

Some modification algorhythm's answer.
The idea is to "cover" the link by a transparent element. You can use a pseudo element (e.g. :after).
To prevent "tab key" set tabindex:
<a href="..." tabindex="-1">
Mark link with a class "disabled" on click:
$('a').on('click', function(){ $(this).addClass('disabled') })
Add css:
a.disabled:after {
position: absolute;
content: "";
display: block;
background: white;
opacity: 0.5; // optional
z-index: 999;
left: 0;
top: 0;
bottom: 0;
right: 0;
}
$('a').on('click', function(){ $(this).addClass('disabled') });
a.disabled:after {
position: absolute;
content: "";
display: block;
background: white;
opacity: 0.5; // optional
z-index: 999;
left: 0;
top: 0;
bottom: 0;
right: 0;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<a hreh="#" tabindex="-1">The Link</a>

Wait cursor over entire html page

Is it possible to set the cursor to 'wait' on the entire html page in a simple way? The idea is to show the user that something is going on while an ajax call is being completed. The code below shows a simplified version of what I tried and also demonstrate the problems I run into:
if an element (#id1) has a cursor style set it will ignore the one set on body (obviously)
some elements have a default cursor style (a) and will not show the wait cursor on hover
the body element has a certain height depending on the content and if the page is short, the cursor will not show below the footer
The test:
<html>
<head>
<style type="text/css">
#id1 {
background-color: #06f;
cursor: pointer;
}
#id2 {
background-color: #f60;
}
</style>
</head>
<body>
<div id="id1">cursor: pointer</div>
<div id="id2">no cursor</div>
Do something
</body>
</html>
Later edit...
It worked in firefox and IE with:
div#mask { display: none; cursor: wait; z-index: 9999;
position: absolute; top: 0; left: 0; height: 100%;
width: 100%; background-color: #fff; opacity: 0; filter: alpha(opacity = 0);}
<a href="#" onclick="document.getElementById('mask').style.display = 'block'; return false">
Do something</a>
The problem with (or feature of) this solution is that it will prevent clicks because of the overlapping div (thanks Kibbee)
Later later edit...
A simpler solution from Dorward:
.wait, .wait * { cursor: wait !important; }
and then
Do something
This solution only shows the wait cursor but allows clicks.

If you use this slightly modified version of the CSS you posted from Dorward,
html.wait, html.wait * { cursor: wait !important; }
you can then add some really simple jQuery to work for all ajax calls:
$(document).ready(function () {
$(document).ajaxStart(function () { $("html").addClass("wait"); });
$(document).ajaxStop(function () { $("html").removeClass("wait"); });
});
or, for older jQuery versions (before 1.9):
$(document).ready(function () {
$("html").ajaxStart(function () { $(this).addClass("wait"); });
$("html").ajaxStop(function () { $(this).removeClass("wait"); });
});

I understand you may not have control over this, but you might instead go for a "masking" div that covers the entire body with a z-index higher than 1. The center part of the div could contain a loading message if you like.
Then, you can set the cursor to wait on the div and don't have to worry about links as they are "under" your masking div. Here's some example CSS for the "masking div":
body { height: 100%; }
div#mask { cursor: wait; z-index: 999; height: 100%; width: 100%; }

This seems to work in firefox
<style>
*{ cursor: inherit;}
body{ cursor: wait;}
</style>
The * part ensures that the cursor doesn't change when you hover over a link. Although links will still be clickable.

I have been struggling with this problem for hours today.
Basically everything was working just fine in FireFox but (of course) not in IE.
In IE the wait cursor was showing AFTER the time consuming function was executed.
I finally found the trick on this site:
http://www.codingforums.com/archive/index.php/t-37185.html
Code:
//...
document.body.style.cursor = 'wait';
setTimeout(this.SomeLongFunction, 1);
//setTimeout syntax when calling a function with parameters
//setTimeout(function() {MyClass.SomeLongFunction(someParam);}, 1);
//no () after function name this is a function ref not a function call
setTimeout(this.SetDefaultCursor, 1);
...
function SetDefaultCursor() {document.body.style.cursor = 'default';}
function SomeLongFunction(someParam) {...}
My code runs in a JavaScript class hence the this and MyClass (MyClass is a singleton).
I had the same problems when trying to display a div as described on this page. In IE it was showing after the function had been executed. So I guess this trick would solve that problem too.
Thanks a zillion time to glenngv the author of the post. You really made my day!!!

Easiest way I know is using JQuery like this:
$('*').css('cursor','wait');

css: .waiting * { cursor: 'wait' }
jQuery: $('body').toggleClass('waiting');

Why don't you just use one of those fancy loading graphics (eg: http://ajaxload.info/)? The waiting cursor is for the browser itself - so whenever it appears it has something to do with the browser and not with the page.

To set the cursor from JavaScript for the whole window, use:
document.documentElement.style.cursor = 'wait';
From CSS:
html { cursor: wait; }
Add further logic as needed.

Try the css:
html.waiting {
cursor: wait;
}
It seems that if the property body is used as apposed to html it doesn't show the wait cursor over the whole page. Furthermore if you use a css class you can easily control when it actually shows it.

Here is a more elaborate solution that does not require external CSS:
function changeCursor(elem, cursor, decendents) {
if (!elem) elem=$('body');
// remove all classes starting with changeCursor-
elem.removeClass (function (index, css) {
return (css.match (/(^|\s)changeCursor-\S+/g) || []).join(' ');
});
if (!cursor) return;
if (typeof decendents==='undefined' || decendents===null) decendents=true;
let cname;
if (decendents) {
cname='changeCursor-Dec-'+cursor;
if ($('style:contains("'+cname+'")').length < 1) $('<style>').text('.'+cname+' , .'+cname+' * { cursor: '+cursor+' !important; }').appendTo('head');
} else {
cname='changeCursor-'+cursor;
if ($('style:contains("'+cname+'")').length < 1) $('<style>').text('.'+cname+' { cursor: '+cursor+' !important; }').appendTo('head');
}
elem.addClass(cname);
}
with this you can do:
changeCursor(, 'wait'); // wait cursor on all decendents of body
changeCursor($('#id'), 'wait', false); // wait cursor on elem with id only
changeCursor(); // remove changed cursor from body

I used a adaptation of Eric Wendelin's solution. It will show a transparent, animated overlay wait-div over the whole body, the click will be blocked by the wait-div while visible:
css:
div#waitMask {
z-index: 999;
position: absolute;
top: 0;
right: 0;
height: 100%;
width: 100%;
cursor: wait;
background-color: #000;
opacity: 0;
transition-duration: 0.5s;
-webkit-transition-duration: 0.5s;
}
js:
// to show it
$("#waitMask").show();
$("#waitMask").css("opacity"); // must read it first
$("#waitMask").css("opacity", "0.8");
...
// to hide it
$("#waitMask").css("opacity", "0");
setTimeout(function() {
$("#waitMask").hide();
}, 500) // wait for animation to end
html:
<body>
<div id="waitMask" style="display:none;"> </div>
... rest of html ...

My Two pence:
Step 1:
Declare an array. This will be used to store the original cursors that were assigned:
var vArrOriginalCursors = new Array(2);
Step 2:
Implement the function cursorModifyEntirePage
function CursorModifyEntirePage(CursorType){
var elements = document.body.getElementsByTagName('*');
alert("These are the elements found:" + elements.length);
let lclCntr = 0;
vArrOriginalCursors.length = elements.length;
for(lclCntr = 0; lclCntr < elements.length; lclCntr++){
vArrOriginalCursors[lclCntr] = elements[lclCntr].style.cursor;
elements[lclCntr].style.cursor = CursorType;
}
}
What it does:
Gets all the elements on the page. Stores the original cursors assigned to them in the array declared in step 1. Modifies the cursors to the desired cursor as passed by parameter CursorType
Step 3:
Restore the cursors on the page
function CursorRestoreEntirePage(){
let lclCntr = 0;
var elements = document.body.getElementsByTagName('*');
for(lclCntr = 0; lclCntr < elements.length; lclCntr++){
elements[lclCntr].style.cursor = vArrOriginalCursors[lclCntr];
}
}
I have run this in an application and it works fine.
Only caveat is that I have not tested it when you are dynamically adding the elements.

BlockUI is the answer for everything. Give it a try.
http://www.malsup.com/jquery/block/

This pure JavaScript seems to work pretty well ... tested on FireFox, Chrome, and Edge browsers.
I'm not sure about the performance of this if you had an overabundance of elements on your page and a slow computer ... try it and see.
Set cursor for all elements to wait:
Object.values(document.querySelectorAll('*')).forEach(element => element.style.cursor = "wait");
Set cursor for all elements back to default:
Object.values(document.querySelectorAll('*')).forEach(element => element.style.cursor = "default");
An alternative (and perhaps a bit more readable) version would be to create a setCursor function as follows:
function setCursor(cursor)
{
var x = document.querySelectorAll("*");
for (var i = 0; i < x.length; i++)
{
x[i].style.cursor = cursor;
}
}
and then call
setCursor("wait");
and
setCursor("default");
to set the wait cursor and default cursor respectively.

Lots of good answers already, but none of them mentions the <dialog> element.
Using this element we can create a solution similar to the masking <div>.
Here we use showModal() to "hide" elements, and we use ::backdrop to set the cursor style to wait on the entire page:
function showWaitDialog() {
document.getElementById('id_dialog').showModal();
}
#id_dialog, #id_dialog::backdrop {
cursor: wait;
}
<button onclick="showWaitDialog()">click me</button>
<dialog id="id_dialog">busy...</dialog>
The dialog is hidden by default, and can be shown using either the show() method, or the showModal() method, which prevents clicking outside the dialog.
The dialog can be forced to close using the close() method, if necessary.
However, if your button links to another page, for example, then the dialog will disappear automatically as soon as the new page is loaded.
Note that the dialog can also be closed at any time by hitting the Esc key.
CSS can be used to style the dialog however you like.
The example uses the html onclick attribute, just for simplicity. Obviously, addEventListener() could also be used.

Late to the party but simply give the Html tag an id by targeting
document.documentElement
and in the CSS place at the top
html#wait * {
cursor: wait !important;
}
and simply remove it when you want to stop this cursor.