let wheelObserverOptions = {
root: dateWheelNode,
rootMargin: '100px',
}
const dateWheelObserver = new IntersectionObserver(wheelObserverCallback, wheelObserverOptions);
// const dateWheelPastDateObserver = new IntersectionObserver(wheelObserverCallback, wheelObserverOptions);
function wheelObserverCallback(entries, observer) {
entries.forEach(entry => {
if(entry.isIntersecting) {
debugMsg('triggered')
if (entry.target === dateWheelNode.lastChild) loadFutureDates()
if (entry.target === dateWheelNode.firstChild) loadPastDates()
// observer.unobserve(entry.target)
}
});
};
prepending new elements when scrolling the dateWheelNode - which is the parent container
function loadPastDates() {
dateWheelDateFuture.subtract(1,'day')
dateWheelDatePast.subtract(1,'day')
wheelCheckDays(dateWheelDatePast)
}
appending
function loadFutureDates() {
dateWheelDateFuture.add(1,'day')
dateWheelDatePast.add(1,'day')
wheelCheckDays(dateWheelDateFuture)
}
now regardless if prepending or appending this is in the wheelCheckDays() function (which works as intended)
dateWheelNode.scroll(0, dateWheelNode.scrollTop);
dateWheelObserver.observe(dateWheelElementDOM);
this also makes sure regardless of the scrolling direction the elements do not jump and the scrolling remains smooth (works on chrome & edge) and is on the bottom of wheelCheckDays() after
also dateWheelNode gets initial 30 elements when opening it with (and which are not being removed - only if appending/prepending additional ones by scrolling)
for (let i = 0; i <= 30; i++ ) {
if (i === 0) {
wheelCheckDays(dateWheelDateFuture, true)
wheelYearObserver.observe(document.querySelector(`.dateWheelDay${dateWheelDateFuture.format("YYYYMMDD")}`));
wheelMonthObserver.observe(document.querySelector(`.dateWheelDay${dateWheelDateFuture.format("YYYYMMDD")}`));
} else if (i > 0 && i <= 15) {
dateWheelDatePast.subtract(1,'day')
wheelCheckDays(dateWheelDatePast, true)
} else if (i > 15) {
dateWheelDateFuture.add(1,'day')
wheelCheckDays(dateWheelDateFuture, true)
}
}
besides that dateWheelNode has the height set to min(350px, 80%)
other than that wheelCheckDays() function does modify the new elements before prepending/appending it and removes the last or first child of dateWheelNode every time depending on if a element gets appended a prepended
now my problem is that on chrome and edge kinda works as it tends occasionally to stop the scrolling abruptly and sometimes (rarely) scroll infinitely upwards, but on firefox it happens 100% of times and additionally when scrolling down (loadFutureDates()) the scrolling is not smooth at all and does jump dates very fast at once too and when scrolling upwards loadPastDates() it scrolls infinitely and won't stop until scrolling down
what I'm missing here and how to fix the infinite automatic scroll and smooth scrolling (still though not throttling the scrolling in order to be able to switch the dates fast too - just like normal scrolling behaviour)
changing dateWheelNode.scroll(0, dateWheelNode.scrollTop) into dateWheelNode.scroll({top: dateWheelNode.scrollTop, behaviour: 'smoooth'}) does not help with that scrolling either as the infinite scroll upwards happens then on all browsers
PS: it is intentioned being viewed mostly on mobile, but the issues described happens also on desktop
PS2: couldn't really post a working example as the code is a mess and I've cut out the (seemingly) important parts of it and and that's also why the solution/answer shouldn't be a totally different approach (unless the rewriting wouldn't take too much time) and also not over complicated as I'm still a junior dev
UPDATE: I managed to make a a example on jsfiddle
https://jsfiddle.net/DadoIrie/a8cge9o6/34/
best way to test that scrolling issue is just move the scrollbar on top with firefox - it just starts scrolling infinitely - while chrome doesn't even allow to bring the scrollbar on top - bottom works perfectly
UPDATE (temporary ugly solution) well, temporary solution is if (dateWheelNode.scrollTop < 1) document.querySelector('#dateWheelDays').scroll(0, 100); ... which is quite ugly, but at least stops firefox from infinitely auto-scroll upwards
still open for sugestions regarding this
I need to know if the end of a div element is currently visible in the users' browser.
I tried something I saw on the web, but scrollTop() always gave me zero in my Browser. I read something about an issue in Chrome, but I didn't understand quite well.
jQuery(
function($) {
$('#flux').bind('scroll', function() {
if ($(this).scrollTop() + $(this).innerHeight() >= $(this)[0].scrollHeight) {
alert('end reached');
}
})
}
);
My idea is the following:
1- User loads page and sees a Bar (sticky div at bottom visible page) with some information.
2- After scrolling a bit, and reaching the end of a div element, this bar will position there, after the div. This is the bar's original position
I wasn't really able to know when I was at the end of the div element. Eventually I found this code:
if ($(window).scrollTop() >= $('#block-homepagegrid').offset().top + $('#block-homepagegrid').outerHeight() - window.innerHeight) {
$('.hero-special-message').removeClass('hero-special-messege-scrolling');
} else {
$('.hero-special-message').addClass('hero-special-messege-scrolling');
}
});
I see that it's working, but I'm having a bit of trouble understanding what it does.
I know the following:
1. $(window).scrollTop();
this gives me the amount of pixels the user has scrolled, pretty self explanatory.
2. $('#block-homepagegrid').offset().top;
I THINK this is the distance between the start of the page and the start of the div. I know it's the current coordinates, but what is top exactly here?
3. $('#block-homepagegrid').outerHeight();
this gives the height of the element, I know there are 3, like
height(), innerHeight() and outerHeight(), if you want to take into
account border, margin, padding, which is the better to use?
4. window.innerHeight;
I understand this is what the user sees, but I'm having troubles understanding why does it matter for my situation.
Thanks!
You may be interested in the native JavaScript IntersectionObserver API. It automatically figures out what percentage of a given element is visible in the window and triggers callbacks based on that. So then you can do this:
function visibleHandler(entries) {
if (entries[0].intersectionRatio >= 1.0) {
// The whole element is visible!
} else {
// Part of it is scrolled offscreen!
}
}
const observer = new IntersectionObserver(visibleHandler, {threshold: 1.0});
observer.observe(document.getElementById('flux'));
Now, whenever the element with ID flux is 100% in view, it will trigger the visibleHandler. It will also trigger again if it's scrolled back out of view; that's why the function checks the ratio of visibility to see if it just hit 100% or just got reduced from 100%. You could be more fancy and use the observer entry's insersectionRect, which gives you the rectangle containing the visible portion of the element, and use that to determine top/bottom visibility.
I'm updating a table header and its first column positions programatically based on how the user scrolls around to keep them aligned.
The issue I'm experiencing is that as soon as my data sets gets big enough, the scrolling gets more and more choppy/less smooth.
The relevant code is at the very bottom of the fiddle:
iScroll.on('scroll', function(){
var pos = $('#scroller').position();
$('#pos').text('pos.left=' + pos.left + ' pos.top=' + pos.top);
// code to hold first row and first column
$('#scroller th:nth-child(1)').css({top: (-pos.top), left: (-pos.left), position:'relative'});
$('#scroller th:nth-child(n+1)').css({top: (-pos.top), position:'relative'});
// this seems to be the most expensive operation:
$('#scroller td:nth-child(1)').css({left: (-pos.left), position:'relative'});
});
I know that this can be written a lot more efficent by caching the elements and so on. For example, I have tried saving the elements in to an array and updating their position in a more "vanilla" fashion:
headerElements[i].style.left = left + 'px'; // etc...
No matter how fast I make the callback, I'm still not happy about the result. Do you have any suggestions?
https://jsfiddle.net/0qv1kjac/16/
Just use ClusterizeJS! It can handle hundreds of thousands of rows and was built exactly for this purpose.
How does it work, you ask?
The main idea is not to pollute DOM with all used tags. Instead of that - it splits the list to clusters, then shows elements for current scroll position and adds extra rows to top and bottom of the list to emulate full height of table so that browser shows scrollbar as for full list
To be able to handle big amounts of data you need data virtualization. It has some restrictions, though.
First you need to decide the size of a view port. Let's say you want to render 10 items in a row and 20 items in column. It would be 10x20 items then. In you fiddle it's div with id wrapper.
Then you need to know total amount of data you have. From your fiddle it would be 100x100 items. And, also you need to know height and width of a item (cell). Let's take 40x120 (in px).
So div#wrapper is a view port, it should have fixed sized like 10x20 items. Then you need to set up correct width and height for table. The height of table would be equal to total amount of data in column including head by item height. Width for table would be total amount of items in single row by item width.
Once you set up these, div#wrapper will receive horizontal and vertical scrolls. Now you able to scroll left and bottom, but it will be just empty space. However this empty space is able to hold exact amount of data you have.
Then you need to take scroll data left and top (position), which comes in pixels and normalize it to amount of items, so you could know not how many pixels you've scrolled, but how many items you've scrolled(or rows if we scroll from top to bottom).
It could be done by division of pixels scrolled on item height. For example, you scrolled to left by 80px, that's 2 items. It means these items should be invisible because you've scrolled past them. So you know that you scrolled past 2 items, and you know that you should see 10 items in a row. That means you take your data array which has data for row with 100 items, and slice it like this:
var visibleItems = rowData.slice(itemsScrolled, itemsScrolled + 10);
It will give you items which should be visible in viewport at current scroll position. Once you have these items you need to construct html and append it to table.
Also on each scroll event you need to set top and left position for tbody and thead so they would move with scroll, otherwise you will have your data, but it will be at (0; 0) inside a viewport.
Anyway, code speaks thousand of words, so here's the fiddle: https://jsfiddle.net/Ldfjrg81/9/
Note, that this approach requires heights and widths to be precise, otherwise it will work incorrectly. Also if you have items of different sizes, this also should be taken into consideration, so better if you have fixed and equal sizes of items. In jsfiddle, I commented out the code which forces first column to stay in place, but you can render it separately.
It's a good solution to stick to some library as suggested in comments, since it handles a lot of cases for you.
You can make rendering even faster if use react.js or vue.js
This won't be the answer your are looking for but here's my 2 cents anyway.
Javascript animation (especially given the amount that the DOM has to render) will never be as smooth as you want it. Even if you could get it smooth on your machine, chances are that it will vary drastically on other peoples (Older PC's, Browsers etc).
I would see 2 options if I were to tackle this myself.
Go old school and add a horizontal and vertical scrollbar. I know it's not a pretty solution but it would work well.
Only render a certain amount of rows and discard those off screen. This could be a bit complicated but in essence you would render say 10 rows. Once the user scrolls to a point where the 11th should be there, render that one and remove the 1st. You would pop them in and out as needed.
In terms of the actual JS (you mentioned putting elements in to an array), that isn't going to help. The actual choppyness is due to the browser needing to render that many elements in the first place.
You're experiencing choppy / non-smooth scrolling because the scroll event fires at a very high pace.
And every time it fires you're adjusting the position of many elements: this is expensive and furthermore until the browser has completed the repaint it's unresponsive (here the choppy scrolling).
I see two options:
Option number one: display only the visible subset of the whole data set (this has been already suggested in another answer so I won't go futher)
Option number two (easier)
First, let animations on left and top css changes occurr via transitions. This is more efficient, is non-blocking and often let the browser take advantage of the gpu
Then instead of repeteadly adjust left and top, do it once a while; for example 0.5 seconds. This is done by the function ScrollWorker() (see code below) that recalls itself via a setTimeout().
Finally use the callback invoked by the scroll event to keep the #scroller position (stored in a variable) updated.
// Position of the `#scroller` element
// (I used two globals that may pollute the global namespace
// that piece of code is just for explanation purpose)
var oldPosition,
newPosition;
// Use transition to perform animations
// You may set this in the stylesheet
$('th').css( { 'transition': 'left 0.5s, top 0.5s' } );
$('td').css( { 'transition': 'left 0.5s, top 0.5s' } );
// Save the initial position
newPosition = $('#scroller').position();
oldPosition = $('#scroller').position();
// Upon scroll just set the position value
iScroll.on('scroll', function() {
newPosition = $('#scroller').position();
} );
// Start the scroll worker
ScrollWorker();
function ScrollWorker() {
// Adjust the layout if position changed (your original code)
if( newPosition.left != oldPosition.left || newPosition.top != oldPosition.top ) {
$('#scroller th:nth-child(1)').css({top: (-newPosition.top), left: (-newPosition.left), position:'relative'});
$('#scroller th:nth-child(n+1)').css({top: (-newPosition.top), position:'relative'});
$('#scroller td:nth-child(1)').css({left: (-newPosition.left), position:'relative'});
// Update the stored position
oldPosition.left = newPosition.left;
oldPosition.top = newPosition.top;
// Let animation complete then check again
// You may adjust the timer value
// The timer value must be higher or equal the transition time
setTimeout( ScrollWorker, 500 );
} else {
// No changes
// Check again after just 0.1secs
setTimeout( ScrollWorker, 100 );
}
}
Here is the Fiddle
I set the Worker pace and the transition time to 0.5 secs. You may adjust the value with higher or lower timing, eventually in a dinamic way based on the number of elements in the table.
Yes! Here are some improvements to the code from your JS Fiddle. You can view my edits at: https://jsfiddle.net/briankueck/u63maywa/
Some suggested improvements are:
Switching position:relative values in the JS layer to position:fixed in the CSS layer.
Shortening the jQuery DOM chains, so that the code doesn't start at the root element & walk all the way through the dom with each $ lookup. The scroller is now the root element. Everything uses .find() off of that element, which creates shorter trees & jQuery can traverse those branches faster.
Moving the logging code out of the DOM & into the console.log. I've added a debugging switch to disable it, as you're looking for the fastest scrolling on the table. If it runs fast enough for you, then you can always re-enable it to see it in the JSFiddle. If you really need to see that on the iPhone, then it can be added into the DOM. Although, it's probably not necessary to see the left & top position values in the iPhone.
Remove all extraneous $ values, which aren't mapped to the jQuery object. Something like $scroller gets confusing with $, as the latter is the jQuery library, but the former isn't.
Switching to ES6 syntax, by using let instead of var will make your code look more modern.
There is a new left calculation in the <th> tag, which you'll want to look at.
The iScroll event listener has been cleaned up. With position:fixed, the top <th> tags only need to have the top property applied to them. The left <td> tags only need to have the left property applied to them. The corner <th> needs to have both the top & left property applied to it.
Remove everything that's unnecessary, like the extraneous HTML tags which were used for logging purposes.
If you really want to go more vanilla, change out the .css() methods for the actual .style.left= -pos.left + 'px'; and .style.top= -pos.top + 'px'; properties in the JS code.
Try using a diff tool like WinMerge or Beyond Compare to compare the code from your version to what's in my edits, so that you can easily see the differences.
Hopefully, this will make the scrolling smoother, as the scroll event doesn't have to process anything that it doesn't need to do... like 5 full DOM traversing look-ups, rather than 3 short-tree searches.
Enjoy! :)
HTML:
<body>
<div id="wrapper">
<table id="scroller">
<thead>
</thead>
<tbody>
</tbody>
</table>
</div>
</body>
CSS:
/* ... only the relevant bits ... */
thead th {
background-color: #99a;
min-width: 120px;
height: 32px;
border: 1px solid #222;
position: fixed; /* New */
z-index: 9;
}
thead th:nth-child(1) {/*first cell in the header*/
border-left: 1px solid #222; /* New: Border fix */
border-right: 2px solid #222; /* New: Border fix */
position: fixed; /* New */
display: block; /*seperates the first cell in the header from the header*/
background-color: #88b;
z-index: 10;
}
JS:
// main code
let debug = false;
$(function(){
let scroller = $('#scroller');
let top = $('<tr/>');
for (var i = 0; i < 100; i++) {
let left = (i === 0) ? 0 : 1;
top.append('<th style="left:' + ((123*i)+left) + 'px;">'+ Math.random().toString(36).substring(7) +'</th>');
}
scroller.find('thead').append(top);
for (let i = 0; i < 100; i++) {
let row = $('<tr/>');
for (let j = 0; j < 100; j++) {
row.append('<td>'+ Math.random().toString(36).substring(7) +'</td>');
}
scroller.find('tbody').append(row);
}
if (debug) console.log('initialize iscroll');
let iScroll = null;
try {
iScroll = new IScroll('#wrapper', {
interactiveScrollbars: true,
scrollbars: true,
scrollX: true,
probeType: 3,
useTransition:false,
bounce:false
});
} catch(e) {
if (debug) console.error(e.name + ":" + e.message + "\n" + e.stack);
}
if (debug) console.log('initialized');
iScroll.on('scroll', function(){
let pos = scroller.position();
if (debug) console.log('pos.left=' + pos.left + ' pos.top=' + pos.top);
// code to hold first row and first column
scroller.find('th').css({top:-pos.top}); // Top Row
scroller.find('th:nth-child(1)').css({left:-pos.left}); // Corner
scroller.find('td:nth-child(1)').css({left:-pos.left}); // 1st Left Column
});
});
Is it necessary that you create your own scroller? Why don't you just style the data in HTML/CSS and just use the overflow attribute? JavaScript needs work on it's ability to adjust framerates. I was using your jFiddle earlier and it worked just fine with the native overflow handler.
Found this in the manual. Probably not what you wanna hear but it's the way it is:
IScroll is a class that needs to be initiated for each scrolling area. There's no limit to the number of iScrolls you can have in each page if not that imposed by the device CPU/Memory.
Try to keep the DOM as simple as possible. iScroll uses the hardware compositing layer but there's a limit to the elements the hardware can handle.
The reason the performance degradation is happening is that your scroll event handler is firing again and again and again instead of waiting for a reasonable and imperceptible interval.
The screenshot shows what happened when I tracked how many times the event handler fired, while scrolling for just a few seconds. The computationally-heavy event handler was fired over 600 times!!! This is more than 60 times per second!!!
It may seem counter-intuitive, but reducing the frequency that the table is updated will vastly increase perceived response times. If your user scrolls for fraction of a second, about 150 milliseconds, and the table is updated ten times, freezing the display during the scrolling, the net result is far worse than if the table were updated only three times and moved fluidly rather than freezing. It is just wasted processor burn to update more times than the browser can handle without freezing.
So, how do you make an event handler that fires at a maximum frequency, for example 25 times per second, even it is triggered much more often, like 100 times per second?
The naive way of doing it is to run a setInterval event. That is better, but horribly inefficient as well. There is a better way of doing it, by setting a delayed event handler, and clearing it on subsequent invocations before setting it again, until the minimum time interval has passed. This way it only runs no more often than at the maximum desired frequency. This is one major case for why the ``clearInterval'' method was invented.
Here is live working code:
https://jsfiddle.net/pgjvf7pb/7/
Note: when refreshing continuously like this, the header column may appear out of position.
I advise to do the update only when the scrolling has paused for about 25ms or so, rather than continuously. This way, it appears to the user that the header column is dynamically calculated as well as being fixed in place, because it appears instantly after scrolling rather than seeming to scroll with the data.
https://jsfiddle.net/5vcqv7nq/2/
The logic is like this:
variables outside your event handler
// stores the scrolling operation for a tiny delay to prevent redundancy
var fresh;
// stores time of last scrolling refresh
var lastfresh = new Date();
operations inside your event handler
// clears redundant scrolling operations before they are applied
if (fresh) clearTimeout(fresh);
var x = function() {
// stores new time of scrolling refresh
lastfresh = new Date();
// perform scrolling update operations here...
};
// refresh instantly if it is more than 50ms out of date
if (new Date() - lastfresh > 50) x();
// otherwise, pause for half of that time to avoid wasted runs
else fresh = setTimeout(x, 25);
Demo: https://jsfiddle.net/pgjvf7pb/7/
Once again, I recommend that you remove the line of code that refreshes the data instantly, and the else condition after that, and simply use one line
fresh = setTimeout(x, 25);
This will appear to instantly calculate the header column the moment any scrolling is finished, and saves even more operations. My second link to JS Fiddle shows what this looks like, here: https://jsfiddle.net/5vcqv7nq/2/
I don't know what this scrolling effect is called so don't know how to search for my answer, and I can't find it in the source code. What is the code responsible for the scrolling effect at Paragon where scrolling will cause the page to scroll down to the next div I assume. Or down a certain height.
I've thrown together a CodePen. It hase no animations but explains the general mechanics (the Paragon site does it differently but to start the following might be better suited).
The core part is this:
window.onwheel = function ( e ) {
e.preventDefault();
var wDelta = e.deltaY > 0 ? 'down' : 'up';
if (wDelta === "down") {
// scroll Down
} else {
// scroll Up
}
}
To know where to scroll we'll of course need to know where we are. There are several ways to do that. What I did is check the current top of the viewport against it's height.
var offset = window.pageYOffset,
viewportHeight = document.documentElement.clientHeight;
switch (parseInt(offset/viewportHeight,0)) {
case 0:
// we are in the first viewport
break;
case 1:
// we are in the second viewport
break;
...
}
I just checked it for functionality. Performance wise it can be improved upon. You should also bind keydown (to catch pageUp, pageDown, space and so on) but it can be done in a similar fashion. To ensure backwards compatibility you'll need to expand the code (e.g. a binding to the onmousewheel event). But this will give you a place to start.
PS
Also consider what behaviour you want when reloading the page (if the user reloads while between viewports it will stay between them until another scroll occurs).
This answer could also interest you.
I have a content slideshow:
slide container
|--> wrapper
|------> slide1, slide2, etc.
that works as simple as calculating wrapper's position X and slide's position X to determine where to slide the wrapper for the next/previous slide to show up within container's viewport. It's pretty straight forward.
For Firefox and Chrome I am using CSS3 transform and transition-duration to animate the slides. Everything works perfect. Almost.
The problem is only when I click next button very fast. I am using jQuery's
$(selector).position().left
to read the slide's position X (left) and position becomes 0 (instead of expected, say, 300px). I do have a flag isAnimating to prevent users from going too fast but that does not help either. It does prevent from scrolling content too fast but position left may still be 0 as if something else is causing it to fail to determine.
I did a brief search and discovered that if it was image being loaded, some browsers would fail to determine its position until loading is over. However, each slide has an image but inside of it. The slide's CSS seems to have all widths and margins set fine.
The question is why may this be happening based on the scenario I described and possibly what can be improved to determine position X at all times for Firefox, Chrome browsers?
I've decided that if offsetLeft is not reliable for me at all times, I could use width of an element and its index position within container to figure out position X
var newWrapperPos = undefined;
$(lotWrapper).children('div').each(function(index){
if($(this).attr("id") === "slot"+id){
var width = $(this).width();
newWrapperPos = index * width;
return false;
}
});
//now I can shift wrapper to position = newWrapperPos
Sorry I couldn't share the code - it is a bit time consuming to rip off all pieces of functionality involved. But if somebody has a better answer, let me know. For now this works fine for me.