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/
So I have these DIVs which I have arranged to slide left an right inside of the parent.
See the following JSFiddle to see the design:
http://jsfiddle.net/StevP/C9WL7/
You can see that by adjusting the margin-left of the first child DIV by multiples of -100%, it's rather simple to correctly horizontally position the DIVs inside the parent. Therefore, it's very easy to animate.
Now, this brings me to my issue. I'm using jQuery to move them left and right. It works great. However, I'd like to choose which child the parent gets its height from.
I know, I can just add...
$('#parent').height($('.child:eq()').outerHeight());
...Which is what I have it currently doing. However, the contents of the children are likely to change causing them to resize (by animate) and, therefore, be cut off. So, having a set height isn't a possibility.
I need to use height:auto; on the parent and somehow cause it to ignore the heights of specific children. I can't for the life of me think of a way.
I don't want to use a timer and onresize/.resize() don't seem to work with my Chrome.
You could use jQuery to monitor the DOM subtree and adjust the height of your parent div in the callback like this:
$('.content').bind('DOMSubtreeModified', function(e) {
if (e.target.innerHTML.length > 0) {
$(".parent").height($(".content").height());
}
});
Here's a working jsfiddle: http://jsfiddle.net/9386d/
And a question explaining the dom subtree: jQuery watch for domElement changes?
jQuery docs for bind(): http://api.jquery.com/bind/
Well... To be perfectly honest I'm not really a huge fan of jQuery anymore so I feel bad offering this answer. It just feels so frik'n inefficient, but here is a solution that does three things: 1) it resizes the hight of the container on step and uses a CSS transition attribute for eye candy (works just as well without). 2) it sets the child height of all but the current child to 0 and uses overflow:hidden so they don't affect the flow of the document anymore. 3) it resets these children to automatic height on animation start so they are visible during transition. All I can say is "yuck", but it does work.
CSS
.child{
...
overflow:hidden;
}
jQuery
var animation_prefs = {
duration: 3000,
start: function() {
$('.child').height('auto');
},
step: function(now) {
var current_index = (Math.floor((now + 50) / 100) * -1);
$('#parent').height($('.child:eq(' + current_index + ')').outerHeight());
$('#parent').data('current', current_index);
},
complete: function() {
$('#parent').height('auto');
$('.child:not(:eq('+$('#parent').data('current')+'))').height(0);
}
}
$('.child:eq(0)').animate(
{
marginLeft:'-200%' //~ Move it back 2 children
},
animation_prefs
).animate(
{
marginLeft:'-100%' //~ Move it back 1 child
},
animation_prefs
).animate(
{
marginLeft:'-200%' //~ Move it back 2 children again
},
animation_prefs
);
Demo
http://jsfiddle.net/Gq4xs/show
Source
http://jsfiddle.net/Gq4xs/
I am using wordpress, and we have there dynamic sidebar. in the sidebar we have many widgets. what am I trying to do is to show the divis (widgets) that visible on the screen (onload - after the page is load). the others widgets will be hidden(opacity 0 or something like that) but when I will scroll I want that widget(that was not visible on screen) will appear in fade effect.
I using this code that hide all my sidebar block is on opacity=0 on load.
I need help to show always all widgets that is visible on screen and then make the fade effect on scroll to others.
$(document).ready(function(){
tiles = $("#sidebar1 div").fadeTo(0, 0);
});
$(window).scroll(function(d,h) {
tiles.each(function(i) {
a = $(this).offset().top + $(this).height();
b = $(window).scrollTop() + $(window).height();
if (a < b) $(this).fadeTo(500,1);
});
});
the function for scrolling is working. the problem is that when the page is full load my sidebar class that hold all widgets is on opacity 0 (like display:none). what I need is when the page load it will give opacity=1 to all widgets that visible on screen (for example 2 of 10 widgets). then when user will scroll it will show others widgets each by other with fade effect.
Extract the block of code that makes these widgets visible and put it in a function. Then add a handler to both scroll and "DOM ready" pointing to this function.
// Determine show or hide
function showOrHide(){$(document).ready(function(){
$("#sidebar1 div").each(function(i) {
var a = $(this).offset().top + $(this).height();
var b = $(window).scrollTop() + $(window).height();
if (a < b) $(this).fadeTo(500,1);
});
}
// Assign to both
$(document).ready(showOrHide);
$(window).scroll(showOrHide);
Now there's a performance penalty here. On scroll fire several times per second. You wouldn't want to query the DOM for these elements and run each on them multiple times a second. For that' I'll leave it to you to search (It's asked frequently on both SO and CodeReview)
I want to change the background color of in-viewport elements (using overflow: scroll)
So here was my first attempt:
http://jsfiddle.net/2YeZG/
As you see, there is a brief flicker of the previous color before the new color is painted. Others have had similar problems.
Following the HTML5 rocks instructions, I tried to introduce requestAnimationFrame to fix this problem to no avail:
http://jsfiddle.net/RETbF/
What am I doing wrong here?
Here is a simpler example showing the same problem: http://jsfiddle.net/HJ9ng/
Filed bug with Chromium here: http://code.google.com/p/chromium/issues/detail?id=151880
if it is only the background color, well why don't you just change the parent background color to red and once it scroll just change it to pink?
I change your CSS to that
#dad
{
overflow-y: scroll;
overflow-x: hidden;
width: 100px;
height: 600px;
background-color:red;
}
I remove some of you Jquery and change it to this
dad.bind('scroll', function() {
dad.css('background-color', 'pink');
});
And I remove this line
iChild.css('backgroundColor', 'red');
But is the Red color it is important that won't work for sure http://jsfiddle.net/2YeZG/5/
I like Manuel's Solution.
But even though I don't get what you're exactly trying to do, I want to point out a few things.
In your fiddle code, I saw that you included Paul Irish's Shim for requestAnimationFrame.
But you never use it.
(It's basically a reliable setTimeOut, nothing else) it's from frame based animations.)
So since you just want to change some CSS properties, I don't see why you would need it. Even if you want transitions, you should rely on CSS transitions.
Other than that your code could look something like
dad.bind('scroll', function() {
dad.css('background-color', 'pink');
eachElemNameHere.css('background-color','randomColor');
});
Also you should ideally not use something like that if you can help it. You should just add and remove class names and add all these properties in your CSS. Makes it work faster.
Also, again I don't quite get it, but you could use the jQuery function to find out each elements' position from the top to have better control.
Your problem seems to be that you only change the background color of the elements which have already been scrolled into view. Your code expects that the browser waits for your code to handle the scroll event before the browser redraws its view. This is most probably not a guarantee given by the HTML spec. That's why it flickers.
What you should do instead is to change the elements which are going to be scrolled into view. This is related to off screen rendering or double buffering as it is called in computer games programming. You build your scene off screen and copy the finished scene to the visible frame buffer.
I modified your first JSFiddle to include a multiplier for the height of the scroll area: http://jsfiddle.net/2YeZG/13/.
dad.bind('scroll', function() {
// new: query multiplier from input field (for demonstration only) and print message
var multiplier = +($("#multiplier")[0].value);
$("#message")[0].innerHTML=(multiplier*100)-100 + "% of screen rendering";
// your original code
var newScrollY = newScrollY = dad.scrollTop();
var isForward = newScrollY > oldScrollY;
var minVal = bSearch(bots, newScrollY, true);
// new: expand covered height by the given multiplier
// multiplier = 1 is similar to your code
// multiplier = 2 would be complete off screen rendering
var newScrollYHt = newScrollY + multiplier * dadHeight;
// your original code (continued)
var maxVal;
for (maxVal = minVal; maxVal < botsLen; maxVal++) {
var nxtTopSide = tops[maxVal];
if (nxtTopSide >= newScrollYHt) {
break;
}
}
maxVal = Math.min(maxVal, botsLen);
$(dadKids.slice(minVal, maxVal)).css('background', 'pink');
});
Your code had a multiplier of 1, meaning that you update the elements which are currently visible (100% of scroll area height). If you set the multiplier to 2, you get complete off screen updates for all your elements. The browser updates enough elements to the new background color so that even a 100% scroll would show updated elements. Since the browser seldom scrolls 100% of the area in one step (depends of the operating system and the scroll method!), it may be sufficient to reduce the multiplier to e.g. 1.5 (meaning 50% off screen rendering). On my machine (Google Chrome, Mac OS X with touch pad) I cannot produce any flicker if the multiplier is 1.7 or above.
BTW: If you do something more complicated than just changing the background color, you should not do it again and again. Instead you should check whether the element has already been updated and perform the change only afterwards.
I do not know how to solve this situation:
I`ve got the html/css looks like this:
Image showing how my css/html looks like and what is displayed on the screen after landing on page:
The when I scroll down I see green element:
scrolling down ->
After continuing to scrolling down I saw full green element and the if I scroll down I want to have this element like in css language: position fixed bottom 0. See image below:
I ve saw full element -> same link but image called problem3.png
and then I scroll below and I want to have it fixed at the bottom of the page, like on this image:
Fixed element on screen - What I want and I do not know how to do that -> same link but image called problem4.png (stupid spam prevention mechanism)
Is it possible to solve this situation ?
To sum up: I`ve got two divs, one above and second below, Wheen I scroll down I suddenly see another element (green div) and when i continue to scroll down I WANT TO HAVE THIS GREEN DIV FIXED AT THE BOTTOM OF THE PAGE.
Ofcourse, when I scroll up (back on the top) I want to "park" that green div at the top of the second div.
Is there any way to solve this situation with jQuery (Javascript) / html / css ?
Thank you in advance
I think you'll have to show some of your html structure. There are lots of ways to achieve this kind of effect. Fundamentally, in javascript terms you'll be looking to:
Add an event listener to the window scroll that checks whether the green element is fully in view
If it is in view, add a class (or change it's css) that fixes it's position where you want
Change your window scroll method so that it's checking the relative offset of the red div to the top of the screen. If it goes below the position where the green div should be fixed, remove the class you added earlier.
That sounds complicated, but it's not too bad. The javascript would be something like:
$(function() {
$(window).scroll(function() {
if($(".divToFix").hasClass("fixedAtBase")){
if(Utils.underView($(".redDiv"), $(".divToFix").height())) $(".divToFix").removeClass("fixedAtBase");
} else {
if(Utils.inView($(".divToFix"))) $(".divToFix").addClass("fixedAtBase");
}
});
});
Utils = {
underView: function(element, offset) {
return (($(window).height() + $(window).scrollTop() - offset) <= element.offset().top);
},
aboveView: function(element) {
return ($(window).scrollTop() >= element.offset().top + element.height());
},
inView: function(element) {
return (Utils.aboveView(element) !== true && Utils.underView(element, element.height()) !== true);
}
};
Bear in mind I've not tested that or anything.
edit - here's a demo