Scroll to bottom (and forced reflow performance issues) - javascript

I'm trying to use the vanilla JS to scroll to the bottom of a div (inside my scrollable webpage) upon receiving a message (WebSocket, not important). The message adds a new element el into the div, and I want the div to scroll to the el:
div.append(el); // or ...array
// clear div if too many messages here,
// using while (childNodes.length > ...) firstChild.remove();
div.scroll...(el);
Using div.scrollTo(0, div.scrollHeight) (edit: or div.scrollTop = div.scrollHeight) would be fine, if it was not that unbelievably slow - I receive a lot of messages quite often, and it basically freezes the browser whenever I have to force reflow with scrollHeight.
Using el.scrollIntoView() (edit: or its variants) is actually much faster (accumulated from brief uneducated profiling sessions, 20s of scrollTo and 0.6s of scrollIntoView, given relatively same load), however, my div happens to be inside a scrollable page, and scrollIntoView causes the whole page to scroll to make the el appear in the view. Basically, I want it to scroll to bottom of the div even off-screen (or achieve a similar effect).
Are there any other solutions to this problem, or is it possible to fix one of the top two variants?
UPDATE:
Using div.scrollTo(0, Number.MAX_SAFE_INTEGER); and similar works only on Chrome, not Firefox. Runs fast though (comparable to the 2nd solution). Similar variant div.scrollTop = Number.MAX_SAFE_INTEGER actually performs quite poorly for some reason.

Try div.scrollTop = div.scrollHeight:
var contents = document.querySelector('.contents');
const before = new Date().getTime();
contents.scrollTop = contents.scrollHeight;
const after = new Date().getTime();
const diff = after - before;
console.log(`Took ${diff} milliseconds`);
.contents{
height:200px;
overflow-y:auto;
}
.section{
height:197px;
border:1px solid;
}
<div class="contents">
<div class="section">1</div>
<div class="section">2</div>
<div class="section">3</div>
</div>

div.scrollIntoView(false);
This will take you to the bottom of the div.

Related

Skrollr Image Flicker. Firefox preload issue

Im in the process of developing a 'flipbook-style' animation using Skrollr by triggering background image changes when the user scrolls to indicated positions on the page. The issue i'm having is that in browser the image changes are delayed, creating what can only be defined as a 'flicker' of white between the frames.
<div class="section" style="background: url('frame1.png')"
data-560-top="background-image:!url('frame1.png');"
data-440-top="background-image:!url('frame2.png');">
The HTML is simple; it basically states that at 560 pixels from the top of the div (in relation to the browser window), the background should be at frame 1, then as the user scrolls closer to the div (440 pixels from the top of the div) the background image changes to frame 2. I plan to use up to around 20 frames and the images are quite large.
I have created a JSBin here which includes a very simplified sample with images from placehold.it. This includes the Skrollr script and an example layout of a section of my project. The key difference being that the images in my project are of much larger scale.
(function($) {
var cache = [];
// Arguments are image paths relative to the current page.
$.preLoadImages = function() {
var args_len = arguments.length;
for (var i = args_len; i--;) {
var cacheImage = document.createElement('img');
cacheImage.src = arguments[i];
cache.push(cacheImage);
}
};
})(jQuery);
jQuery.preLoadImages(
'http://www.placehold.it/300x200.png',
'http://www.placehold.it/300x200.png'
);
The above snippet seems to be working on Chrome, however the flicker issue remains in Firefox. Based on research, firefox handles cached images differently from Chrome? (e.g Where an image is not considered needed by firefox at a given time, it is trashed?)
I would like to know how I could possibly force all browsers to preload the images efficiently, to potentially avoid the background image flicker upon change. I am still quite new to Javascript/JQuery.
I hope I have provided a clear explanation. All assistance appreciated.
Dan
You can preload images using CSS only, no need for JS. Check out this article for more info. Another interesting way to do it is in the comment section of the article. Basically you assign the background image to a pseudo-element so that is is cached and ready to be used whenever. See this code for an example:
#something:before {
content: url("./img.jpg");
width:0;
height:0;
visibility:hidden;
}

window scroll method flickers in IE

This may come as a huge surprise to some people but I am having an issue with the IE browser when I am using the $(window).scroll method.
My goal:
I would like to have the menu located on the left retain it's position until the scroll reaches > y value. It will then fix itself to the top of the page until the scroll returns to a < y value.
My error:
Everything seems just fine in Chrome and Firefox but when I go to Internet Explorer it would seem the browser is moving #scroller every time the scroll value changes, this is causing a moving/flickering event.
If someone could point me to a resource or give me a workaround for this I would be very grateful!
Here is a fiddle:
http://jsfiddle.net/CampbeII/nLK7j/
Here is a link to the site in dev:
http://squ4reone.com/domains/ottawakaraoke/Squ4reone/responsive/index.php
My script:
$(window).scroll(function () {
var navigation = $(window).scrollTop();
if (navigation > 400) {
$('#scroller').css('top',navigation - 220);
} else {
$('#scroller').css('top',183);
$('#scroller').css('position','relative');
}
});
You might want to take a look at the jQuery Waypoints plugin, it lets you do sticky elements like this and a lot more.
If you want to stick with your current method, like the other answers have indicated you should toggle fixed positioning instead of updating the .top attribute in every scroll event. However, I would also introduce a flag to track whether or not it is currently stuck, this way you are only updating the position and top attributes when it actually make the transition instead of every scroll event. Interacting with the DOM is computationally expensive, this will take a lot of load off of the layout engine and should make things even smoother.
http://jsfiddle.net/WYNcj/6/
$(function () {
var stuck = false,
stickAt = $('#scroller').offset().top;
$(window).scroll(function () {
var scrollTop = $(window).scrollTop();
if (!stuck && scrollTop > stickAt) {
$('#scroller').css('top', 0);
$('#scroller').css('position','fixed');
stuck = true;
} else if (stuck && scrollTop < stickAt) {
$('#scroller').css('top', stickAt);
$('#scroller').css('position','absolute');
stuck = false;
}
});
});
Update
Switching the #scroller from relative to fixed removes it from the normal flow of the page, this can have unintended consequences for the layout as it re-flows without the missing block. If you change #scroller to use an absolute position it will be removed from the normal flow and will no longer cause these side-effects. I've updated the above example and the linked jsfiddle to reflect the changes to the JS/CSS.
I also changed the way that stickAt is calculated as well, it uses .offset() to find the exact position of the top of #scoller instead of relying on the CSS top value.
Instead of setting the top distance at each scroll event, please consider only switching between a fixed position and an absolute or relative position.All browsers will appreciate and Especially IE.
So you still listen to scroll but you now keep a state flag out of the scroll handler and simply evaluate if it has to switch between display types.
That is so much more optimized and IE likes it.
I can get flickers in Chrome as well if I scroll very quickly. Instead of updating the top position on scroll, instead used the fixed position for your element once the page has scrolled below the threshold. Take a look at the updated fiddle: http://jsfiddle.net/nLK7j/2/

Content flicker/jump on infinite scroll/loop

I am looking for help / a point in the right direction / or a solution for a flicker/jump, when scrolling on a looping/infinite website, which can be seen in this fiddle.
What seems to be causing the jump is:
"$(window).scrollTop(half_way - child_height);", and what could also be a Chrome windows scrollTop bug, but it is happening in all browsers at the moment.
If I remove "- child_height" there is no longer a flicker but the page no longer scrolls correctly, which can be seen in this fiddle.
Also, on the very first scroll the right hand column jumps up by three boxes - also because of 'half_way', which I can fix by giving it a "bottom: -600px;"
The full code:
http://jsfiddle.net/djsbaker/j3d8r/1/
var num_children = $('#up-left').children().length;
var child_height = $('#up-left').height() / num_children;
var half_way = num_children * child_height / 2;
$(window).scrollTop(half_way);
function crisscross() {
$('#up-left').css('bottom', '-' + window.scrollY + 'px');
$('#down-right').css('bottom', '-' + window.scrollY + 'px');
var firstLeft = $('#up-left').children().first();
var lastLeft = $('#up-left').children().last();
var lastRight = $('#down-right').children().last();
var firstRight = $('#down-right').children().first();
if (window.scrollY > half_way ) {
$(window).scrollTop(half_way - child_height);
lastRight.appendTo('#up-left');
firstLeft.prependTo('#down-right');
} else if (window.scrollY < half_way - child_height) {
$(window).scrollTop(half_way);
lastLeft.appendTo('#down-right');
firstRight.prependTo('#up-left');
}
}
$(window).scroll(crisscross);
Okay - here is a 'working' version - and by works I mean it less flickery than before. I thought it was flicker free, and it was when I was on battery power, but plugged into the mains and the CPU is fast enough to get flicker.
As I mentioned, to get rid of the flicker you need to clone the objects, manipulate them and then replace them into the DOM, rather than just manipulating the DOM directly.
I did this by getting the contents of <div id="content"> manipulating them and then replacing them into that <div>.
Also, it's a good idea to only find things in the DOM once, and from then on use a reference to that object rather than searching repeatedly. e.g.
var leftSide = $(clone).find('.up-left');
....
lastRight.appendTo(leftSide);
....
$(leftSide).css('bottom', '-' + window.scrollY + 'px');
rather than:
lastRight.appendTo('#up-left');
$('#up-left').css('bottom', '-' + window.scrollY + 'px');
Searching the DOM is relatively slow, and so storing references can improve performance/reduce flicker.
Storing the object also makes the code easier to understand (imho) as you can easily see that you're referencing the same thing, rather than possibly different things.
I still get flickering in chrome on windows with Danack solution. For this site I would control all the scrolling (you already scroll manually one of the sides), and give elements absolute positions.
Or if you insist on using the browser scrolling, may be use animations: animate the height of the last elements till 0px then use appendTo, and then animato from 0px to the normal height...
This might be a long shot, but I had the same flickering when working with infinitescroll,
and ended up using imagesLoaded.I ended up appending the additional images (now loaded) with a fade in, and that prevented them from flickering because of the fact they were loaded.
So maybe by using the imagesloaded - or a callback on the images, you can solve the flickering. It does decrease the speed though. I can image that if you want to scroll through everything as fast as possible, this might not be the solution. Good luck!
A solution would be to not use the native scrolling functionality but to simulate scrolling. This would be done by setting the overflow of your content to "hidden" in addition with capturing the "mousewheel" event on it and triggering some action when it is called. I started to try this out here (using MooTools instead of jQuery since I'm more fimilar with it). It's currently just "working" on the left side by altering the margin-top of the first element.
My next steps would be:
Check if the negative margin-top of the first element is bigger than the height of it and move it to the right side if so.
Same logic for the last box on the right side with a negative margin-bottom.
This has some downsides, though. Simulating scrolling doesn't feel as natural as the native scrolling functionality and clicking the mousewheel doesn't work. These might be solveable but it would require some more coding to get it to work smoothly. Anyway, in the end you would have a solution without any flickering and with no sticky scrollbar at the side (An idea for a replacement could be a small area on the side that triggers the scrolling on mouseover).

How to solve element flicker while scrolling with parallax effect in JavaScript?

I am trying to re-create website with parallax effect using JavaScript. That means that I have two or more layers, that are moving different speeds while scrolling.
In my case I'm moving only one layer, the other one remains static:
layer 1 = website text;
layer 2 = element background;
for this I'm using simple source code (with jQuery 1.6.4):
var docwindow = $(window);
function newpos(pos, adjust, ratio){
return ((pos - adjust) * ratio) + "px";
}
function move(){
var pos = docwindow.scrollTop();
element.css({'top' : newpos(pos, 0, 0.5)});
}
$(window).scroll(function(){
move();
});
The Problem:
- All calculations are done right and the effect "works" as expected. But there is some performance glitch under some browsers (Chrome MAC/Windows, Opera MAC, IE, paradoxically not Safari).
What do I see during scrolling?
- While scrolling the background moves in one direction together with scroll, but it seems to occasionally jump few pixels back and then forth, which creates very disturbing effect (not fluid).
Solutions that I tried:
- adding a timer to limit scroll events
- using .animate() method with short duration instead of .css() method.
I've also observed, that the animation is smooth when using .scrollTo method (scrollTo jQuery plugin). So I suspect that there is something wrong with firing scroll events (too fast).
Have you observed the same behavior?
Do you know, how to fix it?
Can you post a better solution?
Thanks for all responses
EDIT #1:
Here you can find jsfiddle demonstration (with timer): http://jsfiddle.net/4h9Ye/1/
I think you should be using scrollTop() instead and change the background position to fixed. The problem is that setting it to absolute will make it move by default when you scroll up or down.
The flicker occurs because the position is updated as part of the default browser scroll and updated again as part of your script. This will render both positions instead of just the one you want. With fixed, the background will never move unless you tell it so.
I've created a demo for you at http://jsfiddle.net/4h9Ye/2/ .

Use Javascript to create a space at the bottom of page for toolbar widget

I am creating a toolbar widget that is loaded via an external javascript file. The toolbar floats at the bottom of the screen, which works fine, but the content at the bottom of the screen gets covered up (as seen in Figure A). Figure B is my goal.
The toolbar should always be visible, fixed to the bottom of the screen. If scrolling is needed on the page, the content will flow under it until it is all visible when scrolled all the way to the bottom, so that nothing gets covered up on any length page.
My first thought was to set a bottom margin of 30px (toolbar height), but since most of the websites this is designed for are setup to use the full screen (with body height set to 100%), this won't always work. Decreasing the body scrollHeight by 30px fixes this issue, but only if scrolling isn't required on the page (which sometimes is).
JSFiddle example: http://jsfiddle.net/ZbMDr/1/
Does this example work for you? http://limpid.nl/lab/css/fixed/footer
So here's a somewhat hacky solution I've come up with, that seems to work so far (I haven't done extensive testing yet). If anyone has a cleaner way of accomplishing this it would be interesting.
var bodyCH = document.body.clientHeight,
bodySH = document.body.scrollHeight;
/* insert the toolbar here */
if (bodyCH === bodySH) {
document.body.style.height = parseInt(bodySH, 10) - 30 + 'px';
} else {
var spacer = document.createElement('div');
spacer.style.height = '30px';
document.body.appendChild(spacer);
}

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