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Performance drop when fading element based on scrollTop

seen afew websites with this effect, however it seems to drop the framerate in my attempt. I basically want to change the opacity of an element the more the user scrolls.
$(window).scroll(function(event){
$("#responsive-slider-with-blocks-1").css("opacity", 1 - $(window).scrollTop() / 1500);
}
Is there a better way to do this? (would be ace just CSS, but not possible).
I'm really not a fan of binding to the scroll event.
Edit:
Due to changing the opacity on an element which covers the entire viewport could be why the framerate drops so much. Would fading in black div covering the element maybe not drop the framerate so much?

Scroll events fire so fast, you're right, every little optimization will help. The docs for the scroll event have advice along those lines:
Since scroll events can fire at a high rate, the event handler shouldn't execute computationally expensive operations such as DOM modifications. Instead, it is recommended to throttle the event using requestAnimationFrame, setTimeout or customEvent...
You can adapt the example they have there to your purposes (and I'm trying to leave out jquery on purpose to remove the overhead):
var last_known_scroll_position = 0;
var ticking = false;
var responsiveSlider = document.getElementById('responsive-slider-with-blocks-1');
function doSomething(scroll_pos) {
responsiveSlider.style.opacity = 1 - scroll_pos / 1500;
}
window.addEventListener('scroll', function(e) {
last_known_scroll_position = window.scrollY;
if (!ticking) {
window.requestAnimationFrame(function() {
doSomething(last_known_scroll_position);
ticking = false;
});
}
ticking = true;
});
This is certainly longer, and there are some global scope messes to consider, but something like this may make the performance difference you are looking for.

Scroll event I believe will be triggered very often during scrolling. When scroll event triggered, jQuery needs to find DOM element based on the selector. This operation alone is quite expensive.
Changing the opacity make it worse as more pixels had to be processed.
Move code to select DOM using jQuery selector outside scroll event handler. That way you can avoid jQuery to lookup DOM element each time scroll event fires.
Limit size of element to reduce number of pixels need to be compute when opacity changed.
Change opacity at certain time interval helps reduce number of paint operations that browser need to do during scrolling operation. So instead of changing opacity everytime event fires, you wait until certain time has elapsed and then change opacity.

Get element position relative to screen. (Or alternative solution)

I am aware this had been asked before, but no answer actually did the trick as far as I tested them.
Basically what I need is to change some element styles as soon as it "hits" the top border of the screen while scrolling down. This element is a 'Back to Top' button that will be sitting in a section and start following the user when they scroll pass said section.
I am not asking about CSS properties, I am asking about some JS property or method that allow me to know this. IE:
$('#back').distanceFromTopOfTheScreen() // This value will decrease as I scroll down
I know there are other soultions, but the client has asked for this behavior.
Any idea?

You can :
distance = $('#eleId')[0].getBoundingClientRect().top;
For more about getBoundingClientRect() look at the MDN Documentation
Note: This value change when you're scrolling, it gives you the distance between the top border of the element and the top of the Page

Sometimes JQuery make's everything more confusing than Native Javascript, even forgothing the very basics functions:
window.onscroll = function() { fixPosition()};
function fixPosition() {
var Yplus = 4; //number of lines in every scroll
document.getElementById('element').style.top = document.body.scrollTop + Yplus ;
}
This will allows you to move an "element" static on the window following the scroll.

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/

javascript bind an event handler to horizontal scroll

Is there a way in javascript to bind an event handler to a horizontal scroll as opposed to the generic scroll event which is fired when the user scrolls horizontally and vertically? I want to trigger an event only when the user scrolls horizontally.
I searched around for an answer to this question, but couldn't seem to find anything.
Thanks!
P.S. My apologies if I'm using some terminology incorrectly. I'm fairly new to javascript.
UPDATE
Thanks so much for all your answers! In summary, it looks like you are all saying that this isn't supported in javascript, but I that I can accomplish the functionality with something like this (using jQuery) (jsFiddle):
var oldScrollTop = $(window).scrollTop();
$(window).bind('scroll', function () {
if (oldScrollTop == $(window).scrollTop())
//scrolled horizontally
else {
//scrolled vertically
oldScrollTop = $(window).scrollTop();
}
});​
That's all I needed to know. Thanks again!

Answering from my phone, so unable to provide code at the moment.
What you'll need to do is subscribe to the scroll event. There isn't a specific one for vertical/horizontal.
Next, you'll need to get some measurements about the current display area. You'll need to measure the window.clientHeight and window.clientWidth.
Next, get window.top and window.left. This will tell you where position of the viewport is, ie if it's greater than 0 then scroll bars have been used.
It's pretty simple math from here to get what you need. If no one else has provided a code example in the next few hours I'll try to do so.
Edit:
A bit further information.
You must capture the scroll event. You also need to store the initial window.top and window.left properties somewhere. Whenever the scroll event happens, do a simple check to see if the current top/left values differ from the stores value.
At this point, if either are different you can trigger your own custom events to indicate vertical or horizontal scrolling. If you are using jQuery, this is very easy. If you are writing js without library assistance, it's easy too but a little more involved.
Do some searches for event dispatching in js.
You can then write any other code you want to subscribe to your custom events without needing to tie them together with method calls.

I wrote a jQuery plugin for you that lets you attach functions to the scrollh event.
See it in action at jsfiddle.net.
/* Enable "scrollh" event jQuery plugin */
(function ($) {
$.fn.enableHScroll = function() {
function handler(el) {
var lastPos = el
.on('scroll', function() {
var newPos = $(this).scrollLeft();
if (newPos !== lastPos) {
$(this).trigger('scrollh', newPos - lastPos);
lastPos = newPos;
}
})
.scrollLeft();
}
return this.each(function() {
var el = $(this);
if (!el.data('hScrollEnabled')) {
el.data('hScrollEnabled', true);
handler(el);
}
});
}
}(jQuery));
It's this easy to use:
$('#container')
.enableHScroll()
.on('scrollh', function(obj, offset) {
$('#info').val(offset);
});
Please note that scroll events come very fast. Even if you click in the scrollbar to jump to a new position, many scroll events are generated. You may want to adjust this code to wait a short time and accumulate all the changes in position during that time before firing the hscroll event.

You can use the same scroll event, but within your handler use the scrollLeft function to see if the scrollbar moved horizontally from the last time the event was fired. If the scrollbar did not move then just return from your handler. Otherwise update your variable to the new position and take action.

You can check if the the x value of the page changes and ignore your y value.
If the x value changes: There is your horizontal scroll.

With page-load, store the initial scrollbar positions for both in two variables (presumably both will be 0). Next, whenever a scroll event occurs, find the scrollleft and scrolltop properties. If the scrollleft property's value is different and scrolltop's value is same as compared to their earlier values, that's a horizontal scroll. Then set the values of the variables to the new scroll values.

No, there is no special event for scroll horizontal (it is for global scroll), but you can try to check the position of content by property .scrollLeft and if it's different from the previous value it means that the user scrolled content horizontally.

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/ .