Develop Reference

How to apply a jquery function with a jquery object as a parameter

I found an easy code to create a parallax effect with jquery:
function parallax(intensity, element) {
$(window).scroll(function() {
var scrollTop = $(window).scrollTop();
var objPos = scrollTop / intensity + 'px';
element.css('transform', 'translateY(' + objPos + ')');
});
}
I completly understand how this code works, but how do I apply this on different elements?
So for example #div1 with intensity 3, #div2 with intensity 5.
Thank you for you help in advance! :)

You created the function, now you just need to call it:
parallax(3, $('#div1'));
parallax(5, $('#div2'));
Try this and let me know how it goes.

Scrolling content in a div when it's passed

Trying to accomplish something like on this website:
http://www.strangelove.nl/cases/kpmg-meijburg
The part where the responsive design is showcased, the image inside the devices start to scroll when a visitor scrolls past that point. I've tried to replicate it and I see a .js in the footer which is probably contributing. For now I have the css and html working on my test page.
Any help is gladly appreciated.

Strangelove is using their own Kubrick-js, which is available here: Kubrick-js
If you just want to have the 'images scrolling inside of frame while scrolling by'-effect, you can do it like this:
$(window).scroll(function() {
var animStart = 0, // the point where the animation starts
animEnd = 500, // the point, where the animation ends
scrollStartPos = 0, // the position your inside scrolling element starts
scrollEndPos = -300, // the position your inside scrolling element should end
winPosY = window.pageYOffset, // the scroll distance from top of document
scrollElement = $('.picture'); // the element to scroll
if(winPosY > animStart && winPosY < animEnd) {
// how far through the animation are we?
var howFar = (winPosY - animStart) / (animEnd - animStart),
scrollPos = Math.round(scrollStartPos + howFar * (scrollEndPos - scrollStartPos));
scrollElement.css('top', scrollPos + 'px');
$('.show-stats').html('How far: ' + howFar + '<br>scroll Position: ' + scrollPos);
}
});
Here is a fiddle for it: Fiddle
hope that helps.

How might I tell if an HTML element is being rendered on the screen?

I'd like an element to do a CSS3 animation once the page is scrolled down enough for it to be visible, and I'm wondering if there's any way to accomplish this. Anything involving JavaScript or CSS would work. I've done many Google searches and Stackoverflow searches and can't find exactly what I need.

Depending on the complexity of your layout, it could be as simple as finding the scroll position, the height of the window, and where the element is on the page.
function scrollEvent() {
var el = document.getElementsByTagName('a')[0];
var body = document.getElementsByTagName('body')[0];
var posY = (window.innerHeight + body.scrollTop) - el.offsetTop;
var onScreen = (posY > 0 && posY < window.innerHeight) ? true : false;
}
window.onscroll = scrollEvent;
Use the same technique if you're worried about horizontal positioning, as well.

It depends on what you want to do specifically. I would look at these resources:
http://daneden.github.io/animate.css/
http://www.w3schools.com/css/css3_animations.asp
http://css-tricks.com/almanac/properties/a/animation/

Put your CSS3 animation style in a class, but don't assign it to your element until it has been scrolled completely into view.
Assuming your element has an id of sprite, this should get you going:
<style>
.animate {
//CSS3 animation style
}
</style>
window.onscroll= function() {
var sprite = document.getElementById('sprite');
if(sprite.getBoundingClientRect().top>=0 && sprite.getBoundingClientRect().bottom<=window.innerHeight) {
sprite.className= 'animate';
}
}

Why are my animations delayed in Firefox? How can I improve this scroll script?

I'm having troubles getting this code to execute in a timely manner in Firefox. It seems to work just fine in Chrome.
JSFiddle here: http://jsfiddle.net/EXDhb/
Real live example page I'm working with here: http://mindevo.com/tests/tacos.html
I'm not sure if I'm leaving something out. I kind of hacked this together from reading a bunch of page-scroll scripts other people have put together. Not sure if this is even the best way for me to do what I'm trying to accomplish (which is to darken the next area until it's somewhat revealed. (I used halfway for this).
Here's my javascript:
$(document).ready(function(){
$(window).scroll(function(){
$('.dark').each(function(i){
var half_object = $(this).position().top + ($(this).outerHeight()/2);
var bottom_window = $(window).scrollTop() + $(window).height();
var bottom_object = $(this).position().top + $(this).outerHeight();
if(bottom_window > half_object){
$(this).animate({'opacity':'1'},200);
}
else if(bottom_object > $(window).scrollTop()) {
$(this).animate({'opacity':'.5'},200);
}
});
});
});
Is there a better way to do this? I tried adding/removing css classes but it invoked some crazy Chrome bug I was not pleased about.
Why does it work so slowly in Firefox?

Start by not having 6 separate jQuery $(this) operations and multiple $(window)! Use temp variables whenever you can to avoid requerying.
JSFIddle: http://jsfiddle.net/TrueBlueAussie/EXDhb/9/
$(document).ready(function () {
// window never changes
var $window = $(window);
$window.scroll(function () {
// Window height may have changed between scrolls
var windowHeight = $window.height();
var scrollTop = $window.scrollTop();
$('.dark').each(function (i) {
var $this = $(this);
var top = $this.position().top;
var outerH = $this.outerHeight();
var half_object = top + (outerH / 2);
var bottom_window = scrollTop + windowHeight;
var bottom_object = top + outerH;
console.log(half_object);
if (bottom_window > half_object) {
$this.stop().animate({
'opacity': '1'
}, 200);
} else if (bottom_object > scrollTop) {
$this.stop().animate({
'opacity': '.5'
}, 200);
}
});
});
});
And so on until you do not do anything twice that has an overhead that you do not need to have.
Update: Stop previous animations
The pause was not caused by the speed of the code above, but by not stopping multiple animations. The problem is that scroll fires frequently, so without .stop() animations get queued up and fire one after the other. This made it look much slower that it actually was.
Further optimizations might involve only processing elements that are actually onscreen, but that is pretty pointless given the apparent speed now.

You can cache your variables, which should help slightly:
$(document).ready(function(){
var $window = $(window);
$window.scroll( function(){
$('.dark').each(function(i){
var $this = $(this);
var outerHeight = $this.outerHeight();
var positionTop = $this.position().top;
var half_object = positionTop + (outerHeight/2);
var bottom_window = window.scrollTop() + window.height();
var bottom_object = positionTop + outerHeight;
if(bottom_window > half_object){
$this.animate({'opacity':'1'}, 200);
} else if(bottom_object > window.scrollTop()) {
$this.animate({'opacity':'.5'}, 200);
}
});
});
});

I realize there is already an accepted answer, but many times it is useful to do something only after the user has stopped scrolling, and not each time the "scroll" event fires. This event can can fire upwards of 50 times per second, leaving you with ~20ms to do what you need to do. This other StackOverflow question shows you how to do something only after scrolling has stopped. As #TrueBlueAussie mentioned in his answer, you would still want to stop any animations that were currently running.

javascript scroll to bottom of div class

Hi I am trying to implement a simple chatbox in django and was wondering how to scroll to the bottom of a div class using javascript? Basically when the page loads I would like so that users can see the most recent message sent to them instead of the least recent.

I had to do this recently for a similar thing. I found a basic jquery plug-in that will smoothly scroll an element onto the screen.
(function($) {
$.fn.scrollMinimal = function() {
var cTop = this.offset().top;
var cHeight = this.outerHeight(true);
var windowTop = $(window).scrollTop();
var visibleHeight = $(window).height();
if (cTop < windowTop) {
$('body').animate({'scrollTop': cTop}, 'slow', 'swing');
} else if (cTop + cHeight > windowTop + visibleHeight) {
$(jQuery.browser.webkit ? "body": "html")
.animate({'scrollTop': cTop - visibleHeight + cHeight}, 'slow', 'swing');
}
};
}(jQuery));
which is used like this:
$('#chat').scrollMinimal();

Well, the basic script is set the scrollTop equal to scrollHeight, so you need a script like this:
var DIV = document.getElementById('theDIVElement');
DIV.scrollTop = DIV.scrollHeight;
You only need to change theDIVElement to your DIV id.

This is the script I used in my chat:
<SCRIPT LANGUAGE="JavaScript">
<!--
function myScroll() {
window.scrollBy(0,01)
setTimeout('myScroll()',100); }
if (document.layers || document.all)
myScroll()
//--></SCRIPT>
This is also nice for when new messages are added, if you scroll to the bottom too fast, it's hard on your eyes while you're trying to read.