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trigger animation at the end of debounced requestanimationframe

I followed Paul Lewis's guide to debounce and requestAnimationFrame. I'm translating an image across the screen on scroll when it comes into view.
var bicycles = $('.tandem-bike', context),
lastScrollY = 0,
ticking = false;
function update() {
var windowHeight = window.innerHeight,
windowWidth = $(window).width(),
bikeTop = [];
bicycles.each( function (i, el) {
bikeTop[i] = $(this).offset();
});
bicycles.each(function(i, el) {
var position = bikeTop[i];
var fromTop = position.top - windowHeight;
var imgHeight = $(this).height();
// When this image scrolls into view.
if (lastScrollY > fromTop && lastScrollY < position.top + imgHeight && i == 1 ) { // 375 ~= height of image
var translate = Math.floor((lastScrollY - fromTop) / ((windowHeight + imgHeight + 300) / windowWidth));
console.log('add tp tranlate ', translate);
$(this).css('transform', 'translateX(' + (translate - 275) + 'px)');
}
});
ticking = false;
}
function onScroll() {
lastScrollY = window.scrollY;
requestTick();
}
function requestTick() {
if(!ticking) {
requestAnimationFrame(update);
ticking = true;
}
}
window.addEventListener('scroll', onScroll, false);
This works great and the bicycle-built-for-two slides effortlessly across the screen. However, I want the image to "bounce" when the user stops scrolling. I figure an easy way would be to add a class when the animation ends, and pull it off when the animation starts. The obvious place to do that is within the if block in requestTick().
if(!ticking) {
$('.tandem-bike').removeClass('bounce');
requestAnimationFrame(update);
$('.tandem-bike').addClass('bounce');
ticking = true;
}
or
if(!ticking) {
requestAnimationFrame(update);
$('.tandem-bike').addClass('bounce');
ticking = true;
} else {
$('.tandem-bike').removeClass('bounce');
}
}
Neither works, and I don't love then because I'm whole-sale adding classes to all the animated images on the page. (I would live with that if it worked)

How to make script resize images and divs on window resize and orientation change

I am currently using the following javascript to resize an image to the size of it's parent, while maintaining aspect ratio and keeping the parent div square. So i have a square box with a rectangle stretched to either the max width or max height depending on orientation. This works great on first load however I cannot get the images and divs to resize on page orientation change or resize to work. Any ideas. I have tried using the window.resize and window.orientation listeners.
Original code was from:
Scale, crop, and center an image...
var aspHt = $('.aspectcorrect').outerWidth();
$('.aspectcorrect').css('height', aspHt + 'px').css('width', aspHt + 'px');
function ScaleImage(srcwidth, srcheight, targetwidth, targetheight, fLetterBox) {
var result = {
width : 0,
height : 0,
fScaleToTargetWidth : true
};
if ((srcwidth <= 0) || (srcheight <= 0) || (targetwidth <= 0) || (targetheight <= 0)) {
return result;
}
// scale to the target width
var scaleX1 = targetwidth;
var scaleY1 = (srcheight * targetwidth) / srcwidth;
// scale to the target height
var scaleX2 = (srcwidth * targetheight) / srcheight;
var scaleY2 = targetheight;
// now figure out which one we should use
var fScaleOnWidth = (scaleX2 > targetwidth);
if (fScaleOnWidth) {
fScaleOnWidth = fLetterBox;
} else {
fScaleOnWidth = !fLetterBox;
}
if (fScaleOnWidth) {
result.width = Math.floor(scaleX1);
result.height = Math.floor(scaleY1);
result.fScaleToTargetWidth = true;
} else {
result.width = Math.floor(scaleX2);
result.height = Math.floor(scaleY2);
result.fScaleToTargetWidth = false;
}
result.targetleft = Math.floor((targetwidth - result.width) / 2);
result.targettop = Math.floor((targetheight - result.height) / 2);
return result;
}
function RememberOriginalSize(img) {
if (!img.originalsize) {
img.originalsize = {
width : img.width,
height : img.height
};
}
}
function FixImage(fLetterBox, div, img) {
RememberOriginalSize(img);
var targetwidth = $(div).width();
var targetheight = $(div).height();
var srcwidth = img.originalsize.width;
var srcheight = img.originalsize.height;
var result = ScaleImage(srcwidth, srcheight, targetwidth, targetheight, fLetterBox);
img.width = result.width;
img.height = result.height;
$(img).css("left", result.targetleft);
$(img).css("top", result.targettop);
}
function FixImages(fLetterBox) {
$("div.aspectcorrect").each(function(index, div) {
var img = $(this).find("img").get(0);
FixImage(fLetterBox, this, img);
});
}
window.onload = function() {
FixImages(true);
};

Call .resize() after $(window).resize():
$(window).resize( function(){
var height = $(window).height();
var width = $(window).width();
if(width>height) {
// Landscape
$("#landscape").css('display','none');
} else {
// Portrait
$("#landscape").css('display','block');
$("#landscape").click(function(){
$(this).hide();
});
}
}).resize();

I figured out what I was missing. The first bit of javascript is setting the style of height and width. When recalling the .outerHeight it was still using the inline style to calculate the width, and hence not resizing the div. I simply used .removeAttr('style') to remove that property first and then did the resize. Working now. I simply used $(window).on("resize", resizeDiv) and wrapped my resizing into a function named resizeDiv
function resizeDiv() {
var asp = $('.aspectcorrect');
asp.removeAttr("style");
var aspHt = asp.outerWidth();
asp.css('height', aspHt + 'px').css('width', aspHt + 'px');
FixImages(true);
}

Efficiently creating a simple parallax effect with jQuery

So for one of my new projects, I decided to write a super simple parallax script for some background images on scroll. This is what I came up with:
$(document).ready(function(){
parallaxScroll();
$(window).bind('scroll', function() {
parallaxScroll();
});
});
function parallaxScroll() {
$(".parallax").each(function() {
if($(this).hasClass('reverse')) {
$(this).css("background-position","center " + (($(this).offset().top - $(window).scrollTop())/2) + "px");
} else {
$(this).css("background-position","center " + (($(this).offset().top - $(window).scrollTop())/-2) + "px");
}
});
}
My question is, is this efficient enough? If not, is there a better solution? I wasn't sure if using an .each() would be best for performance, but it seems to work fine. The reason I have the function run at document load is so when you scroll the page for the first time, the background image doesn't jump.

Instead of css which sets the value immediately, consider using animate instead. It defers setting values using timers/requestAnimationFrame, ensuring that your animation does not block the UI, is async (runs pseudo-parallel to other code), and ensures that the animation is smooth.

This is a plain JS solution, but you'll be able to port it to jQuery really easily:
var lastScrollY = 0;
var backgroundImageY = 0;
var requestAnimationFrame = window.requestAnimationFrame ||
window.msRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame;
window.addEventListener('load', processScrollEvent);
function processScrollEvent() {
var innerHeight = window.innerHeight;
var scrollHeight = document.body.scrollHeight;
var backgroundImage = document.querySelector('#background img');
lastScrollY = document.body.scrollTop;
var currBackgroundImageY = Math.round(((backgroundImage.scrollHeight - innerHeight) / 100) * ((lastScrollY / (innerHeight - scrollHeight)) * 100));
if(currBackgroundImageY != backgroundImageY) {
backgroundImageY = currBackgroundImageY;
requestAnimationFrame(processScrollAnimationFrame);
}
}
function processScrollAnimationFrame() {
var backgroundImage = document.querySelector('#background img');
var transforms = ['transform', 'oTransform', 'msTransform', 'mozTransform', 'webkitTransform'];
for(var i = 0; i < transforms.length; i++) {
backgroundImage.style[transforms[i]] = 'translate3d(0, ' + backgroundImageY + 'px, 0)';
}
}

Check if element is visible on screen [duplicate]

This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
jQuery - Check if element is visible after scroling
I'm trying to determine if an element is visible on screen. In order to to this, I'm trying to find the element's vertical position using offsetTop, but the value returned is not correct. In this case, the element is not visible unless you scroll down. But despite of this, offsetTop returns a value of 618 when my screen height is 703, so according to offsetTop the element should be visible.
The code I'm using looks like this:
function posY(obj)
{
var curtop = 0;
if( obj.offsetParent )
{
while(1)
{
curtop += obj.offsetTop;
if( !obj.offsetParent )
{
break;
}
obj = obj.offsetParent;
}
} else if( obj.y )
{
curtop += obj.y;
}
return curtop;
}
Thank you in advance!

--- Shameless plug ---
I have added this function to a library I created
vanillajs-browser-helpers: https://github.com/Tokimon/vanillajs-browser-helpers/blob/master/inView.js
-------------------------------
Intersection Observer
In modern browsers you can use the IntersectionObserver which detects where an element is on the screen or compared to a parent.
The Intersection Observer API provides a way to asynchronously observe changes in the intersection of a target element with an ancestor element or with a top-level document's viewport.
Today I would probably lean toward this API if I need to detect and react to when an element has entered or exited the screen.
But for a quick test/lookup when you just want to verify if an emelemt is currently on screen I would go with the version just below using the getBoundingClientRect.
Using getBoundingClientRect
Short version
This is a lot shorter and should do it as well:
function checkVisible(elm) {
var rect = elm.getBoundingClientRect();
var viewHeight = Math.max(document.documentElement.clientHeight, window.innerHeight);
return !(rect.bottom < 0 || rect.top - viewHeight >= 0);
}
with a fiddle to prove it: http://jsfiddle.net/t2L274ty/1/
Longer version
And a version with threshold and mode included:
function checkVisible(elm, threshold, mode) {
threshold = threshold || 0;
mode = mode || 'visible';
var rect = elm.getBoundingClientRect();
var viewHeight = Math.max(document.documentElement.clientHeight, window.innerHeight);
var above = rect.bottom - threshold < 0;
var below = rect.top - viewHeight + threshold >= 0;
return mode === 'above' ? above : (mode === 'below' ? below : !above && !below);
}
and with a fiddle to prove it: http://jsfiddle.net/t2L274ty/2/
A more traditional way to do it
As BenM stated, you need to detect the height of the viewport + the scroll position to match up with your top position. The function you are using is ok and does the job, though its a bit more complex than it needs to be.
If you don't use jQuery then the script would be something like this:
function posY(elm) {
var test = elm, top = 0;
while(!!test && test.tagName.toLowerCase() !== "body") {
top += test.offsetTop;
test = test.offsetParent;
}
return top;
}
function viewPortHeight() {
var de = document.documentElement;
if(!!window.innerWidth)
{ return window.innerHeight; }
else if( de && !isNaN(de.clientHeight) )
{ return de.clientHeight; }
return 0;
}
function scrollY() {
if( window.pageYOffset ) { return window.pageYOffset; }
return Math.max(document.documentElement.scrollTop, document.body.scrollTop);
}
function checkvisible( elm ) {
var vpH = viewPortHeight(), // Viewport Height
st = scrollY(), // Scroll Top
y = posY(elm);
return (y > (vpH + st));
}
Using jQuery is a lot easier:
function checkVisible( elm, evalType ) {
evalType = evalType || "visible";
var vpH = $(window).height(), // Viewport Height
st = $(window).scrollTop(), // Scroll Top
y = $(elm).offset().top,
elementHeight = $(elm).height();
if (evalType === "visible") return ((y < (vpH + st)) && (y > (st - elementHeight)));
if (evalType === "above") return ((y < (vpH + st)));
}
This even offers a second parameter. With "visible" (or no second parameter) it strictly checks whether an element is on screen. If it is set to "above" it will return true when the element in question is on or above the screen.
See in action: http://jsfiddle.net/RJX5N/2/
I hope this answers your question.

Could you use jQuery, since it's cross-browser compatible?
function isOnScreen(element)
{
var curPos = element.offset();
var curTop = curPos.top;
var screenHeight = $(window).height();
return (curTop > screenHeight) ? false : true;
}
And then call the function using something like:
if(isOnScreen($('#myDivId'))) { /* Code here... */ };

JS/jQuery delay loop to get desire result (delay() not working)

I'm trying to create an loading icon by moving the css 'background-position' of an image in a loop:
$('#LoginButton').click(function () {
var i = 1, h = 0, top;
for (i = 0; i <= 12; i++) {
h = i * 40;
top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top).delay(800);
}
});
The problem here is that it runs to fast so I don't se the 'animation' of the moving background.
So I added jquerys delay(), but:
delay(800) is not working because delay() only works in jquery animation effects and .css() is not one of those.
How to delay this loop?

I'd suggest using jQuery timer plugin: http://jquery.offput.ca/js/jquery.timers.js
$('#LoginButton').click(function () {
var times = 13;
var delay = 300;
var h = 0, top;
$(document).everyTime(delay, function(i) {
top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top);
h += 40;
}, times);
});
In case you don't want any plugins, use setInterva/clearInterval:
$('#LoginButton').click(function () {
var delay = 300;
var times = 13;
var i = 0, h = 0, top;
doMove = function() {
top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top);
h += 40;
++i;
if( i >= times ) {
clearInterval( interval ) ;
}
}
var interval = setInterval ( "doMove()", delay );
});

Have you looked at using animate() instead of css()? I'm not 100% sure I understand what you're trying to accomplish, so this is kinda a shot in the dark.
http://api.jquery.com/animate/

Chrome, Safari and IE3+ should support background-position-y, so if you're targeting these specific browser, using jquery you could just make a timed animation() on backgroundPositionY property - http://snook.ca/archives/html_and_css/background-position-x-y
(On Firefox the effect won't work)

You can use setTimeout() and clearTimeout() functions in order to accomplish that.
IE:
var GLOBAL_i = 0;
function doAnimation() {
var h = GLOBAL_i * 40;
var top = h + 'px';
$('#ajaxLoading').css('background-position', '0 -' + top);
if (GLOBAL_i < 12) {
GLOBAL_i++;
t=setTimeout(doAnimation, 800);
}
}
$('#LoginButton').click(function () {
doAnimation()
});