Develop Reference

Dynamic bottom value based on element position in browser

I am attempting to adapt this JS solution to keep a floating element above the footer of my site.
The adaption I am attempting is instead of changing the element position to absolute, I would have a dynamic bottom px value based on the position of the top of the footer, relevant to the client window.
function checkOffset() {
var onlineFloat = document.querySelector('#online-ceo');
var footer = document.querySelector('.site-footer');
function getRectTop(el){
var rect = el.getBoundingClientRect();
return rect.top;
}
if((getRectTop(onlineFloat) + document.body.scrollTop) + onlineFloat.offsetHeight >= (getRectTop(footer) + document.body.scrollTop) - 20)
var newBottom = ((getRectTop(footer) + document.body.scrollTop) - 40).toString().concat('px');
onlineFloat.style.bottom = newBottom;
if(document.body.scrollTop + window.innerHeight < (getRectTop(footer) + document.body.scrollTop))
onlineFloat.style.bottom = '20px';// restore when you scroll up
}
document.addEventListener("scroll", function(){
checkOffset();
});
The output of newBottom is currently a px value which changes on scroll, however, I am having issues setting this position to the element.
Where am I going wrong? Thanks.

With your approach (changing the bottom property), you can just calculate where the "float" should be if the footer's top position is in view (as in window.innerHeight) on scroll.
function checkOffset() {
var onlineFloat = document.querySelector('#online-ceo');
var footer = document.querySelector('.site-footer');
function getRectTop(el) {
var rect = el.getBoundingClientRect();
return rect.top;
}
var newBottom = 10 + (getRectTop(footer) < window.innerHeight ? window.innerHeight - getRectTop(footer) : 0) + 'px';
onlineFloat.style.bottom = newBottom;
}
document.addEventListener("scroll", function () {
checkOffset();
});

How can I fix this parallax animation?

I'm new to web development.
I'm doing this animation with a sprite that allows you to move the image when the user scrolls or up. The problem is that the image shakes when I scroll. How can I fix this bug?
`
var rotator = $('#rotator');
var container = $(document);
var viewport = $(window);
var images = 10;
var imageHeight = 5930 / images;
var scrollHeight = container.height();
var position = images/scrollHeight;
viewport.scroll(function(event) {
rotator.css('background-position', (-position) + 'px 0');
if(position < 5930) {
position = position + imageHeight;
if (position >= 5930) {
position = 0;
}
} else {
position = 660;
}
});
`

How to prevent randomly positioned images from overlapping using Angular

I have an Angular application that loads multiple images on to the page at random locations by utilizing the following code:
HTML:
<div ng-repeat="s in selectedImages" class="container">
<img ng-src="{{s.img}}" class="sImage" ng-style="s.pos"/>
</div>
CSS:
.wordImage {
position:absolute;
width:100px;
}
JS Controller:
function loadImages() {
$scope.myImages = ['img1.png', 'img2.png', 'img3.png', 'img4.png', 'img5.png']
$scope.selectedImages = [];
for (i in $scope.myImages) {
$scope.selectedImages.push(addRandomLocationToImage($scope.myImages[i]));
}
}
function addRandomLocationToImage(image) {
image.pos = {};
var preTop = getRandomHeight(); // get Height for this image
var preLeft = getRandomWidth(); // get Width for this image
image.pos = {top:preTop,
left:preLeft};
return image; // returns the same image object but contains pos{} for ng-style
}
function getRandomHeight() {
var imgHeight = 100;
var winHeight = $(window).height();
var randomH = Math.random() * (winHeight - 100); // subtract 100 for the header. and also footer padding
if (randomH < 150) {
randomH += 150; // add to keep it out of the header
}
if(winHeight - randomH < 100) { // if image will be on bottom edge of page
randomW -= imgHeight; // subtract 100 because that is the height of the images, this will prevent them from being partially off the page
}
return randomH;
}
function getRandomWidth() {
var imgWidth = 100;
var winWidth = $(window).width();
var randomW = Math.random() * winWidth;
if (randomW < 0) { // make sure it is not less than zero, then assign new number until it is greater than zero
while (randomW < 0) {
randomW = Math.random() * winWidth;
}
}
if (winWidth - randomW < 100) { // if image will be on right edge of page
randomW -= imgWidth; // subtract 100 because that is the width of the images, this will prevent them from being partially off the page
}
return randomW;
}
loadImages();
This definitely generates random images on a page...but they overlap very easily. My question is, how can I prevent them from overlapping? Here is some code that I have been working on.
var newLeft = currentImage.pos.left;
var newTop = currentImage.pos.top;
for (i in $scope.selectedImages) {
var originalLeft = $scope.selectedImages[i].pos.left;
var originalTop = $scope.selectedImages[i].pos.top;
if ((originalLeft - newLeft < 100 && originalLeft - newLeft > -100) && // could overlap horizontally
(originalTop - newTop < 100 && originalTop - newTop > -100)) { // could overlap vertically
//do something to select a new random location.
}
}

Basically you have to check a image position with every other image. You can use Array.some for this:
Considering that you store the image position in the image object as
x and y properties
function checkCollision(testImage) {
return $scope.myImages.some(function(img) {
if (img == testImage)
return false;
if (!img.x || !img.y) // Image has no position yet
return false;
return
testImage.x < img.x + imgWidth &&
testImage.x + imgWidth > img.x &&
testImage.y < img.y + imgHeight &&
testImage.y + imgHeight > img.y;
});
}
You have to be aware that depending of the available space and image sizes there might be a situation where is not possible to find a suitable position for a image.
I made a functional example.

Auto scrolling to element in scrollable div

I have 5 elements that are within a div larger than the screen (on a mobile phone).
I want the user to be able to click on one of the elements and have that element scroll to the centre of the screen.
I've tried writing this with jQuery myself, but I can't seem to get the logic quite right. I've got it kind of moving but the element selected doesn't go to the centre of the screen.
Here's a Fiddle of what I have do far: http://jsfiddle.net/geQ64/1/
Here's the JS from the fiddle also:
$(window).on('load', function() {
$('.tab-3').trigger('click');
var width = $(window).width();
if (width < 651) {
$('.ul-wrap').scrollLeft( $('.tab-3').offset().left );
}
});
$('.single-tabs').on('click', function() {
var offset = $('.tabs').width();
offset = offset/5;
var center = offset/2;
var tab = $(this).data('tab');
$('.tabs-content').hide();
$('.tab'+ tab +'').show();
var width = $(window).width();
if (width > 650) {
var arrow = tab*20-12;
$('.arrow-up').css('margin-left', '' + arrow + '%');
} else {
tab = tab - 1;
var position = offset * tab - center;
$('.ul-wrap').scrollLeft(position);
}
});

Found a fix, here's the JS is anyone needs it.
The - 55 in the var position is for an arrow that sits in the centre of the page below the elements I'm moving with this script.
$(window).on('load', function() {
$('.tab-3').trigger('click');
var width = $(window).width();
if (width < 651) {
var offset = $('.tabs').width();
offset = offset/7;
var center = offset/2;
var position = offset * 2 + center - 50;
$('.ul-wrap').animate({
scrollLeft: position
}, 200);
}
});
$('.single-tabs').on('click', function() {
var offset = $('.tabs').width();
offset = offset/7;
var center = offset/2;
var tab = $(this).data('tab');
$('.tabs-content').hide();
$('.tab'+ tab +'').show();
var width = $(window).width();
if (width > 650) {
var arrow = tab*20-12;
$('.arrow-up').css('margin-left', '' + arrow + '%');
} else {
tab = tab - 1;
var position = offset * tab + center - 50;
$('.ul-wrap').animate({
scrollLeft: position
}, 200);
}

Deferred loading of page content using JavaScript or jQuery

I have seen a few websites where their home page is too big and when user scroll down to read the content at the end of the page then a few areas of that page load dynamically. How do they design their page?
As an example the site is http://blog.rainbird.me/ where you can see the effect. How can it be achieved it via jQuery and Ajax?

You do it like this:
1: figure out the maximum browser height for your users (it's probably safe to assume 1920px as very few users have larger than 2560x1920 displays)
2: render your list so it is slightly longer than the 1920px, you can even double it to have a safe margin
3: hook into the scroll event on the document $(document.body).scroll(myScrollHandler)
4: when document.body.scrollTop gets close enough to document.body.scrollHeight you append more data on your page
$.get(urlToGetMoreDataFrom,function(data){ $(document.body).append(data)});

Lazy load of content: http://www.appelsiini.net/projects/lazyload
Load content while scrolling: http://www.webresourcesdepot.com/load-content-while-scrolling-with-jquery/

function CheckIfElementIsInsideViewport(element)
{
var jElement = jQuery(element);
var jElementTop = jElement.position().top;
var jElementBottom = jElement.height() + jElementTop;
var jElementLeft = jElement.position().left;
var jElementRight = jElement.width() + jElementLeft;
var windowTop = jQuery(window).scrollTop();
var windowBottom = jQuery(window).height() + windowTop;
var windowLeft = jQuery(window).scrollLeft();
var windowRight = jQuery(window).width() + windowLeft;
var topVisible = jElementTop > windowTop && jElementTop < windowBottom;
var bottomVisible = jElementBottom > windowTop && jElementBottom < windowBottom;
var leftVisible = jElementLeft > windowLeft && jElementLeft < windowRight;
var rightVisible = jElementRight > windowLeft && jElementRight < windowRight;
return (topVisible && (leftVisible || rightVisible)) || (bottomVisible && (leftVisible || rightVisible));
}
/* Magazine sneakpeak loader (Only loads content when visible in viewport!) */
var magazineSneakPeakHtml = "<p>Loaded!</p>";
jQuery(function()
{
var sneakPeak = jQuery(".box-newestmagazinepeek");
jQuery(window).bind("scroll", function() { SneakPeakMaybe(sneakPeak); });
SneakPeakMaybe(sneakPeak);
});
function SneakPeakMaybe(jElement)
{
if (CheckIfElementIsInsideViewport(jElement))
{
jQuery(".box-newestmagazinepeek .box-content").html(magazineSneakPeakHtml);
jQuery(window).unbind("scroll");
}
}
/**/
How to do it without jQuery:
How to tell if a DOM element is visible in the current viewport?
This will check if the element is entirely visible in the current viewport:
function elementInViewport(el) {
var top = el.offsetTop;
var left = el.offsetLeft;
var width = el.offsetWidth;
var height = el.offsetHeight;
while(el.offsetParent) {
el = el.offsetParent;
top += el.offsetTop;
left += el.offsetLeft;
}
return (
top >= window.pageYOffset &&
left >= window.pageXOffset &&
(top + height) <= (window.pageYOffset + window.innerHeight) &&
(left + width) <= (window.pageXOffset + window.innerWidth)
);
}
You could modify this simply to determine if any part of the element is visible in the viewport:
function elementInViewport2(el) {
var top = el.offsetTop;
var left = el.offsetLeft;
var width = el.offsetWidth;
var height = el.offsetHeight;
while(el.offsetParent) {
el = el.offsetParent;
top += el.offsetTop;
left += el.offsetLeft;
}
return (
top < (window.pageYOffset + window.innerHeight) &&
left < (window.pageXOffset + window.innerWidth) &&
(top + height) > window.pageYOffset &&
(left + width) > window.pageXOffset
);
}
You can place elements on your page that note the end of content, when this element then enters the viewport you can load and append new content below it using jQuery ajax (get): http://api.jquery.com/jQuery.get/
Please note that this method is very cpu intensive, since it check if the element is inside the viewport everytime the client scroll!