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Detect when the end of a div is visible

I need to know if the end of a div element is currently visible in the users' browser.
I tried something I saw on the web, but scrollTop() always gave me zero in my Browser. I read something about an issue in Chrome, but I didn't understand quite well.
jQuery(
function($) {
$('#flux').bind('scroll', function() {
if ($(this).scrollTop() + $(this).innerHeight() >= $(this)[0].scrollHeight) {
alert('end reached');
}
})
}
);
My idea is the following:
1- User loads page and sees a Bar (sticky div at bottom visible page) with some information.
2- After scrolling a bit, and reaching the end of a div element, this bar will position there, after the div. This is the bar's original position
I wasn't really able to know when I was at the end of the div element. Eventually I found this code:
if ($(window).scrollTop() >= $('#block-homepagegrid').offset().top + $('#block-homepagegrid').outerHeight() - window.innerHeight) {
$('.hero-special-message').removeClass('hero-special-messege-scrolling');
} else {
$('.hero-special-message').addClass('hero-special-messege-scrolling');
}
});
I see that it's working, but I'm having a bit of trouble understanding what it does.
I know the following:
1. $(window).scrollTop();
this gives me the amount of pixels the user has scrolled, pretty self explanatory.
2. $('#block-homepagegrid').offset().top;
I THINK this is the distance between the start of the page and the start of the div. I know it's the current coordinates, but what is top exactly here?
3. $('#block-homepagegrid').outerHeight();
this gives the height of the element, I know there are 3, like
height(), innerHeight() and outerHeight(), if you want to take into
account border, margin, padding, which is the better to use?
4. window.innerHeight;
I understand this is what the user sees, but I'm having troubles understanding why does it matter for my situation.
Thanks!

You may be interested in the native JavaScript IntersectionObserver API. It automatically figures out what percentage of a given element is visible in the window and triggers callbacks based on that. So then you can do this:
function visibleHandler(entries) {
if (entries[0].intersectionRatio >= 1.0) {
// The whole element is visible!
} else {
// Part of it is scrolled offscreen!
}
}
const observer = new IntersectionObserver(visibleHandler, {threshold: 1.0});
observer.observe(document.getElementById('flux'));
Now, whenever the element with ID flux is 100% in view, it will trigger the visibleHandler. It will also trigger again if it's scrolled back out of view; that's why the function checks the ratio of visibility to see if it just hit 100% or just got reduced from 100%. You could be more fancy and use the observer entry's insersectionRect, which gives you the rectangle containing the visible portion of the element, and use that to determine top/bottom visibility.

Show the button at the table bottom even when the window is very small

I have a table sorter html page, the sample is here.
$('table').tablesorter({
theme: 'blue',
widgets: ['zebra', 'scroller'],
widgetOptions: {
scroller_height: 400
}
});
How can I make the bottom button visible even when the windows height is very small (say, can only show one or two rows)? Ideally scroller_height can be some type like $(window).height()/2 and it can automatically update when the window is resized.
The expected is that even when the window is small, the bottom button appears in the screen without scroll action.

If you want to make the scroller window dynamically adjust its height, there are two demos on the main wiki page under Widgets > Scroller.
http://jsfiddle.net/Mottie/txLp4xuk/2/
http://jsfiddle.net/Mottie/abkNM/8037/
Essentially, all you need to do is adjust the outer scroll window height
$('.tablesorter-scroller-table').css({
height: '',
'max-height': height + 'px'
});
Here is the demo you shared updated, and has a minimum height set to 100px.

I'd say that there are a few ways to achieve what you want, and one easy way is to:
create a function that checks the visibility of your table versus the viewport;
Code below:
function checkVisible() {
var bottom_of_table = $("#mytable").offset().top + $("#mytable").outerHeight();
var bottom_of_screen = $(window).scrollTop() + $(window).height();
if(bottom_of_screen > bottom_of_table){
$("#buttons-container").removeClass('bottom-fixed');
}
else {
$("#buttons-container").addClass('bottom-fixed');
}
}
If it exceeds the viewport, add a CSS class to your buttons container that fixes it to the bottom of the screen. Otherwise, remove this class and display the button container normally, at the bottom of the table.
You'd want to run this function-check on load and on window resize, as follows:
$(document).ready(function() {
checkVisible();
$(window).on('resize', checkVisible);
});
I've updated your fiddle: http://jsfiddle.net/12nt19vg/12/show/
Try resizing the window and let me know if this is the behavior you're looking for.
EDIT: Incorporating your additional spec in the comments, I've added an outer div to your buttons container and modified your CSS to visually create the effect that I think you're looking for.
Please take a look at this fiddle: http://jsfiddle.net/12nt19vg/27/show/

implementing image gallery that lazy loads images of unknown size on scroll and positions them optimally

I need to implement an image gallery with the following spec:
images need to have a max height and width. they keep their aspect ratio within these bounds.
based on the final size of the images after the max size constraints, order them on the page in a way that reduces empty blank spaces.
as the container scrolls down, load more images.
libraries I have researched such as masonry and this lay load lib
all expect width and height to be known ahead of time.
It seems that I may need to resort to loading the images in an invisible state in order to get the width and height params before positioning them on the page.
this will help with the 'masonry' aspect, but contradict the lazy load mechanism.
I would appreciate any pointers in the right direction.

I'm using Masonry right now and I think that it fits to your needs. I have different width&height images and I load with a fixed max-width (with a fixed width or a relative to the page one) and then, the layouts reorders to avoid blank spaces and keep aspect ratio of the images. When I reach the bottom of the page, I ('manually') load more items. This is my code
//Load the first page
loadMore(1);
function loadMore(page){
var div = "";
var html = "";
var item_num = 1 + ((page-1)*10);
$('.loader').show();
$('#container').hide();
$.post( "loadMore.php", {'page':page }, function( data ) {
data=JSON.parse(data);
$.each(data, function (key,value) {
//here create the div with the data
html = html + div;
item_num++;
});
$("#container").append(html).each(function(){
$('#container').masonry().masonry('reloadItems');
});
var $container = $('#container');
$container.imagesLoaded(function(){
$('#container').masonry();
});
$('.loader').fadeOut('fast',function(){
$(this).remove().delay( 1500 );
});
$('#container').show();
});
}
//On bottom page, load more images
$(window).scroll(function () {
if (ready && $(document).height() <= $(window).scrollTop() + $(window).height()) {
ready = false; //Set the flag here
setTimeout(function(){
loadMore(page);
page++;
},1000);
ready = true; //Set the flag here
}
});
You can check the result at http://pintevent.com (is a beta page)
Then, is easy to add LazyLoad to all images, here is a working example:
http://jsfiddle.net/nathando/s3KPn/4/ (extracted from a similar question: Combining LazyLoad and Jquery Masonry )
Also, if it not works for you, here's a bunch of jquery LazyLoad libraries for galleries you could check: http://www.jqueryrain.com/demo/jquery-lazy-load/
Hope it helps to you!

How can I create overlapping images that reveal themselves as you scroll

I am looking to create a scrolling effect similar to that shown here: http://www.seaham-hall.co.uk/
However I am unable to achieve the desired effect, and inspecting the sites code gives me no hints. Quite difficult to google for as it is also quite difficult to describe. The closest I can get to finding a solution is this JSFiddle:
http://jsfiddle.net/xtyus/1/
(function($){
/* Store the original positions */
var d1 = $('.one');
var d1orgtop = d1.position().top;
var d2 = $('.two');
var d2orgtop = d2.position().top;
var d3 = $('.three');
var d3orgtop = d3.position().top;
var d4 = $('.four');
var d4orgtop = d4.position().top;
/* respond to the scroll event */
$(window).scroll(function(){
/* get the current scroll position */
var st = $(window).scrollTop();
/* change classes based on section positions */
if (st >= d1orgtop) {
d1.addClass('latched');
} else {
d1.removeClass('latched');
}
if (st >= d2orgtop) {
d2.addClass('latched');
} else {
d2.removeClass('latched');
}
if (st >= d3orgtop) {
d3.addClass('latched');
} else {
d3.removeClass('latched');
}
if (st >= d4orgtop) {
d4.addClass('latched');
} else {
d4.removeClass('latched');
}
});
})(window.jQuery);
However I am not sure that is going in the right direction, this pulls images up and covers the previous image, but notice on the Seaham Hall site the images don't appear to move up at all, they are stationary and become revealed as you scroll.
How do I recreate this effect? My initial thought was to have the first image shrink as you scroll from 1000px down to 0px, and the second image grow to 1000px, and as you continue to scroll this image then shrinks and the third grows, and so on. However this means that after the first image all the other images have a starting size of 0px and there would technically be no scrolling on the page to begin with, so that is an issue.
My second thought is that perhaps the second image is fixed to the page, the first image slides up revealing the second as you scroll, the second image would not appear to move. Once the first image has gone off the top of the page the second image is detached from the page and allowed to move up with scrolling, while the third image is attached and revealed as the second moves up, this would give the exact effect seen in the Seaham website but I have no clue of it is the correct answer.
If anyone can point me to tutorials or a JSFiddle with a basic concept I can probably figure it out from there. Just stumped what direction to approach this from.

That's a nice effect. Here's one way to do it.
Put each image in a fixed position div, which takes up the entire viewport (initially) and has overflow:hidden.
Set each div's z-index to be higher than the next div's.
As the window scrolls, adjust the height of the divs as a function of the window height times the div's position (index) in the DOM, minus the window's scrollTop:
$(window).scroll(function() {
$('.D').each(function(index) {
$(this).css({
height: $(window).height()*(index+1) - $(window).scrollTop()
});
});
});
Additional content will need a higher z-index than the image divs. And note that z-index works with positioned elements only.
Fiddle

Your desired effect isn't technically a parallax background, but it's close enough that parallax jQuery frameworks should work for you.
I would suggest you research jQuery Parallax plugins as they'll likely provide the functionality you'd like without much custom work. Of course since you're dealing with large images it's also best to keep an eye on the resource management; a good plugin should be fairly efficient but others may be slow or resource intensive.

Check this jquery plugin:ScrollMagic
usage: taken from github
The basic ScrollMagic design pattern is one controller, which has several scenes attached.
Each scene has a definite start and end position and defines what happens when the container is scrolled to the specific offset.
/*
Basic workflow example
*/
// init controller
var controller = new ScrollMagic();
// assign handler "scene" and add it to controller
var scene = new ScrollScene({duration: 100})
.setPin("#my-sticky-element") // pins the element for a scroll distance of 100px
.addTo(controller); // add scene to controller
// adding multiple scenes at once
var scene2 = new ScrollScene();
var scene3;
controller.addScene([
scene2,
scene3 = new ScrollScene({duration: 200}), // add scene and assign handler "scene2"
new ScrollScene({offset: 20}) // add anonymous scene
]);

Jquery change div based on another div's position

Let me start of by saying, I'm just now learning JS and Jquery, so my knowledge is very limited.
I've been looking around for 2 days now, and tried all sorts of combinations. But I just can't get this to work.
Below is an example of the layout
I'm looking for a way to trigger an event when div 1 is X px from the top of the screen. Or when div 1 collides with div 2.
What I'm trying to accomplish is to change the css of div 2 (the fixed menu) when div 1 is (in this case) 100px from the top of screen (browser window). Alternatively, when div1 passes div2 (I'm using responsive design, so the fixed height from top might become a problem on smaller screens right? Seeing as the header for example won't be there on a hand held.). So maybe collision detection is better here? Would really appreciate some thoughts and input on this matter.
Another issue is, div2 has to revert back to is previous css once div1 passes it (going back (beyond the 100px)).
This is what I have but it has no effect
$(document).ready(function() {
var content = $('#div1');
var top = $('#div2');
$(window).on('scroll', function() {
if(content.offset().top <= 100) {
top.css({'opacity': 0.8});
}else{
top.css({'opacity': 1});
}
});
});

I am not sure of the reason but $("#content").offset().top was giving a constant value on console. So I added window.scrollTOp() to check its distance from top, here is how it works,
$(document).ready(function() {
var top = $("#menu");
$(window).on('scroll', function(){
if(($('#content').offset().top - $(window).scrollTop()) <= 100){
top.css({'opacity': 0.4});
}else{
top.css({'opacity': 1});
}
});
});
And DEMO JSFIDDLE....