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Hide a div until scrolled to the bottom of the page

I am making a web page (kind of like those music release pages, here is an example), and I would like certain div's at the bottom not to be shown until the user has scrolled to the bottom of the page, delay a second or two, then pop up. Kind of like a hidden feature thing.
You can also think of it like an infinite scroll, like when you drag down your Instagram feed at the top it refreshes it, and new posts show up. That's the user experience I'm looking for, only in my case it is a "finite scroll", just with some div's hidden by default.
I currently have two implementations of it, neither fully achieves the desired experience. Both used jQuery Slim.
In both implementations, #hidden is the id of my hidden-by-default div, it has style="display: none;" inline, on the div tag.
The first one looks like this:
$(window).scroll(function() {
var x = $(document).height() - $(window).height() - 20;
if( $(window).scrollTop() > x ) {
$("#hidden").delay(1000).show(0);
}
else {
$("#hidden").hide(0);
}
});
The problem with this one is that when the div shows up it changes the document height, so when you get to the bottom of the page it kind of flickers (due to recomputing the document height), and sometimes goes back to being hidden. Really bad user experience.
The second one looks like this:
$(window).scroll(function() {
if( $(window).scrollTop() > 75 ) {
$("#hidden").delay(1000).show(0);
}
else {
$("#hidden").hide(0);
}
});
This one got rid of the flickering problem by keeping the threshold static altogether, slightly better user experience, but not really flexible, in the case that my page gets longer I'll have to set a new threshold for the div to show up.
In neither of the above solutions did the delay(1000) work. The div showed up as soon as the page gets scrolled to the bottom.
Is it possible to make this design work out?

You can try this code:
$(window).on("scroll", function() {
var scrollHeight = $(document).height();
var scrollPosition = $(window).height() + $(window).scrollTop();
if ((scrollHeight - scrollPosition) / scrollHeight === 0) {
$("#hidden").delay(1000).show(0);
}
});

Fade in div once user scrolls past element

Problem:
I'm trying to fadeIn and fadeOut div class="audioBox" once the user scrolls past the header. What I have seems to work fine, except for when the page is loaded and I'm already past the 835px height of the header/
Q: What I'm seeing is when I scroll the audioBox quickly fades in and then fades out, despite scroll >= header How do I prevent this from happening?
scripts.js
// If the reader scrolls past header, show audioBox
var scroll = $(window).scrollTop();
var header = $("header").height();
if (scroll >= header) {
$(".audioBox").fadeIn();
} else if (scroll <= header) {
$(".audioBox").fadeOut();
}

I tried implementing what you're describing in jsfiddle at http://jsfiddle.net/3wqfp2ch/1/.
I'd approach it a bit differently, based on the following ideas:
I personally prefer letting CSS take care of visual stuff via classes, and let jQuery take the simple responsibility of controlling when the classes should be added/removed. I think it makes for a better relationship between the two systems and allows each to do their thing better & more neatly.
I didn't see where you were listening for scroll events on the window, which is essential for figuring out whether a user's scroll position is before or after the header, so have included this in my code
I don't think we need multiple if conditions - there's just one question: "Is the scroll position greater than the header height?".
Here's the JS:
var headerHeight = $("header").height();
var audioBox = $('#audioBox');
$(window).on('scroll', function(){
var scrollPosition = $(window).scrollTop();
if (scrollPosition > headerHeight) {
audioBox.addClass('is-visible');
} else {
audioBox.removeClass('is-visible');
}
});
Check out my fiddle at http://jsfiddle.net/3wqfp2ch/1/ for the HTML & CSS that this relates to, and the working demo putting it all together.
I can't test whether this suffers from the same issue regarding you loading at a point already past the header height from jsfiddle unfortunately, but I wouldn't be expecting the behaviour you described using the code above.
Let me know how you get on!

Calling .fadeIn() or .fadeOut() all the time and having an overlap in the conditions might be the problem.
Try this:
// If the reader scrolls past header, show audioBox
var scroll = $(window).scrollTop();
var header = $("header").offset().top + $("header").height(); // should include the header's offset as well
if (scroll >= header) {
$(".audioBox:hidden").fadeIn();
} else if (scroll < header) {
$(".audioBox:visible").fadeOut();
}

Modify Sidenavigation Which Highlights Which Part of Page is Viewed

I currently have a sidenavigation bar which continually checks the users scroll position and if it is greater than a specified .slide height, it adds a class .current to a certain div on a sidebar making it turn orange and thus indicates which part of a page the user is on. Right now, the code only works for one specific height of .slide but I would like to modify it so that each slide (i.e. slide red, slide green, slide blue which are the divs with the colored background) can be of different heights since my content for each section will vary in length.
The fiddle can be found here
JavaScript:
$(document).scroll(function() {
if($(window).scrollTop() > $('.slide').height()*$('.current').index()){
$('.current').removeClass('current');
var newSlide = Math.floor($(window).scrollTop() / $('.slide').height());
$('.sidenavigation li:eq('+newSlide+')').addClass('current');
}
if($(window).scrollTop() < $('.slide').height()*$('.current').index()){
$('.current').removeClass('current');
var newSlide = Math.floor($(window).scrollTop() / $('.slide').height());
$('.sidenavigation li:eq('-newSlide-')').addClass('current');
}
});

I was trying to help you with your code and then i realize how hard it is, so I know it is probably not what you really want, but I recommend you a great jQuery plugin, which will solve your problem very fast: http://imakewebthings.com/jquery-waypoints/

Floating elements on scroll

I was wondering how sites like Facebook, with their timeline feature, float a certain element (usually a menu bar, or sometimes a social plugin, etc) when the user has scrolled past a point such that the top of the element is off the screen, etc.
This could be seen as a more general JavaScript (jQuery?) event firing when the user has scrolled to a certain element, or scrolled down a certain number of pixels.
Obviously it would require toggling the CSS property from:
#foo { position: relative; }
to
#foo { position: fixed; }
Or with jQuery, something like:
$('#foo').css('position', 'fixed');
Another way I have seen this implemented is with blogs, where a popup will be called when you reach the bottom, or near the bottom of a page. My question is, what is firing that code, and could you link or provide some syntax/ semantics/ examples?
Edit: I'm seeing some great JS variants coming up, but as I am using jQuery, I think the plugin mentioned will do just nicely.

Take a look at this jsfiddle: http://jsfiddle.net/remibreton/RWJhM/2/
In this example, I'm using document.onscroll = function(){ //Scroll event } to detect a scroll event on the document.
I'm then calculating the percentage of the page scrolled based on it's height. (document.body.scrollTop * 100 / (document.body.clientHeight - document.documentElement.clientHeight)).
document.body.scrollTop being the number of pixels scrolled from the top, document.body.clientHeight being the height of the entire document and document.documentElement.clientHeight being the visible portion of the document, a.k.a. the viewport.
Then you can compare this value to a target percentage, an execute JavaScript. if(currentPercentage > targetPercentage)...
Here's the whole thing:
document.onscroll = function(){
var targetPercentage = 80;
var currentPercentage = (document.body.scrollTop * 100 / (document.body.clientHeight - document.documentElement.clientHeight));
console.log(currentPercentage);
if(currentPercentage > targetPercentage){
document.getElementById('pop').style.display = 'block';
// Scrolled more than 80%
} else {
document.getElementById('pop').style.display = 'none';
// Scrolled less than 80%
}
}
​If you prefer jQuery, here is the same example translated into everybody's favorite library: http://jsfiddle.net/remibreton/8NVS6/1/
$(document).on('scroll', function(){
var targetPercentage = 80;
var currentPercentage = $(document).scrollTop() * 100 / ($(document).height() - $(window).height());
if(currentPercentage > targetPercentage){
$('#pop').css({display:'block'});
//Scrolled more than 80%
} else {
$('#pop').css({display:'none'});
//Scrolled less than 80%
}
});​

An idea would be to handle the window.scroll event and determine if the user has scrolled to the bottom of the page. Here is an example:
http://chrissilich.com/blog/load-more-content-as-the-user-reaches-the-bottom-of-your-page-with-jquery/
Hope it helps!

There is a jquery plugin that might help you in the right direction.
http://imakewebthings.com/jquery-waypoints/

I just answered basically the same question here. In that case it was a table and its header, and the basic idea is like this:
function placeHeader(){
var $table = $('#table');
var $header = $('#header');
if ($table.offset().top <= $(window).scrollTop()) {
$header.offset({top: $(window).scrollTop()});
} else {
$header.offset({top: $table.offset().top});
}
}
$(window).scroll(placeHeader);
Here's a demo.
Quoting myself:
In other words, if the top of the table is above the scrollTop, then
position the header at scrollTop, otherwise put it back at the top of
the table. Depending on the contents of the rest of the site, you
might also need to check if you have scrolled all the way past the
table, since then you don't want the header to stay visible.
To answer your question directly, it is triggered by checking the scrollTop against either the position of an element, or the height of the document minus the height of the viewport (for the scrolled to bottom use case). This check is done every time the scroll event is fired (bound using $(window).scroll(...)).

How to make div appear from the top when scrolling down?

I would like a div to appear and slide down once you scroll pass the header.
Here's what it should look like:
http://www.space.com/11425-photos-supernovas-star-explosions.html
Here's what I got so far but it's not working.
http://jsfiddle.net/nHnrd/

You'll need to find out the height of the header and its position on the page then just show or hide the div depending on the scrollTop value using jquery.
For example:
// Get the headers position from the top of the page, plus its own height
var startY = $('header').position().top + $('header').outerHeight();
$(window).scroll(function(){
checkY();
});
function checkY(){
if( $(window).scrollTop() > startY ){
$('.fixedDiv').slideDown();
}else{
$('.fixedDiv').slideUp();
}
}
// Do this on load just in case the user starts half way down the page
checkY();
Then you'll just need to set the .fixedDiv to position:fixed: top: 0; left: 0;
Edit: I've added a checkY() function that you can call whenever the page loads as well as on scroll. To hide it initially though, just use CSS.

You might want to just show and hide your div rather than pseudo class AND hide and show
initially:
$("#mydiv").hide();
then (on scroll):
$("#mydiv").show();
set what you want your div to look like i.e. 0,0 and fixed
Use the Keep It Simple method!

I've updated your jsfiddle with something you can try.
Try this:
http://jsfiddle.net/nHnrd/10/
Also, this article was helpful:
http://www.wduffy.co.uk/blog/keep-element-in-view-while-scrolling-using-jquery/