We Keep Coding

How do I find the browser scroll bars total scrollable height

So I know that $(window).scrollTop() will give me the current position of the browser scroll bar, but how do I find the total scrollable area?
i.e. If I scroll all the way down the final $(window).scrollTop() might equal 300px and scrolling back to the top would return it back to 0px, but suppose I wanted to find the total $(window).scrollTop() area before hand? How would I do that?
i.e. If I use $(window).scrollTop() I want something to happen when it get's to a certain point.
So pretty much is there a way to find out that $(window).scrollTop() total is 300px before hand? If the browser height is changed/resized then the $(window).scrollTop() will change, so I I'll need to find out what the new $(window).scrollTop() total is once the browser is resized.
Thanks.

You should use this to get the maximum scrolleable value:
$(document).height() - $(window).height()
You get the entire web height and substract the window height (the height that you can see on your window), so the rest of it is what is left to scroll

Can someone explain why this code works-making div stick to top after scoll?

I love that this code works, but I cannot, for anything, wrap my head around WHY it's working?
Here is the jfidddle
Here is the code:
jQuery(document).ready(function($) {
clone = $('div').clone();
$('div').after(clone);
$('div:last').hide();
offset = $('div:first').offset();
var fromtop = offset.top;
$(document).scroll(function() {
doc = $(this);
dist = $(this).scrollTop();
if (dist >= fromtop) {
$('div:last').show();
$('div:first').css({
'position': 'fixed'
});
} else {
$('div:first').css({
'position': 'static'
});
$('div:last').hide();
}
});
});
I guess I am not understanding how scrolltop and offset are interacting or what they REALLY are, as in their true positions on the page. The code says if ScrollTop (the scrollbar position?) is higher than the value of the div's offsettop , then make the div sticky. But if ScrollTop is the position of the scrollbar, isn't it true that sometimes the scroll bar position could be lower than the div's position BEFORE the div is at the top of the page? What is it about being at the top of the page (offsettop of 0?)--and only at the top of the page, never before-- that makes offsettop a smaller value than scrolltop?
Really confused, and I don't want to just copy the code without understanding what it's really doing.

scroll Top is actually how many pixels 'up' the page has moved (or how many pixels you have moved down the page)
Basically all that happens is the .offset sees how far down the page (from the top of the page) the 'sticky' menu is
When you scroll to that point the bar becomes fixed (which is basically relative to the window instead of the document)
When you scroll back up it just switches back to being positioned in the document.
For clarity
.offset = 200px say - this is how far down the document the sticky menu is
.scrollTop - is 0 when the page loads
When you scroll down the page 201px
.scrollTop > .offSet -> so make the bar fixed (remember fixed is relative to the window - not the document)
If you scroll back up the process is reversed.

It's actually very simple. Let me try if I can make it a bit clear to you:
Whenever you want something (let's say some div) to get fixed on top as you scroll down, you need two things:
You need the current vertical position of your div. And you calculate that by using offset().top
You need to track how much user has scrolled. And you calculate that by using scrollTop()
So in your case, if the current position of your div is top: 100, then as soon as your scrollbar reaches the number 101, your div will get the class of .fixed
By default, the scrollbar vertical position is 0 when the page loads.

Get scrollable height of a page

First of all,I would like to know the difference between these terms:
- $(window).height()
- $(document).height()
- $(window).scrollTop()
These terms look somewhat similar to me and I am unable to understand the clear difference between them. Here are my answers:
$(window).height() : Gives the height of window which a user can see.
$(document).height() : Gives total height of document. This can be more/less than window height depending upon the content on the page.
$(document).scrollTop() : gives the vertical position of scrollbar in window.
Real Question:
I am trying to implement lazy loading kinda thing where I need to make a call to server when scrollbar has crossed a point 200px from bottom of page. I am unable to use the above values to get this.
Any help would be appreciated.

The window is the area that you can see - as if your screen is a window and you are looking through at the document. The document is the entire document - it could be shorter or much longer than the window.
This is the math you need:
if( $(document).height() - $(document).scrollTop() < 200 ){
//Do something
}

$(window).height(); // returns height of browser viewport
$(document).height(); // returns height of HTML document
$(window).scrollTop(); //Get the current vertical position of the scroll bar for the first element in the set of matched elements or set the vertical position of the scroll bar for every matched element.
$(window).scrollHeight(); //Height of the scroll view of an element; it includes the element padding but not its margin.

Eventually, I figured out what should be the calculations after understanding these terms. Thanks to the answers. I was almost right in my definitions.
function (isScrollable) {
var isUserAtBottom = ($(window).height() + $(window).scrollTop() + 200 > $(document).height());
if (isUserAtBottom) {
// Do something (Like Ajax call to server to fetch new elements)
return true;
}
}

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 do I get scrollable div to not add height to containing divs when screen resolution height is too small to fit the scrolling div?

I'm using javascript to move a div down the page as you scroll. I found the code online and it works for what I needed. The problem I'm running into is for lower screen resolutions (ipad) where you have to scroll down to see the footer past the main content area, the scrolling div pushes down to get onto the screen, changing the height of the divs and body, which makes you be able to endlessly scroll down the page. The div scrolls by adding a margin to the top of the div being moved as you scroll. I've tried setting heights on all the containing divs and body but nothing seems to be working css-wise, and I don't know enough about javascript to set some sort of condition.
The page I'm working on is http://gwa-inc.com/pages.aspx?pid=31&name=Americana
If you make your browser window height smaller and scroll down the page, you'll see what I'm talking about. Is there an easy fix to this that I'm missing?
Script being used is:
var $sidebar = $(".subMenuWrap"),
$window = $(window),
offset = $sidebar.offset(),
topPadding = 30;
$window.scroll(function () {
if ($window.scrollTop() > offset.top) {
$sidebar.stop().animate({
marginTop: $window.scrollTop() - offset.top + topPadding
});
} else {
$sidebar.stop().animate({
marginTop: 0
});
}
});

You should absolutely position the box that needs to scroll, so that it will be pulled out of the flow of the page. Then you can more closely control where that box goes and can keep it from pushing the footer down further.