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How to get the new size of a dynamically sized div?

I have a div that slides up from the bottom of my pagewhen a button is clicked. i do this using a css transition and changing the css "top" attribute of the div. works fine if the div size never changes. So for example if the div is 400px high, i just move it up 400px and it's now in position. cool.
BUT... what if the div has dynamically generated content and will be a different height every time? how can i figure out how much to move the div up in order to be 100% showing?
so in pseudo code i want something like
function movemydiv() {
var howMuchToMoveIt = ??? (somehow getting the dynamic containers height)
document.getelementbyId("mydiv").style.top = bottomOfScreen - howMuchToMoveIt
any tips on most straightforward way to do this??

You can use either clientHeight or offsetHeight to measure the height of your div.
Both clientHeight and offSetHeight include padding , but offsetHeight will also take into account borders and horizontal scrollbars (if rendered) - see MDN link.
So your js would be something like:
var howMuchToMoveIt = document.getElementById('mydiv').clientHeight;
The var will then contain the height of your element.
Hope this helps

Get content width of an element

offsetWidth isn't good enough for me right now, as this includes padding and border width. I want to find out the content width of the element. Is there a property for that, or do I have to take the offsetWidth and then subtract the padding and border width from the computed style?

Since this comes up first when googling but doesn't have an appropriate answer yet, here's one:
function getContentWidth (element) {
var styles = getComputedStyle(element)
return element.clientWidth
- parseFloat(styles.paddingLeft)
- parseFloat(styles.paddingRight)
}
Basically, we first get the element's width including the padding (clientWidth) and then substract the padding left and right. We need to parseFloat the paddings because they come as px-suffixed strings.
I've created a little playground for this on CodePen, check it out!

It sounds to me like you want to use getComputedStyle on the element. You can see an example of getComputedStyle vs. offsetWidth here: http://jsbin.com/avedut/2/edit
Or:
window.getComputedStyle(document.getElementById('your-element')).width;

I would suggest either scrollWidth or the clientWidth depending on whether you want to account for the scrollbar.
Check out Determining the dimensions of elements or the specification itself.

I have the similar issue where my parent element isn't the window or document... I am loading an image by Javascript and want it to center after loading.
var parent = document.getElementById('yourparentid');
var image = document.getElementById('yourimageid');
image.addEventListener('load'),function() {
parent.scrollBy((image.width-parent.clientWidth)/2,(image.height-parent.clientHeight)/2);
}
Whenever you set the src then it will scroll to the center of the image. This for me is in the context of zooming into a high res version of the image.

How to animate div using jQuery to the height of another div

I have a div called .A coded as height:auto that has a height rendered based on the text contained within. I have another div on the page called .B that I need to animate down using jQuery based on the height of the first div, .A.
I have attempted using the following jQuery function, without much luck. The idea was to have jQuery ascertain the height of .B then apply a padding to .B, however it is not grabbing the correct height. I have also tried using 'marginTop'
jQuery('div.A').animate({'paddingTop': jQuery('div.B').height()},500);
Desparate for help! Will pay with up-votes and generous compliments.

I think you need .outerHeight(true):
jQuery('div.A').animate({ paddingTop : jQuery('div.B').outerHeight(true)},500);
Description for .outerHeight() from docs
Get the current computed height for the first element in the set of matched elements, including padding, border, and optionally margin. Returns an integer (without "px") representation of the value or null if called on an empty set of elements.
Note:
The top and bottom padding and border are always included in the .outerHeight() calculation; if the includeMargin argument is set to true, the margin (top and bottom) is also included.

Get width of element with no css or width attribute

Scenario: You have a div with some text, this div has no css width, no jquery width, no width attribute assigned to it in any way. However it has a width due to the content that is inside it, this is undefined, reports as "null" in jQuery. My question is: is there any way to retireve the width of this div?

$(element).width() should give you the actual width. With $(element).outerWidth(includeMargin) you can even get the width including padding, border, and, if desired, the margin.

with jquery you can do below
$('#id').width()

How do I get the CSS width value with Javascript?

I'm trying to calculate the width of an element so that when I use JavaScript to wrap a parent element around it, I can set the width of the parent to match the width of the child. The obvious $('#element').css('width'); isn't quite what I want because it only seems to return the calculated value in pixels. Is there some way that I can return the actual CSS value, whether it be 300px or 20% or auto, instead of the calculated value?
Here's generally how it's set up, but I'd like to know the CSS value of #child instead of the calculated value.
$(document).ready(function(){
$('#child').wrap('<div id="parent"></div>');
$('#parent').each(function(){
var childWidth = $(this).children('#child').css('width');
$(this).css('width', childWidth)
});
});

I don't believe you can do that. The best you will get is offsetWidth or clientWidth which return the calculated value, with and without counting margins, padding and borders.

You need to read the stylesheet itself.
See: How can I read out the CSS text via Javascript as defined in the stylesheet?

Everyone but IE supports window.getComputedStyle(element), which you can use like so:
getComputedStyle($('#child')).width; // returns actual width of #child
Doesn't help you with IE, though.