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javascript - Why would jquery return 0 for an offsetHeight when firebug says it's 34?

So I have a div whose content is generated at runtime it initially has no height associated with it. When it's generated according to firebug and from what I can alert with js the div still has a height of 0. However, looking at the read-only properties with firebug I can see that it has an offset height of 34. It's this value that I need. Hopefully it's obvious but in case it isn't, this number is variable, it's not always 38.

So, I thought that I could just get that by doing this via jquery...

$("#parentDiv").attr('offsetHeight');

or this with straight js...

document.getElementById("parentDiv").offsetHeight;

But all that is returned is 0. Does it have anything to do with the fact that offset height is a read-only property in this instance? How can I get this height? I mean firebug is figuring it out somehow so it seems like I should be able to.

Edit: Here's a sample of what the div looks like right now...

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML Strict//EN"><META http-equiv="Content-Type" content="text/html; charset=utf-8">

<HTML style="OVERFLOW: hidden; HEIGHT: 100%" xmlns="http://www.w3.org/1999/xhtml"><BODY><FORM id="aspnetForm" name="aspnetForm" action="blah.aspx" method="post"><DIV id="container">

<DIV id="ctl00_BodyContentPlaceHolder_Navigation" style="Z-INDEX: 1; LEFT: 1597px; POSITION: absolute; TOP: 67px">
    <DIV class="TransparentBg" id="TransparentDiv" style="MARGIN-TOP: 10px; MARGIN-RIGHT: 10px; HEIGHT: 94px; TEXT-ALIGN: center">
    </DIV>
    <DIV class="Foreground" id="ForegroundId" style="MARGIN-TOP: 10px; MARGIN-RIGHT: 10px; TEXT-ALIGN: center">
        <DIV id="ctl00_BodyContentPlaceHolder_Navigation1" style="WIDTH: 52px; COLOR: black; HEIGHT: 52px; BACKGROUND-COLOR: transparent; -moz-user-focus: normal">
            <IMG style="FILTER: progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod = scale src='../images/image.gif'); CURSOR: pointer" height="52" hspace="0" src="..." width="52" /> 
        </DIV>
        <DIV id="ctl00_BodyContentPlaceHolder_UserControl" name="ctl00_BodyContentPlaceHolder_UserControl">
            <IMG style="DISPLAY: block; VERTICAL-ALIGN: bottom; CURSOR: pointer" height="17" src="..." width="16" />
            <IMG style="VERTICAL-ALIGN: top; CURSOR: pointer" height="17" src="..." width="16" />
        </DIV>
    </DIV>
</DIV>

</DIV></FORM></BODY></HTML>

This code is being generated by a control in a separate library. So here's the actual code creating it in my .aspx page.

<blah:blahControl ID="control" runat="server" />

Ok, it's edited slightly but thats a whole lot more HTML than I had before. The div I was referring to as "parentDiv" before is called "ctl00_BodyContentPlaceHolder_UserControl" up there. That code includes the div in question, it's sibling, parent, grandparent and children. It's almost a direct copy from firebug.

Update: I should have mentioned this is being done in IE 7. It seemed to work fine one time in Firefox, but it's returning 0 now. Does this provide any new insights of possible work-arounds or anything?

... You all must think I'm nuts.

Update: Some styling...

.TransparentBg 
{
    background-color: white;
    filter:alpha(opacity=50);
    -moz-opacity:0.5;
    -khtml-opacity: 0.5;
    opacity: 0.5;
}

.Foreground
{
    position: absolute;
    top: 0px;
}
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1 Answer

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Are you sure the element is included in the document tree, and rendered? (ie. not “display: none”, but “visibility: hidden” is OK.)

An element that is not actually taking part in the document render process has no dimensions, and will give an offsetWidth/Height of 0.

ETA after code sample added: with your exact code, I get offsetHeight on the div of ‘17’. The first image is sized correctly, the second has no size.

This is correct as rendered(*). Any images that fail to load are replaced by their alt text as an inline span. Your image has no alt text, so it is replaced by an empty string. Normally, as an inline element, this cannot be set to any particular size. The exception is the first image, because you've given it ‘display: block’, which makes it amenable to the explicit sizing provided by width/height.

In Quirks Mode, you would have got little ‘broken image’ icons sized the same as the images were supposed to be. This does not happen in Standards Mode because it is assumed that you know how to use alt text properly if you're using standards.

Either way, the dimensions measurement works fine for me if I replace the "..." URLs with real working addresses.

(*: although you can't actually see it because of the rather weird ‘overflow-hidden’ on html and ‘left: 1597px;’ combo. Well, unless you have a really wide monitor!)


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