Inherited CSS Values via Javascript

On my page I am changing some css styles via javascript. When I try and pull a value that has been inherited - it comes up blank. Consider the following:

    .Sliding
    {
        display: none;
        overflow: hidden;
    }

    .Sliding #FilterBox
    {
        height: 185px;
        background-color: Fuchsia;
    }

And the html:

<div class="Sliding" id="FilterBox">
        <h3>Test Form</h3>
        This is a test/<br />
        12345
</div>

If I look at the element 'document.getElementById(objname).style.display' its blank? How can I read the display value via via javascript?

Answers:

Answer

You'll want to use getComputedStyle.

The .style property is a means of accessing and setting inline style (i.e. like the style attribute).

Note, however, that your example has nothing to do with inheritance. Just rule-sets that apply directly to the elements you are interested in. Inheritance is when an element takes on the same style as its parent via the inherit keyword.

span {
    color: inherit;
}

getComputedStyle will give the final computed value though, so it will pick up inherited values too.

Answer

Your second CSS rule:

.Sliding #FilterBox
{
    height: 185px;
    background-color: Fuchsia;
}

will match anything with id "FilterBox" that is a descendant of anything with a class "Sliding", so this rule does not apply to your div.

And to get the computed style, you can refer to Fabien's answer, or consider using jQuery, which makes this stuff a lot easier:

using jQuery, $("#FilterBox").css("display") would return the current value for "display".

Answer

You need to look at the computed style, see here

Answer
if (!window.getComputedStyle) 
{
    window.getComputedStyle = function(el, pseudo) 
    {
        this.el = el;
        this.getPropertyValue = function(prop) {

        var re = /(\-([a-z]){1})/g;
        if (prop == 'float') 
            prop = 'styleFloat';
        if (re.test(prop)) 
        {
            prop = prop.replace(re, function () {

            return arguments[2].toUpperCase();
           });
        }

        return el.currentStyle[prop] ? el.currentStyle[prop] : null;
      }

      return this;
   }
}

function GetCompStyle()
{   
    var compStyle = window.getComputedStyle(document.getElementById('FilterBox'), "");
    alert(compStyle.getPropertyValue("display"));   
}

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