function isVisible(obj)
{
    if (obj == document) return true
    
    if (!obj) return false
    if (!obj.parentNode) return false
    if (obj.style) {
        if (obj.style.display == 'none') return false
        if (obj.style.visibility == 'hidden') return false
    }
    
    //Try the computed style in a standard way
    if (window.getComputedStyle) {
        var style = window.getComputedStyle(obj, "")
        if (style.display == 'none') return false
        if (style.visibility == 'hidden') return false
    }
    
    //Or get the computed style using IE's silly proprietary way
    var style = obj.currentStyle
    if (style) {
        if (style['display'] == 'none') return false
        if (style['visibility'] == 'hidden') return false
    }
    
    return isVisible(obj.parentNode)
}

Determines if a given element is visible, by checking a variety of things. Will work for CSS or inline style declarations of visible:hidden or display: none. Will check if it's inside of an invisible element, as well.

JavaScript DOM Element Visibility Checker

DOM

JavaScript