How To Determine Wether A Node Is Rendered Visible Or Not?

i came up zero when trying to find a direct method/value in the javascript object of the Node to determine wether an object is shown or not. So i wrote the following function. it checks relative to a parent (which could by document.body or a form or something) if somewhere on the way to that parental fixpoint a display='none' is found.
If theres a better/faster or even direct way to do this please let me know, otherwise enjoy this function.

P.S. i did not optimize it for IE since it doesn't support the prototype anyway

Node.prototype.visibleByInherit=function(s) {
var p=this;
var v=true;
do {
if(p.style!=null)
if(p.style.display!=null)
if(p.style.display.toLowerCase()=='none')
v=false;
p=p.parentNode;
} while(p!=null && p.parentNode!=null && p!=s.parentNode && v);
return v;
}