Computed Styles

The style object offers no information about the styles that have cascaded from style sheets and affect the element. DOM Level 2 provide a method called getComputedStyle(). This method accepts two arguments: the element to get the computed style for and a pseudo-element string (such as ":after"). The second argument can be null if no pseudo-element information is necessary.  IE doesn't support getComputedStyle(), though it has a similar concept. Every element that has a style property also has a currentStyle property.

 function getStyle(obj, name) {
     if (obj.currentStyle) {
         return obj.currentStyle[name];
     } else {
         return getComputedStyle(obj, null)[name];
     }
 }