How to get the actual rendered font when it's not defined in CSS?

How do I get the actual font face and font size of an element when the CSS font-face and font-size properties are not defined? For example, the JavaScript snippet object.style.fontFamily does not return any value. That's pretty obvious, assuming CSS hasn't applied a style to object anywhere. But, of course, a certain font is used to render the text, probably the system font or the webbrowser defau