[devote]

function style( elem ) {
    if ( elem.ownerDocument && elem.ownerDocument.defaultView ) {
        return elem.ownerDocument.defaultView.getComputedStyle( elem, null );
    } else if ( elem.currentStyle ) {
        return elem.currentStyle;
    }
    return null;
}

var fontTD = style( document.getElementById("ID") ).fontSize;

alert( fontTD );