tmavnuti, akce se neprovede

function setOpacity(tmavnuti) {
        element = document.getElementById('jsconfirmfade');
        element.style.opacity = tmavnuti;
        element.style.MozOpacity = tmavnuti;
        element.style.KhtmlOpacity = tmavnuti;
        element.style.filter = "alpha(opacity="+(tmavnuti*100)+");";
}

function fadeOut() {
       
        for (level = 83; level >= 0; level -= 1) {
          level2 = level/100;
          setTimeout("setOpacity("+level2+")", level2*400);          
        }
        element = document.getElementById('jsconfirmfade');
        tmavnuti = element.style.opacity;
        alert(tmavnuti); //alertko mi vypise ze hodnota je 0.83 ..preco nie je nula?
}