if (alpha>iTarget) {
                speed=-10;
            }
            else{
                speed=10;
            }
            if (alpha==iTarget) {
                clearInterval(timer);
            }
            else{
                alpha+=speed;
                oDiv.style.filter='alpha(opacity:'+alpha+')';
                oDiv.style.opacity=alpha/100;        
            }

这里两个if/else，不是顺序执行吗？感觉条件判断就会停在前一个if/else啊，搞不明白。