Div渐隐渐现

<script type="text/javascript">
    var i;
    var j;
    var sobjTimer=null;
    var sobjTimer2=null;
    function ShowSupport()
    {
        i=0;  //一定要在该处初始化
        j=100;//一定要在该处初始化
        dvZz.style.display="block";
        dvhelp.style.display="block";
        sobjTimer =window.setInterval(change,1);
    }
    function change()
    {
        i++;
        dvhelp.style.filter = "Alpha(Opacity=" + i + ")"; //for IE
        dvhelp.style.opacity = i/100;                     //for FF
        if(i>100)
        {
            window.clearInterval(sobjTimer);
            sobjTimer=null;
        }
    }
    function change2()
    {
        j--;
        dvhelp.style.filter = "Alpha(Opacity=" + j + ")"; //for IE
        dvhelp.style.opacity = j/100;                     //for FF
        if(j<0)
        {
            window.clearInterval(sobjTimer2);
            dvZz.style.display="none";
            dvhelp.style.display="none";
            sobjTimer2=null;
        }
    }
   function HiddenSupport()
    {
        sobjTimer2 =window.setInterval(change2,1);
    }
</script>