下面的哪错了?
<HTML>
<HEAD>
<Script language=JavaScript>
var b=1;
var c=true;
function shade() {
if(document.all);
if(c==true) {
b++;
}
if(b==100) {
b--;
c=false;
}
if(b==1) {
b++;
c=true;
}
if(c==false) {
b--;
}
}
xy.filters.alpha.opacity=0+b;
setTimeout("shade()",100);
</Script>
</HEAD>
<BODY>
<img src="../Output/1.gif" name="xy" border="0" style="filter:alpha(opacity=0)">
</BODY>
</HTML>