学习了，不错
window.onload=function(){
var oDiv=document.getElementById('div1');
oDiv.onmouseover=function(){
startMove(100);
};
oDiv.onmouseout=function(){
startMove(30);
}
};
var timer=null;
var alpha=30;
function startMove(iTarget){
var oDiv=document.getElementById("div1");
clearInterval(timer);
timer=setInterval(function(){
var speed=0;
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;
}
},30)
}
